40047675 Partial Denture FAYAD

2010

MOSTAFA FAYAD

Assistant Lecture of

Removable Prosthodontic

PARTIAL DENTURE THEORYAND PRACTICE

OBJECTIVES AND CLASSIFICATION

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OBJECTIVES AND CLASSIFICATION OF PARTIAL DENTURES

TERMINOLOGY

• Prosthesis: Is an artificial replacement of an absent part of the human body.

• Prosthetics: The art and science of supplying an artificial replacement for

missing parts of the human body.

• Appliance used only for device worn by patient in course of treatment. e.g.

orthodontic appliance and splint

• Prosthodontics: The branch of dentistry pertaining to the restoration and

maintenance of oral functions, comfort, appearance, and health of the patient

by the restoration of natural teeth and/or the replacement of missing teeth

and contiguous oral and maxillofacial tissue with an artificial substitute.

• Dentulous Patients: Patients having a complete set of natural teeth.

• Edentulous Patients: Patients having all their teeth missing.

• Partially Edentulous Patient: Patients having one or more but not their entire

natural teeth missing.

• Removable Partial Denture (RPD): An appliance that restores one or more but

not all of the missing natural teeth and associated oral structures for partially

edentulous patients.

• Abutment: A tooth, a portion of a tooth, or that portion of a dental

implant that serves to support and/or retain prosthesis.

• Free End Edentulous Area (Distal extension edentulous area): An edentulous

area, which has an abutment tooth on one side only.

• Bounded Edentulous Area: An edentulous area, which has an abutment tooth on each end.

• Dental cast: a positive life size reproduction of a part or parts of the oral

cavity.

The word cast is preferable than word model which used only for

demonstration


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Andrews Bridge

The combination of a fixed dental prosthesis incorporating a bar with a

removable dental prosthesis that replaces teeth with the bar area, usually

used for edentulous anterior spaces. The vertical walls of the bar may

provide retention for the removable component. By James Andrews.

Gillett Bridge

Eponym for a partial removable dental prosthesis utilizing a Gillett clasp

system, which was composed of an occlusal rest notched deeply into the

occlusal axial surface with a gingivally placed groove and a circumferential

clasp for retention. The occlusal rest was custom made in a cast restoration.

MORA Device

Acronym for mandibular orthopedic repositioning appliance, a type

of removable dental prosthesis with a modification to the occlusal surfaces

used with the goal of repositioning.

Angle of Gingival Convergence

According to Schneider, the angle of gingival convergence is located

apical to the height of contour on the abutment tooth. It can be identified by

viewing the angle formed by the tooth surfaces gingival to the survey line

and the analyzing rod or undercut gauge in a surveyor as it contacts the

height of contour.

Continuous Gum Denture

An artificial denture consisting of porcelain teeth and tinted porcelain

denture base material fused to a platinum base.

Fulcrum Line

It is an imaginary line, connecting occlusal rests, around which a partial

removable dental prosthesis tend to rotate under masticatory forces. The

determinants for the fulcrum line are usually the cross arch occlusal rests

located adjacent to the tissue borne components.

Semi precision Rest

A rigid metallic extension of a fixed or removable dental prosthesis that

fits into an intracoronal preparation in a cast restoration.


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Nesbit Prosthesis

Eponym for a unilateral partial removable dental prosthesis design, that

De. Nesbit introduced in 1918.

Resilient Attachments

An attachment designed to give a tooth borne/soft tissue borne

removable dental prosthesis sufficient mechanical flexion, to withstand the

variations in seating of the prosthesis due to deformation of the mucosa and

underlying tissues without placing excessive stress on the abutments.

CONSEQUENCES OF TOOTH LOSS

1- A loss of ridge volume—both height and width—can be expected

Bone loss is greater in the mandible than the maxilla, more pronounced

posteriorly than anteriorly, and it produces a broader mandibular arch while

constricting the maxillary arch.

2- Alteration in the oral mucosa

The attached gingiva of the alveolar bone can be replaced with less

keratinized oral mucosa, which is more readily traumatized.

3- Aesthetic impact

Facial features can change Secondary to altered lip support and/or

reduced facial height as a result of a reduction in occlusal vertical dimension.

4- Reduction in masticatory efficiency

It is the ability to reduce food to a certain size in a given time frame. It

has been shown that there is a strong correlation between masticatory

efficiency and the number of occluding teeth in dentate individuals.

5.T.M.J.dysfunction

6. Tipping, migration, rotation and superimposition of remaining teeth.

7.Altered speech


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Partial Dentures:

Partial dentures are appliances restoring one or more but not the whole

set of natural teeth . These Appliances maybe in form of:

I- Fixed partial prosthesis ( bridge ):

An appliance which restores one or more missing teeth it is permanently

cemented to the neighboring natural teeth and cannot be removed by the

patient.

II- Removable partial prosthesis:

An appliance which restores missing teeth and the associated oral

structures for a partially edentulous patient " it can be removed by the patient .

Removable partial dentures may restore :

(a) Bounded edentulous area : which has an abutment tooth on each end.

(b) Free end edentulous area : which has an abutment tooth on one side

only . Partial dentures restoring free end cases are called distal- extension

partial dentures.

III- Partial over dentures : Partial over dentures are removable partial

dentures that are constructed to overly and gain additional support

from either :

Natural teeth that are reduced in height and contour or :

Implants inserted in the edentulous areas .

IV- Removable partial Dentures for Maxillo facial Defects :

These are removable prostheses restoring tissue defects which are

either developmentally or traumatically acquired. They are usually

retained by clasps on the remaining natural teeth.


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Types of removable partial dentures :

( 1 ) Unilateral partial dentures : Partial dentures which restore teeth on one

side of the arch without being extended to the opposite side

( 2 ) Bilateral partial dentures : partial dentures restoring missing teeth and

extended on both sides of dental arch .

According to retention to natural teeth

a- Extra coronal retention

b- Intracranial retention

According to material

-Metallic - acrylic -flexible

OBJECTIVES OF REMOVABLE PARTIAL DENTURES

1- Preservation of the Remaining Tissues:

The primary purpose of RPD is the preservation of the health of the remaining

tissues.

A- Preservation of the health of the remaining teeth.

The loss of teeth leads to migration, tilting or drifting of the

remaining natural teeth into the edentulous spaces (Fig.1-3), such

movements leads to unequal distribution of load on the remaining

teeth. In addition to food impaction in the interstitial spaces leading to

caries and /or gingivitis.

B- Prevention of muscles and TMJ Dysfunction.

Absence or movements of posterior teeth may cause:

A- Changes in the pattern of mandibular closure (Fig.1-4).

B- Change in the vertical and horizontal relations of the

mandible and maxilla. Consequently muscles and TMJ Dysfunction

may arise.


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C-Preservation of the residual ridge.

By preventing rapid bone resorption which may happen due to

lack of function.

D-Preservation of the tongue contour and space.

2 Restore the Continuity of the Dental Arch to Improve Masticatory

Function:

A reduction of the number of teeth leads to a decrease in the chewing

efficiency and greater effort on the digestive organs leading to digestive

disorders, accordingly replacing lost teeth will greatly improve the chewing

capability of the patients, distribute the load over the entire arch and improve

the balance over the whole masticatory system.

3- Improvement of Esthetics, and Providing Support to the Paraoral

Muscles, Lips and Cheeks:

Teeth and the alveolar ridge give support to the musculature of the lips

and cheeks. Non-replacement of the missing teeth gives the patient a senile

appearance characterized by nose-chin approximation and wrinkles around

the lips. Missing teeth can be replaced with predictable results using partial

denture.

4- Restoration of Impaired speech:

Anterior teeth play an essential role in phonetics, particularly in the

production of labio and linguo-dental sound. Loss or wrong position of

anterior teeth and subsequent alveolar ridge resorption can result in phonetic

impairment.

Proper replacement of artificial teeth in relation to the lip، tongue and alveolar

ridge، also the proper contouring of dentures help in restoration of speech

defects.


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5- Enhance psychological comfort:

Partial dentures should restore and correct the appearance for the

psychological benefits of the patient, by providing socially acceptable

esthetics. A comfortable prosthesis will encourage and help in patient

rehabilitation .

INDICATIONS FOR REMOVABLE PARTIAL DENTURES

1. No abutment tooth posterior to edentulous space (Free end edentulous

area)).

2. After recent extraction, usually done only to improve esthetics, or for

patient satisfaction.

3. Long edentulous bounded span, too extensive for fixed restoration.

4. Periodontally weak teeth not sufficiently sound to support fixed- partial

denture.

5. With excessive loss of residual bone, the use of labial flange or need to

restore lost tissues.

6. Need of bilateral bracing (cross arch stabilization).after periodontal

diseases treatment ,fixed prosthesis provide only antero-posterior

stabilization only not mediolateral .

7. Enhancing esthetics in anterior region, by the use of translucent

artificial teeth instead of dull fixed partial denture pontic.

8. Young age (less than 17 years).

9. Geriatric patients

10. Immediate replacement.

11. Economic considerations, attitude and desire of the patient.

12. Physical problems.

13. Unfavorable maxillo-mandibular relation.

Contraindication

1- Large tongue.

2- Mentally retarded.

3- Poor oral hygiene.


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ADVANTAGES OF REMOVABLE PARTIAL DENTURE OVER FIXED

PARTIAL DENTURE:

1- They can be constructed for any case whilst fixed P.D. are confined to

short spans bounded by healthy teeth and with a normal occlusion.

2- Cheaper than fixed partial denture.

3- They are more easily cleaned.

4- They are more easily repaired.

5- No tooth reduction is required.

Disadvantages of a Removable Partial Denture:

1- It can cause caries: by harboring food debris in close contact with the

natural teeth a partial denture may promote caries. This will depend on

several factors, chief of which are:

a) The age of the patient, up to the age of 25 years caries susceptibility is

greatest, there after it tends to decrease.

b) The oral hygiene of the patient.

c) The design of the denture: this is all important because well designed

dentures will cause for less damage to the mouth than those of through

less design.

2- It can damage the supporting tissues of the teeth: removable partial

dentures may cause damage to the gum margins by:

a) Fitting too closely into the gingival tissues: through and causing

mechanical injury to it.

b) Allowing food to pack down between the denture and the teeth.

3- It may loosen the natural teeth by leverage: clasps which grip the teeth

too tightly or indirect retainers which are badly placed may cause excessive

stresses to be induced in the natural teeth .

4- It can cause traumatic damage to the palate.

5. Clasps can be unesthetic, particularly when they are placed on visible tooth

surfaces.


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HAZARDS OF IMPROPERLY DESIGNED PARTIAL DENTURES

An improperly designed and constructed partial denture may adversely

affect the tissues in the following manner:

1- Stagnation of food around component parts of partial denture in contact

with tooth surfaces that are not readily cleaned causes tooth decay .

2- Induce stresses on abutment teeth and tissues. If these stresses exceed the

physiologic limits of tissue tolerance, pathologic and destructive changes may

occur:

a) Excessive stresses on abutment teeth cause periodontal membrane

destruction, pocket formation, mobility, and even loss of these teeth.

b) Inflammation, ulceration and gingival recession may occur due to

excessive stresses and undue coverage of tissues with the restoration.

Inadequate denture support due to inadequate stoppers, this causes

displacement of the restoration towards the tissues causing gum stripping.

c) Stresses may also cause bone resorption and loss of the bony foundation

necessary to support the prosthesis.

3- Improper occlusion of teeth or the presence of premature contact may cause

T.M.J. disorders.

PHASES OF PARTIAL DENTURE SERVICE

1- Education of patient: the process of informing a patient about a health matter

to secure informed consent, patient cooperation, and a high level of patient

compliance. Patient education should begin at the initial contact with the

patient and continue throughout treatment.

2- Diagnosis, treatment planning, design, treatment sequencing, and mouth

preparation.

3- Support for Distal Extension Denture Bases.


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4- Establishment and Verification of Occlusal Relations and Tooth

Arrangements.

5- Initial Placement Procedures.

6- Periodic Recall.

REASONS FOR FAILURE OF CLASP-RETAINED P.D.

Diagnosis and treatment planning1. Inadequate diagnosis2. Failure to use a surveyor or to use a surveyor properly during treatment

planningMouth preparation procedures1. Failure to properly sequence mouth preparation procedures2. Inadequate mouth preparations, usually resulting from insufficient planning of

the design of the partial denture or failure to determine that mouth preparations have been properly accomplished

3. Failure to return supporting tissue to optimum health before impression procedures

4. Inadequate impressions of hard and soft tissueDesign of the framework1. Failure to use properly located and sized rests2. Flexible or incorrectly located major and minor connectors3. Incorrect use of clasp designs4. Use of cast clasps that have too little flexibility, are too broad in tooth

coverage, and have too little consideration for estheticsLaboratory procedures1. Problems in master cast preparationa. Inaccurate impressionb. Poor cast-forming procedures


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c. Incompatible impression materials and gypsum products2. Failure to provide the technician with a specific design and necessary

information to enable the technician to execute the design3. Failure of the technician to follow the design and written instructionsSupport for denture bases1. Inadequate coverage of basal seat tissue2. Failure to record basal seat tissue in a supporting formOcclusion1. Failure to develop a harmonious occlusion2. Failure to use compatible materials for opposing occlusal surfacesPatient-dentist relationship1. Failure of the dentist to provide adequate dental health care information,

including care and use of prosthesis2. Failure of the dentist to provide recall opportunities on a periodic basis3. Failure of the patient to exercise a dental health care regimen and respond to

recall

CLASSIFICATION OF PARTIALLYEDENTULOUS ARCHES

Need for classification:

1- To differentiate between different partial denture.

2- It facilities writing or speaking about partial denture designs and referral or

prescription writing to the laboratory thus facilitating communication.

3- To formulate good treatment plane.

4- To anticipate difficulties commonly to occur for each class.

Requirements of an Acceptable Classification:

Classifications are important to facilitate communication between the dentist

and the laboratory technician. Acceptable classification should satisfy the

following requirements:

1.Permit immediate visualization of the type of partially edentulous arch.

2.Permit immediate differentiation between bounded and free extension

partial dentures.

3. It should be universally accepted.


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4. Serve as guide to design used.

Classifications

Several methods of classification based on various factors have

been proposed.

A- Classification According to the Extent of the Removable

Partial Denture:

1- Unilateral RPD (Removable Bridge): which restore missing teeth on one

side of the arch without being extended to the other side. This unilateral

design provides least amount of tooth preparation and least amount of tooth

and soft tissue contact.

For unilateral removable partial denture to be successful:

1. clinical crown of abutment tooth must be long enough to

resist rotational forces.

2. The buccal and lingual surfaces of the abutment tooth

must be parallel to resist tipping forces.

3. Retentive undercuts should be available on both the

buccal and lingual surfaces of each abutment.

* Unilateral removable partial denture should be used with caution. as

the chance of the denture becoming dislodged and aspirated is too great.

Bilateral RPD: which restore missing teeth and extended on both sides

of the dental arch.

B- Cummer's classification :

This classification mainly based upon various the position of

the direct patner of the finished restoration . The direct retainer

may be diagonally, diametric, unilaterally or multilaterally placed.

This classification describes the restored rather than the unrestored

arch, so it is of line value because it follows denture design .


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C - Bailyn classification :

Bailyn,s classification is based on the support afforded to the

denture by the tissues . the restorations may be :

o Tissue born prosthesis : the denture is enterily supported by

the mucosa and the underlying bone .

o Tooth –born prosthesis : the denture is entirely supported by

abutment teeth .

o Tooth –tissue supported prosthesis : the denture is supported

bu both abutment teeth and moucosa.

D- Fridman's classification :

Fridman classified partial dentures in to :

Group A – for anterior restoration

Group B- For bounded posterior restoration

Group C- For posterior free end restoration (c= cantilever) .

E - Osborne and Lammie (1974)

• Class I: Denture supported by mucosa and underlying bone

• Class II: Denture supported by teeth

• Class III: Denture supported by a combination of mucosa and tooth-

borne means.

• Class IV: Denture supported by implants.

F.Beckett and Wilson

Class I: Bounded saddle and the abutment can’t support the saddle

• Class II: Free end saddle

A. Tooth and tissue support

B. Tissue support

• Class III: Bounded saddle and the abutment can support the saddle


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Skinner's Classification

He introduced the classification in 1959. He said that about 1,31,072

combinations of partially edentulous arches are possible.

His classification is based on the relation of the edentulous arches to the

abutment teeth.

• Class I: Abutment teeth are present anterior and posterior to the edentulous

space. It may be unilateral or bilateral.

• Class II: All the teeth are present posterior to the denture base which

functions as a partial denture unit. It may be unilateral or bilateral.

• Class III: All abutment teeth are anterior to the denture base which

functions as a partial denture unit. It may be unilateral or bilateral.

• Class IV: Denture bases are located anterior and posterior to the remaining

teeth, and these may be unilateral or bilateral.

• Class V: Abutment teeth are unilateral in relation to the denture base, and

these may be unilateral or bilateral.

H- Kennedy's Classification:

Dr. Edward Kennedy proposed this classification in 1923. This is the

most popular classification. It is based on locations and number of

edentulous areas.

Class I: Bilateral edentulous areas (free-end saddles) located posterior to the

remaining natural teeth.72%

Class II: A unilateral edentulous area (free-end saddle) located posterior to

the remaining natural teeth.14%

Class III: A unilateral edentulous area with natural teeth remaining both

anterior and posterior to it.8,5%


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Class IV: A single, but bilateral (crossing the midline ), edentulous area

located anterior to the remaining natural teeth.3%

Applegate later added two classes

Class V: A unilateral edentulous area with natural teeth remaining both

anterior and posterior to it but the anterior abutment is not suitable for

support.

Class VI: A unilateral edentulous area with natural teeth remaining both

anterior and posterior to it with abutments capable for total support.

FISET'S ADDITIONS

Class VII A partially edentulous situation in which all remaining natural

teeth are located on one side of the arch, or of the median line

Class VIII A partially edentulous situation in which all remaining natural

teeth are located in one anterior corner of the arch

Class IX A partially edentulous situation in which functional and cosmetic

requirements or the magnitude of the interocclusal distance require the use

of a telescoped prosthesis (partial or complete).The remaining teeth are

capable of total or partial support for the prosthesis.

Class X A partially edentulous situation in which the remaining teeth are

incapable of providing any support. If the teeth are kept to maintain

alveolus integrity, the arch must be restored with an OVERDENTURE

which is a complete denture supported primarily by the denture foundation

area


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The numeric sequence of the classification system is based on the

frequency of occurrence of each class. Class I being the most common While

class IV is the least common. This classification was then modified by

Applegate .

Why a unilateral edentulous area is considered as class II?

Because it include features of both class I and class III especially if

modification is present.

Advantages

1- It is the most widely used method of classification of the partially

edentulous arches.

2- It is simple and can be easily applied to nearly all partially

edentulous bases.

3- It permits immediate visualization of the partially edentulous arch

and permits a logical approach to the problems of design.

Applegate has provided the following eight rules governing the

application of the Kennedy system.

Applegate's Rules for Applying the Kennedy Classification:

Rule (1) : Classification should follow rather than precede any

extraction of teeth that might alter the original classification.

Rule (2) : If the third molar is missing and not to be replaced, it is not

considered in the classification.

Rule (3) : If a third molar is present and is to be used as an abutment, it

is considered in the classification.

Rule (4) : If a second molar is missing and is not to be replaced (that is,

the opposing second molar is also missing and is not to be replaced ), it is not

considered in the classification.

Rule (5) : The most posterior edentulous area or areas always determine

the classification.


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Rule (6) : Edentulous areas other than those determining the classification

are referred to as modification spaces and are designated by their number.

Rule (7) : The extent of the modification is not considered, only the

number of additional edentulous areas.

Rule (8) : There can be no modification areas in Class IV arches. Any

edentulous area lying posterior to the "single bilateral area crossing the

midline" would instead determine the classification.

Class IV Partial dentures especially those having long edentulous areas

are considered mesial extension bases. They require the same denture design

principles as class I partial dentures.

ACP classification system for partial edentulism J Prosthodont 2002;11:181-193.

Prosthodontic Diagnostic Index ( PDI )

The American College of Prosthodontists (ACP) has developed a classification

system for partial edentulism based on diagnostic findings. This classification

system is based on diagnostic findings. Four categories of partial edentulism

are defined, Class I to Class IV, with Class I representing an uncomplicated

clinical situation and class IV representing a complex clinical situation. Each

class is differentiated by specific diagnostic criteria.

Diagnostic Criteria

1. Location and extent of the edentulous area(s)

2. Condition of abutments

3. Occlusion

4. Residual ridge characteristics.

Class I

This class is characterized by ideal or minimal compromise in the

location and extent of edentulous area (which is confined to a single arch),


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abutment conditions, occlusal characteristics, and residual ridge conditions.

All 4 of the diagnostic criteria are favorable.

1. The location and extent of the edentulous area are ideal or minimally

compromised:

● The edentulous area is confined to a single arch.

● The edentulous area does not compromise the physiologic support of the

abutments.

● The edentulous area may include any anterior maxillary span that does

not exceed 2 incisors, any anterior mandibular span that does not exceed

4 missing incisors, or any posterior span that does not exceed 2 premolars

or 1 premolar and 1 molar.

2. The abutment condition is ideal or minimally compromised, with no

need for preprosthetic therapy.

3. The occlusion is ideal or minimally compromised, with no need for

preprosthetic therapy; maxillomandibular relationship: Class I molar and

jaw relationships.

4. Residual ridge morphology conforms to the Class I complete

edentulism description.

Class II

This class is characterized by moderately compromised location and

extent of edentulous areas in both arches, abutment conditions requiring

localized adjunctive therapy, occlusal characteristics requiring localized

adjunctive therapy, and residual ridge conditions.

1. The location and extent of the edentulous area are moderately

compromised:

● Edentulous areas may exist in 1 or both arches The edentulous areas do

not compromise the physiologic support of the abutments.

● Edentulous areas may include any anterior maxillary span that does not

exceed 2 incisors, any anterior mandibular span that does not exceed 4

incisors, any posterior span (maxillary or mandibular) that does not exceed


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2 premolars, or 1 premolar and 1 molar or any missing canine (maxillary or

mandibular).

2. Condition of the abutments is moderately compromised:

● Abutments in 1 or 2 sextants have insufficient tooth structure to retain or

support intracoronal or extracoronal restorations.

● Abutments in 1 or 2 sextants require localized adjunctive therapy.

3. Occlusion is moderately compromised:

● Occlusal correction requires localized adjunctive therapy.

● Maxillomandibular relationship: Class I molar and jaw relationships.

4. Residual ridge morphology conforms to the Class II complete


Class III

This class is characterized by substantially compromised location and

extent of edentulous areas in both arches, abutment condition requiring

substantial localized adjunctive therapy, occlusal characteristics requiring

reestablishment of the entire occlusion without a change in the occlusal

vertical dimension, and residual ridge condition.

1. The location and extent of the edentulous areas are substantially

compromised:

● Edentulous areas may be present in 1 or both arches.

● Edentulous areas compromise the physiologic support of the abutments.

● Edentulous areas may include any posterior maxillary or mandibular

edentulous area greater than 3 teeth or 2 molars, or anterior and posterior

edentulous areas of 3 or more teeth.

2. The condition of the abutments is moderately compromised:

● Abutments in 3 sextants have insufficient tooth structure to retain or

support intracoronal or extracoronal restorations.

● Abutments in 3 sextants require more substantial localized adjunctive

therapy (ie, periodontal, endodontic or orthodontic procedures).

● Abutments have a fair prognosis.


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3. Occlusion is substantially compromised:

● Requires reestablishment of the entire occlusal scheme without an

accompanying change in the occlusal vertical dimension.

● Maxillomandibular relationship: Class II molar and jaw relationships.

4. Residual ridge morphology conforms to the Class III complete


Class IV

This class is characterized by severely compromised location and

extent of edentulous areas with guarded prognosis, abutments requiring

extensive therapy, occlusion characteristics requiring reestablishment of

the occlusion with a change in the occlusal vertical dimension, and residual

ridge conditions.

1. The location and extent of the edentulous areas results in severe occlusal

compromise:

● Edentulous areas may be extensive and may occur in both arches.

● Edentulous areas compromise the physiologic support of the abutment

teeth to create a guarded prognosis.

● Edentulous areas include acquired or congenital maxillofacial defects.

● At least 1 edentulous area has a guarded prognosis.

2. Abutments are severely compromised:

● Abutments in 4 or more sextants have insufficient tooth structure to

retain or support intracoronal or extracoronal restorations.

● Abutments in 4 or more sextants require extensive localized adjunctive

therapy.

● Abutments have a guarded prognosis.

3. Occlusion is severely compromised:

● Reestablishment of the entire occlusal scheme, including changes in the

occlusal vertical dimension, is necessary.

● Maxillomandibular relationship: class II division 2 or Class III molar and

jaw relationships.


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4. Residual ridge morphology conforms to the class IV complete


Other characteristics include severe manifestations of local or systemic

disease, including sequelae from oncologic treatment, maxillomandibular

dyskinesia and/or ataxia, and refractory patient (a patient who presents with

chronic complaints following appropriate therapy).


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Implant-Corrected Kennedy (ICK) Classification System for Partially Edentulous Arches Journal of Prosthodontics 17 (2008) 502–5

Guidelines for the new classification system

The new classification system will follow the Kennedy method with

the following guidelines:

(1) No edentulous space will be included in the classification if it will be

restored with an implant-supported fixed prosthesis.

(2) To avoid confusion, the maxillary arch is drawn as half circle facing up

and the mandibular arch as half circle facing down. The drawing will appear as

if looking directly at the patient; the right and left quadrants are reversed.

(3) The classification will always begin with the phrase "Implant-Corrected

Kennedy (class)," followed by the description of the classification. It can be

abbreviated as follows:

(i) ICK I, for Kennedy class I situations,

(ii) ICK II, for Kennedy class II situations,

(iii) ICK III, for Kennedy class III situations, and

(iv) ICK IV, for Kennedy class IV situations.

(4) The abbreviation “max” for maxillary and “man” for mandibular can

precede the classification. The word modification can be abbreviated as “mod.”

(5) Roman numerals will be used for the classification, and Arabic numerals

will be used for the number of modification spaces and implants.

(6) The tooth number using the American Dental Association (ADA) system is

used to give the number and exact position of the implant in the arch. (Note:

other tooth numbering systems such as F´ed´eration Dentaire Internationale

[FDI] can be used, as can the tooth name. The ADA system was used by the

authors because of familiarity).


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Universal numbering system table

Permanent Teeth

upper left upper right

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

lower left lower right

(7) The classification of any situation will be according to the following

order: main classification first,

then the number of modification spaces,

followed by the number of implants in parentheses according to their

position in the arch preceded by the number sign (#).

(8) The classification can be used either after implant placement to describe

any situation of RPD with implants, or before implant placement to indicate the

number and position of future implants with an RPD.

(9) A different name, ICK Classification System, is given to this classification

system to be differentiated from other partially edentulous arch classification

systems.


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ICK I (#2, 15).

ICK I (#2).

ICK I mod 3 (#18, 22, 28, 31).

ICK II (#2).

ICK II mod 1 (#21, 26, 30).

ICK III mod 3 (#23, 26).

ICK IV (#6, 11)


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Component Parts of removable partial dentures

Denture bases.

Artificial teeth .

Supporting rests.

Connectors: Major connectors

Minor connectors

Retainers : Direct retainers

Indirect retainers

These components may provide one or more of the following functions:

1-Support:

a. The resistance of a denture to tissue ward movement.

b. Adequate and wide distribution of the load to the teeth and mucosa.

2- Retention: The resistance of a denture to vertical displacement force (to

move away from its tissue foundation)).

3- Indirect retention: The resistance of denture rotation away from the

tissues about an axis.

4- Bracing: The resistance of a denture to lateral forces.

5- Reciprocation: The resistance of lateral forces on the abutment during

insertion and removal of the removable partial denture .

Reciprocation is required as the denture is being displaced occlusally

whilst the bracing function, comes into play when the denture is fully

seated.

6- Stability: The resistance of a denture to tipping movement.

Tipping movement: Vertical rotation around a line parallel to ridge crest

(twisting of the denture base)

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COMPONENT PARTS OF RPD

Components of metallic removable partial dentures are all rigid, with

the exception of the flexible retentive clasp arm located in an undercut area for

retaining the restoration against dislodging forces.

The components of removable partial denture are:

1. One or More Denture Bases.

2. Artificial teeth.

3. Supporting rests.

4. Major connectors.

5. Minor connectors.

6. Direct retainers.

7. Indirect retainers.

These Components May Provide One or More of the Following Functions:

1-Support: The resistance of a denture to tissue ward movement.

2- Retention: The resistance of a denture to vertical displacement force (to move

away from its tissue foundation).

3- Indirect retention: The resistance of denture rotation away from the tissues

about an axis.

4- Bracing: The resistance of a denture to lateral forces.

5- Reciprocation: The resistance of lateral forces on the abutment during insertion

and removal of the removable partial denture.

Reciprocation is required as the denture is being displaced occlusally whilst the

bracing function, comes into play when the denture is fully seated.

6- Stability: The resistance of a denture to tipping movement.

Tipping movement: Vertical rotation around a line parallel to ridge crest

(twisting of the denture base)

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Denture Base

The denture base is the part of the denture, which rests on the foundation

tissues and to which artificial teeth are attached. The denture base helps in

transferring occlusal stresses to the supporting oral structures.

Types of Denture Bases

1- Bounded partial denture bases

The bounded partial denture base covers an edentulous span between two

abutment teeth.

2- Free-end partial denture bases (distal-extension base)

The base bounded by a natural tooth only on one side, while the other side is

free. This type is sometimes called distal extension base.

3- Bar type saddle

In case of posterior bounded saddle, where esthetic is not important, a bar of

metal is attached directly to the connector to form occlusal surface and no mucosal

contact .

Functions of the Denture Base

1. Carries the artificial teeth.

2. Transfers occlusal stresses to the supporting oral structures.

3. Provides support in distal-extension and long span bounded dentures.

The snowshoe principle, which suggests that broad coverage furnishes the best

support with the least load per unit area, is the principle of choice for providing

maximum support. Therefore support should be the primary consideration in

selecting, designing, and fabricating a distal extension partial denture base.

4. Provides denture retention for distal-extension dentures by physical means.

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5. Provides denture bracing against horizontal movement when extended to cover

lateral borders of the ridge for distal-extension dentures.

6. Provides stabilization against tipping of the distal-extension dentures (On the

contra-lateral side).

7. The denture base and the artificial teeth serve to prevent migration and over

eruption of the remaining teeth.

8. Provide stimulation by massage of the underlying tissues of the residual ridge.

Oral tissues placed under functional stress within their physiological tolerance

maintain their form and tone better than similar tissues suffering from disuse.

9. A the tooth-supported partial denture base that replaces anterior teeth must

perform the following functions:

(1) Provide desirable esthetics;

(2) Support and retain the artificial teeth in such a way that they provide

masticatory efficiency and assist in transferring occlusal forces directly to

abutment teeth through rests;

(3) prevent vertical and horizontal migration of remaining natural teeth;

(4) Eliminate undesirable food traps (oral cleanliness);

(5) Stimulate the underlying tissue.

Requirements of an Ideal Denture Base Material

1- Accuracy of adaptation to the tissues، with minimal dimensional changes.

2- Sufficient strength in order to resist fracture and distortion.

3- Low specific gravity, i.e. light in weight in the mouth.

4- Biological acceptability, non-allergic and non-irritating surface capable of receiving

and maintaining a good finish

5- Allow thermal conductivity necessary for tissue stimulation.

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6- Can easily be kept clean.

7- Esthetic acceptability.

8- Potential for future relining.

9- Low initial cost.

CRITERIA FOR SELECTION

A. NEED TO RELINE.

1. Tooth-mucosa borne partial dentures direct functional forces as

pressure to the mucoosseous tissues. When resorptive changes occur, the

base requires relining to maintain optimum support. Resin bases are

easily relined.

1. In tooth borne partial dentures with long span bases, the base

may require periodic relining to compensate for idiopathic or pressure

induced resorptive changes

B. NEED TO RESTORE MISSING TISSUES. A resin base may be shaped

and shaded to restore anatomic contour and esthetics.

C. LIMITED VERTICAL SPACE. When vertical space is limited, the

minimal space may require a stronger metal base.

D. MAGNITUDE OF APPLIED FORCES. The anticipated occlusal forces

may influence the choice of materials.

E. EASE OF ADJUSTMENT. Resin bases are more easily adjusted than

metal bases.

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Denture Base Material

I- Metallic denture bases

Metallic denture bases are generally used in thinner sections than resin bases.

They are made in the form of metal plates having metal posts that allow for

mechanical attachment with the acrylic resin layer holding the artificial teeth.

Metal such as chrome cobalt alloy, gold, or stainless steel is used. Chrome cobalt

alloy is the most commonly used alloy the material is used in cast form only. It

provides the needed rigidity for removable partial dentures even in thin section. It

has low specific gravity which is nearly half that of gold and provides high

resistance to corrosion.

Advantages of Metal bases as compared to resin bases:

1- Accuracy and Permanence of Form

Denture bases fit more accurately to the underlying tissues. Accurate

metal castings are not subject to distortion by the release of internal

strains as are acrylic denture resins.

The metal base provides an intimacy of contact that contributes

considerably to the retention of denture prosthesis. (called interfacial

surface tension).

Additional posterior palatal seal may be eliminated entirely when a

cast palate is used for a complete denture, as compared with the need for

a definite post-dam when the palate is made of acrylic resin.

Permanence of form of the cast base is also ensured because of its

resistance to abrasion from denture cleaning agents.

2- Comparative Tissue Response

Cast metal base contributes to the health of oral tissue when

compared with an acrylic resin base. Perhaps some of the reasons for this

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are the greater density and the bacteriostatic activity contributed by

ionization and oxidation of the metal base.

Acrylic resin bases tend to accumulate mucinous deposits

containing food particles and calcareous deposits.

3- Thermal Conductivity

Cast metal base has Greater thermal conductivity, while

denture acrylic resins have insulating properties.

4- Weight and Bulk

Metal alloy may be cast much thinner than acrylic resin and

still have adequate strength and rigidity. Cast gold must be given

slightly more bulk to provide the same amount of rigidity but may still

be made with less thickness than acrylic. less weight and bulk are

possible when the denture bases are made of chrome or titanium

alloys.

an acrylic resin base may be preferable to the thinner metal

base in (1) extreme loss of residual alveolar bone may make it

necessary to add fullness to the denture base to restore normal facial

contours and (2) to fill out the buccal vestibule to prevent food from

being trapped in the vestibule beneath the denture.(3) Denture base

contours for functional tongue and cheek contact can best be

accomplished with acrylic resin.(4) acrylic resin bases may be

contoured to provide ideal polished surfaces that contribute to the

retention of the denture, restoration of facial contours, and prevention

of the accumulation of food at denture borders.

5- More hygienic as the fitting surface is polished and non-porous with

less tendency for food accumulation.

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6- Stimulation to the underlying tissue so prevents some alveolaratrophy that would otherwise occur under a resin base and thereby would prolong the health of the tissue that it contacts.

7- Disadvantages of Metal Bases

1. Metal bases are difficult to rebase or reline when ridge resorption

occurs.

2. They are difficult to repair.

3. The color of metal bases does not simulate the natural appearance or

oral tissues.

Retentive post used with metal base.

Indication: 1- short span posterior tooth born 2- when maximum strength is required

3- vertical height limited 4- significance anterior overlap

The choice of alloy is based on several factors:

(1) weighed advantages or disadvantages of the physical properties of the alloy;

(2) The dimensional accuracy with which the alloy can be cast and finished;

(3) The availability of the alloy;

(4) The versatility of the alloy; and

(5) The individual clinical observation and experiences with alloys in respect to

quality control and service to the patient.

A-Chrome cobalt alloy:

It is used in cast form only, needs special investments and special casting

and polishing machine and high casting temperature (2400 f).

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Advantages:

Accurate and rigid even in thin sections.

Low specific gravity 7-9 gram/cm3 nearly 1/2 of that of gold.

Highly polished surface.

High resistance to corrosion and abrasion.

Low density (weight), high modulus of elasticity (stiffness),

Cheaper than gold..

A low-fusing, chrome-cobalt alloy or gold alloy can be cast to

wrought wire, and wrought-wire components may be soldered to

either gold or chrome-cobalt alloys

B-Gold (type 4)

Disadvantages in relation to chrome cobalt:

1-Heavier than chrome cobalt (specific gravity 15 gm/ cm3).

2- More rigid than acrylic resin but less than chrome cobalt. Modiolus of

rigidity 14×106 P.S.I

3- More expensive.

Some times used for lower partial denture to help in retention due to more

specific gravity (weight).

The modulus of elasticity refers to stiffness of an alloy. Gold alloys have a

modulus of elasticity approximately one half of that for chromium-cobalt

alloys for similar uses.

The greater stiffness of chromium-cobalt alloy is advantageous but

at the same time offers disadvantages. The hardness of chromium-cobalt

alloys presents advantages when Greater rigidity can be obtained with the

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chromium-cobalt alloy in reduced sections in which cross-arch stabilization

is required, thereby eliminating an appreciable bulk of the framework. Its

greater rigidity is also an advantage when the greatest undercut that can be

found on an abutment tooth is in the nature of 0. 05 inch. A gold retentive

element would not be as efficient in retaining the restoration under such

conditions as would the chromium-cobalt clasp arm. The hardness of

chromium-cobalt alloys presents a disadvantage when a component of the

framework, such as a rest, is opposed by a natural tooth or by one that has

been restored. We have observed more wear of natural teeth opposed by

some of the various chromium-cobalt alloys as contrasted to the Type IV

gold alloys.

A high yield strength and a low modulus of elasticity produce higher

flexibility. The gold alloys are approximately twice as flexible as the

chromium cobalt alloys, which is a distinct advantage in the optimum

location of retentive elements of the framework in many instances. The

greater flexibility of the gold alloys usually permits location of the tips of

retainer arms in the gingival third of the abutment tooth.

The stiffness of the chromium-cobalt alloys can be overcome by

1- Including wrought-wire retentive elements in the framework.

2- The bulk of a retentive clasp arm for a removable partial denture is often

reduced for greater flexibility when chromium-cobalt alloys are used as

opposed to gold alloys. This, however, is inadvisable because the grain size

of the chromium-cobalt alloys is usually larger and is associated with a lower

proportional limit, and so a decrease in the bulk of chromium-cobalt cast

clasps increases the likelihood of fracture or permanent deformation.

The retentive clasp arms for both alloys should be approximately the

same size, but the depth of undercut used for retention must be reduced by

one half when chromium-cobalt is the choice of alloys.

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It has been observed that gold frameworks for removable partial dentures are

more prone to produce uncomfortable galvanic shocks to abutment teeth

restored with silver amalgam than frameworks made of chromium-cobalt

alloy.

c- Stainless steel:

It is used mainly in swaged form.

The disadvantages of this type are;

1- Less accurate than chrome cobalt or gold

2- Less commonly used.

d- TI/AL/vanadiaum / e- Commercial pure titanium

Commercially pure (CP) titanium and titanium in alloys containing

aluminum and vanadium, or palladium (Ti-0 Pd), should be considered potential

future materials for removable partial denture frameworks.

Currently, when CP titanium is cast under dental conditions, the material

properties change dramatically. During the casting procedure, the high affinity of

the liquid metal for elements such as oxygen, nitrogen, and hydrogen results in their

incorporation from the atmosphere.

The typical Young's modulus of elasticity of titanium alloy is half that of

chromium-cobalt and just slightly higher than type IV gold alloys. This would

require a different approach to clasp design than with chromium-cobalt alloys and

present some advantages. Wrought titanium alloy

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II- Non-metallic, acrylic resin denture bases

Acrylic removable partial dentures are considered as temporary partial dentures. It

is made of acrylic denture base, artificial teeth and wrought wire clasps.

Advantages:

1. Esthetically acrylic resin is satisfactory and looks better in the mouth due to

its pink colour.

2- Acrylic bases are light in weight.

3- The material is easy to reline, rebase or repair.

4- Needs simple processing procedures.

Disadvantages of resin base:

1. Resin bases are weak, brittle and are liable to fracture.

2. In order to attain enough strength, resin bases are made bulky

3. Acrylic bases have low thermal conductivity.

4. The fitting surface is porous and not polished which may lead to

retention of soft food particles and plaque causing bad oral hygiene, bad

odour and inflammation of the tissues.

Indications of Acrylic removable partial dentures:

1- When age and time factors may prohibit the construction of the definitive

prosthesis.

2- During the healing process after extraction until the permanent restoration is

made.

3- Cases with extreme bone loss. The presence of acrylic resin is necessary to

restore the original contour of the ridge, giving more satisfactory results than

metal bases.

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4- When cost is a prime requisite.

5- Acrylic bases of temporary acrylic removable partial dentures.

6- Immediate denture

7- Transitional and interim denture

8- Only few isolated teeth remaining.

Contraindications:

1. Single tooth edentulous spaces.

2. Where protrusive or lateral occlusal guidance will be on the prosthetic teeth.

Types of resin.

a.Polymethylmethacrylatc. (PMMA) (Most commonly used.)

b.Grafted polymethylmethacrylate.

c. 4-meta (4-methacryloxyethyl trimellitate anhydride) containing PMMA.

Potential to chemically bond to alloys capable of oxidation so it

reduce microleakage at metal-resin interface.

d. Polyvinyl.

e. Composite resin.

III- Combined Metallic and Acrylic Resin Bases:

Acrylic resin bases attached to metallic denture framework through

metallic minor connectors.

Metal resin interface exhibits a potential space which may enlarge during

thermo cycling and permit the entrance of microorganisms and fluids. This may

lead to discoloration, plaque accumulation and resin deterioration at the interface.

They are used in the following conditions:

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1. Free-end saddle cases as in Kennedy class I, II and IV and in class III cases

having long edentulous spans to facilitate future relining. Relining is required

to compensate for bone resorption and loss of support, which frequently

occur in these cases.

2. Patients vulnerable to an increased rate of bone loss as diabetic patients or

patients on steroid therapy.

3. Cases with extreme bone loss. The presence of acrylic resin is necessary to

restore the original contour of the ridge giving more satisfactory results than

metal bases.

4. Long span cases.

5. Recent extraction cases which will need early relining.

6. Cases with bone resorption prognosis as diabetic patients.

7. Class IV for appearance.

Methods of Attaching Denture Bases

Denture Base Retention (Grid-work) minor Connector

Acrylic resin bases are attached to metallic denture framework by

means of a minor connector designed so that a space exists between it

and the underlying tissues of the residual ridge. (Relief of at least a 20-gauge

thickness over the basal seat areas of the master cast is used to create a raised

platform on the investment cast on which the pattern for the retentive frame

is formed)

The minor connectors are either made in the form of

a) Lattice work construction.

b) Mesh construction.

c) Bead, wire, or nail-head minor connectors (used with a metal base).

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Retentive mesh and retentive lattice are used when a plastic denture base will

contact the edentulous ridge.

Loops, beads, and posts are used with a metal base to which prosthetic teeth

are attached with processed plastic.

This type of minor connector must be

strong enough to anchor the denture base securely;

rigid enough to resist breakage or flexing,

Must not interfere as possible with arrangement of the artificial teeth.

Extension:

In the maxillary arch if the denture base is a distal extension base (no

tooth posterior to the edentulous space), the minor connector must extend

the entire length of the residual ridge to cover the tuberosities.

When a distal extension ridge in the mandibular arch is being treated, the

minor connector should extend two-thirds the length of the edentulous

ridge.

1- An open latticework (ladder-like pattern).

The latticework consists of two struts of metal, pieces of

12- or 14-gauge half-round wax and 18-gauge round wax are

used to form a ladder like framework., extending longitudinally

along the edentulous ridge.

A longitudinal strut should not be positioned along the ridge crest as it may

act as a wedge in the resin and may cause resin fracture.

In the mandibular arch one strut should be positioned buccal to the crest of

the ridge and the other lingual to the ridge crest.

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In the maxillary arch one strut is positioned buccal to the ridge crest, and the

border of the major connector acts as the second strut.

Smaller struts, usually 16 gauge thick, connect the two struts and form the

latticework. These connecting struts run over the crest of the ridge and should be

positioned to interfere as little as possible with arrangement of the artificial teeth.

Generally, one cross strut between each of the teeth to be replaced should be

satisfactory.

The latticework minor connector can be used whenever multiple teeth are to

be replaced. It provides the strongest attachment of the acrylic resin denture base to

the removable partial denture. It is also the easiest of the denture base retainers to

reline if this becomes necessary because of ridge resorption.

In construction, wax forms of the struts are positioned on the refractory

(investment) cast, which is duplicated from the master cast.

It is necessary to provide a relief space over the dentulous ridges for both the

latticework and the mesh minor connector so that there will be a space between

the struts or mesh and the underlying ridge.

It is in this space and around the struts or mesh that the acrylic resin denture

base will be formed. The locking of the acrylic resin around and through the

latticework provides the retention of the denture base.

Relief under the grid-work should not be started immediately adjacent to the abutment tooth but should begin 1.5 - 2 mm from the abutment tooth.

The junction of grid works to the major connector should be in the form of a butt joint with a slight undercut in the metal.

The grid work on a mandibular distal extension should extend about 2/3 of the way from abutment tooth to retromolar pad but not on the ascending portion of the ridge mesial to the pad. It should has a “tissue stop” at their posterior limit to provide direct contact with the ridge.

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Maxillary distal extension grid-works should extend at least 2/3 of the length of the ridge to the hamular notch. However, the junction or finishing line of the maxillary major connector should extend fully to point to the hamular notch area so that the acrylic resin base can be extended into this area and provide a smooth transition from the connector to the base.

2- in a closed meshwork configuration (plastic mesh pattern).

The mesh type of minor connector consists of a thin sheet of metal with multiple small holes that extendsover the crest of the residual ridge to the same buccal, lingual, and posterior limits as does the latticework minor connector.

It can be used whenever multiple teeth are to be replaced.

The mesh pattern is less satisfactory as the space available for incorporating acrylic resin between metallic strips is narrow so it makes it more difficult to pack the acrylic resin dough because more pressure is needed against the resin to force it through the small holes and not allow for enough bulk of resin which become weak and may detached from the metal base. It also does not provide as strong an attachment for the denture base.

The major difference between retentive mesh and retentive lattice is the size of the openings. Retentive mesh has small openings while retentive lattice has much larger openings.

The mesh type tends to be flatter, with more potential rigidity, but may provide less retention for the acrylic if the openings are insufficiently large.

The lattice type has superior retentive potential, but can interfere with the setting of teeth, if the struts are made too thick or poorly positioned.

Denture Base

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Both types are acceptable if correctly designed.

3- Metal denture bases

Posts, loops, beads , nail head, wire loop retention or metal stop may be used to for retention of the resin. with metal denture base, which is cast so that it fits directly against the edentulous ridge; no relief is provided beneath the minor connector.

The retention is gained by the projection of metal on this surface. These projections may be

beads (made by placing beads of acrylic resin polymer in the waxed denture base and investing, burning out, and casting these beads);

wires that project from the metal base,

In the form of nail-head.

This form of denture base is hygienic because of better soft tissue response to metal than acrylic resin. But it can not be relined adequately in the event that ridge resorption takes place.

This type should be used on tooth-supported, well-healed ridges and when

inter arch space is limited and the available vertical space is so limited that an

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acrylic resin base would be thin and weak. Because relining is not possible metal

bases are generally not indicated for extension RPDs.

Minor connectors forming mandibular distal extension bases extend

posteriorly about two-thirds the length of the edentulous ridge. They should be

slightly extended onto the buccal and lingual surfaces of the ridge. This design adds

strength to the acrylic denture base and helps to minimize-distortion of cured resin

bases, which occurs due to the release of strains after processing. However, minor

connectors for maxillary distal extension bases may sometimes be extended to

cover the entire length of the residual ridge.

Minor connectors forming denture bases should include tissue stops and

finishing line:

Tissue stops:(tissue foot)

It is a foot included in the fitting surface of minor connector designed for

retaining acrylic base.

Tissue stops are integral parts of minor connectors.

They provide stability to the framework during the stages of transfer and

processing. They are particularly useful in preventing distortion of the

framework during acrylic resin processing procedures.

Altered cast impression procedures often necessitate that tissue stops be

augmented subsequent to the development of the altered cast. This can be

readily accomplished with the addition of autopolymerizing acrylic resin.

Tissue stops are essential parts in the fitting surface of minor connectors.

They are usually two or three in number that contact the cast.

Tissue stops stabilize the framework on the master cast during processing

as acrylic resin is packed in the retention spaces.

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Tissue stops elevate the minor connectors, forming the denture base, from the

ridge, by a space equal to the thickness of acrylic bases.

They are formed by making holes 2×2 mm in the relief wax placed over the

ridge during preparation of the master cast before duplication.

a b

Tissue stops prevent settling of the framework downwards, and elevate the minor connectors by a

space equal to the thickness of acrylic base.

Finishing index tissue stop:

It is located distal to the terminal abutment and is

a continuation of the minor connector contacting the

guiding plane. Its purpose is to facilitate finishing

of the denture base resin at the region of the

terminal abutment after processing.

Finishing Lines:

Finishing lines are butt joints created at the junction of major connectors

with the denture bases.

Finish lines must be provided on all partial denture frameworks wherever

denture base resin and the metal join.

A finish line allows the resin to terminate in a butt joint to produce a

smooth surface.

In distal extension bases, these butt joint finishing lines, are made on both

the external and internal surfaces of the major connector where acrylic resin is

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Mostafa Fayad 20

processed, while in short bounded metallic bases, the butt joint is required only on

the external surface where acrylic resin is packed, for the attachment of teeth.

External finish lines-:

An external finish line is located on the polished surface of a partial denture

and is formed in the wax pattern.

a. External finish lines are formed during the formation of the wax

pattern by carving a sharp definite angle in the wax pattern at the junction between

the major connector and the minor connectors forming the denture base.

b. This angle should be less than 90 degrees to lock the acrylic resin

securely to the minor connectors and for the acrylic base to blend smoothly and

evenly with the major connector.

c. External finish line is positioned just far enough lingual to the ridge

crest to position the artificial teeth.

d. External finish line fades into minor connectors or proximal plates as

it approaches the occlusal surfaces of the contacting teeth.

e. The external finish line should never be placed directly over the

internal finish line. It should be placed superiorly to the internal finish line so that a

minimum amount of denture base resin is used on the lingual aspect of the teeth.

For maxillary RPDs. the palatal finish line should be located so that it allows

for proper positioning of the artificial teeth while still maintaining normal tissue

contours and a smooth transition from metal to plastic. It should be located 2 mm

medial from an imaginary line that would contacts lingual surfaces of missing

posterior teeth.

For a mandibular distal extension RPD, the external finish line begins at the

distolingual aspect of the terminal tooth and angles posteriorly as it progresses

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toward the floor of the mouth. The lingual finish line for a mandibular tooth-

supported RPD should be located just far enough lingually to allow for setting of

the artificial teeth. If it is placed too far lingually (and thus inferiorly), the major

connector will be weakened.

Internal finish lines:

An internal finish line is located on the internal or tissue surface and is

formed while blocking out the master cast.

If the resin ends in a thin edge, saliva and debris will accumulate between

the denture base resin and the metal. The resin will also fracture if left too thin in

this area.

a. Internal finish lines are formed by carving the relief wax used to create

space for packing acrylic resin under mesh minor connector. This relief wax is

applied on the master cast before duplication.

b. In tooth-mucosa borne RPD the internal finishing line (IFL), it is placed

approximately at the junction of the vertical and horizontal planes of the palate to

permit proper relining since resorption of bone occurs all the way up to this level.

While in case of maxillary tooth borne PD, the IFL is slightly palatal to the EFL.

c. The internal finish line is located on the tissue surface side of the

framework. It is formed by the 24- to 26-gauge relief wax placed on the master cast

prior to duplication.

d. The internal finish line is normally placed farther from the abutment

tooth or residual ridge than the external finish line.

e. Internal finish line should be located to allow resin to cover mueo-

osseous areas where resorptive changes are anticipated. This permits the base to be

relined to reestablish mueo-osseous support.

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f. Internal finish line should be located 3-4 mm from the natural teeth.

This allows a highly polished metal surface to be placed adjacent to the free

gingival margins.

g. Internal finish line should form a well defined butt joint with the

denture base resin.

h. Internal line angle of the internal and external finish lines should be

less than 90 degrees to provide mechanical retention for the denture base resin.

i. Internal and external finish lines should not be superimposed. A

staggered (offset) relationship maintains framework strength.

j. The palatal extension of the internal finish line is determined primarily

by the need to reline the partial denture to compensate for anticipated bone

resorption.

For tooth borne partial dentures, the internal finish lines should be

placed slightly palatal to the external finish lines. This staggered

relationship contributes to increased framework strength and an

adequate thickness of resin between the finish lines. Placement of

the internal finish line more palatally is usually not indicated,

since only minimal resorptive changes occur.

For tooth-mucosa borne partial dentures, the internal finish lines

in the edentulous regions should be placed close to where the

vertical and horizontal planes of the palate meet. This position is

approximately 10 mm lingual to the previous position of the

lingual gingival margins of the missing teeth. This permits proper

relining, since bone resorption may occur up to this level. The

horizontal portion of the hard palate is relatively resis¬tant to

pressure-induced resorptive changes.

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1 2 3

1: black arrow indicates the external finishing line(EFL) in tooth-mucosa borne RPD.

2:. a case of maxillary tooth-mucosa borne RPD. arrow (A) indicates The internal finishing

line(IFL), it is placed approximately at the junction of the vertical and horizontal planes of

the palate to permit relining. Arrow (B) indicates the EFL

3: in case of maxillary tooth borne PD, the IFL is slightly palatal to the EFL

External finish lines: junction of major

connector and minor connectors at palatal

finishing line should be located 2 mm

medial from an imaginary line that would

contacts lingual surfaces of missing

posterior teeth.

Denture base extension

Maximum coverage of the edentulous ridge is always desirable to allow

greatest area of bone to share in resisting the occlusal stresses exerted during

mastication. This helps in decreasing the force per unit area and keeping the forces

within the physiologic tissue tolerance.

a) Antero-posterior extension

- In bounded spaces: It is determined by the abutment teeth.

- In free-end spaces: The base extends to cover the retromolar pad in the lower arch and hamular notches and tuberosity in the upper`.

b) Buccally: The flange should extend to the mucosal reflection. The labial flange is sometimes omitted for esthetic reasons.

Denture Base

Mostafa Fayad 24

c) Lingually: The flange of the lower denture base should extend to the full depth of the lingual sulcus as permitted by muscle function.

Lingual surfaces usually are made concave except in the distal palatal area.

Buccal surfaces are made convex at gingival margins, over root prominences, and at

the border to fill the area recorded in the impression. Between the border and the

gingival contours, the base can be made convex to aid in retention and to facilitate

the return of the food bolus to the occlusal table during mastication. Such contours

prevent food from being entrapped in the cheek and from working under the

denture.

Occasionally, the path of insertion can cause the denture flanges to impinge

on the mucosa above undercut portions of the residual ridge, when the partial

denture is being seated. In these instances, it is usually preferable to shorten the

flange, rather than relieving the internal surface. If the internal surface is

relieved significantly, a space will exist between the denture base and the tissues

when the denture is fully seated. Food may become trapped in the space and work

its way under the partial denture.

Relationship of denture base to abutment

The ideal relationship between the denture base carrying the artificial teeth and the

adjacent abutment should either be:

1- Close contact between the denture and the proximal surface of the abutment. In

this condition relieving the gingival margin is necessary to avoid its traumatization.

2- Open Contact between artificial teeth carried by the denture base and the

abutment above the contact point allowing enough space between them to create a

cleansable area.

On the other hand improper contact between the denture and the abutment tooth

leaving only a small space between the neck of the abutment tooth and the artificial

tooth is undesirable. This small space is difficult to clean predisposing to caries,

gingivitis and pocket formation.

Denture Base

Mostafa Fayad 25

Ideal base/abutment tooth relationship

1-Close contact between the denture and the proximal surface of the abutment

2- Open Contact. Enough spaces are self-cleansing.

AESTHETICS OF RPD IN RELATION TO THE LABIAL FLANGE:

LONG ANTERIOR SADDLE

The natural appearance presented by the labial and buccal flange of a long

saddle is dependent upon:

� The shaping of the gingival papillae,

� The shaping of the gingival margins,

� The overall contouring of the flange as a whole, and

� coloring and shading.

In shaping the gingival papillae, the space between the teeth should be

filled. The resin representing the papilla may then be lightly polished to give a

surface, which is readily self-cleansing.

The shape of the entire gingival margin is usually more sharply curved if the

neck of the tooth is not prominent, but is higher and straighter if the neck is

prominent. A more vigorous expression may be obtained by emphasizing the

convexity of the gingival margin. The whole area of the gingival margin should be

polished highly to avoid food debris accumulating round the necks of the teeth.

Denture Base

Mostafa Fayad 26

In ageing, both the interdental papilla and the gingival margin require

modification. The papilla is positioned higher on the neck of the tooth, and the

gingival margin regresses up the root of the tooth and a pointed rather than a curved

form should be used, especially at the neck of a prominent tooth such as the canine.

Contouring of the labial flange should be carried out to simulate the

development of bony prominences over the roots of teeth and Interdental

depressions. Stippling of the attached gingiva, as well as giving a pleasing natural

appearance, has been found to restrict lip movement in some cases. The lateral

margins of labial flanges must be reduced to wafer thinness and be extended over

the root eminences of the abutment teeth.

The thin edge allows the colour of the flange to blend more naturally with

the mucosa. Coloring and shading of labial flanges must be considered to blend

harmoniously with the natural tissues of the patient. Many manufacturers supply

acrylic materials containing colored fibers, to which may be added additional stain

and shaded polymers.

SHORT ANTERIOR SADDLE

�The general principles discussed in relation to long anterior saddles apply equally

to shorter ones:

�The artificial papilla must be shaped to match the natural closest papilla.

�The shape and contour of the gingival margin must be similar to that of the

natural teeth.

�The junction between artificial and natural gum tissue as mixed together as

possible.

The margins of the flanges must be reduced to water thinness, and whenever

possible, extended over the eminences of the abutment teeth. Such thin edges not

only blend inconspicuously with the natural tissues, but also allow their colour to

Denture Base

Mostafa Fayad 27

show through. It will be necessary to employ a path of insertion that will allow the

thin acrylic to pass over the eminence.

2. A gum-fit can be done by using a longer tooth than is really indicated which is

unsightly when the necks of the teeth are revealed by the patient. Usually it is better

to use a small flange if possible since this can be very thin and discreet and nearly

undetectable at normal distances. The use of a flange also increases the saddle area

which is desirable whenever possible. Fitting to the gum is recommended in some

cases where the first premolar has to be replaced and the canine is still standing.

The ridge just posterior to the canine is often quite prominent and the tooth

angulations will be better if no flange is used. In addition, a flange in this area is

often noticeable when the patient smiles.

RESTS AND REST SEATS

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Definitions

Rests:

Are rigid extensions of a partial denture, fitted into rest seats, which are prepared on either the occlusal, lingual surfaces or incisal edges of the teeth, providing support to the partial denture.

Support:

The quality of the prosthesis to resist displacement towards denture supporting structures.

Rest seat:

The prepared recess in a tooth or restoration created to receive occlusal, incisal, or lingual rest.

Types of Rests:

A- EXTRACRONAL (EXTERNAL) REST: which used with an extracronal clasp assembly-type direct retainer although it is primarily within the contours of the abutment tooth.

According to their shape and location on the tooth surface they may be classified as:

1- Occlusal rest.

(1) Proximal occlusal (conventional),

(2)Interproximal

(3) Transocclusal (embrasure).

(4) Extended

2- Incisal rest.

3- Lingual rest.

4- Embrasure Hooks

5- Rest Recess


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B- INTRACRONAL (INTRENAL) RESTS fit into rest preparations within the contours of an abutment tooth crown. It is used with many precision and semiprecision attachments.

PRECISION RESTS consists of two metal components manufactured to fit together precisely. One component is a box type rest seat, keyway or matrix which is incorporated into the crown of an abutment tooth. The other component is a rigid metal extension (patrix) which fits the matrix precisely and is incorporated into the RPD.

A SEMIPRECISION REST is a box-type rest seat, keyway or matrix which is fabricated in the dental laboratory byincorporating a preformed plastic pattern into the wax pattern for the crown of the abutment tooth, or by waxing the crown pattern around a special mandrel in the dental surveyor thus forming the contour of the rest preparation. After the crown is cast, the matrix is machined (milled) with a bur held in a surveyor. The patternfor the patrix of the semi precision rest is formed by a performed plastic pattern or by waxing directly to the matrix (rest preparation) in a crown or a cast of the crown. The patrix is cast as part of the RPD framework.

Rests may be classified into

A- according to relation to direct retainer

1- Primary rest: it is a component of direct retainer

2- Secondary rest: it is an additional rest used on other than abutment teeth for gaining extra support or act as indirect retainer.

B- According to shape:

1- Saucer shape. 2- Box shape

3- Dove tailed 4- Triangle

5- V- shape. 6- Saddle shape

7- Boomerang shape 8- Circular (conservative).

C- According to the abutment tooth

1- Posterior rests

2- Anterior rests


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I- Occlusal Rest:

A rigid extension of a removable partial denture located on the occlusal surface of a posterior tooth, on a rest seat specially prepared to receive it.

Requirements of the Occlusal Rest:

1. The occlusal rest must fit the tooth accurately to minimize the food collection beneath it and preserve its location in relation to the tooth.

2. The angle formed by the occlusal rest and the vertical minor connectorshould be less than 90 o so that the transmitted occlusal forces are directed toward the long axis of the tooth.

3. It should have sufficient thickness of metal to withstand the loads without deformation or breakage.

4. It must not raise the vertical dimension of occlusion.

5. In bounded partial denture: occlusal rests are placed in the near zone of the occlusal surface of the two abutments bounding the edentulous span.

6. In free end partial dentures: the occlusal rest is placed on the far zone of the occlusal surface of the abutment, in order to decrease the torque action on the abutment tooth.

Functions of the Occlusal Rest

1. Support: it transmits forces from the prosthetic teeth to the abutment teeth so the main function of occlusal rest is to provide support to the partial dentureagainst vertical forces, this prevent settling of the denture towards the underlying tissues, which will:

a- Prevent a spreading of the clasp arms, and maintains the components of the dentures in their planned positions.

b- Prevents impingement of the gingival tissues adjacent to the abutment teeth.

N.B. partial denture without occlusal rests is called “gum stripper”.

2. Assist in distributing the occlusal load among two teeth or more so that each can bear a proportionate share of the masticatory load in concert with the residual ridges.


Mostafa Fayad - 4 -

3. Help maintain the plane of occlusion in the region of the abutment teeth.The occlusal rest can be shaped to improve the existing occlusion by building out the occlusal surface of the tooth to allow contact with the opposing teeth.

4. It may act as indirect retention along with its minor connector if they are placed beyond the fulcrum.

5. Maintain the clasp in the correct position on the abutment tooth thus helping

to maintain the effectiveness of the retentive and reciprocal components of the

clasp.

4. Serve as a reference point for evaluating the fit of the framework to the teeth.

5. Help prevent extrusion, tipping, or migration of the abutment teeth.

8. In addition to these functions, an internal rest may provide some bracing and

retention for the RPD.

Effect of occlusal rest location on the tooth :

- An extended occlusal rest covering the whole occlusal surface of the

tooth "Onlay rest" allows for the transmission of the vertical load over the whole

occlusal surface and directs the forces along the long axis of the tooth.

- An improperly extended occlusal rest placed on one side of the

occlusal surface causes torque on the tooth when vertical forces are applied. - To

prevent this torque either:

a) Extend the occlusal rest across the mesio-distal center of the tooth,

b) Use two short oppositely placed occlusal rests one on the mesial and the other

on the distal surface of the tooth,

Forms and Requirements of Rest Seat Preparation:

1- Preparations for the occlusal rest must precede making master cast and follow proximal preparation (guiding planes and elimination of undesirable undercuts).

2- Rest seats are prepared in sound enamel, cast restoration or rarely amalgam alloy. The use of amalgam restoration as support for an occlusal rest is the least desirable because of its tendency to flow under pressure and also because of the comparative weakness of a marginal ridge made of this alloy. Occlusal rests can be prepared in an old amalgam restoration.

3- When a metal restoration (inlay, onlay or crown) is planned for an abutment tooth, the rest seat must be carved in the wax pattern of the


Mostafa Fayad - 5 -

restoration and refined in the cast metal before the restoration is seated in the mouth.

4- The out line form of an occlusal rest seat should follow the outline form of the fossa present on the occlusal surface and should be rounded triangular in shape, the base of the triangle – located at the marginal ridge- is about one third to one half the mesiodistal width of the tooth, it is about 2.5 mm in width, and its rounded apex is directed towards the center of the tooth .

5- it should be one half the buccolingual width of the tooth from cusp tip to cusp tip which correspond to one third of the whole buccolingual diameter of the tooth

6- The marginal ridge is lowered approximately one to 1.5 mm to permit sufficient bulk of metal to provide strength and rigidity to the rest without interference with the opposing teeth.

7- The rest seats may be prepared in either a box shaped or saucer shaped form:

Saucer- Shaped Rest Seat: preparation have concave, spoon or saucer shaped form to prevent locking of the occlusal rest and transmission of lateral and tipping forces to the abutment. They are used in free end saddle cases and bounded cases having weak abutments.

Boxed Shaped Occlusal Rest have vertical walls and flat floor, they are rarely used in bounded cases having strong abutments.

8- The rest seat should have smooth gentle curves with no sharp walls, angles or ledges.

9- It should be deep enough to have sufficient space for sufficient bulk of the rest to be rigid without interference with occlusion. A rest seat is prepared to make room for the occlusal rest. Space for the rest should not usually be created by grinding the upper palatal cusp as this is a supporting cusp contributing to the stability of the intercuspal position.

10- A The floor of the seat should be

a- Inclined apically as it approaches the center of the tooth to direct the force

towards the long axis of the tooth.


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b- The angle formed by the seat & the vertical minor connector should be

also less than 90o for directing the load towards the long axis of the abutment

and prevent slipping of rest creating an orthodontic like force and to direct the

forces along the long axis of the tooth.

c- For distal extension partial denture it should be saucer or spoon to prevent

transmission of lateral forces to the abutments. The rest may move slightly in

function, like a ball and socket to dissipate horizontal forces.

d- For bounded cases having strong abutments it may have relatively box-

shape.

When an existing occlusal rest preparation is inclined apically toward the

reduced marginal ridge and cannot be modified or deepened because of fear of

perforation of the enamel or restoration, then a secondary occlusal rest must be

employed to prevent slippage of the primary rest and orthodontic movement of

the abutment tooth.

Preparation of occlusal rest seats

Rest seat preparations should be made in sound enamel.

The preparation of occlusal rest seats always must follow proximal preparation, never precede it. Only after the alteration of proximal tooth surfaces is completed may the location of the occlusal rest seat in relation to the marginal ridge be determined.

Occlusal rest seats in sound enamel may be prepared with burs and polishing points that leave the enamel surface as smooth as the original enamel.

Occlusal rest seats in crowns and inlays are generally made somewhat larger and deeper than those in enamel. Those made in abutment crowns for tooth-supported dentures may be made slightly deeper than those in abutments that support a distal extension base; thus they approach the effectiveness of boxlike internal rests.

1- The larger round bur is used first to lower the marginal ridge and to establish the outline form of the rest seat.

2- A slightly smaller round bur is then used to deepen the floor of the occlusal rest seat.


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When a small enamel defect is encountered in the preparation of an occlusal rest seat, it is usually best to ignore it until the rest preparation has been completed. Then, with small burs, prepare the remaining defect to receive a small restoration.

3- A fluoride gel should be applied to abutment teeth following enamel

recontouring. If the master cast will be fabricated from an irreversible

hydrocolloid impression, application of the gel should be delayed until after

impressions are made. This is because some fluoride gels and irreversible

hydrocolloids may be incompatible.

Existing restoration may be perforated in the process of preparing an ideal

occlusal rest seat. The rest seat may be widened to compensate for shallowness,

but the floor of the rest seat should still be slightly inclined apically from the

marginal ridge. When this is not possible, a secondary occlusal rest should be

used on the opposite side of the tooth to prevent slipping of the primary rest.

Special Considerations for Rest Seat Preparation

1- Boxed shaped occlusal rest

The box shaped rest seat is preferably prepared in a cast gold restoration. If it is sufficiently deep it is also provide guide-surfaces to control the path of insertion of the denture.

It can be employed only on a strong periodontally healthy abutment.The rest seat has a flat floor, sharp line angles and nearly vertical walls. The box shaped rest helps in preventing lateral movement of the denture; it provides some bracing and retention for the RPD.

It can be used on few occasions in bounded cases as it applies more torque on the abutment tooth.

2- Dove tailed occlusal rest: it may prepared in short span bounded saddle

3- Extended occlusal rest

It may extend to the center of the tooth or entirely across the occlusal

surface. The purpose of extending the rest to the center of the tooth or across the

entire occlusal surfaces is to:


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1) Direct forces more parallel to the long axis of the root than if the rest is

just on the mesial or distal of the tooth,

2) Provide increased stabilization (bracing) of the tooth and sometimes.

3) Provide occlusal contacts with the opposing teeth.

The occlusal rest preparation which extends mesiodistally through the

occlusal surface of a tooth is sometimes called a CONTINUOUS REST

PREPARATION.

The function of extended occlusal rest:

1. Gain support from both teeth.

2. Restores occlusion.

3. Prevent the posterior molar from elongation.

4. Eliminates the need for maxillary prosthesis/

Indication

In Kennedy Class II , modification 1, and Kennedy Class III situations in which the most posterior abutment is a mesially tipped molarto minimize further tipping of the abutment and to ensure that the forces are directed down the long axis of the abutment.

4- Interproximal Occlusal Rest Seats

The design of a direct retainer assembly may require that interproximal occlusal rests be used. The rest seats are prepared as individual occlusal rest seats, with the exception that the preparations must be extended farther lin-gually than is ordinarily accomplished.

They are used to avoid interproximal wedging by the framework. Additionally, the joined rests will shunt food away from contact points.

It is located in a fossa adjacent to another tooth. Its size, shape and dimensions are similar to the proximal occlusal rest preparation EXCEPT that the flare of the facial margin is limited by the proximal contact with the adjacent tooth. The embrasure occlusal rest preparation rarely extends beyond the primary fossa.

In preparing such rest seats


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1. Avoid weakening or eliminating contact points of abutment teeth.

2. Sufficient tooth structure must be removed to allow for adequate bulk of the component for strength.

3. Occlusion should not be altered.

4. Rest seat preparations are extended lingually to provide strength (through bulk) without overly filling interproximal space with minor connector. This type of preparation is rather difficult, and care must be exercised to avoid violation of contact points. The marginal ridge of each abutment should be sufficiently lowered (1.5 mm).

5- Transocclusal rests (Embrasure rest):

A transocclusal rest preparation is similar in size and shape to an embrasure occlusal rest preparation EXCEPT that the preparation is extended facially to create space for the rest and clasp arm to extend onto the facial surface of the tooth

The embrasure type of clasp is, basically, two simple circle clasps jointed together, and the rest recesses should be fashioned on the two abutment teeth.

This rest can be used to bridge a gap between teeth, thus providing an effective roof over the vulnerable interdental area. It also prevents food impaction between the spaced teeth.

As a general rule, if an embrasure or interproximal occlusal rests are to be used, the occlusal fossa of the adjacent tooth is also prepared with an embrasure occlusal rest preparation UNLESS THERE IS A REASON NOT TO such as occlusion, existing restorative material, etc.

6- Internal Rest (the milled rest, the semi precision attachment)

The internal rest consists of narrow slot or key way, built into a metal casting that has been constructed for an abutment tooth, and into which is fitted a male attachment that has been made an integral part of removable partial denture framework.

An intracoronal rest is not a retainer and should not be confused with an attachment . The form of the rest should be parallel to the path of placement, slightly tapered occlusally, and slightly dovetailed to prevent dislodgment proximally.

Advantages:


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1- It facilitates the elimination of a visible clasp arm buccally

2- Permits the location of the rest seat in a more favorable position in relation to the tipping axis(horizontal) of the abutment.

3- Provide both occlusal support and horizontal stabilization

Indication: in partial denture that is totally tooth supported by means of cast retainers on all abutment teeth.

7- Onlays:

They are extended occlusal rests covering the whole occlusal surface and extending buccally and lingually. They are retained by mechanical or adhesive means. Onlays may be cast in gold or chrome cobalt.

Functions or Onlays:

1. Provide partial denture support.

2. Help in improvement of occlusion by increasing the reduced vertical dimension. (Correction of close bite).

3. It could be constructed with reduced cusp angle to minimize the lateral component of force, which is destructive to the abutment teeth.

4. Splinting: onlays can be constructed on multiple abutments and joined together during casting to help in splinting periodontally weak teeth.

8- Rotated tooth: the preferred treatment is either to:

1- Cover the crown with a restoration that realigns the surfaces of the tooth with the other teeth in the arch.

A Correctly-shaped onlay B: lncorrectly-shaped onlay



2- Alter its axial surfaces sufficiently to render it more suitable for clasping and to place the occlusal rest in the mesial or distal fossa of the buccal or lingual side of the alveolar ridge.

3- If it is not practical to place the rest in either fossa, it should be remembered that the occlusal rest might be placed anywhere on the surface of the tooth where a properly designed recess can be prepared to support it.

9- Tipped molar (Mesially inclined mandibular molar):

The severely tipped mandibular molar sometimes presents a problem for the placement of an occlusal rest because it is so difficult to engineer the recess in such a manner that stresses are directed along the long axis of the tooth. Failure to direct the stress axially may permit the forces of occlusion to tilt the tooth farther mesially.

The recess for a typical mesially inclined mandibular molar should be prepared with the floor perpendicular to the long axis of the tooth to avoid tipping the tooth farther mesially.

The rest should be designed to prevent further tipping, it must direct forces down the long axis of the tooth by either of one of these ways: -

A) An additional occlusal rest in the distal fossa: A rest positioned in this way tends to counteract any tendency of the tooth to tip farther mesially.

B) A rest preparation that extended from the mesial marginal ridge to the distal triangular fossa to minimize further tipping.

C) When a casting is required, such as full veneer crown or onlay, it should be constructed with flat occlusal surface perpendicular to the long axis. A one to two millimeters bevel on the buccal and lingual surfaces and a two to three millimeter guide plane on the mesial surface will provide bilateral bracing and prevent further tipping of the tooth. The occlusion is restored with a chrome cobalt or gold occlusal overlay as part of partial denture. Such type of rest construction takes advantages of the inclined plane effect directing forces along the long axis of the tooth.



II-Lingual Rests:

A- Cingulum Rest (inverted V Rest).

B. Ball Rest.

C. Canine Ledge.

A- Cingulum Rest (inverted V Rest):

The cingulum rest is a portion of a partial denture that is placed in an enamel seat at the cingulum or just incisal to it. This is confined to maxillary canines that have a gradual lingual incline and prominent cingulum. It is rarely satisfactory on mandibular anterior teeth due to inadequate thickness of enamel (Fig،3-94).

The most satisfactory preparation is that placed on a prepared seat in a cast restoration (cast veneer crown, a three-quarter crown or an inlay) (Fig،3-95,3-96).

When preparing a cingulum rest in a cast restoration, the rest seat should be planned and done on the wax pattern before casting the restoration.

Cingulum Rest

Specification of Cingulum Rest Seat:

1. A rounded inverted V-shaped preparation (half -moon shaped), on the lingual surface of anterior teeth, having 2.5: 3 mm mesiodistal length, 2 mm. Labiolingual width and 1.5 mm. in depth.

2. All sharp angles and undercuts should be eliminated.

5. The rest seat is broadest at the center and as it approaches the proximal surfaces it merges with the normal anatomy of the tooth.

2 mm

1:1.5 mm 2.5:3



6. Properly designed cingulm rest on the canine, prevents movement of the rest in a gingival direction and maintains tooth position.

B. Ball Rest

Cingulum ball rests with rounded outline are placed on the mesial or distal halves on the lingual surfaces of all anterior teeth, usually atthe junction of the gingival and middle one thirds. Having 1.5 mm depth and 2.5 mm width.

Ball rest permits rotational movements to occur during function of tooth-mucosa born RPDs.

Such rest may be prepared on tooth surfaces with sufficient enamel thickness or may be prepared in restorations placed in teeth with inadequate enamel thickness (Amalgam or pin ledge, cast restoration, etc.).

Ball burnisher placed in rest seat preparation to verify contour. When an axially directed force is applied on the ball burnisher it should not slip out of the rest seat.

C. Canine Ledge

* It is a step-like preparation placed on the mesial or distal halves of the lingual surfaces of the maxillary canine. Usually at the junction of the gingival and middle one thirds. Having 1.5 mm depth.

* The ledge rest seat should be perpendicular to the long axis of the tooth. All undercuts and sharp line angles should be avoided.

They are generally used where the tooth does not have a prominent cingulum or where a finger-type rest is to be used .

D. Lingual dimple-shaped rest preparation : it is employed when there is limited surface on anterior teeth due to occlusal contacts.



E. individually cast chromium-cobalt alloy rest seat forms (attached to lingual surfaces of anterior teeth by use of composite resin cements with acid-etched tooth preparation), laminates, and composite resins have been successfully used as conservative approaches to forming rest seats on teeth withunacceptable lingual contours.

F. Sapphire ceramic orthodontic brackets have also been bonded to the lingual surfaces of mandibular canines and shaped as rest seats. These have advantages over the metal acid-etched retained rest in that a laboratory step is avoided and increased bond strengths are achieved.

The major disadvantage to using orthodontic brackets is that removal of the rest seat would necessitate that they be ground off with the potential of heat generation and possible pulpal damage.

Preparation of an anterior tooth to receive a lingual rest

Preparation may be started by using an inverted, cone-shaped diamond

stone and progressing to smaller, tapered stones with round ends to complete the

preparation. All line angles must be eliminated, and the rest seat must be

prepared within the enamel and must be highly polished.

Shaped, abrasive rubber polishing points, followed by flour of pumice,

produce an adequately smooth and polished rest seat. The floor of the rest seat

should be toward the cingulum rather than the axial wall. Care must be taken not

to create an enamel undercut, which interferes with placement of the denture

III- Incisal rest:

It is a rigid extension of a removable partial denture that are placed at theincisal angles of anterior teeth on prepared rest seats. They are used predominantly as auxiliary rests or as indirect retainers.

It is more applicable on mandibular teeth due to lack of adequate thickness of enamel on the lingual surface.



The rest seat is a saddle- shaped preparation in the form of a small, V-shaped round notch located approximately 1.5 to 2.0 mm from the proximal -incisal angle of the tooth. It is having about 2.5 mm wide and 1.5 mm deep.

An incisal rest is more likely to lead to some orthodontic movement of

the tooth because of unfavorable leverage factors than is a lingual rest. The notch

should extend slightly onto the facial surface to prevent the tooth from moving

labially.

An incisal rest seat is prepared in the form of a rounded notch at the

incisal angle of a canine or on the incisal edge of an incisor, with the deepest

portion of the preparation apical to the incisal edge. The notch should be

beveled both labially and lingually, and the lingual enamel should be partly

shaped to accommodate the rigid minor connector connecting the rest to the

framework. All borders of rest seat are rounded to avoid sharp line angles.

Proximal edge of rest seat is rounded rather than straight.

N.B.: Whereas the most preferred site for a rest, is the occlusal surface of a molar and premolar. If anterior tooth is the only abutment available, a canine is preferred over an incisor. In the absence of canine multiple lingual rests are prepared on anterior teeth.

A- Lingual view demonstrates inclination of floor of rest seat, which allows forces to be directed along the long axis of tooth as nearly as possible.

The Lingual Rest is Preferable to an Incisal Rest because:

It is placed closer to the center of rotation of the abutment tooth, thus it will exert less leverage and reducing its tendency to tipping.

More esthetic, as it can be discreetly hidden from view.

It tends to be less bothersome to a curious tongue.

1.5

2.0



Use of Incisal rest may be justified by the following factors:

1. They may take advantage of natural incisal faceting.

2. Tooth morphology does not permit other designs.

3. Such rests can restore defective or abraded tooth anatomy.

4. Incisal rests provide stabilization.

5. Full incisal rests may restore or provide anterior guidance.

IV- Embrasure Hooks:

Rests placed in embrasures between natural teeth extending slightly over the buccal or labial surface but never extend below the survey line.

They provide support, splinting of natural teeth, resistance to lateral and anteroposterior movement and may act as indirect retainer.

Their disadvantages are poor esthetics and wedging action on teeth.

Functions:

1- Resistance to anteroposterior movements.

2- Help in splinting of the periodontally effected teeth.

3- Support the denture

4- Brace the denture

Disadvantages of embrasure hooks:

1- Bad esthetic.

2- May cause separation of teeth by wedging action.

V- Rest Recess

In mandibular bicuspid with a rudimentary (undeveloped) cusp or in the

abraded tooth



The most satisfactory solution is to cover such a crown with a cast

restoration, building a cingulum rest into the wax pattern similar to the type used

for the canine tooth.

VI-Quasicingulum rest

It is prepared for lower first premolar having rudimentary lingual cusp

and consists of accentuated cingulum rest seat prepared in wax up of retainer.

DESIRABLE MATERIALS FOR REST PREPARATIONS

Enamel and cast metal are ideal materials for rest preparations. Porcelain is less desirable because of its propensity to fracture.

Rest preparations may be prepared as an economic necessity in amalgambut the flow and low yield strength of amalgam and the possibility of recurrent caries and fracture of the tooth and/or restoration make amalgam an undesirable material for a rest preparation.

Dentin is an undesirable material for a rest preparation because of its lowabrasion resistance and propensity for caries. Unfortunately, dentin is frequently exposed when placing rest preparations in natural teeth. In these situations the tooth does not need to be restored unless it is sensitive or caries is anticipated.

Conventional and resin composite are unacceptable materials for restpreparations because of their low yield strength and low abrasion resistance.

Major Connectors

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CONNECTORS

The various components of removable partial dentures are connected together by connectors. Connectors are described as being either

A- Major connectors. B. Minor connectors

Major Connectors

A major connector is the unit of R.P.D., which joins parts of the prosthesis located on one side of the arch with those on the opposite side.

Functions of connectors:

1. Join the component parts of the denture together.

2. Contribute to the support of the prosthesis, by distribution of stresses applied to the prosthesis.

3. They may contribute to the functions of bracing and reciprocation.

4. Contribute to retention of the prosthesis

5. Connectors resting on prepared dental or firm oral tissues provide indirect retention. Connectors that are relieved from the underlying tissues or lie on inclined surfaces do not provide indirect retention.

Classification:

a) According to the materials: Metallic or non metallic .

b) According to the rigidity: Rigid or non-rigid (stress breaking)

c) According to the dimensions: Bar, strap or plate.

d) According to the location: Maxillary or mandibular .

Principles for design for major connectors: see biomechanics

L-bar or L-beam principle.

Circular configuration.

Strut configuration.

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General requirements of major connector:

1-Rigid: Rigidity is necessary to transmit and distribute stresses over the entire

supporting area and from one side of the arch to the other.

Other components of the partial denture such as retentive clasps, occlusal rests,

and indirect retainers can be effective only if the major connector is rigid.

2- Must not impinge on the marginal gingiva: It should provide vertical

support and protect the soft tissue to avoid impingement of the gingival margin.

In the maxillary arch the border of the major connector should be located at

least 6 mm from the gingival margin, and 3mm in the mandible.

The border of the M C should be run parallel to the gingival margin of the teeth.

If the gingival margin must be crossed, the crossing should be at right angles to

the margin to produce the least possible contact with the soft tissues. Relief, or a

space, must be provided between the metal and soft tissue.

3- Must be properly located in relation to gingival and moving tissues. Bony or

soft tissue prominences should be avoided

4- Provide a means of obtaining indirect retention where indicated: The MC

may act as indirect retainer as in the form of lingual plate.

4- Provide an opportunity of positioning denture bases where needed; the

selection of the type of MC will at time be dictated by the location of the denture

bases replace the missing teeth. The location and number of denture bases

influence the type of MC that must be used.

5- Self cleansble not allow trapping of food particles

6- Not interfere with phonetics by using proper thickness and avoid covering the

rugae area if possible.

8- All adjoining minor connectors should cross-gingival tissues abruptly, and

should join major connectors at nearly a right angle.

7- Maintain patient comfort: Should provide patient's comfort through:

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- Tapering the edges toward the tissues

- Prevent sharp angles or corners to prevent annoying tongue

- Prevent crossing of bony prominences as tori.

- Never place the connector on convex tooth surface or incisal third of teeth.

- The border should not end on the crest of prominent rugae but in the valleys

between these crests.

- They should be symmetric on both sides and cross the palate in straight line

MAXILLARY MAJOR CONNECTORS

A maxillary major connector is the unit of R.P.D., which joins parts of the prosthesis located on one side of the maxillary arch with those on the opposite side. Intimate contact between the tissue side of the maxillary major connector and the palatal tissues is necessary for accommodation of RPD to enhance its support, retention, and bracing.

General form of maxillary major connectors

Maxillary major connectors are either in the form of bars, straps or plates. The bars and straps are usually made of metals; the plates could be entirely made of metal or sometimes a combination of metal and non-metal. However bars cover less amount of tissues than plates.

The term bar is used whenever the anteroposterior width of the major-connector is less than 8 mm. If the anteroposterior width of the major connector is in the 8 to 12 mm. range the term strap is applied. When more than 12 mm is covered the term palatal plate is used. If the entire palate is covered, the term complete palatal plate is used.

1-Bars

a. Bars are usually narrow, less than 8 mm in width (6-8 mm) and half oval in cross section. Their margins are beveled and gently curved.

b. They cover lesser amounts of tissues.

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c. However, bars require more bulk of metal in order to gain the required rigidity; this bulk may interfere with proper speech and may be untolerated by patients.

2-Straps

a. They are wide and thin palatal bars, more than 8 mm in width to gain the necessary rigidity.

b. Having a uniform thickness, its width could be increased in distal extension base.

c. The palatal strap is well tolerated because it is not bulky.

d. A wide strap helps in the distribution of stresses of mastication over a wider area of the palate and thus provides adequate support.

3-Extended palatal plates:

a. the words palatal plate are used to designate any thin, broad, contoured palatal coverage used as a maxillary major connector and covering one half or more of the hard palate.

b. The maximum area coverage contribute to

i. Wide distribution of the stresses falling on denture.

ii. Better support and retention of the prosthesis.

iii. Better horizontal stabilization of the prosthesis

Structural Requirements of Maxillary Major Connectors

1. PLACEMENT OF BORDERS

a. The borders are placed at least 6 mm from the gingival margins.

b. When a 6 mm distance from the gingival margins cannot be

obtained, the metal may be extended onto the cingula of anterior

teeth or onto the lingual surfaces of the posterior teeth.

c. All borders should be tapered slightly towards the tissues to be

less perceptible to the patient.

d. The finished borders should be smoothly curved.

e. In the rugae region the border should pass through the valleys

between the crests of the rugae when possible.

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f. The posterior border should not extend onto the movable soft

palate,

g. The borders should be beaded.

h. Both anterior and posterior borders should cross the midline at

right angles, never diagonally.

i. The borders should run parallel rather than diagonal to the

gingival margin and if they cross the gingival margin they should

be crossed abruptly and at right angle to the margin in order to

produce the least possible soft tissue coverage.

2. THE METAL SHOULD NOT BE HIGHLY POLISHED ON THE

TISSUE SURFACE: to preserve intimate tissue contact, except where it

crosses the gingival margin

3. RELIEF OF THE MAJOR CONNECTOR.

Usually no relief is required on the tissue surface of the major

connector. When crossing the gingival margins, the tissue surface should

be lightly relieved and highly polished. Little relief may be required in the

presence of palatal tori or prominent median

4. THICKNESS OF THE METAL should be uniform throughout the palate.

5. FUTURE LOSS OF ATURAL TEETH. When future loss of natural

teeth is anticipated a plate type design may be used. The plate should

extend onto the cingula of anterior teeth or onto the lingual surfaces of

posterior teeth.

6. INTERNAL AND EXTERNAL FINISH LINE: see denture base

7. TISSUE STOPS: see denture base

8. BEADING

Beading is a term used to denote the scribing of a shallow groove on the maxillary master cast outlining the palatal major connector exclusive of rugae areas

1. A palatal major connector should have a specially prepared seal along the border of the connector where it contacts the soft tissues.

Major Connectors

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2. The seal is formed by a beading at the border of the major connector that displaces the soft tissues slightly, this preventing food from collecting under the maxillary major connector and help in preventing over growth of the palatal tissues.

3. Beading is readily accomplished by using an appropriate instrument, such as a cleoid carver. Care must be exercised to create a groove not in excess of 0. 5 mm in width or depth at the edge of the design of the maxillary major connector. The groove must fade out as it approaches within 6mm of the marginal gingiva. It also should fade out over the center of the cast when a hard midline suture is present.

Advantages of beading:

1- Prevents food debris from collection under the MC.

2- Provide a thinnest metal on the polished surface while maintain the necessary

strength. This is due to the extra thickness of metal provided by the beading.

The purposes of beading are as follows:

1. To transfer the major connector design to the investment cast

2. To provide a visible finishing line for the casting

3. To ensure intimate tissue contact of the major connector with selected palatal

tissue

Six basic types of maxillary major connectors are considered: Mac

1. Single palatal bar

2. Anterior-posterior palatal bars connector

3. Single palatal strap

4. U-shaped palatal connector

5. Combination anterior and posterior palatal strap type

6. Palatal plate-type connector

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MAXILLARY MAJOR CONNECTORS

I- PALATAL BARS

Palatal bars may be in the form of single palatal bars or combined palatal bars.

1- Anterior palatal bar

Indication:

It is rarely used alone but might be included in the design in conjunction with posterior palatalbar when indirect retention is required as in Kennedy class I and II or long span class III.

Design:

It is located in the anterior palatal region, sometimes used when anterior teeth are missing.

The bar should be located 6-8 mm behind the gingival margin of anterior teeth.

Disadvantages

a. The anterior palatal bar is intolerable by patients as it crosses the palatal rugae where tongue activity is marked.

b. Speech difficulties may be encountered.

2- Middle palatal bar

Indication:

The middle palatal bar is single bar, mainly used in short bounded edentulous spans.

Design:

-The bar crosses the middle portion of the palate away from the rugae area.

Advantages:

a. It is comfortable, well tolerated and inconspicuous by the tongue, hence speech is not affected as the bar crosses the mid-palatal area away from both the rugae area and the tongue.

b. It provides some support since it lies on the horizontal part of the palate.

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c. Bracing is achieved because the bar prevents lateral movement of the appliance.

Disadvantage:

a. It lacks the required rigidity unless made bulky.

b. It cannot be used in cases having large torus palatinus or prominent median palatine raphe.

3-Posterior palatal bar

Indication:

The single posterior palatal bar has limited indications for use. It is used in tooth supported posterior dentures and in unilateral distal extension partial denture replacing one or two teeth.

Design:

a. It is located in close relation to the junction of the hard and soft palate, or placed in level with the second molar.

b. The bar is narrow and half oval in cross-section.

Advantages

a. The bar exhibits limited palatal coverage and well tolerated by the tongue if made with proper thickness. It is not likely to affect taste.

b. Bracing is provided by the part of the bar contacting the lateral side of the palate.

c. The posterior palatal bar provides indirect retention for Kennedy class IV cases.

Disadvantages:

a. It is rarely used nowadays, because it cannot be made bulk, thus lacks the required rigidity.

b. It cannot be used in cases having an extended large torus palatinus.

Major Connectors

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Single Posterior Palatal Bar:

Indications: In tooth- borne partial denture when second premolars and or

first molars are missing.

Design:

1. It is a narrow half oval with its thickest point at the center.

2. It is gently curved and should not form a sharp angle at the junction with the

denture base.

3. It should not be placed further anterior to the second premolar. This position

is favorable for the tongue action.

Disadvantages:

1. For a single bar to maintain any degree of rigidity it should be bulky (less

acceptable by the patient).

2. It drives little support from the bony palate because its narrow anteroposterior

width.

3. Its use is limited to replace one ore two teeth on each side of the arc.

4. It is used only in interim PD until the definitive treatment can be rendered.

Anterior PB Middle PB Posterior PBLocation Nearly 6mm away

from the gingival margin

Between the 1st molars Its posterior border lies at the junction between the hard and soft palate

Cross section Flat Flat Half ovalFunction Connection and

indirect retention in class I & II

Connection Connection and indirect retention in class IV

Tolerance Poor Well tolerated Well toleratedStability Gives lateral stabilityIndications When a torus prevent

usage of middle or posterior PB

Class IIIUnilateral free end saddle

Esthetics Satisfactory Satisfactory Satisfactory

Major Connectors


4- Anteroposterior palatal bar (Ring Design, A-P bar)

Indication

1. It can be used in any class especially when the anterior and posterior abutments are widely separated.

2. When a patient objects a large amount of palatal coverage.

3. It is almost used in any design especially in the presence of torus palatinus and in dentures restoring anterior teeth.

Design:

Anterior palatal bar

-Flat thin, wide bar located 6 mm away from the gingival margin of anterior teeth. Its borders should be placed in the depressions and slopes of the rugae, never on their crests.

Posterior palatal bar

- Thick bar, half oval in cross-section, located as far posteriorly on the hard palate, preferably in level with the second molar.

- Both anterior and posterior connectors should cross the midline at a right angle rather than diagonally.

Longitudinal bars:

- Two bars, one on each side of the palate, at the junction of its horizontal and vertical planes. They join the anterior and posterior bars forming the ring or circle configuration. Thus, the metal forming the connector lies in two different directions giving the connector strength and rigidity.

Advantages:

a. The A-P bar is the most rigid bar type palatal major connector because it lies at different planes.

b. It attains minimal soft tissue coverage

Disadvantages:

The anteroposterior bars should not be considered as the first choice because of the following disadvantages:

1. Provides little support from the palate.

Major Connectors


2. The anterior bar covers the rugae area and may interfere with phonetics and patient's comfort.

3. Because the bars are narrow, extra bulk is required for rigidity.

4. The multiple borders and edges of the bars may annoy the tongue and are intolerable by some nervous patients.

Contraindications:

a. The A-P bar is contraindicated in the following cases.

b. Patients exhibiting high, narrow palatal vault.

c. Patients having large tori extending to the junction of the hard and soft palate.

II- PALATAL STRAPS

The palatal strap is a wider and thinner than palatal bar, having uniform thickness.

1- anterior palatal strap (palatal horse-shoe, U-shaped)

Indications:

a. When several anterior teeth are being replaced. The palatal horse-shoe is primarily indicated when posterior teeth are to be replaced especially when a large torus exists.

b. In tooth-borne partial dentures with anterior and posterior teeth are missing.(bounded saddle).

c. When a hard midline suture or palatal torus cannot be covered.

d. Tooth-supported unilateral edentulous situations with provision for cross-arch attachment by either extracoronal retainers or internal attachments.

Characteristics and Location:

a. It consists of U-shaped thin band of metal. The anterior border placed 6 mm away from the gingival margin lying in the valleys rather than the crests of the rugae area.

Major Connectors


b. Posterior border at right angle to median suture line.

c. If the strap carried onto the cingula, the gingival margin must be lightly relieved.

d. The lateral borders lies at the junction of the horizontal and vertical slopes of the palate.

e. All borders should be curved, smooth and beaded.

f. Strap should be 8 mm wide or approximately as wide as the combined width of a maxillary premolar and first molar.

g. Confined within an area bounded by the four principal rests.

When increased rigidity is required, metal thickness in the central portion

may be increased to 1.5 mm, or the width of the major connector may be

increased to lie in two planes.

A common error in the design of a U-shaped connector, is its proximity to or

actual contact with gingival tissue.

Blockout and Relief of Master Cast

(1) Usually none required except slight relief of elevated medial palatal raphe or any exostosis crossed by the connector.

(2) One thickness of baseplate wax over basal seat areas (to elevate minor connectors for attaching acrylic resin denture bases).

Beading

Waxing Specifications

Anatomic replica pattern equivalent to 22- to 24-gauge wax depending on arch width.

Finishing Lines

(1) Undercut and slightly elevated.

(2) No farther than 2 mm medial from an imaginary line contacting lingual surfaces of principal abutments and teeth to be replaced.

(3) Follow curvature of arch.

Major Connectors


Advantages:

a. The connector provides some vertical support.

b. Indirect retention may be provided.

c. It solves the problem of missing anterior teeth especially when there is deep anterior vertical overlap.

Disadvantages:

a. The palatal horse-shoe is a poor connector because it lacks the necessary rigidity, this major connector should be avoided whenever possible

b. Lack of rigidity causes movement or spreading of the lateral borders of the connector when vertical force is applied.

c. To obtain enough rigidity it should be made bulky, but this could interfere with phonetics and might cause discomfort.

d. It covers the rugae area and interferes with phonetics and patient's comfort.

Contraindication:

For reasons of torque and leverage, a single palatal strap major connector should not be used to connect anterior replacements with distal extension bases.

2-Middle Palatal Strap: [some text consider posterior palatal = (midpalatal) strap.]

The middle palatal strap is the most versatile and widely used maxillary major connector.

Indications:

a. Tooth borne and tooth and tissue borne unilateral edentulous spaces for cross arch stabilization.

b. May be used for most maxillary tooth borne

partial dentures when posterior teeth are missing.

c. May be used for tooth-mucosa borne partial dentures when minimal

palatal support is required.

Major Connectors


Design:

The strap lies on the central portion of the hard palate.

It consists of a wide, thin band of metal that crosses the palate.

Its anterior border should be posterior to the rugae area and the posterior border should terminate short of the junction of the hard and soft palate

The anteroposterior dimension of the middle palatal strap is usually little greater than the posterior palatal strap.

Advantages of the middle palatal strap:

1. Provide greatest rigidity with less bulk of metal, because it is located in three planes (horizontal, or vault of the palate; the vertical or lateral slopes of the palate; the sagittal, or anterior slope of the palate).

2. Reduces gingival margin coverage to a minimum.

3. It is well tolerated because it can be kept away from the sensitive area around the rugae and incisive papilla.

4. The anterior border lies just posterior to the commencement of the rugae area, where the number of tactile receptors is smallest.

5. It is rarely annoying to the patient.

6. It can be made relatively narrow, for the small tooth supported prosthesis, or much wider when the edentulous spaces are longer and the requirement for support is correspondingly greater.

7. There is also minimal interference with phonetics.

8. It provides support to the partial denture since it covers a relatively large area of the palate.

Disadvantages:

The patient may complaint from excessive palatal coverage.

3-Posterior Palatal Strap

This is basically a wide palatal bar, because it is wider it may be made thinner, it should be a minimum of 8 mm. in width, and 1.5mm thickness.

Indication:

Major Connectors


- In maxillary unilateral tooth borne RPDs of short span.

Advantages:

1. It provides better support than a palatal bar.

2. It distributes stresses of mastication over a wider area than a palatal bar.

Disadvantages:

1. The increased coverage of the palate as compared to the palatal bar may be objectionable to some patients.

2. There may be some alteration of taste if made very wide.

Structural details:

1. The border should be beaded.

2. Should be wide (a minimum of 8 mm width) and thin (1.5 mm thickness).

3. Thicker central area for increased rigidity.

4- Anteroposterior palatal strap (Closed Horseshoe):

The anteroposterior palatal strap is a rigid connector; indication:

(1) Class I and II arches in which excellent abutment and residual ridge support exists, and direct retention can be made adequate without the need for indirect retention.

(2) Long edentulous spans in Class II, modification 1arches.

(3) Class IV arches in which anterior teeth must bereplaced with a removable partial denture.

(4) Inoperable palatal tori that do not extend posteriorly tothe junction of the hard and soft palates.

(5) In tooth borne, and mucosa borne partial dentures when replacement of anterior and posterior teeth is required.

Major Connectors



The connector has similar location and structure to that of the anteroposterior palatal bar except that both the anterior and posterior components are in the form of straps.

(1) Parallelogram shaped and open in center portion.

(2) Relatively broad (8 to 10 mm) anterior and posterior palatal straps.

(3) Lateral palatal straps (7 to 9 mm) narrow and parallel to curve of arch; minimum of 6 mm from gingival crevices of remaining teeth or should extend above the height of contour of the teeth..

(4) Anterior palatal strap:

anterior border positioned as back as possible on the rugae area to minimize interference with speech , not placed farther anteriorly than anterior rests and never closer than 6 mm to lingual gingival crevices; follows the valleys of the rugae at right angles to the median palatal suture.

Posterior border, if in rugae area, follows valleys of rugae at right angles to the median palatal suture.

(5) Posterior palatal connector: posterior border located at junction of hard and soft palates and at right angles to median palatal suture and extended to hamular notch area(s) on distal extension side(s).

(6) Anatomic replica or matte surface.


(1) Usually none required except slight relief of elevated median palatal raphe where anterior or posterior straps cross the palate.



(1) Anatomic replica patterns or matte surface forms of 22-gauge thickness.

(2) Posterior palatal component—A strap of 22-gauge thickness, 8 to 10mm wide (a half-oval form of approximately 6-gauge thickness and width) may also be used.

Major Connectors


Finishing Lines

Same as for single broad palatal major connector.

Advantages:

a. Rigidity and strength of the connector because it lies at two different planes, allow the metal to be used in thinner sections.

b. Provides good support due to wide palatal coverage.

c. Good retention and stability could be achieved.

III- Extended palatal plate (Complete Palatal Coverage)

A palatal plate connector covers half or more of the palatal surface. It is a uniformly shaped, thin plate reproducing the anatomic contour of the palate. It is characterized by wide palatal coverage contributing to maximum support and retention, also helps in horizontal stabilization and bracing of the restoration..

Types of complete palatal plates

1- Metal plate: Complete cast metal plate covering more than half of the palate.

2- Resin plate: Complete resin plate covering the whole palate. see denture base for detail

3- Combination, metal, and resin plate: Anterior metallic part having provisions for mechanical retention to attach an acrylic posterior portion.

Indications:

1. Class I partially edentulous arches when all posterior teeth are to be replaced. (Only six remaining anterior teeth).

2. If anterior edentulous areas are present in conjunction with bilateral distal-extension bases.

3. Class II arch with a large posterior modification space and some missing

anterior teeth.

4. Cases having shallow vault or flat ridge as the complete plate will provide good stabilization.

5. Where heavy occlusion demands maximum support.

Major Connectors


6. Class III Kennedy with modifications, when the condition of the abutment is poor.

7. Patients with cleft palate.

8. When the partial denture is considered a transitional prosthesis (acrylic palatal plate is used).

9. Should be used whenever maximum tissue support is desired.

10. V- or U-shaped palates


The anterior border of the plate is either placed 6: 8mm away from the gingival margin following valleys ofrugae as near right angle to median suture line, or the anterior border may be extended to lie on the survey line or above cingulae of anterior teeth, in this case-the gingival margin should be slightly relieved.

The posterior border of the plate at right angle to the median suture line; extended to pterygomaxillary notches (hamular notch )area(s) on distal extension side. It extends to the junction of the hard and soft palate. It should provide a peripheral seal, which adds to the retention of the denture.

The borders are beaded to prevent debris from collecting beneath the plate.

The posterior palatal seal that is used with complete dentures can not be used with a removable partial denture. Because of the rebound of the tissues under compression, place unnecessary extra forces on the abutment teeth. The intimate contact of the cast metal palate aids retention through adhesive and cohesive forces.

The palatal plate should be located anterior to the posterior palatal seal area. The maxillary complete denture's typical posterior palatal seal is not necessary with a maxillary partial denture's palatal plate because of the accuracy and stability of the cast metal.


(1) Usually none required except relief of elevated median palatal raphe or any small exostoses covered by the connector.


Major Connectors



Anatomic replica pattern equivalent to 24-gauge sheet wax thickness.

Finishing Lines

(1) Provision for butt-type joint at pterygomaxillary notches.

(2) Undercut and slightly elevated.

(3) No farther than 2 mm medial from an imaginary line contacting the lingual surfaces of the missing natural teeth.

(4) Following curvature of arch.

Advantages:

1. The plate is well tolerated by most of the patients. Its uniform thinness and the thermal conductivity of the metal are designed to make the palatal plate more readily acceptable to the tongue and underlying tissue.

2. The plate covering different palatal planes provide more rigidity.

3. The extensive area coverage contributes to:

a- Wide distribution of load and maximum support of the prosthesis.

b- Horizontal stabilization (reduce the movement of the base during function).

c- Direct-indirect retention due to the extended extension thatincreased interfacial surface tension, good peripheral seal and physiologic retention by dorsum of the tongue.

4. The plate may help in splinting periodontally weak teeth.

5. It offers maximum rigidity, support and retention to the partial denture

Disadvantages:

a- The plate cannot be used in the presence of palatine tori.

b- Full coverage may cause tissue inflammation if adequate oral hygiene is not practiced and it may cause alteration in taste.

c- Complete palatal coverage may alter taste and tactile sensation.

Major Connectors


The palatal plate may be used in any one of three ways.

1- As a plate of varying width that covers the area between two or more

edentulous areas,

2- As a complete or partial cast plate that extends posteriorly to the junction

of the hard and soft palates,

3- or in the form of an anterior palatal connector with a provision for

extending an acrylic resin denture base posteriorly.

Modified palatal plate

Indications:

a. Tooth-Mucosa Borne RPDs.

b. When complete palatal coverage is either not required or unacceptable to the patient.

The width varies proportionate1y with

1- The requirement for muco-osseous support

2- The length of the edentulous span

3- Amount of anticipated occlusal forces

4- Bone index of abutment teeth or the residual ridge

5- Periodontal status of abutment teeth

Split maxillary major connectors

Permits a variable degree of independent movement of the muco-osseous supported segment of the RPD.

Indications.

a.May be used where some stress release from the abutment teeth is desired through the major connector.

b.May be used in place of stress releasing clasps or stress directors.

Major Connectors


Design:

a.Degree of stress release is determined by the width and thickness of the connection remaining and by the type of metal used.

b.Separation of the segments should be wide enough or very narrow to avoid pinching the tongue or palatal mucosa.

c.The cast framework can flex in a single plane without work hardening and eventual fracture.

Sequence of design considerations for a maxillary major connector:

In 1953 Blatterfein described a systematic approach to designing maxillary major connectors. His method involves five basic steps and is certainly applicable to most maxillary removable partial denture situations.

Step 1: Outline of primary bearing areas. The primary bearing areas are those that will be covered by the denture base(s).

Step 2: Outline of nonbearing areas. The nonbearing areas are the lingual gingival tissue within 5 to 6 mm of the remaining teeth, hard areas of the medial palatal raphe (including tori), and palatal tissue posterior to the vibratingline. (Nonbearing areas outlined in black).

Step 3: Outline of connector areas. Steps 1 and 2, whencompleted, provide an outline or designate areas that are available to place components of major connectors.

Step 4: Selection of connector type.

Selection of the type of connector(s) is based on four factors: mouth comfort, rigidity, location of denture bases, and indirect retention.

To achive mouth comfort connectors should be of (1) minimum bulk ,(2)positioned so that interference with the tongue during speech and mastication is not encountered.

Major Connectors


Connectors should have a maximum of rigidity to distribute stress bilaterally.The double-strap type of major connector provides the maximum rigidity without bulk and total tissue coverage.

In many instances the choice of a strap type of major connector is limited by the location of the edentulous ridge areas. When edentulous areas arelocated anteriorly, the use of only a posterior strap is not recommended. By the same token, when only posterior edentulous areas are present, the use of only an anterior strap is not recommended.

The need for indirect retention influences the outline of the majorconnector. Provision must be made in the major connector so that indirect retainers may be attached.

Step 5: Unification. After selection of the type of major connector, the denture base areas and connectors are joined.

Major Connectors


B- MANDIBULAR MAJOR CONNECTORS

Mandibular major connectors used in partial dentures are either in the form of bars or plates. The bars are usually located on the lingual side of the ridge between the gingival margin and the floor of the mouth, while the plates may be extended above the gingival margin to end on the lingual surfaces of the natural teeth.

Structural Requirements for Mandibular Major Connectors:

1- PLACEMENT OF BORDERS.

a. The superior borders are placed a t least 3 mm from the gingival marginsand parallel to the free gingival margin or for the lingual plate it should beextends to the cingulae of the anterior teeth in which the gingival margin should be relieved.

Where a 3 mm distance from the gingival margins cannot be obtained, the metal should extend on to the cingula of anterior teeth or onto the lingual surfaces of the posterior teeth.

b. The inferior border should be gently rounded above the moving tissues of the floor of the mouth and should not interfere with the soft tissue movement of the floor of the mouth.

2. Beading is never indicated because of the need for relief under all mandibular major connectors,

3- The metal should be highly polished on the tissue side to minimize plaque accumulation.

4-RELIEF: Relief (0.5-1mm) must be provided between the mandibular major connectors and the soft tissue to prevent the margins of the connectors from inflammation or laceration the friable lingual mucosa during movement.

The amount of relief depends on

a) The type of removable partial denture.

- For an all tooth-supported prosthesis a minimum of relief is needed

because the denture does not tend to move, (30 gauge, 0.010 inch)

- Where in a distal extension partial denture needs more relief because

it tends to rotate during function.

b) The slope of the lingual tissue.

Major Connectors


If the lingual slope is near vertical, this needs minimal relief. If the lingual

slope is toward tongue, maximum relief is needed. If lingual slope have

undercut, sufficient space which may create during blocks out the

undercut, and not need additional relief.

A. Slope of tissue is nearly vertical; minimal relief is needed

B- Tissue slope toward the tongue, maximum relief is needed

C- Lingual ridge is undercut; no additional relief is required .

c) Relationship of the fulcrum line to the major connector.

1. When the fulcrum line is posterior to the major connector less

relief is usually required (28 gauge, 0.013 inch to 26 gauge, 0.016 inch).

2. When the fulcrum line is anterior to the major connector more

relief is usually required (26 gauge, 0.016 inch to 24 gauge, 0.020 inch).

d) Quality of supporting structures.

1 - Periodontal status of the abutment teeth. Increased mobility of the

abutment teeth requires more relief of the major connector.

2 - Quality of the muco-osseous supporting tissues. Residual ridges with

increased displaceability may require more relief of the major connector.

Major Connectors


3- Bone index. Where the residual ridge exhibits a poor bone index, more

relief may be required to compcnsate for resorptive changes occurring prior

to anticipated relining.

e) Movement of the dento-alveolar segment.

When the anterior teeth have a pronounced labial inclination, more relief

may be required. It may be impossible to direct the occlusal forces along the

long axes of the teeth. With such an inclination, a continued labial migration of

the teeth may occur. The labial migration may result in the major connector

impinging on the soft tissues.

Loading force (F) applied to tooth. Force is

not directed along long axis, tooth may move

labially. Lingual bar may impinge on soft tissues

f) Lingual tori may require additional relief.

Six types of mandibular major connectors are: Mac

1. Lingual bar

2. Sublingual bar

3. Cingulum bar (continuous bar)

4. Lingual bar with cingulum bar (continuous bar)

5. Linguoplate

6. Labial bar

Major Connectors


1- Lingual bar

The lingual bar is the simplest of the mandibular connectors, and should be used in preference to other mandibular major connectors whenever possible.

Indication:

It is the first choice major connector, should be used whenever the functional depth of the lingual vestibule equal or exceed 7 mm. (sufficient space exists between the slightly elevated alveolar lingual sulcus and the lingual gingival tissue).

If future additions of prosthetic teeth to the framework to replace extracted natural teeth are not anticipated.

Diastemas or open cervical embrasures of anterior teeth.

Overlapped anterior teeth.


1. The lingual bar is and located on the lingual side of the alveolar ridge.

2. It should be a half-pear shape in cross section, tapered superiorly with the broader and thicker portion at the inferior border.

3. Superior inferior dimension is 3-5 mm, and it is 2 mm in thickness.

4. Upper border of the connector should be 3-4 mm below and parallel to the free gingival margin to avoid hypertrophy to the soft tissues.(3-4mm from gingival margin)

5. The inferior border should be gently rounded above the moving tissues of the floor of the mouth; to avoid irritation or injuring the sub adjacent tissues when the restoration moves.( vestibule must be 7mm at least)

6. The bar should be relieved sufficiently but not excessively over the underlying tissues, Lingual tori are generously relieved when surgery is contraindicated.

7. The normal thickness is a 6-gauge, it may be altered to some degree if

additional rigidity is needed, but care must be taken to avoid tongue

interference during speech or mastication.

Major Connectors



(1) All tissue undercuts parallel to path of placement.

(2) An additional thickness of 32-gauge sheet wax when the lingual surface

of the alveolar ridge is either undercut or parallel to the path of placement.

(3) No relief is necessary when the lingual surface of the alveolar ridge

slopes inferiorly and posteriorly.

(4) One thickness of baseplate wax over basal seat areas (to elevate minor

connectors for attaching acrylic resin denture bases).


(1) Six-gauge, half-pear-shaped wax form reinforced by 22- to 24-gauge

sheet wax or similar plastic pattern adapted to the design width.

(2) Long bar requires more bulk than short bar; however, cross-sectional

shape is unchanged.

Finishing Lines

Butt-type joint(s) with minor connectors) for retention of denture base(s).

Advantages of the lingual bar:

1. Simplicity and efficiency.

2. Patient tolerance.

3. Limited tissue coverage (hygienic).

4. It does not contact teeth or gingival tissues allowing normal physiologic stimulation of the tissues.

Disadvantages

Long lingual bars may attain some flexibility, especially if they are poorly constructed or designed.

Difficult to add additional prosthetic teeth to framework.

Framework goes from thick (at the minor connectors) to thin (at the bar) to thick again which is metallurgically and structurally complicated. The result may be weak areas in the casting with the potential to fracture.

Contraindications:

Major Connectors


1- Inadequate space between the free gingival margin and the floor of the mouth. Less than 7 mm exists between the marginal gingiva and the activated lingual frenum and floor of the mouth.

2- Extreme lingual inclination of lower anterior teeth.

3- Patients having high lingual frenular attachment.

4- The presence of bilateral torus mandibularis contraindicates the use of the lingual bar because they interfere with the proper placement of the bar. Tori require adequate relief, which minimize the rigidity of the connector.

5- The presence of an undercut on the lingual side of the ridge could cause gross food entrapment and discomfort in the presence of the lingual bar.

The lingual bar functions only as a major connector. It does not provide

neither support nor indirect retention.

2- The Sublingual bar

The sublingual bar is a modification of the lingual bar.

Indications:

1. When the lingual bar cannot be used because of a lack of functional depth of the lingual vestibule (depth of 5-7mm).

2. Reduced height of the alveolar ridge, due to bone resorption or elevation of the floor of the mouth during functional movement.

3. Highly attached lingual frenum.

4. Distal extension RPD situations with sloped or parallel lingual alveolar ridges where a lingual bar would rotate into the lingual alveolus as the base area rotates tissue-ward.

5. Diastemas and open cervical embrasures of anterior teeth.

Contraindications

• When lingual bar or lingual plate is sufficient.

• When future additions of prosthetic teeth to the framework are anticipated.

Remaining natural anterior teeth severely tilted toward the lingual.

Major Connectors



The sublingual bar is essentially a lingual bar rotated 45 degrees. (Half-pear shape as a lingual bar except that the bulkiest portion is located to the lingual and the tapered portion is toward the labial).

• it may described as having a tear drop configuration in cross section whose base is towards the base of the tongue.

The superior border of the bar should be located at least 3 mm from the gingival margins of all adjacent teeth.

The inferior border is located at the height of the alveolar lingual sulcus when the patient's tongue is slightly elevated. This necessitates a functional impression of the lingual vestibule to accurately register the height of the vestibule.

The sublingual bar is located on the alveo-lingual sulcus inferior to the usual site of the lingual bar; extending over and parallel to the anterior floor of the mouth.


(1) All tissue undercuts parallel to path of placement.

(2) An additional thickness of 32-gauge sheet wax when the lingual surface of the alveolar ridge is either undercut or parallel to the path of placement.



(1) Six-gauge, half-pear-shaped wax form reinforced by 22- to 24-gauge sheet wax or similar plastic pattern adapted to design width.

(2) Long bar bulkier than short bar; however, crosssectional shape unchanged.Finishing Lines Butt-type joint(s) with minor connectors) for retention of denture base(s).

Advantages of the sublingual bar

1. It is well tolerated by most of the patients.

Major Connectors


2. It does not cover the teeth or tissues. It permits exposure of the gingival tissue and the lingual surfaces of anterior teeth allowing for the natural physiologic stimulation of the gingiva.

3. Proper oral hygiene conditions could be maintained as the sublingual bar allows for proper tooth and tissue cleaning.

4. Some dentists suggested the use of sublingual bar because the under side of the tongue is relatively sparsely provided with tactile receptors.

5. More rigid than a lingual bar in the horizontal plane.

Disadvantages:

A functional impression of the vestibule is required to accurately register

the position and contour of the vestibule.

To determine the relative height of the floor of the mouth:

a) The first method is to measure the height of the floor of the mouth in relation

to the lingual gingival margins of adjacent teeth with a periodontal probe.

During these measurements, the tip of the patient's tongue should be just lightly

touching the vermilion border of the upper lip. Recording of these measurements

permits their transfer to both diagnostic and master casts, thus ensuring a rather

advantageous location of the inferior border of the major connector.

b) The second method is to use an individualized impression tray having its

lingual borders 3 mm short of the elevated floor of the mouth and then to use

an impression material that will permit the impression to be accurately molded

as the patient licks the lips. The inferior border of the planned major connector

can then be located at the height of the lingual sulcus of the cast resulting from

such an impression. Of the two methods, we have found the measuring of the

height of the floor of the mouth to be less variable and more clinically

acceptable.

3- Mandibular cingulum bar (continuous bar)

Indication

Major Connectors


Where there is insufficient room for the lingual bar, between gingival margin and the floor of the mouth, and unless the periodontal health is well maintained.

The teeth should have good mesiodistal contact with sufficient crown length.

Kennedy bar

It is known as secondary lingual bar, continuous bar or cingulurn bar.

It is used alone or in conjunction with a lingual bar forming the double lingual bar, to add to the strength and rigidity of the denture.

Kennedy bar is not indirect retainer by itself.

Contraindications

(1) Anterior teeth severely tilted to the lingual.

(2) When wide diastemata exist between the mandibular anterior teeth and the cingulum bar would objectionably display metal in a frontal view.


(1) Thin, narrow (3 mm) metal strap located on cingula of anterior teeth,scalloped to follow interproximal embrasures with inferior and superior borders tapered to tooth surfaces.

(2) Originates bilaterally from incisal, lingual, or occlusal rests of adjacent principal abutments.


No relief for cingulum bar except blockout of interproximal spacesparallel to the path of placement.


Cingulum bar pattern formed by adapting two strips (3 mm wide) of 28-gauge sheet wax, one at a time, over the cingula and into interproximal embrasures.

Finishing Lines

Butt-type joint(s) with minor connectors for retention of denture base(s).

Advantages

Permits exposure of the gingival tissue that allows natural stimulation but

Major Connectors


It eliminates the need of indirect retainer,

Disadvantages

The metal bulk of the bar may be disadvantage and esthetic may be compromised, if spacing is present.

The open space may traps food and may exacerbate gingival trauma and it may be objectionable to the tongue.

4- The Double lingual bar:

The double lingual bar is a major connector, which consists of a lingual barand a cingulum bar (Kennedy bar).

Indication

1-When indirect retention is required.

2-When periodontally affected teeth that require splinting are present.

3- When a linguoplate is indicated but the axial alignment of anterior teeth is such that excessive blockout of interproximal undercuts would be required.

4- When wide diastemata exist between mandibular anterior teeth and a Linguoplate would objectionably display metal in a frontal view.

Contraindications:

- When the teeth have short clinical crowns or inclined lingually.


a- The upper bar

1. The Kennedy bar is a thin, narrow, scalloped, 3 mm wide metal strap which located on or slightly above the cingulae of anterior teeth.

2. It should be half-oval in cross section and approximately 2 to 3mm. high and 1mm. thick at its greatest diameter.

3. It is joined to the lingual bar via two rigid minor connectors, which are located in the interproximal spaces, usually between the canines and first premolars.

4. Two supporting rests must be placed one on each end of the Kennedy bar. These rests prevent settling of the bar during function,

Major Connectors


thus preventing laceration of the gingiva and ulceration of the mucosa covering the floor of the mouth.

b- The lower bar

It should have the same design as a single lingual bar, half pear-shaped in cross section with the greatest diameter at the inferior margin.


(1) Lingual surface of alveolar ridge and basal seat areas same as forlingual bar.

(2) No relief for continuous bar except blockout of interproximal spaces parallel to path of placement.


(1) Lingual bar major connector component waxed and shaped same as lingual bar.

(2) Continuous bar pattern formed by adapting two strips (3 mm wide) of 28-gauge sheet wax, one at a time, over the cingula and into interproximalembrasures.

Finishing Lines

Butt-type joint(s) with minor connectors) for retention of denture base(s).

Advantages of the double lingual bar:

1. The open space allows natural stimulation of gingival tissue.

2. Provides stabilization against lateral forces.

3. The configuration of this bar adds to the strength and rigidity of the denture.

4. Proper distribution of the stresses acting on the partial denture to all teeth.

5. Helps in splinting of periodontally affected teeth.

6. The double lingual bar acts as an indirect retainer through its terminal rests.

7. The continuous bar may be considered with excessive interproximal undercuts and the linguoplate major connector cannot be used.

8. It may be modified to circumvent a diastema between teeth.

Major Connectors


Disadvantages:

1. It is objectionable to the tongue and thus poorly tolerated by patients.

2. If the open space is insufficient may collect food and produce tissue irritation.

3. May cause phonetic problems.

6- Lingual Plate (closed Kennedy bar)

The lingual plate is the most rigid mandibular major connector. It provides better bracing than do other mandibular connectors. It also provides cross-arch stabilization and splinting for weak teeth.

Indications:

1- When the space available is insufficient for the construction of a rigid lingual bar as in cases with high lingual frenular attachment or high floor of the month. May be used when the functional depth of the lingual vestibule is less than 5 mm

2 When additional strength is required in cases having mandibular tori which are contraindicated for surgical removal.

3- In distal extension bases where indirect retention is required.

4- In Kennedy class I cases exhibiting excessive loss of the residual ridges where the lingual plate can provide resistance against horizontal movement of the partial denture.

5- When future replacement of teeth is expected.

6- In patients intolerable to lingual bars.

7. It is particularly useful in stabilizing periodontally weakened teeth


It is an extended lingual bar that crosses the relieved gingival margin to terminates above the cingulae of anterior teeth or survey line of posterior teeth in the form of a plate.

1. Half-pear shaped with bulkiest portion inferiorly located.

Major Connectors


2. Thin metal apron extending superiorly to contact cingula of anterior teeth and lingual surfaces of involved posterior teeth at their height of contour.

3. Apron extended interproximally to the height of contact points, i. e., closing interproximal spaces.

4. Scalloped contour of apron as dictated by interproximal blockout.

5. Superior border finished to continuous plane with contacted teeth.

6. Inferior border at the ascertained height of the alveolar lingual sulcus when the patient's tongue is slightly elevated.

7. The superior border must positively contact the lingual surfaces of the teeth above the survey line to avoid food entrapment.

8. The superior border should be thin, knife edged scalloped border,sharply projected between the teeth, and should never be placed above the middle third of the teeth.

9. The inferior border of the lingual plate is a half-pear shaped placed at the functional limit of the floor of the mouth.

10. Adequate block-out is required for teeth and soft tissue undercuts.

11. Gingival margins should be relieved to avoid gingival irritation. Excessive relief should be avoided because tissues tend to fill a void, resulting in the overgrowth of abnormal tissue. The amount of relief used, therefore, should be only the minimum necessary to avoid gingival impingement

12. The lingual plate must always be supported at each end by rests, to provide indirect retention.

13. when a single diastema exists a notched lingual plate could be used to avoid display of metal.

Interrupted linguoplate

When the anterior teeth are quite spaced and the patient strenuously objects to metal showing through the spaces,the linguoplatecan then be constructed so that the metal will not appreciably show through the spaced anterior teeth. Rigidity of the major connector is not greatly altered.

Major Connectors


However, such a design may be as much of a food trap as the continuous bar type of major connector.


(1) All involved undercuts of contacted teeth parallel to the path of placement.

(2) All involved gingival crevices.

(3) Lingual surface of alveolar ridge and basal seat areas the same as for a lingual bar.


(1) Inferior border—6-gauge, half-pear-shaped wax form reinforced with 24-gauge sheet wax or similar plastic pattern.

(2) Apron—24-gauge sheet wax.

Finishing Lines

Butt-type joint(s) with minor connectors for retention of denture base(s).

Advantages

1. The most rigid mandibular major connector.

2. It gives indirect retention to the partial denture.

3. Deflect food from impacting on lingual tissues.

4. Provide resistance against horizontal or lateral forces.

5. Permits the replacement of lost tooth without remaking the PD.

6. Help in splinting and prevent super-eruption of the anterior teeth.

7. Patients frequently consider the lingual plate to be more comfortable and more acceptable for tongue comfort and ease in phonetics than the lingual bar.

The lingual palate is the most rigid mandibular connector, and provides more support and stabilization than do the other connectors.

Disadvantages of the lingual plate:

1. It prevents normal physiologic stimulation of the gingival tissue and the self cleansing action of the teeth by the saliva and tongue.

Major Connectors


2. Encourages plaque formation, and may contribute to caries and periodontal disease in patient with poor oral hygiene.

3. Covers more tooth and gingival tissues than other mandibular major connectors.

Contraindications:

A lingual bar may be used.

Overlapped anterior teeth where the undercuts in the area of the superior edge of the plate can not be removed. Frequently this criteria can not be met and a lingual plate which will have small gaps between the superior edge of the plate and the teeth must be used.

Lingually inclined teeth.

Diastemas, unless the lingual plate can have slots in it to avoid the display of metal.

Open cervical embrasures where the plate would be visible.

The linguoplate does not in itself serve as an indirect retainer. When

indirect retention is required, definite rests must be provided for this purpose.

Both the linguoplate and the cingulum bar should ideally have a terminal rest at

each end regardless of the need for indirect retention. However, when indirect

retainers are necessary, these rests may also serve as terminal rests for the

linguoplate or continuous bar.

6-Labial and buccal bars:

The labial bar connector situated in the labial or buccal sulcus.

Indications:

1. In case of extreme lingual inclination of mandibular anterior and premolar teeth that prevents the use of a lingual major connector.

2. When large lingual tori exist and surgery is precluded.

3. When severe and abrupt lingual tissue undercuts make it impractical to

use a lingual bar or lingual plate major connector.

Design:

Major Connectors


1. It should be made with greater thickness and bulk than a lingual bar to counteract the increased flexibility due to increased length.

2. It is half-pear shaped with bulkiest potion located inferiorly, runs across the labial and buccal mucosa. Superior border tapered to soft tissue located at least 4 mm. below the gingival margin.

3. Relief is required beneath the bar. It must be relieved over the canine eminence.

4. It is half pear shaped in cross-section.

5. Labial vestibule should be adequate to allow the superior border to be place at leas 3-4 mm below the free gingival margins.

6. Inferior border located in the labial-buccal vestibule at the juncture of

attached (immobile) and unattached (mobile) mucosa.


(1) All tissue undercuts parallel to path of placement, plus an additionalthickness of 32-gauge sheet wax when the labial surface is either undercut or parallel to the path of placement".

(2) No relief necessary when the labial surface of the alveolar ridge slopes inferiorly to the labial or buccal.

(3) Basal seat areas same as for lingual bar major connector.


(1) Six-gauge, half-pear-shaped wax form reinforced with 22- to 24-gauge sheet wax or similar plastic pattern.

(2) Long bar necessitates more bulk than short bar; however, cross sectionalshape unchanged.

(3) Minor connectors joined with occlusal or other superior components by a labial or buccal approach.

(4) Minor connectors for base attachment joined by a labial or buccalapproach.

Finishing Lines

Butt-type joint(s) with minor connector(s) for retention of denture base(s).

Major Connectors


Advantages:

The labial bar obviates the need for surgical intervention to permit use of a lingual major connector.

It solves the problem of severely inclined teeth and avoids surgical intervention to remove a large torus.

Disadvantages:

1. The labial bar usually lacks sufficient rigidity.

2. Labial vestibular depth must be adequate especially in the presence of gingival recession.

3. The least comfortable mandibular major connector.

4. It distorts the lower lip and the presence of the metal between the gingival tissue and the lip causes patient discomfort.

5. Difficult to add prosthetic teeth to framework.

Contraindications:

When lingual major connector may be used.

Facial tori or exostoses.

The facial alveolar ridge is undercut.

High facial muscle attachments which would result in less than 3 mm of space between the superior edge of the labial bar and the marginal gingiva of the teeth.

7- The Swing Lock Partial Denture:

The hinged continuous labial bar called the Swing-lock design partial denture is a modification of the labial bar.

Indications

1- Missing key abutments such as a canine.

2- Unfavorable tooth contours: When existing tooth contours (uncorrectable by recontouring with appropriate restorations) or excessive labial inclinations of anterior teeth prevent conventional clasp designs,

Major Connectors


3- Unfavorable soft tissue contours. Extensive soft tissue undercuts may prevent proper location of component parts of a conventionalremovable partial denture

3- Periodontally affected Teeth with questionable prognosis: The Swing lock partial denture provides splinting.

Design

It is consists of a labial or buccal bar that is connected to the major connector by a hinge on one end and a latch at the other end.

The labial bar is connected to a lingual plate major connector by a hinge device at one end and a locking device at the other end. Vertical minor connectors arise from the labial bar and may touch the anterior teeth either below or above the survey line.

Support is provided by multiple rests on the remaining natural teeth. Stabilization and reciprocation are provided by a linguoplate contacting the remaining teeth and are supplemented by the labial bar with its retentive struts. Retention is provided by a bar type of retentive clasp arms projecting from the labial or buccal bar and contacting the infrabulge areas on the labial surfaces of the teeth.

Advantages:

1- Helps in providing both retention and stabilization.

2- The labial bar together with the lingual plate provides the required rigidity, thus the labial bar does not require much bulk.

Contraindications

1- Poor oral hygiene.

2- The presence of shallow buccal or labial vestibule.

3- The presence of high labial frenal attachment

8- Split lingual major connector:( SPLIT MANDIBULAR)

Major Connectors


It is a flexible connector, used where some stress release from the abutment teeth is desired. Inevitably, this stress broken design is a more complex construction and thus more costly, and may also pose greater demands on plaque control and be less well tolerated by the patient.

Indications.

a. May be used where some stress release from the abutment teeth is desired through the major connector.

b. May be used in place of stress releasing clasps or stress directors.

Design:

a. May be fabricated in a single casting or in combination with a soldered wrought wire of large diameter.

b. Due to the stress concentration, there may be a tendency to fracture at the union of the bars.

9- Dental bar

On occasions, there is insufficient room between gingival margin and floor of the mouth for either a sublingual or lingual bar. A lingual plate should be avoided wherever possible because it might well tip the delicate balance between health and disease in favour of the latter.

An alternative connector, where the clinical crowns are long enough, is the dental bar. Patient tolerance inevitably places some restriction on the cross-sectional area of this connector and thus some reduction in rigidity may have to be accepted.

Major Connectors


Sequence of design considerations for a mandibular major connector

Step 1: Outline the basal seat areas on the diagnostic cast

Step 2: Outline the inferior border of the major connector

Step 3: Outline the superior border of the major connector

Step 4: Connect the basal seat area to the inferior and superior borders of the major connector, and add minor connectors to retain the acrylic resin denture base material

Selection of maxillary major connector

1- Function:

Maxillary: support, retention and stability: The width of the major connector may be varied according to the amount of support required. e,g anterior and posterior palatal strap when good abutment support ,Complete palatal coverage when mucosal support is desired

Mandibular: need for indirect retention

Major Connectors


2- Anatomical consideration :

Maxillary: palatal tori

Mandibular:

Lingual tori

Lingual gingival recession

High lingual frenal attachment

Inclination of remaining anterior teeth

3- Hygiene:

oral hygiene is better with lingual bar

4- Rigidity:

The rigidity of the major connector may be increased by varying the thickness or by placing the metal in two different planes.

5- Patient acceptability:

Strap or plate type major connectors, because they can be made thinner, usually have a greater patient acceptance than the bar types. Some patients may find the increased palatal coverage uncomfortable due to alterations in gustatory, thermal or tactile perception. Generally, posterior or mid palatal straps are less objectionable than anterior palatal straps or bars.

6- Location of edentulous area:

The major connector must connect the components of the partial denture.

7- Anticipated loss of natural teeth

8- Location of fulcrum line:

The portion of the major connector located posterior to the indicated fulcrum line may provide muco-osseous support for the RPD.

Major Connectors


Indications for Maxillary Major Connectors:

a) If the periodontal support of the remaining teeth is week, a wide palatal strap or completely palatal coverage is indicated.

b) If the remaining teeth have adequate periodontal support and little additional support is needed, a palatal strap or double palatal bar can be used.

c) For long-span distal extension bases, a closed horseshoe or complete palatal coverage is indicated.

d) When anterior teeth must be replaced, a horseshoe, closed horseshoe, or completely palatal coverage may be used.

e) If a torus is present and is not to be removed, a horseshoe, closed horseshoe, or anteroposterior palatal bar may be used.

f) A single palatal bar is rarely indicated.

g) The combination anterior-posterior connector design may be used with any Kennedy class of partially edentulous arch. It is used most frequently inClasses II and IV, whereas the single wide palatal strap is more frequently used in Class III situations. The palatal plate-type or complete coverage connector is used most frequently in Class I situations.

Class 1 palatal plate-type

Class I partially edentulous arches with residual ridges that have undergone

little vertical resorption and will lend excellent support: SINGLE BROAD PALATAL

Class I and II arches in which excellent abutment and residual ridge support exists, and direct retention can be made adequate without the need for indirect retention. ANTERIOR-POSTERIOR STRAP-TYPE

only some or all anterior teeth remain. COMPLETE PALATAL COVERAGE

Class I arch with one to four premolars and some or all anterior teeth remaining, and abutment support is poor and cannot otherwise be enhanced; residual ridges have undergone extreme vertical resorption; direct retention is difficult to obtain. COMPLETE PALATAL COVERAGE

Major Connectors


Class 2 : ANTERIOR-POSTERIOR STRAP

Long edentulous spans in Class II, modification 1 arches. ANTERIOR-POSTERIOR STRAP

Class II arch with a large posterior modification space and some missing

anterior teeth. COMPLETE PALATAL COVERAGE

Class 3: single wide palatal strap

Bilateral edentulous spaces of short span in a tooth-supported restoration: SINGLE PALATAL STRAP

Class 4 : ANTERIOR-POSTERIOR STRAP

Class IV arches in which anterior teeth must be replaced with a removable

partial denture. ANTERIOR-POSTERIOR STRAP

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V- or U-shaped palates: SINGLE BROAD PALATAL

No interfering tori. SINGLE BROAD PALATAL

absence of a pedunculated torus. COMPLETE PALATAL COVERAGE

Inoperable palatal tori that do not extend posteriorly to the junction of the hard

and soft palates. ANTERIOR-POSTERIOR STRAP

inoperable tori extend to the posterior limit of the hard palate. U-SHAPED PALATAL

Indications, for Mandibular Major Connectors:

1-For a tooth-supported, the lingual bar is normally the mandibular major connector of choice

2- For long-span edentulous ridges in which there is no posterior abutment tooth and indirect retention is needed ,the lingual plate is indicated .

3- When the anterior teeth have reduced periodontal support and need stabilization, the lingual plate or double lingual bar may be used .

4- When mandibular tori are present, or when a high lingual frenum is present, a lingual plate must be used.

Major Connectors


5- For patient who have large inter-proximal spaces that cause esthetic problems by the display of the metal of a lingual plate ,a double lingual bar may be indicated.

6- The labial bar is rarely indicated.

Sufficient space exists between the slightly elevated alveolar lingual sulcus and the lingual gingival tissue. MANDIBULAR LINGUAL BAR

height of the floor of the mouth in relation to the free gingival margins will be less than 6 mm MANDIBULAR SUBLINGUAL BAR

alveolar lingual sulcus so closely approximates the lingual gingival crevicesMANDIBULAR LINGUOPLATE

periodontally weakened teeth in group function to furnish support to the

prosthesis and to help resist horizontal (off vertical) rotation of the distal

extension type of denture. MANDIBULAR LINGUOPLATE

future replacement of one or more incisor teeth MANDIBULAR LINGUOPLATE

linguoplate is indicated but the axial alignment of anterior teeth is such that

excessive blockout of interproximal undercuts would be required.

MANDIBULAR LINGUAL BAR WITH CONTINUOUS BAR

wide diastemata exist between mandibular anterior teeth and a Linguoplate

would objectionably display metal in a frontal view. MANDIBULAR LINGUAL

BAR WITH CONTINUOUS BAR

lingual plate or sublingual bar is otherwise indicated but the axial alignment of

the anterior teeth is such that the excessive blockout of interproximal undercuts

would be required. CINGULUM BAR

lingual inclinations of remaining mandibular premolar and incisor teeth cannot

be corrected LABIAL BAR

severe lingual tori cannot be removed LABIAL BAR

severe and abrupt lingual tissue undercuts make it impractical to use a lingual

bar or lingual plate LABIAL BAR

class 1

Class I arch residual ridges have undergone such vertical resorption that they will offer only minimal resistance to horizontal rotations of the denture through its bases.MANDIBULAR LINGUOPLATE

Major Connectors


MINOR CONNECTORS

A minor connector is that part of removable partial denture, which joins the major connector or the partial denture base to other components of the prosthesis.

A minor connector is a component that links the major connector or base and other components of the partial denture such as rests, indirect retainers and clasps.

Design Specifications:

Minor connectors that contacts the axial tooth surfaces or contacts the guiding plane surfaces of the abutment teeth whether as a connected part to the clasp assembly or as a separate entity should fulfill the following requirements:

1. Minor connectors must have sufficient bulk to be rigid.

A typical minor connector is 2mm width and 1.5mm thickness in cross section.

2. The bulk of the minor connectors must be as unobjectionable as possible.

3. Where the minor connector joins a rest, a minimum metal thickness of 1.5mm at the junction is required for base metal alloys (2 mm for gold alloys).

4. Minor connector contacting the axial surface of an abutment should contact guiding plane surfaces and should never be located on convex surfaces (why?).

5. Minor connector conforms to the interdental embrasure, (as in case of embrasure clasp or that used as indirect retainer) passing vertically from the major connector and covers as little of the gingival tissues as possible.

6. The surface of metal facing the tongue should be smooth and beveled. The minor connector should be thickest toward the lingual surface and tapering toward the contact area, to provide space for the arrangement of

Major Connectors


teeth. In this case they are triangular in shape, the base of the triangle faces the tongue and the apex lies toward the lingual contact area of teeth.

7. Should exhibit minimal gingival coverage; the lingual minor connector should cross the gingival margins directly, joining the major connector at rounded right angle

8. The junction between minor connector and major connector should be rounded rather than angular. Sharp angles should be avoided and spaces should not exist for the trapping of food debris.

9. The marginal gingiva crossed by any minor connectors should be relievedespecially in tooth-mucosa borne dentures.

10. There should be a minimum of 5 mm space between any two neighboring minor connectors or from other vertical components.

11. Should be highly polished to minimize plaque accumulation.

Functions of minor connectors:

1. Joining different parts of the prosthesis to the major connector, or to denture bases.

2. Transfer and distribute functional stresses to the abutment teeth.

3. Transfer the effect of retainers, rests, and stabilizing units to the denture.

4. Minor connectors contacting guiding planes add to the retention and stability of dentures (How).

Types of minor connectors:

I-Minor Connectors That Joint Indirect Retainers or Auxiliary Rests to The Major Connector:

It is generally arising from the major connector. They should form a right angle with the major connector, but the junction should be a gentle curve rather than a sharp angular connection. The minor connector should be designed to lie in the embrasure between teeth to disguise its bulk as mush as possible.

a- Proximal Minor Connectors

Major Connectors


Proximal minor connectors contact an abutment tooth adjacent to an edentulous space. Proximal minor connectors are usually termed Proximal Plates but are sometimes call Guiding Plates, Struts and Finishing Plates.

Design

Proximal plates extend from the proximal facial line angle to, or slightly past, the proximal lingual line angle of the abutment tooth. They are thin mesio-distally and taper slightly toward the occlusal (incisal).

They extend from the occlusal/incisal of the tooth to the major connector. The junction of rests and clasp arms with proximal minor connectors, and proximal minor connectors to major connectors are rounded right angles.

They should be broad bucco-lingually to provide strength and thin mesio-distally to minimize encroachment on the saddle area. This will enable the artificial teeth to be positioned closely to the abutment tooth to achieve satisfactory aesthetics.

They extend cervically and contact the mucosa of the ridge crest for 2-3mm.

The part of the proximal minor connector which contacts the ridge crest is called the Foot of the proximal plate

Functions of Proximal plates

Connect rests and clasp arms to the major connectors,

Provide frictional retention by contact with guiding planes on the teeth,

Help reciprocate the force of the direct retainer,

Unite the dental arch by substituting for lost proximal tooth contacts

Distribute forces (bracing).

Contact proximal guiding planes on the teeth thus helping to determine the path of placement of the RPD,

Prevent food impaction between the proximal surface of the tooth and the RPD,

Provide a definite finish line for the junction of the denture base and major and minor connectors,

Major Connectors


b- Embrasure Minor Connectors

If the direct retainer or auxiliary rest to be placed between two adjacent teeth, the minor connector must be positioned in the lingual embrasure between the two teeth. Using this triangular space for the metal results in sufficient bulk without encroaching on tongue space.

Design

It should be designed into the lingual embrasure between two adjacent teeth to disguise bulk as much as possible.

They extend from the occlusal, incisal or cingulum surface of the tooth to the major connector. They join the major connector in a rounded right angle to avoid sharp corners and they taper slightly toward the occlusal (incisal).

Triangular shaped in cross section

Relief placed so connector not directly on soft tissue

Contact teeth above height of contour, so prevents wedging & tooth mobility

Functions of embrasure minor connectors

• Connect rests and clasp arms to the major connectors,

• Provide frictional retention by contact with guiding planes on the teeth,

• Help reciprocate the force of the direct retainer,

• Unite the dental arch by substituting for lost proximal tooth contacts

• Distribute forces (bracing).

• Contact inter-proximal guiding planes thus helping to determine the path of placement of the RPD,

c- Surface Minor Connectors

Surface minor connectors are located on the lingual surface of incisors and canines. They connect lingual rests to the major connector.

Major Connectors


Design

Their junction with the major connector is a rounded right angle and they taper toward the occlusal (incisal).

The lateral borders extend into the proximal embrasures to hide these edges from the tongue.

The surface minor connector may be penetrated by the tip of the lingual cingulum rest preparation. This "open" design facilitates fitting the framework and cleaning the tissue surface of the minor connector. Another modification of the surface minor connector is a "finger rest" in which the rest extends from the proximal or embrasure minor connector into the rest preparation.

Radford modification:

A modification of the conventional removable partial denture minor connector has been proposed by Radford.

He limits the application of this variation in minor connector design to the maxillary arch only.

He suggests placing the minor connector in the center of the lingual surface of the maxillary abutment tooth.

Advantages:

reduces the amount of gingival tissue coverage

provides enhanced guidance for the PD during insertion and removal

increased stabilization against horizontal and rotational forces.

Disadvantages:

encroach on the tongue space and provide more obvious borders and a greater potential space between the connector and the abutment for food entrapment.

II-Minor connectors that serve as approach arm for vertical projection or bar-type clasp:

It is the only one that is not required to be rigid.

Major Connectors


It supports a direct retainer (clasp) that engages an undercut on a tooth; from below rather than above.

It approaches the tooth from the gingival margin. It should have a smooth, even taper from its origin to its terminus. It must not cross a soft tissue undercut.

It must be relieved from the tissue to avoid tissue injury.

III-Minor connectors that join the denture base to the major connector:

(Denture Base Retention (Grid-work) minor Connector) see denture base

it is the means by which the plastic denture base is mechanically attached to the framework.

It may be:

a) Open Lattice work construction.

b) Mesh construction.

c) Bead, wire, or nail-head minor connectors (used with a metal base).

RELATIONSHIP OF MINOR CONNECTORS TO THE TOOTH SURFACE

If the tooth surface is not entirely parallel to the path of placement and removal of the RPD, a space will be created between the minor connector and the tooth surface below the height of contour.

There is a difference of opinion as to how large this space should be.

1- Kratochvil suggest that there should be no space between the proximal minor connector, tooth and ridge to prevent hypertrophy of tissue into the space.

Major Connectors


2- Others suggest that the space should be kept large so that it may be easily cleaned by the tongue while the RPD is in the mouth ("self-cleansing design") and thus less likely to cause periodontal damage andmucosal irritation.

3- Actually the space is usually determined by the anatomy of the tooth, its angulation in relation to the path of placement and removal of the RPD and esthetic considerations.

The dentist has little control over the size of this space unless the tooth is going to be restored with a surveyed crown. And, other factors are much moreimportant in the success of RPD treatment than the space between the proximal plate and the tooth.

-

Variations in the space between the proximal minor connectors and the abutment tooth ,

a) minimum space to prevent tissue hypertrophy into the space,

b) “self-cleansing” design,

c) space determined by anatomy of tooth, angulation of the tooth relative to the path of placement and removal of the RPD, and limitation of the amount the tooth can be reshaped to decrease the space

-

State rules of thumb for the form and length of minor connectors connecting acrylic resindenture bases to major connectors.

Give a rule of thumb for how far the minor connector attaching the resin base to the majorconnector should extend posteriorly.

The thickness of impression material when rubber-base material is used should be about 3 mm (1/8 inch) for accuracy and stability. Does this equally apply to a hydrocolloid impressionmaterial? If not, give a rule of thumb for the desired thickness of the hydrocolloid material inthe impression.

Sufficient relief must be provided beneath a major connector to avoid impingement and/ordisplacement of soft tissue resulting in an inflammatory response. What is meant by the word

Major Connectors


relief? Rationalize planned relief for a lingual bar and give quantitative rules of thumb that depend on the contour of the anterior, lingual alveolar ridge.

There are definite rules of thumb for the location of the anterior and posterior borders of all palatal major connectors. Describe the relationship of the borders to rugae, junction of hard and soft palates, gingival crevices, pterygomaxillary notches, and palatal tori.

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Mostafa Fayad 1

Retention Of Partial Denture

Retention is the resistance of the partial denture to vertical displacement away from

the tissues.

Retention of an RPD can be achieved by:

- Using the inherent physical forces which arise from coverage of the mucosa by the

denture.

- Physiologic factors: Harnessing the patient’s muscular control acting through the

polished surface of the denture.

- Using mechanical means such as clasps which engage undercuts on

the tooth surface.

A] Physical means of retention:1-Adhesion; is the attraction of the saliva to the denture and the tissues.

2-Cohesion; is the attraction of saliva molecules to each other.

3-Interfacial surface tension; is the attraction of the surface molecules.

4-Atmospheric pressure; Which is dependent on a border seal and results in a partial

vacuum beneath the denture base when a dislodging force is applied.

The difference between the greater pressure acting on the polished surface of the

denture and the lesser pressure acting on the fitting surface causes a positive force,

which helps in retaining dentures.

The effect of atmospheric pressure in retaining partial dentures is limited because a

complete border seal cannot be obtained as can be accomplished with complete

dentures.

5 -Gravity; The effect of gravity tends to seat lower dentures, but displace upper

dentures.

6- Plastic molding between tissues / denture polished surfaces aid to little extent in

retention of partial denture

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Mostafa Fayad 2

The effect of physical forces is less applicable to lower dentures than upper denture

because:

a- Lower dentures have less surface area.

b- Lower dentures are bathed in saliva.

c- Lower major connectors are relieved from the underlying tissues

contrary to upper major connectors that are well adapted and their borders

are beaded against the underlying tissues.

d- Strong movements of the tongue tend to break the seal in lower

dentures.

B]The Physiological means of retention:

1- The physiologic molding of the tissues around the polished surfaces of the denture

helps to perfect the border seal.

2- Neuromuscular control: The patient ability to control the denture with the lips,

cheeks, and tongue can be a major factor in the retentiveness of the denture.

C] Mechanical means of retentionThe primary retention of the removable partial denture is accomplished

mechanically by placing retaining elements on the abutment teeth, which are

achieved by:

1. Direct retainers:

The components of partial denture that are used primarily to retain the

denture and resist vertical dislodging forces applied to it.

Types of direct retainers:-

a- Intracoronal retainer.

Usually called as an internal attachment or a precision attachment.

It is developed by Dr Herman E.S.Chayes in 1906.

b- Extracoronal retainers.

A-Clasps: which are metal projections engaging abutments to hold

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Mostafa Fayad 3

denture in place.

B- Attachments:

These are ready or tailor made, male and female components.

One component is fixed to the abutment, and the other attached to the

denture. They are either extra coronal or intracoronal attachment.

2. Indirect retainers: They are components of partial denture that are used to resist vertical

displacement of a distant part of the denture.

3. Frictional fit between the natural and artificial teeth.

4. Parts of the denture engaging tooth undercuts.

5. Parts of the denture engaging tissue undercuts.

Clasp Retainers

A Clasp is a metal projection of the partial denture engages the external

surface of an abutment in an area cervical to the height of contour (undercut) to

retain the partial denture. It is also called an extra-coronal retainer.

It is first appeared in dental literature in 1899 by G.V.Bonwill

Components of a clasp:

A classic clasp consists of the following parts:

1-A minor connector

(Called truss arm, tail, tang, upright arm, clasp stalk )

It is a rigid part of the clasp placed on the proximal surface of abutment tooth

extending from the marginal ridge to the junction between the middle and

gingival third of the abutment crown..

Functions: -It Joins clasp to framework.

- It acts as a proximal plate dictating the path of insertion .

- Bracing and stabilization of the denture.

2-A rest:

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Mostafa Fayad 4

It is a part of the clasp placed on prepared occlusal, lingual or incisal surfaces of teeth.

Function:! It supports the denture.

3-A retentive clasp arm:

The retentive clasp arm of the occlusally approaching clasp comprises a

rigid part located above the height of tooth contour to provide bracing then

tapers and ends in a flexible terminal, which engages an undercut area below

the height of tooth contour. The terminal end of the clasp arm provides direct

retention.

Function:- Retention, bracing and stabilization.

The retentive arm of the clasp may approaches the undercut area from the gingival

direction and called bar type clasp. It provides retention only for the partial denture

4-A Reciprocal arm (guiding arm) is a rigid, half round, arm located occlusal to the

survey line on a surface of the tooth opposing the retentive arm.

Its main function is to counteracts stresses generated by the retentive arm as it

crosses the height of contour during insertion and removal of the denture,

causing lingual (or buccal) movement of the abutment tooth.

In order to reciprocate forces properly, it should remain in contact

with the tooth during function of the retentive arm. Rigid major connectors,

or minor connectors contacting lingual surfaces of the teeth substitute

reciprocal arm.

- Reciprocal arm also stabilizes the denture against lateral movements.

One arm clasp may be used to encircle the tooth. The rigid part of the arm starts on one side of the tooth and cross-proximal surface to reach the other side of the tooth as a tapered (retentive) end.

Basic Principles of a Properly Designed Clasp:

The function of a properly designed clasp is contributed to the following basic

principles:

1. Encirclement: The clasp must encircle more than half of the circumference of the tooth either through continuous or interrupted contact. This is to

preclude movement of the tooth and to prevent the clasp from slipping offthe tooth when stresses are applied.

2. Support of partial dentures: It is the property of the clasp that enables it to

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Mostafa Fayad 5

resist displacement in a gingival direction. The occlusal (lingual or incisal) rest is the prime support unit of the clasp.

3. Bracing of partial dentures: It is the resistance against horizontal displacement of the prosthesis. This is achieved by the rigid parts of the

clasp.

4. Stabilization of partial dentures: It is the resistance against Rotational forces

acting on the partial denture either in vertical or horizontal direction causing rotation (torque) of the denture base around an axis.

5. Reciprocation: It is the counteraction of the effect of the retentive clasp arm on the abutment tooth during insertion and removal of the prosthesis. It is

provided by the non-retentive clasp arm. .

6. Clasp arms should be placed at the lower part of the middle third of the axial tooth surfaces. While the retentive terminal should be placed at the gingival third below the survey line.

7. Minor connector (or proximal plate) must contact a definite guiding plane to dictate path of insertion.

8. Passivity: the retentive clasp arm should be passive and should not exert any pressure against the tooth until a dislodging force is applied.

9. The clasp should be designed on biologic as well as mechanical bases.

a- Whenever possible Minimum area contact between clasp and tooth surface

is provided to minimize food stagnation and incidence of carious lesions.

b- The clasp should not interfere with normal gingival stimulation and its

terminal should be away from the gingival margin.

c- The clasp should be smooth on both its inner and outer surfaces.

d- Clasp retainers indicated in cases of free end saddles must possess a stress breaking action to minimize excessive force on the abutment.

10. Retention: Retention is the basic function of a clasp. The retentive tip of clasp

arm enables the clasp to resist dislodgment from the tooth in an occlusal direction.

a- Tip of retentive clasp arm is the only part of the clasp that is flexible and located in an undercut.

b- Amount of retention should be the minimum necessary to resist

reasonable dislodging force.

c- Retentive clasps should be bilaterally opposed (balanced retention), i.e.

buccal retention on one side of the arch is preferably opposed by buccal

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Mostafa Fayad 6

retention on the opposite side to be effective in retaining the denture.

d- The path of removal of the clasp terminal must not be parallel to the

path of removal of the denture.

Factors Determining the Retentive Force of a Clasp:

Retentive force of a clasp depends on the undercut engaged, flexibility of the

clasp arm, and angle of approach of clasp arm with the tooth surface.

1- Depth of undercut used

The greater the depth of undercut present on the abutment tooth the more

will be the retention generated by the clasp engaging this undercut. The

retentive undercut has three dimensions. It is measured by undercut gauges

0.01, 0.02, 0.03 of an inch.

The retentive undercut have three dimensions:-

1- Buccolingual depth:- It may be measured by undercut gauge. Most clasps

made of cast chrome alloy are placed in undercuts of 0.010inch. Cast gold clasp

engage 0.015 inch. While the wrought wire clasps engage 0.020 inch undercuts.

2- Distance between survey line and the tip of retentive clasp:- It is affected the

clasp arm length, which influence the flexibility of the clasp.

3- Mesiodistal length of the clasp below the height of contour :- The longer of this

measurement, the more flexibility of the clasp.

2-Angle of approach.

Occlusally approaching clasps are easier in occlusal displacement than gingivally approaching clasps. Occlusally approaching clasps are pulled up to move occlusally. Gingivally approaching clasps are pushed up to move occlusally (Trip action, push or crip action)

Not all gingivally approaching clasps exhibit trip action for example T or modified T clasp may approach under cut from occlusal direction.

2- The Amount Of Clasp Arm Extends Below The Height Of Contour

The retentive clasp terminal is placed below the height of contour of an abutment.

The greater distance of the retentive clasp terminal, give greater retentive action.

3- Angle of gingival convergence (distance to height of contour)

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Mostafa Fayad 7

The angle formed between the analyzing rod and tooth surface apical to

the height of contour.

A two clasps may engage the same depth of undercut but the distance to

the height of contour varies.

Less gingival convergence (i.e. the retentive tip is at long distance from

height of contour) leading to less resistance to vertical dislodging force .

4- Position of clasps in relation to fulcrum axis

Direct retainer hould be as far away from the fulcrum axis for mechanical

advantages

6- Flexibility of clasp arm:

The more flexible the clasp arm, the less will be the retention. In tooth

supported partial dentures, more rigid clasps can be used compared to tooth-

tissue supported dentures.

By increase the flexibility of the clasp. The magnitude of horizontal stresses

against an abutment tooth can be reduced.

More increase the flexibility should not be occurring, because this leads to

decrease the clasp ability to provide retention.

The degree of Flexibility possessed by the clasp arm depends on the

following factors:

a) The length of the clasp arm:

The length of the clasp measured from the point at which uniform

taper begains .The greater the length, the greater will be the flexibility of

the clasp arm.

The length of retentive arm should be at least 15 mm , 7mm in cast and

wrought wire clasp respectively

D= Ewt3!! 4PL3

D= deflection E= elastic modulus w= width t= thickness p=

applied force l= length

b) The diameter of the retentive arm:

The smaller the diameter, the greater will be its flexibility, all

other factors being equal. The flexibility is increased by a factor of eight.

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Mostafa Fayad 8

The thickness of the tip of the clasp should be half the thickness at

the origin.

c) The tapering:

The clasp arm should be uniformly tapered in such away that the diameter

at its origin is twice that at its tip (Fig. 3-121).

d) The cross sectional form:

A round clasp arm is more resilient than half round or oval cross

section; that are difficult to flex in certain directions.

The round clasp is the only universally flexible clasp. Practically it is

impossible to obtain this universally flexibility by casting & polishing.

Therefore all cast clasps are half rounds in form.

In the half round, the flexibility is limited only one direction. It

flexible only in tooth ward direction, but the flexibility in the edge wise

direction is limited. Also the adjustment of this clasp is in the tooth ward

direction only. The edge wise direction means moving the clasp cervically

or occlusally.

e) The material of alloy:

Gold alloys are more flexible than cobalt chrome alloys.

The chrome alloys have higher modular of elasticity than the gold alloys,

therefore it is less flexible.

The modular of elasticity defined as the constant of proportionality between stress &

strain. It is represents the slope of the elastic portion of stress strain curve.

ξ = elastic modulus = STRESS

STRAIN

f) The type of alloy:

The wrought form is more resilient than the same alloy of identical diameter in cast form, because of its internal structure

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Mostafa Fayad 9

Location of the Retentive Terminal

The retentive terminal is normally positioned at mesiofacial or

distofacial line angle. The facial or buccal position is preferred over the use of

the lingual surface as it permits increased length of retentive armand improve

flexibility.

1- Placement of retentive arm on the lingual surface of premolar is contraindicated

.most premolars has limited mesiodistal dimensions so the lingaual retentive arm

is short and inflexible. The mandibular premolars have a decided lingual axial

inclination, and as a result the height of contour is located near the occlusal

surface. Therefore, if lingual retentive area is selected, the clasp would have

insufficient length provide the flexibility needed.

2- The maxillary premolars have buccal inclination; this lead to the retention from

the lingual surface cannot be considered.

3- In the molar teeth the undercut exhibit on either or both the buccal & lingual

surface. Therefore, either buccal or lingual retention may be used, depending on

the most desirable undercut. Particularly mandibular molar which have

increased mesiodistal dimension and lingual under cut

General Roles in the Location of the Retentive terminals:-

If buccal retention is selected for used on one side of the arch, it should be opposed

by buccal retention on the opposite side of the arch. Also if the lingual retention

is selected for used on one side of the arch, it should be opposed by lingual

retention on the opposite side of the arch.

If two retentive clasp are to be used on each side of the arch, it is possible to have

one clasp on each side engage a buccal under cut

When unilateral distal extension ridge is being treated, one clasp on the dentulous

side, usually on the molar. The other two clasps, usually on the premolars or

canine on the opposing side of the arch will engage the buccal undercut.

How many clasps for a denture

Clasps could be located at each end of the denture , this clasping is not biologically accepted due to more tooth coverage

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Mostafa Fayad 10

Instead , two clasps can be used in away that a straight line joining them bisect the denture

If the denture tend to rock about the line joining two clasps , a thirdclasp is added as far as possible from others .

Factors affecting the selection of clasp

1- Type of survey line2- Amount and position of under cut3- Position of tooth in arch4- Occlusion5- Appearance6- Amount of retention needed7- Type of denture support and load distribution.8- Anatomic limitations.

The advantages of any particular clasp design should lie in an affirmative answer to

most (or all) of the following questions:

1. Is it flexible enough to satisfy the purpose for which it is being used? (On an

abutment adjacent to a distal extension base, will tipping and torque be avoided?)

2. Will adequate stabilization be provided to resist horizontal and rotational

movements?

3. Will rigidity be provided where it is needed?

4. Is the clasp design applicable to malposed or rotated abutment teeth?

5. Can it be used despite the presence of tissue undercuts?

6. Can the clasp terminal be adjusted to increase or decrease retention?

7. Does the clasp arm cover a minimum of tooth surface?

8. Will the clasp arm be as inconspicuous as possible?

9. Will the width of the occlusal table remain the same or be decreased?

10. Is the clasp arm likely to become distorted or broken? If so, can it be replaced?

The essential function of clasp are :

1-Retention: by the flexible part of the arm.

2- Support: by occlusal rest.

3- Bracing: by the rigid part of the arm.

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Mostafa Fayad 11

Cone theory In 1916 protherio present a cone theory to explain clasp retention , he described

the crown form as two cones sharing common base.

De van ‘s concept

De van divided the abutment into suprabulge and infrabulge portions

Types of Clasp Retainers

Clasp Classified On basis of design into:

I- Occlusal1y Approaching clasps (Circumferential clasp) class Π

I- Gingivally approaching clasp (Bar-type clasp, infrabulge or roach) class I

II-Combination

Clasps can be classified according to the material used into:

1. Cast clasps

2. Wrought wire clasps.

3. Combination cast and wrought wire clasp.

Clasp Classified On basis of movement accommodation

- Clasps accommodate functional movement

RPI

RPA

Bar clasp

Combination clasp

- Clasps without movement accommodatation

Circumferential clasp

Ring

Embrasure clasp

Back action

Multiple clasp

Half and half clasp

Reverse action

-

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Mostafa Fayad 12

Clasp Classified On basis of design into:

I- Occlusal1y Approaching clasps (Circumferential clasp)

The retentive terminal approaches the undercut of the tooth from above

the survey line, the retentive arm originates at the minor connector usually

near the occlusal rest. e.g. Akers, back action, reverse back action, ring clasps.

II- Gingivally approaching clasp (Bar-type clasp, infrabulge or roach):

The retentive terminal originates from the denture base buccal to the edentulous ridge, crosses the free gingival margin to approaches the retentive undercut from below the survey line. The tip of the retentive arm may be in the form I• T, U• C or Y.

I- Occlusally Approaching Clasps.Called encircling, circumferential, or suprabulge clasps.

Definition: it is a retainer that encircles a tooth by more than 180 degrees, including

opposite angle, and which generally contacts the tooth throughout the extent of the

clasp, with at least one terminal located in an undercut area.

Component parts of the clasp assembly:-

1- Rest: location: - it is lie on the occlusal or lingual surface or

on the incisal edge.

Function: provide support for RPD.

2- Body Location: - above the height of contour.

Function: - connect the rest and clasp arms to the minor

connector.

3- Reciprocal arm Location: - above the height of contour on the side

of the tooth opposing the retentive clasp arm.

Function: - 1- Resist the tipping force generated by

retentive terminal.

2- Help in stabilization of RPD against

lateral movements.

3- Support the prosthesis due to it lie on

the supra bulge.

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Mostafa Fayad 13

The reciprocal clasp arm must be contact to the tooth before retentive clasp arm pass

over high of contour, and remain in contact while the retentive terminal passes the

height of contour, to resist the tipping force.

4- Retentive arm: - it includes two parts:-

A) Shoulder Location:- above the height of contour (NOT

FLEXABLE)

Function:- connect the body of the clasp terminal.

B) Retentive terminal Location: - below the height of

contour (FLEXABLE).

Function:- provide direct retention.

5- Minor connector:- It is the part of clasp that joints the body of the clasp to the

remainder of the framework ( IT MUST BE REGIDE).

CAST CIRCUMFERENTIAL CLASP

RULES FOR USE

The retentive clasp arm should originate above the height of contour &

terminated below it. While, the retentive terminal should be pointed toward the

occlusal surface, never toward the gingiva.

These produce a curved clasp which increase the length of the arm as well as

increase the flexibility. The retentive tip should be terminating at the mesial or distal

line angle of the abutment tooth.

Problems of cast circumferential clasp:-

1- Obtaining Sufficient Occlusal Clearance: - if the opposing occlusion is tight, it

is often difficult to obtain adequate clearance to place the rests & clasp without

removing a prohibitive amount of tooth structure on the abutment & it is

antagonist teeth.

2- Protection of The Marginal Gingiva Adjacent to The Abutment tooth:- when

the occlusal rest is placed on the surface of the tooth away from the edentulous

space, this does not protect the marginal gingiva adjacent to the abutment

tooth. This marginal gingiva may be traumatized if food pecks between the

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Mostafa Fayad 14

denture & the proximal surface of the tooth. Therefore advisable to place an

additional occlusal rest next to the edentulous space to eliminated this problem.

But this additional rest will decrease or eliminate the releasing action of the

clasp tip as the denture base is depressed on the distal extension side.

3- Poor esthetic result with excessive display of metal.

1- Aker’s clasp simple circlet clasp

It is most often the clasp of choice on tooth support RPD this clasp usually

approaches the undercut on the abutment tooth from the edentulous area.

Engages an undercut of 0.01inch (1/4 mm) on the buccal (or lingual) surface of

molars or premolars far from the edentulous area

Indications:

a. Acker clasp is considered best suited for strong abutments teeth because it

transmits the force directly to the tooth and reduce stress on the residual

ridge.

b. It is, therefore more often used in unilateral and bilateral tooth borne

partial denture.

Advantages of Aker clasp

1-This clasp fulfills the requirements of support, stability, encirclement,

reciprocation, and passivity better than any other types of clasp.

2- It is easy to construct and simple in repair.

3 - Does not distort easily.

Disadvantages of Aker clasp

a. More tooth surface is covered than with bar clasps. This may cause

enamel decalcification or caries.

b. The Aker clasp changes the morphology of the abutment crown. This

may interfere with the normal food flow pattern and with the

physiologic stimulation of the gingival tissues.

c. Due to its half round cross-section, the Aker clasp can be adjusted to

the tooth surface in an inward or outward (Bucco-lingual) and not

upward or downward (occluso-gingival) direction. This mode of

adjustment may only increase or decrease friction on the tooth

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surface but does not change the retentive qualities arising due to

engagement of an undercut.

d. The clasp cannot be used in free-end saddle cases due to its rigidity,

except with a stress equalizing design.

Cotra-indications: Free end saddle cases (Kennedy class I and II).

Other forms are modifications of the circlet to suit the location of

retentive undercut, position of the abutment, or to modify the flexibility of the

clasp arm.

Modifications of the Aker's clasp

A- The reverse circumferential clasp: reverse approach It is a cast circumferential clasp consists of:

1. Occlusal rest located away from the edentulous area.

2. Retentive arm that engages an undercut near the edentulous area

(near zone).

3. A rigid reciprocal arm.

Indication:

It can be used in distal extension cases when the bar clasp is contraindicated

(when?).

The effect on the abutment tooth is reversed from that of the conventional

circumferential clasp.

Advantage:

As when occlusal load is applied to the denture base, the retentive terminal

moves further gingivally into the undercut area and loses contact with the

abutment tooth (disengagement). In this manner torque is not transmitted to

the abutment tooth.

Disadvantage:

The reverse circlet clasp, because it normally projects between two

teeth, may produce some wedging force. This can usually be countered by

occlusal rests on the approximating surfaces of both teeth.

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B- The Multiple Aker Clasp (Multiple circlet clasp)

The multiple Aker clasp consists of two opposing Aker’s clasps, Two

Lingual rigid reciprocal arms are connected together at the terminal ends to

augment their rigidity.

Indications:

The multiple Aker clasp is used

Splinting of periodontally affected teeth is needed.

Multiple clasping is needed in instances in which the partial denture replaces

an entire side of the dental arch.

Available retentive areas are only adjacent to each other.

disadvantage : utilizing two embrasures rather than a common one.

C- The Hair-pin Clasp (C- Clasp – Fishhook)

It is a circlet clasp with its retentive arm turned back (curved ) to engage

an undercut near the edentulous area (below the point of origin).

Indication

1- when the retentive clasp must engage an undercut adjacent to the occlusal rest

or edentulous space and a soft tissue undercut precludes the use of a bar

clasp.

2- When the reverse circlet clasp cannot be used because of lack of occlusal space.

3- when a proximal undercut must be used on a posterior abutment and when

tissue undercuts or high tissue attachments prevent the use of bar type clasp.

Its disadvantages are:

1. greater coverage of tooth surface, that increase the functional load on the

abutment.

2. food trapping at the loop of the arm, and

3. inferior esthetics.

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D- The half and half clasp (Split cast assembly):

It consists of a circumferential retentive arm arising from one side of the

tooth and a reciprocal arm arising from the other direction on the opposite side

of the tooth. Since the second arm must arise from a second minor connector,

therefore an auxiliary rest may sometimes be used.

It is used with isolated premolars and molars for bounded and free end

partial denture.

This clasp was designed originally to provide dual retention, and it should

be apply only unilateral denture designed.

E- The Extended-arm Clasp

The extended arm clasp has the same form as an Aker clasp but its arms

are extended to cover the abutment tooth and the tooth adjacent to it. The

bracing arm lies above the survey line of both teeth. The retentive arm also lies

above the survey line of both teeth and then tapers to engage the undercut of

the second tooth. It is more liable to distortion if its thickness is incorrect.

If this clasp is made in gold alloy the uses is restricted to the premolars,

but with chrome cobalt alloy along arm can be used and two molars can be

clasped.

Indication:

The clasp is used when the undercut on the tooth near the edentulous area

is poor, while that on the adjacent tooth is suitable.

Advantages of extended arm clasp

a. The clasp has splinting action.

b. Distributes the lateral load over the two teeth.

F- The Double Aker Clasp

The double Acker clasp is also called embrasure clasp, Compound clasp,

Butterfly , modified crib clasp, Bonwill clasp or Interdental clasp.

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It consists of two Acker clasps arising from a common body and from the same

minor connector, which is located in the embrasure between the two clasped teeth.

Indication

1- on the dentulous side of unilateral edentulous cases (Kennedy class II or

III having no modifications).

2- Kennedy class IV (on the posterior teeth).

It is used primarily to provide bilateral stabilization, and bracing, in addition to

retention. It also splints the two teeth

The retentive arms of embrasure clasps are always of

the supra bulge type. Although double or single infra

bulge clasps have been used, they tend to create food

repositories and are therefore not the retainers of choice

except in rare cases.

g- Anterior circumferential clasp

2- RPA clasp (RPC clasp)

Mesial Rest, Proximal plate and Aker arm ,

(circumferential Clasp).

The clasp is formed of:

A mesial occlusal rest arising from a minor connector located in the mesiolingual

embrasure,

A proximal plate placed on the occlusal third of the distal surface of the abutment

and properly extended towards the distolingual line angle of the tooth, in

contact with a prepared guiding plane, and

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An Aker circumferential retentive arm arising from the superior portion of the

proximal plate. and extends around the tooth; tapered to engage the mesio-

buccal undercut.

The rigid bracing portion of the arm should contact tooth only along

superior border of the survey line. When an occlusal load is applied to the

denture base, the retentive arm can move into the undercut because of the

relief under its rigid section and release from the abutment tooth.

If a conventional Akers clasp is used, with the retentive arm coming off

the proximal plate above the survey line and crossing the survey line in the

middle of the tooth to engage the undercut then the vital releasing capability will

be lost.

Indication:

It is indicated in distal extension RPDs presented with shallow

vestibule or severe tissue undercut that contraindicate the use of the gingivally

approaching clasps.

Advantages:

1. The RPA assembly is designed with the rest on the mesio-occlusal surface of

the tooth, permitting the other components to release from the tooth and drop into

undercuts when occlusal loads are placed on the denture base. This in turn prevents

tipping of the abutment.

2. Absence of a lingual rigid reciprocal arm minimizes rotational forces falling

on the abutment.

3- RLS Clasp

(Mesial Rest, L-bar direct retainer and Stabilizer)It is a lingually retained clasp assembly for distal extension removable

partial dentures. This clasp assembly fulfills the biomechanical principles and

the esthetic requirements of patients.

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The RLS clasp assembly consists of:

1) A mesioocclusal rest.

2) A distolingual L-bar direct retainer,

located on the distal surface of

the abutment tooth. Engages the

distolingual undercut adjacent to

the edentulous ridge.

3) The distobuccal stabilizer (proximal plate): Reciprocate the horizontal force,

transmitted to the tooth by the activated retentive tip of the direct retainer, The

distobuccal stabilizer emerges from the framework distobuccally and ascends

to the height of contour, then it diverges distally and/or lingually to complete

the encirclement of the tooth.

Cross-arch stabilization is provided by the minor connectors located

lingually, and the L-stabilizers located buccally

Advantages:1. The mesio-occlusal rest reduces the anterior component of movement of the

denture and reduces torque on the abutment tooth.

2. A retentive clasp tip placed on the most distal part of the tooth will undergo a

downward vertical movement and disengage as the distal extension base

moves tissue-ward in function.

4- Back Action Clasp

The back action clasp is a single arm clasp, provide single bracing only .

The minor connector originates from the major connector. It starts at the of

mesiolingual line angle.

The bracing arm extends above the survey line on the palatal surface till the

proximal surface, then starts its taper to engage a mesiobuccal undercut of

0.01 of an inch.

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The occlusal rest is located distally,and some times an additional rest could be

employed on the mesial side to improve support.

Indications:

(1) The back action clasp is usually used on

maxillary premolars and molars. Because of the

natural tendency of upper teeth to incline buccally,

they usually have undercuts on the buccal side.

(2) The clasp is sometimes used in posterior free-end

saddle cases due to its flexibility and stress breaking action.

Disadvantages of back action clasp

The back action clasp is both biologically and mechanically unsound. it has the

following disadvantages:

1. Excessive tooth coverage.

2. Easily distorted because of length and difficult to adjust.

3. Excessive display of metal, hence it is esthetically unsatisfactory.

4. The occlusal rest is supported by the clasp arm and not by a rigid minor

connector, hence the rest cannot function adequately.

5. The clasp provides poor bracing and reciprocation.so it is contraindicated in

unilateral partial denture

6. Food is trapped between the palatal arm and the major connector due to

insufficient space (clearance) between them.

5- Reverse back action clasp

The Reverse back action is similar in structure to the back action but it is

located in the reverse direction.

The minor connectors originates buccally from the saddle starts at the

mesiobuccal line angle and ends to engage a mesiolingual undercut of 0.01 or

0.02 of an inch.

The clasp is Frequently used on lingually tipped bicuspids. It also provides

single bracing only. It has an additional esthetic disadvantage.

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6- Ring Clasp

The ring clasp is a single-arm clasp, indicated on tilted, isolated molars.

It originates mesially and the single arm encircles nearly all the tooth surface

resembling a ring.

It is generally exhibiting a mesiobuccal undercut in case of upper molars and a

mesiolingual undercut on lingually tilted lower molars. The clasp engages a

0.02 or 0.03 of an inch undercut.

The occlusal rest is located on the mesial marginal ridge.

An auxiliary distal rest is preferably added to prevent further mesial tilting of the

tooth.

A reinforcing supporting strut arm located on the non-retentive side is usually

considered to limit the flexibility of the clasp.

Disadvantages of ring clasp:

(1) Excessive tooth coverage that may result in enamel

decalcification and caries.

(2) Easily distorted because of length and difficult to adjust.

(3) Reinforcing arm may cause marginal irritation and inflammation and

may act as a food trap.

7- Onlay Clasp

It is an extended occlusal rest with buccal and lingual clasp arms. The clasp may

originate from any point on the onlay that will not create occlusal interferences.

Indications:

1- when the occlusal surface of the abutment tooth is below the occlusal plane.

If the onlay clasp is constructed of chrome alloy and is opposed by a natural tooth,

the occlusal surface should be constructed of acrylic resin or gold.

II- Gingivally Approaching Clasps

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These clasps are also called Infra-bulge, I-Bar, Vertical Projection or Roach

clasps.

The bar clasps approach the undercut or retentive area on the tooth from a

gingival-direction, resulting in a "push" type of retention. This push retention of bar

clasps is more effective than the "pull" retention characteristic of circum.

Disadvantages of bar clasps:-

1- Greater tendency to collect and hold food debris.

2- The increased flexibility of the retentive arm, it does not contribute as much

to bracing and stabilization. Additional stabilizing units.

The flexibility of the bar clasp can be controlled by the taper and length of the

approach arm.

Contraindication:

It is contraindicated if the undercut is more than 1mm or the depth of the buccal sulcus

is less than 4mm.

Component parts of clasp

1- Approach arm : It is a minor connector that joins body and retentive terminal of

clasp to framework.

2- Retentive clasp arm and retentive terminal: It must be flexible and located gingival

to the survey line.

3- Reciprocal clasp arm is usually in the form of a circumferential clasp arm and

rarely in the form of bar arm

4- Occlusal rest

Indications: -It is used mainly in unilateral and bilateral free end cases to minimize the

torque on the abutments.

-It provides better retention and better esthetic but less bracing than Aker's

-It can utilize different amount of undercut.

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Contra-indications: - Deep cervical undercut on abutment or excessive tissues undercut. To avoid

food impaction. - Shallow sulcus.

RULES FOR USE:-

1- The approach arm of the bar clasp must not impinge on the soft tissues it is

crosses. It is not desirable to provide an area of relief under the arm, but the

tissue side of the approach arm should be smooth& polished.

2- The approach arm should cross the gingival margin at a 90-degree angle.

3- The approach arm must extend on the abutment tooth to the height of contour.

The retentive terminal leaves the approach arm at that point and extends into

the undercut area. The tip of the retentive terminal must be end toward the

occlusal surface. (The approach arm contacts the tooth only at the height of

contour).

4- The bar clasp should also be placed as low on the tooth as possible while

honoring the height of contour to reduce the leverage-induced stress to the

abutment tooth.

5- Functional depth of vestibule at least 5mm.

6- Superior border away from gingival margin by at least 3mm.

7- The approach arm must be tapered uniformly from it is attachment to the clasp

terminal. It must never be designed to bridge soft tissue a undercut, to avoid the

tapering of food & to avoid the irritation of cheeks or lips.

8- The approach arm should taper gradually and uniformly from its origin to the

retentive end.

9- It must not bridge a soft tissue undercut to avoid food trapping and irritation .

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10- The tip of the retentive arm may be in the form of I.T.U.C or Y . One end of

the T or Y engage undercut while the other end placed above the survey line

the only function of this additional end is to encircle more than 180º of the

tooth, if the retentive undercut is near to minor connector and occlusal rest.

11- The bar--type clasp is said to have a "push" type of retention (Trip action of

the clasp). As this arm is relatively longer than occlusally approaching arm, it

is considered as a more flexible arm. However, curvature of the arm in more

than one plane minimizes this expected high flexibility.

12- Tripping action is attributed to clasp arms that engage the undercut directly

from a gingival direction. Not all bar clasp arms have tripping action, since

the retentive terminal may actually engage the undercut from an occlusal

direction as is true with the "T" bar or modified "T" bar

Types of Bar Clasps

1- The I-bar clasp (Roach clasp arm)

The I- bar clasp consists of:

A retentive clasp arm originating from the denture base• approaching the buccal

undercut from a gingival direction. It provides retention only.

A rigid reciprocal clasp arm on the opposite side of the tooth. This arm is

usually in the form of a circumferential clasp arm and rarely in the form of a

bar arm. This arm is located above the survey line. It provides bracing and

reciprocation.

An occlusal rest and a minor connector joining the rest with the framework.

It is used on the distobuccal surface of maxillary canines for esthetic reasons.

There is a definite danger involved in using this clasp. Because the only

contact of the retentive clasp with the abutment tooth is the tip of the clasp,

an area of 2-3 mm, encirclement and horizontal stabilization may be

compromised.

a- T Clasp

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The T clasp is used most often in combination with a cast circumferential

reciprocals arm.

Indications of T clasp:-

1- The T clasp is used most frequently on a distal extension ridge where the

usual undercut is on the distobuccal surface of the abutment tooth. When

tissue ward forces occur on the denture base, the terminal clasp tip rotates

cervically into a greater undercut, this reduces the torquing stresses to the

abutment tooth.

2- In class I or II R P D where the retentive undercut on the distobuccal surface

of the abutment. This retention can best be secured by T clasp.

3- The T clasp can also be used for a tooth-supported partial denture

when the retentive undercut is located on the abutment tooth adjacent to the

edentulous space.

Contraindications:-

1- The T clasp should not be used on a terminal abutment adjacent to distal

extension base if the usable undercut is located on a fare zone of the abutment

tooth.

2- Also, this clasp can never be used if the approach arm must bridge a soft tissue

undercut.

3- T clasp should be avoided if height of contour of abutment tooth lies close to

occlusal surface. Because a large space would be created between approach

arm of clasp and tooth. Space would trap food. High position would also be

unaesthetic.

b- Modified T Clasp

The modified T clasp is essentially a T clasp with the nonretentive finger (usually

mesial).

This clasp is most often used on canines or premolars for esthetic reasons.

The potential danger in its use is that encirclement, or 180-degree coverage, of the

abutment tooth may be sacrificed to esthetics.

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Esthetics should always be considered when the partial denture is being designed,

but its consideration must not supersede the necessity of making the prosthesis

mechanically acceptable. An esthetically superior denture that leads to ultimate

destruction of the remaining oral tissues is not in the best interests of the patient.

c- Y Clasp

The Y clasp is basically a T clasp; it's used when the height of contour on the facial

surface of the abutment tooth is high on the mesial and distal line angles but low on

the center of the facial surface.

On occasion, careful recontouring of the enamel surface of the abutment tooth

will permit the Y clasp to be converted to the standard T clasp.

d- L clasp

It is a modified T clasp.

e- U clasp

There are two bars effectively engage the undercut, retention will be improved.

2- The RPI clasp (Kratochvill’s system)

(Rest, Proximal Plate and I Bar)

The RPI clasp is a current concept for bar clasp design, as the full “T” bar should

not be used since it covers an unnecessary amount of tooth structures compared with

the RPI clasp.

Basically the clasp assembly consists of:

1- A mesio-occlusal rest:

A mesio-occlusal rest with the minor connector placed into the

mesiolingual embrasure.

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2- A proximal plate:

a- It is placed on a distal guiding plane, extending from the marginal ridge to

the junction of the middle and gingival third of the abutment tooth.

b- The proximal plate minor connector should contact approximately 1 mm of

the gingival portion of the guiding plane in distal extension cases.

c- The bucco-lingual width of the proximal plate is determined by the proximal

contour of the tooth.

- The proximal plate together with the mesiolingually placed minor

connector provides stabilization and reciprocation of the assembly.

3- The I bar arm:

a- It should be located in the gingival third of the buccal or labial surfaces

of the abutment in 0.01 of an inch undercut.

b- The I-bar approaches the undercut in a vertical direction at the center

of the abutment tooth.

c- It may be placed towards the mesial but not towards the distal to avoid

torquing of the abutment tooth when a vertical load is applied on the distal

extension base (.

d- The whole arm of the I-bar should be tapered to its terminus, with no

more than 2 mm of its tip contacting the abutment.

e- The base of the I-bar must be located at least 4 mm from the gingival

margin.

f- Slight relief is required where the arms crosses the gingival margin.

Indications:

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The RPI clasp is indicated:

a- In distal extension cases, as it provides a stress releasing action.

b- When tissue undercuts are not severe.

Contraindications:

The RPI clasp is contraindicated with:

a- Shallow vestibule (the base of the I-bar should be at least 3mm from

the gingival margin).

b- High floor of the mouth which necessitates the use of lingual plate.

c- When buccal undercut is absent or only distobuccal undercut exists.

d- In cases with severe tissue undercut to avoid food or tissue trap.

e- If the facial surfaces of teeth are facial to the tissue surface, the RPA

clasp may be used.

3- The RII clasp

This clasp is basically indicated for posterior teeth or a single isolated last

molar. The RII clasp is composed of:

a- Occlusal Rest (R) located on the side of the tooth near the edentulous area.

b- Two I bar arms (II): one arm Located on the lingual or palatal surface of the

abutment above the survey line, this arm is usually rigid for bracing.

The other arm is a flexible retentive arm located on the buccal surface of

the abutment tooth. The retentive terminal uniformly tapered engages an

undercut of 0.01 of an inch below the survey line (Fig.3-150).

Support is provided by occlusal rest,

Bracing is provided by mesial minor connector and rigid lingual I bar.

Retention is provided by buccal I bar, and

Reciprocation is provided by mesial minor connector and rigid lingual I bar.

4- The Ball and Socket clasp

It is a bar type clasp, used when the tooth surface having no undercut.

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The retentive arm is a round platinized gold wire, with a ball at one end.

This end engages a dimple on the buccal surface of the tooth prepared in a

gold inlay..

5 - CLASPS UTILIZING PROXIMAL UNDERCUTS

a- Infrabulge clasp (the DeVan clasp):

It is designed so that the Lingual aspect may be open or plated.

Two occlusal rests on each abutment are used. The bar arm arises from the

border of the denture base, either as an extension of a cast base (C), or it may be

in the form of wrought wire clasp attached to the border of a resin base. Wrought

wire clasp arm could be used if additional flexibility is required (D)

It has a small head that bears on the tooth interlay below the survey line.

The De Van clasp should be reciprocated by a lingual or palatal strut which

contact the tooth at the junction between the lingual or palatal & fare proximal

surface. This strut end in a lingually or palatally placed occlusal, the primary

occlusal rest being placed on the near proximal part of occlusal surface. This

reciprocating arm may be replaced by an embrasure hook.

The DeVan clasp is highly retentive and esthetically agreeable due to its

proximal location. But food debris may be entrapped between the arm and the

denture base.

Advantages of De Van clasp:-

1- It can used when a buccal or lingual survey line are unfavorable.

2- Good esthetics even when used on premolars& canine. Because, it is can be hidden

behined the buccal convexity of the tooth.

3- Good retention/ due to the angle of approach of the clasp to the undercut which gives

a marked trip action.

4- It is compact design in relation to the saddle periphery helps to prevent it is

accidental displacement.

b- Mesio-distal clasp

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It may be used when clasping canines. specially when little undercut on the buccal

surface of canine, or to avoid the clasping of the buccal surface which is esthetically

displacing. This clasp is always cast in gold & embraces the canine on the mesial,

palatal & distal sides.

The mesial surface of the canine should be cut or reduced to create a necessary

space. If a diastema is exists between the canine and lateral incisor this space

provides an accommodation for the mesial part of the clasp without reduction of the

mesial surface of canine.

In free end saddle cases, it must be employed without using a stress breaker.

Advantages of mesio-distal clasp:

1 It is accepted esthetically.

2- Give good retention& grips the tooth rigidly.

Comparison Between Occlusally and Gingivally

Approaching Clasps

Both occlusally and gingivally approaching clasps are cast clasps

achieving the same design principles, however, they exhibit the following

differences:

1. Retention:

Gingivally approaching clasp gives better retention than occlusally

approaching clasps through the trip action of the clasp, as it pushes toward the

occlusal surface to resist displacement, while the occlusally approaching clasp

pulls toward the occlusal surface to resist displacement.

2. Bracing:

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Since the occlusally approaching clasp arm generally has a rigid portion

lying in contact with the non-undercut zone of the tooth, its bracing effect is

greater than the gingivally approaching clasp.

3. Caries Susceptibility:

The incidence or caries under clasp arms may said to be inversely

proportional to the efficiency of the patient's oral hygiene. If cementum is ex-

posed, there is some risk of cemental caries with gingivally approaching arms.

While the occlusally approaching clasp covers more of the tooth surface,

this increases the susceptibility of enamel caries.

4. Gingival Health:

When properly designed, clasps are used in combination with adequate

tooth support of the denture. Gingival health is rarely affected.

Traumatic gingivitis, however, more often seen with gingivally

approaching clasps, either as a result of inadequate relief of the clasp arm, or

through its accidental displacement.

5. Esthetics:

The gingivally approaching clasp has sometimes to be preferred

than the other, due its proximity to gingival margin, hence are less visible.

However, in cases, where the gum is shown as in the gumy smile

patients, the gingivally approaching clasp is even more noticeable than

occlusally approaching clasp.

7-Tolerance:

The gingivally approaching is less tolerated specially if excessive

block-out is done leading to food and tissue trap.

8- indication:

The occlusally approaching clasp is indicated in case of Tooth

Supported RPD, when esthetic s not important because of its stabilizing

ability.

The gingivally approaching is indicated incase of Tooth- Tissue

Supported RPD, because of its stress releasing action. And in case of Tooth

Supported RPD when esthetic is the prime concern.

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Classification of Clasps according to the mode of construction and the

material used:

Clasps can be classified according to the material used into:

1 - Cast clasps

2 - Wrought wire clasps.

3 - Combination cast and wrought wire clasp.

1-Cast metal clasp:

a. The cast clasp is either gold or cast chromium alloy.

b. It is half round in cross section.

c. It contacts tooth surface at an area.

d. It flexes in one plane (to or away from tooth surface) only.

Advantages of cast clasps:

a. They exhibit an accurate fit to tooth surface.

b. Can easily be varied in thickness, form and taper during their

construction.

2- Wrought wire clasp

a. The wrought wire is a buccal retentive arm. Usually made of either

0.7 or 0.8 mm round stainless steel, or gold alloy wires embedded

in the acrylic base.

b. This type of clasp is extremely resilient, however, it possesses poor

stabilization properties.

c. It flexes in two planes (to or away from tooth surface and up or

down parallel to tooth surface).

d. It has line contact with tooth surface creating less friction.

e. Due to its flexibility it can be easily distorted.

f. Its common use is in acrylic dentures.

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Wrought wire clasps may be in the form of :

1- Simple circlet clasp

a. The clasp is either soldered to metal framework or embedded in the acrylic

resin lining the denture base. The clasp is used on teeth adjacent to the

edentulous area.

b. It should pass 3-4 mm away from the proximal surface of the clasped tooth

to allow for the adjustment of the denture during insertion.

2. Jackson-Crib Clasp (Modified Crozat Clasp)

a. This is a completely encircling clasp with no free flexible terminal.

b. It provides retention because those parts of the clasp, which are situated on

the proximal embrasures of the tooth, are springy and grip the undercuts in

these areas. It acts as a clasp and occlusal rest.

c. It is used with acrylic denture and made of 0.7-mm gauge wrought wire.

d. It indicated on molars and premolars when no edentulous space exists on

either side of the tooth to be clasped.

e. It starts at the point of attachment of the base on the lingual side and passes

up to cross the occlusal surface and then down to the buccal surface along the

gingival margin and then up again to cross the occlusal of the other contact

point to gain attachment to the base of the lingual side.

1. Split crip

When cut at the middle of buccal surface

2. Half crip

When it does not reach the other embrasure.

Advantages of wrought wire clasps

a. Less tooth coverage as the clasp makes a line rather than an area of contact

with the tooth surface.

b. Minimum friction.

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c. The clasp is highly flexible, hence can be used in distal extension bases

requiring stress breaking action.

d. Easily constructed.

Wrought-wire direct retainer arms may be attached to the restoration by

1- Embedding a portion of the wire in a resin denture base,

2- By soldering to the fabricated framework, or

3- By casting the framework to a wire embedded in the wax pattern.

Wrought-wire retainer arm has been contoured to follow the design and is

incorporated into the wax pattern

3-Combination clasp

It is essentially a cast clasp in which wrought wire has substituted the

buccal cast retentive arm. If this term is used the term wrought wire clasp is limited

to wrought wire retention arms reciprocated by acrylic or metal lingual or palatal

plates

If the partial denture framework is to be constructed of gold or low-heat

chrome alloy, the wrought wire clasp can be incorporated into the framework

during the waxing step and the alloy can be cast directly to the wrought wire clasp.

If a high-heat chrome alloy is used, the wrought wire must be soldered to the

completed framework.

Indication:

- on an abutment tooth adjacent to a distal extension space when the usable

undercut on the tooth is on the mesiobuccal surface.

Advantages of the combination clasp

1- Combines both the resiliency and flexibility of the wrought retentive arm

and stabilizing effect of the cast clasp.

� The clasp has a stress breaking action. The wrought wire acts as a

stress equalizer preventing the undesirable forces created by the lever action

of the retentive clasp tip from lifting or torquing the abutment tooth as

downward forces occur on the denture base.

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� The greater flexibility of this clasp allows it to place in a greater or

deeper undercut.

2- Adjustability:-

The round wrought wire clasp can flex in all spatial planes, which allow it

to dissipate torquing forces exerted on the abutment tooth & to be adjusted in all

planes.

3- appearance:-

The wrought wire clasp may be used in small diameters than the cast clasp.

Since it is round, light is reflected in such a manner that the display of metal is less

noticeable than with the border surface of the cast clasp.

4- Caries less:-

The round wire makes only a line contact with the surface of the abutment tooth.

This minimal contact of makes it is used in caries- prone mouths some what may

beneficial.

Disadvantages of combination clasp:-

1- It does require extra steps in laboratory fabrication.

2- It is also more prone to breakage or damage than a cast clasp.

3- It can be easily distorted by careless handling by patients, who tend to

remove the partial denture from the mouth by lifting on the retentive portion of the

wrought wire clasp.

Because of the increased flexibility of the retentive arm, it does not possess

the bracing or stabilizing qualities of most circumferential clasps. If stabilization of

the teeth or of the partial denture against horizontal forces is needed, the

combination clasp would not be a good choice.

These disadvantages should not prevent the use of this clasp regardless of the

type of alloy being used for cast frame work. The technical problems are

minimized by selecting the beast wrought wire for this purpose.

The patient may be taught to avoid distortion of the wrought wire by explaining

that the fingernail should always be applied to it is point origin, where it held rigid

by casting.

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OTHER TYPES OF RETAINERS

Grasso’s clasp (VRHR clasp concept)

The VRHR clasp assembly consists of:-

1- Distal occlusal rest supported by minor connector.

2- Lingual Vertical Reciprocal arm originated from major connector.

3- Horizontal Retentive arm fixed either to the major connector or to the

framework.

Each arising separately fram the denture base.

This clasp design is especially useful on mandibular molars and premolars

that have heights of contour in the occlusal third of the crown.

The reciprocal component of this clasp designed to contact the lingual

height of contour at the greatest mesiodistal prominence.

The horizontal retentive arm is generally parallel to the occlusal plane&

placed completely below the height of contour with only the terminal third of the

clasp contacting the abutment tooth; the remaining two third is positioned slightly

out of contact with the tooth surface. The degree of the space between a rigid part

of the retentive clasp & the tooth surface is determined by the amount of the

undercut that usually fracture of mm.

Advantages of VRHR clasp:-

1- Make a minimal contact with the teeth.

2- Providing continuous contact during insertion and removal of the

prosthesis.

3- No need to developed lingual ledges.

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4- Suitable for posterior teeth with high survey line .

5- Placement of retentive arm is more esthetic

6- Doesnot require preparation f guide line .

7- The balance between the retentive arm and the reciprocal component

prevent the whiplash effect of the retentive arm.

NavasCampo (NC) clasp

It is suggested by Navas & Campo. It is a special design for a tissue -

supported, distal extension RPD for patients who require a combined fixed

removable prosthesis and this system provides to overcome the esthetic problem,

retention, bracing, and support for distal extension base RPD with minimal damage

to the abutment teeth and the supporting tissues. This clasp is intended to minimize

loads on the abutment teeth during functions:

The “NC” design consists of:

- The minor connector: connects a ball - shaped pin to the major connector,

and helps guide the RPD into place. It has no retentive properties and is free to

slide up and to down the prepared slot, acting as stabilizer. There are no vertical

stops on hard tissue because this is a soft tissue supported type of prostheses.

- An active arm in close contact with the abutment tooth separates from it

under the forces of mastication, with the denture base forming a hollow space that

protects the marginal gingiva.

- The retention is gained through a ball pin, which fit into machined grooves

in fixed partial denture. The ball shaped pin, serves as the guide for insertion and

removal of the prosthesis, it is made to rest midway along the superior and inferior

limits of the grooves.

- Under the pressure of mastication, the NC clap is deactivated and the balls

can move downward along the transverse axis with a slightly rotational movement.

- When the mouth is opened, the NC clasp is activated and the balls move

upward along the transverse axis with a slightly rotational movement.

- The esthetic problem is solved because no metal is visible on the facial

surface of the arches. The size of the ball and gauged groove is shown in.

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Retention is provided by the anatomical alveolar ridges and muscles and by

mechanical factors such as the NC clasp, which keeps the prosthesis joined to the

abutment tooth. Bracing is provided by the ball inside the groove, the well fitting

denture bases, and the proper placement and articulation of the teeth. In a tissue

supported type of denture,and Stabilization is achieved by a good bilateral balanced

occlusion.

Oddo hinge clasp

The Oddo hinge clasp modification is primarily

indicated when anterior abutments have more than

average labial inclination and, thus, a height of contour

very near the 'nasal edge The hinge is opened, the

prosthesis seated, and the hinge closed The tip of the bar

clasp can be located in a much greater undercut than

normal. The retentive tip is located in the gingival third of the tooth, and the

body of the arm is hidden in the labial vestibule Relatively simple adjustments

in the housing will compensate for minor wear The entire assembly can be

replaced without remaking the RPD

Lingual retention in conjunction with internal rests

It is emphasized that the internal rest is not used as a retainer but that its near-

vertical walls provide for reciprocation against a lingually placed retentive clasp

arm. For this reason, visible clasp arms may be eliminated, thus avoiding one of

the principal objections to the extracoronal retainer.

Such a retentive clasp arm, terminating in an existing or prepared infrabulge area

on the abutment tooth, may be of any acceptable design. It is usually a

circumferential

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arm arising from the body of the denture framework at the rest area. It should be

wrought, because the advantages of adjustability and flexibility make the wrought

clasp arm

preferable. It may be cast with gold or low-fusing chromium-cobalt alloy, or it may

be assembled by being soldered to one of the higher-fusing chromium-cobalt

alloys. In

any event, future adjustment or repair is facilitated.

The use of lingual extracoronal retention avoids much of the cost of the internal

attachment yet disposes of a visible clasp arm when

esthetics must be considered. Often it is employed with a tooth-supported partial

denture only on the anterior abutments and, when esthetics is not a consideration,

the posterior abutments are clasped in the conventional manner

One of the dentist's prime considerations in clasp selection is the control of stress

transferred to the abutment teeth when the patient exerts an occluding force on

the artificial teeth. The location and design of rests, the clasp arms, and the

position of minor connectors as they relate to guiding planes are key factors in

controlling transfer of stress to abutments.

Errors in the design of a clasp assembly can result in uncOntrolled stress to

abutment teeth and their supporting tissues. The choice of clasp designs should be

based on biologic as well as mechanical principles. The dentist responsible for

the treatment being rendered must be able to justify the clasp design used for

each abutment tooth in keeping with these principles.

Incisal cervical prong clasp

The retentive arm runs nearly vertically on the distal part of the tooth from

distoincisal rest

Esthetic solutions in the smile zone

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AESTHETICS OF RPD IN RELATION TO RETAINERS:

Basic types of esthetic direct retainers:

•Intracoronal retainers (Internal attachments): It has better appearance since there is

no need for buccal and labial clasp arm.

•Extracoronal retainers:

� Prefabricated extracoronal (attachment)

� Esthetic clasps:

Clasp showing may be overcome by the following:

1. Better to use posterior clasp.

2. Use of gingivally approached clasps better esthetically than

occlusally approached clasps.

3. Designed to utilize the proximal and lingual retentive undercuts.

4. Better to use attachment (instead of clasps).

5. Esthetic solutions:

� Hidden in Teflon-in tube or plastic tube.

� hidden clasps

� Covered by porcelain.

� Made of tooth colored material (metal free clasps): Thermoplastic acetal,

thermoplastic polycarbonate, thermoplastic Acrylic and thermoplastic

Nylon.

A- Hiding Denture Clasps

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1- Mesiodistal grip clasps:

It engage only the mesial and distal surfaces of the tooth . They rely upon sound

enamel surfaces and long guiding planes.

2- The Equipoise Clasp :

It relies upon a mesial guide plane with clasp extending around to the distal surface .

3- The RLS lingually retained clasp:

Used for distal extension partial dentures which consists of mesio-occlusal rest a

distolingual "L" bar and distobuccal stabilizer .

4- Dual path or rotational path of insertion :

It involves rigid retentive components and the initial placement of one segment with

the denture being fully seated by rotating the denture into place .

5- Guiding planes :

Guide planes may reduce or eliminate the need for conventional clasp retention in

tooth-borne RPDs. Guide planes themselves serve to provide retention.

6- MGR clasp.

It is an esthetic extracoronal retainer for maxillary canines. Retention is provided by

19 gauges round l-bar and retentive dimple located at distobuccally on the tooth.

Reciprocation is provided by mesial groove or rest and distal proximal plate.

7- Estheti clasp:

The Estheti clasp is recommended for patients with required abutment teeth in the

esthetic zone (incisors and bicuspids). The Estheti clasp design may NOT be indicated

for maxillary canines if the patient is edentulous bilaterally in the posterior.

Advantages

Optimum esthetics,

no attachment maintenance cost.

It utilizes the proximal undercuts and encircles the tooth by 181°. Estheti clasp may be

in the form of Lclasp or C-clasp.

L-clasp: The design consists of the clasp arm extending from lingual minor connector

with an independent reciprocal rest. The L-clasp has greater rigidity than the C-clasp.

C-clasp: It consists of a modified back-action clasp with rest incorporated in clasp.

C-clasp has greater flexibility than L-clasp.

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8- Saddle lock:

The saddle-lock system eliminates facial clasp display while achieving natural

esthetics with superior stability and retention. Saddle lock eliminates facial clasps by

using the available mesial! distal concave surfaces of the abutment teeth for retention

instead of the buccal undercuts.

The benefits of saddle lock

Superior esthetics, without visible clasps,

improved retention with little or no adjustment,

easy vertical insertion that protects abutments,

applicable in most partial denture cases,

simple preparation procedures for less chair time.

Limitations

There is no metal horizontal shoe extension,

the retentive arm is short.

9- Spring clasp ( Twin-Flex technique)

This consists of a wire clasp soldered into a channel that is cast in the

major connector. Because this clasp is flexible instead of rigid, it does not generate as

much torque when the distal extension is depressed. The ability to adjust this clasp and

its conventional path of insertion provides an excellent design option for retention

adjacent to an anterior edentulous segment.

Disadvantages of this technique include extra thickness of the major connector

over the wire clasp tang, the extra laboratory steps with increased cost, and difficulty

in repairing the clasp if breakage occurs. (J Prosthet Dent 1997;77:450-2.)

10 - Internally braced clasp

This design is especially suited for cases, in which anterior abutment tooth is a

crowned mandibular canine and is excellent for Kennedy Class III cases.

In this crown, a deep cingulum wedge-shaped rest is prepared with occlusally

diverging walls and a rounded floor. An undercut is prepared in the gingivolingual

third of the crown to accept the retentive arm of the RPD. The rest and the clasp arm

emerge from the saddle to occupy their respective areas of the crown. The retentive

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arm engages the lingual undercut and the rest seats accurately in the wedge shaped

preparation.

Esthetics is improved by the absence of a buccally placed retentive area.

Support is provided by the rounded floor and wedge-shaped walls in the prepared

crown. Retention is provided by the undercut. Bracing and reciprocation are provided

by the internal walls of the preparation.

Disadvantages

This design can be used only in teeth with adequate crown height.

It is generally not applicable in maxillary teeth.

The abutment tooth must be crowned

11- Equipoise System

Esthetic retentive concept for distal extension situations proposed by J.J.

Goodman. The Equipoise semi-precision "E" clasp and precision "C" & "L" clasp

are specifically designed so that all masticatory forces are oriented down the long

axis of the tooth.

The Equipoise Balance of Force Principle

This is accomplished through the use of

Equipoise Class II Lever design. The Class II lever

design has the rest (fulcrum) opposite of the retentive

tip of the clasp (resistance arm) and the denture base

(the effort arm). The clasp arm always moves in the

same direction as the denture base while directing all

forces down the long axis of the retaining abutment

tooth.

Advantages

The Equipoise principle of partial denture design protects, preserves and

strengthens abutment teeth while directing all masticatory forces down the long

axis of the abutment tooth. With the Class II lever design you always obtain

stability during mastication and retention only when needed against dislodging

forces.

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Equipoise RPD System:

- Rests placed away from edentulous span

- 1 mm vertical inter-proximal reduction between abutment and adjacent

tooth.

- Optional Bu- Li retentive groove at mid and gingival third junction on

distal surface of abutment tooth.

- The retentive clasp terminal extends from the mesial and circles around

the lingual and distal surfaces of the tooth and engages the distobuccal

undercut. It is kind to the abutment tooth as it disengages when the partial

denture is in function.

Disadvantages

Lack of reciprocation and retention can be a problem. Goodman advocated

removal of 0.5 mm of tooth structure from adjacent teeth so that rigid metal of the

RPD framework can extend into the area and provides reciprocation.

The interproximal tooth reduction makes it a caries susceptible preparation.

Mesial proximal plate may introduce torque.

Potential loss of proximal space with a noncompliant patient.

Requires greater surveillance.

During processing, excess acrylic may be allowed to surround the clasp. When

this happens the clasp is not able to flex into the retentive undercuts. Therefore, the

clasp may not seat completely in the mouth or may place unfavourable forces on

the abutment tooth. 'Freeing up' the clasp after processing is difficult and time

consuming. To counter this, stalite spacer is placed around the clasp during

processing. This spacer can be easily removed during finishing and polishing

procedures.

Equipoise Clasp(E-clasp)

The E-clasp is a lingual back-action clasp that is fully reciprocated, vertically and horizontally.

E-clasp Tooth Preparation

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Rest Preparation

The occlusal rest is prepared with a cylindrical diamond stone.

On bicuspids, the rests should be spoon-shaped and encompass 1/3 the mesiodistal width of the tooth and at least 2/3 of the buccolingual width.

Rests on incisors are prepared over the cingulum or on the incisal edge of the tooth. The cingulum rest should be at least 1 millimeter deep and one-half the width of the tooth mesiodistally away from the edentulous area. The incisal rest should be at least 1.5 mm deep and 1.5 mm wide.

Interproximal Preparation

An interproximal access of at least 1 mm is necessary to give the minor connector enough strength to support a well contoured rest. This preparation is made by removing 1/2 mm of enamel from the abutment and 1/2 mm enamel from the adjacent tooth. A 1 mm tapered diamond stone is recommended. Rubber wheel or polish cut surfaces.

Equipoise C&E Milled Design

The C&E Milled Design features the application of a milled abutment crown ( 1/2 degree milled undercut) with a precision c-rest ( for stabilization and reciprocation) and conventional E-clasp ( for retension). This semi-precision design shows no metal while maintaining proper contact with the adjacent tooth.

The C&L Precision Attachment

The C&L Attachment was designed specifically to fulfill Equipoise Class II Lever design principles. The Counterpoise(C-rest) is a precision made, pre-fabricated attachment available in three shapes with corresponding males. The male is made with a functional clearance of .15 inches tolerance. The L-Spring is a removable L- shaped band with ball-point retention that allows for simplified chairside replacement.

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Impression Procedure

A quality, single phase impression material is recommended. The impression tray and material should extend into the retromolar and tuberosity areas on distal extensions.

12- Esthetic clasp for maxillary canine:

An esthetic modified circumferential clasp, which resembles a small Class

III gold inlay, is described. An ear-lobe-shaped pattern is made of casting wax

below the height of contour of the tooth and extends the connecting compound into

the embrasure. The lost wax casting process is used to cast the clasp in type-III

noble alloy; this is then soldered to the chrome-cobalt partial denture framework.

Disadvantage

Soldering becomes an additional step in the laboratory procedure,

success of the partial denture is dependant on the soldering procedure.

B - Masking the direct retainer

1- Acrylic or composite coating

A number of techniques that facilitate metal-resin bonding have been reportedly

used to mask the direct retainer with either acrylic or composite. The use of

composite resin to disguise metal clasps is in harmony with current esthetic trends.

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However, the technique has not been refined primarily because the composite

resins are designed for restorative purposes. Therefore, they are strong but rigid.

The difficulty of using acrylic/composite resin to veneer RPD metals lies

in the difference between their abilities to flex and their coefficient of thermal ex-

pansion. Non noble metals possess strength and resist flexure. However, acrylic

and composites are subject to greater deformation from physical and thermal

conditions. The composite is brittle past its elastic limit. As a result the abilities of

metals and composites to plastically deform are incompatible. Therefore, the less

flexible the clasp, the more likelihood there is that the bond will endure.

The various methods used to mask the metallic direct retainer are as

follows:

Macromechanical retention:

Retentive beads and meshwork have been used to retain facing of either acrylic or

composite resin.

Disadvantages

Bulk that is created by adding the veneer will enlarge the total size of the clasp

thus defeating the purpose of disguising the clasp,

bonding is unreliable.

GAP formation and micro leakage when used in combination with composites

Micromechanical retention:

It involves air borne particle abrasion. This helps to improve retention between the

alloy and the resin.

Disadvantages

Bond strengths obtained after the use of micro mechanical systems are insufficient

especially after thermal conditioning.

2- Silica coating:

This technique is based on adhesion of resin to silane bonding agents.

These silanes, however, failed to bond directly to metals. The reason for such a

failure is the lack of preferred substrate and groups required for a good chemical

bond of silane to metal. Such end groups maybe Si-OH and AI-OH, which are not

readily supplied by the alloys used.

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This new technique involves coating the metal with silica intermediate

layer (SiOx-C) that bonds to metal and also supplies the -OH group for silane

bonding. The tribochemical effect of air borne particle coated with silicic acid on

the alloy surface renders it amiable to silane bonding agents. This coating allows

the development of superior bond strengths to electro etching or chemical etching.

Hence, even in the presence of the flexing retentive clasps the bond strengths are

significant to prevent debonding.

Disadvantages

Lack of long-term controlled studies limits the use of this technique.

C- METAL-FREE CLASPS

1- Dental D clasps

They are the perfect solution to unsightly metal clasps either on chrome or acrylic

dentures and can be prescribed for new or existing dentures. Dental D comes in a

choice of shades to match the patients own teeth or pink shades to match the patients

gum. The Dental D clasps are very tough, flexible and does not distort.

2- Opti= flex invisible clasp partials

With the Opti= Flex acetyl resin clasps, metal-free, lightweight partial dentures that

provide natural esthetics and a comfortable fit can be designed. Using the Opti= Flex

Coating applied to metal clasps, it is possible to give new or existing metal partial

dentures a new esthetic appeal. It is available in 16 tooth-colored shades (matched to

the base Vita Shades) and hence Opti- Plex can meet every patient's esthetic

requirements.

3- Flexite plus cast thermoplastic

Flexite Plus 'Flexible' partial dentures eliminate the use of metal, providing

patients with a metal partial denture alternative. Flexite Plus is fabricated from a

flexible thermoplastic material that is available in three tissue shades. The material is

monomer-free, virtually unbreakable, lightweight, and impervious to oral fluids.

Flexite Plus may also be combined with a metal framework to eliminate the display of

metal labial clasps.

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4- NaturalFlex: Based on acetyl resin technology.

Available in 20 shades with three pink hues. The tooth or tissue coloured resin clasps

though as slim as those made of metal provide superior strength. They are flexible and

light weight. They are also up to 20 times harder than restorations fabricated from

standard acrylic materials.

5- Proflex clear wire clasps:

Clear wire is an excellent new way to fabricate clear, strong, flexible clasps in

minutes. This new material and technique can be used to make T-bars, l-bars, Roaches,

Acers, and most other types of clasps. It can also be used to add or repair clasps in an

existing partial denture. It should be noted that the technician must have a good

working knowledge of partial design before trying to incorpo rate a Pro flex Clear

Wire technique into their work.

6- Smile-Rite partials:

Smile Rite is a high strength acetyl resin-polymer used for making tooth coloured

clasps on cobalt-chrome alloy partial frameworks.

The combination of Smile Rite with a metal frame gives patients the proven long-term

reliability of a cobalt-chrome alloy framework with the durability and esthetics of

Smile-Rite tooth coloured clasps. Existing metal frameworks can be retrofitted with

SmileRite clasps for esthetically conscious patients. Smile Rite is colour stable and is

resistant to staining and plaque buildup.

The high strength of Smile Rite makes it possible to fabricate the entire framework

metal free. The framework can be made from either tissue colour or tooth colour

monomer-free Smile-Rite acrylic.

7- DUET CLASPS

Estheti-fl ex 'Duet': Developed with the esthetically driven patient in mind, the Estheti-

Flex 'Duet' combines the support of a Vitallium or Titanium cast framework with the

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comfort of Estheti-Flex tooth coloured clasp system for the ultimate in function and

esthetics. The Estheti-Flex 'Duet' appliance is recommended for patients requiring cast

rests for support combined with Vita shaded or clear resin clasps for improved

appearance in the esthetic zone)

8- Themoflex thermoplastic clasps

Thermoflex is an improved acetal resin system that brings the many benefits of

metal-free restorations without the pitfalls associated with acrylic)15]

Thermoflex is so flexible that it can flex around the largest tooth, and then use its

superior elastic memory to cling deeper into the undercut for a rigid functional hold.

It is a Hypoallergenic, monomer-free material ideal for patients with allergies or

patients that cannot tolerate a metal partial framework. It is hydrophobic; hence does

not absorb water or saliva.

Thermoflex has unsurpassed durability and it bonds well with conventional acrylics, as

well as, to itself, which means it can be repaired, relined or rebased. It is available in

19 shades, 16 tooth coloured and 3- tissue coloured. The Thermoflex partials are

injection molded using heat and pressure which makes the final product dense

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Flexible tooth colored clasps

Combination of cast metal and flexible tooth colored clasps.Acetal Tooth-colored Clasp

Check Mate Denture

Pain-less denture system by Dr.Sakurai. Certain adjustment with a pilot denture.We can real ize denture to be able to fit closely with high technique of plas tic molding.

FIN Denture

Fin DENTURE st ick to the jaw when anterior l ingual occlusal pressure.Because FIN DENTURE is at tached with Fin Valve

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and i t is c linging to the jaw. This cl inging function make patient bi te whole apple.

Clasp under cut

Aker's clasp 0.01 inch

Ring Clasp 0.02 - 0.03 inch

Back Action Clasp 0.01 0.02 inch

Reverse back action 0.01 0.02 inch

Bios clasp system

In the Bios clasp system the retentive force of the clasp is related to the depth of

undercut and the length of the clasp arm .

The retentive force of a clasp arm is dependent on the following factors:

- The length from its tip to its point of attachment

- The shape of its cross-section

- The metal alloy used

- The depth of the undercut

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The basis for all clasps is a standard wax shape. It has a uniform taper and its

cross-section forms half of an elipse with a width-to-height ratio of 10:8.

The length of the clasp is measured with a device built similar to those used for

measuring the mileage on maps. In order to form a clasp arm with the desired

retentiveness after the depth of the undercut and the length ofthe clasp have been

determined, it is only necessary to read from the table how many millimeters to

cut from the tip of the standard wax shape.

Bios Clasp System

In the Bios system the retentive force ofthe clasp is related to the depth of

undercut and the length ofthe clasp arm. All clasps should exert almost the same

retentive force.

This standard shape has made it possible to draw up a table in which the

retentive force, the depth of undercut, the clasp length, and the dimensions of the

clasp crosssection are specified.

The retentive force of a clasp arm is dependent on the following factors:

- The length from its tip to its point of attachment

- The shape of its cross-section

- The metal alloy used

- The depth of the undercut

The basis for all clasps is a standard wax shape. It has a uniform taper and

its cross-section forms half of an elipse with a width-to-height ratio of 10:8.

The length of the clasp is measured with a device built similar to those used for

measuring the mileage on maps. In order to form a clasp arm with the desired

retentive¬ness after the depth of the undercut and the length ofthe clasp have

been determined, it is only necessary to read from the table how many

millimeters to cut from the tip of the standard wax shape.

Direct retainers

Mostafa Fayad 55

The Bios standard clasp arm shape serves as a basic element for all types of clasps.

The flexibility 01 a clasp arm is determined by how much length is removed from

the small end of the pattern.

The exact depth of undercut for the previously drawn

clasp tip is determined with a special measuring device.

The undercut depth can be read directly within a range of

0-1 mm.

Stress and its control by clasp design

Retention should not be considered the prime objective of design:

(1) The main objectives should be the restoration of function and appearance

and the maintenance of comfort, with great emphasis on preservation of the

health and integrity of all the oral structures that remain.

(2) The retentive clasp arm is the element of the RP.D that is responsible for

transmitting the most of the destructive forces to the abutment teeth. A

removable partial denture should always be designed to keep clasp retention

to a minimum yet provide adequate retention to prevent dislodgment of the

denture by unseating forces.

(3) Close adaptation and proper contour of an adequately extended denture base

and accurate fit of the framework against multiple, properly prepared guide

planes should be used to help the retentive clasp arms retain the prosthesis.

By exploiting retentive potential in various widely separated areas of the

mouth, both support and stability may be enhanced at the same time that

stress is effectively reduced.

Biomechanical Considerations in Clasp Design

1. The simplicity of the clasp: The simplest type of the clasp that will

accomplished the design objectives should be employed

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2. Clasps should be designed to minimize interference with normal

stimulation of gingival tissues and demote plaque formation• to preserve

periodontal health.

3. There should be at least 5 mm. clearance between vertical components,

e.g. minor connectors, proximal plates, etc.,

Note: The reason for the different distances of major connectors from

gingival margins is that maxillary casts are beaded to insure positive

adaptation of the major connector whereas mandibular casts are relieved to

prevent contact of the major connector against the delicate mucosa.

4. There should be at least 3mm. Clearance between the approach arm of

bar clasps and the gingival margin.

5. Maxillary major connectors comprising part of a clasp assembly should be

located at least 6mm from the gingival margins.

6. Mandibular lingual bars comprising part of a clasp assembly should be

located at least 3mm from the gingival margin.

7. Qualities of clasp:

a- Clasp should have good stabilizing qualities, remain passive until

activated by functional stress, and accommodate a minor amount

of movement of the base without transmitting a torque to the

abutment tooth. The more flexible the retentive arm of the clasp,

the less stress is transmitted to the abutment tooth.

b- As the flexibility of the clasp increases, both vertical and lateral

stresses transmitted to the residual ridge increase.

8. Materials and type of alloy used in clasp construction:

a. A clasp constructed of chrome alloy will normally exert greater stress on

the abutment tooth than gold clasp, all other factors being equally. To

compensate for this property, clasp arms of chrome alloys are constructed

with a smaller diameter than a gold clasp would be to accomplish the

same purpose.

b. Wrought wire is more resilient than the same alloy of identical diameter

and length in cast form, because of its internal structure.

9.Strategic clasp positioning (Location of clasps) as a method of stress control:

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o Clasps should be strategically positioned in the arch to achieve the

greatest possible control of stress and leverages.

o Clasps could be placed at each end of the denture, so that the resultant of

their forces is near the center of gravity of the denture. Biologically, this

clasping distribution is not well accepted, as more teeth are prone to

coverage. Instead, two clasps diagonally placed can be used.

o If two clasps are insufficient and the denture tends to rock about the line

joining the two clasps, a third clasp placed as far as possible from the

others is added.

o Molars are the most suitable teeth for clasping due to their contour,

strength and size, followed by premolars, canines then upper central

incisors.

o Incisors specially lower incisors and upper laterals are not preferred due

to esthetic and mechanical reasons. Tooth supported dentures may

require more clasps to distribute the load on more teeth.

Quadrilateral configuration:

It is indicated most often for class III arches particularly when there is a

modification space on the opposite side of the arch (Fig. 11-9). When four

abutment teeth are available for clasping, and the partial denture can be

confined within these four clasps, all leverage is neutralized.

Tripod configuration:

It is used primarily for class II arches if there is a modification space on

the dentulous site. When the distal abutment on one side of the arch is

missing, the inevitable lever is created by the distal extension base. In this

case, the leverage may be controlled, to some degree, by creating a triangular

pattern of clasp placement.

Bilateral configuration (Kennedy class I):

When two distal extension bases must be dealt with, the designer has

little choice but to clasp the two distal abutments.

In this circumstance, the clasps exert little neutralizing effect on the

leverage-induced stresses generated by the base, and they must be

controlled by some other means.

Unilateral prosthesis

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Leverage per se is not a problem with the unilateral type of edentulous

span . However, torsional stress on the abutments is generated by the prosthesis

because of its tendency to rotate in a buccolingual plane. The conventional

solution is to cross the arch with a major connector and to clasp teeth on the

contralateral side, thus making the prosthesis, in effect, bilateral in design.

Ordinarily this is the preferred approach to the problem. If the unilateral design

must be used, all four clasp arms should be made retentive in order to minimize

the tendency of the prosthesis to rotate around a line that extends mesiodistally

through the two abutment teeth.

11- Selection of Clasp form:

The form of any clasp is determined according to the following factors:

1-Position of the tooth.

Clasps on anterior teeth should be gingivally approaching.

Occlusally approaching clasps on premolars should start distally to

keep the body of the retentive arm on the distal half of the buccal

surface to be less visible.

2-Condition of the tooth.

Wrought wire and gingivally approaching clasps are preferred

for teeth with questionable periodontal support.

3-Position of the edentulous area.

In bounded areas, occlusally approaching clasps provide good

retention, bracing and stabilization. In free-end areas, Flexible rather

than rigid clasping is preferred to provide retention and allow slight

movement of the denture base without stressing the abutments. The

RPI, I-bar, RPA, RLS, combination clasps, back action, reverse back

action or reverse circlet clasps can be used.

4-Axial inclination of the abutment.

Ring clasp is preferred on tilted molars to prevent further tilting.

5-Position of occlusal rest.

Rests are placed near to bounded edentulous areas, and far from

free-end areas.

6-Position of retentive undercut.

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Retentive undercuts are selected far from bounded edentulous

areas, and near to free-end areas.

If the abutment tooth exhibits an undercut on the disto-buccal side, then

a reverse circlet clasp can be used.

If the undercut is on the mesio buccal side, a combination wrought wire

clasp, RPI clasp or back action can be used.

If the undercut is on the distolingual side, RLS clasp can be used.

If precision attachments or rigid clasping are used to retain a class I

partial denture, a stress breaker should be used.

12- Leverage and Esthetics is clasp design:

A fundamental aspect of clasp design is that the arms should be

placed as low on the crown, within limits, as the survey line will permit, in

order to reduce the effect of leverage.

13- Number of the clasps:

The retention is not proportional to the number of clasps.

Satisfactory amount of retention, is that required to keep or just to retain

the denture in its place during function and rest.

INDIRECT RETAINERS

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INDIRECT RETAINERS

Rational for indirect retention

Tooth-tissue supported partial dentures are subjected to vertical displacing forces

acting in an occlusal direction. These forces may totally displace the denture if

the direct retainers are not functioning adequately. However if the direct

retainers are adequate, rotation of the denture around a fulcrum axis rather

than total displacement occurs. This rotation is counteracted by the unit of the

partial denture called "Indirect retainer".

In tooth supported partial dentures; tissue away movement of the prosthesis is

prevented by the action of direct retainers and rests placed on the abutment

teeth (self indirect retainer).

In mucosa supported partial dentures;(full palatal coverage) tissue away

movement of the prosthesis is prevented by mechanical means (clasps) and by

the action of physical means of retention on a well fitting denture base and the

connector (direct indirect retention).

Definitions:

Indirect Retention: The resistance to rotational movement of a tooth-tissue

supported denture base and palatal major connector away from the denture

foundation area when occlusal forces (sticky foods) are applied to the denture

base.

Indirect Retainers are “components of removable partial denture that are used to

reduces the tendency of the denture to rotate in an occlusal direction about the

fulcrum axis”.

The fulcrum line (prothero 1916) is an imaginary line, connecting occlusal rests,

around which a partial removable dental prosthesis tends to rotate under

masticatory forces. The determinants for the fulcrum line are usually the cross

arch occlusal rests located adjacent to the tissue borne components.

It is a theoretical line passing through the point around which a lever functions

and at right angles to its path of movement

INDIRECT RETAINERS

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Direct retainers are retaining elements (clasps) used to retain near ends of partial

dentures. However, Indirect retainers are supportive elements (rests) used to

retain far ends of partial dentures

This movement of the saddle may be caused by the action of sticky food or by

gravity in the upper jaw. Indirect retainers do not prevent displacement towards

the ridge. This movement is resisted by the occlusal rest on the abutment tooth and

by full extension of the saddle to gain maximum support from the residual ridge.

The concept of indirect retainer is advanced by Dr W.E.Cummer as means of

resisting rotational movement

Movement of a distal extension base RPD in function can be summarized as rotation around:

The 1st fulcrum The 2nd fulcrum The 3rd fulcrumHorizontal plane Sagittal plane Vertical plane

extends through the two principal abutments

(Fulcrum line)

extends through the occlusal rest on the terminal abutment and along the crest of the residual ridge on one side of the arch.

located in the vicinity of the midline just lingual to the anterior teeth.

controls the rotational movement of the denture in the sagittal plane- denture movement toward or away from the supporting ridge).

controls the rotational movements of the denture in the vertical plane– rocking, or side to side,

movements over the crest of the ridge).

controls the rotational movement of the denture in the horizontal plane,- flat circular movements of the denture.

The degree and direction of the denture base movement are greatly influenced by the quality of the supporting residual ridge, the design of the RPD and the extent of the forces exerted on the denture during function

INDIRECT RETAINERS

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Indications for Indirect Retainers

Indirect retainers are used in removable partial dentures having one or more

free extension bases as in Kennedy class I, class II and long span class IV.

Indirect retainers may also be used in Kennedy class III where a long

edentulous span is bounded with one distal abutment having guarded prognosis.

The loss of this abutment would create a distal-extension base.

Functions of indirect retainers:

The main function is to resist occlusally displacing forces acting on the free end

saddle by creating a resistance on the opposite side of the fulcrum axis.

Auxiliary Function of Indirect Retainer:

1- Reduce anteroposterior tilting on abutment tooth, especially on an

isolated tooth.

2- Aids in stabilization against horizontal movement of the denture.

3- Splints anterior teeth against lingual movement.

4- Acts as an auxiliary rest against vertical forces.

5- Serves as a third point of reference when orienting the framework

during reline procedures.

6- It may provide the first visual indications for the need to reline an

extension base partial denture. Deficiencies in basal seat support are

manifested by the dislodgement of indirect retainers from their prepared rest

seats when the denture base is depressed and rotation occurs around the

fulcrum.

The indirect retainer works as mechanical disadvantage. by incorporating indirect

retainer in free end situation , the resistance to effort arm is increased.

Mechanical disadvantage = resistance arm / effort arm

= distance between clasp and IR / distance between point of effort and IR

INDIRECT RETAINERS

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Factors Influencing the Effectiveness of Indirect Retainers

Factors that influence the proper function of indirect retainers are:

1- Effectiveness of the direct retainers:

For the indirect retainers to be effective, the direct retainers must prevent

the rests and dentures from being lifted, as this lift causes displacement rather

than rotation of the denture base..

2- Proper location of indirect Retainers:

1- Well-supported indirect retainers should be placed as far from the fulcrum

line as possible. The greater the distance, the more effective is the indirect

retention.

2- A perpendicular line projecting anteriorly from the fulcrum axis is the most

effective location of indirect retainers and affords the best resistance against

vertical dislodging forces.

Although the most effective location of an indirect retainer is commonly in the

vicinity of an incisor tooth, that tooth may not be strong enough to support an indirect

retainer and may have steep inclines that cannot be favorably altered to support a rest. In

such a situation, the nearest canine tooth or the mesio-occlusal surface of the first

premolar may be the best location for the indirect retention, despite the fact that it is not

as far removed from the fulcrum line. Whenever possible, two indirect retainers closer to

the fulcrum line are then used to compensate for the compromise in distance.

3- Rigidity of the denture frame:

The minor connector joining the indirect retainer to the framework

should be rigid. Flexing of the connector multiplies rather than dissipates the

applied forces.

INDIRECT RETAINERS

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4- Effectiveness of the supporting surface:

1. Indirect retainer in the form of rest should be placed in a definite, properly

prepared rest seat that allows transmission of the forces along the long axis of

the tooth without slippage of the rest or movement of the tooth.

2. Indirect retainers should never be placed on weak teeth or on inclined

surfaces.

5- The length, fitness and the extent of the distal extension base:

1. Well fitted and adapted base provide more effective indirect retention.

2. The shorter the base the more effective is the indirect retention.

Forms of indirect retainers:

Indirect retainers may have one of several forms; each is effective in

proportion to the degree of support and the distance from the fulcrum axis. These

forms are

A-Indirect Retainers Used In Mandibular Partial Dentures:

1- Auxiliary occlusal rests: This is the most common form of indirect retainers. It is

placed on an occlusal of the tooth as far away from the fulcrum axis as possible on

mesial marginal ridges of first premolars..

2- Canine extension from occlusal rests: A finger like extension arising from the

principal premolar rest and placed on the prepared cingulum of the adjacent canine

tooth. It indicated in long distal extension cases, as it is used instead of locating of

the indirect retainers on an incisor tooth which may not be strong enough to support

the denture

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3- Canine rests (cingulum rest): The canine rest is used as an indirect retainer in

cases where the mesial marginal ridge of the first premolar is too close to the

fulcrum axis.

4- Principal occlusal rest of modification area:

The occlusal rest on the anterior abutment of modification space provides indirect

retention.

5- Auxiliary rests at the terminal ends of lingual plate or Kennedy bar:

The continuous bar is a metal band passing continuously over the cingulum of

anterior teeth, ending at each side with terminal auxiliary occlusal or canine rests. The bar

itself is not considered as an indirect retainer because it is located on the unprepared

lingual surfaces of anterior teeth. However, the terminal rests on either side are the

components providing indirect retention.

6- Lingual plate or continues bar

The bar itself is not consider indirect retainer as it is placed on un prepared tooth

surface , however the terminal rests on either side are providing indirect retention .

7- Embrasure hooks

B- Indirect Retainers Used in Maxillary Partial Dentures:

Auxiliary occlusal rests, canine extension from an occlusal rest, terminal rests of

the continuous bar and cingulum rests on maxillary canines are used as maxillary

indirect retainers. In addition, there are other forms of indirect retainers that are

supported by the palate, these are:

1) Cummer arm :

It is a maxillary indirect retainer that extends either from the denture base or

from a palatal major connector and rests on a canine tooth. This type exerts excessive

load on the supporting tooth causing movement of the tooth labially. It is also liable to

distortion.

INDIRECT RETAINERS

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2) Palatal arm

It is an extension of the palatal major connector on the opposite sides of the

fulcrum line. The projections may initiate bad tongue habits, interfere with speech,

and are liable to cause irritation of the palatal mucosa underneath the end of the arm..

3) Anterior palatal bar

The anterior palatal bar is a maxillary major connector provides indirect

retention for a posterior denture base as in Kennedy class I and II. However, the

anterior palatal bar is not well tolerated by some patients because it crosses the rugae

area.

4) Posterior palatal bar

The posterior palatal bar is a maxillary major connector that gains support from

the posterior palatal region. It acts as an indirect retainer for long span class VI

denture bases

5) Palatal strap and Rugae support

The anterior palatal strap is a maxillary major connector, which may provide

indirect retention for class I and II bases because it covers a considerable area of the

hard palate. However, tissue support is less effective than positive tooth support .

C) Indirect Retainers Used in Maxillary and mandibular Partial Dentures

1- indirect retention from major connector

In tooth tissue support partial denture in which the indirect retention is achived

by covering the tissue areas anteriorly for support. As rugae support.

Well fitting denture bases of upper class I RPD connected by broad palatal

plate seldom need anterior indirect retainers. Physical retention gained by the bases

and connector, and physiologic retention affected by upward thrust of the tongue

retain the posterior ends of the denture. This is actually direct retention that

compensates absence of clasps at posterior ends .

2- Direct-indirect retaintion

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Some times the reciprocal arm of direct retainer located anerior to the fulcurum

line and act as indirect retainer

3- Modification areas

If occlusal rest on the secondry abutment is far from the fulcurum line it can act as an

indirect retainer

I- Indirect retainers placed on tooth structure:

1-Auxillary occlusal rest

2- Canine extension from occlusal rest:

3- Canine (cingulum) rests:

4- Secondary lingual bar:

5- Cummer arm:

II- Indirect retainer placed on the palate (for maxillary denture only)

1- Palatal arm:

2- Anterior palatal bar:

3- Posterior palatal bar:

4- Rugae support:

5- Palatal strap:

Attachments in RPD

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Attachments And Their Use In Removable Partial Denture

Is a retainer consisting of two or more parts, one part is connected to a root, tooth or implant and other part to the prosthesis.

A precision attachment is an accurately fitting interlocking device for fixing removable

restoration to the natural teeth

• Many names have been given to describe these attachments as male and female, patrix

and matrix, key and keyway, parallel, frictional, internal and slot attachment.

Requirements for success

– A well motivated patient with good oral & physical health

- A good level of knowledge of attachment & team work between the clinician & technician

- Regular adjustment of the attachment & relining of the prosthesis

- The patient must be aware of the cost and time required for this type of treatment

Indication of Precision Attachments

There are several situations in which the use of attachment is indicated

- use of resilient attachment to relieve stress.

¬- To accommodate mal-aligned fixed partial denture abutments.

- Esthetics in case of horizontal or vertical bon loss of abutment teeth

- Support in case of “RPD, free end saddle, splinting , over denture

Contra indication

a - Abutment not suitable for attachment retainer

- short clinical crown - Narrow bucco-lingual crown

-Large pulp horn -Insufficient bone support

b - Improper mucosal condition

-No room for attachment (vertical and horizontal)

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- Inflammation - No bone support ( wiry ridge)

c- Greater coast to the patient.

Advantages of precision attachment:-

1- Better esthetics due to the labial or buccal clasp arms on canines or premolars are not required.

2- Vertical and horizontal lodes are applied more directly to the abutment teeth than by clasps or rests. This advantageous only if the supporting structures of this tooth are perfect.

3- The efficiency of retention is not affected by the contour of the abutment tooth.

4- The number of the component of the denture is reduced and hence tolerance should be better.

5- When used with lower free end saddles, posterior movement of the denture is prevented.

6- Their use may be indicated when retentive clasp arm reciprocation can not be achieved.

7-Positive retention and stability

8- Reduced bulk of the prosthesis

Disadvantages of precision attachment:-

1- Extensive preparation of all abutment teeth, with construction of the necessary crown or onlays.

2- When the crowns of the abutment teeth are small or short, this attachment can not be used.

3- Teeth with large pulps can not be used.

4- It can not be used for free end saddle due to rigidity of the union between the tooth and saddle.

5- Owing chair and laboratory time involved and the high coast of the attachments.

6- No sufficient space for accommodation

7- Expensive cost and need highly qualified technicians

Attachments in RPD

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1- Since the principle of the internal attachment does not permit horizontal movement, all horizontal, tipping, and rotational movements of prosthesis are transmitted directly to the abutment tooth. The internal attachment therefore should not be used in conjunction with tissue support distal extension denture base unless some form of stress breaker is used between the base and the rigid attachment.

2- The Intracoronal attachment engages the vertical walls built into the crown of the abutment teeth to created frictional resistance to removal.

Classification of attachments

1 – according to manner of fabrication :-

A ) semi – precision attachment B – Precision attachment

2 – according to location

A ) Intra coronal attachment B ) Extra coronal

C ) Radicular / intraradicular stud type D )Bar type E) Auxillary

3 - According to behavior during action

A ) class I :- -rigid , non resilient attachment -used with bounded saddle

- -Frictional grip intra coronal attachment

-e.g. : - -Dalbo bar unit , -non resilient dalbo stud attachment ,- non resilient Ceka

B ) class II :- - Allow for vertical resiliency -used with short free end saddle

-e.g.:- schatzman intra coronal attachment, dalbo extra coronal attachment,

CEKA extra coronal attachment , dalbo stud attachment , CEKA stud attachment

C ) classIII :- - allow for hinge movement - used with long span free end saddle

– e.g. :- -dalbo extra coronal attachment , resilient dalbo stud attachment,

resilient CEKA stud attachment

D )class IV :- - allow for hinge & vertical movement - used with long span free end saddle

-eg :- -as class III

E) class V :- -vertical & hinge movement as well as buccolingual rotation

-used with long span free end saddle

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4- According to retention manner

A) Frictional :-

. Is resistance to relative motion oe two or more surface s in intimate contact with each other

. E.g. :- The Beyeler attachment

. Caution :- if attachment is over polished , frictinal retention may be lost

B) Mechanical :-

. Is resistance to the relative motion of two or more surfaces due to a physical under cut

. E.g. :- The Hannes Anchor attachment

.Caution :- if the plunger of the a achment doesn̕t engage the female undercut there will be no Mechanical retention

C) Frictional & Mechanical

. Combines both features of frictional& mechanical retention

E.g. :- The Score-PD attachment

d)Magnetic :-

. is the resistance to movement caused by a magnetic body that attracts certain materials by virtue of a surrounding field of force produced by the motion of its atomic electrons and alignments of its atoms

Caution :- it does not provide lateral stability and contra indicated for flat ridges

e) Suction : -

Is a force created by a vacuum that causes a solid object to adhere to a surface .

E.g. :- a well fitting denture

Caution :- Most removable restoration require a periodic check of tissue condition and if deficiency occur reline it

Attachments in RPD

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1 – according to manner of fabrication :-

A) semi – precision attachment

- It is fabricated in the lab by the direct casting of wax pattern, plastic, or refractory pattern

- they are considered " semi – precision" since in their fabrication they are subject to inconsistent water/powder ratio , burn out temperature , and other variables so resultant component varies to a small degree

Advantages: -

1 – Economy ( low cost)

2 – Easy fabrication

3 – Ability to be cast in a wide choice of alloys without the problem of co efficiency differences between the cast and machined alloy

Disadvantages: -

1 – liable for dimensional changes during casting (less accuracy)

2 – difficult to repair

Blatterfein classified the laboratory-fabricated attachments according to their occlusal outline form into:

(a) Locking types Semiprecision attachments. These includes:

i- Dovetail rest system.

ii- Circular rest system.

(b) Non-locking types Semiprecision attachment: In the form of rectangular rest system.

Attachments in RPD

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B) Precision attachment

- They are ready made & their component are maintained in special meta alloys under precise tolerance & these tolerances are within 0,01mm

- One component is soldered to metal crown & other to frame work

- They are very accurate and easily repair

According to retention mechanism between the two components of the attachments, two types are available:

(a) The active friction grip attachments: These include an adjustable spring. This is usually accomplished by designing a split patrix so that part of it forms a leaf spring, which can be opened to compensate wear to give retention

(b) The active snap grip attachments: In this group, the active element consists of a spring -loaded plunger, a split ring or U-spring, which engages in a prepared pit or groove.

Advantages: -

1 –give a splinting effect & less wear on abutment

2 – The load fall down with the long axis of the abutment

3 – Standard parts which allow the component to be interchangeable

4 – Not affected with the contour of the abutment

5 – More tolerated by the patient

6 – Eliminate the food stagnation

Disadvantages: -

1 – Extensive preparation to abutment

2 – Need long chair side time

3 – Wear & lose retention by time

4 – Very expensive

Attachments in RPD

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2 – According to location :

A ) Intra coronal attachment

Usually called as an internal attachment or a precision a achment. It is developed by Dr Herman E.S.Chayes in 1906.

An intracoronal attachment is one which is contained within the normal contours of the crown portion of a natural tooth. The placement of the attachment requires that the abutment tooth be restored with a full or partial coverage (3/4) crown.

Made of

I- Matrix ( metal receptacle) : -

*usually contained within the normal or expanded contour of the crown of abutment

*it may also be attached to the fitting surface of denture framwork

II- Patrix ( closely fitting part ) :-

*usually attached to pontic or denture framwork

*it is always solid (not hollow)

- Their function is to provide positive direct retention for a partial denture. They may prove more retention than the clasp, but the clinical situation in which they are used required careful assessment and the standard of the patient oral hygiene must be good. OSBORNE

- It is supply in two forms : readymade attachment (Precision attachment) or Fabricated by the dental technician (semi – precision attachment )

Design:- - Support is achieved by floor of matrix

- Bracing is achieved by walls of matrix

- Retention is achieved by friction

- An intracoronal attachment usually requires a box preparation to allow the attachment to fit within the crown contour. if it is not possible to create a box preparation that will totally incorporate the female element , then extra coronal attachment should be considered

Attachments in RPD

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Advantages:-

1 – stress fall near the long axis of the tooth

2 – excellent support & bracing

Disadvantages:-

1- Not used with young patient

2 – Not used with short crown

Types

A) Universal Intra Coronal Attachment

- The IC attachment is a popular spring loaded retaining attachment that provides free movement for abutment protection without requiring an abutment crown.

- The IC a achment requires a 180 degree reciprocal lingual arm. The attachment consists of a male anchor and female inlay.

- It is made of a stainless, chrome-alloy like those used for casting partials. It will not tarnish or corrode, and when properly installed, will not malfunction even after years of wear.

- Other benefits include no pulpal involvement, no gingival retraction before impressions, easy to adjust at the chair, and this is a reversible procedure.

B ) McCollum attachment

- retention by frictional grip

-rigid used with bounded saddle

C) Crisman's attachment

Retention by friction & mechanical through :-

1 – Active friction grip ( friction)

2 – Active snap grip { mechanical - more retention}

Attachments in RPD

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- rigid, used with bounded saddle

D ) schatzman's attachment

- retention by active snap grip ( frictional & mechanical )

- resilient so used with free end saddle

- the patrix is attached to a spring to increase resiliency

B ) Extra coronal

- Extracoronal Precision attachments are normally resilient to allow free movement of the prosthesis to distribute potentially destructive forces or loads away from the abutments to supportive bone and tissue. Three distinctive movements are defined in function: (1) Hinge,

(2) Ver cal, and

(3) rota onal

- The fewer abutments remaining, and the weaker the abutments are, the greater the need for resiliency or free movement to direct the forces away from the abutments to the supportive bone and tissue via the base of the prosthesis.

Indication

- Retaining abutments are small to avoid over-contoured intracoronal attachment abutments and/or pulpal exposure

- used for patients with limited manual dexterity, or the prosthesis has a difficult path of insertion and removal.

Design:-

- The matrix or patrix is attached to outside contour of abutment

Advantages:-

1 – The normal tooth contour can be maintained

2 – Minimal tooth reduction & the possibility of devitalizing the tooth is reduced

3 – The path of insertion is easier for patient with dexterity problems

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4- Intracoronal females in retaining abutments will collect food and present problems when the patient attempts to seat the intracoronal retained prosthesis.

Disadvantages:-

- It is ,however , more difficult to maintain hygiene with extra coronal attachment and patients should be instructed on the use of dental floss and hygiene accessories.

Types

A ) Dalbo attachment ( ball & socket ) :-

- the patrix is attached to the abutment

- the ball "patrix" give a hinge movement & the spring in the matrix give a vertical resiliency

-so it can be used with a free end saddle

B ) Ceka attachment

- The Traditional Ceka and Ceka Revax systems provide for hinge, vertical, and rotational movements to provide maximum abutment protection.

- Each attachment consists of three angulations of plastic female profiles with precision metal insert, male spring pin, and retention component. The three angulations allow the user to design the case for the patient’s needs.

- The matrix is attached to the abutment , -the patrix has a split in it's center to enhance friction , - a spacer ring can be placed between matrix & patrix to increase vertical resilience

Adhesive prosthetic techniques are innovative methods for employing extracoronal attachments. They enable cobalt chrome appliances to be retained without clasps therefore achieving optimum aesthetics .

The adhesive units are retained on the abutment teeth by micropreparations in the enamel

The metal surface is coated with silicate and silane to bond the resin adhesive to the adhesive anchor. The enamel should be conditioned using conventional techniques.

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C ) Radicular / intraradicular stud type

- Stud precision attachments are primarily used on roots and implants for retaining removable partial dentures or over dentures. All stud attachments MUST be parallel to each other to provide ease of insertion and removal and reduce wear potential.

- Do not engage labial soft tissue undercuts with the denture base flange, as this will alter the path of insertion and cause excessive wear and servicing requirements.

- Stud attachments are low in profile to reduce leverage upon the retaining abutments, are easy for patient hygiene maintenance, allow physiologic independent movement of abutments, and are easy to service

advantages :-

- that they promote better oral hygiene .

-the crown root ratio is also enhanced with the low profile of the stud type attachment

indication :-

1 – used with remaining root or v. short crown

2 – used with over denture

Types

A ) Extra radicular type

1 ) Dalbo a achment :-

- the patrix is attached to remaining root

-the matrix got fingers that are protected using a Teflon ring

-Teflon ring provide compressibility during function

- A new over denture attachment system that allows the user to replace both the male (threaded sphere) and female. The females engage the undercuts of the sphere to allow for superior retention and less wear on the height of contour.

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- Components are less than 4mm in ver cal height.

- types :- - resilient type ( fabricated with spacer ) , -non- resilient type(no spacer used)

2 ) Ceka stud attachment :-

The patrix has attached to remining root

- patrix has asplit to increase the friction

- -types :- -resilient type - non resilient type

- The new Ceka Revax (M2):-

is the smallest fully adjustable and serviceable stud attachment system. This adjustable spring pin attachment may be utilized as a traditional stud (with cast copings), or inverted as an intraradicular connector for over dentures or removable partial dentures on roots and implants.

- It may be used for a resilient or tissue born prosthesis, or for a combination abutment and tissue supported prosthesis. The small size allows for usage when space is at a premium--ideal for ‘close bite’ situations. Clinical, laboratory, and servicing are routine procedures that are adaptable to the individual’s needs and/or techniques. Space requirements for the Revax (M2) are 3.8mm in height, and 3.4mm in diameter.

- Tradi onal Ceka Axial (M3)

The tradi onal Ceka Axial has been in use for over 30 years. As a result, it is one of the most widely used attachments in the world. It is much like the Ceka Revax Axial, but for one major difference--the Ceka requires 0.45 mm more ver cal clearance. When space is available, select the tradi onal M3 Ceka as it is stronger and easier to service.

B ) intra radicular type

1 ) Zest anchor

Zest concepts: lowering the fulcrum (force application), the intradicular female (inside root), and the easy replacement of the male.

- Advancements allow the male to freely rotate and

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move within the housing or denture cap

- the wide band on the male allows for increased retention and reduced wear (less bending and breakage), the female has a titanium coating for hardness and a smoother internal surface

The males may be placed "chairside." The female may be used with a cast coping or directly placed into a root. -There are two sizes--regular (4.0 mm height, 3.8 mm width) and mini (2.3 mm height, 3.3 mm width)

D )Bar type

indication:-

1 - overdentures, to connect between 2 roots

2 - removable par al dentures to connect between 2 teeth

3 - implant prosthesis

4 – in case in presence of few teeth or long edentulous area

- Bars may be rigid or resilient, permitting free movement of the prosthesis to direct forces away from the retaining abutments to the supportive bone and tissue.

The shape of the bar is indicated by

the amount of room available.

the shape of the alveolar ridge.

the type of construction.

the round plasti-wax bar, more easily bent to follow the alveolar crest. Do not engage labial soft tissue undercuts with the denture base flange, as this will alter the path of insertion and cause excessive wear and servicing requirements.

Bar systems are generally in one of three types:

1. Prefabricated ‘Dolder’ type

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Dolbar bar joint Dolbar bar unit

oval in cross section rectangular cross section

resilient Rigid

weak abutment Ceramic) abutment(strong

Regular Mini

2. Plastic ‘Ackermann &Hader’ type

Hader Ackermann

Key hole shape oval in cross section

used in curved arch as can follow the ridge curvature & be used in anterior maxilla the matrix is the bar & the patrix is the sleeve

* Hader attachment:- the most popular of all bar systems due to its economy and simplicity.

*advantage :-

1 - superior stability,

2 –retention

3 - abutment splinting Ackermann Clips

3. Round ‘Clip" bars and riders

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A round bar is useful in situations where the bar must be bent to accommodate the ridge anatomy, or in close-bit situations.

Round Bar

E) Magnet

F) Locator Root

The Self-Aligning feature of the LOCATOR attachment allows a patient to easily seat their overdenture without the need for accurate alignment of the attachment components.

o Long Lasting--good for 110,000 inser on cycles!

o Self-Aligning--patient can bit prosthesis to place!

o Patented Dual Retention

o Unique Pivoting Denture Cap

o Choice of Retention--5, 4, 3, and 1.5 lbs

o Extra-Radicular Design

G ) Auxillary attachment

- they include component such as plunger , hingers & screws these types of attachment must be incorporated into the design of the prosthesis

*types:-

1) plungers

2 ) screw units

-used in Fixed removable partial denture

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-the anterior part of denture is fpd & posterior part is screwed to it

3 ) hinged flanges ( swing lock p .d ) :-

-labial flange is connected from one side by a joint & a lock on other side

- used with R.p.d where labial under cut is found

-so in much R.p.d , labial undercut & teeth interdental area are used to increase retention

- Usually made of co /cr to splint weak abutment

indication & adv of swing lock p .d :-

1 – Splinting of weak abutment 2 –unfavorable tooth contour

3 – Unfavorable so ssue contour 4 – for maxilla facial cases

5 – for arch with expected further extraction

Contraindication:-

1 – shallow labial vestibule 2 – expensive

3 – un co-opertive patient 4 –where esthetic are needed

4) Distal Stress Equalizers (DSE)

- The DSE Hinge is intended for use on bilateral claspretained free end removable partial dentures to reduceloading or torquing of abutments. The small size is easy to work with and eliminates multiple inventory requirements. The unique design provides for easy freeing after casting and provides total lateral stability.

- For patients, it allows patient comfort and abutment protection by allowing independent unilateral function eliminating torquing leverage on the abutments on the nonfunctioning side. The miniaturized size allows utilization in short vertical spaces and provides for good esthetics.

5) Telescopic prosthesis with isoclip attachment or spring loaded plunger.

6) Sectional denture prosthesis with Mechanical locking -PW Bolt or Frictional resistance PW split post.

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Overview attachments used in :-

A ) R.P.D : -

1 ) extracoronal a achment 2 ) intracoronal a achment

3 )bar a achment 4 ) auxillary a achment

B )partial over denture :-

1 ) stud a achment 2 ) bar a achment

c ) implant supported partial denture :-

1 ) extracoronal a achment 2 ) stud a achment

3 ) screw on

Treatment planning

A) Intra oral assessment

intra oral examination should include assessment of the soft & hard tissues.

The teeth should be assessed for :-

a – caries

b – vitality

c – bone support

d– mobility & angulation

e- clinical crown length

f- crown root ratio

A thorough periodontal , occlusal & radiographic examination is also required to complete intra oral assessment

periodontal examination :-

a full periodontal assessment should be carried out this should include full arch pocket charting , an assessment of oral hygiene status & a full radiographic assessment of bone support as fixed or removable prosthesis may influence the pattern of health & disease of periodontium .

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pre - prosthetics treatment :-Hard &soft tissue problems such as : -

A – poor gingival contourb – soft tissue hyperplasia C – in adequate crown lengthd – bonitori & high frenal attachment

After initial pdl therapy has been completed any surgical treatment should be carried out next

prosthetic consideration :-- the possible design features with regard to retainers & fram work

design should always be thought by the dentist & technician with both the surveyed diagnostic casts mounted on an articulator & patient present

- the selection of abutment teeth is influenced by 3 factors :-1 – the number & distribution of the remaining teeth 2 – adequacy of p d l support 3 – analysis of occlusion

Stress breaker

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Stress breaker

It is a device, which allows movement between the denture base and the retainer

to reduce lateral and tipping forces on abutment teeth. It is also called "Stress

director" or "Stress equalizer".

The term articulated prosthesis is applied to a broken-stress partial denture.

Strain on the abutment teeth is minimized through:

1. Broad tissue coverage,

2. The use of functional basing.

3. Use of narrow teeth and harmonious occlusion.

4. Placing the artificial teeth on the anterior two-thirds of the base.

5. Correct choice of direct retainer. Using a flexible clasp causes less

transmission of torque due to the release of stresses which occur when the

clasp tends to deform. This principle is fulfilled by stress breakers.

Indications:

1- When internal attachments are used.

2- In distal extension removable partial dentures to distribute the load between the

abutment teeth and the ridge.

3- In cases exhibiting weak abutment teeth and well formed ridges.

Advantages:

1- Decrease horizontal forces acting on the abutment teeth thus it preserve alveolar

support of these teeth

2- Distribute the stress between the abutment teeth and the residual ridge.

3- Prevent the quick damage of abutment teeth if relining is needed but not done.

4- Providing physiological stimulation of bone which prevent bone resorption.

Disadvantages:

1- Difficult to construct and expensive.

2- Concentration of vertical and horizontal forces on the ridge may increase ridge

resorption.

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3- If relining is not done when needed it will leads to the increase of ridge

resorption.

4- Less tolerated by the patient.

5- Flexible connectors may be bent and distorted.

6- Some split connectors pinch the underlying soft tissue or tongue as they open

and close under function.

7- The effectiveness of indirect retainers is reduced or eliminated.

8- Repair and maintenance of any stress breaker is difficult.

9- All mechanical devices that are free to move in the mouth may collect debris

and become unclean.

Types of stress breakers:

Type I - Those utilising a hinge or moveable joint.

Type 2 - Those utilising flexible connection

1- Type 1 Stress-breakers : Those having a movable joint between the direct

retainers and the denture base.

This joint may be in the form of hinges, sleeves and cylinders or ball and socket

devices. They are necessary when internal attachment is used , but can also be used

with clasp.

The joint allows vertical and hinge movement of the base to prevent direct

transmission of tipping forces to the abutment. Dalbo extra-coronal retainer and

Chrisman intra-coronal retainer are examples of this group.

2- Type 2 Stress-breakers : Those having a flexible connection between the direct

retainer and the denture base. (The articulator partial denture design) These include :

a- Wrought wire connectors:

Double lingual bars of wrought metals, one supporting the

clasps of other components and the other supporting and connecting

the distal extension bases. They may be united at midline by soldering.

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Torsion bars

These may be used in the design of a lower partial denture

carrying bi-lateral free-end saddles. Bars extend anteriorly

from the clasp units on each side to join a lingual bar near

the mid line. Flexibility can be controlled by varying the

cross-section of the torsion bars, the method of construction (cast or wrought) and the

material of construction (normally gold alloys or cobaltchromium alloys).

Disadvantages are associated with the use of the torsion bar structure in that the

double bar system is liable to trap food and cause irritation to the tongue.

b- Split major connectors: (used with long saddle)

This includes split bar major connector and split plate

major connector. The major connector is split into two portions,

upper rigid part which carries the clasp units, and lower slightly

flexible part which attached to the saddle.

Forces applied to the base pass anteriorly along the lower

bar and then along the more rigid upper bar reaching the abutment. Tipping forces are

thus dissipated by the flexibility of the lower bar and through the distance traveled.

- Split casting modifying the lingual plate: a split of appropriate length is made at

the inferior border of the plate. The saddle is joined to the more flexible part of

the plate. The lower part must be flexible in the vertical direction, than

horizontal direction, so that the appliance will have lateral rigidity to distribute

horizontal force widely. This design applied in long class II cases.

Disadvantages: The slit opens slightly in function and theoretically is liable to trap

either the tongue or food particles. With a long saddle, however, the slit is anteriorly

placed and in this position may be intolerable to some patients. The patient using

dental floss can clean the slit easily.

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c- Mesial placement of occlusal rests

This offers the simplest available approach to stress-breaking. The degree of stress-

breaking achieved is, though, much less than that available where more complex

devices are employed. It may be used in the design of either upper or lower dentures.

By positioning the rest of the clasp unit on the mesial instead of on the distal fossa of

the abutment tooth and by using a minor connector to link the rest to a major

connector (for example, a lingual bar) some flexibility may be introduced into the

clasp unit/saddle link

- The use of semi-flexible bar: (used with short saddle)

This is more applicable with short saddles, it involves mesial placement of

an occlusal rest. The occlusal rest is placed on the far zone of the abutment tooth.

The abutment is rigidly clasped, and joined to the clasp onto the opposite dentulous

side by a rigid connector (lingual bar). The saddle is joined to the retainer unite by

a semi-flexible bar that allows some movement and provides stress breaking action.

An embrasure clasp is usually used on the dentulous side.

- A lingual bar connector with a flexible distal extension:

The lingual bar connector used to join two saddle is distally extended on each side

and then recurved along the residual ridge to allow attachment into the matrix resin

of the saddle. The support is design on mesial aspect of the abutment to increase

the length of the bar and better distribute the load.

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d- Clasps having stress breaking action:

1. Gingivally approaching resilient I-bar clasp.

2. Occlusally approaching clasp having resilient retentive wrought gold wire arm (Combination clasp).

3. Back-action clasp.

4. Reverse back-action clasp.

5. Extended-arm clasp.

6. Ring clasp.

7. Wrought wire clasp.

8. RPI clasp.

9. RPA clasp.

ARTIFICIAL TEETH

Selection of artificial teeth for form• colour and material is made easy by the

presence of natural teeth.

FUNCTIONS:

1. Cutting, chewing and grinding of food.

2. Restoration of esthetics.

3. Functional performance as speech.

4. Maintaining both the horizontal and vertical occlusal relations and

maintaining the proper temporo-mandibular joint function.

5. Preserving the remaining oral structures by preventing over-eruption

and drifting of the remaining natural teeth

DESIRABLE CHARACTERISTICS

1. Have the color(shade), translucency, size, shape, and characterization

similar to the natural teeth they replace.

2. Be easily shaped with conventional dental burs.

3. Be easily characterized with conventional dental stains.

4. Have a hardness and abrasion resistance similar to the opposing enamel or

dental material.

5. Chemically bond to the denture base material or RPD alloy to which they

are attached.

6. Be resistant to staining by oral fluids and microorganisms

7. Be chemically inert.

8. Be odorless and tasteless and not pick up odors or tastes from oral fluids.

9. Have a surface which is dense to avoid harboring oral fluids and

microorganisms.

10. Be capable of being cleaned by customary oral hygiene technics and

materials.

11. Be of low initial cost and inexpensively repaired or replaced.

12. Be capable of being repaired and replaced by customary dental technics

and materials.

13. Be strong enough to resist the forces which will be applied.

14. Not soften or warp in hot water or conventional denture cleansing

solutions.

Bonding between the teeth and the denture base

1- Mechanically

2 - Chemically

3 - Chemomecanical

4 - Acid etching microretention

5 - Silnation (tribo-chemical method): combination of chemical bonding and acid

etching

Types of tooth replacements

Artificial teeth may be attached to denture bases in one of the following

manners

1) COMMERCIALLY AVAILABLE DENTURE TEETH:

Acrylic resin or porcelain teeth attached to denture bases by an

intermediate layer of acrylic resin. Mechanical attachment in the denture

base may be accomplished by loops, mesh or nail heads retention.

a- Porcelain teeth are mechanically retained to the denture bases. The

posterior porcelain teeth are attached by acrylic resin in their

diatoric holes, while the anterior teeth are attached by acrylic resin

around retentive pins located on the lingual surfaces of teeth.

b- Acrylic resin teeth are retained by chemical union with the acrylic

resin covering metallic denture bases during laboratory processing

procedures.

c- Reinforced acrylic pontics (RAP): RAP is made of modern cross-

linked copolymers. It is a solid, hard plastic which provides good

esthetics and shade control and provide better attachment to the metal

base compared to cementation.

d- Metal reinforced denture teeth

They are prosthetic teeth constructed from denture teeth. The facial

portion of a denture tooth attached to the framework with a tooth-

colored resin. Retentive loops,beads, or posts are used to mechanically

attach the tooth to the framework. The tooth may also be adhesively

bonded to the framework

e- Acrylic resin teeth with amalgam stops

This type of teeth is used to slow and control the occlusal wear when

the acrylic teeth is opposite by porcelain or natural teeth as in case of

single denture. The amalgam stops can be inserted when the teeth are

balanced on the articulator before delivery to the patient, or they can be

inserted after a period of patient use so the individual wear pattern of a

generated occlusion is apparent.

f- Acrylic resin teeth with gold occlusal surfaces

Gold occlusal surfaces are considered the best material to oppose

natural teeth as in case of single denture.

One or more occlusal surfaces on each side of the denture can be

casted in gold to stop the abrasion of the acrylic teeth and protect the

opposite teeth from abrasion. This type of teeth is impractical for most

patients because it is expensive and takes more time for fabrication.

g- IPN resin

This material consists of an unfilled, highly cross-linked, inter-

penetrating polymer network. The wear resistance of this material is

higher than that

A

b

c

Mechanical means of attachment of teeth to metal base.

INDICATIONS:

1. When a processed plastic base will be used to attach the prosthetic teeth to the

framework.

CONTRAINDICATIONS:

1. Where there is insufficient space occlusal/incisalgingival or mesiodistally for a

denture tooth-plastic base combination.

a) Less than 5 mm between the occlusal plane and the edentulous ridge.

b) Single tooth edentulous space.

2. Where protrusive or lateral occlusal guidance will be on the prosthetic teeth.

3. When available denture teeth do not satisfy esthetic or occlusal requirements. In

these situations a custom made prosthetic tooth is necessary.

ADVANTAGES:

1. Denture teeth are prefabricated by several manufactures.

2. There is a large selection of shades, sizes, and shapes. An acceptable denture

tooth can

usually be found.

3. Available in plastic and porcelain.

4. Can be easily adjusted (particularly plastic) to fit the framework, available

space, existing occlusion, and desired size and shape of the tooth.

5. There is great flexibility of arrangement of denture teeth.

6. The denture tooth arrangement can be tried in the patient's mouth to preview the

esthetics of the completed denture.

7. Replacement of denture teeth on a processed plastic base is fairly easy and rather

inexpensive.

DISADVANTAGES:

1. Plastic and porcelain denture teeth may fracture where as metal prosthetic teeth

will not.

2. Plastic denture teeth are not as abrasion resistant as metal prosthetic teeth.

3. Cannot be used in small spaces, or where occlusal guidance will be on

2) PROCESSED PLASTIC TEETH

Processed plastic teeth are custom made prosthetic teeth processed from tooth

colored heat polymerized acrylic resin. They are attached to the framework by

retentive mesh, loops, beads, or posts. They may be used with or without a

processed plastic base.

INDICATIONS:

1. A posterior edentulous space which is too small occlusal/incisal- cervically or

mesiodistally for a denture tooth.

2. Where available denture teeth do not satisfy the esthetic or size requirements.

CONTRAINDICATIONS:

1. Where a simpler prosthetic tooth-denture base combination may be used.

2. As anterior prosthetic teeth (custom facings are used because of superior

esthetics).

ADVANTAGES:

1. Can be utilized in very small spaces.

DISADVANTAGES:

1. Difficult to obtain esthetic shade match with processed plastic teeth.

2. Processed plastic teeth abrade more than commercial available denture teeth.

3. A wax try-in is not possible.

3) ACRYLIC RESIN OR PORCELAIN FACINGS (STEEL’S

BACKING):

a- Readymade facings

Facings used on RPDs are

manufactured prosthetic teeth consisting of

two parts: a veneer of tooth colored porcelain

or plastic (the FACING) and a BACKING

made of a plastic material.

The backing is incorporated into the

wax-up of the framework. The facing and

backing are related by a slot and groove. The

facing is cemented onto the framework with a

dental adhesive.

Because of their many disadvantages and the advent of custom made

facings using light-cured composite resin materials, the use of commercially

purchased facings is being phased out of RPD prosthodontics.

b- custom made facings

Acrylic resin or porcelain facings are cemented to metal backings.

The metal backing forms the lingual half of the tooth and is an extension

from the partial denture framework. Tooth replacements in the form of

facings are fabricated by the laboratory and cemented by the dentist at the

time of denture insertion.

This causes difficulty in obtaining satisfactory occlusion and lack of

providing adequate contours, adding to the unesthetic display of metal at

gingival margin.

A modification of this method is the attachment of ready-made acrylic

resin teeth to the metal base with acrylic resin of the same shade. This is

called pressing on a resin tooth and is not the same as using acrylic resin

for cementation. It is particularly applicable to anterior replacements, since it

is desirable to know in advance of making the casting that the shade and

contours of the selected tooth will be acceptable. After a labial index of the

position of the teeth is made, the lingual portion of the tooth may be cut

away or a posthole prepared in the tooth for retention on the casting.

Subsequently the tooth is attached to the denture with acrylic resin of the

same shade. Because this is done under pressure, the acrylic resin attachment

DISADVANTAGES:

1. Not as esthetic as denture teeth because the backing shows through the veneer.

2. A wax try-in is difficult.

3. If occlusion is placed on the backing the refractory cast must be mounted on an

articulator so the occlusion can be developed in the wax pattern for the framework.

4. Limited selection of sizes, shapes, and shades.

5. Selection more difficult than for denture teeth because there is no mold guide.

Selection is made from mold chart with sizes indicated.

6. More difficult to obtain than denture teeth.

7. Subject to fracture (particularly porcelain).

Steel’s Backing

4) Tube teeth

Acrylic resin or porcelain tube teeth are prepared by drilling a channel

from the base of the tooth upward to form a tube. A metal post casted with

the partial denture framework is specially designed for the attachment of the

tube teeth. The tube teeth is fixed to the post by cement.

Tube teeth are usually used as single tooth replacements, where a

maximum of three teeth are used.

INDICATIONS:

1. Single tooth edentulous spaces which preclude the use of a processed plastic

base.

2. Short (occlusal/incisal cervical) edentulous spaces in conjunction with a metal

base. The tube tooth will be cemented to the post, not attached by a processed

plastic base.

Anterior tube teeth are usually butted to the edentulous ridge; posterior tube teeth

usually have metal facial and lingual finish lines

CONTRAINDICATIONS:

1. Where a denture tooth processed plastic base may be used.

2. Where the occlusion must be on metal.

3. Where the space is too narrow or too short for a denture tooth. A metal pontic,

custom made facing, or processed plastic tooth is used in these situations.

DISADVANTAGES:

1. Subject to fracture.

2. No wax try-in possible to preview the esthetics of the completed denture.

3. No chemical bond between the tube tooth and the framework. The 4-Meta luting

cements show promise when bonding denture teeth to the metal framework.

A tube tooth. A metal post casted with the partial denture framework specially designed for

the attachment of the tube teeth.

5) Braided post

It is similar to tube teeth , both forms depend on a centrally located reinforcement strut , however

the method used for strut configuration re significantly different .

A braided post is created by twished two small diameter wax ropes around one another in a helical

fashion the frame work then casted . the acrylic resin tooth is attacted to the frame work using heat or self

cure acrylic resin

6) Metal teeth

Metal teeth are usually used as replacements of posterior teeth where

space is limited for the attachment of an artificial tooth. Second molars

may be replaced as part of partial denture casting as a space filler to

prevent migration of an opposing second molar. The metal teeth are

esthetically unsatisfactory, difficult to attain any occlusal adjustment and

are abrasion resistant; hence occlusal contact should be held to a

minimum to avoid damage to the periodontium of the opposing teeth.

Metal teeth• self cleansing pontic.

Metal teeth with acrylic window

In cases of reduced space and esthetic requirement the buccal surface

of the pontic is removed and tooth couloured acrylic is packed into the

buccal surface

* Replacements with chemical bonding

Recent developments provide means of direct chemical bonding of

acrylic resin to metal frameworks without using loops, mesh or

mechanical locks.

1-Sections of a metal framework that are to support replacement teeth

can be roughened with abrasives and then treated with a vaporized silica

coating. On this surface an acrylic resin bonding agent is applied,

followed by a thin film of acrylic resin to act as a substrate for later

attachment of replacement acrylic resin teeth or for processing of the

acrylic resin tissue replacements.

2-A second method of fusing a microscopic layer of ceramic to the

metal is accomplished by a process referred to as tribochemical coating.

This system involves sandblasting the metal framework with a special

silica particle material, Rocatec-Plus. Silica from these particles is at-

tached to the framework by impact. A silane is added to this ceramic-like

film to form a chemical bond between the silicate layer and the denture

base acrylic resin.

3-Denture base acrylic resins formulated with 4-Meta are also available

and provide a mechanism of bonding acrylic resin to metal.

INDICATIONS:

1. A posterior edentulous space which is extremely small mesiodistally or

occlusocervically.

CONTRAINDICATIONS:

1. Anterior edentulous spaces.

2. Where a simpler or more esthetic type prosthetic tooth may be used.

ADVANTAGES:

1. Can be used where other prosthetic teeth can not.

2. Have all the advantages of cast metal such as permanence of form, wear

resistance, dense surface, etc.

DISADVANTAGES:

1. Not as esthetics as other types of prosthetic teeth even when veneered with tooth

colored plastic.

2. All the disadvantages of metal such as hardness, wear of opposing teeth and

tooth materials, etc.

3. May require that the refractory cast be mounted in an articulator to develop the

occlusion of the pontic.

4. No wax try-in possible.

Acrylic Resin Versus Porcelain Teeth

PORCELAIN DENTURE TEETH

Porcelain denture teeth have the following advantages in comparison to

plastic denture teeth:

1. More esthetic.

2. More dense surface which is hard, abrasive, resistant, less prone to stains and

easier to clean.

Porcelain denture teeth have the following disadvantages in comparison to

plastic denture teeth:

1. Harder therefore transmit more force.

2. More abrasive, particularly when the glaze is broken. Should be used opposing

porcelain surfaces only.

3. More brittle. More apt to crack, chip and fracture.

4. Adjusting (grinding) to fit the framework and opposing occlusion is more

difficult.

5. Do not chemically bond with plastic.

Must be mechanically attached to the denture base. The retentive pins and

diatorics limit the amount of tooth modification which can be done. The tooth-base

interface will eventually stain because of the ingress of bacteria and fluids into the

space.

6. An objectionable "clacking" noise may be heard when porcelain teeth occlude

with enamel, cast metal or porcelain surfaces of opposing teeth.

PLASTIC DENTURE TEETH

Plastic denture teeth have the following advantages in comparison to

porcelain denture teeth:

1. Easier to adjust to fit the framework, space limitations and existing occlusion.

2. Chemically bond with plastic making a one piece denture tooth-plastic base

combination.

3. Softer so forces are dampened.

4. Will not abrade opposing enamel, amalgam, or cast metal restorations.

5. Can be restored with cast metal occlusal surfaces and amalgam restorations.

6. Less noise from tooth contact.

7. Can be custom “stained” to match the color and characterization of the natural

teeth.

Plastic denture teeth have the following disadvantages in comparison to

porcelain denture teeth:

1. Less hard. Will have more occlusal wear and may be abraded by brushing with

an abrasive cleaner.

2. Less esthetic.

3. Surface is more porous and will stain easier.

4. More difficult to remove wax from tooth during the wax-up of the denture.

5. More difficult to finish and polish denture.

THE CHOICE OF PORCELAIN OR PLASTIC DENTURE TEETH

Plastic denture teeth are used on RPDs almost exclusively because the

available space precludes the use of porcelain denture teeth. The esthetics of plastic

denture teeth is acceptable and their advantages far outweigh their disadvantages.

The Portrait IPN teeth by Dentsply have greatly improved esthetic characteristics.

Acrylic Teeth Porcelain Teeth

- Have strong chemical bond with denture bases.

-Less efficient mechanical bonding with denture bases.

- Tough, having good resistance to breakage hence are used in closed bite cases and narrow space.

Tendency to fracture specially in patients having heavy biting force.

- Require adequate space to ensure strong bonding.

- Resilient, causing less trauma to residual ridges.

- Hard.

Can be altered by grinding to fit limited inter-ridge space.

- Chip during grinding. Excessive grinding may alter the diatoric holes and causes difficulty to restore the highly polished surface.

- Light in weight. - Heavy weight.

- Have tendency to stain and change in colour.

- Resist staining.

- Have tendency to excessive wear, thus affecting both vertical and horizontal occlusal relations.

- Resist wear and maintain occlusal vertical dimension.

- Rebasing dentures is not easily done , as it is difficult to remove teeth.

- Teeth can be easily separated facilitating rebasing procedures.

- Can be used opposing gold restorations as they cause minimum amount of wear.

- Cause wear in opposing gold restorations.

- Clicking sounds

Selection of prosthetic teeth

A) SELECTION OF ANTERIOR TEETH

1- Color (shade) of the teeth selection

- The selection of a suitable color for the teeth is a simple procedure by using a shade guide. For single or partial denture the shade must be harmonized with the remaining natural teeth.

- The artificial teeth should be moistened before marching it with a shade guide.

- Natural light is better than artificial light.

- Avoid fatigue by providing intermittent rest to the eyes.

2- MOULD SELECTION

- The artificial teeth should be in harmony with the facial feature and natural teeth.

- Space regaining measurements (e.g. proximal slicing or crown fabrication) are considered when the edentulous apace is decreased due to migration of natural teeth.

3- Selection of material for anterior teeth

1- Acrylic denture tooth

2- Porcelain denture tooth

3- Inter changeable facing

4- Tube teeth

5- Pressed on / post

B ] Selection of posterior teeth

1- The selection of the proper tooth-size or mold is based on:- The capacity of the ridge to receive and resist the forces of mastication.

- The space available for the teeth.

- The esthetic requirements.

2- Shade

The shade of the posterior teeth should be in harmony with the shade of the natural teeth. The maxillary bicuspids may be slightly lighter than the other posterior teeth but not lighter than the anteriors.

3- Occlusal form

The ridge form can be used as an index for the amount of cusps angulation. The ridge form can be used as an index for the amount of cusp modification.

The available three major groups of occlusal forms are:

- Anatomic teeth of 30, 33 degrees cusps or more.

- Semi-anatomic teeth of 20 degrees cusps.

- Non-anatomic of 0 degree, cuspless teeth (flat teeth).

The anatomic teeth give greater efficiency and bilateral balance. They are commonly used for patients having normal ridge relations and well- developed ridges.

Advantages of non-anatomic teeth

1- They are more adaptable to universal jaw relations and class II and class III jaw relationships.

2- They are more easily used in cross-bite situations.

3- They permit long centric freedom.

4- They give the patient a sense of freedom as they do not lock the mandible in one position only.

5- They eliminate horizontal forces that may be more damaging than verticalforces (less bone resorption).

6- No need for adjustable articulator and setting is easier.

7- Balance can be obtained through balances ramp, compensating curve or pleasure curve.

The non-anatomic teeth offer less masticatory efficiency. However, they may be used in the following cases:

- Cross-bite relationship.

- Flat ridge.

- Knife-edge ridges.

- Patients with T.M.J problem or neuromuscular in-coordination.

- Large inter-ridge space.

- Milling type of chewing pattern.

4- Selection of material for artificial teeth Artificial teeth may be:

1- Acrylic denture tooth

- Acrylic resin teeth with amalgam stops.

- Acrylic resin teeth with gold occlusal surface

- IPN resin.

2- Porcelain denture tooth

3- Tube teeth

4- Metal tooth

5- Pressed on acrylic

6- Braided post

Factors Influencing the Selection of Posterior Teeth

The selection of the size and form of posterior teeth is influenced by

1) The size and form of the remaining natural teeth which acts as a guide for tooth selection.

2) The cusp height of the remaining natural teeth which determines whether to use cusped or non cusped teeth.

3) The condylar inclination A steep condylar inclination requires the use of cusped posterior teeth.

4) The condition of the remaining residual ridge, where a flat ridge necessitates the use of flat (cuspless) teeth.

5) The amount of available space determines the size of the replacement teeth.

6) Type of tooth material present in any restoration in the mouth.

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THE DENTAL SURVEYOR

Surveying is the procedure of locating and delineating the contour and position of the abutment teeth and associated structures before designing a removable partial denture. The instrument utilized for surveying is termed the dental surveyor .

The dental surveyor is an instrument used to survey the abutment teeth and associated structures.

The survey line

The survey line or the height of contour is a line encircling a tooth designating its greatest circumference at a selected position determined by the dental surveyor. The area of the tooth above this line is non-undercut area and the area below is the undercut area.

Undercut: An undercut is formed when the base of an object is smaller than its top. Undercut on abutment teeth is a dig or a burrow lie below the height of contour.

The primary purpose of surveying is to plan the design necessary to fabricate a removable partial denture which can be easily inserted in the mouth and retained in place during function.

Dr. A. J. Fortunati was the first to demonstrate the advantages of using a mechanical device to map the contours of the abutment teeth. At a 1918 clinic in Boston, Fortunati replaced the steel analyzing rod of a “Bridge Parallelometer” with a graphite rod, then accurately traced survey lines of the greatest convexities of the teeth.

Around 1920, Dr. Chayes developed the Parallelometer. This instrument could be used both intraorally and at the laboratory bench to ensure parallelism of precision attachments. The instrument also could be used to identify non-parallel and/or undercut surfaces of prepared teeth.

Types of dental surveyors

There are two types of dental surveyors: electronic and mechanical. Theelectronic surveyors are complicated and expensive and their use is restricted toresearch and large commercial dental laboratories.

The original Ney surveyor was introduced in 1923

A recently designed surveyor dramatically exposes undercut areas byprojecting a beam of laser light. Some of these modifications are applied to the

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newly developed surveyors which have been already introduced to the dental market be feb.2008 and of these trends:

*The Da Vinci is distinguishes by its dual, multi-jointed arm design, allowing the user to effortlessly switch between the primary milling, drilling arm and the secondary tapping, surveying arm.

Microsurveyor Compass (Denstply Sankinkk, Tokyo, Japan) from Japan is a small hand-held surveyor. It establishes the path of insertion by tilting its vertical arm rather than its cast holder.

Micro analyzer: it is a surveying instrument for measuring the amount of under cut electronically.

Stress –o- graph : it is type of surveyor with two vertical tool holder.

Parts of the dental surveyor

The principal parts of the Ney surveyor are as follows:

1. Horizontal Platform on which the base is moved.

2. Base equipped with a lock screw, on which the table swivels by ball and socket joint, permits movements of the table in all directions.

3. Survey Table (cast holder): to which the cast is attached، it is equipped with a clamp to lock the cast in place؛ the table can be tilted in any horizontal plane to help in analyzing the model in relation to vertical plane. The surveying table consists of a top and a base joined together by a ball and socket joint which permits tilting of the top in any direction. A lower locking device is used to fix the tilt of the top part. The top of the table is equipped with a clamp to lock the cast in place.

4. Vertical arm that supports the superstructures.

5. Horizontal arm with spindle housing and a tightening screw, from which the surveying tool suspends.

6. A surveying arm (spindle): It drops from the horizontal arm and moves vertically at right angles to the base. It can be fixed at the desired height by a locking device. The lower end of the spindle arm contains a tool holder and a tightening screw to fix the tool.

7. Paralleling Surveying tools that will be used for surveying:

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A- Analyzing rod: is a rigid metal rod used for diagnostic purposes in the selection of the path of placement.

B-Carbon marker: is used for the actual marking of the survey lines on the cast. A metal shield is used to protect it from breakage.

C- Undercut gauges: are used to measure the extent of the horizontal undercuts that are being used for clasp retention. Usually there are three sizes: 0.01، 0.02and 0.03 of an inch.

D- Wax trimmer is used to trim excess wax that may be inserted into those undercut areas, which are to be obliterated.

E- Reinforcing sheath : It is a metal sheath (usually half round) used to maintain the carbon marker from breakage.

Ney dental surveyor Jelenko (Wills) surveyor Williams surveyor

Parts of the dental surveyor: 1.Horizontal Platform، 2.Vertical arm، 3. Horizontal arm، 4. Table with clamp، 5. Base، 6. Mandrel (spindle)، 7. Storage compartment for storing the tools، 8. Tightening screw، 9. Screw to lock spindle, 10. locking screw for tilt top, 11,Rack for accessories.

The most widely used dental surveyors are the Ney and the Jelenko , they differ principally in

1- In Jelenko surveyor: by loosening the nut at the top of the vertical arm, the horizontal arm may be made to swivel. The objective of this feature, originally

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designed by Dr. Noble Wills, is to permit freedom of movement of the arm in a horizontal plane rather than to depend entirely on the horizontal movement of the cast.

To some this is confusing because two horizontal movements must thus be coordinated. For those who prefer to move the cast only in a horizontal relationship to a fixed vertical arm, the nut may be tightened and the horizontal arm used in a fixed position.

2- The vertical arm of the Jelenko surveyor is spring mounted and returns to the top position when it is released. It must be held down against spring tension while it is in use. The vertical arm on the Ney surveyor is retained by friction within a fixed bearing. The shaft may be moved up or down within this bearing but remains in any vertical position until again moved. The shaft may be fixed in any vertical position desired by tightening a set screw.

To some it is a disadvantage. The spring may be removed, but the friction of the two bearings supporting the arm does not hold it in position as securely as does a bearing designed for that purpose.

3- Reinforcing sheath present in Ney surveyor used to maintain the carbon marker from breakage.

4- Jelenko surveyor has one undercut gauge with different ends but the Ney surveyor has three different undercut gauge with different sizes.

4-Williams surveyor has Gimbal stage table that is adjustable to any desired anterior, posterior, or lateral tilt. Degree of inclination can be recorded for repositioning of cast at any time. Distinct advantage of this table over universal tilt table is that center of rotation always remains constant. Superstructure of this surveyor consists of jointed arm and spring-supported survey rod, all components of which can be locked in fixed position if desired. This surveyor is perhaps best suited for placement of internal attachments rather than for cast analyzing and other purposes.

Because the shaft on the Ney surveyor is stable in any vertical position it may be used as a drill press when a handpiece holder is added. The handpiece may thus be used to cut recesses in cast restorations with precision by using burs or carborundum points of various sizes in a dental handpiece.

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Objectives of surveying

Surveying of both the study and the master casts is essential for proper diagnosis، designing and treatment planning. Surveying of the master castfollows mouth preparations. The objectives of surveying are:

1. Permit an accurate charting of the required restorative procedures and mouth preparations.

2. Determine the most acceptable path of placement and removal which;

a. Allows easy placement of the prosthesis and free from any interference .

b. Avoids impingement of oral mucosa.

c. Provides adequate clasp retention.

d. Satisfies the requirements of guiding planes،

e. Provides the best esthetic requirements.

3. Delineate height of contour (survey line) on the abutment teeth .

4. Determine soft، bony or tooth undercuts and areas of interferences that should be blocked out or eliminated.

5. Identify and measure tooth undercuts that may be used for retention and locate the flexible components in their position below the survey line of the tooth.

6. Determine the relative parallelism of teeth surfaces that act as guiding planes.

7. Recording the cast position in relation to a selected path of placement for future reference (tripoding or scoring).

8. Trimming blockout material on the master cast parallel to the path of placement prior to duplication.

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PURPOSES OF SURVEYOR

The surveyor may be used for surveying the diagnostic cast, recontouring abutment teeth on the diagnostic cast, contouring wax patterns, measuring a specific depth of undercut, surveying ceramic veneer crowns, placing intracoronal retainers, placing internal rests, machining cast restorations, and surveying and blocking out the master cast.

A - Surveying the diagnostic cast

1. To determine the most desirable path of placement that will eliminate or minimize interference to placement and removal.

2. To identify proximal tooth surfaces that are or need to be made parallel so that they act as guiding planes during placement and removal.

3. To locate and measure areas of the teeth that may be used for retention.

4. To determine whether tooth and bony areas of interference will need to be eliminated surgically or by selecting a different path of placement.

5. To determine the most suitable path of placement that will permit locating retainers and artificial teeth to the best esthetic advantage.

6. To permit an accurate charting of the mouth preparations to be made. This includes the preparation of proximal tooth surfaces to provide guiding planes and the reduction of excessive tooth contours to eliminate interference and to permit a more acceptable location of reciprocal and retentive clasp arms. using an undercut gauge to estimate the amount of tooth structure that may safely (without exposing dentin) be removed ( marking these areas on the diagnostic cast in red).

7. To delineate the height of contour on abutment teeth and to locate undesirable tooth undercut areas that are to be avoided, eliminated, or blocked out. This will include areas of the teeth to be contacted by rigid connectors, the location of non retentive reciprocal and stabilizing arms, and the location of retentive clasp terminals.

8. To record the cast position in relation to the selected path of placement for future reference.

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B- Contouring wax patterns

The surveyor blade is used as a wax carver so that the proposed path of placement may be maintained throughout the preparation of cast restorations for abutment teeth.

Guiding planes on all proximal surfaces of wax patterns adjacent to edentulous areas should be made parallel to the previously determined path of placement. Similarly, all other tooth contours that will be contacted by rigid components should be made parallel.

The surfaces of restorations on which reciprocal and stabilizingcomponents will be placed should be contoured to permit their location well below occlusal surfaces and on non retentive areas.

Those surfaces of restorations that are to provide retention for clasp armsshould be contoured so that retentive clasps may be placed in the cervical third of the crown and to the best esthetic advantage.

C- Surveying ceramic veneer crowns

The surveyor is used to contour all areas of the wax pattern for the veneer crown except the buccal or labial surface.

Before the final glaze is accomplished, the abutment crowns should be returned to the surveyor on a full arch cast to ensure the correct contour of the veneered portions or to locate those areas that need recontouring. The final glaze is accomplished only after the crowns have been recontoured.

D- Placement of intracoronal retainers (internal attachments)

1. To select a path of placement in relation to the long axes of the abutment teeth that will avoid areas of interference elsewhere in the arch.

2. To cut recesses in the stone teeth on the diagnostic cast for estimating the proximity of the recess to the pulp (used in conjunction with roentgenograph to estimate pulp size) and to facilitate the fabrication of metal or resin jigs to guide the preparations of the recesses in the mouth.

3. To carve recesses in wax patterns, to place internal attachment trays in wax patterns, or to cut recesses in castings with the handpiece holder

4. To place the keyway portion of the attachment in the casting before investing and soldering; each keyway must be located parallel to the other keyways elsewhere in the arch

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E- Placement of internal rest seats

The surveyor may be used as a drill press, with a dental handpiece attached to the vertical arm by a handpiece holder. Internal rest seats may be carved in the wax patterns and further refined with the handpiece after casting, or the entire rest seat may be cut in the cast restoration with the handpiece. It is best to carve the outline form of the rest seat in wax and merely refine the casting with the handpiece.

Internal rest seats may be made in the form of a non retentive box, a retentive box fashioned after the internal attachment, or a semi retentive box. [In the latter the walls are usually parallel and non retentive, but a recess in the floor of the box prevents proximal movement of the male portion. Small round burs are used to cut recesses in the floor of the rest seat . Tapered or cylindrical fissure burs are used to form the vertical walls].

The ball-and socket, spoon-shaped occlusal or non interlocking rest should be used in distal extension partial denture designs. The use of the dove-tailed or interlocking internal rest should be limited to tooth-supported removable restorations, except when it is used in conjunction with some kind of stress-breaker between the abutments and the movable base.

F- Machining cast restorations

With handpiece holder attached axial surfaces of cast and ceramic restorations may be refined by machining with a suitable cylindricalcarborundum point. Proximal surfaces of crowns and inlays, which will serve as guiding planes, and vertical surfaces above crown ledges may be improved by machining, but only if the relationship of one crown to another is correct.

G- Surveying the master cast

1. To select the most suitable path of placement by following mouth preparations that satisfy the requirements of guiding planes, retention, noninterference, and esthetics

2. To permit measurement of retentive areas and to identify the location of clasp terminals in proportion to the flexibility of the clasp arm being used.

Retention depend on (a) the flexibility of the clasp arm, (b) the magnitude of the tooth undercut (the magnitude of the angle of cervical convergence below the point of convexity), and (c) the depth the clasp terminal is placed into this undercut

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3. To locate undesirable undercut areas that will be crossed by rigid parts of the restoration during placement and removal; these must be eliminated by blackout

4. To trim blockout material parallel to the path of placement before duplication

Principles and Rules for Surveying

1. By surveying the prosthesis goes smoothly into place without interference

2. All casts are originally surveyed with the occlusal-plane parallel to the base of the surveyor (zero tilt).

3. When the surveyor blade contacts a tooth on the cast at its greatest convexity، a triangle is formed, the apex of the triangle is at the point of contact of the surveyor blade with the tooth, and the base is the area of the cast representing the gingival tissues. The apical angle is called the angle of cervical convergence. This will indicate the areas available for retention and the existence of tooth and other tissue interference to the path of placement.

4. A cast in a horizontal relationship to the vertical arm represents a vertical path of placement; a cast in a tilted relationship represents a path of placement toward the side of the cast that is tilted upward.

5. Any areas cervical to the height of contour may be used for the placement of retentive clasp components, whereas areas occlusal to the height of contour may be used for the placement of non-retentive, stabilizing or reciprocating components.

6. Whenever possible, undesirable undercuts and areas of interference are removed during mouth preparation by recontouring teeth or making necessary restorations.

7. The location of the undercut area can be changed by tilting the cast anteriorly or laterally.

8. Deciding the tilt of the cast depends on path of placement and removal.

9. A combination between two tilts could be used.

10. An anterior tilt is sometimes preferred in distal extension bases this increases resistance to vertical displacement by the denture base by engaging undercuts distal to abutment teeth.

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11. The retentive tips of clasps must engage undercuts, which are present, when the cast is surveyed with the occlusal plane parallel to the base of the surveyor، i.e.undercut areas should be present at both zero tilt and the new tilt

12. The retention on all principal abutments should be as nearly equal as possible.

13. Without guiding planes, clasp retention will either be detrimental or practically nonexistent.

Uniform clasp retention depends on depth (amount) of tooth undercut rather than on distance below the height of contour at which clasp terminus is placed.

The fallacy of attempting to create retentive undercuts by tilting the cast on the surveyor

A. No retentive undercut on the buccal surface of the abutment.

B. The cast is tilted to create an under-cut.

C. The clasp tip engages this created undercut.

D. During mastication the dislodging force will be perpendicular to the occlusal plane and since the retentive undercut is not present, in this plane, the prosthesis is dislodged.

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D

Clasps designed at tilt are ineffective without development of corresponding guide planes to resist displacement when restoration is subject to dislodging forces in occlusal direction.

Step by step procedures in surveying and determination of the path of placement:

a) Placement of the cast: The cast is attached to adjustable surveyor table by means of the clamp provided, in a horizontal position (zero ti1t).

b) Guiding planes: Analyze the proximal abutment tooth surfaces with the surveyor-analyzing rod. Alter the cast position anteroposteriorly until their proximal surfaces are in parallel relation to one another or near enough that they can be made parallel by recontouring. The end result should provide parallel proximal surfaces that may act as guiding planes.

c) Retentive areas: By contacting buccal and lingual surfaces of abutment teeth with the surveyor blade, the amount of retention existing below their height of convexity may be determined. This is best accomplished by directing a small source of light toward the cast from the side away from the dentist. The angle of cervical convergence is best observed as a triangle of light between the surveyor blade and the apical portion of the tooth surface being studied .

Alter the cast position by tilting it laterally until similar retentive areas exist on the principal abutment teeth.

If only two abutment teeth are involved, as in a Kennedy Class I partially edentulous arch, they are both principal abutments. However, if four abutment teeth are involved (as they are in a Kennedy Class III, modification 1 arch), they are all principal abutments, and retentive areas

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should be located on all four. But if three abutment teeth are involved (asthey are in a Kennedy Class I I , modification 1 arch), the posterior abutment on the tooth-supported side and the abutment on the distal extension side are considered to be the principal abutments, and retentionneeds to be equalized accordingly. The third abutment may be considered to be secondary, and less retention is expected from it than from the othertwo.

An exception is when the posterior abutment on the tooth-supported sidehas a poor prognosis and the denture is designed to ultimately be a Class I. In such a situation, the two stronger abutments are considered to be principal abutments.

In tilting the cast laterally, it is necessary that the table be rotated without disturbing the anteroposterior tilt previously established.

d) Interferences: It should be noted that areas of interference to proper placement of clasp arm can be eliminated by reshaping tooth surfaces during mouth preparations.

If there is bilateral soft، bony or tooth interferences that may prevent the insertion and removal of rigid connector, surgery and/or recontouring of lingual tooth surfaces may be unavoidable. If interference is only unilateral, change the path of insertion at the expense of guiding planes and retention.

e) Esthetics: If a choice between two paths of equal merit, one permits a more esthetic placement of clasp arms than the other, that path should be preferred.

f) After selection of the proper path of insertion, the cast is secured in place before the following steps are made

1. Drawing of the survey line

The analyzing rod is replaced with a carbon marker and the survey line is drawn on abutment teeth.

2. Location of the clasp terminals

The carbon marker is removed from the tool holder and the suitable undercut gauge is fixed in the holder. The undercut gauge is placed in contact with the tooth to be clasped with its shaft touching the tooth surface at the survey

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line. The head will indicate the undercut area where the clasp will terminate. A sharp pencil is used to mark this point.

It is preferable that undercuts be present on both zero tilt and lateral tilt to avoid creation of apparent undercuts. Retentive terminals located in apparent undercuts will be displaced by occlusally displacing forces.

3.Blocking the undesirable undercuts

The undesirable undercuts especially on the proximal surfaces are filled with wax. The wax trimmer is fitted in the tool holder to trim the excess wax.

4.Tripoding or scoring the cast to preserve the established cast tilt.

All these steps are performed while the master cast is still mounted on the survey table without changing the tilt.

Recommended method for manipulating dental surveyor Right hand is braced on horizontal arm of surveyor، and fingers are used, as illustrated, to raise and lower vertical shaft in its spindle. Left hand holding cast on adjustable table slides horizontally on platform in relation to vertical arm. Right hand must be used also to loosen and tighten tilting mechanism as suitable anteroposterior and lateral tilt of cast in relation to surveyor is being determined.

Recording the cast position:

Preserving the established cast tilt in relation to the selected path of insertion and repositioning of the cast on the surveyor table to its original position is performed by rather of the two methods .

Tripoding:

Tripoding is done by drawing three widely separated cross marks on the tissue side of the cast lingual or palatal to the remaining natural teeth while the cast and the vertical arm is locked at a certain vertical height. The cast can be repositioned to the same tilt by allowing the analyzing rod to touch one of the cross marks, the spindle is then locked at this vertical height and the tilt of the

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cast is modified until the rod touches the three cross marks. Then locking the surveyor table.

A, Tripoding the cast

Scoring : analyzing rod method

Two sides and the dorsal aspect of the base of the cast are scored with a sharp instrument held against the surveyor blade. By tilting the cast until all three lines are parallel to the surveyor blade, the original tilt can be re-established.

B, Scoring the cast

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Path of Placement (Insertion)

It is the specific direction in which a prosthesis is placed on the abutment teeth.

The path of insertion of the partial denture is "The direction of movement in which a prosthesis moves from the point of initial contact with the supporting teeth to the terminal resting position where the occlusal rests are seated and the denture base is in contact with the tissues".

The path of removal of the partial denture is "The direction of movement of the restoration from its resting position to the last contact with the supporting teeth". It is the reverse of the path of insertion.

Types of path of insertion

1. Single path

Two or more parallel axial surfaces on abutment teeth which can be used to limit the path of insertion and improve the stability of a removable prosthesis. Guide surfaces may occur naturally on teeth but more commonly need to be prepared.

2. Double path

Two distinct paths of insertion will be employed for a sectional, or two-part denture illustrated here by a diagram in the sagittal plane of a Kennedy Class IV denture. The abutment teeth on either side of the saddle are not shown.

3. Multiple path:

Multiple paths will also exist where point contacts between the saddle of the denture and the abutment teeth are employed in the ‘open’ design of saddle.

4. Rotational path

A single path of insertion may be created if sufficient guide surfaces are contacted by the denture; exist mostly in bounded saddle.

Multiple paths of insertion will be exist where guide surfaces are not utilized where the abutment teeth are divergent or where point contact between the saddle and the abutment teeth is employed.

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Factors Affecting Path of Insertion of the Partial Denture

1-Interferences: The prosthesis must be designed so that it may be placed and removed without encountering any tooth or tissue interferences.

Interferences may be eliminated during mouth preparation by either:

a) Changing the path of placement.

b) Relief of the denture.

c) Alters tooth Contours with restorations.

d) Extraction.

e) Surgery to remove interfering structures as bony exostosis, tori or undercuts.

f) A combination of any one of the above.

2- Retentive undercuts

Retentive undercuts must be present on the abutment teeth, both at thehorizontal (zero) tilt and at the tilt of the selected path of placement, to counteract any dislodgment of the denture in that direction.

Those undercuts should be equal in depth and should also permit the location of clasp tips in the gingival third of the tooth. The tilt is normally changed to lower the height of contour on an abutment tooth so that the clasp arms, retentive or reciprocal, can be positioned no more occlusal than the junction of the gingival and middle third of the tooth. This position is more esthetic and lowering the torque forces transmitted to the tooth by the clasp

- Retentive clasp arms must be located so that they lie in the same approximate degree of undercut on each abutment tooth. Clasp retention is no more than the resistance of metal to deformation.

- Retention should be the minimum acceptable only to resist reasonable dislodging forces.

- Retentive surfaces may be made by altering tooth contours or by placing cast restorations with similar contours.

- The size of the angle of convergence will determine how far into that angle a given clasp arm should be placed. Retention will depend on the location of the retentive part of the clasp arm, not in relation to the height of contour, but in relation to the angle of cervical convergence.

DENTAL SURVEYOR


- Retention may be obtained by one or two means:

1- Change the path of placement to increase or decrease the angle of cervical convergence of opposing retentive surfaces of abutment teeth.

2- Alter the flexibility of the clasp arm by changing its design, its size, and length or the material of which it is made.

3- Health of teeth used as abutment

For example, in tooth-bearing dentures, if the molar is weaker than the bicuspid, an anterior tilt may be advisable, in order to place the clasp on the stronger tooth.

4- Esthetics:

The retentive area should be selected with the most esthetic clasp location. The most esthetic placement of artificial teeth is made possible with less clasp metal and less base material displayed.

A vertical path of placement is necessary when missing anterior teeth must be replaced to avoid modifying the natural teeth.

5- Guiding planes:

Guiding planes are formed by two or more parallel axial surfaces on abutment teeth which can be used to limit the path of insertion and improve the stability of a removable prosthesis. Guide surfaces usually need to be prepared.

Proximal tooth surfaces that bear a parallel relationships to one another must either be found or be created to act as guiding planes during placement and removal of the prosthesis.

When anterior teeth must be replaced with partial denture vertical path of placement may be necessary to avoid excessively altering abutment teeth and supplied teeth.

DENTAL SURVEYOR


Selection of the Path of Insertion

The most favorable path of insertion is that perpendicular to the occlusal plane, Survey analysis should start first with the occlusal plane parallel to the base of the surveyor (zero tilt). This path is preferred because most patients tend to seat their dentures under biting force. However, this inclination (zero tilt) may not be convenient with respect to the factors affecting selection ofthe path of insertion.

Thus, if undercuts are present but not efficient at the zero tilt and if displacement of the prosthesis is anticipated with the least displacing forces, another path of insertion should be decided. This is achieved either by:

1- A rotating or curved path: In this path one section of the prosthesis is seared first and the remainder is then rotated into position.

2- Tilting the cast to:

a- Create suitable undercuts.

b- Equalize undercuts on both sides of the arch.

c- Place the clasp tips in a better esthetic position.

The path of placement may also be slightly off of the zero tilt to allow for reduction in the amount of undercut when rigid minor connectors contacting guiding planes are planned to help in providing retention.

Since the path of dislodgment resulting at the end of each masticatory cycle tends to pull the denture on a direction perpendicular to the occlusal plane, therefore, undercut areas should be present at both zero tilt and the new tilt,Gross inclination of the cast to create apparent undercuts should be avoided.

DENTAL SURVEYOR


Blocking Out and Relief of the Master Cast:

After the establishment of the path of placement and the location of undercut areas on the master cast, any undercut areas that will be crossed by rigid parts of the denture (which are every part of the denture framework except the retentive clasp terminal) must be eliminated by block out.

In the broader sense of the term, blockout includes not only the areas crossed by the denture framework during seating and removal but also (1) those areas not involved that are blocked out for convenience; (2) ledges on which clasp patterns are to be placed; (3) relief beneath connectors to avoid tissue impingement; and (4) relief to provide for attachment of the denture base to the framework.

Severe undercuts in retromylohyoid or buccal regions of the cast have to be blocked-out to prevent possible distortion of duplicating mould when the master cast is removed.

All guiding planes areas must be parallel to path of placement and all other areas that will be contacted by rigid parts of dentures frameworks must be made free of undercut by parallel blockout.

All guiding planes areas must be parallel to the path of placement and all other areas that will be contacted by rigid parts of framework must be made free of undercut by parallel blockout. Relief also must be provided for the gingival crevice and gingival margin.

DENTAL SURVEYOR


PARALLELED BLOCKOUT, SHAPED BLOCKOUT, ARBITRARY BLOCKOUT, AND RELIEF

Paralleled blockout

1. Proximal tooth surfaces to be used as guiding planes.

2. Beneath all minor connectors.

3. Tissue undercuts to be crossed by rigid connectors.

4. Tissue undercuts to be crossed by origin of bar clasps.

5. Deep interproximal spaces to be covered by minor connectors or linguoplates beneath bar clasp arms to gingival crevice.

Shaped blockout

1. On buccal and lingual surfaces to locate plastic or wax patterns for clasp arms.

2. Ledges for location of reciprocal clasp arms to follow height of convexity so that they may be placed as cervical as possible without becoming retentive.

3. Ledges for location of retentive clasp arms to be placed as cervical as tooth contour permits; point of origin of clasp to be occlusal or incisal to height of convexity، crossing survey line at terminal fourth, and to include undercut area previously selected in keeping with flexibility of clasp type being used

Arbitrary blockout (Smoothed arbitrarily with wax spatula)

1. All gingival crevices

2. Enough to just eliminate gingival crevice Leveled arbitrarily with wax spatula

3. Gross tissue undercuts situated below areas involved in design of denture framework

4. Tissue undercuts distal to cast framework

5. Labial and buccal tooth and tissue undercuts not involved in denture design

DENTAL SURVEYOR


Relieving the Master Cast:

1. Beneath lingual bar connector.

2. Areas in which major connectors will contact thin tissues such as hard areas so frequently found on the lingual surface of the mandibular ridges and elevated median palatal raphes.

3. Beneath framework extensions onto ridge areas for attachment of resin bases.

DENTAL SURVEYOR


SURVEY LINES

A SURVEY LINE is a line produced on a cast by a surveyor or scribe marking the greatest prominence of contour in relation to the planned path of placement of a restoration.1

A survey line marks the HEIGHT OF CONTOUR (greatest prominence)of a tooth or bony prominence AT THE SELECTED PATH OF PLACEMENT of the denture (TILT OF THE CAST). If the tilt of the cast is changed (changingthe path of placement of the denture) the height of contour (survey line) willchange.

IDENTIFYING SURVEY LINES

Survey lines are marked on a cast by first orienting the cast in the castholder at the tilt indicating the path of placement for the denture and then sliding the cast holder along the surveyor table so that the cast surface is lightly rubbed against a carbon marker held in the chuck in the spindle of the surveyor .

Survey lines are marked on non-polished metal and non-glazed porcelain crown surfaces with a carbon marker in a similar fashion.

Survey lines are marked on wax patterns for crowns by dusting the surface with zinc stearate or powdered white wax, then sliding the cast holder on the surveyor table so that the surface of the wax pattern is lightly rubbed against an analyzing rod held in the chuck in the spindle of the surveyor.

Survey lines are marked on polished metal and glazed porcelain crownsurfaces in a similar manner substituting a layer of disclosing medium (i.e.Occlude, Die Mark, etc.) on the surface of the crown.

USES OF SURVEY LINES

Survey Lines on Teeth

The survey line on the facial and lingual of abutment teeth is important in selecting clasps and planning the modifications of the teeth necessary for the selected clasps.

The survey line on the proximal tooth surface is important to minorconnector design.

The survey line on non-abutment teeth involved in the RPD design is important in selecting and designing major and minor connectors.

DENTAL SURVEYOR


Survey Lines on Bony Prominences

Survey lines are marked on all bony and soft tissue prominences locatedin the area of the denture. These lines are important in the selection, location, and design of major and minor connectors, and bar clasp approach arms,

CLASSIFICATION OF SURVEY LINES

Blatterfein divided the buccal and lingual surface of the tooth adjacent to the edentulous area into two halves by a line passing through the center of this surfaces along the vertical axis of the tooth .

The area closer to edematous area called near zone and the area away from the edematous area called far zone.

Survey lines can be classified as:

High survey line

Medium survey line

Low survey line

Diagonal survey line.

High survey line :

High survey line passes from the occlusal third in the near zone to the occlusal third in the far zone. When a high survey line is present, the undercut will be deep and hence a wrought wire clasp which is more flexible should beused.

It is commonly found in inclined teeth and in teeth with a larger occlusal diameter compared to its diameter at the cemento-enamel junction.

Medium survey line

It passes from the occlusal third in the near zone to the middle third in the far zone – Either Aker's or Roach clasp is used for teeth with a medium survey line. Aker's clasp is preferable. During survey, the cast should be tilted such that maximum number of teeth have a medium survey line.

Low survey line

This survey line is closer to the cervical third of the tooth in both near and far zone. A modified T-clasp is used for teeth with low survey lines.

DENTAL SURVEYOR


It is common in teeth with marked inclination, when it is associated with a high survey line on the opposite side. The retentive clasp tip cannot be placed in such cases, because the undercut will be very close to the gingiva and difficult to maintain oral hygiene.

In such cases one of the following designs can be followed.

A bracing or reciprocal arm is placed along the low survey line and a retentive wrought wire clasp is placed to engage the undercut on the opposite side.

Extended clasp can be used.

Re-contouring the tooth with a crown can be done.

Proximal undercut can be used for retention.

Diagonal survey tine

This survey line runs from the occlusal third of the near zone to the cervical third of the far zone. Here, a reverse circlet clasp is used. It is more common on the buccal surfaces of canines and premolars. It can be managed byusing reverse action (hair pin) or ring type Aker's clasp (occlusally approaching) , or L or T type roach clasp (gingivally approaching).

Undercuts

The term undercut, when used in reference to an abutment tooth, is that portion of a tooth that lies between the height of contour and the gingivae.

When used in reference to other oral structures, it means the contour or cross section of residual ridge or dental arch that would prevent the placement of a denture.

Generally, a small amount of undercut 0.02 inch (0.375 mm) or less is sufficient for retentive purposes.

The gingival retentive zone : It is triangular area bounded by horizontal flange and vertical arm of undercut gauge and tooth surface.

Depth of under cut: the horizontal measured by undercut gauge

DENTAL SURVEYOR


Distance of undercut: the vertical distance between the flange of undercut gauge and survey line

Retention depend on

(a) the flexibility of the clasp arm,

(b) The magnitude of the tooth undercut (the magnitude of the angle of cervical convergence below the point of convexity), and

(c) The depth the clasp terminal is placed into this undercut

Partially edentulous mouth has many undercut areas that result due to:

a- Bulbous shape of the crowns of natural teeth resulting in buccal and lingual undercuts.

b- The inclination of the long axes of teeth in relation to a vertical line drawn from the occlusal surface, resulting in undercut on the proximal surfaces of these teeth.

c- The inclination of soft tissues or bone to a vertical line drawn from the occlusal surface resulting in soft tissue or bony undercuts.

d- Proliferation of soft tissues covering the edentulous ridge due to the rapid pattern of bone resorption .

The undercuts might be:

1) Desirable undercuts:

Desirable undercuts are used for retaining the partial denture against dislodging forces. Discerning the angle of cervical convergence is important in developing uniform retention through clasps.

2) Undesirable undercuts:

Undercuts other then those used for retention are considered undesirable and should be eliminated. This done by

Blocking out the undercut with wax on the master cast .

preparation and reduction of the tooth surface in the mouth

Placing properly contoured crown restoration

DENTAL SURVEYOR


The under cut may be classified into

True undercut : which present in relation to analizing rod and in relation to undercut in opposite side. Desirable undercuts must be present at the path of placement of the RPD.

False undercut: Tilting the cast away from the path of placement of the RPD may create undercuts, but these are FALSE UNDERCUTS because they do not provide retention (resistance to movement of the prosthesis away from the tissues along the path of placement and removal of the denture) since they are not present along the path of placement and removal of the denture.

The amount of undercut is measured in hundredths of an inch, with the gauges allowing measurements up to 0.03 inch. Theoretically the amount of undercut used may vary with the clasp to be used up to a full 0.03 inch. However, undercuts of 0.01 inch are often adequate for retention by cast retainers.

Tapered wrought-wire retention may safely use up to 0.02 inch without inducing undesirable torque on the abutment tooth, provided the wire retentive arm is long enough (at least 8 mm). The use of 0.03 inch is rarely, if ever, justified with any clasp. When greater retention is required, such as when abutment teeth remain on only one side of the arch, multiple abutments should be used rather than increasing the retention on anyone tooth.

Guiding planes

Guiding planes are flat axial surfaces in an occluso-gingival direction on the proximal or lingual surfaces of teeth. They are made parallel to the path of placement, help in guiding the prosthesis during placement and removal.

They are prepared on the enamel surface after the path of Insertion is selected according to the other three factors.

A guide surface should be produced by removing a minimal and fairly uniform thickness of enamels usually not more than 0.5 mm, from around the appropriate part of the tooth. It should extend vertically for about 3 mm and should kept far from the gingival margin

They are 2 - 4 mm in height, and extend bucco-lingually according to the width of the component that is contacting them.

Guiding plane surface should be like area of cylindrical object. It should be continuous surface unbounded by even rounded line angle.

DENTAL SURVEYOR


Minor connector contacting guiding plane surface has same curvature as does that surface. From occlusal view it tapers buccally from thicker lingual portion, thus permitting closer contact of abutment tooth and prosthetically supplied tooth. Viewed from buccal aspect, minor connector contacts enamel of tooth on its proximal surface about two-thirds its length.

Prevention of clasp deformation; without guide surface the patient may tilt or rotate the denture on removal causing the clasp to flex beyond their proportional limit

A guide surface allows a reciprocating component to maintain continuous contact with a tooth as the denture is displaced occlusally. The retentive arm of the clasp is thus forced to flex as it moves up the tooth. It is this elastic deformation of the clasp, which creates the retentive force.

Increased stability is achieved by the guide surfaces resisting displacement of the denture in directions other than along the planned path of displacement.

Components of the denture that contacts the guiding planes during placement are:

I-Those contacting proximal surfaces:

a. The minor connector that joins the clasps to the saddle.

b. Proximal plates that are used with I-bar or RPI clasps.

II. Those contacting axial (lingual) surfaces:

DENTAL SURVEYOR


a. Reciprocal clasp arms.

b. Lingual plates that act as reciprocal arms.

c. Minor connectors that join the auxiliary rests to the major connector.

The benefits of the guiding planes include

1- Guide the prosthesis for easier path of placement and removal.

2- Eliminate detrimental strain to the framework components and minimize wedging stresses on the abutment teeth (Fig.6-10).

3- The frictional contact of the prosthesis against these parallel surfaces can contribute significantly to the overall retention of the prosthesis، and assisting the reciprocal clasp arm to perform its intended function.(Fig.6-11)

4- Aid in stabilizing the prosthesis against horizontal stress (Fig.6-12). Guiding planes are particularly effective when the edentulous spaces are tooth bounded.

5- Well-prepared guiding planes tend to reduce undercuts between the proximal surface of the teeth and the minor connectors of the partial denture, thus making the prosthesis more hygienic.

6- A properly prepared guiding plane lowering the height of contour of the proximal surface of the tooth permits the placement of some of the rigidportion of the clasp closer to the gingival margin of the tooth. This provides a more esthetic and biomechanical advantages (How).

Guiding planes and the distal extension base:

For bounded base a well-engineered guiding planes are contacted by the proximal plates of the framework as the prosthesis is inserted and removed, thus horizontal wedging is virtually eliminated. and all transverse stresses transmitted to the tooth are effectively neutralized.

In contrast to this the creation of a flat distal surface on the abutment tooth next to an edentulous space in distal extension case has the effect of magnifying the stress that the denture base transmits to the abutment as the base moves in function.

DENTAL SURVEYOR


A pronounced guiding plane is not recommended for the abutment tooth that supports a distal extension base to decrease the stress that the denture base transmits to the abutment as the base moves in function.

The interface between the tooth surface and the clasp should be such that a slight degree of movement of the base and the clasp is permitted without transmitting torsional stress to the tooth.

Enough flattening of the distal surface of the tooth should be accomplished to reduce the amount of the undercut between the minor connector and the abutment tooth.

A) For bounded base a well-engineered guiding planes are contacted by the truss arms of the framework. B:F، the proximal plates engages the bottom of 1 to 2 mm. of guide plane and is meant to vertically disengage with extension base loading

DENTAL SURVEYOR


Diagrammatic illustration showing comparative width of the proximal plates for differently contoured teeth. (A). Proximal plate (p) relatively wide due to the square contour of the 2nd bicuspid. (B). Proximal palate (p) relatively narrow due to the tapering contour of the 1st bicuspid.

Guiding planes are most effective when they are :

parallel

Include more than one common axial surface (e.g. proximal and lingual surfaces)

Are directly opposed by another guiding plane (e.g. facing guiding planes in a modification space)

Are placed on several teeth

Cover a large surface area (long and/or broad)

Should be at least 1/2 to 1/3 of the axial height of the tooth (generally a minimum of 2 mm in height).

Guide planes for distal-extension cases should be slightly shorter to avoid torquing of the abutment teeth.

Lingual guiding planes for bracing or reciprocal arms should be 2-4mm and ideally be located in the middle third of the crown, occluso - gingivally.

LABORATORY PROCEDURES

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LABORATORY PROCEDURES FOR FRAMEWORK CONSTRUCTION

The construction of metallic removable partial dentures comprises both

clinical and laboratory steps that are done following the sequence shown in the

previous table.

The laboratory steps include:1- Construction of the study cast

2- Primary surveying the study cast

3- Construction of a customized tray

4- Construction of the master cast

5- Surveying of the master cast

6- Drawing the design on the master cast

7- Preparation of the master cast

a) Spraying the master cast

b) Beading the maxillary master cast

c) Waxing the master cast:

Blocking-out the undesirable undercuts

Relief

Tissue Stops

Formation of internal finishing lines

8- Duplication

9- Waxing the framework on the refractory cast

10-Sprueing the Framework

11-Investing the sprued pattern

12-Burnout of the wax pattern

13-Casting the partial denture framework

14-Finishing and Polishing of the framework

15-Fitting the framework to the cast

16-Processing of acrylic resin.


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1-Construction of the study cast:It is a positive reproduction of the form of the dental arch. It is obtained

by pouring the preliminary impression using dental stone to avoid abrasion or fracture during handling. It should accurately reproduce the remaining teeth, residual ridge and the adjoining structure.

Uses of diagnostic cast: Maxillary and mandibular diagnostic casts can be mounted using an inter-occlusal registration record to serve the following purposes:

1 Diagnosis and treatment planning2 Evaluation of the occlusion and the need for any occlusal adjustments.3 Surveying and design drawing.4 Provides information on the need for mouth and abutment preparations.5 Case presentation and patient discussion.6 Patient records for future reference.7 Construction of special tray.

2-Primary surveying the study cast: The study cast is surveyed using a dental surveyor to:

- Permit an accurate charting of the required mouth preparations.

- Determine desirable and undesirable undercuts.

- Determine proximal tooth surfaces used as guiding planes.

- Determine the best path of placement and removal of the prosthesis.

3-Construction of a customized tray:- Acrylic resin is the material of choice but shellac tray may be used.

- Spacer is adapted to the cast and trimmed to the proper peripheral

outline. It is made of two layers wet asbestos. Wax or clay might also be used.

The wax spacer is omitted on the buccal shelf of bone in the mandible in order to gain more support from this 1ry stress bearing area.

-

4-construction of the master cast: After mouth preparation the final impression is recorded. The impression

is poured in hard stone to obtain the master cast.

The master cast is obtained by pouring the final impression using type IV (extra hard) dental stone because of its superior properties such as higher abrasion resistance, higher strength and less dimensional changes.


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The cast is then allowed to final set 40 to 60 minutes before it is separated. Proper trimming is also essential.

The master cast should be duplicated into working cast with the same type of stone) type IV). The procedures from now on will be carried out on the working cast while keeping the master cast as a reserve should any damage occurs. However, the terms master cast and working cast will be used synonymously.

Uses of master cast1 Construction of record blocks for jaw relation record.2 Second surveying in the same tilt of the first surveying.3 Design drawing as has been planned for.4 Preparation and duplication into refractory cast.

5- Surveying of the master cast: The master cast is surveyed to determine:

1- Determine the most acceptable path of placement and removal which is

free from any interference and، satisfy the requirements of guiding

planes، retention، noninterference and esthetics.

2- Determine soft، bony or tooth undercuts and areas of interferences that

should be blocked out or eliminated

3- Determine the relative parallelism of teeth surfaces that act as guiding

planes.

4- Identify and measure tooth undercuts that may be used for retention and

locate the flexible components in their position below the survey line of

the tooth.

5- Aid in determining restorative procedures and mouth preparation.

6- Delineate height of contour (survey line) on the abutment teeth.

7- Trimming blockout material parallel to the path of placement prior to

duplication.

8- Recording the cast position in relation to a selected path of placement

for future reference (tripod).

6-Drawing the design on the master cast: The outline form of the partial denture framework is carefully drawn on

the master cast guided the design present on the study cast.


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7-Preparation of the master cast: The master cast should be modified prior to its duplication as follows:

a) Spraying.

b) Beading.

c) Blockout.

d) Relief.

a) Spraying the master cast:

The working cast is sprayed with sealer spray for the following purposes:a) Protection of the cast and drawn design from scratching,b) Providing the cast with smooth surface before duplication.c) Preventing the cast from absorbing the water of the colloid (agar)

duplicating material.

b) Beading the maxillary master cast:

Beading is accomplished with a small spoon excavator by scraping

along the anterior and posterior borders of the major connector.

Beading depth and width should not exceed 0.5 to 1 mm and should

fade out (beveled) as the gingival margins or a prominent area in the

midline of the palate are approached.

Beading on the borders of maxillary major connectors serves to

prevent food particles from collecting beneath the framework and

producing discomfort to the patient. The beading is also used by

prosthodontists to help in transferring the major connector design to the

investment cast.

Beading is not done along the borders of the mandibular major

connectors because of the thin underlying mucosa that cannot tolerate

positive contact.

The aim of beading is to:a) Compensate for metal solidification shrinkage and hence, ensures positive contact of the metal with palatal tissues.b) Prevent food particles from collecting under the RPD.c) Better for pronunciation.d) Help in transferring the design to the refractory cast.


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c) Waxing the master cast:

1- Blocking-out the undesirable undercuts:

The elimination of undesirable undercuts on the master cost

before duplication has different forms: paralleled blockout, shaped

blockout and arbitrary blockout. There are three patterns of block out

Paralleled blockout

The blockout wax is trimmed parallel to the path of insertion and removal by using the wax trimmer surveyor tool while the cast is positioned in the predetermined tilt. It is done in the following areas:

- Proximal tooth surfaces to be used as guiding planes

- Beneath all minor connectors

- Tissue undercuts to be crossed by rigid connectors

- Tissue undercuts to be crossed by origin of bar clasps

- Deep interproximal spaces to be covered by minor connectors or

linguoplates beneath bar clasp arms to gingival crevice

Shaped blackoutIt is done in the form of ledges on the buccal and lingual surfaces of

abutment teeth. It will help in proper positioning and carving of the clasp arms.

- On buccal and lingual surfaces to locate plastic or wax patterns for clasp arms.

- Ledges for location of reciprocal clasp arms to follow height of convexity so that they may be placed as cervical as possible without becoming retentive

- Ledges for location of retentive clasp arms to be placed as cervical as tooth contour permits; point of origin of clasp to be occlusal or incisal to

height of convexity, crossing survey line at terminal fourth, and to include undercut area previously selected in keeping with flexibility of clasp type

being used.

Arbitrary blockout (Smoothed arbitrarily with wax spatula)This will cover the undercuts that may interfere with removal of the

duplicating material otherwise it may be subjected to tearing or distortion. This includes:

- All gingival crevices - Enough to just eliminate gingival crevice Leveled arbitrarily with

wax spatula


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- Gross tissue undercuts situated below areas involved in design of denture framework

- Tissue undercuts distal to cast framework- Labial and buccal tooth and tissue undercuts not involved in denture

design

2-Relief

It is done for creating a space between the metal framework and the cast as in the following areas:

- Beneath lingual bar connectors or the bar portion of linguoplates

when indicated

- Areas in which major connectors will contact• thin tissue such as hard

areas so frequently found on lingual side of mandibular ridges and elevated median palatal raphea.

- Beneath framework extension onto ridge areas for attachment of resin bases

3-Tissue Stops:

Tissue stops is done by removal of two small squares of 2 mm, usually an anterior and posterior, of relief wax at the distal end the

edentulous ridge. It provides stability of the framework during clinical work and during acrylic resin processing.

They will result in metal projections resting on ridge areas. Hence, the framework maintains its position while being subjected to the pressure

of packing later on.

Arrows indicate three small “nail head” minor connectors in which individualized impression

trays may be attached when secondary impression is used.


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4-Formation of internal finishing lines:

Internal finish lines are carved in the relief wax covering the

edentulous ridge at the metal resin junction. This line is trimmed with

blade held at 900 to the cast surface in order to produce a sharp

junction having a uniform depth of at least 1mm.

8- DuplicationDuplication is the procedure of accurately reproducing a cast.The

modified master cast is duplicated to form a refractory cast made of investment

material.

A duplicating flask is used for this procedure. The most commonly used

material for duplication is the reversible hydrocolloid agar agar. The solid

agar material is heated to melt and then cooled to 55 degree C to be poured

gently into the duplicating flask that contains the modified cast. The flask is put

in a shallow container filled with one inch water to allow the agar to cool from

the bottom upwards (compensation for gelation shrinkage).

This duplication is essential to:

A) The stone of the master cast can not withstand the high temperature

during casting.

B) The stone cast will not allow thermal or hygroscopic expansion to

compensate for casting shrinkage.

C) The stone material is not porous and will not allow for gas to escape

during burnout of the wax pattern.

Duplicating flask is metal case that consists of:

a)Bottom.

b)Ring.

c)Feeding top.

Ticoniurn duplicating flask is used because of its simple design and

reliability in controlling shrinkage.

1- Ticoniurn duplicating flask is used because of its simple de-sign and reliability in controlling shrinkage.


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2- Securing the master cast to the base of the duplicator with clay or utility wax. After placing the pouring reservoir, flow the melted colloid.

3- After setting of the colloid material, remove the base of the flask and retrieve the master cast by prying with two plaster knives where the clay or wax is placed for stability.

4-Mix the investment material. 5- Pouring of the refractory material in the mold.

6- Break the hydrocolloid away from the cast.

7- Drying the refractory cast.

8- Immersing the refractory cast into molten bees wax, to provide sealing.

9- Cooling the dipped wax on absorbent paper.


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Refractory cast is a cast made of material that will withstand high temperature without disintegration and when used in partial denture

casting, has expansion to compensate for metal shrinkage.

Duplicating colloids are capable of being re-used many times. They must be cleaned and melted after each use. They may be prepared and

stored in automatic duplicating machine. If this machine is not available, a double boiler can be used to prepare the colloid for

duplication.The clean colloid can be cut into small pieces and re-heated

in this double boiler to a fluid consistency. When cooled to working

temperature, it will be cool enough to flow easily without melting

the blockout wax. A 630C is a suitable working temperature.

Investment material is used for making the refractory cast. The type of investment depends on the type of the alloy used.

Gypsum-bounded investment is used for low heat alloys

(Type IV Gold + Ticonium)

phosphate-bound investment is used for high heat alloys (vitallium and nobilium). A special liquid is needed with

phosphate-bonded investment.

Investment materials must be measured and mixed accurately

according to the manufacturer instructions, to ensure that the expansion of the metal during burnout will match the shrinkage of

the alloy.When the refractory material has completely set, the cast is

removed from the colloid mold and placed in drying oven at 180 –

200o F for half to one hour. The cast is then either dipped into bees

wax at 280 - 300 0F for 15 seconds or sprayed while it is still warm .

Spraying the cast is done for the following purposes: - To provide a smooth and dense surface.

- To allow for better adherence of the wax or plastic patterns.- To prevent scratches of the cast.

-


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9- Waxing the framework on the refractory cast:

Design transfer: Before the actual waxing can begin• the design must

once again be drawn by transferring from master cast.

Materials: Waxing the framework is done by contouring wax, preformed

wax patterns or preformed plastic patterns to form the pattern of the

removable partial denture framework. These patterns have almost

replaced freehand waxing.

Wax pattern specifications for partial denture components:


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10- Sprueing the Framework:Sprueing: It is the process by which wax, metal or plastic form sprues

are attached to the wax pattern, to provide an entrance or pathway channel to

the mold space and to serve as a reservoir of metal during casting procedure.

There are certain general basic principles which should be followed:

1 It should be attached to the most bulky portion of the wax pattern.

2 The thickness of the sprue should be larger than that of thickest part of

the wax pattern

3 The diameter of the sprues should increase gradually from inside

outward.

4 The pathway should be smooth and direct. No sharp angles are allowed

throughout the course of the spure.

5 Reinforce all junctions with additional wax to act as reservoirs and

avoid constrictions

Types of Sprueing:

1- Single Sprueing (horizontal Sprueing): it has a limited application• it is used

in small castings.

2- Multiple Sprueing: Is used in big castings and has three forms:

a- Top (direct) Sprueing.

b- Inverted( bottom- indirect) Sprueing.

c- Horizontal (rear)Sprueing.

1) Top Sprueing

It consists of the sprue originating from the top of the wax

pattern.The sprue has a diameter of a pencil, it consists of a main

wide central sprue from which narrower auxiliary sprues run to each

corner of the wax pattern. Done for majority of maxillary cases.

2) Inverted Sprueing:

In which the base of the refractory cast should have a hole in

its center. A cone-shaped metal sprue of suitable size is placed into

the hole. Auxiliary sprues are then placed between the main sprue

and the thick sections of the wax pattern.


Mostafa Fayad 12

By this method of Sprueing, contraction of the metal during

cooling tends to pull the casting towards the model rather than away

from it. Done for majority of mandibular cases

3) Horizontal Sprueing:

In which sprueing is from the posterior edge of the casting. Used

with complete cast palatal major connector

Single Sprueing. Inverted Sprueing

A central hole prepared to receive the

central sprue.

Horizontal Sprued pattern.

11- Investing the sprued pattern:

Casting investment is a process of covering or enveloping of the sprued

wax pattern by an investment material before casting. It is performed in order

to enclose a mold resulting from the burn-out of the pattern.

When the wax pattern and sprues are burned out, a space will be created

where a molten metal is forced to take the same shape of that pattern.

Investing a partial denture wax pattern therefore consists of two

components:

a) The refractory investment cast upon which, the wax pattern has been

performed


Mostafa Fayad 13

b) The outer cast investment surrounding the cast and pattern. This portion is

confined by a ring (cylinder), winch is made of metal. The ring will not be

removed till the end of casting procedure. It should be lined with a wet layer

of cellulose to allow for both setting and thermal expansion of the investment.

Investment provides the following purposes

1- Strength necessary to hold forces exerted by the entering stream of

molten metal until solidification of the metal occurs.

2- Smooth surface for the mold cavity so that the final casting will require

as little finishing as possible.

3- An avenue of escape for most of the gases entrapped in the mold cavity

by the entering stream of molten metal.

4- Investment together with other factors provide necessary compensation

for contraction of the metal from the molten to the solid State.

Casting investment material!!

It is a refractory material in which the mold is made!

Gypsum bonded casting investment material!

! This material can be used for casting gold alloys

! The expansion of the mold counteracts the casting shrinkage gold alloys!

! It can be burnt out at 7040C (13000F) without breakdown!

Phosphate -Bonded Casting Investment Material!

! This material is used for casting chromium-cobalt alloys.

It can!counteract the casting shrinkage of chrome cobalt alloys!

It can be burnt out to 10370 C without breakdown.

Technique of Investing the Refractory Cast:

1) Line the investment ring with one layer of strip substitute asbestos.

Leave about 7 mm short of sprue end.


Mostafa Fayad 14

2) The refractory cast is dipped into slurry water to moisten its

surface. This wetting keeps the dry cast from taking up water from

the investment material mix.

3) Mix Investment and distilled water according to the manufacturer’s

instructions. Al-ways add powder to water.

4) Investment mix is applied in two coats (two-part mold):

a) First Coat (3 to 4 mm) painted on to ensure that no air bubbles are

trapped.

b) Second Coat: After the initial set of the paint on . The investment

mix is poured into the investment ring around the pattern. The cast

should be centered in the ring with at least 1/4 inch from the sides

of the ring.

REMENBER

- The investment ring is lined with one layer of asbestos casting ring

liner. The liner should be 6:7 mm shorter than the ring at the crucible end to

act as a lock against investment rotation inside the ring. The asbestos

permits for the escape of hot gases and allows space for investment

expansion.

- The refractory cast is dipped in slurry water to moisten its surface

and to prevent it from absorbing water from the investment material.

- The pattern is painted with a wetting agent to allow the outer

investment to adhere to the pattern.

Top Ring

Asbestos Substitute

¼ inch clearance of Asbestos Substitute

Investing the wax pattern.


Mostafa Fayad 15

12-Burnout of the wax pattern:It is the elimination of the wax by heat of the invested pattern to

prepare the mold to receive the molten metal.

The burn out procedures serves the following functions:

Dries the investment (Driving off moisture from the mold)

Burning , vaporization and elimination of the wax pattern, thus leaving a

cavity.

Thermal expansion of the mold to compensate for contraction of the

metal on cooling (solidification).

The investment is placed in the burn out furnace with the sprue

hole downwards. The investment should be moist before starting the

burn out cycle to allow the investment to heat uniformly.

The burnout should start in a cold oven, and then the temperature

should be slowly increased to 12500F over a period of two hours. This

temperature is maintained for half an hour (heat soaking).

The time and temperature required to eliminate the wax should

be according to the Manufacturer’s instructions.

- Burnout furnaces are either electric or gas and must be vented to allow

the noxious fumes that result from the burnout, to escape the work area.

Modem furnaces are controlled electronically to permit time/temperature

relationship to be set exactly to the alloy manufacturers specifications. With

these modern furnaces, over and under-heating are avoided.

13- Casting the partial denture framework:

Casting is to produce an object in a mold.

Mold is a cavity in which metal is cast.

Crucible is a container made of porcelain used for melting metal. It

sustains high degrees of temperature.

Casting Procedure:

The method of casting will vary according to the alloy and equipment used. All methods use force to inject the molten alloy quickly into the mold cavity. This force is usually centrifugal.


Mostafa Fayad 16

Molten metal is faced into the pre-heated mold by the use

of centrifugal force casting material. Heat and force to the metal

during casting are critical.

Heat applied to melt the metal may be applied by a blowtorch

using gas and air, gas and oxygen, acetylene, electrical conduction,

or induction.

Recovering the Casting:

When the casting step is completed, the mold is removed

from the machine and allowed to cool according to the

manufacturer’s instructions. The outer layer of the investment is

broken off by tapping it with a wooden mallet or a hammer.

The first layer of investment is then removed by stiff brush

under running water. Sandblasting machine is used to remove any

remaining investment. The casting can now be examined for de-

fects.

14- Finishing and polishing of the framework:

Finishing the framework; is to refine its surface. It is accomplished by

cutting the sprues carefully using separating disks and grinding off

excess metal flashes by suitable stones Rubber abrasive wheels,

disks and points are used to refine the surface.

The following precautions should be maintained

1- Avoid overheating of the framework by continuously soaking it

in cold water. Overheating may cause warpage of the casting.

2- Avoid undue pressure to the sprues or the casting. This is

accomplished by using high speed hand piece.

Polishing the framework

It is making its surface smooth and glossy. Polishing is

accomplished first by smoothing the surface of the casting by

coarse disks and stones, followed by finer forms. Final polish is


Mostafa Fayad 17

attained by polishing compounds on felt wheels and high speed

lathe in chrome cobalt castings and by rouge on felt wheels for

gold castings.

Finishing and polishing chrome cobalt castings should be done with

special high speed equipments (sand blasting and electrolytic

polishing).

Hard heat treatment of gold castings

When the gold casting has been quenched in water, it is

removed from the investment in a soft and most ductile condition.

All grinding and finishing operations are performed while it is in

this condition. After finishing and just before final polishing, it

should be heat hardened as follows:

1.Stabilize the furnace at the desired temperature 600-7000F for

yellow gold castings and 800o F for white gold alloys.

2.Place the casting on a metal tray in the furnace and allow to

heat soak for l5 minutes.

3.Remove the tray with the casting and leave it to bench cool.

Heat treatment will produce from 85% to 100% of the

strength of gold casting and will prevent the possibility of

warpage.

N.B.: Chrome cobalt alloys cannot be heat hardened. They

originally have satisfactory physical properties.

15- Fitting the framework to the cast:

The casting is checked for accuracy on the master cast. Any

point of interference should be ground until the casting fits properly

on the cast. The casting is now ready for try-in in the patient’s

mouth.

16- Processing of acrylic resin

The acrylic is processed in the conventional manner.


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! !! !

! !

! !

! !! !

! !


Mostafa Fayad 19

CLINICAL AND LABORATORY PROCEDURES FOR RPD CONSTRUCTION

Clinical procedures Laboratory procedures

1- Diagnosis and treatment planning:

- Extra and intra-oral examinations.

- X-ray Examinations.

- Examination of each arch separately.

- Examination of both arches.

2- Making primary impression: With an elastic material as alginate impression material in a perforated stock tray.

3- Mouth Preparation which includes a–Conservative, periodontal and surgical

treatment. b-Preparation of occlusal rest seat, guiding planes

and probable recontouring of abutments.

4-Making the final impression either with A-Alginate impression material in case of tooth

supported partial dentures.B-Functional impression in case of tooth and tissue

supported partial dentures.

5-Testing the framework on the master cast and then try in of the metal in the patient’s mouth.

6- Functional impression with framework in mouth in distal extension partial denture cases.

7- Jaw relation registration and tooth selection.

8- Try-in of the waxed partial denture.

9- Delivery and final adjustment.10-Periodic check-up and relining when necessary.

a- Pouring the impression in stone plaster to construct a study cast.

b- Surveying the study cast.c- construction of the special tray on the study

cast.

d-Pouring the final impression in stone plaster to construct a master cast.

e- Surveying the master cast to draw the survey line on abutment teeth and to determine the path of placement of the partial denture.

f- Drawing the design of the partial denture.g- Preparation of the master cast for duplication

1.Blocking the undesirable tooth undercuts in wax.

2.Establishing the relief areas in wax.3.C-Making the ledges in wax.4.Blocking the tissue undercuts.

h-Duplication of the master cast into a refractory cast (investment cast). This is done by the use of agar-agar material in a duplicating flask.

i- Construction of the wax pattern on dried refractory cast.

j-Spruing, investing, wax elimination (burn out) and casting in metal (gold or Chrome cobalt alloy)

K-Pickling, finishing and polishing the metal framework.

l-Pouring of the functional impression, and construction of wax blocks.

m-Mounting the cast on an articulator and setting-up of artificial teeth

n- Flasking and Processing in acrylic resin.o- Finishing and polishing the acrylic denture.

Diagnosis of partially edentulous patients

Mostafa Fayad 1

EXAMINATION, DIAGNOSIS

AND TREATMENT PLANNING

Objectives of any prosthodontic treatment:

(1) The elimination of disease;

(2) The preservation, restoration, and maintenance of the health of the remaining teeth and oral tissues (which will enhance the removable partial denture design);

(3) The selected replacement of lost teeth for the purpose of restoration of function in a manner that ensures optimum stability and comfort in an esthetically pleasing manner.

Indications for a removable in preference to a fixed partial denture

A. Edentulous areas too long for a fixed prosthesis.

B. Need to restore soft and hard tissue contours.

C. Absence of adequate periodontal support.

D. Structurally or anatomically compromised abutment teeth.

1. Lack of clinical crown height.

2. Lack of sound tooth structure.

3. Unfavorable position, contour or inclination.

E. Need for cross-arch stabilization. F. Eed for an extension base.

G. Anterior esthetics.

H. Physical and emotional problems precluding fixed partial dentures.

1. Attitude and desires of patient.

J. Ease of plaque removal from the natural teeth and partial de ture.


Mostafa Fayad 2

BASIC CRITERIA FOR PATIENT SELECTION

A. Acceptable emotional and physical health.

1. Basic health observations. 2. Complete health history.

B. General physical and mental capacity to tolerate a prosthesis.

1. Previous number of prostheses. 2. Physical handicaps.

C. Degree of patient motivation.

1. General personal appearance.

2. Past oral hygiene habits and response to sug¬gested change.

3. Patient's desire to preserve remaining teeth and surrounding structures.

4. Physical and mental capabilities to augment motivation.

5. Patient's response to scientific evidence.

D. Patient's comprehension of pote - tia success or failure of treat¬ment.

E. Types and amounts of drugs or med-ications the patient co sumes including alcohol and tobacco.

F. Patient's dietary habits.

G. Periodontal health.

H. Oral indices of tissue tolerance.

Indicate the capacity of supporting structures to resist mechanical forces.

1. Muco-osseous (ridge) resistance. Bone index of the residual ridge (reaction of bone after extraction and ridge loading),

2. Dento-alveolar (abutment) resistance. Bone index around the abutment teeth (reaction of bone to increased force).

3. Soft tissue resistance to biological or mechan¬ical irritation.

I. Oral manifestations of pathology.

J. Consultations with other medical and dental specialists.


Mostafa Fayad 3

PURPOSE AND UNIQUENESS OF TREATMENT

The purpose of dental treatment is to respond to a patient's needs.Although there are similarities between partially edentulous patients, significant differences exist making each patient, and treatment, unique.

The delineation of each patient's uniqueness occurs through the patient interview and diagnostic clinical examination process. This includes fourdistinct processes:

(1) Understanding the patient's desires or chief concerns/complaints regarding their condition (including its history) through a systematic interview process.

(2) Ascertaining the patient's dental needs through a diagnostic clinical exam.

(3) Developing a treatment plan that reflects the best management of the desires and needs (unique to their medical condition or oral environment).

(4) Appropriately sequenced execution of the treatment with planned follow up.

Complex treatment planning often requires two appointments.

The first appointment includes

a preliminary oral examination (to determine the need for management of acute needs),

a prophylaxis,

full-mouth radiographs,

diagnostic casts, and

Mounting records if baseplates are not required.

The follow-up appointment includes

mounting of the diagnostic casts (when baseplates and occlusion rimsare needed),

a definitive oral evaluation,

review of the radiographs to augment and correlate with clinicalfindings,

arrangement of additional consultations where required,


Mostafa Fayad 4

I- FIRST DIAGNOSTIC APPOINTMENT

A. Patient interview:

B. Cursory (initial) examination

C. Oral prophylaxis

D. Collecting diagnostic data: • Photography • Radiography • Casts

II-SECOND DIAGNOSTIC APPOINTMENT

A-Definitive oral examination:

B-Radiographic survey

C-Analysis of mounted diagnostic casts:

D. Consultation requests:

E. Development of treatment plane.

III-TREATMENT PLANE IN RPD

Prosthodontic Diagnostic Index ( PDI ): see classification

The American College of Prosthodontists (ACP) has developed a classifi cation

system for partial edentulism based on diagnostic findings.


Mostafa Fayad 5

A ] PATIENT INTERVIEW

1- Structure of interview:

HISTORY TAKING

1.Personal history

2.Chief complaint

3.Phy health and medical history.

4.Psychological health.

5.Frequency of dent examinations.

6.Previous dental treatment.

7. Habits and type of Diet.

8. Patient expectations

2- Objectives:

a. Establishing of a rapport:

We should meet the mind of the patient before we meet his mouth.

b. Gaining insight into the psychological makeup of the patient

(patient attitude):

De Van stated, "Meet the mind of the patient before meeting the mouth

of the patient". Hence, we understand that the patient's attitudes and

opinions can influence the outcome of the treatment.

Dr. MM House proposed the first one in 1950, which is widely

followed. House's Classification Based on patient’s mental attitude,

The philosophical patients. (Well adjusted and easygoing)

The exacting patients. (Precise in everything they do)

The hysterical patients. (Are emotionally unstable and

convinced that they will never be able to wear a prosthesis)

The indifferent patients. (are uncooperative)


Mostafa Fayad 6

c. Evaluating the systemic disturbances that may affect the

patient’s treatment:

These systemic disturbances include the following:

� Diabetes

� Arthritis

� Paget’s disease

� Acromegaly

� Parkinson’s disease

� Pemphigus vulgaris

� Epilepsy

� Cardiovascular diseases

� Cancer

� Transmissible diseases

Systemic disturbances that can have a significant effect on the treatment

of the patient include the following:

Diabetes: multiple small abscesses and poor tissue tone frequently

accompany uncontrolled diabetes. The diabetic patient often has

excessive rate of bone resorption, hence, frequent relining may be

necessary. And reduced salivary output, which significantly reduced the

ability of patient to wear prosthesis with comfort, and increases the

possibility that caries will occur.

Vitamin deficiency which cause inflammation and bleeding of the

gingiva and fissures in the corners of the mouth.

Oral Malignancies: The most common oral complications of radiation

and chemotherapy for malignancies are mucosal irritation, xerostomia

and bacterial and fungal infections. Tissues having bronze colour and

loss of tonicity are not suitable for denture support. Once the dentures

are constructed, the tissues should be examined frequently for

radionecrosis.

Blood disease e.g. anemia; patients have pale mucosa, sore and red

tongue and gingival bleeding.

Transmissible diseases; e. g. hepatitis and tuberculosis pose a

particular hazard for the dentist, patients and dental auxiliaries.


Mostafa Fayad 7

Diseases of the Joints: patients with osteoarthritis affecting the finger

joints may find it difficult to insert and clean dentures. With limited

mouth opening and painful movements of the jaw, it becomes necessary

to use special impression trays. It may also become necessary to repeat

jaw relations and make post-insertion occlusal adjustments due to

changes in the joint.

Cardiovascular Diseases: Cardiac patients will require shorter

appointments.

Diseases of the Skin: Skin diseases like Pemphigus have oral

manifestations, which vary, from ulcers to bullae. Such painful

conditions make the denture use impossible without medical treatment.

Neurological Disorders: Diseases such as Bell's palsy and Parkinson's

disease can influence denture retention and jaw relation records. Add

sufficient bulk to buccal surface contour of maxillary RPD to support

flaccid muscles.

Climacteric Conditions :Climacteric conditions like menopause can

cause Tendency to gag, burning sensation, xerostomia, vagueareas of

pain, taste alterations , glandular changes, osteoporosis and psychiatric

changes in the patient.

Pernicious anaemia : Xerostomia , disturbance of taste sensation,

Susceptibility to denture trauma.

Chronic pulmonary disease : Shortness of breath,wheezing, increased

respiratory rate, persistent cough and Occlusal vertical dimension is

difficult to record because of patient ’ s tendency to mouth breathe.

Salivary gland disorders : Xerostomia, painful and burning mucosa

d . Evaluating the drugs that can affect prosthodontic treatment:


Mostafa Fayad 8

These drugs include the following:

*Anticoagulants

*Antihypertensive agents: cause decrease in salivary flow

*Endocrine therapy: cause sore mouth and discomfort

*Saliva-inhibiting drugs

*Dilantine: cause gingival enlargement

e. Dental history:

The cause of teeth loss: If the teeth were lost because of caries,

special emphasis will have to be placed on oral hygiene

procedures. If the teeth were lost because of periodontal disease,

every effort must be made to discover and eliminate its cause.

If a removable partial denture has been constructed previously for

the patient, it is important to learn as much as possible about the

patient' experience during and following treatment.

Expectation of treatment: If the patient has unrealistic expectation

e.g. a removable partial denture without major connector crossing

the palate) the patient expectation should be changed through

education.

Chewing habits: The patient is asked about the preferred and non

preferred side for chewing. This will determine the amount of

support, retention and bracing of the denture on each side.

Para functional habits: clinching and bruxism has adverse effect

on the denture supporting structures.

f. Ascertaining patient’s expectations of treatment, assessment of

patient motivation and attitudes towards dentures:


Mostafa Fayad 9

The patient's attitudes and psychological status of the patient have

considerable influence on the success of the treatment.

3- Obstacles:

a. From the dentist:

Not listening to the patient

Choicing words misunderstanding by the patient

Failure to use the obtained information in the treatment of the

patient

b. From the patient:

- Fearful of his condition - Lack of response

4- Aids for successful interview:

1. Dentist attitude and behaviour 2. Phrasing of questions

INFECTION CONTROL

Recommended Infection Control Practices for Dental Treatment

Gloves should be worn in treating all patients.

Masks should be worn to protect oral and nasal mucosa from

splatter of blood and saliva.

Eyes should be protected with some type of covering to protect

from splatter of blood and saliva.

Sterilization methods known to kill all life forms should be used

on dental instruments. Sterilization equipment includes steam

autoclave, dry heat oven, chemical vapor sterilizers, and chemical

sterilants.


Mostafa Fayad 10

Attention should be given to cleanup of instruments and surfaces

in the operatory. This includes scrubbing with detergent solutions

and wiping down surfaces with iodine or chlorine (diluted

household bleach solutions).

Contaminated disposable materials should be handled carefully

and discarded in plastic bags to minimize human contact. Sharp

items, such as needles and scalpel blades, should be contained in

puncture-resistant containers before disposal in the plastic bags.

B] Clinical examination

PATIENT EVALUATION

• Gait : People with neuromuscular disorders show a different gait.

Such patients will have difficulty in adapting to the denture.

• Age : patients belonging to the fourth decade of life will have good

healing abilities and patients above the sixth decade will have

compro¬mised healing.

• Sex : Male patients are generally busy people whoappear indifferent

treatment. They are only bothered about comfort and nothing else.On

the other hand, female patients are more critical about aesthetics

• Complexion and Personality : Evaluating the complexion helps to

determine the shade of the teeth. Executives require smaller teeth.

• Cosmetic Index : It basically speaks about the aesthetic expectations

of the patient. Based on the cosmetic index, patients can be classified

as:

Class I: High cosmetic index. They are more

concerned about the treatment and wonder if their

expectations can be fulfilled.


Mostafa Fayad 11

Class II: Moderate cosmetic patients. They are

patients with nominal expectations.

Class III: Low cosmetic index. These patients are not

bothered about treatment and the aes-thetics. It is

very difficult for the dentist to know if the patient is

satisfied with the treatment or not.

Extraoral examination

o Facial examination:

Facial Form

Facial Features

o Muscle Tone

o Muscle Development

o Complexion

o Lip Examination

o TMJ Examination

o Neuromuscular

Examination

Speech

Co-ordination

a-Facial Features :If the face appears collapsed, it indicates the loss of

vertical dimension (VD). Decreased VD produces wrinkles around the

mouth. Excessive VD will cause the facial tissues to appear stretched.

b. Complexion :The colour of the eye, hair and the skin guide the selection

of artificial teeth.

Oral Examination

A complete oral examination should precede any treatment decision. It

should include a visual and digital evaluation of the teeth and surrounding tissue

Sequence for Oral Examination


Mostafa Fayad 12

An oral examination should be accomplished in the following

sequence:

visual examination,

pain relief and temporary restorations,

oral prophylaxis,

radiographs,

evaluation of teeth and periodontium,

vitality tests of individual teeth,

determination of the floor of the mouth position,

and impressions of each arch.

Relief of pain and discomfort and placement of temporary

restorations

management of acute needs

relieve discomfort arising from tooth defects

Determine as early as possible the extent of caries and to arrest

further caries activity.

By restoring tooth contours with temporary restorations, the impression

will not be torn on removal from the mouth, and a more accurate diagnostic cast

may be obtained.

A Thorough and Complete Oral Prophylaxis

An adequate examination can be accomplished best with the teeth free of

accumulated calculus and debris. Also, accurate diagnostic casts of the dental


Mostafa Fayad 13

arches can be obtained only if the teeth are clean; otherwise the teeth reproduced

on the diagnostic casts are not a true representation of tooth and gingival contours.

Cursory examination may precede an oral prophylaxis, but a complete

oral examination should be deferred until the teeth have been thoroughly cleaned.

Initial (Cursory) oral examination

Objective:

1. Detection of problems requiring immediate attention

2. Evaluation of oral hygiene

3. Evaluation of caries susceptibility

4. Detection of oroantral or oronasal communications

5. Assessment of applied forces

1. Opposing occlusion.

2. Muscular force and elevator muscle development.

3. Parafunctional habits.

a. Clenching. b. Bruxism

4. Length of edentulous span.

5. History of prosthesis failure.

a. Solder joint failure. b. Porcelain failure.

c. Fractured RPD components.

6. History of poor tissue tolerance.

a. Chronic sore spots.


Mostafa Fayad 14

b. Excessive bone resorption.

c. Abutment tooth mobility.

d. Fracture or attrition of natural teeth.

e. Attrition, abrasion, erosion, abfraction

Definitive visual oral examination:

Complete oral examination to evaluate the following:

A] The teeth and periodontium:

1. Caries and existing restorations: All carious teeth must be restored prior to

starting definitive prosthodontic treatment,

2. Pulp to detect pulpitis or pulp necrosis

3. Sensitivity to percussion

4. Mobility and C/R ratio: The degree of mobility of all teeth should be

recorded using a scale commonly used for classifying mobility:

■ Class 1: A tooth demonstrates greater than normal movement, but less

than 1 mm of movement in any direction.

■ Class 2: A tooth moves 1 mm from normal position in any direction.

■ Class 3: A tooth moves more than 2 mm in any direction, including

rotation or depression. A change from normal physiologic movement may

indicate traumatic occlusion or periodontal disease. Teeth exhibiting

Class 3 mobility have a poor prognosis and usually will require

extraction.

Causes:

Trauma from occlusion


Mostafa Fayad 15

Inflammatory changes of the PDL

Loss of alveolar bone support

Treatment:

Scaling

Learning and ascertaining good oral hygiene

Splinting when:

• All the remaining teeth have reduced support

• Only two or three widely spaced retainable teeth

• The first premolar and all molars have been lost and the

second premolar is to serve as the abutment

5. Periodontium:

The health of the PDL is determined by findings that need periodontal

treatment are:

1. Pocket depth in excess of 3 mm

2. Furcation involvement

3. Deviations from normal colour and contour in gingiva indicating

gingivitis

4. Marginal exudate

5. Less than 2 mm of attached gingiva

6. Pulling of muscle or frena on attached gingiva


Mostafa Fayad 16

B] . Oral mucosa:

Pathologic changes

Tissue reactions to the wearing of old prosthesis:

Soft tissue displacement

Palatal papillary hyperplasia: It is associated most often with a

poorly fitting prosthesis that has been worn for a prolonged

periods. It consists of numerous small papillary growths.

Epulis fissuratum: It is a tumour like hyper plastic growth in the

sulcus caused by an ill- fitting or overextended border of a

removable prosthesis.

Denture stomatitis: It is characterized by generalized

erythematic for all the tissues covered by the prosthesis.

Candida albicans has been shown to be present in much higher

percentage of denture stomatitis. Traumatic occlusion, poor fit

of the prosthesis, poor oral hygiene and continuous wearing of

the prosthesis have all been suggested as contributing factors to

this condition.

C]. Hard tissue abnormalities:

Torus palatinus: Removal of a torus palatinus is not usually necessary; a

major connector can be designed to circumvent the torus.

Torus mandibular. It is exostoses, usually occurring bilaterally on the

lingual surface of the body of the mandible.

Undercuts and bulbous maxillary tuberosities:

The effect of some undercut areas may be minimized by:

o Change in the path of insertion of the RPD in case of unilateral undercut.


Mostafa Fayad 17

o Relieving the denture base or reducing the length of the denture border

o Surgical correction of undercuts.

o Flexible denture base or flexible border

o Reduce length of denture border

The mylohyoid ridge: Some of these ridges are felt to be

pronounced and the soft tissue covering is thin and is easily

traumatized by insertion and removal of prosthesis.

D]. Soft tissue abnormalities:

Labial frenum: If the frenum is attached highly at the crest of the

ridge, or it was bulky, the notch in the maxillary denture should be

done to accommodate this frenum shape and position.

Lingual frenum: It can greatly compromise the rigidity and

adjustement of the major connector.

Flabby gingiva: Atrophy of the residual ridge does occur

occasionally, and the gingiva loses its bony support and becomes

freely, Tnis area should be evaluated to determine whether it requires

conservative treatment or surgical removal.

Tongue size & mobility: The tongue should be examined for :

• Size: Presence of a large tongue decreases the stability of lower

denture and ate also a hindrance to impression making. Tongue-biting is

common after insertion of the denture. A small tongue does not provide

adequate lingual peripheral seal.

• Movement and coordination: Tongue movements and coordination

are important to register a good peripheral tracing. They are also

necessary in maintaining the denture in the mouth during functional

activities like speech, deglutition and mastication, etc.

E] Occlusal relationships:

It is the relation between the opposing teeth and between the teeth and


Mostafa Fayad 18

the opposing ridge is examined for.

a- Available interarch space for placement of artificial teeth.

b- The degree of anterior vertical overlap.

c- Super eruption and tilting of the remaining teeth.

d- Cuspal interference.

F] - Temporomandibular joint (TMJ) examination:

TMJ disorders can be detected by one or more of the following signs:

a- Reduced inter incisal opening (Normal maximum opening is 55mm +

15mm).

b- Pain and tenderness over the TMJ at rest and during movement.

C- Clicking during opening and closing.

d- Midline deviation during wide opening.

e- Muscle pain and tenderness.

f- Headache and ear pain.

G]. Quality and quantity of saliva:

� Dry mouth >>>> no lubricating effect >>>> saliva substitute

� Thick and ropy saliva or copious amounts of serous saliva

>>>> problems during impression.

Thick ropy saliva alters the seat of the denture because of its tendency

to accumulate between the tissue and the denture. Thin serous saliva

does not produce such effects.

Xerostomic patients show poor retention and excessive tissue

irritation whereas excessive salivation complicates the clinical

procedures. use of synthetic saliva, with a carboxymethyl cellulose

base, which can be enriched with fluoride in an effort to counteract

caries. Frequent use provides an excellent means of maintaining high


Mostafa Fayad 19

fluoride intraorally for long periods of time, thus enhancing the

remineralization of incipient caries.

H] . Space for mandibular major connector:

The superior margin of the connector should be located 3 mm

below the free gingival margins of the mandibular teeth >>>>>

to avoid damage to the gingival tissues.

The inferior border of the connector should be positioned at or

slightly above the position of the active floor of the mouth

>>>>> to prevent interference with the functional movements

of the floor of the mouth and to help avoid the packing of food

under the major connector.

A minimum of 7 to 8 mm. of space should be available if a

lingual bar major connector is to be used. Available space is

measured with a calibrated periodontal probe (William's

probe) , while the patient raising the tongue toward the palate.

Measurements are made at several positions; the probe is then

used to transfer it to the cast.

I] Oral hygiene and caries susceptibility:

Evaluation of patient's oral hygiene is critical to the prognosis of the

patient's treatment. Disclosing tablets or solution is used to detect plaque,

which will indicate the patient motivation towards oral hygiene.

The presence of large number of restored teeth, signs of recurrent caries

and evidence of decalcification indicate that the patient is susceptible to caries.

J]. Modification Spaces

For short spans (<=3 missing teeth), natural tooth, implant-

supported fixed prostheses, and removable partial dentures can generally

be considered.


Mostafa Fayad 20

Longer span modification spaces (>=4 missing teeth) present a

greater challenge for natural tooth-supported fixed prostheses.

Consequently, the options for treatment are the removable partial denture

or the implant supported prosthesis.

K] Abutments With Guarded Prognoses

If the prognosis of an abutment tooth is questionable, or if it becomes

unfavourable during treatment, it might be possible to compensate for its

impending loss by a change in denture design.

It is sometimes possible to design a removable partial denture so that a

single posterior abutment, about which there is some doubt, can be retained

and used at one end of the tooth-supported base. Then if the posterior abutment

is lost, it could be replaced by adding an extension base to the existing denture

framework. Such an original design must include provisions for future indirect

retention, flexible clasping of the future abutment, and provision for

establishing tissue support.

Anterior abutments that are considered poor risks may not be so freely

used because of the problems involved in adding a new abutment retainer when

the original one is lost. It is rational that such questionable teeth be condemned

in favor of more suitable abutments, even though the original treatment plan

must be modified accordingly.

Kennedy Class II, mod I in which molar abutment has a guarded prognosis. Premolar clasp assembly is a

mesial rest, distal guide plane, and wrought wire retainer design that will accommodate future distal extension

movement.


Mostafa Fayad 21

L] Examination of old denture:

a- the design and quality of construction should be noted and any associated

problems in relation to gingival and mucosal inflammation or to decalcification

of contacting tooth surfaces.

b- It is important to evaluate whether the denture is still fit accurately against

the teeth and under lying mucosa or not.

C -Radiographic survey:

1. Complete mouth periapical and bite-wing survey.

2. Panoramic.

3. Obtain previous radiographs if possible for purpose of comparison.

1. Examination of residual ridge to evaluate:

All radiolucent and radiopaque areas that vary from normal ranges

to determine whether a pathologic condition is present.

Root fragments and other foreign bodies to determine whether

their removal is indicated.

Un erupted third molars to determine whether they should be

retained or removed.

Evaluate quantity of bone.

oAlveolar.

oResidual ridge.

oBasal.

a. Bone Index (bone factor):

The bone factor provides an assessment of the relative response

of bone to stimulation or irritation. This assessment is made by

analyzing bone index areas.

Bone index areas are those areas of bony support which disclose

the reaction of bone to increased force, e.g. areas of bone around

abutment teeth or any other teeth subjected to increased loading.


Mostafa Fayad 22

These areas are compared to areas of bone around teeth in

normal function without increased loading.

A similar consideration may be given to the residual ridge or an

edentulous area of bone supporting a complete or an extension base

removable partial denture.

Evaluation of past response is important in predicting the future

potential for dento-alveolar (abutment teeth) and muco-osseous (ridge)

resistance to forces transmitted by an RPD.

The bone index is difficult to determine from radiographs alone.

The history of the patient is important in evaluating the rate of

resorption that may be expected based on previous occurrences. The

length of time from previous extractions together with morphological

changes in the residual ridge gives some indication of the host response

to various forces.

b. Bone Density

Denser bone (more highly mineralized) offers greater resistance to

resorption. The reduced rate of resorption of cortical bone compared to

cancellous bone is likely due to the degree of cellularity and

mineralization, which may influence metabolic activity, as well as to bone

factors. These factors appear to account for the pattern of resorption of the

residual ridges in the edentulous or partially edentulous patient.

In the mandibular arch the external oblique ridge, the mylohyoid ridge

and the genial tubercles, which are areas of muscle attachments, continue

to resist resorption even when the residual ridge is greatly resorbed.

The presence of dense cortical bone is often the result of applied forces

arising from ligamentous or muscle attachments which provide tension to

the underlying bone.

c. Extrinsic bone factors. Localized forces applied to bone.


Mostafa Fayad 23

1. Pressure-Bone tends to resorb in response to compressive forces.

The rate of resorption most likely depends on the bone density,

intrinsic bone factors, and the nature of the applied forces and on the

interaction of pressure and tension. The remodelling that occurs under

the extension base of a removable partial denture is an example of

pressure induced resorption.

11. Tension-Bone under tensional stimuli tends to increase in density

and in some instances may increase in quantity. The lamina dura is a

response to tensional forces transmitted by the periodontal ligament.

Orthodontic movement of teeth is a good example of the pressure -

tension theory. The lamina dura resorbs on the pressure side and bone

apposition occurs on the opposite side.

d. Intrinsic bone factors which May influence the rate of resorption.

Genetic.

Hormonal.

Nutritional.

Pathologic.

Biochemical.

Other.

Wolff’s law of bone physiology-

Intermittent stimulation can cause bone apposition, constant stimulation

(irritation) causes bone resorption

Theilmann’s diagonal law of occlusion-

An interceptive posterior occlusal contact can cause elongation of the

teeth in the arch diagonal to the prematurity

2. Examination of remaining teeth with special attention focused on

prospective abutments to evaluate:

The presence and extent of caries and the relation of the carious lesion

to the dental pulp


Mostafa Fayad 24

Existing restorations to determine the adequacy of proximal contours

and the presence of overhanging or deficient margins and recurrent

caries.

Root canal fillings: an abutment for a distal extension that is

endodontically treated carries a greater risk for complications than a

similar tooth not involved in removable partial denture function.

Root length, size and form

Teeth with multiple and divergent roots will resist stresses better

than teeth with fused and conical roots, because the resultant

forces are distributed through a greater number of periodontal

fibers to a larger amount of supporting bone

C/R ratio: The radiographic crown - root ratio is a commonly used

index for classifying the degree of existing support for teeth being

evaluated as probable abutments.

The length of the tooth occlusal from the crest of the alveolar

bone is compared with the length of the tooth root apical from the

alveolar crest, and the comparison is expressed as an approximate ratio.

A tooth with normal, undiminished alveolar support will have a

crown - root ratio of approximately 1:2. As a general diagnostic guide, a

tooth with a crown - root ratio of more than 1:1 is considered to have an

unfavorable prognosis as an abutment tooth.

Unerupted third molars: should be considered as prospective future

abutments to eliminate the need for a distal extension removable partial

denture

PDL space: The width of the periodontal ligament around the roots of

the teeth is of significance in evaluating the stability of the teeth. A thin,

uniform ligament space is a more favorable sign than is a widened,

irregular space.


Mostafa Fayad 25

Widening in periodontal ligament space: indicate trauma,

mobility or heavy function

Lamina dura: The lamina dura is the thin layer of hard cortical bone

that normally lines the sockets of all teeth. In a roentgenogram, the

lamina dura is shown as a radiopaque white line around the radiolucent

dark line that represents the periodontal membrane.

Uneven lamina dura: During the active tipping process, the

lamina dura is uneven, with evidence of both pressure and tension on the

same side of the root. For example, in a mesially tipping lower molar the

lamina dura will be thinner on the coronal mesial and apicodistal aspects

and thicker on the apicomesial and coronal distal aspects because the

axis of rotation is not at the root apex but is above it. The lamina dura on

the side to which the tooth is sloping becomes uniformly heavier, which

is nature's reinforcement against abnormal stresses.

Partial or total absence of lamina dura may be found in

systemic disorder as: hyperparathyroidism and Paget disease. When

systemic disease is associated with faulty protein metabolism and when

the ability to repair is diminished, bone is resorbed and the lamina dura

is disturbed. Therefore the loading of any abutment tooth must be kept

to a minimum inasmuch as the patient's future health status and the

eventualities of aging are unpredictable.

Thickening of lamina dura : occur if the tooth is mobile , has

occlusal trauma or is under heavy function.

D] DIAGNOSTIC CASTS

Impressions should be made for making accurate diagnostic casts to be

mounted for occlusal examination.

A diagnostic cast should be an accurate reproduction of all the

potential features that aid diagnosis. These include the teeth locations, contours,

and occlusal plane relationship; the residual ridge contour, size, and mucosal

consistency; and the oral anatomy delineating the prosthesis extensions


Mostafa Fayad 26

(vestibules, retromolar pads, pterygomaxillary notch, hard and/or soft palatal

junction, floor of the mouth, and frena). Additional information provided by

appropriate cast mounting includes occlusal plane orientation and the impact on

the opposing arch; tooth-to-palatal soft tissue relationship and tooth-to-ridge

relationship, both vertically and horizontally.

A diagnostic cast is usually made of dental stone because of its strength,

and it is less easily abraded than is dental plaster.

The diagnostic cast impression is usually made with an irreversible

hydrocolloid (alginate) in a stock (perforated or rim lock) impression tray.

Purposes of accurate diagnostic casts:

1. Analysis of the contour of hard and soft tissues of the mouth

2. Preliminary design of the partial denture .Determine of the types of

restorations to be placed on the abutment teeth

3. Determine the need for surgical correction of exostoses, frena,

tuberosities and undercuts

4. Used to permit a topographic survey of the dental arch that is to be

restored by means of a removable partial denture and the proposed design

is drawn on them. To determine the need for mouth preparation including

(a) Proximal tooth surfaces, which can be made parallel to serve as

guiding planes;

(b) Retentive and non retentive areas of the abutment teeth; (c)

areas of interference to placement and removal; and

(d) Esthetic effects of the selected path of insertion.

5. Serve as a plan for the placement of restorations, the recontouring of

teeth, and the preparation of rest seats.


Mostafa Fayad 27

6. Designed casts aid in the presentation of the proposed treatment to the

patient.

7. Permitting a view of the occlusion from the lingual and buccal

aspects.

8. Individual impression trays may be fabricated on the diagnostic casts

8. Used as a constant reference as the work progresses. Pencilled marks

indicating the type of restorations, the areas of tooth surfaces to be

modified, the location of rests, and the design of the removable partial

denture framework along with the path of placement and removal, all may

be recorded on the diagnostic cast for future reference

9. Diagnostic casts on a suitable articulator permit analysis of:

Occlusion,

The adequacy of interarch space

The presence of over erupted or malposed teeth

The presence of tuberosity interferences.

10. Unaltered diagnostic casts should become a permanent part of the

patient's record because records of conditions existing before treatment

are just as important as are preoperative radiographs.

Analysis of mounted diagnostic casts:

The mounted diagnostic casts provide visual access from all directions and

enable the dentist to make a detailed analysis of the patient’s occlusion.

1. Mounting of maxillary cast to articulator

It is better that the casts be mounted in relation to the axis-orbital

plane to permit better interpretation of the plane of occlusion in relation to

the horizontal plane. Although it is true that an axis orbital mounting has


Mostafa Fayad 28

no functional value on a nonarcon instrument because that plane ceases to

exist when opposing casts are separated, the value of such a mounting lies

in the orientation of the casts in occlusion. MAC

2. Jaw Relationship Records for Diagnostic Casts (Vertical dimension of

occlusion and centric jaw relation record)

One of the first critical decisions that must be made in a removable

partial denture service involves the selection of the horizontal jaw

relationship to which the removable partial denture will be fabricated

(centric relation or the maximum intercuspal position).

It is recommended that deflective occlusal contacts in the maximum

intercuspal and eccentric positions be corrected as a preventive measure.

If most natural posterior teeth remain—and if no evidence of

TMJ disturbances, neuromuscular dysfunction, or periodontal

disturbances related to occlusal factors exists—the proposed

restorations may safely be fabricated with maximum

intercuspation of the remaining teeth. When diagnostic casts are

hand related by maximum intercuspation for purposes of

mounting on an articulator, it is essential that three (preferably

four) positive contacts of opposing posterior teeth are present,

having wide spread molar contacts on each side of the arch.

When most natural centric stops are missing, the proposed

prosthesis should be fabricated so that the maximum intercuspal

position is in harmony with centric relation. Correction of the

remaining natural occlusion to create a coincidence of centric

relation and the maximum intercuspal position is indicated in

such situations.

Clinical situation suggest construction of partial denture at centric

relation:


Mostafa Fayad 29

1- Absence of posterior tooth contact

2- When all posterior tteeth will be restored with fixed

restoration

3- Few remaining posterior contacts

4- Clinical symptoms of occlusal trauma

5- Coincidence of centric jaw relation and maximum

intercuspal position

Materials available for recording centric relation are

(1) wax;

(2) modeling plastic;

(3) quick-setting impression plaster;

(4) metallic oxide bite registration paste;

(5) polyether impression materials;

(6) silicone impression materials.

3. Inspection of:

Occlusal plane

Occlusion

Tipped or malposed teeth

Traumatic vertical overlap

The presence of tuberosity

interferences

interarch space

Malrelation of jaws

Diagnostic wax up

Interarch distance

Lack of sufficient interarch distance for the placement of artificial teeth:

Caused by


Mostafa Fayad 30

A maxillary tuberosity that is too large in vertical height.

A segment of teeth that has been unopposed for a prolonged period will

frequently overerupt, carrying the alveolar process with it. Subsequent

removal of the teeth will produce a situation in which it is impossible to

establish a functionally and aesthetically acceptable plane of occlusion.

Management

The surgical reduction of the vertical height of the tuberosity and at times

the adjacent residual ridge is necessary if satisfactory replacement of the

missing teeth is to be accomplished. The area and amount of tissue that should

be removed can be indicated on the diagnostic east. This provides an excellent

guide for the oral surgeon or dentist who performs the surgical correction. The

radiographs are a valuable aid in planning the surgical of fibrous tissue.

Healing is usually complete in 7 to 10 days. The healing period is extended to 2

to 5 weeks when bone removal is necessary.

Maxillary tuberosity interferences.

The maxillary tuberosity area may be undercut on one or both

sides.

The path of insertion of a complete denture can usually be compatible

with an unilateral tuberosity undercut, but a removable partial denture, with a

more controlled path of insertion, presents greater problems.

Management

The undercut must be evaluated with the aid of the dental surveyor.

With the cast on the surveying table at the predetermined path of insertion, a

determination is made as to the amount of relief that will be required in the

denture if the undercut is not reduced. Moderate to severe tuberosity undercuts

usually require surgical correction with bone removal.

bulbous tuberosities


Mostafa Fayad 31

Occasionally the tuberosities are so bulbous that the coronoid process

of the mandible may actually rub against the tuberosity during functional

movements.

Management

Surgical reduction of such a tuberosity is necessary if the patient is to

wear a removable partial denture.

Occlusal plane

1. Irregular occlusal plane: (because extrusion of one or more unopposed

teeth)

Management

Available treatments depend on the degree of extrusion and the condition of the

tooth:

• Enameloplasty can effectively reduce a moderately extruded tooth.

Approximately 2 mm of enamel can be removed in many situations. At times

the reduction of a single cusp improves the occlusal plane.

• Placement of an extracoronal cast metallic restoration If the extrusion is

greater than 2 mm or if the tooth does not lend itself to enameloplasty, The

degree of reduction is limited as much or more by the clinical crown length of

the tooth as by the size of the dental pulp.

The clinical crown length can often be increased by appropriate

periodontal therapy if crown lengthening is needed to obtain adequate retention

for the restoration. Useful crown lengthening procedures include tissue

shrinkage, gingivectomy, apical positioning flaps, and osseous surgery.

• Endodontic therapy and crown, when sever reduction to be made.

Extruded teeth can also be repositioned through orthodontic tooth movement

procedures.


Mostafa Fayad 32

• Severely extruded teeth such as those contacting the opposing ridge present

greater problems. If the alveolar bone has followed the eruption of the

offending tooth, it may be necessary to extract the tooth and remove the

surrounding bone.

• At times endodontic treatment and & drastic reduction of the tooth will enable

it to be used as an overdenture abutment. This treatment can provide valuable

support for a distal extension base. Extruded teeth must always be evaluated

with the occlusal plane in mind.

• Retention of a tooth that will jeopardize the development of a functional and

aesthetic occlusal plane is rarely justified.

2. Malposed occlusal plane: (because of extrusion of an entire segment of an

arch with concomitant drop of the alveolar process):

Extrusion of maxillary molars or premolars, or both, with drop of the alveolar

process till contact the opposing residual ridge, causing obvious space

problems and malposition of the occlusal plane.

Management

• One approach to treatment is the removal of the extruded teeth in

conjunction with an extensive alveolectomy.

• Consideration should be given to the use of one of the newer orthognathic

surgical procedures. A posterior segmental osteotomy can be effective in

correcting the problem. Close cooperation and communication between the

prosthodontist or dentist and the oral surgeon are essential. Because the dentist

must construct the prosthesis for the postsurgical tooth and ridge relations, he

should determine the ideal position of the segment. The oral surgeon must

determine the procedures and techniques to employ in making the correction.


Mostafa Fayad 33

Anterior maxillary osteotomy can also be effective in repositioning the

anterior teeth and alveolar ridge for patients with severe protrusion of the

anterior teeth or deep vertical overlap.

Malrelation of jaws:

Severe malrelation of the jaws can prevent the restoration of adequate function

and esthetics.

Management:

Several maxillary and mandibular osteotomy procedures are useful in

correcting these problems. Close cooperation, consultation, and communication

between the prosthodontist or dentist and the oral surgeon are essential in

treating patients with malrelation of the jaws.

Tipped or malposed teeth

Management:

• Limited orthodontic procedures for minor tooth movement can be used to

upright the tipped tooth to allow the placement of an artificial tooth of more

normal size.

• Teeth in severe buccoversion or linguoversion should be evaluated. At times

the removal of the malposed tooth will simplify the design of the prosthesis.

Traumatic vertical overlap

Classification:

Akerly (1977) has classified traumatic vertical overlap into the following

four basic types:

Type I -The mandibular incisors extrude and impinge into the palate.

Type II-The mandibular incisors impinge into the gingival sulci of the

maxillary incisors.


Mostafa Fayad 34

Type Ill-Both maxillary and mandibular incisors incline lingually with

impingement of the gingival tissues of each arch.

Type IV-The mandibular incisors move or extrude into the abraded

lingual surfaces of the maxillary anterior teeth.

Clinical symptoms:

Abrasion,

Mobility,

Migration of the teeth,

Inflammation and ulceration of the gingiva and oral mucosa.

Management:

1. Early recognition and treatment with orthodontic or combined

orthodontic and orthognathic surgery.

2. Establishing stable occlusal contacts at centric jaw relation

3. With advanced clinical symptoms, the removal of teeth is indicated.

Alveolectomy at the time of extraction will help provide space for some

improvement.

4. If the teeth are retainable, reduction of the length of the mandibular

anterior teeth will relieve symptoms temporarily.

5. A treatment prosthesis that plates the lingual surfaces of the maxillary

anterior teeth must be used to prevent further extrusion of the mandibular

incisors until more definitive treatment can be accomplished.

6. Definitive treatment is based on:

The degree of horizontal overlap,

The number and the occlusal relationships of the remaining teeth


Mostafa Fayad 35

The health of the supporting structures.

The need for RPD and its type and location.

� If all the maxillary teeth are present and have healthy support, it may

be possible to build up the cingula of the anterior teeth with cast

restorations >>>>> not feasible if the horizontal overlap is too great.

� If a maxillary removable partial denture is indicated, the major

connector can be extended onto the lingual surfaces of the anterior

teeth with a thin plate of metal >>>>> a vertical stop to prevent further

eruption of the mandibular anterior teeth.

� If only a mandibular removable partial denture is required, a lingual

plate major connector can be designed to prevent continued eruption of

the anterior teeth. The plating should cover the cingula of the teeth

with projections extending to the contact points. Rest seats should be

placed on the canines or first premolars to prevent labially directed

forces from being applied to the teeth.

Occlusion

The mounted diagnostic casts are also used for an evaluation of the patient’s

occlusion. The information obtained from the analysis of the occlusion should

be correlated with other clinical findings.

Occlusal interferences:

Partially edentulous patients have an even greater probability of having

premature occlusal contacts because of the drifting and migration of teeth that

usually accompany the loss of continuity of the dental arch.

Bruxism:

Severe bruxism can injure the teeth, the periodontium, and the

Temporomandibular joint and may initiate muscle spasm, pain, or discomfort.


Mostafa Fayad 36

The most common causes of bruxism are:

1. Occlusal interferences between centric jaw relation and centric

occlusion and

2. Balancing side contacts.

The clinical symptoms of traumatic occlusion follow:

• Excessive wear of the teeth, which may include chipping or

fracture of the teeth.

• A change in, or a loss of, the supporting structures, which may

include increased mobility, tooth migration, and pain during and

after occlusal contact.

• Involvement of the neuromuscular mechanism of the

temporomandibular joint, which may include muscle spasm,

muscle pain, and joint symptoms.

The radiographic signs of traumatic occlusion follow:

• Widening of the periodontal ligament space with either

thickening or loss of lamina dura.

• Periapical or furcation radiolucency.

• Resorption of alveolar bone.

• Root resorption.

Management of occlusal interferences and bruxism:

Occlusal equilibration: it is the selective grinding or coronal

reshaping of teeth with the intent of equalizing occlusal stress,

producing simultaneous occlusal contacts, or harmonizing cuspal

relations.


Mostafa Fayad 37

Occlusal equilibration should not be accomplished for every

patient with occlusal interferences. Many patients have a great

enough resistive capacity that occlusal forces are not destructive

regardless of the occlusal relationships of the teeth. If occlusal

equilibration were accomplished on these individuals, an “occlusal

sense or continued “awareness of the occlusion” may be developed

E. Consultation requests:

A.THE PATIENT SHOULD BE MADE AWARE OF THE FOLLOWING.

1. The nature and severity of the existing dental problems.

2. Any limitation in function, phonetics, esthetics, and longevity related to the

prosthesis.

3. The physical aspects of the prosthesis with regard to bulk and tissue

coverage.

4. Any treatment options that may be considered.

5. The risks, benefits and alternatives related to any treatment plan.

B . PATIENT MUST UNDERSTAND AND ACCEPT RESPONSIBILITY

FOR PREVENTIVE HOME CARE AND PROFESSIONAL RECALL.

F. Development of treatment plane:


Mostafa Fayad 38

III-TREATMENT PLANE IN RPD

Elimination of Infection

Sources of infection like infected necrotic ulcers, periodontally weak

teeth, and nonvital teeth should be removed. Infective conditions like

candidiasis, herpetic stomatitis, and denture stomatitis should be treated and

cured before commencement of treatment.

Elimination of Pathology

Pathologies like cysts and tumours of the jaws should be removed or

treated before complete denture treatment begins. The patient should be

educated about the harmful effects of these conditions and the need for the

removal of these lesions. Some pathologies may involve the entire bone. In

such cases, after surgery, an obturator may have to be placed along with the

complete denture.


Mostafa Fayad 39

Preprosthetic Surgery

Preprosthetic surgical procedures enhance the success of the denture.

Some of the common preprosthetic procedures are:

Labial frenectomy.

Lingual frenectomy.

Excision of denture granulomas.

Excision of flabby tissue.

Reduction of enlarged tuberosity.

Alveoloplasty.

Alveolectomy

Reduction of genial tubercle.

Reduction of mylohyoid ridge.

Excision of tori.

Vestibuloplasty.

Lowering the mental foramen.

Ridge augmentation procedures.

Implants

Tissue Conditioning

The patient should be requested to stop wearing the previous denture for

at least 72 hours before commencing treatment. He/she should be taught to

massage the oral mucosa regularly.

Special procedures should be done in patients who have adverse tissue

reactions to the denture. Denture relining material should be applied on the

tissue side of the denture to avoid denture irritation. Treatment dentures or

acrylic templates can be prepared to carry tissue-conditioning material during

the treatment of abused tissues.

Nutritional Counseling

Nutritional counseling is a very important step in the treatment plan of a

complete denture. Patients showing deficiency of particular minerals and


Mostafa Fayad 40

vitamins should be advised a proper balanced diet. Patients with vitamin B2

deficiency will show angular cheilitis. Prophylactic vitamin A therapy is given

for xerostomic patients. Nutritional counseling is also done for patients show-

ing age-related changes such as osteoporosis.

PROSTHODONTIC CARE

The type of prosthesis, denture base material, anatomic palate, tooth

material and teeth shade should be decided as a part of treatment planning.

Depending upon the diagnosis made, the patient can be treated with an

appropriate prosthesis. For example:

For a patient with few teeth, which are likely to be extracted an immediate

or conventional, definitive or interim, implant or soft tissue supported

dentures can be given.

For patients with acquired or congenital deformities, a denture with an

obturator can be given.

In addition to the initial diagnosis the success or failure of denture

depend on also the treatment planning. In partially edentulous patient, there are

5 alternatives

1-fixed bridge.

2-removable partial denture

3-complete denture .

4-any combination.

5-leave condition as it.

6.Overdenture

1-fixed bridge

Indication:

A-GENERAL INDICATIONS:


Mostafa Fayad 41

1-for eliminating psychological trauma.

2-in pt suffering from sudden bout of unconsciousness as in epilepsy.

3-for orthodontic needs.

4-as apart of overall periodontal and occlusal therapy.

5-for better correction of speech.

6-for better function and stability.

B-LOCAL INDICATIONS:.

1-healthy abutments with suitable c/r ratio.

2- if the abutment requires restoration.

3- short span.

4-lack of space for a suitable replacement.

5-if the morphology of the abutment need changing.

6-unfavourable angulations of the teeth for R P D ( Telescopic bridge)

Contraindication:

A-GENERAL CONTRAINDICATIONS:

1-inability of the patient to cooperate.

2-young or very old patient.

In young, poor prognosis because of:

• Short clinical crown

• Large pulp

• High caries rate

• Increase liability to trauma

• some teeth are not in

occlusion

• incomplete growth of the

bone of the jaw


Mostafa Fayad 42

in very old patient :

• lack of P.D.L resiliency

• increase abrasion

• poor cooperation

• the expectation of life short

• excessive bone resorpation

3- contraindication to L.A

4- high caries rate

5-gingival and periodontal disease

6- bad oral hygiene

7- un favorable reaction to the M.M

B- LOCAL CONTRA INDICATION

1- long span

2- when the bridge will occlude with opposing teeth on its end or 1/2 or less of

its length

3- unfavorable supporting structures of the abutment

4- any apical infection

5- insufficient effective root surface area

6- weak crowns or small formed abutment

7- deep sub gingivally carious abutment

8- extensive bone resorpation of edentulous ridge

9- unfavorable tilting or rotation of abutment

10- increase possibility of further tooth loss in the same arch

11- if the form of the bridge is an arc of a circle


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12- abnormal occlusion, abnormal forces

2-Complete denture

Indication:

1-poor abutment

2- poor oral hygiene and rampant decay

3- cosmetically unacceptable ant. Teeth

4- rejection of professional advice

5- refusal mouth preparation

6- poor alignment

7- radiation therapy

3- Removable partial denture

Indicaton

1-long span with well supported abutment

2- free end saddles

3- multiple missing ant. teeth

4- weak abutment

5- presence of deep subgingival caries on abutment

6- increased caries index

7- need of cross arch stabilization (bracing) of remaining teeth

8- immediate replacement


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9- excessive bone loss

10- need for complete denture in future( due to increase possibility of further

tooth loss)

11- physical or emotional problems of pt.

12- patient desire (economic and time and preserve of sound teeth )

13- youth (< 17 y.) and old age

14- restore facial contour

15- alteration vertical dimension

16- transitional prosthesis

17- obdurate palatal cleft

18- extreme atrophic ridge

19- patient with previous unsatisfactory prosthetic

20- diabetic pt

Containdications:

A-Intraoral contraindication

1-poor oral hygiene

2- advanced P.L disease

3- increase caries rate

4- if morphology of abutment need changing (fixed)

5- unfavorable angulations of the teeth

6- short span (fixed)

B-Patient contraindication


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1- un cooperative pt.

2- with sudden pouts & unconsciousness or fits

3- low and bad attitude

4- poor general health

5- patient unable to pay money

EXTRAORAL FACTORS THAT INFLUENCE TYPE OF

PROSTHODONTIC SURFACE:

1-AGE:

a- young patient under 25 y.

• Not be rendered completely edentulous.

• Avoid extraction

• Age of man chronologic

Physiologic

psychologic

b- old patient :

need special care.

2-GENERAL HEALTH:

• Poor health : trauma

• Interim partial denture : prostheses of choice

• Temporary partial denture instead of fixed partial denture

• Rebase and relief & tissue materials need

3- SEX:


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Female:

• Higher vanity index

• Avoid loss of teeth and age changes

• Need more esthetics ( P A P D avoid R P D )

• First look is very important

4- ECONOMIC CONSIDERATION

R P D may need root canal treatment and crown inlays thus more cost.

5- SOCIOECONOMIC BACKGROUND

6- DESIRES AND ATTITUDE OF PATIENT

7- OCCUPATIONAL FACTORS

8- TIME FACTORS

Removable partial denture . may be used for long term prognosis, the best

R.P.D, service for many years.

Or for short term prognosis and in future the patient need complete denture,

must be simple in design and permit the addition of future teeth (additive

partial denture)

This temporizing treatment gives the patient experience in denture wearing and

in adaptation to artificial dentition.

The additive partial denture is particularly indicated in lower jaw. It is a

devisable to retain standing lower teeth, especially single standing canines to

delay recourse to the full lower denture and preserve the alveolar ridge

( support ). Overdenture: partial or complete overdenture


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Clinical factors related to metal alloys used for removable partial denture

frameworks: see denture base

Various alloys can be considered for use, Practically all cast frameworks

for removable partial dentures are made from a chromium-cobalt alloy.

The choice of the alloy from which the framework of a removable

partial denture will be constructed is logically made during the treatment-

planning phase.

Mouth preparation procedures, especially the recontouring of abutment

teeth for the optimum placement of retentive elements, depend to a large extent

on the modulus of elasticity (stiffness) of a particular alloy.

Questions

1. Disscuss factors affecting selection the type of prostheses

2. Mention types of removable prostheses

BIOMICHANICS OF REMOVABLE PARTIAL DENTURE

Definition: The relationship between the biologic behavior of oral structures and the physical influence of an R P D.

Bio ------ pertaining to living systems-----inflammation, Caries, b. resorption….etc

Mechanical ----- related to forces and its application to object-----looseness of teeth , bon resorption……etc

Mechanics may be classified into two general categories: Simple & complex.

Complex machines are combination of many simple machines.

There are six simple machines

1 - lever

2 - inclined plane

3 – wedge

4-screw

5 –wheel

6 – axle & pulley

A removable partial denture in the mouth can perform the action of two simple

machines, LEVER & INCLINED PLANE,

LEVER : The lever is a rigid bar supported at some point along it is length.

There are three types of lever:

Classification is based on location of fulcrum (support), resistance, and direction of effort (force).

The first type: the fulcrum (F) is in center of the bar, resistance (R) is at one and the force (E) is at opposite end (called cantilever).

A cantilever: It is a beam supported only at one end, when force is directed against unsupported end of beam cantilever can act as first class lever.

The second-class lever: the fulcrum at one end, the force at opposite end & the resistance in center. This type is seen as indirect retention in R P D.

The third class lever: the fulcrum t one end & the resistance at opposite end & the force in the center. This type is not encountered in R P D. (e.g. tweezers)

Mechanical advantage = Effort arm / Resistance arm

The length of fulcrum to resistance is called Resistance arm, while the length of lever from fulcrum to the point of application of force is called Effort arm.

CLINICAL APPLICATION OF LEVER:

Every effort should be done to avoid class I lever (cantilever). To avoid this cantilever (lever class I) we can made either lever class II or using stress release direct retainer.

a) Lever class II

Where the fulcrum at one end, the force at opposite end & the resistance in center. This type called equipoise force system.{see direct retainer}

In this class, the occlusal rest (F) located mesially, while the retentive tip (R) positioned distally, and the saddle (E) located distal to the retentive tip i.e. the (R) located in between the (F) & (E).

b) Stress release direct retainer

In general, if stress release is desirable, a mesial rest with a mesial undercut or distal rest with distal undercut should be used. A clasp with distal rest and a wrought wire clasp arm engaging the mesial undercut is the exception.

This can explain the difference between location of rest and retentive tip mesially in gingivally approaching clasp as (McCr), and distally location as (Stew). The both authors depending on the concept of stress release.

Inclined plane

Inclined plane is nothing but two inclined surfaces in close alignment to

one another. The direct retainers and the minor connectors slide along the guide

plane of the teeth and can act as inclined planes if no prepared correctly.

When a force is applied against an inclined plane it may produce two

actions:

Deflection of the object, which is applying the force (Denture).

Movement of the inclined plane itself (tooth) .These results should

be prevented to avoid damage to the abutment teeth.

BIOMECHANICAL CLASSIFICATION OF R.P.D. ( Based on the nature of the supporting tissues)

A. TOOTH BORNE (tooth supported or dentoalveolar supported).

1. Abutment teeth border all edentulous areas where tooth replacement is planned.

2. Functional forces are transmitted through abutment teeth to bone.

B. TOOTH - MUCOSA BORNE (tooth and mucosa supported, den to-alveolar and muco-osseous supported or extension base ).

1. Exhibits one or more edentulous areas which are not bordered by abutment teeth (extension base RPDs).

2. forces are transmitted through abutment and mucosa to bone.

3. The majority of these are distal extension RPDs.

4. This category may apply to tooth bordered situations when excessive abutment tooth mobility is present or when long span tooth bordered edentulous areas are present precluding primarily tooth support.

C. MUCOSA BORNE. (muco-osseous supported)

1. Regardless of the natural teeth present, support is derived entirely from the mucoosseous segment.

2. This category includes prostheses fabricated from hard or combinations of resilient and hard denture base materials such as stayplates which function as interim or transitional prostheses.

3. These prostheses usually do not contain a metal framework and usually should not be considered definitive treatment.

CHARACTERISTICS OF FAVORABLE DENTO-ALVEOLAR SUPPORT A.TEETH.

1. Structurally sound. 2. Anatomically favorable.

a. Root surface area. b. Root morphology. c. Presence of multiple

roots.

d. Presence of divergent roots.

e. Crown to root ratio. f. Axial inclination.

B.PERIODONTIUM. 1. Normal (absence of periodontal disease).

a. Gingival indices within normal limits.

b. Absence of increasing mobility or hyper mobility. 2. Anatomically favorable.

a. orrnal epithelial and connective tissue attachment. b.Adequate zone of attached gingiva.

C. ALVEOLAR BONE. 1. Favorable bone index. 2. Anatomically normal.

a. Bone height. b. Degree of

mineralization. c. Presence of lamina dura.

CHARACTERISTICS OF FAVORABLE MUCO-OSSEOUS SUPPORT A.MUCOSA.

1. Normal. 2. Keratinized. 3. Firmly bound.

B. SUBMUCOSA.

1. Normal sub mucosa serves as an "hydraulic cushion". 2. Firmly bound and dense.

C. BONE. 1. Cortical bone. 2. Favorable bone index.

3. Presence of muscle attachments which direct tension to bone (or the equivalent in terms of resistance to pressure induced resorption).

OPTIMAL FORCE BEARING MUCOOSSEOUS ANATOMIC REGIONS

A.MAXILLARY. 1. Horizontal hard palate.

a. Keratinized mucosa.

b. Presence of fatty (anterior) and glandular (posterior) submucosa (excluding midline suture).

c. Cortical bone. 2. Posterior ridge crest.

a. Keratinized mucosa. a. Presence of dense firmly bound submucosal connective tissue

which may contribute to clinically observed resistance to pressure induced resorption.

Maxillary primary (10) supporting areas are the horizontal hard palate

and posterior ridge crest.

The periphery of the denture bearing area is non-contributory (N/C).

The midline suture often requires relief (R)

and the anterior ridge crest serves as a secondary (2°) supporting area.

B. MANDIBULAR. 1. Buccal shelf. A primary force bearing area which is comprised of

cortical bone. It extends from the base of residual ridge in the poste-rior part of the mandible to the external oblique ridge. a. Presence of submucosa. b. Cortical bone. a. Buccinator muscle attachment. The longitudinally directed fibers

apply tension to the underlying bone but do not dislodge the denture base during contraction.

2. Pear-shaped pad. The most distal extension of keratinized tissue covering the ridge crest. It is formed by the scarring pattern following the extraction of the most distal mandibular molar. It should be differentiated from the m~e posterior retromolar pad during clinical examination. a. Keratinized mucosa. a. Presence of dense firmly bound submucosa. a. Medial tendon of the temporalis muscle inserts lingually in the

area of the apices of the mandibular third molars and applies tension to the underlying bone.

Mandibular primary (10) supporting areas are the buccal shelf and pear-shaped pad. The anterior facial incline of the ridge is non-contributory (N/C). The lingual ridge inclines may require relief (R)and the genial tubercle area

and ridge crest serve as secondary (2") supporting areas.

Stresses acting on a partial denture are transmitted to the teeth, and

tissues of the residual ridges. The stresses, which tend to move the denture in

different directions, may be summarized as follows:

1- Masticatory stresses.

2- Gravity tends to displace a maxillary denture downwards.

3- Sticky food tends to pull the denture occlusally away from the tissues.

4- Muscle pull and tongue action tend to displace a denture from its

position.

5- Intercuspation of teeth may tend to produce horizontal and rotational

stresses unless the occlusion is balanced.

FORCES ACTING ON REMOVABLE PARTIAL DENTURES

The Supporting structures for removable partial are structurally adapted to receive and absorb forces within their physiological tolerance. The ability of these structures to tolerate forces is largely dependent upon the magnitude, the duration and the direction of these forces in addition to the frequency of force application.

The magnitude of forces acting on partial dentures depends on age and sex of the patient, the power of the muscles of mastication and the type of opposing occlusion.

Natural teeth are better able to tolerate vertical directing forces acting on them. This is because more periodontal fibers are activated to resist the application of vertical forces. On the other hand, lateral forces are potentially destructive to both teeth and bone. Lateral forces should be minimized in order to be within the physiologic tolerance of the supporting structures.

TYPE OF FORCES ACTING ON RPD

I- Vertical forces

A) Tissue-ward movements B) Tissue-away movements

II- Horizontal forces:

A) Lateral movements B) Antero-posterior movements.

III- Rotational forces:

They are due to the variation in compressibility of supporting structures, absence of distal abutment at one end or more ends of denture bases, and /or absence of occlusal rests or clasps at any end of the bases.

1-Rotation of the anterior and posterior extension denture base around coronal (transverse) fulcrum axis:

A) Rotation of the denture base towards the ridge around the fulcrum axis joining the two main occlusal rests:

B) Rotation of the denture base away from the ridge around the fulcrum axis joining the retentive tips of the clasps.

2-Rotation of all bases around a longitudinal axis parallel to the crest of the residual ridge (Buccolingual or labiolingual).

3-Rotation about an imaginary perpendicular axis, this axis either near the center of the dental arch in class I, or is the long axis of abutment tooth in class II partial denture.

I- Tissue-ward movements

a) Tissue-ward forces are, “Vertical forces acting in gingival direction tending to move the denture towards the tissues”.

They occur during mastication, swallowing and aimless tooth contact. Biting forces falling on artificial teeth are transmitted to the soft tissues and bone underlying the denture base.

b) The partial denture should be designed to resist this movement byproviding adequate supporting components. This function of the partial denture is called “Support”.

Support is the function of partial denture which prevents movement of the denture towards the tissues.

Support is mainly provided by:

a) Properly designed supporting rests placed in rest seats, which are prepared on the abutment teeth,

b) Broad accurately fitting denture bases in distal extension partial dentures. Therefore, the entire available ridge posterior to the abutment teeth must be covered with the denture.

c) Rigid major connectors that are neither relieved from the tissues nor placed on inclined planes also provide support.

d) Rigid portion of clasps placed over the survey line

II- Tissue-away movements

a) Tissue-away dislodging forces are, "Vertical forces acting in an occlusal direction tending to displace and lift the denture from its position”.

Tissue-away forces occur due to: The action of muscles acting along the periphery of the denture, gravity acting on upper dentures or by sticky foodadhering to the artificial teeth or to the denture base.

b) The partial denture should be designed to resist this movement byproviding adequate Retention.

Retention is “The function of partial denture which prevents the denture from being displaced in an occlusal direction (away from the tissues)".

Retention in partial dentures is mainly provided by: {see direct retainer for detail}

a- physical forces which arise from coverage of the mucosa by the denture.

b- Physiologic factors: Patient’s muscular control acting through the polished surface of the denture.

c- Mechanical means such as clasps which engage undercuts on the tooth surface.

In order to retain the denture, the anticipated intensity of occlusally displacing force exerted during function should be less than the force required for retaining the denture.

3) Horizontal movements:

A) Lateral movements

a) Lateral forces are “Horizontal forces developed when the mandible moves from side to side during function while the teeth are in contact”.

Lateral movements have a destructive effect on teeth leading to tilting, breakdown of the periodontal ligament and looseness of abutment teeth. The application of lateral forces causes areas of compression of the periodontal membrane, which leads to bone resorption. Hence lateral forces play a major role in bone resorption,

b) Partial dentures should be designed to prevent the deleterious effects of lateral forces by using stabilizing or bracing components.

Bracing is "The function of partial denture which resists lateral movement of the appliance".

Stabilizing components are "Rigid components of the partial denture that assist in resisting horizontal movement of the denture". They help in distributing lateral stresses to all supporting teeth:

1. Bracing clasp arms placed at or above the survey line of the tooth.

2. Minor connectors in contact with axial (vertical) surfaces of abutment teeth

3. Proximal plates.

4. Adequate extension of the flanges of the denture helps to stabilize the prosthesis against horizontal forces.

5. Rigid portions of clasps.

6. Lingual plates.

7. Rests - When the walls of the rest seat are relatively parallel to the path

of placement (e.g. channel rests).

The magnitude of lateral forces could also be minimized by:

1. Reducing cusp angles of artificial teeth.

2. Providing balanced occlusal contacts free of lateral interference.

The removable partial denture being anchored to both sides of one arch and joined by a rigid major connector can provide cross arch stabilization to forces acting in bucco-lingual direction.

B) Antero-posterior movements

a) Antero-posterior forces are "Horizontal forces which occur during forward and-backward movement of the mandible while the teeth are in contact". This may result in movement of the denture.

There is natural tendency for the upper denture to move forward and for the lower to move backward.

b) Partial dentures should be designed to prevent the deleterious effects of antero-posterior forces by

Forward movement of the upper denture could be resisted by:

1. Anterior natural teeth.

2. Palatal slope.

3. Maxillary tuberosity.

4. The natural teeth bounding the edentulous space.

The backward movement of the lower denture could be resisted by:

1. The slope of the retromolar pad.

2. The natural teeth bounding the saddle area.

3. Proximal plates.

VI- Rotational movements:

a)Rotational forces are “Forces acting on the partial denture either in vertical or horizontal direction causing rotation (torque) of the denture base around an axis.

In tooth supported removable partial dentures, the abutment teeth on both sides of the edentulous area provide adequate support and resistance to rotational forces through supporting rests and clasps placed on them.

In distal extension partial denture when vertical forces are applied the difference in displaceability of the supporting structures often results in rotation of the partial denture around a fulcrum axis and application of torque on abutment teeth.

Rotational movements must be counteracted in the partial denture design to minimize their destructive effect on both, teeth and the residual ridge.

Rotational forces acting on distal extension partial denture may result in three possible rotational movements these are

I- Rotation of the denture base around the fulcrum axis (Torque).

II- Rotation about a longitudinal axis formed by the crest of the residual ridge (Tipping movement).

III- Rotation about an imaginary perpendicular axis near the center of the dental arch (Fish tail movement).

I-Rotation of the denture base around fulcrum axis joining the principal abutments:

Movement of the component parts of the denture lying on the opposite side of the fulcrum axis occur in a direction opposite to that of the applied force. This leads to rotation of the denture:

The fulcrum axis is an “imaginary line passing through teeth and component parts of the partial denture around which the distal extension partial denture rotates when a vertical force is applied”.

More than one fulcrum lines may identified for the same removable partial denture depending on the direction and location for force application.

(a) Rotation of the denture base towards the ridge:

This movement results from occlusal stresses occurring during mastication and occlusion of teeth. The free extension denture base moves tissue-ward while other components on the opposite side of the fulcrum line moves away from the tissues. This result in rotation of the denture about a diagonal supportive fulcrum line joining two occlusal rests on the most posterior abutments on either side of the dental arch

Tissue ward movement of the base could be limited by supporting structures, which are:

1. Supportive form of the residual ridge,

2. Accurate and properly extended bases.

3. Artificial teeth set on the anterior two third of the base

Flexible clasps are preferred over rigid clasping to reduce stresses and torque applied on abutments. If the clasps are rigid, the abutments tend to rotate distally during tissue ward movement of the denture base resulting in periodontal breakdown and looseness of teeth.

(B) Rotation of the denture base away from the ridge.

This movement occurs due to the pulling effect of forces applied by sticky food, gravity on upper dentures and the elastic rebound of soft tissues covering the edentulous areas.

Tissue-away rotation of denture base is counteracted by:

1- Indirect Retainers: which are the components of partial denture located on the side of the fulcrum axis opposite to the distal extension base.

2- The retentive tip of the clasp arm.

3- Adequate coverage and extension of the base (direct indirect retention )

4- Effect of gravity on mandibular bases.

II-Rotation around a longitudinal axis formed by the crest of the residual ridge (Tipping movement)

This rotation occurs due to application of vertical forces on one side of the arch only. It causes twisting of the denture base.

This movement is counteracted by:

1- Cross arch stabilization (The action of clasps on the opposite side of the arch).

2- Broad base coverage.

3- Proper placement of artificial teeth (teeth on the ridge or lingualized occlusion).

4- Narrow teeth bucco-lingually.

5- The effect of rigid major connectors.

III- Rotation around an imaginary perpendicular axis near the center of the dental arch

Application of horizontal or off-vertical force results in rotation around an imaginary vertical axis located either about the axis of abutment in class II or near the center of the dental arch, lingual to anterior teeth in class I.

It results due to the application of masticatory forces falling on distal extension bases causing buccolingual movement of the base. This rotation is called fishtail movement.

This movement is counteracted by :

1- Providing adequate bracing components in the partial denture.

2- A rigid major connector.

3- Broad base coverage.

4- Balanced contact between upper and lower teeth.

Forces accruing through a removable restoration can be widely distributed, directed, and minimized by the selection, the design, and the location of components of removable partial dentures and by developing a harmonious occlusion.

Force Cause of the Force Counteraction of the force Function

I- Vertical Forces :

1- Tissue-ward displacing

forces.

Functional movements

during mastication,

swallowing and

occlusion of upper and

lower teeth.

- Rests placed on abutments in

bounded saddles.

- Rests & proper base coverage in

free end bases.

- Maxillary connectors

- Support

2- Occlusally displacing

forces.

Pulling effect of sticky

food Gravity on upper

dentures. Muscles acting

on periphery of denture

- Retainers.

- Adhesion & cohesion between

denture base & tissues

- Retention

II- Horizontal Forces

1- Lateral forces.

Side to side movement of

the mandible while teeth

are in contact.

- Rigid bracing clasp arms.

- Major connectors.

- Balanced occlusion.

- Maximum extension of the flanges

- Bracing

(Stabilization

2- Antero-posterior forces Forward and backward

movement of mandible

while teeth are in contact

- Abutments adjacent to the denture.

- Guiding planes.

-

Stabilization

III- Rotational forces :

1- Vertical forces in gingival

direction in free-end saddles.

- Functional movements

while teeth are in

occlusion.

- Supporting rests.

- Properly adapted bases.

.

- Support

2- Vertical forces in occlusal

direction in free-end saddles.

- Sticky food, gravity on

upper dentures, elastic

rebound of tissues under

the base.

- Indirect retainers.

- Direct retainers.

-Indirect

retention.

Factors affecting stress generation and transfer

1- Length of span: - the longer edentulous span, the greater force will be transmitted to the abutment. so the Posterior teeth should be preserved as far as possible to reduce the length of the edentulous span

2- Quality of the supporting tissues:

Form of the residual ridges: large well developed ridges, absorb more amount of force than small, thin ridge.

Type of mucosal covering : atrophic and flabby mucosa are not preferred.

3- Quality of clasp: - the more flexible clasp arm, the less force transmitted

to the abutment.

4- Clasp design: - a passive clasp when it is completely seated on the

abutment teeth will exert less stress on the tooth than the non passive.

A clasp should be designed so that the reciprocal arm contacts the

tooth before the retentive tip passes over the greatest bulge of the tooth

during insertion and it should be the last component to lose tooth

contact during removal of the prosthesis.

5- Length of the clasp.

Doubling the length increases the flexibility by five times. This

decreases the stress on the abutment tooth. Using a curved rather than a

straight clasp on an abutment tooth will aid to increase the clasp length

6- Material used in clasp construction A clasp constructed of chrome alloy will exert more stress on

the abutment tooth than a gold clasp because of its greater rigidity. To decrease the stress, the chrome alloy clasps are constructed with a smaller diameter.

7- Abutment tooth surface: - the surface of a gold crown or restorationoffers more functional resistance to clasp arm movement than does of enamel surface of a tooth therefore greater stress is exerted on the abutment.

8- Occlusal relationship of the remaining teeth and orientation of the

occlusal plane.

Type of the opposing occlusion

Harmony of the occlusion should be present.

Improper occlusal relationship and a steep occlusal plane tend to

increase the amount of force acting on the denture. The force

applied on natural teeth is 300 pounds and the force acting on

artificial teeth is about 30 pounds. Poor occlusal relationship can

lead to supra-eruption of the opposing natural teeth.

9- Musculature of the patient.

10- Response of oral structures to previous stress. The periodontal

condition of the remaining teeth, need for splinting and the amount of

abutment support remaining are all a result of the previous stress

subjected on the oral tissues.

RESPONSE OF FORCE BEARING TISSUES TO MECHANICAL LOADING

The forces directed to the supporting tissues will be partially absorbed and partially transmitted to adjacent tissues.

The percentage of force absorbed or transmitted will vary depending upon which tissue is involved.

Bone is the tissue which ultimately absorbs the greatest amount of the force applied to both the muco-osseous and dento-alveolar segments.

A.DENTO-ALVEOLAR SEGMENT.

1.Tooth.

a. Structurally sound vital teeth are capable of withstanding normal functional forces.

b. Excessive forces may result in adverse effects.

Structural failure (tooth fracture).

Tooth movement.

Pulpal irritation. Reversible pulpitis (hyperemia) or irreversible pulpitis,

c. Structurally compromised teeth may fail in response to normal functional forces.

Teeth with large intracoronal restorations.

Endodontically treated teeth.

2.Periodontium

including gingiva, crevicular epithelium, junctional epithelium, connective tissue attachment, cementum, periodontal ligament and alveolar bone.

a. A normal periodontium permits some force absorption without damaging effects.

b. Excessive forces may increase the width of the periodontal ligament and result in increased tooth mobility.

c. Plaque induced inflammation may compromise the periodontium. It can lead to apical migration of the crevicular epithelial attachment (functional epithelium) and destruction of the fibroblasts and connective tissue of the connective tissue attachment. In the presence of inflammation normal functional forces may accelerate the rate of periodontal attachment loss.

3.Alveolar bone.

a. Pressure - tension theory. Bone tends to resorb in response to compressive force and to be stimulated by tensional force. In order to preserve remaining alveolar bone, it is important that functional forces be transmitted to bone primarily as tension rather than pressure whenever possible.

In tooth borne situations the majority of functional forces are transmitted as tension to bone through proper rest design and rest seat preparation. In tooth-mucosa borne situations some of the vertical seating forces are transmitted as tension to the bone through the rests. Horizontal forces are transmitted as a combination of compressive and tensional forces to the alveolar bone (e.g. those forces directed through bracing clasps, proximal plates and minor connectors contacting proximal tooth surfaces and guiding planes). Vertical displacing forces are transmitted to the bone as both compressive and tensional forces (e.g. sticky foods or retentive clasps engaging undercuts).

b.Bone index or Bone factor. The response of bone to pressure varies in terms of the rate of resorption depending on genetic, nutritional, hormonal and biochemical and other intrinsic factors. The bone index is determined by analyzing the previous response of bone to force.

c. Cortical vs. cancellous bone. Cortical bone is more dense, more highly mineralized, less cellular, and less metabolically active. It tends to be more resistant to pressure induced resorption than cancellous bone. Lamina dura is cortical bone.

d. Excessive forces which increase compressive components of forces transmitted to bone may increase the rate of bone resorption.

e. Periodontal disease. The presence of plaque induced periodontal disease is associated with a loss of bone height. Moderate forces may accelerate the disease process resulting in further bone loss, less bone support, and increased mobility of the teeth.

B. MUCO-OSSEOUS SEGMENT.

1.Mucosa.

a.Normal. firmly bound, keratinized tissues withstand mechanical forces within physiologic limits.

b. Excessive mechanical forces may cause mucosal ulceration (e.g. denture sore spots).

2.Submucosa

a. Provides an "hydraulic cushion" effect.

b. Increased thickness of the submucosa improves tolerance of the residual ridge to applied forces.

3.Bone

a. Pressure-tension theory. The functional loading of a tooth-mucosa borne denture base transmits force to the bone of the rnuco-oss ous segment almost exclusively as pressure which tends to cause resorptive changes. Resorption occurs in proportion to the intensity, duration, and direction of the applied force and as influenced by the bone factor. With some longer span tooth borne partial dentures or when excessive mobility of abutment teeth is present some force may also be delivered through the mucosa to the underlying bone as pressure.

b. Bone index. The bone index of the alveolar bone surrounding natural teeth may differ from that of the bone comprising the residual ridges. (Fig. 3-6)

c. Cortical vs. cancellous bone. The residual ridge crest is comprised mainly of cancellous bone and is less resistant to resorption. The facial and lingual inclines of the residual ridges are comprised of cortical bone and are more resistant to remodelling. The rate of cancellous bone resorption has been described as being approximately three times that of cortical bone.

d.Excessive forces may increase the rate of bone resorption.

e. Moderate forces may result in accelerated bone resorption when intrinsic factors, local abnormalities or systemic disorders compromise the bone index of the individual.

REACTION OF TISSUE TO METALLIC COVERAGE

The reaction of tissue to coverage by the metallic components of a removable partial denture has been the subject of significant controversy, particularly in regions of marginal gingiva and broad areas of tissue contact.

These tissue reactions can result from

1) Pressure from lack of support,

2) lack of adequate hygiene measures,

3) prolonged contact through continual use of a prosthesis.

Pressure occurs at regions where relief over gingival crossings and other areas of contact with tissue that are incapable of supporting the prosthesis is inadequate. Impingement will likewise occur if the denture settles because of loss of tooth and/or tissue support. This may be caused by failure of the restareas as a result of improper design, caries involvement, fracture of the rest itself, or intrusion of abutment teeth under occlusal loading. It is important tomaintain adequate relief and support from both teeth and tissue. Settling of the denture because of loss of tissue support may also produce pressure elsewhere in the arch, such as beneath major connectors. Settling of a prosthesis must be prevented or corrected if it has occurred. Excessive pressure must be avoided whenever oral tissue must be covered or crossed by elements of the partial denture.

Lack of adequate hygiene measures can result in tissue reactions because of an accumulation of food debris and bacteria. Coverage of oral tissue with partial dentures that are not kept clean irritates those tissue because of an accumulation of irritating factors. This has led to a misinterpretation of the effect of tissue coverage by prosthetic restorations. An additional hygiene concern relates to the problem of maintaining cleanliness of the tissue surface of the prosthesis.

The first two causes of untoward tissue reaction can be accentuated the longer a prosthesis is worn. It is apparent that mucous membranes cannot tolerate this constant contact with a prosthesis without resulting in inflammation and breakdown of the epithelial barrier. Some patients become so accustomed to wearing a removable restoration that they neglect to remove it often enough to give the tissue any respite from constant contact. This is frequently true when anterior teeth are replaced by the partial denture and the individual does not allow the prosthesis to be out of the mouth at any time except in the privacy of the bathroom during tooth brushing. Living tissue

should not be covered all the time or changes in those tissue will occur. Partial dentures should be removed for several hours each day so that the effects of tissue contact can subside and the tissue can return to a normal state.

Clinical experience with the use of linguoplates and complete metallic palatal coverage has shown conclusively that when factors of pressure, cleanliness, and time are controlled, tissue coverage is not in itself detrimental to the health of oral tissue.

Controlling Stress by Design Considerations

1- Direct Retention :

1. Clasp The retentive clasp arm is the element of RPD that is responsible for

transmitting most of destructive forces to the abutment teeth. A RPD should always be designed to keep clasp retention to a minimum yet provide adequate retention to prevent dislodgment of the denture by unseating forces. It should also be remembered that the retentive clasp should be designed such that it is active only during insertion and removal.

2. Forces of adhesion and cohesion To secure the maximum possible retention through the use of forces of

adhesion, the denture base should cover the maximum area of availablesupport and must be accurately adapted to the underlying mucosa.

3. Frictional control The RPD should be designed so that guide planes are created on as many

teeth as possible. Guide planes are areas on teeth that are parallel to the path of insertion and removal of the denture. The plane may be created on the enamel surfaces of the teeth or restorations placed on teeth. The friction of RPD against parallel surfaces can contribute significantly to retention of the denture.

4. Neuro-muscular control The design and contour of the denture base can greatly affect the ability of

lips, checks and tongue to retain the prosthesis. Any over-extension of the denture base either facially, lingually in the mandible or posteriorly onto the soft palate will contribute to the loss of retention and the abutment teeth bearing the direct retainers will be over stressed.

5. Clasp Position a- Quadrilateral configuration

Four abutments are utilized for clasping. Quadrilateral configuration is indicated in Class III particularly when there is a modification space on the opposite side of the arch. A retentive clasp should be positioned on each abutment adjacent the edentulous space. This result in denture being confined within the outline of four clasps

b- Tripod ConfigurationTripod clasping is used primarily for class II arches. If there is a modification

space on the edentulous side the teeth anterior and posterior to the space are clasped. If a modification space is not present. One clasp on the edentulous side of the arch should be positioned as far posterior as possible and the other, as far anterior as factors such as interocclusal space, retentive undercut, and esthetic considerations will permit. By separating the two abutments on the tooth-supported sides as far as possible, the largest possible area of the denture will be enclosed in the triangles formed by the clasps.

c- Bilateral configuration

Most RPD with bilateral distal extension group in class I fall into bilateral configuration. In the bilateral configuration the clasp exert little neutralizing effect on the leverage induced stresses generated by the denture base. These stresses must be controlled by other means.

6. Clasp design : a- Circumferential clasp : The conventional circumferential cast clasp originating from a distal occlusal

rest on the terminal abutment tooth and engaging a mesio-buccal retentive undercut should not be used on a distal extension RPD. The terminal of this clasp reacts to movement of the denture base toward the tissue by placing a distal tipping, or torquing, force on the abutment teeth. This particular force is the most destructive force a retentive clasp can exert. This clasping concept must be avoided.

On the other hand if the circumferential clasp with mesial occlusal rest approaches a disto-buccal undercut form the mesial surface of the abutment, is acceptable. The effect on the abutment is reversed from that of the conventional clasp. As the occlusal load is applied to the denture base, the retentive terminal moves further gingivally into the undercut area and loses

contact with the abutment teeth. In this manner torque is not transmitted to the abutment tooth.

b- Vertical projection or Bar clasp :

The vertical projection clasp, or bar clasp is used on the terminal abutment tooth on a distal extension RPD when the retentive undercut is located on the disto-buccal surface. As the denture base is loaded toward the tissue, the retentive tip of the clasp rotates gingivally to release the stress being transmitted to the abutment tooth.

c- Combination clasp :

When a mesio-buccal undercut exist on abutment tooth adjacent to a distal extension edentulous ridge, the combination clasp can be employed to reduce the stress transmitted to the abutment tooth. wrought alloy wire, by virtue of its internal structure, is more flexible than a cast clasp. It can flex in any plane, whereas a cast clasp flexes in the horizontal plane only. The wrought wire retentive arm has a stress-breaking action that can absorb torsional stress in both vertical and horizontal planes.

Flexible clasps produce the least stress and rigid cast circumferential clasps produce the maximum stress in an abutment.

2- Indirect Retention

The indirect retention is essential in the design of class I and II RPD, byusing the mechanical advantages of leverage; it counteracts the forces attempting to move the denture base away from the residual ridge by moving the fulcrum farther from the force.

In class I prosthesis, the fulcrum line would be moved from the tips of the retentive clasp to the most anteriorly located component, the indirect retainer. Because the indirect retainer resists lifting forces at the end of a long lever arm, it must positioned in a definite rest seat so that the transmitted forces are diverted apically through the long axis of abutment tooth. Theindirect retainer also contributes to a lesser degree, to the support and stability of the denture.

Class I : indirect retainer must always used.

Class II: it is not as critical as in class I but still required. Modification space can provide indirect retention. A definitive occlusal rest seat anterior may increase the effectiveness of indirect retention.

Class III : indirect retention is not ordinarily required except in :

- long lingual bar major connector to provide additional vertical support. - Lingual plate major connector.

Class IV : is considered reverse of class I and II. The lever arm is anterior to the fulcrum line, so the indirect retainer must be located as far posterior as possible. Occlusal rests and clasp assemblies are placed on the most posterior teeth for both direct retention and support.

3- Occlusion

The occlusal surfaces, or food table, of artificial teeth can transmit various amounts of stress to the supporting structures. A large or broad occlusal surface deliver more stress than does one that has been reduced in bucco-lingual width. The number of teeth replaced may also be reduced to decrease stress. Harmonious occlusion should be developed.

4- Denture Base

The denture base should be designed to cover as extensive an area of supporting tissue as possible. The stress created by the partial denture in function will thus be distributed over a large area, so no single area will be subjected to stress beyond its physiologic limit. The denture base flange should be made as long as possible to help stabilize the denture against horizontal movements.

The distal extension denture base must always extend onto the retromolar pad area in the mandible and cover the entire tuberosity of the maxilla. Both structures are capable of absorbing more stress than alveolar ridge anterior to them.

The type of impression used to record the residual ridge will influence the amount of stress the residual ridge can effectively absorb. Several techniques are used to make functional impression of the residual ridge. Each technique is based on the theory that if the ridge were recorded in its

functional state rather than its resting form, when the denture base is actually subjected to occlusal loading, the tissue would not displaced to any great stint. The magnitude of stress transmitted to the abutment teeth, therefore, would be minimal.

Denture base should be accurate and stable. The polished surfaceshould have the proper form and contour.

5- Major Connector

In the mandibular arch the lingual plate major connector that is properly supported by rests can aid in the distribution of functional stresses to the remaining teeth. It is particularly effective in supporting periodontally weakened anterior teeth. The lingual plate also adds rigidity to the major connector. The added rigidity contributes to the effectiveness of cross-arch stabilization.

In the maxillary arch the use of a broad palatal major connector that connects several of the remaining natural teeth through lingual plating can distribute stress over a large area. The major connector must be rigid and must receive vertical support through rests from several teeth.

It should distribute the occlusal load over a wide area and at the same time produce the least amount of stress. There are three important principles for design exclusively used for a major connector. They are:

L-bar or L-beam principle.

Circularconfiguration.

Strut configuration.

L-bar or L-beam principle

The L-beam or L-bar or Linear beam theory states that the flexibility of a bar is directly proportional to the length of the bar and inversely proportional to its thickness.

When a load is placed on the bar or beam supported at its ends, maximum stress is present in the centre and zero stress at the supported ends.

A bar supported at both its ends can be divided into two parts namely the parabolic and quartic parts. The parabolic part forms the middle2/4th of the distance between the supports and the remaining l/4th on either sides of the bar form the quartic part.

The parabolic part shows maximum stress concentration and thequartic part shows minimum or zero stress concentration. Hence, if we design a bar such that it has a smaller parabolic part and a larger quartic part it will be less flexible. The material becomes more rigid (less flexible) without adding bulk to the bar.

The next question is how do we do this? The answer is very simple. IT we bend the bar on either side, the length of the bar lying in the quartic part will increase.

Now apply this concept in the design of a major connector. The palate has a flat vault and two lateral slopes.

If the slopes are shallow, the quartic part of the major connector also decreases leading to increased flexibility of the prosthesis under occlusal load. The major connector should be located and designed such that it lies over thesteeper slopes in the palate.

Hence, broad palatal major connectors, palatal strap major connectors can be fabricated with lesser bulk of material (but with adequate rigidity)because it extends in three planes (one central vault and two lateral slopes) with the length of the quartic part (the two lateral slopes) being greater than the parabolic part.

Circular configuration

The advantage of a circle is that it is a continuous unit without an end. Any force acting on a circular bar can be easily distributed all along the circumference. Hence, a circular bar is more rigid than a linear bar with the same area of cross section. This concept can be used to reduce the bulk of themajor connector with a circular configuration anteroposterior double palatal bar and closed horseshoe.

Strut configuration

According to this configuration, a straight bar bent at its ends near thesupport is more rigid because, the bent slopes of the bar aid to transfer the load acting on the horizontal portion.

This is similar to the linear bar theory (L-beam discusses stressconcentration but struts discuss stress distribution).

The major connector on a narrow vault is more rigid than a major connector extending over a shallow vault. In other words, the major connector extending in two different planes has more rigidity.

This concept is seen in the anterior plate of the double palatal bar, where the slope of the rugae area acts as an additional strut.

6- Minor Connector

The most intimate tooth-to-partial denture contact takes place between the minor connector joining the clasp assembly to the major connector and the guiding planes on the abutment tooth surfaces. This close metal-to-enamel contact serves two purposes:

1- It offers horizontal stability of RPD against lateral forces. 2- Through the contact of the minor connector and the abutment teeth, the

teeth receive stabilization against lateral stresses. 7- Rests

One of the most critical points of the rest seat is that the floor of the preparation must form an angle of less than 90 degrees with the long axis of the tooth. This permits the rest, whether occlusal, incisal or lingual, to grasp

the tooth securely and prevent its migra on. If more than 90 degrees, an inclined plane action is set up and stress against the abutment tooth is magnified.

In class I and II RPD the rest seat preparation must be saucer-shaped, completely devoid of any sharp angles or ledges. As the forces are applied to the partial denture, the rest must be free to move within the rest seat to release stresses that would otherwise be transferred to the tooth. The more teeth bear rest seats, the less will be the stress placed on each individual tooth.

8- Splinting of abutment teeth :

Adjacent teeth may be splinted by means of crowns to control stress transmitted to a week abutment tooth. splinting two or more teeth actually increases the periodontal ligament attachment area and distributes the stress over a large area of support. It also stabilizes the abutment teeth in a mesio-distal or antro-posterior direction.

Splinting could be achieved by clasping more than one tooth on each side of the arch using a number of rests for additional support and stabilization and preparing guiding planes on as many teeth as possible to contribute to horizontal stabilization of the teeth and the prosthesis. The multiple clasps should not all be retentive.

Splinting is indicated for the following clinical conditions.

Abutments with a tapered or short root.

Terminal abutments located on the edentulous side of a distal extension denture base.

Fixed splinting is given if there is some loss of periodontal attachment, after a periodontal disease and therapy.

PARTIAL DENTURE DESIGN

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ESSENTIALS OF PARTIAL DENTURE DESIGNDecision Making in RPD Design

Designing of partial denture necessitates a proper planning for the form and

extent of a dental prosthesis and studying of all the factors involved.

The prosthesis must be designed following the most favorable biomechanical

principles, as the proper design helps in reducing the harmful effects on the

supporting structures.

A Properly constructed partial denture must achieve:

A-Support: Adequate distribution of the load to the teeth and mucosa.

B-Retention: Sufficient resistance to vertical displacing forces.

C- Bracing: Anchorage sufficient to resist lateral and rotational forces.

D- Stabilization: Sufficient resistance to resist tipping forces.

C- Reciprocation: Nullifying the effect of pressure on one side of a tooth by the

application of pressure, equal in amount but in an opposing direction, on the

opposite side of the tooth.

PHILOSOPHYOF PARTIAL DENTURE DESIGN

There are four design concepts, which can be used to distribute the force evenly along

the tissues and supporting tooth structure. They are :

Conventional rigid design.

Stress equalization.

Physiologic basing.

Broad stress distribution.

Conventional Rigid Design

The denture is designed with rigid component which act like a raft foundation to

evenly distribute the forces on the supporting tissues. This design is used in all general

cases. The flexible component of these dentures is their retentive terminal.

Advantages


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Easy to construct and economical.

Equal distribution of stress between the abutment and the residual ridge.

Reduced need for relining as the ridge and abutment share the load.

Indirect retainers prevent rotational movement and also stabilize the denture

during horizontal movements.

Less susceptible to distortion.

Disadvantages

Increased torquing forces on the abutment teeth.

Rigid continuous clasping may damage the abutment teeth.

Dovetail intracoronal retainers cannot be used in these cases as tipping forces

from the denture base will be directly transmitted to the abutment teeth.

Tapered wrought wire retentive arm (combination clasp) cannot be used, as it is

difficult to construct.

Relining is difficult and inappropriate relining leads to damage of the abutment

teeth.

Stress Equalization or Stress Breaker or Stress Directing Concept

A stress breaker is defined as, “A device which relieves the abutment teeth of

all or part of the occlusal forces" - GPT.

A stress director is a device that allows movement between the denture base

and the direct retainer which may be intracoronal or extracoronal. Dentures with a

stress breaker are also called a broken stress partial dentures or articulated prostheses.

We know that the soft tissues are more compressible than the abutment teeth. In

a tooth tissue supported partial denture, when an occlusal load is applied, the denture

tends to rock due to the difference in the compressibility of the abutment teeth and the

soft tissue As the tissues are more compressible, the amount of stress acting on the

abutments is increased. This can produce harmful effects on the abutment teeth.

In order to protect the abutment from such conditions, stress breakers are

incorporated into a denture.

There are two types of stress breakers:

Type I


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Here a movable joint is placed between the direct retainer and denture base.

This joint may either be a hinge or a ball and socket or a sleeve and cylinder. Adding

these stress breakers to the junction of the direct retainer and the denture base, allows

the denture base to move independently.

This decreases the amount of force acting on the abutment. The combined

resiliency of the periodontal ligament and the stress director will be equal to the

resiliency of the oral mucosa overlying the ridge.

Examples for hinges include DALBO, CRISMANI, ASC 52 attachments.

Type I I

It has a flexible connection between the direct retainer and the denture base. It

can be a wrought wire connector, divided or split major connector or a movable joint

between two major connectors.

In a split major connector, the major connector is split by an incomplete cut

parallel to the occlusal surface of the teeth into two units namely the upper unit (more

near to the tooth) and the lower unit. The denture base is connected to the lower unit

and the rests and direct retainers are connected to the upper unit.

Advantages

The alveolar support of the abutment teeth is preserved as the stresses acting on

the abutment teeth are reduced.

The stress on the residual ridge and the abutment teeth are balanced.

Weak abutment teeth are well splinted even during the movement of the denture

base. Abutment teeth are not damaged even if relining is not done appropriately

(after the denture wears out).

Minimal requirement of direct retention.

Movement of the denture base produces a massaging effect on the soft tissues..

This avoids the frequent need for relining and rebasing.

Disadvantages

Design is complicated and expensive.

The assembly is very weak and tends to fracture easily. Distorts to rough

handling.

It is difficult to repair.


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It can be used only to counter the vertical forces on the denture. Inability to

counteract lateral stress acting on the ridge leads to ridge resorption.

Reduced stability against horizontal forces.

Both vertical and horizontalforces are concentrated on the ridge leading to

resorption.

Inappropriate relining leads to excessive ridge resorption.

Reduced indirect retention.

The split major connector tends to collect food debris at the area of split.

Physiologic Basing

This technique distributes the occlusal load between the abutment teeth and the

soft tissues by fabricating a denture based on a functional record. Functional record is

obtained by recording the tissues under occlusal load or by relining the denture under

functional stress. This technique involves making an impression of the soft tissues in a

compressed state.

The denture fabricated using a functional impression has one major

disadvantage. That is the denture tends to compress the soft tissues even at rest. This

can lead to excess ridge resorption. Since the denture is fabricated using a functional

record (compressed tissues), the soft tissues offer more resistance to further

compression. This increased resistance to compression provided by the oral mucosa

equates to that of the periodontal ligament of the abutment tooth. In this manner the

abutment tooth is protected from excessive forces and the denture can distribute

occlusal load evenly to the teeth and tissues.

Requirements for Physiological Basing

rigid metal framework

Functional occlusal rests

Indirect retainers to provide additional stability.

Well-adapted, broad coverage denture bases.

Advantages

Good adaptation of the denture base.

Simple design and economical.

Minimal direct retention decreases the


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functional stress on the abutment tooth.

Disadvantages

Decrease in the number of retentive components provides less stability.

The denture tends to lift at rest. This leads to premature contacts.

Indirect retention is decreased due to vertical movement of the denture due to

tissue rebound at rest.

Broad Stress Distribution

According to this philosophy of design, the occlusal load acting on the denture

should be distributed over a wider soft tissue area and maximum number of teeth. This

is achieved by increasing the number of direct retainers, indirect retainers, and rests

and by increasing the area of the denture base.

Advantages

This design with multiple clasps acts as a form of removable splinting.

It increases the health of the abutment teeth (due to splinting action).

Easier to construct and economical.

Disadvantages

Less comfortable.

Difficult to maintain adequate oral hygiene.

Designing of Partial Denture

Sequence of designing partial dentures:

1- Denture base designing.

2- Designing for support.

3- Providing retention.

4- Designing for bracing and reciprocation.

5- Designing for resistance to anteroposterior movements of the saddles.

6- Connecting the saddles and retainers.

7- Esthetics


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I- Denture base designing:

It is the part of the partial denture which rests on the mucoperiosteum and to which

the denture teeth are attached.

Functions:

1-Retain the artificial teeth.

2-It provides addition retention to the prosthesis.

3-It provides addition stabilization for the RPD against the horizontal forces.

4-It provides support for the distal extension base RPD.

5-the contour of its polished surface provide a stabilizing and retentive effect when

acted on by the oral musculature.

Design:

It is desirable to extend the denture saddles into the sulcus to assure the

maximum coverage especially in mucosa and tooth-mucosa supported RPD.

Types of contact between the denture and abutment teeth:

1- Closed design with long guiding plane.

2- Open design with short guiding plane.

3- Open design without guiding plane and with wide embrasure.

II-Designing for support:

Definition:

It is the resistance against the vertical seating forces which occurring during

{mastication, swallowing and Para function}.

Classification of RPD according to their support:

(1) tissue-borne dentures:

Gets all its support from the soft tissue covering the jaws.

(2) tooth-borne dentures:

Gets all its support from the natural teeth.


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They are a very small dentures which replacing one or two teeth on one side only and

often they are called (removable bridges).

(3) Tooth-and tissue born dentures:

They are supported by the soft tissue and the natural teeth.

The best example of this type is the RPD with distal extension bases. The tooth

structure provides the support interiorly, where soft tissue supports the denture base

posteriorly.

Support can provided from:

1- Denture base.

2- Maxillary major connectors.

3- Rests.

4- Rigid portions of the clasps placed above the survey line.

Number of rests:

1- Required number if possible 4 well distributed rest. Such a case will be considered

as self-indirect retained case.

2- If not possible, 3 will be required, 2 will make fulcrum line (the two main

posteriors) and the 3rd one will act for support and indirect retention.

3- In some cases the possible number will be only 2 , in such case , the indirect

retention will be from the resistance form by maximum coverage & seal, as complete

denture base.

III-Designing for retention:

It is the resistance to vertical dislodging force; which occurs during:

1- Mastication of sticky food.

2- Muscles of lips, tongue, and cheeks.

3- Gravity on maxillary denture.

Means of retention: {see direct retainer for detail}

A] Physical factors

Adhesion between saliva / denture & tissue

Cohesion between saliva molecules

surface tension


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Atmospheric Pressure

Effect of Gravity

Plastic molding between tissues / denture polished surfaces aid to little extent in

retention of partial denture

b] Mechanical means

(1) Direct retainers:

A- Intracoronal (precision attachments).

B- Extracoronal (clasps)

(2) Frictional fit between the denture and the abutment teeth.

(3) Parts of the denture base engaging in undercuts on the teeth.

(4) Parts of the denture base engaging in undercuts on the soft tissues.

(5) Indirect retainers. {Prevent rocking movements of the denture}.

C] Physiological means of retention:

1- The physiologic molding of the tissues around the polished surfaces of the

denture helps to perfect the border seal.

2- Neuromuscular control

Direct retainers:

A- precision attachments:

• They are fitted more to the small unilateral RPDs (side-plates).

• They are bought ready-made (usually the mail portion is attached to the

denture, while the other is soldered into a crown or large inlay in an abutment

tooth.)

B- Clasps:

1- To resist displacement of the denture by vertically applied forces .

2- To resist displacement of the denture by horizontal applied forces.

Selection of clasp:

Selection of the clasp depends mainly on (type of support, presence of

undercut area, and esthetics).

1- For bounded saddles: the retentive undercut present is used with any acceptable

clasp type.


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2- for distal extension base: Retainers for distal extension partial dentures, although

retaining the prosthesis, must also be able to flex or disengage when the denture

base moves tissueward under functional. stress releasing clasp is desired, which

equitably distribute the force between the abutment and the ridge;

a) If a mesiobuccal undercut is available on the terminal abutment, a combination

clasp with the wrought wire, back action, RPI, RPA clasps are used.

b) If the retentive undercut is located on the distobuccal surface, a bar clasp, and

the C clasp are used.

c) If mesiolingual undercut is present a reverse back action clasp is used.

Evaluating the ability of a clasp arm to act as a stress-breaker,

One must realize that flexing in one plane is not enough. The clasp arm must be

freely flexible in any direction, as dictated by the stresses applied. Bulky, half-round

clasp arms cannot do this, Round, tapered clasp forms offer advantages of greater and

more universal flexibility, less tooth contact, and better esthetics.

Either the combination circumferential clasp, with its tapered wrought-wire

retentive arm, or the carefully located and properly designed circumferential or bar

clasp can be considered for use on all abutment teeth adjacent to the extension denture

bases if the abutment teeth are properly prepared, the tissue support is effectively

achieved, and if the patient exercises good oral hygiene.

Factors that control numbers of clasps used:

(1) The amount of retention required by the denture depends on:

a- Number teeth which be replaced.

b- Displacing force.

C- Patients need maximum stability.

(2) The retention that provided by other methods than clasping.

(3) The numbers of teeth available for clasping.

The following rules apply for the number of clasps used:

a) It is better to have too much retention than too little. (Clasps that prove to be

unnecessary can easily be removed from the denture).

b) The greater the number of clasps, the less will be the force applied.


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Keys to selecting a successful clasp design:

(1) Avoid direct transmission of tipping or torquing forces to the abutment;

(2) Accommodate the basic principles of clasp design by definitive location of

component parts correctly positioned on abutment tooth surfaces.

(3) provide retention against reasonable dislodging forces (with consideration for

indirect retention).

(4) Be compatible with undercut location, tissue contour, and esthetic desires of the

patient. It is most important single factor in selecting a clasp.

The placing of clasps:

Clasps should be placed so that the direct retention they give is distributed as widely

as possible.

► For class I partially edentulous arch, a bilateral clasping configuration is

required.

► When two clasps are used an imaginary line drawn between them should divide

the denture into two equal halves.

► If this (retention line) runs diagonally across an upper denture, it is considered

an advantage for the resistant against the gravity displacement force.

III-Designing for bracing and reciprocation:

Bracing:

It is the resistance to horizontal (lateral and antero-posterior ) movements of the

denture caused by lateral forces which occurred during:

1- Mastication as a component of the obliquely applied force.

2- Para function.

Resistance to lateral shifting is gained by:

1- Maximum extension and coverage of the sides of the residual ridge with the

denture base within the physiological limit.

2- Rigid bracing clasp arms.

3- Use of a continuous bar resting on the lingual surfaces of natural standing

teeth (Kennedy bar).

4- Rigid major and minor connectors

5- The magnitude of the lateral forces may reduced by:


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- Reducing the steepness of the Cuspal angles of the teeth.

- Reducing the size of the occlusal table.

- Ensuring that the cusps are efficient during mastication.

Reciprocation:

It is the resistance to horizontal forces exerted on a tooth by the retentive clasp

arm during insertion and removal of the RPD.

This can be obtained by bracing clasp arm or plate contacting the tooth surface

while the movement of the retentive tips over the height of contour of the abutment.

Resistance of the antero posterior movement of the saddles:

As there is a tendency of the upper denture to move forwards and the

lower denture to move backwards, Resistance to anteroposterior

movement is gained by:

1. The presence of healthy well supported natural anterior teeth in the upper

jaw and molar tooth or teeth in lower jaw.

2. Covering the anterior slope of the hard palate, and the tuberosity.

3. The use of posterior abutment.

4. Steeply sloping mucosa in the retro molar region.


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Stabilizing Components

- Stabilization is the resistance of partial denture to tipping forces.

Causes of tipping, rocking and rotation of RPD:

1- Different quality in the nature of the supporting structures

In tooth supported RPDs, the abutment teeth on both sides of the edentulous

area provide adequate support and resistance to rotational forces through

supporting rests and clasps placed on them.

In Tooth-tissue supported distal extension partial dentures derive support from

two different tissues. This results in vertical movement of the denture base either

in tissue-ward or tissue-away direction when occlusal forces act on artificial

teeth.

2- Sticky foods and muscle pull, acting on the periphery of the denture.

3- Intercuspation and occlusion of teeth

Resistance to vertical and lateral tipping forces (rocking) is gained by:1. Adequate base coverage.

2. The use of three, and if possible four, widely separated areas of tooth support

3. Rigid bracing clasp arms

4. Balanced occlusal contact and reduction of cusp slope.

5. The use of additional rests serves as, indirect retainers.

6. Coverage of the rugea area acts as an indirect retainer.

Stabilizing components of the removable partial denture framework are those rigid

components that assist in stabilizing the denture against horizontal movement.

o minor connectors that contact vertical tooth surfaces

o reciprocal clasp arms

Minor connectors

• should have sufficient bulk to be rigid

• Little bulk to the tongue as possible.

• Should be confined to interdental embrasures whenever possible.

• When minor connectors are located on vertical tooth surfaces, it is best that these

surfaces be parallel to the path of placement.

A modification of minor connector design has been proposed that places the minor

connector in the center of the lingual surface of the abutment tooth. Proponents of this design

claim that it reduces the amount of gingival tissue coverage and provides enhanced bracing

and guidance during placement. Disadvantages may include increased encroachment on the

tongue space, more obvious borders, and potentially greater space between the connector and

the abutment.


Mostafa Fayad 13

Reciprocal clasp arms

It must be rigid, and they must be placed occlusally to the height of contour of

the abutment teeth

When crown restorations are used, a lingual reciprocal clasp arm maybe insert

into the tooth contour by providing a ledge on the crown on which the clasp arm may

rest. This permits the use of a wider clasp arm and restores a more nearly normal tooth

contour, at the same time maintaining its strength and rigidity.

Guiding Plane

It is defined as two or more parallel, vertical surfaces of abutment teeth, so

shaped to direct a prosthesis during placement and removal.

Guiding planes may be contacted by various components of the partial denture:

the body of an extracoronal direct retainer, the stabilizing arm of a direct retainer, the

minor connector portion of an indirect retainer, or by a minor connector specifically

designed to contact the guiding plane surface.

The functions of guiding plane surfaces are as follows:

(1) To provide for one path of placement and removal of the restoration (to eliminate

detrimental strain to abutment and framework during placement and removal).

(2) To ensure the intended actions of reciprocal, stabilizing, and retentive components

(to provide retention against dislodgment of the restoration when the dislodging force

is directed other than parallel to the path of removal and also to provide stabilization

against horizontal rotation of the denture).

(3) To eliminate gross food traps between abutment teeth and the denture.

Dimensions of guiding plane surfaces:

As a rule, proximal guiding plane surfaces should be about one half the width of the

distance between the tips of adjacent buccal and lingual cusps or about one third of the

buccal lingual width of the tooth. They should extend vertically about two thirds of the

length of the enamel crown portion of the tooth from the marginal ridge cervically.

Guiding planes squarely facing each other should not be

prepared on lone standing abutment. Minor connectors of

framework (gray areas) would place undue strain on abutment when

denture rotated vertically either superiorly or inferiorly.


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V-Designing for indirect retention:

Methods of indirect retention:

► For distal extension bases (Class I and II) indirect retainers placed on the

anterior part of the jaw are necessary.

► A class III denture whose saddles cannot, for some reasons, be clasped

adequately may require anterior and posterior indirect retainers.

► Consequently, indirect retainers may be divided into those placed in the anterior

and those in the posterior part of the mouth.

- In the upper jaw either the teeth or the hard palate can be used to place an indirect

retainer, whereas in the lower the teeth only can be used.

► Class IV dentures require an indirect retainer placed posteriorly to counteract a

displacement of the anterior saddle away from the ridge

- The forms of indirect retention shown in the following table are popular types:

Contrary to common use, a cingulum bar or a linguoplate does not in itself

act as an indirect retainer. Because these are located on inclined tooth surfaces, they

serve more as an orthodontic appliance than as support for the partial denture. When a

linguoplate or a cingulum bar is used, terminal rests should always be provided at

either end to stabilize the denture and to prevent orthodontic movement of the teeth

contacted. Such terminal rests may function as the indirect retainers,


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VI- Designing the connector:

Types of maxillary major connector:

1- Single palatal bar.

2- Anteroposterior or double palatal bar.

3- Single palatal strap.

4- Horseshoe or U-shaped palatal bar.

5- Closed shoe or Anteroposterior palatal strap.

6- Complete palatal plate.

Types of Mandibular major connector:

1- Lingual bar.

2- Sublingual bar.

3- Double lingual bar.

4- Lingual plate.

5- Labial bar.

VII-Minor connectors:

Design considerations:

-it should be ensuring that there is 5 mm of space between adjacent vertical minor

connectors to prevent food impaction.

- must contact the guiding plane surfaces of the teeth to facilitate path of insertion

and provide bracing.

-should cross the gingival tissue abruptly and join the major connector at rounded

right angles. These allow them to cover as little as possible of the gingival tissues.

VIII- Esthetic:

The function and esthetics of removable partial denture are dependent on

the correct orientation of the occlusal plane. The main esthetic problem is the

presence of visible retainers in the buccal vestibule. Rotational path partial

denture may be used to improve esthetic


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ADDITIONAL CONSIDERATIONS INFLUENCING DESIGN

Use of a Splint Bar for Denture Support

a removable partial denture should replace only the missing posterior teeth after the remainder of the arch has been made intact by fixed restorations.

Occasionally, it is necessary that several missing anterior teeth be replaced with the RPD rather than by fixed restorations. This may be because of

• The length of the edentulous span,

• The loss of a large amount of the residual ridge by resorption,

• Accident or surgery,

• The result of a situation in which too much vertical space prevents the use of a fixed partial denture or

• If esthetic requirements can better be met through using of teeth added to the denture framework.

It is necessary to provide the best possible support for the replaced anterior

teeth. Ordinarily, this is done through the placement of occlusal or lingual rests, or

both, on the adjacent natural teeth, but when the edentulous span is too large to

ensure adequate support from the adjacent teeth, other methods must be used.

An anterior splint bar may be attached to the adjacent

abutment teeth in such a manner that fixed splinting of the

abutment teeth results, with a smooth, contoured bar resting

lightly on the gingival tissue to support the RPD. the

connecting bar may be cast of a rigid alloy, or a

commercially available bar may be used and cast to the abutments or attached to

the abutments by soldering. The length of the span influences the size of a splint

bar. Long spans require more rigid bars (10 gauge) than short spans (13 gauge).

The proximal contours of abutments adjacent to splint bars should be parallel to

the path of placement. The splint bar must be positioned antero posteriorly just

lingual to the residual ridge to allow an esthetic arrangement of artificial teeth.


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Internal Clip Attachment

The internal clip attachment differs from the splint bar in that the internal clip

attachment provides both support and retention from the connecting bar.

Several preformed connecting bars are commercially available in plastic

patterns. These can be customized for length and cast in the metal alloy of choice.

Internal clip attachments are also commercially available in various metal alloys

and durable nylon.

The cast bar should rest lightly or be located slightly above the tissue. Retention

is provided by one of the commercial preformed metal or nylon clips, which is

contoured to fit the bar and is retained in a preformed metal housing or partially

embedded by means of retention spurs or loops into the overlying resin denture

base. The internal clip attachment thus provides support, stability, and retention for

the anterior modification area and may serve to eliminate both occlusal rests and

retentive clasps on the adjacent abutment teeth.

Overlay Abutment (Overdenture abutments and overlay-type prostheses)

Indications:

1- When salvage the roots and a portion of the crown of a badly broken-down

molar through endodontic treatment.

2- A periodontally involved molar, indicated for extraction, may sometimes be

salvaged by periodontal and endodontic treatment accompanied by reduction

of the clinical crown almost level with the gingival tissue.

3- An unopposed molar may have extruded to such an extent that restoring the

tooth with a crown is inadequate to develop a harmonious occlusion.

4- A molar that is so grossly tipped anteriorly that it cannot serve as an

abutment unless the clinical crown is reduced drastically.


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In these cases, teeth should be considered for possible support.

Endodontic treatment and preparation of the coronal portion of the tooth as a

slightly elevated dome-shaped abutment should be done.

Use of a Component Partial to Gain Support

A component partial is a removable partial denture in which the framework is

designed and fabricated in separate parts. The tooth support and tissue-supported

components are individually fabricated, and the two are joined with a high-impact

acrylic resin to become a single, rigid functioning unit.


Mostafa Fayad 19


Mostafa Fayad 20

Designing Removable Partial Dentures

Problems and General Principles

1- Kennedy Class I Partial Dentures

It is More frequent in lower than upper jaw

Problems associated with bilateral free-end saddles :

1- Lack of posterior abutment is usually associated with lack of adequate

posterior support and retention.

2- Support is derived from both the residual ridge and abutment teeth. The

variation in displaceability providing this support allows some rotational

movements of the free-end base towards the soft tissues. These harmful

movements are transmitted to abutment teeth resulting in loosening of these

teeth.

3- Major support is obtained from the residual ridge especially at the distal part.

This causes frequent residual ridge resorption.

4- If resorption occurs and relining of the denture is neglected further bone

resorption occurs with subsequent torque acting on the abutments.

5- Stability.

6- The need for indirect retainers.

7- Esthetic.

Possible rotational movements of distal extension bases:

• Rotational about the fulcrum axis formed by the two principle occlusal rests.

• Rotational movement along the longitudinal axis of the residual ridge.

• Rotational movement along perpendicular axis passing through the centre of

the arch.


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Factors influencing the support of a distal extension base:

Support of a distal extension partial denture depend on :

1-Total occlusal load applied

The more the load applied the higher the degree of tissue

displacement.

The reduction of the size of the occlusal table reduces the vertical

and the horizontal force. Increase the efficiency of the occlusal surface

of the artificial teeth by addition of supplementary groves & sluice ways

increase in cutting action & improve the masticatory performance of the

teeth. This leads to less force required in chewing and less force will

then be transmitted to the residual ridge. All these actions help improved

the support for the denture base.

2- Quality of the residual ridge.

o Quality of soft tissues covering the edentulous ridge.

o Contour and quality of the residual ridge

o Denture bearing area.

Easily displaceable tissue will not adequately support a denture

base. The thicker the mucoperiosteum the more it is liable to be

displaced. A firm, tightly attached mucosa, several mm thick, will give

greatest support.

3-Extent of residual ridge coverage by the denture base

The broad the coverage, the greater is distribution of the load, thereby

resulting in fewer loads per unit area.

4-Accuracy of the fit of the denture base

The better the base fits the denture foundation the less the degree of

displacement. Metal bases have better fit than acrylic resin bases.

5-Type (anatomical or functional) and accuracy of impression registration

against which the denture bases are fabricated

When an appliance is entirely tissue supported mucosa, tissue-ward

movement of the appliance will take place, to the degree that the tissue

will be displaced by pressure (tissue rebound). Minimization of tissue


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ward movement of the partial denture can be accomplished by wide

coverage.

6- Design of the partial denture Framework

The rotation forces take place around the fulcrum line can be controlled by using of indirect retainers anterior to the fulcrum line. If the distal extension denture is bilateral two indirect retainers are needed one on each side of the arch. If the edentulous space is unilateral only one indirect retainer is needed anterior to the fulcrum line on the opposing side of the arch from the distal extension ridge.

7- Denture- bearing area:

In the maxillary arch: - The buccal slopes of ridge, normally covered by a layer of cortical bone can withstand stress. But the buccal slope is rarely perpendicular to the vertical force occurring against it, so it gives little resistance to them. However the buccal slope will resist the lateral forces, reducing the total force.

In the mandibular arch:- the crest of the ridge can't be used as a primary stress bearing area, because it's composed of cancelous bone, covered by thin & less firm mucosa. The buccal shelf area is excellent primary stress bearing area in the mandible, because it is very dense cortical bone covered by firm & dense mucosa. The buccal shelf area is normally perpendicular or nearly so, to the vertical force would be occurring against it. The buccal & lingual slopes of the residual ridge have cortical bone and can contribute to resisting horizontal forces.

Problems of distal extension bases can be reduced by :

I. Controlling the load applied on abutment and residual:

I- Reduction of the load.

II- Distribution of load can be achieved by:

1- Varying the connection between the clasps and saddles:


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A-Applying the stress-breaking principle

b- Combining rigid connection and flexible clasps

c. Combining rigid connection and rigid clasps. (↑load on the tooth)

2- Anterior placement of occlusal rests

3- Improving the supporting quality of edentulous ridges:

- Improving the condition of the residual ridge

- By muco-compression impression techniques

III- Wide distribution of the load.

IV- Providing posterior abutments.

1- Using an implant at the distal part of the ridge.

2- Salvaging a hopeless posterior tooth.

II. Enhancing support by

1- Converting the case to:

A. Removal partial overdenture using endosseous implant in each side.

B. Fixed bridge connecting endosseous implant to the posterior tooth.

C. Fixed bridge connecting two endosseous implants in each side.

2- Ridge augmentation

3- Splinting of abutment

4- Improving the supporting quality of edentulous ridges:


- By muco-compression impression techniques

III. Achieving good stability: Using Rigid Major & Minor Connectors

IV. Using Indirect retainers

V. Using esthetic retainers

I- Reduction of the load

The vertical load applied on the saddle during mastication should be reduced in order to minimize vertical displacement of the denture base. The vertical load may be reduced by decreasing the size of the occlusal table and by maximum extension of the denture base within the functional limits of muscular movements.

This can be achieved by:


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1- Using canines and premolars instead of premolars and molars.

2- Using narrow teeth (bucco-lingually) or reduction of the width of the selected teeth by removing the lingual cusps.

3- Leaving a tooth off the saddle.

4- Increase the sharpness of the cusps.

5- Increasing efficiency of the occlusal surface of the artificial teeth by addition of supplemental grooves aids the cutting action and improve masticatory performance of the teeth.

II- Distribution of the load between abutment teeth and ridge

Distribution of load can be achieved by:

1) Varying the connection between the clasps and saddles:

a-Applying the stress-breaking principle

Movement of the denture base over displaceable mucosa will be transmitted to the abutment tooth if the tooth is connected to the denture base by a rigid connector. These stresses will induce torque on* the abutment. However, these stresses will be dissipated if some flexibility is allowed. The stress breaking principle will thus apply less stresses and less torque on abutments.

Stress breakers:

A stress breaker or stress equalizer is a device which allows movement between the saddle unit and the retaining unit.

Thus, when a vertical load is applied, the stress breaker will allow movement of the saddle towards the ridge to a greater extent than if the retainer unit is directly connected to the saddle, although the ridge bone will be subjected to an increased load. However, this load is widely distributed antero-posteriorly over the ridge and not on the distal part only. Also flexibility of the stress breaker can be changed to govern the distribution of load between the ridge aril abutments.

Stress breakers may be in the form of:

• Movable joints as hinges between the saddle unit and the retaining unit. e.g.attachments like Dalbo or Crisimany attachments,


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• Designs applying the stress breaking principle used in combination with the

main rigid connector (using flexible connection between the direct retainer and

the denture base ).{for detail see stress breaker}

- � Split major connector ( Split casting modifying the lingual plate)

- � Wrought wire connector soldered to lingual bare.

- � Lingual bar connector with flexible distal extension (having thinner section than lingual bar (use of semi-flexible bar).

- � Disjunct RPD.

b- Combining rigid connection and flexible clasps (stress releasing clasps)

Flexible gingivally approaching clasps (bar clasps)

The retentive tip of gingivally approaching clasps contacting the abutment tooth' originates from the saddle in the form of a bar. The degree of flexibility of the bar can be varied depending on its length, diameter, cross section and die alloy used. Thus a flexible bar may move gingivally into the undercut which in turn dissipates some of the stresses falling on the abutment tooth.

Thus, bar clasps apply the stress-breaking principle. I-bar, RPI clasps are examples of gingivally approaching clasps that provide a stress breaking effectwhen a rigid connector is used in distal extension bases.

Flexible occlusally approaching clasps

Occlusally approaching clasps can be used in distal extension bases when a wrought wire retentive arm is used instead of a cast clasp arm.

The resilient wrought wire arm allows some movement of the clasp over the tooth, thus following the stress breaking principle. Back-action clasps are also used in distal extension bases due to their stress breaking effect. It should be noted that excessive resiliency is not favorable because it results in an unretained denture.

Flexible combination clasps

c. Combining rigid connection and rigid clasps.

It can be rarely used in young age, will developed ridge, and very short saddle.

Clasps with Stress breaker action as:

1. Gingivally approaching resilient I-bar clasp.


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2. Occlusally approaching clasp having resilient retentive wrought gold wire arm (Combination clasp).

3. Back-action clasp.

4. Reverse back-action clasp.

5. Extended-arm clasp.

6. Ring clasp.

7. Wrought wire clasp.

8. RPI clasp.

9. RPA clasp.

2) Anterior placement of occlusal rests:

Placement of the occlusal rest in a more anterior position helps in favorable distribution of occlusal load between the abutment tooth and the residual ridge.

• The farther the anterior placement of the rest, the more vertical will be the forces, the less is the horizontal component of force falling on the ridge,

The rest proximal plate, I bar clasp (RPI) and the reverse circlet clasps have mesially located rests which can fulfill this requirement,

Advantages:

• Achieving a mechanical advantage by changing the stresses acting on the saddle from a .class I lever to a more favorable class II lever

• Greater part of the occlusal load will be borne by the ridge and hence less stresses and less torque on the abutment.

• Even distribution of the load 'in an antero-posterior direction. The bone near the abutment will thus share the distal part of the ridge in bearing the occlusal load,

• Changing the direction of torque on the abutment from the distal to the mesial side of the tooth where resistance to torque action will be supplied from the neighbouring teeth.

Disadvantages:

• Wedging effect

• Food impaction between distal surface of abutment and RPD.

- the RPI System. - The Balance of force system. !!! !!!! !


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3) Improving the supporting quality of edentulous ridges:


- By Functional impression techniques

- Functional impression techniques:

McLean’s physiologic impression (done at the master impression stage) Hindels' physiologic impression (done at the master impression stage) Functional denture base: Functional relining and fluid wax impression

techniques. Selective pressure impression technique.

III- Wide Distribution of Load

Distribution of the occlusal load widely is effective in reducing the force per unit area on the residual ridge.

1- Wide distribution of the load over the ridge.

The denture base should cover the largest possible area and should be adequately extended to the functional limit of the surrounding musculature. The broader the coverage, the greater the distribution of load, the more the ability of the denture to withstand vertical and horizontal stresses.

2- Wide distribution of load over the teeth:

Distribution of the vertical load on teeth can be achieved by placing an additional rest on the tooth adjacent to the abutment, by an embrassure clasp, embrasure hooks or by splinting. Using a Kennedy bar to distribute the lateral load on multiple teeth.

IV- Providing Posterior Abutments

The problem of distal extension bases can be solved by provision of posterior5ahujtrnents and construction of a partial oeverdenture. This can be achieved by:

1- Using an implant at the distal part of the ridge.

2- Salvaging a hopeless posterior tooth.

A hopeless badly decayed tooth, a periodontally affected tooth or a tooth with furcation involvement can be reduced in both contour and height to be used as a partial overdenture abutment.

V- Functional impression


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The normal mucosa covering the ridge can be recorded in its displaced functional form rather than the anatomic form. This reduces movement of the denture base towards the tissues during function, which in turn helps in reducing leverage and torque on the abutment teeth.

However, maximum displacement of the mucosa should be avoided. This is because when the mucosa is subjected to heavy continuous pressure, a decrease in the blood supply and drainage from soft tissues occur, resulting in pain under the denture, atrophic changes and future bone resorption.

VI-Improving the supporting quality of edentulous ridges


The presence of a well formed residual ridge covered by healthy firm mucosa, provides favorable partial denture support. However, the presence of tori or hyperplasic tissues necessitates correction to improve the supportive ability of the ridge.

VII- Using esthetic retainers

Numerous esthetic clasp systems are available for distal extension RPD.These clasps can either utilize the proximal, lingual, labial or buccal retentive undercut.

Examples: Mesiodistal clasp, the De-Van clasp, the Equipoise clasp and twin Flex clasp

Class I partially edentulous cases when the remaining teeth are weak, periodontally affected, and require splinting and stabilization are sometimes treated using swing-lock partial dentures.

Anterior modification spaces of class I cases, are preferably restored separately with a fixed bridge. This helps in simplifying the partial denture design and also helps in saving the anterior ridge from resorption and the anterior abutments from torque. Possible solutions 1.Extraction of weak abutment. 2. Removable partial overdenture.3. Splinting by fixed bridge and conventional RPD. 4. Addititional saddle to the lingual bar with using wrought wire clasp and no occlusal rest on the single standing tooth.

MAXILLARY BILATERAL FREE END SADDLES

1) Under vertical load the posterior sink of the saddle is less marked due to:

- The submucosa covering the tuberosity has dense fibres than retromolar area.


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- Extra palatal coverage >>>> reduce displacement under load

2) Lateral load is shared over a great area of bone (palate) and hence the lateral load

falling on the abutments is less than lower

3) Anteroposterior movement is prevented by: Standing teeth Anterior slope of palate

Tuberosity

Kennedy Class II Partial Dentures

Problems associated with a unilateral free-end saddle:

1- Class II partial dentures have problems resulting from the absence of a posterior

abutment which causes lack of proper posterior support and retention.


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• Being tooth-tissue borne, the difference of displaceability of the supporting

tissues results in tissue ward movement of the denture base with subsequent torque

on the abutment tooth.

• Lack of adequate posterior retention causes displacement of the denture away

from the tissues with subsequent torque on the' abutment.

2- The absence of a saddle on the other side of a class II partial denture

complicates the retention of the appliance. This is due to decrease in the physical

means of retention and due to the lack of the retentive effect of the tongue and

cheek muscles that would rather act in the presence of a modification area on the

other side.

The main problem: is the same as with the bilateral free-end saddle denture including:

a) Torque of abutment.

b) Ridge resorption.

Management: as Class I-Kennedy RPD.

c) The problem of retention (similar saddle is not present on the other side)

Management: Additional retention must be provided on the intact side by:

- Clasping more than one tooth on this side

- More rigid types of clasp.

b) The problem of bracing (due to absence of rigid major connector)

Management:

- Cross-arch bracing (Through a rigid major connector).

- Bracing components.

Problems of unilateral distal-extension bases can be reduced by:

• Load reduction and distribution.

• Provision of adequate posterior support.


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• Using an indirect retainer to counteract rotation of the denture in an occlusal

direction.

• Providing adequate retention on the dentulous side by using rigid clasping or

multiple clasping on the intact side.

• Providing posterior abutment using an implant at the posterior part of the ridge

and the construction of an implant supported partial overdenture.

Designing class II partial dentures:Designing class II partial dentures usually follow the same basic principles.

However, some modifications of the design are required depending on the length of

the saddle and the presence of modification areas.

I- Designing class II partial dentures with no modifications:

Divided into two groups depending on:

� The nature of the edentulous ridge,

� The length of the edentulous ridge and

� The condition of the abutment.

Two basic designs can be followed in unmodified class II partial dentures

1- Designs using rigid clasping and rigid connection between the saddle and the

retainer. (Rigid design)

This design is indicated in:

a- Short edentulous span bounded ,

b- Cases having well formed edentulous residual ridge covered with firm

mucosa of normal thickness.

c- strong abutment with healthy periodontium.

2- Designs applying the stress breaking principle. (flexible design)

A class II partial denture design may require a stress breaking effect when the

condition of the abutment, the length of the saddle and the compressibility of the

mucosa contra-indicate the use of rigid clasping and rigid connection.

An embrasure clasp is usually used on the dentulous side. An indirect retainer

should be provided to counteract rotation of the denture away from the tissues.

Designs applying the stress breaking principle:

- The use of semi-flexible bar: This is more applicable with shot saddles, it

involves anterior placement of an occlusal rest.


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1- The occlusal rest is placed on the far zone of the abutment tooth.

2- The abutment is rigidly clasped, and joined to the clasp onto the

opposite dentulous side by a rigid connector (lingual bar).

3- The saddle is joined to the retainer unite by a semi-flexible bar

that allows some movement and provides stress breaking action.

4- An embrasure clasp is usually used on the dentulous side. (used

with short saddle)

- Split casting modifying the lingual plate: a split of appropriate length is made at

the inferior border of the plate.

1- The saddle is joined to the more flexible part of the plate. The

lower part must be flexible in the vertical direction, than

horizontal direction, so that the appliance will have lateral rigidity

to distribute horizontal force widely.

2- This design applied in long class II cases. (used with long saddle)

3- Disadvantages : The slit opens slightly in function and

theoretically is liable to trap either the tongue or food particles.

With a long saddle, however, the slit is anteriorly placed and in

this position may be intolerable to some patients. The patient

using dental floss can clean the slit easily.

II- Class II with modification spaces:

The presence of modification spaces on the opposite side of a Kennedy class II

simplifies the partial denture design. The problem of retention is solved by the

presence of saddles on the modification areas. The clasps on abutments bounding

the modification area provides retention, bracing and reciprocation together with

indirect retention,


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Retention on the side of the bounded saddle is dependent upon the ability of the

single molar tooth to withstand the loads applied; therefore:

i. If the periodontal condition of such a single standing tooth is good, rigid

construction is employed and frequent inspection of the appliance is essential so that

rebasing may compensate resorption under the free-end saddle. If this is not done, a

damaging torque will be applied to the single standing molar leading at least to

increased tilting and at worst to loosening and eventual loss.

ii. If the periodontal condition of such a single standing tooth is doubtful, it

may be possible to design the denture incorporating a flexible connector to the distal

extension saddle as already described. In addition less stress will be applied to the

tooth if wrought wire instead of cast metal is used for clasp construction.

THE MAXILLARY UNILATERAL FREE-END SADDLE DENTURE

• Unmodified maxillary unilateral free-end saddle dentures are not

common.

• Those with modifications are encountered frequently due to the loss of

teeth due to caries, and hence a well-formed ridge is present.

• Rigid constructions are almost always.

• Clasping of the abutment tooth (Flexible clasping) and suitable

teeth on the opposite side.

• If for any reason complete palatal coverage with a plate is used,

clasping may be unnecessary

• As with bilateral free-end saddles the single standing premolar may be a

complication.


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A ] Essentials of Design for Classes I and II

1- Direct retention

Retention should not be considered the prime objective of design. The main objectives should be the restoration of function and appearance and the maintenance of comfort, with great emphasis on preservation of the health and integrity of all the oral structures that remain.

Close adaptation and proper contour of an adequately extended denture base and accurate fit of the framework against multiple, properly prepared gulde planes should be used to help the retentive clasp arms retain the prosthesis.

2- Clasps

a- The simplest type of clasp that will accomplish the design objectives should be employed.

b- The clasp should have good stabilizing qualities, remain passive until activated by functional stress, and accommodate a minor amount of movement of the base without transmitting a torque to the abutment tooth.

c- Usually stress releasing designs are preferred.

Stress director attachments.

Wrought wire clasps. RPI, I-bar, combination clasps, back action, reverse back action or reverse circlet clasps can be used.

Remote rest and other conventional clasps.

Split major connectors - permit more rigid clasp designs.

d- Clasps should be strategically positioned in the arch to achieve the greatest possible control of stress.

Class I prosthesis usually requires only two retentive clasp arms: one on each terminal tooth.

If a disto-buccal undercut is present, the vertical projection retentive clasp is preferred.

If a mesio-buccal undercut is present, a wrought wire clasp is indicated.

The reciprocal or bracing arm must be rigid. This component of the clasp system can be replaced by lingual plating.

Class II prosthesis should usually have three retentive clasp arms.

The distal extension side should be designed with the same considerations as for a class I prosthesis.


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The tooth supported, or modification, side should usually have two retentive clasp arms : one as far posterior and one as far anterior as tooth contours and esthetics permit. If a modification space is present, it is usually most convenient to clasp a tooth anterior and a tooth posterior to the edentulous space.

- The type of clasp and position of the retentive undercut can be selected for convenience.

- Rigidity is required for all bracing arms. Lingual plating may be substituted.

Stress releasing clasps

a- Clasps with mesial rest

- RPI - RPA

- Combination clasps

b- Clasps with distal rest

- Wrought wire clasps. - I-bar

- Back action - Reverse back action

- Reverse circlet clasps - c-clasp

3- Rests

Rest seats should be prepared so that stress will be directed along the long axis of the teeth.

Although adjacent (proximate) rests may provide efficient force transmission to abutment teeth, remote rest clasp designs are often more desirable since they may decrease unfavourable torquing forces on abutment teeth from clasps.

Rest seats should be carefully located and prepared to avoid torque and allow transmission of stresses along the long axes of abutment teeth.

The floor of the rest seat should inclined apically as it approaches the center of the tooth. The angle between the minor connector and the rest should be less than 90˚ to prevent slippage of the prosthesis creating an orthodontic like force and to direct the forces along the long axis of the tooth.

Mesially placed rests are preferably used on abutment teeth. However, absence of a rest adjacent to the edentulous area may permit packing of food. This could be avoided by using .


Mostafa Fayad 36

Saucer-shaped rest seats are preferred over box shaped seats to avoid locking of the rest and transmission of torque on abutments.

The occlusal rest must fit the tooth to minimize the food collection beneath it and preserve their location in relation to the tooth.

It must be strong enough to withstand the loads without deformation.

It must not raise the vertical dimension of occlusion.

4- Indirect Retention

1. Indirect retention should be employed to neutralize unseating forces.

The indirect retainer should be located as far anterior to the fulcrum line as possible.

Two indirect retainers should generally be used in a class I design, whereas one placed on the side opposite the distal extension base may be adequate in a class II- design.

The indirect retainers should be positioned in teeth prepared with positive rest seats that will direct forces along the long axis of the tooth.

2. Lingual plating can be used to extend the effectiveness of indirect retention to several teeth. It must always be supported by positive rest seats.

5- Major connector

a- The simplest connector that will accomplish the objective should be selected.

1- The major connector must be rigid.

2- Promotes cross-arch force transmission (contributes to cross arch stability and support)

3- It must not impinge on gingival tissue.

b- Support from the hard palate should be used in the design of the maxillary major connector when it would be beneficial.

c- Extension of the major connector onto the lingual surfaces of the teeth may be employed to increase rigidity, distribute or eliminate potential food impaction areas. Lingual plating should always be supported by adequate rest seats.

d- Antero posterior palatal bars and palatal plates are preferred for maxillary class I cases to provide maximum support, direct and indirect retention.

e- For mandibular class I cases, lingual bars with terminal rests are preferred due to their simplicity, limited coverage and patient's tolerance. However, mechanically, lingual plates


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with terminal rests are biologically preferred due to their rigidity, distribution of lateral forces and due to improved indirect retention.

6- Minor connectors

1. Minor connectors must be rigid.

2. Minor connectors should be positioned to enhance comfort, cleanliness, and the placement of artificial teeth.

7- Proximal plates (guiding Plates)

-Guiding planes are flat axial parallel surfaces in an occluso-gingival direction on the

proximal or lingual surfaces of teeth. They are 2-4 mm in height، extending from

the marginal ridge to the junction of the middle and gingival third of the

abutment tooth. The bucco-lingual width of the proximal plate is determined by

the proximal contour of the tooth.

-For bounded base a well-engineered guiding planes are contacted by the truss arms

of the framework as the prosthesis is inserted and removed, thus horizontal

wedging is virtually eliminated.

-In distal extension base a pronounced guiding plane is not recommended

-The proximal plate minor connector is placed on a distal guiding plane. It

should contact approximately 1 mm of the gingival portion of the guiding

plane in distal extension cases. The interface between the tooth surface

and the clasp should be such that a slight degree of movement of the base

and the clasp is permitted without transmitting torsional stress to the

tooth.

-The proximal plate together with the mesiolingually placed minor connector

provides stabilization and reciprocation of the assembly.

Guiding plane surface should be like area of cylindrical object It should be continuous surface unbounded by even rounded line angle. B, Minor connector contacting guiding plane surface has same curvature as does that surface. From occlusal view it tapers buccally from thicker lingual portion, thus permitting closer contact of abutment tooth and prosthetically supplied tooth. Viewed from buccal aspect, minor connector contacts enamel of tooth on its proximal surfaces about two-thirds its length.


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Diagrammatic illustration showing comparative width of the proximal plates for differently contoured teeth. (A). Proximal plate (p) relatively wide due to the square contour of the 2nd bicuspid. (B). Proximal palate (p) relatively narrow due to the tapering contour of the 1st bicuspid. The proximal plate should be designed as narrow as possible but should prevent lingual migration of the tooth. A narrow proximal plane permits greater exposure of the gingival tissue (g).

8- Occlusion

1.Centric occlusion and centric relation should be coincide.

2.A harmonious occlusion should be established with no interceptive contacts and with all eccentric movements dictated by, or in harmony with, the remaining natural teeth.

3.Artificial teeth should be selected and positioned to minimize stresses produced by the prosthesis.

Smaller and/or fewer teeth, and teeth that are narrower bucco-lingually may be selected.

For mechanical advantage teeth should be positioned over the crest of the mandibular ridge when possible.

Teeth should be modified if necessary to produces sharp cutting edges and ample escape-ways.

9- Denture base

1.The base should be designed with broad coverage so that the occlusal stresses can be distributed over as wide an area of support as possible. The extension of the borders must not interfere with functional movements of the surrounding tissues.

2.A selective pressure impression should record the residual ridge in a functional form. Or it may be constructed in the static form if the stress breaking principle is applied.

3.The polished surfaces should be contoured to enable the patient to exercise maximum neuromuscular control.

4. A combined metal-acrylic base is used to allow for future relining as bone resorption is usually anticipated.

Recontouring

The contours of the natural teeth most often require adjustments for the proper placement and functioning of the RPD.


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Recontouring may be required to

1. Improve survey lines (improve clasp loca on),

2.Improve clasp reten on (dimpling)

3.Improve the occlusal plane by grinding of the cusp tips and incisal edges of

anterior teeth.

Excessive tooth contours are reduced by lowering the height of contour so that;

1. The origin of the circumferential clasp is placed preferably at the junction

of the middle and gingival third of the crown

2. The retentive terminal is placed in the gingival third of the crown for

better esthetics and better mechanical advantage.

3. The reciprocal clasp is placed above the height of contour, but not higher

than the cervical portion of the middle third of the crown.

Kennedy Class III Partial Dentures

Problems associated with unilateral bounded saddles:

Two opinions exist to restore short edentulous space by removable partial dentures.

1- Restoring a single tooth or a short span unilateral area is not practical especially in cases having bad oral hygiene and caries susceptibility.

2- Restoration of any missing tooth is necessary in order to: -Restore the integrity of the dental arch, prevent tilting, drifting, rotation or overeruption of the remaining natural teeth.

- Restore the masticatory mechanism.

- Restore aesthetics.

Restoration of the unmodified class III: (Unilateral bounded areas)

I - Implant retained restoration

II - Fixed bridges:

Fixed bridges are usually the treatment of choice for short span bounded edentulous areas when:


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- Implant retained restoration is contraindicated.

- Abutments are strong and healthy

- Aesthetics is of great concern.

- Minimum bone loss exists.

- The oral hygiene is good.

III - Unilateral partial dentures (side plates or removable bridges):

Unilateral partial denture is constructed to restore one side of the arch and not extended to the other side. This prosthesis has less retention and stability, permits limited load distribution and is unsafe to use due to the probability of being inhaled or swallowed.

The following measures are used to avoid instability of unilateral partial dentures:

a- Provision of lingual and buccal cusp contacts on the working side in lateral movement.

b- Maximum extension of the rest seat preparation and the occlusal rest especially to the buccal side. This keeps the axis of rotation as far buccally as possible and ensures transmission of vertical component of force lingual to this axis.

c- Providing adequate bracing against lateral movement especially buccal movement. This can be achieved by:-

- Extending the denture base on the vertical slope of the hard palate.

- Bracing arms located on the abutment tooth and the tooth adjacent to it.

- Clasping adjacent teeth to allow wider load distribution laterally.

- Using box shaped rest seat preparation to increase bracing.

d- Providing adequate retention against both vertical and buccal displacement. This can be achieved by using clasps that provide both buccal and lingual or palatal retention i.e. a clasp with bilateral bracing and retention.

Contra indications of unilateral partial dentures:

Unilateral partial dentures are contra indicated in the following cases:

- Patients employing excessive lateral movement during mastication.

- Patients exhibiting bruxism.


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- Conical shaped abutment teeth, weak teeth, or teeth having short crowns that cannot provide adequate retention and bracing.

- In old patients.

IV - Bilateral partial denture:

A partial denture restoring a unilateral bounded edentulous area is extended to the other side of the intact arch . Bilateral removable partial dentures provide better retention and stability together with wider load distribution.

Bilateral class III partial denture design:

1-Denture base:

The denture base is designed to fit the static rather than the functional form of the ridge because the denture base is adequately supported on both sides by abutment teeth, i.e. tooth supported.

Metal plates are usually used except in the following cases:

- Long span bounded edentulous areas.

- Weak posterior abutments that may be possibly removed and change the case into a Kennedy class II

- Anterior edentulous spans requiring aesthetic that is provided by the colour of acrylic resin.

- Patients susceptible to bone resorption that may require future relining e.g. diabetic patient and after recent extractions.

2- Rests:

Rests are usually placed on the near zone of the abutment teeth to provide adequate support (fig. 6-4). Rest seats can be prepared in either a box-shaped or saucer -shaped configuration depending on the condition of the abutment teeth.

3- Clasps:

Rigid clasps are usually used on abutments bounding the edentulous area. An embrasure clasp is used on the intact (dentulous) side.

4- Major connectors:

A lingual bar is used for mandibular denture and a palatal bar or palatal strap is used for maxillary denture.


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Class III having modification areas:

Modification of class III involving short saddle are common in upper jaw. When the saddles are short and the abutment teeth are supported with sound healthy bone, a number of small fixed bridges may be the treatment of choice. Also a removable partial denture can be constructed.

When a modification space is present, the same principles for designing a bilateral denture are followed. However, four supporting rests should be used one on each abutment bounding the edentulous areas.

When Class III having long edentulous spans and modification spaces, they are usually considered tooth tissue supported dentures. Maximum coverage of the residual ridge and palatal tissues is required to provide adequate denture support retention of the denture abutment from physical forces as adhesion in addition to wrought wire clasps.

When the condition of upper teeth is not good, the best result can be obtained by using Every denture.

Every denture

Indication of Every denture:

Indicated in class III with many modifications and when the condition of the abutment is not good.

Principles of Every's partial denture design

1- Point contact between the abutment and artificial teeth:

By making. contact point, not contact area, the lateral forces are distributed mesiodistally along many teeth in the arch. Porcelain teeth is preferable to reduce wear in this cases. The lateral forces in Every denture are resisted by the palate, the buccal mucosa and anterior abutment teeth if present.

2- Wide embrasures between abutment and artificial teeth:

To allow natural stimulation of the gingiva and cleaning of the teeth .

3- Uncovered gingival

To prevent pockets between the denture and the tooth substance and allow natural stimulation of the gingiva .

4- Contact of the denture with a stabilizer (round Wire) distal surface of the last standing tooth:


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This stabilizer (round Wire) is used to prevent distal drifting of this tooth.

5- Maximum retention following the principles used in complete denture construction:

- Maximum coverage of the palate and full extension of the flanges.

- Peripheral darning antroposterior.

- Proper shaping of the polished surface to allow better muscular control.

- Free sliding occlusion: To reduce denture displacement during lateral movement.

- Free occlusion: Is a type of occlusion which permits the mandible to slide from one position to another, with the upper and lower teeth in contact and without intercuspation.

N.B. The base material will be acrylic resin with straight round wire used to form the stabilizer positioned posterior to the last standing tooth on each side of the arch.

Cobalt Chromium base may be used to overcome the disadvantages of acrylic resin (lack of strength).

Essentials of Design for Class III

I- Direct retention

1.Retention can be achieved with much less potential harmful effect on the abutment teeth than with the class I or II arch.

2.The position of the retentive undercut on abutment teeth is not critical.

2- Clasps :

1.The quadrilateral positioning of direct retainers is ideal.

2.The type of clasp selected is not critical.

Tooth and tissue contours and esthetics should be considered, and the simplest clasp possible selected.

If restorations are required to correct tooth contours, the wax patterns must be shaped with the surveyor.

Bracing arms must be rigid.

3- Rests

1.Rest seats should be prepared next to the edentulous space when possible.


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2.Rests should be used to support the major connector and lingual plating.

4- Indirect retention

1.Indirect retention is usually not required.

2.If one or both of the posterior abutment teeth are used for vertical support alone without retentive clasp arms, the entire design must follow the requirements of a class I or II design.

5- Major and minor connectors

- They must be rigid and meet the same requirements as for a class ! or II design.

6- Occlusion

- The requirements for occlusion are same as for a class I or II design.

7- Denture base

1.A functional type impression is not required.

2.The extent of coverage of the residual ridge areas should be determined by appearance, comfort, and the avoidance of food impaction areas.

Differentiation between two main types of removable partial dentures

Distal extension bases Bounded short saddleManner of support derive their primary support from

the tissue underlying the base and secondary supportfrom the abutment teeth

derives all of its support from the abutment teeth

Method of impression registrationNeed for indirect retentionBase material Necessitates the use of a base

material that can be relined to compensate for tissue changes.

Metal bases are more frequently used

requirements for direct retention

- clasp used in conjunction with a mesial rest, wrought-wire or bar-type retentive arm, combinationclasp- must be able to flex sufficiently to dissipate stresses that otherwise would be transmitted directly to the abutment tooth as leverage.

- Cast retentive arms are generally used- Only requirement of such clasps is that they flex sufficientlyduring placement and removal of the denture to pass over the height of contour of the teeth inapproaching or escaping from an undercut area.


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Kennedy Class IV!!

Kennedy class IV partial dentures are constructed to restore anterior edentulous spans that cross the midline. Long class IV cases are designed following the principles of free end saddle cases because the edentulous area exhibits abutments that lie posterior to the edentulous area and lacks anterior abutments.

Problems associated with class IV cases

1-Class IV cases are tooth-tissue supported; they are supported anteriorly by the tissues and posteriorly by the abutment teeth. Thus they exhibit problems associated with free end saddles. Lack of adequate support and retention causes rotation of the partial denture around the abutment resulting in torque effect on abutment teeth. The amount of torque is affected by:

- The degree of resiliency of the mucosa covering the residual ridge.

- Form of the dental arch; In V-shaped arches the artificial anterior teeth will be more distant from the fulcrum axis, thus, the magnitude of displacing forces will be more leading to excessive torque on abutment teeth.

2- Class IV cases occur at any age but are usually predominant in children and adolescents because anterior teeth especially upper teeth are subjected to trauma.


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3- The need for an esthetic restoration is a pre-requisite due to the anterior location of the edentulous area.

4- Frequent follow-up is usually required to detect the need for relining to compensate for ridge resorption.

Restoration of class IV cases

Missing anterior teeth are preferably restored with fixed partial dentures, implant supported removable or fixed partial dentures, or cast metal partial dentures depending on the condition and length of the edentulous area and the condition of abutment teeth.

I- Temporary restorations for class IV cases

II- Skeleton designs for class IV cases (metal RPDs)A- Skeleton design (metal RPDs) for short anterior spans

The first Design uses an anterior clasping system.The second design uses a posteriorly placed clasping system

B- Skeleton design (metal RPDs) for long anterior spans


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I- Temporary restorations for class IV cases

Temporary acrylic partial dentures may sometimes be required as in the following cases;

-In children where:

*Roots of abutment teeth are still incompletely formed.

*Bone growth is not yet completed.

*Space maintainer is required.

*Danger of further trauma is still expected.

-In adults where:

*Extensive mouth preparation is required.

*Bone remodeling is anticipated after recent extraction of teeth.

The most commonly used temporary appliance for restoring anterior teeth is the Spoon denture. It can be constructed for both children and adults.

Spoon Dentures

-The spoon denture is a tissue supported denture

-usually constructed in acrylic resin but may sometimes be made in cast metal.

-The spoon denture usually covers a large area of the palate to attain adequate support and to overcome the problem of retention usually associated with temporary appliances.

-The lateral borders of the denture are usually placed 3-4mm away from the gingival margin to avoid caries and gingivitis especially in children where adequate oral hygiene measures cannot be fulfilled.

-It is usually extended to the junction of hard and soft palate in order to:

-Gain retention through physical means as adhesion, cohesion and interfacial surface tension.

-Obtain posterior palatal seal required to enhance retention.


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Spoon dentures could be modified to enhance retention by:

- Extending the posterior part of the palatal plate laterally above the survey line of the first permanent molars. The first molar is then clasped by a 7mm stainless steel wire in the form of an Adam's crib. This design may be used where it is possible to adapte thin wire between opposing arches without interfering with occlusion.

- production of a cast cobalt chromium base with clasps engaging the buccal undercuts of the molar teeth (T-shaped cobalt chromium denture).

- Construction of a combined metal acrylic palatal portion. The anterior part is made in the form of cast chromium cobalt base joined to an acrylic resin posteriorextension carrying an Adam's clasp on the first molar.

The success of spoon denture depends on:

o The nature of the mucosa: best retention is obtained from firm mucosa of adequate thickness rather than thin mucosa.

o Form of the hard palate: Large palate having moderate slopes provides better retention by adhesion and cohesion and good stability. Flat palate provides better retention and less stability compared to palates exhibiting steep slopes where better stability and less retention are anticipated.

o Presence of an anterior labial flange to counteract displacement of the posterior part of the restoration.

o The degree of overlap of anterior teeth; the presence of deep overlap usually associated with partial loss of teeth especially in adults induces excessive stresses on the partial denture.

o The closeness of the occlusion: metal backings may have to be provided as an integral part of the casting.

o Incising food by the anterior denture teeth should be avoided to prevent

displacement of the denture.

Advantages:

• Small technical and chairside time.

• Gingivitis and caries are not caused (the gingival margins are left

uncovered and no extensive contact is made with the standing teeth)

Disadvantage:

• Poor retention.

• Displaced during incision so It is advisable to use radio opaque resin .


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II- Skeleton designs for class IV cases (metal RPDs)

Removable partial dentures are alternatives to fixed bridges in the following cases:

Cases where marked bone resorption necessitates the addition of an anterior labial flange to restore esthetics and provide lip support.

Cases having long, markedly curved edentulous spans as this may add excessive stresses to abutments.

Patients who refuse extensive preparations required to prepare abutments for fixed bridges.

A- Skeleton design (metal RPDs) for short anterior spans

Two skeleton designs are proposed for short span class IV cases:

1-The first Design uses an anterior clasping system.

Retainers in the form of attachments or bar clasps are placed on the canines or the first premolars. However, this places excessive stresses on the canines. For this reason," the canines should be diagnosed with long well formed roots to resist torque.

In this case, the denture is designed with a combined denture base, rests on the neighboring natural teeth for support, bar clasps as retainers, preferably on first premolars, and an anterior palatal strap as the major connector.

Anterior retention may gained by using mesio-distal clasping on canine and may reinforce by using Aker on first premolar. M. Connector: U-Shaped horse shoe. Indirect R. : distal O-Rest on 4.

It is indicated only when 1\ 1 are only missed and perfect bone support for canines. Contra-indicated in cases where torque is marked as in excessive bone resorption or more than 2 teeth are missing.

2-The second design uses a posteriorly placed clasping system.

The clasps are placed as far posteriorly as possible. This system is more favorable because it provides better retention and indirect retention. It is also esthetically more satisfactory. Canines are also protected from torque that may be implied by clasping.

In this case, the denture is designed with a combined denture base, rests on the neighboring natural teeth usually canines for support and an Aker clasp (embrasure clasp) or multiple Aker clasp placed on the two last standing molars on each side of the dental arch.


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Support: rests on canines & posterior abutments or tooth supported posteriorly & tissue supported anteriorly.

Retention: Double or Multiple Aker posteriorly and anterior flange engaging tissue undercut.

Major connector: two palatal bar connectors arising from the saddle and placed on the lateral walls of the palate equi-distance between the gingival margins and the midline. The distal ends of the bars are attached to the posteriorly placed double Aker clasps on both sides.

Indirect retention is encountered by the rests of the posterior clasps

3- An alternative form of treatment when the saddle is short is the sectional

denture in cases of large proximal undercuts on the natural anterior teeth.

One section is cast in metal and is inserted from the palatal aspect of the ridge,

which enables the proximal undercuts of the abutment teeth to be engaged. The labial

section which carries the teeth and the labial flange is inserted from below in an

upwards and backwards path. It is frictionally retained to the first section by means of

split post matrices attached to the cast portion, which will engage a stainless steel tube

matrix in the labial section.

A design can also be used which incorporates a hinge between the two parts,

with the anterior flange and teeth being rotated into place and held in position by a

locking bolt. Retention may be improved by use of intracoronal attachments for the

first section.


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Composite Bonded Bridges

When the permanent replacement of a single lost anterior tooth by a

removable partial denture is not entirely satisfactory and fixed bridge is rejected most

of these objections can be overcome by the use of an etched cast ceramometal

restoration which can be bonded to minimally prepared and etched enamel surfaces.

Retention of the framework was improved by subjecting its fitting surface to an

electrolytic etching process. This improved the resin bond by establishing mechanical

retention between the micropores of the etched alloy surface and the composite resin

in a manner similar to its attachment to an etched enamel surface.

Teeth with inadequate support, large carious lesions, extensive restorations, and

evidence of severe attrition are not suitable for use as abutments.

Tooth preparation for this prosthesis should be minimal. Enamel may be

reduced to free the occlusal if necessary, but it must be stressed that it is preferable

that the attachment is placed on a non-functional surface. This will reduce the

possibility of mechanical displacement. A definitive path of insertion should be

created which should be vertical with small grooves or slots prepared on the proximal

surfaces of the abutment teeth Defining a cingulum rest area will also provide

additional vertical support. The whole area of the preparation should be kept clear of

the gingival margin by at least 1 mm. At insertion the tooth surface is prepared in the

normal manner for an acid etched restoration. A bonding agent is used on the enamel

and the luting composite applied to the casting.

The advantages of this technique are that a saddle of limited span can be

restored economically without loss of healthy tooth substance or the wearing of a large

partial denture. For aesthetic reasons it is not suitable where there is obvious soft tissue

loss.


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B- Skeleton design (metal RPDs) for long anterior spans

Long anterior edentulous areas which may extend to include premolars usually

occur in adults. Hence, a permanent restoration in the form of metal partial dentures is

the treatment of choice.

- Denture base: The denture is tooth-tissue supported; therefore a combination metal-

acrylic base is required. In upper class IV dentures the whole of the anterior part of the

hard palate can be covered to provide adequate denture support, resist sinking of the

denture and to increase retention by adhesion.

- Multiple clasping is required to help in splinting of the remaining teeth and in order

to widely distribute the stresses and torque action. Since the remaining naturally teeth

are usually posterior teeth. Therefore the clasping system is usually better than in long

class I cases having anterior teeth as abutments.

- Indirect retention is obtained by extending the palatal plate major connector

posterior to the fulcrum axis and through the rests of the posteriorly located clasps.

- Stress breakers may not be necessarily used in upper class IV cases due to the

good support obtained from palatal coverage. However, a stress broken design may be

required if a long edentulous area covered by compressible tissues is to be restored.

- As with free end saddles frequent inspection and rebasing are necessary since only a

slight degree of rotation about the occlusal rests will open up a space between the

posterior periphery of the denture base and the hard palate, into which food will find

its way.

Class IV in lower denture

Usually required in adults who have lost the four lower anterior teeth through

periodontal disease or rarely caries. In this situation a cast metal denture is the

treatment of choice.

The design consists of bilateral lingual bars extending posteriorly from the

saddle, terminating in clasps; continuous clasping may or may not be present. The

saddle must be adequately tooth supported anteriorly, and this can be accomplished by


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using rests on the mesial aspect of the occlusal surfaces of the premolars. The use

of the canines for support has the advantage of bringing the axis of rotation forward so

that the posterior clasping is consequently more effectively but will necessitate

extensive preparation of the teeth to provide effective seats for the rests on the cingula

or else the use of incisal edge rests with their obvious aesthetic disadvantages.

Essentials of Design for Class IV

1.The movements of this type of removable partial denture and the resulting stresses transmitted to the abutment teeth are unlike the pattern seen in any other type of prosthesis.

2.The esthetic arrangement of the anterior replacement teeth may necessitate their placement anterior to the crest of the residual ridge, resulting in potential tilting leverage.

Every effort should be made to minimize these stresses. Some possibilities follow:

1.As much of the labial alveolar process should be preserved as possible.

2.A central incisor or other tooth should be retained to serve as an intermediate abutment or as an overdenture abutment.

3.A critical evaluation of each remaining tooth in the arch should be made with the intent of retaining as many teeth as possible.

The shorter the edentulous area, the less will be the harmful tilting leverage.

Strategic clasp position should be used. The quadrilateral configuration, with the anterior clasps placed as far anterior and the posterior clasps placed as far posterior as possible, would be the ideal.

The major connector should be rigid, and broad palatal coverage should be used in the maxillary arch.

Indirect retention should be used as far posterior to the fulcrum line as possible.

- An ideal quadrilateral configuration of clasping may preclude the need for an additional indirect retainer.

- A functional type of impression may be indicated if the edentulous area is extensive.

Mouth preparation

Mostafa Fayad 1

PREPARATION OF MOUTH FOR

REMOVABLE PARTIAL DENTURES

Mouth preparation follows the preliminary diagnosis and the

development of a tentative treatment plan. Final treatment planning may be

deferred until the response to the preparatory procedures can be ascertained.

In general, mouth preparation includes procedures in four categories:

Relief of Pain and Infection

oral surgical preparation,

conditioning of abused and irritated tissue,

periodontal preparation,

preparation of abutment teeth.

Relief of Pain and Infection:

Dental conditions that are causing discomfort should be treated as soon

as possible such as necessary endodontic treatment or restorative filling

for carious teeth. Gingival tissues should be treated to prevent

exacerbation of inflammatory response. Also scaling, root planning, and

prophylaxis should be performed.

A] RESTORATIVE PREPARATION

A. Removal of caries.

B. Replacement of defective restorations.

C. Restoration of structurally compromised teeth.

D. Occlusal modification.

E. Correction of malocclusion.

F. Splinting of natural teeth.

Mouth preparation

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G. Correction of unacceptable abutment tooth contours not cor¬rectable through enamel modification.

H. Exposure of dentin during abutment tooth modification.

1. Sensitivity.

2. Caries susceptibility.

B] ENDODONTIC

A. Non-vital teeth. Non-vital teeth should be endodontically treated.

B. Endodontically treated abutment teeth.

1. Placement of conservative intraradicular posts with minimal removal of tooth structure may increase resistance to structural failure.

2. May require restoration with extracoronal cast restorations to resist structural failure.

C] ORTHODONTIC

A. Abutment teeth.

1. Axial inclination may require correction.

2. Infraeruption or supraeruption requiring correction.

B. Occlusal plane. Irregularities may be corrected by orthodontic therapy.

C. Edentulous spans. Asymmetrical or undersized edentulous areas which are not conducive to the artificial replacement of missing teeth may require modification.

D]ORAL SURGICAL PREPARATION:

Oral surgical and periodontal procedures should precede abutment tooth

preparation and should be completed far enough in advance to allow the

necessary healing period. If at all possible, at least 6 weeks, but preferably 3 to

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6 months, should be provided between surgical and restorative dentistry

procedures.

Extractions:

Regardless of its condition, each tooth must be evaluated concerning its

strategic importance and its potential contribution to the success of the

removable partial denture.

Removal of Residual Roots

All retained roots or root fragments should be removed. This is particularly

true if they are in close proximity to the tissue surface or if there is evidence of

associated pathological findings. Residual roots adjacent to abutment teeth may

contribute to the progression of periodontal pockets and compromise the results

from subsequent periodontal therapy.

Impacted Teeth

All impacted teeth, including those in edentulous areas and those adjacent

to abutment teeth, should be considered for removal. If an impacted tooth is

left, it should be recorded in the patient's record and the patient should be

informed of its presence. Roentgenograms should be taken at reasonable

intervals to be sure that no adverse changes occur.

Any impacted teeth that can be reached with a periodontal probe must be

removed to treat the periodontal pocket and prevent more extensive damage

Malposed Teeth

Individual teeth or groups of teeth and their supporting alveolar bone can be

surgically repositioned. Orthodontics may be useful in correcting many

occlusal discrepancies, but for some patients, such treatment may not be

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practical because of a lack of teeth for anchoring orthodontic appliances or for

other reasons.

Cysts and Odontogenic Tumors

The patient should be informed of the diagnosis and provided with various

options for resolution of the abnormality as confirmed by the pathologist's

report.

Exostoses and Tori

Modification of denture design can accommodate for exostoses, this may

results in additional stress to the supporting elements and compromised

function.

The removal of exostoses and tori is not a complex procedure, and the

advantages from removal are great in contrast to the deleterious effects their

continued presence can create.

Hyperplastic Tissue

Hyperplastic tissue is seen in the form of fibrous tuberosities, soft flabby

ridges, folds of redundant tissue in the vestibule or floor of the mouth, and

palatal papillomatosis.

All these forms of excess tissue should be removed to provide a firm base

for the denture. This removal will produce a more stable denture, reduce stress

and strain on the supporting teeth and tissue, and in many instances will

provide a more favorable orientation of the occlusal plane and arch form for the

arrangement of the artificial teeth.

Muscle Attachments and Frena

The maxillary labial and mandibular lingual frena are the most common

sources of frenum interference with denture design. These can be modified

easily with any of several surgical procedures. Under no circumstances should

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a frenum be allowed to compromise the design or comfort of a removable

partial denture.

Bony Spines and Knife-Edge Ridges

Sharp bony spicules should be removed and knifelike crests gently rounded.

If, the correction of (a knife-edge) residual crest results in insufficient ridge

support for the denture base, the dentist should resort to vestibular deepening

for correction of the deficiency or insertion of the various bone grafting

materials that have demonstrated successful clinical trials.

Polyps, Papillomas, and Traumatic Hemangiomas

All abnormal soft tissue lesions should be excised and submitted for

pathological examination before the fabrication of a removable partial denture.

Hyperkeratoses, Erythroplasia, and Ulcerations

All abnormal, white, red, or ulcerative lesions should be investigated regardless

of their relationship to the proposed denture base or framework. A biopsy of

areas larger than 5 mm should be completed, and if the lesions are large (more

than 2 cm in diameter), multiple biopsies should be taken.

Dentofacial Deformity

Patients with a dentofacial deformity often have multiple missing teeth as part

of their problem. Correction of the jaw deformity can simplify the dental

rehabilitation.

Osseointegrated Devices

A number of implant devices to support the replacement of teeth have been

introduced to the dental profession. These devices offer a significant stabilizing

effect on dental prostheses through a rigid connection to living bone.

Augmentation of Alveolar Bone

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Considerable attention has been devoted to ridge augmentation with the use

of autogenous and alloplastic materials, especially in preparation for implant

placement.

E] CONDITIONING OF ABUSED AND IRRITATED TISSUE

Patients who require conditioning treatment often demonstrate the

following symptoms:

1. Inflammation and irritation of the mucosa covering the denture bearing areas

2. Distortion of normal anatomic structures, such as incisive papillae, the rugae,

and the retromolar pads

3. A burning sensation in residual ridge areas, the tongue, and the cheeks and

lips.

These conditions are usually associated with ill fitting or poorly

occluding removable partial dentures. However, nutritional deficiencies,

endocrine imbalances, severe health problems (diabetes or blood dyscrasias),

and bruxism must be considered in a differential diagnosis.

The first treatment procedure should be an immediate institution of a

good home care program.

A suggested home care program includes rinsing the mouth three times

a day with a prescribed saline solution;

massaging the residual ridge areas, palate,and tongue with a soft

toothbrush;

removing the prosthesis at night;

using a prescribed therapeutic multiple vitamin

Prescribed high-protein, low-carbohydrate diet.

Removing the ill-fitting dentures for extended periods.

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Use of Tissue Conditioning Materials

These soft materials apparently have a massaging effect on

irritated mucosa, and because they are soft, occlusal forces are probably

more evenly distributed.

Maximum benefit from using tissue conditioning materials may

be obtained by

(1) Eliminating deflective or interfering occlusal contacts of old

dentures (by remounting in an articulator if necessary);

(2) Extending denture bases to proper form to enhance support,

retention, and stability

(3) Relieving the tissue side of denture bases sufficiently (2 mm) to

provide space for even thickness and distribution of conditioning

material;

(4) applying the material in amounts sufficient to provide support and a

cushioning effect

(5) following the manufacturer's directions for manipulation and

placement of the conditioning material.

Many dentists find that intervals of 4 to 7 days between changes

of the conditioning material are clinically acceptable. If positive results

are not seen within 3 to 4 weeks, one should suspect more serious health

problems and request a consultation from a physician.

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F] PERIODONTAL PREPARATION

The periodontal health of the remaining teeth, especially those to be

used as abutments, must be evaluated carefully by the dentist and corrective

measures instituted before removable partial denture fabrication.

It is strongly recommended that a gross debridement be performed

before tooth extraction when patients have significant calculus accumulation.

This helps limit the possibility of accidentally dislodging a piece of calculus

into the extraction socket, which could lead to an infection.

Objectives of Periodontal Therapy

1. Removal and control of all etiological factors contributing to

periodontal disease, along with a reduction or elimination of bleeding on

probing

2. Elimination of, reduction in, pocket depths of all pockets.

3. Establishment of functional atraumatic occlusal relationships and tooth

stability

4. Development of a personal plaque control program and definitive

maintenance schedule.

Periodontal Diagnosis and Treatment Planning

evaluation procedure :

1) Exploration of the gingival sulcus and

2) Recording of the probing pocket depth

3) Sites that bleed on probing with a suitably designed periodontal

probe.

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4) Dental radiographs can be used to supplement the clinical

examination but should not be used as a substitute for it.

A critical evaluation of the following factors should be made:

(1) Type, location, and severity of bone loss;

(2) Location, severity, and distribution of furcation involvements;

(3) Alterations of the periodontal ligament space;

(4) Alterations of the lamina dura;

(5) Presence of calcified deposits;

(6) Location and conformity of restorative margins;

(7) Evaluation of crown and root morphologies;

(8) Root proximity;

(9) Caries;

(10) Evaluation of other associated anatomic features, such as the

mandibular canal or sinus proximity.

Treatment Planning

Periodontal treatment planning can

Usually be divided into three phases.

The first phase is considered disease control or initial therapy

which include oral hygiene instruction, scaling, and root planning

and polishing along with endodontic, occlusal adjustment, and

temporary splinting,

In the second—or periodontal—surgical phase, any needed

periodontal surgery is accomplished, including free gingival

grafts, osseous grafts, or pocket reduction.

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maintenance of periodontal health (definitive recall) phase ; A

definitive recall schedule should be established with the patient

and is usually kept at 3- to 4- month intervals.

Tooth mobility

Each tooth should be evaluated carefully for mobility. Normal mobility

is in the order of 0. 05 to 0. 10 mm.

Primary mobility caused by; inflammatory changes in the periodontal

ligament, traumatic occlusion, loss of attachment, or a combination of the three

factors. Mobility due to occlusal interference may disappear after selective

grinding.

Secondary mobility resulting from the presence of an inflammatory

lesion may be reversible if the disease process has not destroyed too much of

the attachment apparatus.

Grade I mobility is present when there is less than 1 mm of

movement in a buccolingual direction;

grade II is present when mobility in the buccolingual direction is

between 1 to 2 mm,

grade III is present when there is greater than 2 mm of mobility

in the buccolingual direction and/or the tooth is vertically

depressible.

Management

Teeth may be immobilized during periodontal treatment by acid

etching teeth with composite resin, with fiber reinforced resins, with

cast removable splints, or with intracoronal attachments.

After periodontal treatment, splinting may be accomplished with

cast removable restorations or cast cemented restorations. The

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preferred form of permanent splinting is with two or more cast

restorations soldered or cast together. They may be cemented with

either permanent (zinc oxyphosphate or resin) cements or temporary

(zinc oxide-eugenol) cements. A properly designed removable partial

denture can also stabilize mobile teeth if provision for such

immobilization is planned as the denture is designed.

The night guard is a removable acrylic resin splint, originally

designed as an aid in eliminating the deleterious effect of nocturnal

clenching and grinding. It may be helpful as a form of temporary

splinting if worn at night after the removal of the removable partial

denture. The flat occlusal surface prevents the intercuspation of the

teeth, which eliminates lateral occlusal forces

Elimination of Cross Occlusal Interferences

Traumatic cuspal interferences are removed by a selective

grinding procedure. An attempt is made to establish a positive planned

intercuspal position that coincides with centric relation. Deflective

contacts in the centric path of closure are removed,

The presence of working and nonworking interferences should be

evaluated, and if present, they should be removed.

The indication for occlusal adjustment is based on the presence of

a pathological condition rather than on a preconceived articulation

pattern.

Guide to Occlusal Adjustment:

In evaluation of occlusal disharmony of the natural dentition,

accurately mounted diagnostic casts are essential in determining static

cusp to fossa contacts of opposing teeth and as a guide in the correction

of occlusal anomalies in both centric and eccentric functional relations.

Ground tooth surfaces should be subsequently smoothed and polished.

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Schuyler has provided the following guide to occlusal adjustment

by selective grinding

I-Grinding In Centric Occlusion:

A static coordinated occlusal contact of the maximum number

of teeth (maximum intercuspal position) when the mandible is in centric

relation to the maxilla should be the first objective.

Articulating paper is used with an open and close movement of

the articulator or the mandible in intraoral method, to discover any

traumatic points on the occlusal surfaces of the teeth. These are removed

until even contact throughout the arch is obtained.

In the posterior teeth the surfaces to be reduced are selected

according to two basic rules:

a- If the cusp is high in both centric and eccentric occlusion,

reduce the cusp.

b- If the cusp is high in centric but not in eccentric occlusion,

deepen the fossa.

In anterior teeth:

a- When anterior teeth are in premature contact in centric

relation, or in both centric and eccentric relations, corrections should be

made by grinding the incisal edges of the mandibular teeth.

b- If premature contact occurs only in the eccentric relation,

correction must be made by grinding the lingual inclines of the

maxillary teeth.

Premature contacts in centric relation are relieved by:

- Grinding the buccal cusps of the mandibular teeth,

- The lingual cusps of maxillary teeth,

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- The incisal edges of the mandibular anterior teeth.

Deepening the fossa of a posterior tooth or the lingual contact

area in centric relation of a maxillary anterior tooth changes and

increases the steepness of the eccentric guiding inclines of the tooth.

Although this relieves trauma in centric relation, it may predispose the

tooth to trauma in eccentric relations.

II-Grinding To Obtain Occlusal Balance in Lateral Movements:

A- Anterior teeth:

If the anterior dentition is found to be in traumatic contact reduce

the traumatic areas of contact using the following rules:

a- Reduce the lingual surfaces of the maxillary incisal edges.

b- Reduce the labial surfaces of the mandibular incisal edges.

c- Reduce the disto-lingual slopes of the maxillary cuspids

(canines).

d- Reduce the mesio-labial slopes of the mandibular cuspids.

B- Posterior teeth:

Where the posterior dentition is found to be in traumatic contact

reduce the traumatic area of contact. The attention is directed first to

balancing side contacts. Using the following rules:

1- Care must be exercised to prevent the loss of a static

supporting contact in centric relation. This static support in centric

relation may exist between the mandibular buccal cusp fitting into the

central fossa of the maxillary tooth or between the maxillary lingual

cusp fitting into the central fossa of the mandibular tooth or it may exist

in both situations.

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2- The mandibular buccal cusp is in a static central contact in the

maxillary sulcus more often than the maxillary lingual cusp is in a static

contact in its opposing mandibular sulcus. Therefore corrective

grinding to relieve premature balancing contacts is more often done

on the maxillary lingual cusps.

Evidence of excessive balancing contacts:

It is extremely difficult to differentiate the harmless from the

destructive because we cannot visualize the influence of these fulcrum

contacts on the functional movements of the condyle in the articular

fossa.

- Subluxation,

- Pain,

- Lack of normal functional movement of the joint,

- Loss of alveolar support of the teeth involved

may be evidence of excessive balancing contacts. Balancing-side

contacts receive less frictional wear than working-side contacts, and

premature contacts may develop progressively with wear.

Balancing side:

Corrective grinding to relieve premature balancing contacts is

more often done on the maxillary lingual cusps.

In complete denture reduce the inner inclines of the

mandibular buccal cusps in preference to the opposing maxillary

slope. This is important because grinding usually involves removal in

part or whole of the cusp, which is an established centric occlusal

contact. Therefore the maxillary cusp is left to provide a more

stabilizing effect for the lower denture.

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Working side:

Anterior teeth: necessary grinding must be done on the lingual

surfaces of the maxillary anterior teeth.

posterior teeth: done on the buccal maxillary cusp of premolars

and molars and on the lingual mandibular cusp of the premolars

and molars.

Grind on 'bull' rule, to avoid the supporting cusps (the upper palatal

and the lower buccal cusps) which preserve the vertical dimension of

occlusion

1- Reduce the inner inclines of maxillary buccal cusps.

2- Reduce inner inclines of mandibular lingual cusps.

Grinding of mandibular buccal cusps or maxillary lingual cusps

at this time would rob these cusps of their static contact in the opposing

central sulci in centric relation.

III-Grinding to Obtain Occlusal Balance in Protrusive Movements:

1- If the anterior dentition is found to be in traumatic contact

reduce the traumatic areas of contact by grinding the lingual surface

of the maxillary anterior teeth.

Anterior teeth should never be ground to bring the posterior teeth

into contact in either protrusive position or on the balancing side.

2- If the posterior dentition is found to be in traumatic contact

reduce the traumatic areas of contact, grinding in accordance with

the

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BULL Rule: Grind only cuspal slopes, which are not providing centric

contact. Grind distal inclines of maxillary buccal cusps and mesial

inclines of mandibular lingual cusps.

3- Any sharp edges left by grinding should be rounded off.

G] Preparation of abutment teeth:

CLASSIFICATION OF ABUTMENT TEETH

The subject of abutment preparations may be grouped as follows:

(1) those abutment teeth that require only minor modifications to their

coronal portions, include : teeth with sound enamel, those with small

restorations not involved in the removable partialdenture design, those

with acceptable restorations that will be involved in the removable partial

denture design, and those that have existing crownrestorations requiring

minor modification that will not jeopardize the integrity of the crown.

(2) those that are to have restorations other than complete coverage crowns,

(3) those that are to have crowns (complete coverage). they provide the best

possible support for occlusal rests.

SEQUENCE OF ABUTMENT PREPARATIONS ON SOUND ENAMEL

OR EXISTING RESTORATIONS

Abutment preparations should be done in the following order:

1. Proximal surfaces parallel to the path of placement should be prepared to

provide guiding planes.

2. Tooth contours should be modified, lowering the height of contour so that

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(a) the origin of the circumferential clasp arms may be placed well below

the occlusal surface, preferably at the junction of the middle and gingival

thirds;

(b) retentive clasp terminals may be placed in the gingival third of the

crown for better esthetics and better mechanical advantage; and

(c) reciprocal clasp arms may be placed on and above a height of contour

that is no higher than the cervical portion of the middle third of the crown


3. After alterations of axial contours are accomplished and before rest seat

preparations are instituted, an impression of the arch should be made in

irreversible hydrocolloid and a cast formed in a fast-setting stone. This cast

can be returned to the surveyor to determine the adequacy of axial alterations

before proceeding with rest seat preparations. If axial surfaces require

additional axial recontouring, it can be performed during the same appointment

and without compromise.

4. Occlusal rest areas should be prepared that will direct occlusal forces along

the long axis of the abutment tooth.

Mouth preparation should follow the removable partial denture

design that was outlined on the diagnostic cast at the time the cast was

surveyed and the treatment plan confirmed. Proposed changes to abutment

teeth should be made on the diagnostic cast and outlined in colored pencil

to indicate the area, amount, and angulation of the modification to be done.

Preparation of the abutment teeth may be in the form of:

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A. Reshaping of abutment teeth.

B. Crowns.

C. Rest seat preparation.

A- Reshaping of Abutment Teeth:

1- Enameloplasty:

Conservatism must be the rule when recontouring enamel surface.

Enameloplasty may be performed for:

a) Developing Guiding Planes:

Guiding planes are surfaces on proximal or lingual surfaces of

teeth that are parallel to each other and, more importantly, to the path of

insertion and removal of a removable partial denture

(RPD). There functions are:

- On the proximal walls adjacent to edentulous

spaces they provide parallism needed for ensuring

stabilization.

- Minimize wedging action between RPD and abutment.

- Decrease undesirable space between RPD and the abutment tooth to

increase retention by frictional resistance.

- On the lingual surfaces of teeth provides maximum resistance to

lateral stresses exerted by the retentive clasp arm during insertion and

removal of RPD.

Dimensions of the Guiding Plane:

It is prepared by cylindrical diamond in the following dimensions:

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occlusogingivally it is 2-4 mm in length prepared flat on the occlusal

third of the abutment.

Buccolingually it is 3-4 mm in width and curved in harmony with the

existing tooth contour.

Ideal guiding plane is 2-4 mm occlusogingivally

Normal tooth contour should be maintained

b) Changing Height of Contour:

The retentive clasp arm should be ideally located

at the junction of the gingival and middle thirds not higher, for esthetic

purpose and for definite mechanical advantage.

But when, the height of contour lies near the occlusal surface in the

tipped tooth this can be lowered by grinding

(enameloplasty).

1- High survey line may cause deformation of the clasp.

2- Shaping the enamel to lowering the survey line.

C) Modification of Retentive Undercut:

When there is insufficient under cut and when the patient has good

oral hygiene and low caries index, these teeth can be modified by

increasing amount of the undercut by contouring the

enamel surface; By creation of gentle depression

(concavity) about 4mm in mesiodistal length and

0.01inch deep (not a pit or hole).

This concavity is prepared by using a small, round end tapered diamond

stone.

B- crowns:

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When the remaining teeth do not posses natural contours and the

enamel surfaces cannot be modified to create undercut, cast restoration

should be planed. Cast crown also may be planned in case of extensive

caries, defective restoration, tooth fracture, and endodontically treated

teeth.

To shape the wax pattern of the crown, the wax knife is used to

carve the guiding plane on the surveyor.

The pattern must be hand carved tom place the height of contour

in the middle third of lingual surface if the tooth is to receive a

reciprocal clasp arm and at the junction of the gingival and middle third

of the buccal surface to receive a retentive clasp arm.

The position and depth of the retentive undercut can be verified by use

of an undercut gauge.

Contouring Wax Patterns

Modern indirect techniques permit the contouring of wax patterns

on the master cast with the aid of the surveyor blade. All abutment teeth

to be restored with castings can be prepared at one time and an

impression made that will provide an accurate stone replica of the

prepared arch. Wax patterns may then be refined on separated individual

dies or removable dies. All abutment surfaces facing edentulous areas

should be made parallel to the path of placement by the use of the

surveyor blade

C- Rest Seat Preparation:

The purposes and functions of rests basically, are to:

- Direct the forces of mastication parallel to the long axis of the

associated abutment.

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- Prevents the gingival displacement of a RPD.

- Maintains the relationship between a clasp assembly and the

associated tooth.

- In certain applications a rest may act as an indirect retainer.

- It may be used to close a small space between teeth, which restoring

continuity of the arch and preventing food impaction.

Each seat must be positioned in a properly prepared rest seat. These rest

seats must be prepared before final impression and master cast are made.

Rest Seat Preparation for Posterior Teeth:

1) Occlusal Rest Seat in Enamel:

The basically outline form of an occlusal rest seat is triangular, with its

base directed at the marginal ridge and the apex toward the tooth center,

occupying about one half of the buccolingual width of the occlusal

surface, and the apex should be rounded as all margins of the

preparation.

An occlusal rest must be at least 1 mm thick at its thinnest point if

chrome alloy is used for framework and about 1.5 mm if gold is to be

used.

Extension of the rest seat mesiodistally about one third to one half of the

mesiodistal diameter.

The floor of the occlusal rest seat must be inclined toward the center of

the tooth to place the deepest part of the rest nearly at the center of the

preparation.

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The floor of the rest seat should be spoon in shape.

Any sharp angle should be smoothed.

An occlusal rest seat may be prepared using a variety of rotatory

instruments. Many practitioners use round diamond burs, while others

prefer diamond bur with rounded ends and tapering sides.

When using round diamond bur care must be taken to avoid creation of

mechanical undercut at the peripheries of the preparation.

2) Occlusal Rest Seat as Part of a New Cast-metal Restoration:

When one or more fixed restoration will be placed in conjunction

with RPD, these restorations must be carefully planed and fabricated.

Accordingly, occlusal rest seat for cast gold

restorations should always be carved into

the wax pattern following placement of

guiding planes. (Figure 6)

- A round carbide bur (No 4 or 6) is used to perform the initial shaping

procedure for box-shaped rest

- Upon completion of the casting process, the restoration is finished and

polished using a small round fishing bur.

3) Occlusal Rest Seat on the Surface of an Existing Cast-metal

Restoration:

Sometimes a RPD is indicated for a patient with one or more

cast restorations on proposed partial denture abutments. Although it

would be ideal to replace these restorations, the practitioner should try to

contour these restorations to satisfy the requirements of the designed

RPD.

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- When preparing rest seats in existing cast restoration, the

establishment of sufficient space should be the highest priority; so the

patient must be informed if perforation of this existing restoration

occurred that perforated restoration must be replaced.

- The instrumentation and procedures for preparing rest seats on existing

fixed restorations are identical to those for preparing rest seats on

enamel surfaces.

4) Occlusal Rest Seats on an Amalgam Restoration:

A rest seat preparation on a multiple-surface amalgam restoration is

less desirable than a rest seat preparation on sound enamel or a cast

restoration.

- The amalgam alloy tends to deform when exposed to constant load.

- Care must be taken to avoid weaken the proximal portion of

the amalgam restoration at the ismuth during preparation.

- Experience indicates that rest seat should not be placed entirely

on amalgam. If a substantial portion of the rest seat cannot be placed

on sound tooth structure, then a complete- or partial-coverage casting

should be considered.

5) Embrasure Rest Seat:

This preparation crosses the occlusal embrasure of two

approximating posterior teeth, from the mesial fossa of one tooth to the

distal fossa of the adjacent tooth; to receive an embrasure clasp.

- A diamond bur with a rounded end and

tapering sides is ideal for preparing embrasure rest seats.

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- Contact between the teeth should not be broken since this may result in

tooth migration or food impaction.

Embrasure space dimensions

- The form and depth of the rest seat: at the facial and lingual

embrasures, the embrasure rest seat should be 3.0 to 3.5 mm wide and

1.5 to 2.0 mm deep.

- Occlusal clearance can be checked by laying two pieces of 18 gauge

wires side by side across the preparation.

- The patient should be able to close without contacting the metal.

- The buccal inclines of the preparation must be rounded after the

preparation is completed.

Rest Seat Preparation for Anterior Teeth:

In most cases an occlusal rest seat on a posterior tooth is preferred

than a cingulum or incisal rest seat on an anterior teeth. Because of its

size and position, this permits forces to be directed along the long axis

of the teeth.

1) Lingual or Cingulum Rest Seat:

Indications:

1- When there is no posterior tooth to place an occlusal rest.

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2- Maxillary canine is mainly used for lingual or cingulum rest, because

the morphology of the tooth permits preparation of the seat.

3- It is rarely used on incisors when the canine is missing. In this case

multiple rests should be used to distribute the force over a number of

incisors.

4- To prepare rest seat in the enamel there should be (prominent

cingulum, good oral hygiene, and low caries index).

Design:

1-the outline form of a cingulum rest seat should be crescent shaped

when widowed from the lingual aspect. Its broadest portion is in the

middle of the lingual surface and get less broad as it approaches the

proximal surface.

2- The rest seat should be V-shaped when viewed from the proximal;

with rounded line angles. (This permits direction of the force along the

long axis of the tooth).

3- Mesiodistal length of preparation should be a minimum of 2.5 mm.

labiolingual width about 2 mm, and incisal apical depth a minimum of

1.5 mm.

4- It is often difficult to obtain a positive epically inclined rest seat due

to tooth angulations or anatomy. The use of cast restoration may be

required to establish a definite rest seat.

Preparation:

a) Cingulum Rest Seat in Enamel:

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A lingual or cingulum rest seat may be prepared in enamel if the

tooth is sound, low caries index, good oral hygiene and prominent

cingulum.

A cingulum rest seat is accomplished using a carbide inverted

cone bur (side- and end- cutting surfaces) in a high speed hand

piece. The preparation is finished, polished, smoothen, and gently

rounded using a rubber wheel in a low speed hand piece.

b) Cingulum Rest Seat in Cast Restorations:

The most satisfactory cingulum rest from the stand point of

support is one that is placed on a prepared rest seat in a cast restoration.

The rest seat should be carved in during the wax pattern stage, not cited

or prepared in the cast restoration.

2- Incisal Rest Seats in Enamel:

Incisal rest seats are the least desirable rest seats for anterior

teeth. Because of its bad esthetic, interference with occlusion, and its

damaging effect on the abutment.

Indications:

1- Incisal rests are used mostly on mandibular canines when the

abutment is sound and when a cast restoration is not indicated.

2- It may be used as an auxiliary rest for indirect retention.

Disadvantages:

a) The bad esthetic of metal.

b) Greater mechanical leverage than lingual rests, due to the longer

minor connector required.

Mouth preparation

Mostafa Fayad 27

Design:

1- An incisal rest seat is usually placed near a proximal surface, mostly

on the proximal distal line angle of the tooth for esthetic.

2- When viewed from the facial surface, its floor is concave in shape

and inclined toward the center of the tooth to direct the force along to

the long axis of the tooth.

3- When viewed from the proximal, the outline form is convex (saddle

shape) with buccal and lingual bevels.

4- All borders are rounded and smooth.

5- Its dimensions are approximately (2.5 mm wide and 1.5 mm deep).

Preparation:

An initial depth cut is made, using a tapered cylindrical stone, at the

junction of the middle and the mesial or distal third


The walls of the rest seat are created by flaring the

edges of the depth cut preparation and beveling the

buccal and lingual walls with finishing bur. The

completed preparation should be smooth and comfortable for the patient.

Special consideration

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Abutment preparations using conservative restorations

When an inlay is the restoration of choice for an abutment tooth, certain

modifications of the outline form are necessary. To prevent the buccal and

lingual proximal margins from lying at or near the minor connector or the

occlusal rest, these margins must be extended well beyond the line angles of

the tooth. This additional extension may be accomplished by widening the

conventional box preparation.

The restoration should be with maximum resistance and retention, and

with clinically imperceptible margins. The first requisite can be satisfied by

preparing opposing cavity walls 5° or less from parallel and producing flat

floors and sharp, clean line angles.

Abutment preparations using crowns

One of the advantages of making cast restorations for abutment teeth is

that mouth preparations that would otherwise have to be done in the mouth

may be done on the surveyor with far greater accuracy. It is generally

impossible to make several proximal surfaces parallel to one another when

preparing them intraorally.

The ideal crown restoration for a removable partial denture abutment is

the complete coverage crown, which can be carved, cast, and finished to ideally

satisfy all requirements for support, stabilization, and retention without

compromise for cosmetic reasons.

The preparation should be made to

provide the appropriate depth for the occlusal

rest seat. This is best accomplished by altering

the axial contours of the tooth to the ideal

before preparing the tooth and creating a

depression in the prepared tooth at the

occlusal rest area.

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Ledges on Abutment Crowns

The functions of the reciprocal clasp arm are reciprocation,

stabilization, and auxiliary indirect retention. Any rigid reciprocal arm may

provide horizontal stabilization if it is located on axial surfaces parallel to the

path of placement.

Its function as a reciprocating arm against the action of the retentive

clasp arm is limited only to stabilization against possible orthodontic

movement when the denture framework is in its terminal position. Such

reciprocation is needed when the retentive clasp produces an active orthodontic

force because of accidental distortion or improper design.

The term orthodontic force is incorrect, because the term signifies a

slight but continuous influence that would logically reach equilibrium when the

tooth is orthodontically moved. Instead, the transient forces of placement and

removal are intermittent but forceful, which can lead to periodontal

destruction and eventual instability rather than to orthodontic movement.

True reciprocation is not possible with a clasp arm that is placed on

an occlusally inclined tooth surface because it does not become effective

until the prosthesis is fully seated. When a dislodging force is applied, the

reciprocal clasp arm, along with the occlusal rest, breaks contact with the

supporting tooth surfaces, and they are no longer effective. Thus as the

retentive clasp flexes over the height of contour and exerts a horizontal force

on the abutment, reciprocation is nonexistent just when it is needed most.

True reciprocation can be obtained only by creating a path of

placement for the reciprocal clasp arm that is parallel to other guiding

planes. In this manner the inferior border of the reciprocal clasp makes contact

with its guiding surface before the retentive clasp on the other side of the tooth

begins to flex.

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The presence of a ledge on the abutment crown acts as a terminal stop

for the reciprocal clasp arm. It also augments the occlusal rest and provides

indirect retention for a distal extension removable partial denture.

A reciprocal clasp arm built on a crown ledge is actually inlayed into the

crown and reproduces more normal crown contours. The patient's tongue then

contacts a continuously convex surface rather than the projection of a clasp

arm.

a; Open circle at top and bottom illustrates that retentive clasp is only passive at its first

contact with tooth during placement and when in its terminal position with denture fully

seated. During placement and removal, reciprocal rigid clasp arm placed on opposite side of

tooth cannot provide resistance against these horizontal forces.

b. True reciprocation throughout full path of placement and removal is possible when

reciprocal clasp arm is inlaid onto ledge on abutment crown.

The crown ledge may be used on any complete or three-quarter crown

restored surface that is opposite the retentive side of an abutment tooth. It is

used most frequently on premolars and molars but also may be used on canine

restorations. It is not ordinarily used on buccal surfaces for reciprocation

against lingual retention because of the excessive display of metal, but it may

be used just as effectively on posterior abutments when esthetics is not a factor.

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Spark Erosion

Spark erosion technology is a highly advanced system for producing

the ultimate in precision fit of the reciprocal arm to the ledge on the

casting. This technology uses a tool system that permits repositioning the

casting with great accuracy and an electric discharge machine that is

programmed to erode minute metal particles through periodic spark intervals.

Veneered Crowns for Support of Clasp Arms

Veneered crowns must be contoured to provide suitable retention.

This means that the veneer must be slightly overcontoured and then shaped to

provide the desired undercut for the location of the retentive clasp arm. If the

veneer is of porcelain, this procedure must precede glazing; if it is of resin, it

must precede final polishing.

Porcelain laminates have demonstrated resistance to wear for the

equivalent of 5 years. The porcelain, however, resulted in slight wear on the

clasps. The flat underside of the cast clasp makes sufficient contact with the

surface of the veneer so that abrasion of the resin veneer may result.

Present-day acrylic resins, being cross-linked copolymers, will

withstand abrasion for considerable time but not nearly to the same degree as

porcelain. Therefore acrylic resin veneers are best used in conjunction with

metal that supports the half-round clasp terminal.

SPLINTING OF ABUTMENT TEETH

Splinting to the adjacent tooth or teeth can be used as a means of

improving abutment support. Thus two single-rooted teeth serve as a

multirooted abutment. Splinting should not be used to retain a tooth that would

otherwise be condemned for periodontal reasons.

The most common application of the use of multiple abutments is the

splinting of two premolars or a first premolar and a canine. Mandibular

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premolars generally have round and tapered roots, which are easily loosened by

rotational and tipping forces. They are the weakest of the posterior abutments.

Anterior teeth on which lingual rests are to

be placed often must be splinted together to

prevent orthodontic movement of individual teeth.

Mandibular anterior teeth are seldom used for

support, but if they are, splinting of the teeth

involved is advisable.

When splinting is impossible, individual lingual rests on cast restorations may

be slightly inclined apically to prevent possible tooth displacement, or lingual

rests may be used in conjunction with incisal rests, slightly engaging the labial

surface of the teeth.

USE OF ISOLATED TEETH AS ABUTMENTS

The average abutment tooth is subjected to some distal tipping, rotation,

torquing, and horizontal movement, The isolated abutment tooth, however, is

subjected also to mesial tipping because of lack of proximal contact.

In a tooth-supported prosthesis, an isolated tooth may be used as an

abutment by including a fifth abutment for additional support. Thus rotational

and horizontal forces are resisted by the additional stabilization obtained from

the fifth abutment. When two such isolated abutments exist, a sixth abutment

should be included for the same reason. Thus the two canines, the two isolated

premolars, and the two posterior teeth are used as abutments.

An isolated anterior abutment adjacent to a distal extension base usually

should be splinted to the nearest tooth by means of a fixed partial denture. The

effect is twofold:

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(1) The anterioredentulous segment is eliminated, thereby creating

an intact dental arch anterior to the edentulous space; and

(2) The isolated tooth is splinted to the other abutment of the fixed

partial denture, thereby providing multiple abutment support.

Factors influence the decision to use an isolated tooth as an abutment:

1- Form, length of the root and the supporting bone

2- Esthetic consideration

MISSING ANTERIOR TEETH

When a removable partial denture is to replace missing posterior teeth,

especially in the absence of distal abutments, any additional missing anterior

teeth are best replaced by means of fixed restorations rather than included in

the removable partial denture. In any distal extension situation, some

anteroposterior rotational action will result from the addition of an anterior

segment to the denture.

It is generally advisable that a removable partial denture should replace

only the missing posterior teeth after the remainder of the anterior arch has

been made intact by fixed restorations.

The decision to include an anterior segment on the denture depends

largely on the support available for that part of the removable partial denture.

The greater the number of natural anterior teeth remaining, the better the

available support for the edentulous segment.

FABRICATING RESTORATIONS TO FIT EXISTING

DENTURE RETAINERS

The technique for making a crown to fit the inside of a clasp is as

follows:

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1- An irreversible hydrocolloid impression of the mouth is made with

the removable partial denture in place.

2- This impression, which is used to make the temporary crown, is

wrapped in a wet paper towel or placed in a plastic bag and set aside while the

tooth is being prepared.

Even though several abutment teeth are to be restored, it is usually

necessary that each temporary restoration be completed before the next one is

begun. This is necessary so that the original support and occlusal relationship

of the removable partial denture can be maintained as each new temporary

crown is being made.

3- During the preparation of the abutment tooth, the removable partial

denture is replaced frequently to ascertain that sufficient tooth structure is

removed to allow for the thickness of the casting.

4- When the preparation is completed, an individual impression of the

tooth is obtained from which a stone die is made.

5- A temporary crown is then made in the original irreversible

hydrocolloid impression. It is trimmed, polished, and temporarily cemented,

and the removable partial denture is returned to the mouth.

6- The patient is dismissed after the excess cement has been removed.

7- On the stone die made from the individual impression, a thin,

autopolymerizing resin coping will be formed with a brush technique.

8- The wax pattern buildup on the resin coping is usually not begun until

the patient returns.

9- the occlusal portion of the wax pattern is established by having the

patient close into maximum intercuspation, followed by excursive movements.

The wax pattern is returned to the cast, and additions are made as required to

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dull areas. The process is repeated until a smooth occlusal registration has been

obtained.

10- addition of sufficient wax to establish contact relations with the

adjacent tooth. At this time, the occlusal relation of the marginal ridges also

must be established.

11- wax is added to buccal and lingual surfaces where the clasp arms

will contact the crown, and the wax pattern is again reseated in the mouth.

12- The clasp arms,minor connectors, and occlusal rests involved on the

removable partial denture are carefully warmed with a needlepoint flame,

carefully avoiding any adjacent resin, and the removable partial denture is

positioned in the mouth and onto the wax pattern.

13- Several attempts may be necessaryuntil the removable partial

denture is fully seated and the components of the clasp are clearly recorded in

the wax pattern.

14- the temporary crown may be replaced and the patient dismissed.The

crown pattern is completed on the die by narrowing the occlusal surface

buccolingually, adding grooves and spillways, and refining the margins.

15-Any wax ledge remaining below the reciprocal clasp arm may be left

to provide some of the advantages of a crown ledge. Excess wax remaining

below the retentive clasp arm, however, must be removed to permit the

addition of a retentive undercut later.

16- The wax pattern must be sprued with care so that essential areas on

the pattern are not destroyed. After casting, the crown should be subjected to a

minimum of polishing, because the exact form of the axial and occlusal

surfaces must be maintained.

17- After the crown has been tried in the mouth with the denture in

place, the location of the retentive clasp terminal is identified by scoring the

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crown with a sharp instrument. Then the crown may be ground and polished

slightly in this area to create a retentive undercut.

Ideally, all abutment teeth would best be protected with complete

crowns before the removable partial denture is fabricated. Except for the

possibility of recurrent caries because of defective crown margins or gingival

recession, abutment teeth so protected may be expected to give many years of

satisfactory service in the support, stabilization, and retention of the removable

partial denture.

IMPRESSIONS FOR RPD

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IMPRESSIONS FOR REMOVABLE PARTIAL DENTURE

A- PRIMARY IMPRESSIONS

Primary impressions are used in the preparation of study casts which playa vital

role in the planning and construction of a removable partial denture.

Stock tray

The stock tray used for the primary impression should be

1- large enough to provide adequate thickness of the alginate

impression material (5- 7 mm).

2- Has a mechanical means of retention of impression material.

If the maxillary arch has a high vault, build up the tray with impression

compound to prevent the hydrocolloid from sagging away from the palatal

surface. The margins of the stock tray may need to be lengthened with

impression compound or it may need to be trimmed.

I-Irreversible hydrocolloid (Alginate): -

Common problems in making alginate impressions:

1-Surface inaccuracy due to:

a- Air bubbles.

b- Mucous film on the soft tissue.

2- Dimensional inaccuracy due to:

a- synerisis & imbibition.

b- strain caused by movement or removal during gelation.

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c- dislodgment of impression from the tray.

d- displacement during pouring.

3- Cast has rough surface or chalky appearance:due to

a- insufficient spatulation of stone.

b- saliva retained on impression.

c- poor mix of alginate.

d- impression left long period in contact wit the cast.

e- trapping of air.

4- Low tear strength of alginate.

This may be improved by lifting the impression in the patient mouth one or

two minutes more after setting.

Advantages of alginate:

1-can be used with the presence of saliva.

2-pour well with stone (hydrophilic).

3-has pleasant taste and odor and non expensive.

4-Can be disinfected with 2% glutaraldehyde stored in 100% humidity and

poured within one hour.

Possible Causes of an Inaccurate and/or a Weak Cast of a Dental Arch

1. Distortion of the hydrocolloid impression (a) by use of an impression tray

that is not rigid; (b) by partial dislodgment from the tray; (c) by shrinkage

caused by dehydration; (d) by expansion caused by imbibition (this will be

IMPRESSIONS FOR RPD

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toward the teeth and will result in an undersized rather than oversized cast);

and (e) by attempting to pour the cast with stone that has already begun to set.

2. A ratio of water to powder that is too high. Although this may not cause

volumetric changes in the size of the cast, it will result in a weak cast.

3. Improper mixing. This also results in a weak cast or one with a chalky

surface.

4. Trapping of air, either in the mix or in pouring, because of insufficient

vibration.

5. Soft or chalky cast surface that results from the retarding action of the

hydrocolloid or the absorption of necessary water for crystallization by the

dehydrating hydrocolloid.

6. Premature separation of the cast from the impression.

7. Failure to separate the cast from the impression for an extended period.

B- FINAL IMPRESSION

ANATOMICAL FORM FINAL IMPRESSION

FOR TOOTH SUPPORTED R P D

The anatomic form impression is a one-stage impression method using

an elastic impression material that will produce a cast that does not represent a

functional relationship between the various supporting structures of the

partially edentulous mouth. It will only represent the hard and soft tissue at

rest.

A removable partial denture fabricated from a one stage impression,

which only records the anatomic form of basal seat tissue, places more of the

masticatory load on the abutment teeth and that part of the bone that underlies

the distal end of the extension base.

Technique of making anatomical final impression:

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I. Position of patient and dentist:

II. Verifying and adjusting special impression tray:

III. Mixing impression material:

IV. Loading impression tray:

V. Making the impression:

VI. Removal of impression from the mouth:

VII. Inspecting the impression:

VIII. Cleaning the impression:

IX. Pouring of the cast:

X. Trimming the cast:

Rubber base impression materials:

Advantages:

1- greater dimensional stability.

2- produces a smooth surfaces of the stone cast.

3- higher tear strength.

Types:

A- Mercaptan(Thiokol or polysulphide):-

Indication:

Final impression for RPD & for altered cast impression.

Advantages:

1- longer setting time than alginate , which gives a chance for a better border

molding.

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2- hydrophobic so it can be disinfected in liquid (cold sterilizing solutions).

Disadvantages:

1- the medium and heavy body materials do not recover well from deformation

and so should not be used when large undercuts are present.

2- the long term of dimensional stability of these materials is poor due to water

loss after setting.

It should allowed to rebound foe 7-15 minutes then poured immediately.

B- Silicone:

Indications:

1- final impression for RPD and for altered cast impression.

2- can be used with a compatible putty in a double impression tech.

Advantages:

1- the most accurate elastic impression material (addition type).

2- moderate working time (can be controlled by amount of accelerator).

3- pleasant odor.

4- excellent recovery from deformation.

5- disinfected in sterilizing solutions.

6- the addition reaction silicones can be poured up to one week. While the

condensation reaction silicones should be poured within one hour.

Disadvantages:

1- latex gloves inhibit polymerization of some silicones.

2- the putty forms are expensive and of short shelf life.

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C- polyether:

Indications:

in addition to its use as an impression material it can be used as a border

molding material. However, it is not compatible with the addition reaction

silicone and should not be used for border molding with it.

Advantages:

1- good wetability that produces easy cast forming (hydrophilic).

2- it should be poured within 2 hours ; however if it is kept dry it can be poured

within 7 days.

Disadvantages:

1- Shorter working and setting time.

2- The flow and flexibility are the lowest, which may cause cast breakage

during removal from the impression.

Master cast:

- It the cast obtained from pouring the final impression.

- The impression is poured in two stages; in the first stage the stone is vibrated

into the impression until it is filled.

After initial setting of this layer, the second stage is start for making a base for

the cast.

Removal of cast from impression:

- Stone should be allowed to set for 45 minutes before separating the cast from

the impression.

- The cast is trimmed by a cast trimmer.

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- The cast is rejected if voids or nodules of stones are found in a critical areas

e.g. rest seat area.

Special Impression Techniques

FOR TOOTH TSSUE SUPPORTED R P D

Objective:

When occlusal forces are applied to a tooth-supported removable partial

denture, they are directed through the rests and

transmitted to the abutments.

The edentulous ridges do not contribute to

the support of the RPD because the teeth absorb

these forces before the forces can be transmitted

to the underlying residual ridge.

Since the denture base does not contribute to the support of the partial

denture and the underlying mucosa and bone are not subjected to functional

forces, a tooth-supported RPD can be

constructed on a master cast made from a single

impression that record the teeth and soft tissues

in their anatomic form.

When occlusal forces are applied to a tooth-tissue-supported RPD, these

forces must be equally distributed to the abutments and the tissues of the ridge.

So a dual impression technique is used in which a (corrected cast) is generated.

The impression of teeth is made with a material that records the teeth in

their anatomic positions, while the impression of the residual ridge must record

the soft tissues in their functional form.

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Aims of Dual Impression Technique:

1. Record and relate the tissues under uniform loading.

2. Distribute the load over as large an area as possible.

3. Accurate determination of the peripheral extent of the denture base.

Factors influencing support of distal extension base : see class 1 design

Requirements of accepted impression for distal extension base:

An impression registration for the fabrication of a partial denture must

fulfill the following two requirements:

1. The anatomic form and the relationship of the remaining teeth in the dental

arch and the surrounding soft tissue must be recorded accurately so that the

denture will not exert pressure on those structures beyond their physiological

limits.

A type of impression material that can be removed from undercut areas

without permanent distortion must be used to fulfill this requirement. The

elastic impression materials, such as irreversible hydrocolloid (alginate),

mercaptan rubber base (Thiokol), silicone impression materials (both

condensation and addition reaction), and the polyethers are best suited for this

purpose.

2. The supporting form of the soft tissue underlying the distal extension base of

the partial denture should be recorded so that firm areas are used as primary

stress-bearing areas and readily displaceable tissues are not overloaded. Only in

this way can maximum support be obtained for the partial denture base. An

impression material capable of displacing tissue sufficiently to register the

supporting form of the ridge will fulfill this second requirement. A fluid

mouth-temperature wax or any of the readily flowing impression materials

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(rubber base, silicones, or polyethers in an individual, corrected tray) may be

employed for registering the supporting form. Zinc oxideeugenol paste can also

be used when only the extension base area is involved in the impression .

No single impression material can satisfactorily fulfill both of the

previously mentioned requirements.

Recording the anatomic form of both teeth and supporting tissue will

result in inadequate support for the distal extension base. This is because the

cast will not represent the optimum coordinating forms, which necessitates that

the ridge be related to the teeth in a supportive form. This coordination of

support maximizes the support capacity for the arch and minimizes movement

of the partial denture under function.

Three factors must be considered in the acceptance of an impression

technique for distal extension removable partial dentures:

1- The material should record the tissue covering the primary stress

bearing areas in their function form.

2- Tissues within the basal set area other than the primary stress bearing

areas must be recorded in their anatomic form.

3- Maximum coverage by the impression must be obtained to distribute

the lode over as large an area as can be tolerated by the border tissues.

This is an application of the principle of the snowshoe.

Indications of dual impression technique:

1- In mandibular distal extension ridge, because

a)- there is only a limited ridge area can be used as a primary stress

bearing area.

b) – Difficult to obtaining the proper peripheral extension for denture

base, because a movable tissues in the flower of the mouth.

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In the maxillary arch the dual impression does not often improve the

stress distribution. Because, the maxillary distal extension ridge is usually

covered by a firm, dense will attached mucosal the stress bearing area must be

the crest & buccal slope of the ridge.

2- Long span anterior edentulous ridge where the ridge must supply some

support for the partial denture.

A dual impression technique is used to equalized as much as possible the

support derived from the edentulous ridge& that received from the abutment

teeth.

Impression methods

A – Physiologic or functional impression techniques.

McLean's physiologic impression technique (made before the

framework construction)

Hindel's impression technique (made before the framework

construction)

The Functional Relining method ( made after finishing of RPD ) .

The fluid wax functional impression technique (made after the

framework construction )

B- selected pressure impression.

a- Two stage selected pressure impression technique.

b- One stage selected pressure impression technique

The Altered Cast Techniques

a-The fluid wax functional impression technique.

b- Two stage selected pressure impression technique

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I- Physiologic or functional impression techniques:

1- McLean's physiologic impression technique:-

In this technique the impression of the edentulous areas was made with

impression past loaded in an acrylic tray which was providing with occlusion

rim under biting force.

This impression was then related to the arch by making a hydrocolloid

impression (overall impression) with the original impression set in the mouth.

After removal the composite impression from the mouth a master cast was

poured with the edentulous areas recorded under functional loading.

Disadvantages: - The tray used for over all impression was in contact with

the occlusion rims of the original impression & held in his position with finger

pressure. This pressure does not simulate the occlusal loading. This lead to the

advantage of the technique was lost with this variation.

2- Hindel's impression technique:

in Hindel's technique the imp of the edentulous ridge was not made under

pressure but it is an anatomic imp made with a free-flowing zinc oxide-eugenol

paste. After setting of the impression, a tray with ¾ inch holes in the regions

of the first molar for the second impression is made. So that finger pressure

could be applied through this holes of the tray as the hydrocolloid impression

was made. The pressure had to be maintained until the alginate was completely

set. The finished impression was a reproduction of the anatomic surface ridge

and the surface of the teeth.

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The main purpose of these techniques was to relate an impression of the

edentulous ridge to the teeth under a form of function loading (supported

form).

Disadvantages:

A- If the action of the retentive clasps of the partial denture is sufficient

to maintain the denture base in relation to the soft tissue in the functional form,

this lead to interruption of blood circulation & resorption of the under lying

bone.

B- If functional relationship of the denture base to the soft tissue is

present when the partial denture at rest, this lead to, the partial denture would

be slightly occlusal than the remaining teeth and premature contact occurred.

3- Functional relining method

The functional relining is done to a completed partial denture

constructed on a cast made from a single impression. It can be used before

initial insertion for the purpose of perfecting the fit of the denture base to the

residual ridge.

If relining is planned, a soft metal spacer (ash No 7) is adapted over the

ridge on the cast before processing the denture base. After processing, the

metal is removed, leaving an even space between the base and the edentulous

ridge to allow room for the impression material.

It can also be used for relining an old partial denture to compensate for

bone resorption.

In making the reline impression, the patient must maintain the mouth in

a partially opened position while the border molding and impression are being

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accomplished because the relationship between the partial denture framework

and the teeth must be observed.

A low fusing compound is used to make an impression for the

edentulous ridge. Then the entire surface of the modeling plastic is scraped to a

depth of 1mm. The final impression is made with a free flowing zinc oxide

paste. If undercuts are present on the ridge light bodied polysulphide or silicon

may be used.

b) Impression making:

Placed a flowing law-fusing modeling plastic over the tissue

surface of the denture base.

Tempering the modeling plastic in a water bath, and seating in

the patient’s mouth.

The heating, tempering, and seating must be accomplished

several times until; accurate imp of the ridge is made.

The border extensions are determined by limiting application of

heat to the borders& manipulating he cheek & tongue.

The modeling plastic over ridge is relieved before final imp is

made to provide space for the imp material. This relived

approximately 1mm, or the entire thickness of the modeling

plastic may be removed over the crest of the ridge.

The final imp is made with a free-flowing Z.D.E. paste. If

undercut are present on the ridge, light-bodied rubber base may

be used.

As in all reline procedures, occlusal discrepancies must be

corrected. Because, the open mouth imp technique must be used

it is impossible to maintain previously established occlusal

contacts. If error in occlusion after the denture had been

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processed is slight, the correction may be accomplished in the

mouth. However, in a majority of cases it will be necessary to

remount the partial denture on an articulator to correct & refine

occlusion.

Disadvantage of functional relining:

After relining occlusal discrepancies occurs.

Advantage of functional relining :

a) Improving the fit of the denture base to the residual ridge.

b) Control the amount of soft tissue displacement by controlling the

amount of relief of the modeling plastic before impression making. The greater

the relief the less will be the tissue displacement.

4- The fluid wax functional impression technique: see later

II – The Altered Cast Techniques

The selected pressure impression technique and the fluid wax functional

impression are made after the framework construction for the purpose of

correcting the master cast before processing the denture base ( Altered cast

technique ) . The framework is constructed on a master cast made from a

single impression .

a- The fluid wax functional impression technique :

The term fluid wax is used to denote waxes that are firm at room

temperature & have the ability to flow at mouth temperature.

The most frequently used fluid waxes are (Lowa wax & korrecta wax No.4.)

The korrecta wax is lightly more fluid than Lowa wax.

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The objectives of these techniques are:

1- To obtain maximum extension of the peripheral borders of the denture

base without interfering with the function of movable border tissue.

2- To record the stress-bearing area of the ridge in their functional form,

and to record non-pressure bearing areas in their anatomic form. This technique

made with the patient opened his mouth this lead to less changer of

displacement of ridge by occlusal or vertical forces.

Impression technique

1- Autopolymerizing acrylic resin custom tray is made over the

edentulous ridge framework .

2- Green stick compound is used for border molding the impression tray .

3- Relieving the tray and impression making , relief between the tray

and the ridge of 1-2 mm is provided .

4- Iowa or Korrecta wax No 4, molten in a water bath is painted on the

tray with a brush.

5-The tray is seated in the mouth for about 5 minutes, while the patient’s

mouth is kept opened. The patient is instructed to do functional

movements and border trimming is made .

6-The impression is removed, dried and inspected. Where tissue contact is

present the wax surface will be glossy and where there is no contact the

surface will be dull.

7-Any dull spots or imperfections are coated with wax and the procedure

is repeated. The entire surface of completed impression should have a

glossy appearance and all peripheral margins are definitely turned over.

IMPRESSIONS FOR RPD

Mostafa Fayad 16

8- When the impression is completed, it should be left in the mouth for 12

minutes to be certain that the wax has completely flowed and releasing

any pressure that may be present.

b-The selected pressure impression technique:

it is often referred to as the " Selective Tissue Placement Impression" or

"dynamic" impression. to selectively recording of mucoosseous tissue we use

1- Varying viscosity of impression material

2- Selective venting (escape hole) of tray

3- Selective relief of the tray

Method:

1- Autopolymerizing acrylic custom tray is made over the edentulous ridge

framework. Green stick compound is used for border molding the

impression tray.

2- The mandibular tray is relieved at specific area of the ridge as the crest

of the ridge down to the metal . Only slight relief is provided in the

buccal shelf and lingual slope areas . The tray may be vented over the

ridge crest to allow escape of the impression material and decrease

tissue displacement. Impression is made with zinc oxide paste if the

ridge is free from gross undercuts . Both polysulphide and silicon

impression materials are indicated for those ridges with bony undercuts.

Framework try in

Before the trays are attached, the framework must be fitted in the mouth.

1. Use of a disclosing media to identify interferences to completely seating the

removable partial denture framework

IMPRESSIONS FOR RPD

Mostafa Fayad 17

2. Use of disclosing media to identify the appropriate contact(s) of the

component parts of the framework during the seating of the framework and

when the framework is completely seated in its designated terminal position

3. Adjusting the seated framework to the opposing occlusion. If there are

opposing frameworks, the maxillary framework is removed from the mouth

and the mandibular framework is adjusted to the natural maxillary dentition.

Then the maxillary framework is replaced and it is adjusted to the mandibular

Several types of disclosing media may be used, such as stencil

correction fluid, rouge and chloroform, and disclosing fluids, pastes, a spray

disclosing medium and waxes. the framework is placed with mild pressure.

Making impression tray

1- The metal framework & the master cast must be examined to

eliminate any obliteration in the lingual extension of a

mandibular ridge by trapped of the floor of the mouth or

sublingual gland within the impression.

N.B: One reason for modifying the impression tray with molding plastic is to

prevent the trapping of the floor of the mouth or the sublingual gland within the

impression.

2- The acrylic resin impression tray then adapted & contoured

without any relief at this time. Because the tray should

stabilized during border modeling.

Obtaining support from the primary support areas is achieved by:

the manner in which the flow of the impression material is controlled during

the impression-making procedure.

Restricting the flow of the material in the primary stress-bearing areas

(by minimizing the amount of relief over the area when the custom tray was

made) causes greater pressure to be exerted on the tissue in this area (compared

IMPRESSIONS FOR RPD

Mostafa Fayad 18

with other areas of unrestricted flow where a greater amount of relief or

venting of the impression tray was provided).

B – Correcting peripheral extensions of tray:

1- The framework with the tray attached is seated in the mouth.

The buccal extension of the tray should be observed as the cheek is moved

down word, outward and upward, the edge of the tray should be just shy (1 or

2mm) of the movable tissue.

2- The posterior extension of the tray should be end at two thirds

coverage of the retro molar pad to be directly observed.

3- The distoligual extension of the tray is determined by the patient

protruding his tongue until contact the upper lip. The fingers of

the operator should be rest lightly on the tray, if the tray tends to

lift, even slightly, during this movement, the distolingual length

should be shortened.

4- The patient moves the tongue into each cheek with the operator

fingers resting lightly on the tray to check the lingual flange

extension. If the tray moves during this movement, the lingual

flange opposite the cheek toward which the tongue moves, should

be shortened.

C- Border molding the Impression tray:

The tray may be border molded in two steps:

1- From the anterior extent of the buccal flange to the most posterior

extent of the tray.

2- The remaining of the lingual & distolingual flange:

IMPRESSIONS FOR RPD

Mostafa Fayad 19

A low – fusing modeling plastic, green or gray stick, is used for this

procedure. This step will be as in correcting the peripheral extension. This

processes basically the same as that for complete denture.

D – Relieving trays:

Now the relief under the tray is done at specific area needed .

Correcting the master cast

1- The ridge area(s) of the cast , which will be replaced by corrected cast

impression , is outlined with a pencil and removed with a handsaw .

Retentive grooves on the cut surface of the cast are made. These grooves

will help in retention of the poured new stone to the old cast .

2- The framework with the impression is seated and sealed to the sectioned

cast .

3- The sectioned cast with the impression is inverted , beaded , boxed and

poured into dental stone .

The resultant cast is used to complete the partial denture . The tissue

displacement during impression requires that the metal stop should be adapted

to the cast by self – curing resin before making the record base .

IMPRESSIONS FOR RPD

Mostafa Fayad 20

Areas to be removed from the cast are outlined , removed & retentive grooves are made to

help in retention of the poured new stone to the old cast .

IMPRESSIONS FOR RPD

Mostafa Fayad 21

Beading & boxing of the impression . The corrected cast after hardening of

dental stone.

Steps for correcting the master cast .

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Mostafa Fayad 22

The selective pressure technique described above can be applied to all

varieties of residual ridges as it is customized to mucosal conditions, whereas

the functional impression technique has limited application to a uniformly firm

ridge consistency.

II- One stage selected pressure impression technique:

Dumbrigue and esquivel in 1998 described a technique for selective

pressure impression technique from a single impression prior to framework

construction and after mouth preparation.

Procedure:

1- A custom tray with 2 mm. Short borders is constructed over the study cast

after adaptation of two layer wax on teeth and residual ridge. Aluminium foil is

burnished over the wax.

2- Occlusal stops are placed over the remaining teeth by cutting boxes through

the aluminium foil and wax to ensure proper seating of the tray.

3- Softened modelling compound is applied in the tissue surface of the tray.

4- Reheat compound and place intraorally. Remove, check and then apply

modelling compound to the border

5- Relief the tissue surface of compound 1mm except for primary stress bearing

area.

6- Make complete impression using rubber base material with applying finger

pressure.

IMPRESSIONS FOR RPD

Mostafa Fayad 23

Control of gagging

Procedures that will help to prevent gagging include:

1. The dentist should:

a) Not mention the subject of gagging

b) Ask whether the patient has had impressions made previously.

2. Before the impression is made:

a) Ask the patient to use astringent mouth rinse and cold-water rinses

b) Seat the patient in an upright position with the occlusal plane

parallel with the floor.

c) Ask the patient to take a deep breath and hold the breath while the

dentist quickly checks the size and fit of the tray.

d) Correct the maxillary tray with modeling plastic and leaving

sufficient unrelieved modelling plastic at the posterior border.

3. The impression material must:

a) Have the consistency of thick whipped cream

b) Fast-setting alginate.

c) Set up to a rubbery consistency in few minutes.

4. During the impression procedure:

a) Not overfill the tray with impression material.

b) Seat the posterior part of the tray first and then rotate the tray into

position.

c) Force excess alginate in an anterior direction.

IMPRESSIONS FOR RPD

Mostafa Fayad 24

d) Ask the patient to: • Keep the eyes opened and focused on some

small object. • Breathe through the nose.

5. The “leg lift” procedure is used before and during the making of the

impression.

6. Giving all instructions to the patient in a firm, controlled manner.

7. The use of an anesthetic spray is usually contraindicated.

Control of saliva

If the teeth are too dry, alginate has a tendency to stick to them. Therefore the

teeth should not be air dried before making an impression.

Excessive amounts of saliva, particularly of the thick mucous type, will

displace the alginate impression material and will contribute to an inaccurate

impression.

The excessive saliva can be controlled for most patients by having the

patient rinse the mouth with an astringent mouthwash followed by a rinse

of cold water and then packing the mouth with unfolded 2 x 2 inch gauze:

• In the maxillary arch one gauze strip is placed in the right buccal vestibule

and another in the left vestibule. The dentist must wipe the palatal area just

before making the impression.

• In the mandibular arch one gauze strip is placed in each of the buccal

vestibules and another is placed in the linguoalveolar sulcus by having the

patient raise the tongue, placing the gauze in the sulcus, and then having the

patient relax the tongue to hold the gauze in position. The gauze is removed

immediately before the impression is made.

• With excessive amount of thick mucinous saliva from the palatal salivary

glands, the patients should be instructed to rinse with an astringent mouth rinse.

IMPRESSIONS FOR RPD

Mostafa Fayad 25

Then 2 x 2-inch sponges moistened in warm water should be used to place

pressure over the posterior palate in an attempt to milk the glands. This is

followed by an ice water rinse immediately before the impression is made.

• With copious amounts of saliva, the use of an antisialagogue in combination

with mouth rinses and gauze packs effectively controls this salivation. (A 15-

mg Pro-Banthine tablet taken 30 minutes before the impression appointment)

Establishing occlusal relationship

Mostafa Fayad 1

ESTABLISHING OCCLUSAL RELATIONSHIPS

Establishing of functional, and harmonious occlusion is important in the

treatment of partially edentulous patients. Occlusal harmony between a partial

denture and the remaining natural teeth is a major factor in the preservation of

the residual ridges, and the abutment teeth.

The goal in developing an occlusal scheme for the R P D to provide a

masticatory efficiency & esthetically acceptable, and to distributed the occlusal

loading as evenly as possible to all supporting structures in case of tooth tissue

born R P D.

DESIRABLE OCCLUSAL CONTACT RELATIONSHIP FOR

REMOVABLE PARTIAL DENTURES;

• The following occlusal arrangements are recommended to develop a

harmonous occlusal relationship of removable partial dentures and to

enhance stability of the removable partial dentures

1. Simultaneously bilateral contacts of opposing posterior teeth must occur

in centric occlusion

2. Occlusion for tooth supporetd removable partial denture may be arranged

similar to the occlusion in seen in a harmonous natural dentition

- Stability of such removable partial dentures results from the effect

of the direct retainers at tha both ends of the dentures base

3.Bilateral balanced occlusion in eccentric position should be formulated

when a maxillary complete denture oppose the removable partial denture. This is

a complete primarily to promote the stability of the complete denture.

4. Working side contact should be obtained for the mandibular distal

extension denture. This contacts should occur simultaneously with working side

contacts of the natural teeth to distribute the stress over the greatest possible area


Mostafa Fayad 2

5. Simultaneously working and balancing contact should be formulated for

the maxillary bilateral distal extension removable partial denture whenever

possibe.

6. Only working contacts need to be formulated for either maxillary or

mandibular unilateral distal extension removable partial dentures.

7. In the Kennedy Class IV removable partial denture configuration

contact of opposing anterior teeth in the planned intercuspal position is desired to

prevent a continous eruption of the opposing natural incisors unless they are

otherwise prevented from extrusion by means of a lingual plate, auxillary bar, by

splinting.

8. Balanced contact of opposing posterior teeth in a straight forward

protusive relationship and functional excursive position is desired only when an

opposing complete denture or bilateral distal extension maxillary removable

partial denture is placed.

9. Artificial posterior teeth should not be arranged further distally than the

beginning of a sharp upward incline of the mandibular residual ridge or over the

retromolar pad.

Failure to provide and maintain adequate occlusion on the removable

partial denture is primarily a result of:

(1) Lack of support for the denture base,

(2) The fallacy of establishing occlusion to a single static jaw relation

record.

(3) An unacceptable occlusal plane.

The establishment of a satisfactory occlusion for the removable partial

denture patient should include the following:

(1) An analysis of the existing occlusion;

(2) The correction of existing occlusal disharmony;


Mostafa Fayad 3

(3) The recording of centric relation or an adjusted centric occlusion;

(4) The recording of eccentric jaw relations or functional eccentric

occlusion; and

(5) The correction of occlusal discrepancies created by the fit of the

framework and in processing the removable partial denture.

Vertical Jaw Relation

Vertical diminution (V D) :-

Definition:- it is a vertical measurement of the face between two arbitrary points :

one below the mouth usually on the chin, and other above the mouth generally on

the nose.

Two vertical dimensions are recognized for each patient:-

1- Vertical dimension of rest (V D R): - it is taking when the patient is in an

upright position and is complete at rest, and the natural teeth will not be

touching (free way space).

2- Vertical dimension of occlusion (V D O): - it is taking when the patient

with natural teeth elevates the mandible from the rest position and the

teeth become contact in maximum intercuspal relation.

Altering the Vertical Dimension of Occlusion:-

For most patients requiring RPD measurement of the V D is not necessary. As

the following:-

If natural teeth in opposing arch contact in C O. This should be

considered as a V D O for that patient, and the prosthesis should be constructed

at this V D. increasing this V D O should be occur only; if the patient display

symptoms that suggested the V D O has been dimensioned, shush as tired aching


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muscles, unexplained pain in the head or neck, or an appearance of premature

aging caused by shorting nose-chin distance

Most significance signs of over closure:-

1- Excessive free –way space.

2- Extrem anterior vertical overlap in which the mandibular teeth actually strike

the soft tissue of the palate and migration of the condyles (this seen in

radiographically).

- If these signs and symptoms are present, a temporary increase in existing V D

can be considered with a temporary removable appliance in the form of an

acrylic resin occlusal overlay to cover the maxillary teeth. Because less

interference with the tongue movement. The most importance consideration is

the remaining teeth in both arches must be contact by the prosthesis.

-If the teeth not in contact by the appliance; will tend to erupted to reestablished

the functional contact. - If sufficient number of remaining teeth is not used to

support the appliance, the supporting teeth will be submerged or depressed to an

infraocclusal position.

- If the physiologic response of the patient to this appliance is positive disappears

the signs & symptoms of the decreased V D for several months, permanent

correction must be instituted.

When permanent treatment begins, it must be planned so that all occlusal dimension restoring prosthesis, fixed and removable, are inserted at the same time.

Establishing V D O:-

Only a small percentage of partially edentulous patient( those who have C

D opposed P D & those who have lost all posterior teeth in one or both arch)

need to have the V D O established by measurement. This done by measuring the

V D R and then subtracting 3 mm (the average amount of free way space).


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Horizontal jaw relationship

Two horizontal jaw relationships of mandible to maxilla are of importance

in the occlusion of R P D.

a- The first of these relationships of the mandible to maxilla is centric relation

(CR).

b- The second of these relationships is centric occlusion (C O). In more than

90% of all people, C R & C O does not coincide. The C O will always be anterior

to the C R 1 to 2 mm is most frequently. The patient with partial denture will

always function in these two positions & intervening space, so deflective

occlusal contacts in either position must be avoided.

Deflective occlusal contacts:- it is a contact that displaces a tooth, diverts the

mandible from it is intended movement, or displaces the removable denture from

it is basal seat.

Selection of C R or C O in recording horizontal jaw relation:-

1- C R & C O position coincide with no evidence of occlusal pathology;

therefore the decision should be to fabricate the restoration in centric relation;

2- C R & the C O position do not coincide but the planned C O position is clearly

denned and the decision has been made to fabricate the restoration in the planned

intercuspal position;

3- C R & the planned C O position do not coincide and the intercuspal position is

not clearly denned, therefore the decision should be made to fabricate the

restoration in centric relation;

4- Posterior teeth are not present in one or both arches and the denture will be

fabricated in centric relation.


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Factors influencing development of occlusion

Several factors influence the final occlusal schem for the partial denture patient.

(Hanau Quint)

1. The inclination of the condylar guidance.

2. The prominence of the compensating curve.

3. The inclination of the plane of orientation.

4. The inclination of the incisal guidance.

5. The heights of cusps.

In a patient who has partial dentures, however, the factors governing the

occlusal patterns are already determined.

The presence of some natural teeth means that the prominence of the

compensating curve has been determined& the plane of orientation is present.

The presence of anterior teeth means that the incisal guidance is determined

and the height of the cusps is known.

This means that in partial denture construction the remaining natural teeth will

dictate the form and position of the artificial teeth. The only exceptions are:

1. When the removable partial denture is opposed by a complete denture and

occlusal harmony can be obtained and

2. When only anterior teeth remain in both arches and the incisal relationship is

noninterfering.

METHODS FOR ESTABLISHING OCCLUSSAL RELATIONSHIP

There are basically two methods of establishing the occlusion for a removable

partial denture:


Mostafa Fayad 7

1. The articulator, or static, technique.

2. The functionally generated path technique

I- Articulator Technique

1- Direct Apposition of Casts (Hand Articulation)

Hand articulation may be used when sufficient opposing teeth remain in

contact to make the existing jaw relation ship obvious.

It should be used when only a few teeth are to be replaced.

The occluded casts are secured together with wooden sticks and sticky

wax and mounted arbitrarily on an articulator. A face-bow mounting is generally

not indicated.

The limitations to using this method:-

The principal danger in this technique is that it perpetuates the existing

vertical dimension and any existing occlusal disharmony.

3- Interocclusal records with posterior teeth remaining

- It is a modification to the direct apposition of cast. It is used when sufficient

teeth remain to support the partial denture (Kennedy class III or Class IV), but

the relation of opposing teeth does not permit the occluding of casts.

a- Interocclusal wax records:

- A uniformly softened, metal-reinforced baseplate or set-up wax is placed

between the teeth, and the patient is guided to close in centric relation.

- The wax is then removed & immediately chilled

thoroughly in room–temperature water. It should be

replaced a second time to correct the distortion that

result from chilling & then again chilled after removal.


Mostafa Fayad 8

- All excess wax should now be removed with a sharp knife. All wax that

contacts mucosal surfaces be trimmed free of contact. The chilled wax record

again should be replaced to make sure that no contact with soft tissue exists.

- A wax record should be further corrected with a bite registration paste,

which is used as the final recording medium. The bite registration paste is then

mixed and applied to both sides of the metal reinforced wax record. The patient

is assisted with closing in the rehearsed path, which will time be guided by the

previous wax record. After the paste has set, the corrected wax record is removed

and inspected for accuracy.

The record should seat on accurate casts without discrepancy or

interference. When an intact opposing arch is present, use of an opposing cast

may not be necessary. Instead, a hard stone may be poured directly into the

impression paste record to serve as an opposing cast.

The advantage of having casts properly oriented on a suitable articulator

contraindicates the practice. The only exception to this is if the maxillary cast on

which the partial denture is to be fabricated has been mounted previously with

the aid of a face-bow. In such an instance an intact lower arch may be reproduced

in stone by pouring a cast directly into the interocclusal record.

- The advantages of using a metallic oxide paste over wax as a recording

medium for occlusal records

1- Uniformity of consistency.

2- Ease of displacement on closure.

3- Accuracy of occlusal surface reproduction.

4- Dimensional stability.

5- The possibility of some modification in occlusal relationship after

closure, if it is made before the material sets.

6- Less likelihood of distortion during mounting procedures.


Mostafa Fayad 9

Three important details to be observed when one uses such a material:

1- Make sure that the occlusion is satisfactory before making the

interocclusal record.

2- Be sure that the casts are accurate reproductions of the teeth being

recorded.

3- Trimmed the record with a sharp knife wherever it engages undercuts,

soft tissues, or deep grooves.

B-Using of bite tray:

A ready made bite tray may be used to record the jaw relation. The final

recording medium is placed on both sides of the tray and the patient is guided to

close in centric occlusion.

3 - Jaw Relation Record Made By Using The Framework

In the first jaw relation record made to complete the diagnostic mounting

procedure, baseplates were used to transport occlusion rims and recording media.

The baseplates were constructed of autopolymerizing acrylic resin.

For the final jaw relation record the framework should be used to support the

occlusion rim and recording medium.

1- The framework should be fit & any occlusal interference have been corrected

or eliminated at the framework try-in appointment. This means that the

framework will be a stable and accurate base on which to record the jaw

relationship.

2- If this appointment follows the construction of an altered or corrected cast, as

it usually will. The acrylic resin tray that was used to make the impression must

be removed from the framework. The impression should not be used as a

recording base for the jaw relation record because the impression generally is

distorted as it is removed from the cast.


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Lab procedures:-

a- Making the Record Base:-

If the edentulous space is not too long, hard baseplate wax may be formed over

the acrylic resin retention metal in contact with the edentulous ridge. The normal

precautions must be taking during handling the framework, and using a pressure-

free interocclusal media, to decrease the pressure on the record base.

The baseplate wax record base & the casts must be mounting on an

articulator immediately to avoid the distortion of the wax.

If the edentulous ridge is long or if the interarch space is restricted,

autopolymerizing acrylic resin (sprinkle-on method) or acrylic resin tray material

(finger-molding technique) should be used to construct the record base. But the

danger of damaging the master cast is also slightly greater.

Regardless of the material used to construct the record base, soft tissue undercuts

on the edentulous ridge must be blocked.

Separating medium should be painted over the edentulous ridge before the

framework is seated.

To prevent the dislodge the framework by excessive downward force

during the adaptation of the record base materials. A bead of autopolymerizing

resin can be placed between the tissues stops and the stone ridge and allow to set

before the record base is adapted.

b- Occlusion Rim

An occlusion rim of medium baseplate wax is added to the record base. The

occlusion rim should be centered over the crest of the edentulous ridge. The

mandibular distal extension occlusion rim may be constructed so that the height

will be even with the cusps of the adjacent abutment tooth anteriorly and

posteriorly to two-thirds the height of the retro-molar or pear-shaped pad.


Mostafa Fayad 11

c- Recording Media

1- Zinc oxide-eugenol impression paste it is the first choice as a recording

medium. It can be mixed to form a free-flowing, practically pressure-free

material. The material produces a firm record and not liable to damage. The

record can be kept for an extended time, if needed without fear of distortion.

2- Concentrated slurry solution mixed wit Hydrocal, it is produces a hard and

accurate record. The mix of the material is free flowing and yet will set rapidly.

The record can be kept for an indefinite period without fear of distortion.

3- Modeling plastic, it is hardly a pressure-free material and the accuracy of the

record should be verified. Once chilled, the record is hard, but it still susceptible

to distortion. It should be used to mount the casts immediately.

4- Baseplate wax it is difficult to soften it evenly to obtain an accurate record.

Waxes that contain metallic particles (such as Aluwax) can be uniform, Softened,

but even after this type of wax is chilled' remains pliable and can be distorted.

d- Clinical Procedures

The framework with the record base and occlusion rim attached is tried in the

patient's mouth. The height of the occlusion rims must be adjusted so that no

contact takes place between the opposing teeth and the rim. A space of

approximately 1 mm is desired.

When the opposing occlusion rims are to be used. The mandibular rim is

usual used to establish the ideal occlusal plane because the landmarks that are

normally present. The posterior height of the rim is established at 2\3 the height

of the retromolar pad and anterior to the height of the remaining teeth.

If opposing occlusion rims are to be used, the recording medium is normally

placed on the mandibular rim. The maxillary rim should be indexed with several

V-shaped notches. A separating medium, petrolatum, should also be used over

the surface of the maxillary rim.


Mostafa Fayad 12

The surface of the occlusion rim that is to support the recording medium

should be roughened. To ensure that the record will remain attached to it.

If the record is made at C R position, the patient's mandible should be guide

to the most retruded position& allowed to close. If the CO position is to be used,

the patient should close in that position.

The greatest cause of incorrect jaw relation records is pressure. If any force

occurs on the occlusion rims, the distal extension record base will depress the

soft tissue beneath the base. This is enough to cause an incorrect jaw relation

record.

If the jaw relation record is accurate, the casts may be mounted on the articulator

and the artificial teeth selected and set.

4- Occlusal relations using occlusion rims on record bases

It is used when

one or more distal extension areas are present,

when a tooth-supported edentulous space is large,

when opposing teeth do not meet.

- Occlusion rims on accurate jaw relation record bases must be used.

- Visible light-cured (VLC) or autopolymerizing acrylic resin, cast metal,

compression molded or processed acrylic resin bases can be used to made a

record bases for jaw relation records.

- The recording proceedes much the same as in the previous method, except that

occlusion rims are substituted for remaining teeth.

Jaw relation record bases are useless unless they are made on the same cast

or a duplicate cast on which the denture will be processed, or are themselves the

final denture bases. The latter may be either of cast alloy or a processed acrylic

resin base.


Mostafa Fayad 13

Methods for recording centric relation on record bases:-

There are many ways by which centric relation may be recorded when

record bases are used. The least accurate is the use of softened wax occlusion

rims.

Modeling plastic occlusion rims, on the other hand, may be uniformly softened

by flaming and tempering, resulting in a generally acceptable occlusal record.

This method is time proved, and when competently done, it is equal in accuracy

to any other method.

- Modeling plastic occlusion rims, are uniformly softened by flaming and

tempering, resulting in a generally acceptable occlusal record.

- When wax occlusion rims are used, they should be reduced in height until just

out of occlusal contact at the desired vertical dimension of occlusion. A single

stop is then added to maintain their terminal position while a jaw relation record

is made in some uniformly soft material, which sets to a hard state. Quick-setting

impression plaster, bite registration paste, or autopolymerizing resin may be

used.

- With any of these materials, opposing teeth must be lubricated to facilitate easy

separation.

- When two blocks are being used, one of the bite blocks is inserted first and the

occlusal plane is trimmed to the correct level. Which block is selected depends

upon which arch will be the greater help in aligining the occlusal plane. If a

posterior molar is standing the plane is adjusted to a level indicated by this tooth.

If no posterior teeth are present (Kennedy class I & II ), the lower occlusal plane

should be trimmed first to a level indicated anteriorly by the abutment teeth, and

posteriorly by the center of the retromolar pad.

- The upper block is then inserted and the occlusal plane is trimmed to provide

even contact with the lower at the predetermined occlusal vertical dimension.


Mostafa Fayad 14

5- Jaw relation records made entirely on occlusion rims

It is used when

no occlusal contact exists between the

remaining natural teeth, such as when an

opposing maxillary complete denture is to

be made concurrently with a mandibular

partial denture.

used in those rare situations in which the few remaining teeth do

not occlude and will not influence eccentric jaw movements.

Jaw relation records are made entirely on occlusion rims when

either arch has only anterior teeth present.

In any of these situations, jaw relation records are made entirely on occlusion

rims. The occlusion rims must be supported by accurate jaw relation record

bases. Here the choice of method for recording jaw relations is much the same as

that for complete dentures. Either some direct interocclusal method or a stylus

tracing may be used.

As with complete denture fabrication the use of a face-bow, the choice of

articulator used, the choice of method for recording jaw relations, and the use of

eccentric positional records are optional according to the training, ability, and

desires of the individual dentist.

In this case recording jaw relations is such the same as that for complete

dentures. This includes:

1- Establishing proper facial contour, and orientation of the occlusal plane.

2- Determination of vertical dimension of occlusion.

3- Mounting the upper cast according to a face-bow record.


Mostafa Fayad 15

4- Registration of centric relation,

5- Locking the maxillary and mandibular occlusion blocks and mounting the

lower cast on articulator.

6- Registration of eccentric jaw-relations.

II -Functionally Generated Path Technique

Clinical Procedure : An acrylic resin denture base is

attached to the framework. A specially compounded hard wax

occlusion rim is constructed on the acrylic resin base. This

occlusion rim is constructed slightly high in occlusal contacts

and will keep the remaining natural teeth apart from 0.5 to 0.7mm. The extra

height is necessary to develop the full range of motion. The occlusion rim should

be made several millimeters wider than the buccolingual width of the tooth

opposing the rim. There are two methods of having the patient grind the

occlusal pathways.

The first method:-

The patient take the framework with the denture base and occlusion rim

attached home and to wear it continuously for 24 hour except when eating and

when drinking hot or chilled drinks.

The patient who wears the prosthesis overnight must be reminded to

intermittently close the jaws together firmly and to grind against the wax in all

possible jaw position.

The value of the patient's wearing the denture while sleeping is that

involuntary or bruxing contacts will be recorded. The resulting pathway will be a

record of all possible jaw movements and tooth contacts even though some of the

contacts may be undesirable.

The completed wax pattern will resemble a slightly larger version,

buccolingually, of the teeth that originally occupied the edentulous space.


Mostafa Fayad 16

This wax pattern is boxed and poured in improved dental stone to provide a

permanent record of the generated pathways. The stone record is mounted on an

articulator.

The second method:-

The patient is creating the pathway in the dental office directly under the

supervision of the dentist.

Advantage of this method: - the dentist's being able to observe and correct the

movement the patient is making.

Disadvantage of this method: - normally a patient will require at least 30

minutes of active movement to complete a pathway.

The record should be removed and examined every few minutes. The wax will

exhibit a glossy surface where tooth-wax contact is occurring. Those areas not in

contact will appear dull. Wax may be melted and added to those areas to ensure

complete and even contact. The record is boxed and poured the same as for the

overnight record.

Artificial Teeth Set to the Generated Path

1- The incisal guide pin is opened 1 mm before the artificial teeth are

positioned. This increase in vertical dimension will be returned to normal

by selectively grinding the denture teeth. The selective grinding also

develops the occlusal anatomy of the denture tooth to conform to the

functionally generated stone path.

2- The denture teeth are positioned over the framework in the correct

anteroposterior and buccolingual position. Then the incisal guide pin is

returned to correct vertical dimension of occlusion.

3- A water-soluble Prussian blue dye is painted on the surface of the

generated path. The articulator is locked in C R, and opening and closing

tapping movements are made of the stone path against the denture teeth.


Mostafa Fayad 17

4- The spots of dye transferred from the stone pathway to the denture teeth

indicate the areas of contact and are reduced by grinding.

5- Selective grinding is continued until the incisal pin again contacts the

incisal table.

At this time, intimate contact should be present between the artificial teeth

and the stone pathway. The articulator is not moved into protrusive and lateral

excursions because these positions are incorporated in the pathway.

Advantages:-

1- Eliminates the need for adjusting an articulator with interocclusal record

or a tracing device.

2- Eliminates the need to make a face-bow transfer, because all the in-

formation derived from a face-bow transfer is contained in the pathway.

There are limitations or disadvantages to the use of the generated path.

1- If opposing partial dentures are required, one of the partial dentures

must be completed before the other can be made by the articulator

method and then to functionally generate a pathway for the complete

denture.

2- Can not used in distal extension R P D because during the generation

of the path in the hard inlay wax, movement of a distal extension base

carrying the occlusion rim is possible. This will produce an inaccurate

pattern that will appear to be complete.

3- Verification of a recording in the mouth is difficult.

Numerous studies have also shown that the masticatory cycle differs depending

on the type and texture of food being chewed. This may mean that the pattern

developed in the wax is accurate for the wax only and that food-stuffs may fall

inside or outside the particular chewing cycle.


Mostafa Fayad 18

ESTABLISHIN JAW RELATION FOR A MANDIBULAR RPD

OPPOSING A MAXILLARY CD :

(1) If mandibular removable partial denture occluding with maxillary

complete denture-

- If existing denture is satisfactory and occusal plane is oriented to an

acceptable anatomic, function and esthetics position than complete denture not

need to b replaced and treated as a intact arch.

- A face bow transfer is made of that arch and cast is articulated on the

articulator.

- than face bow and complete denture is remover and irreversible hydrocolloid

impression of the denture is made.

- A cast is formed from the impression and mount on the articulator.

- Than centric relation recorded and transferred to the articulator.

(2) When the removable partial denture replaces all posterior teeth and the

anterior teeth are no interfering.

A central bearing point tracer is used may be mounted im the plate on maxillary

denture. A centric relation are recorded by means of introral stylus tracing

against the stable mandibular base.

When a existing complete denture opposing a arch on which removable partial

denture is fabricated. A cast of complete denture is used during the fabrication

procedure.

(3) If the mandibular removable partial dentures is tooth supported than

mandibular arch resorted first.

In other instance the mandibular arch is restored first and jaw relation are

established if they would be a full complement of opposing teeth. Thus the

maxillary complete denture is occluded with an intact arch.


Mostafa Fayad 19

Establishing appropriate functional balanced occlusion of

partial denture:

In designing occlusion for partial dentures, the location of the edentulous area

and the condition of the opposing arch will significantly influence the desirable

occlusal contacts during functional movement of the mandible.

The objective of creating occlusal contacts during escursive movements of the

mandible is to broadly distribute forces over the supporting structure and to

reduce tipping of the removable partial denture. Simultaneous bilateral contacts

of the opposing posterior teeth must occur in the selected horizontal jaw position

in all cases.

1- For Kennedy class I mandibular partial denture, opposing completely

edentulous maxilla. Balanced occlusion (working balancing and

protrusive contacts of the posterior teeth, with light contact of the

anterior teeth ) should be formulated to promote stability of the

maxillary denture.

2- When maxillary Kennedy class I removable partial denture opposing

mandibular class I partial denture working and balancing sides contact

should be formulated to minimize tipping of maxillary partial denture

and broadly distribute the forces. Such arrangement will compensate in

part for the unfavorable position of the maxillary artificial teeth to the

crest of the ridge, which is usually lateral to the crest of the ridge.

3- For mandibular class I partial denture opposed by natural dentition.

Simultaneous, working side contact only should be formulated.

4- For Kennedy class II mandibular, or maxillary partial dentures only

working side contacts should be formulated.

5- For class IV maxillary removable partial denture, opposing natural

dentition, contact of the opposing anterior teeth in centric occlusion is

desirable to prevent a continuous eruption of the mandibular incisors.


Mostafa Fayad 20

Contact of the opposing teeth in eccentric position should be avoided to

prevent overloading of maxillary arch and the formation of flabby tissue.

6- For Kennedy class III partial denture, opposing natural dentition contact

of the posterior teeth during functional movement is not desirable, since

stability of the denture is maintained by direct retainers on both sides.

Guidelines for the choice of partially edentulous patients occlusal concept.

Maxillary arch Mandibular arch Occlusal scheme

Fully edentulous

restored by C.D.

Kennedy class I restored

by R.P.D.

Fully dentate

Kennedy class II

Fully denture

Class III

Class IV

Kennedyt class I

restored by R.P.D.

Kennedy class I

restored by R.P.D.

Fully dentate

Fully dentate

Kennedy class II

Class III

Fully dentate

Balanced occlusion working

balancing protrusive.

Working side contact

Working and balancing side

contact




Contact in centric no-eccentric

contact

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TRY IN OF RPD

Even the best partial denture frameworks do not fit perfectly in the mouth.

Stewart Rudd and Kuebker have stated that up to 75% of all frameworks may not

fit the mouth on the day of insertion. Since clasp tips are designed to fit passively

into a specified undercut, any discrepancy in seating of the partial denture

framework will cause the direct retainers to become active, thereby causing

orthodontic movement of the teeth. For this reason, frameworks must be adjusted

intraorally.

This stage of treatment may require action in two phases:

1. Trial of a cast metal framework, where one is included in the design of a partial

denture.

2. Trial of the partial denture, with the replacement teeth arranged on a temporary

or 'permanent' (metal) baseplate.

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Mostafa fayad 2

Framework Evaluation

A] Extraoral evaluation of the Framework

a- Check the framework on the master cast

Design drawn on the diagnostic cast was followed

Location of the components

Fit of the framework on the master cast

Amount of undercut and Soft tissue relief

Inspect the rests.

Examine the relationship between the framework and the soft tissue areas.

Check for proper adaptation and placement of clasps:

Check for proper adaptation and placement of the lingual plate:

Check the ease of framework removal

b. Inspect the framework off the master cast:

Cheek for abraded areas of the master cast:

Partial denture component

The finishing and polishing of the framework:

Presence of defects

Finish lines

c. Radiographic evaluation

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Mostafa fayad 3

B] Intraoral evaluation of the Framework

1-Seating the framework (Checking fit):

(a) Fitting the framework to the abutment teeth,

i. Seat the framework in place carefully with minimal force:

ii. Check for rocking of the framework in both anteroposterior and

buccolingual direction:

iii. Check for close adaptation of rests, clasp arms, and lingual plates:

iv. Cheek for physiologic relief on distal extension frameworks:

(b) Fitting the framework to the soft tissue (Check soft tissue contact or relief):

(c) Adjusting the framework to the opposing occlusion.

2- Checking for clicking or tilting during insertion

3- Verifying retention and reciprocation:

4- Checking stability

5 – Checking for deformed clasp :

6- Checking aesthetics

7- Checking occlusion:

8- Finishing and polishing ground surfaces :

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Mostafa fayad 4

A] Extraoral evaluation of the Framework (Pre-clinical Inspection

and Adjustment)

For examination of the completed laboratory work , Careful inspection should be

accomplished using magnification, the following should be observed:

a- Check the framework on the master cast

1-If the design drawn on the diagnostic cast was followed. The dental laboratory

should never change the framework design without consulting the dentist.

Conversely, errors in framework design caused by inaccurate drawing on casts or

omissions in laboratory prescriptions are the fault of the dentist.

2- Location of the components. The position of the framework components

should correspond to the design indicated on the master cast.

3. Fit of the framework on the master cast.

The fit of the framework to the master cast. The framework should fit the master

cast. If it does not, it will probably not fit intraorally. Replace the framework on

master cast as little as possible to prevent abrasion (in case a remake is necessary).

a. Complete and stable seating. The framework should demonstrate

accurate adaptation of the rests to their rest seats without rebound.

b. Adaptation. Confirm intimate adaptation of the framework to the

master cast, where indicated.

c. Relief. Confirm areas of relief between the framework and master

cast, where indicated.

4. Evaluate the amount of undercut and Soft tissue relief.

5. Inspect the rests.

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Mostafa fayad 5

Check to see whether the rests are fully seated: The margins of the rests

should be flush with the margins of the rest seats. If they are not, the source

of interference should be determined and corrected.

Evaluate the contours of the rests: overcontoured rests will interfere with

occlusion, and undercontoured rests may be too thin and weak and subject to

fracture.

6. Examine the relationship between the framework and the soft tissue areas.

Inspect areas where the major connector is in contact with soft tissue,and

make sure there is intimate contact to prevent food from getting beneath the

framework.

Make sure there is adequate gingival exposure around minor connectors

and approach arms for bar-type clasp assemblies. There should be 5 mm between

minor connectors and other vertical components. Horizontal portions of I-bars

should be 3 mm from the gingival margin, and the vertical portion should be 5 mm

from other vertical components.

Check relief under bar clasps and acrylic resin retentive mesh, and make

sure the tissue stop rests on the crest of the edentulous ridge.

7. Check for proper adaptation and placement of clasps:

Clasp arms, guide planes, and reciprocating arms should be in intimate

contact with the tooth structure. Gaps left between clasps and tooth structure will

allow food to collect between the framework and the teeth, which may result in

decalcification, caries, and gingival inflammation.

Clasp arms should have the proper shape, diameter, and taper. Wrought

wire clasps should be long enough and the solder joint placed far enough away

from the tip to allow adequate flexibility.

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Mostafa fayad 6

8. Check for proper adaptation and placement of the lingual plate:

When properly designed and constructed, the lingual plate will be scallop

shaped to close off the interproximal embrasures and cover the cingulum areas.

Open spaces between the lingual plate and the teeth can result in food impaction

and gingival inflammation, which may lead to bone loss in the area. A space may

also encourage the patient's tongue to play with the edge of the framework.

9. Check the ease of framework removal:

In fact retention may be greater on the cast because of friction and the rough

surface of the cast.

b. Inspect the framework off the master cast:

1- Cheek for abraded areas of the master cast:

The abraded areas on the cast correspond to areas of interference in the mouth.

Areas that necessitate close inspection include rest seats, guide planes, the lingual

surfaces of mandibular bicuspids and molars, retentive areas, and the junction

between minor connectors and clasp arms.

2- Partial denture component: The framework should be assessed using the

following criteria:

Rest seats should be fully seated (adequate support)

Reciprocal arms and proximal plates should be contacting the cast

Linguoplates and maxillary palatal major connectors should be in intimate

contact with the cast (food impaction)

Major and minor connectors should be an adequate distance from abutment

teeth (hygiene). Adjust, if possible, or have lab adjust or remake framework

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Major and minor connectors should be of proper proportions (rigidity,

hygiene).

The rigidity of the major connector should be tested with finger pressure

Note especially that cingulum rests should not be carried into embrasures and

that embrasure minor connectors for distal extensions should not be in contact

with the more anterior tooth (unless it has a rest seat preparation). Adjust, if

possible, or have lab adjust or remake framework.

Butt joints should be adequate for acrylic resin (slightly undercut). Adjust,

if possible, or have lab adjust or remake framework

Proper gridwork should have adequate relief

Thickness of the components. The dimensions of the

framework components should be evaluated to ensure

that they are appropriate for the required mechanical

properties.

o a. Major connectors. The major connector should demonstrate

dimensions which provide rigidity and strength.

o b. Rest - minor connector j unction. A minimum metal thickness

of 1.5 mm at the junction of the rest with the minor connector is

required for base metal alloys (2 mm for gold alloys).

o c. Clasp taper. Retentive clasps should taper uniformly in

thickness and width. Bracing clasps should possess dimensions

which provide rigidity and need not be tapered.

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Mostafa fayad 8

3- The finishing and polishing of the framework:

� Finish and polish of the framework should be adequate - no evidence of

pits, nodules and scratches in the metal. Eliminate sharp edges that might impinge

on the oral mucosa.

a- Inner surfaces of the framework should be free from pits , scratches and

bubbles .

b- The framework should be highly polished , except the fitting surface

the fitting surface of the maxillary major connector should be lightly

polished .

c - Both internal and external finish lines should be sharp , definite and

slightly undercut .

d- The taper of the clasp should be uniform and free from nicks and

notches.

4- Presence of defects. The framework should be evaluated for defects that might

compromise its adaptation or strength.

a. Positive bubbles or blebs. May inhibit complete seating of the

framework on abutment teeth or traumatize soft tissue.

b. Voids or porosities. May weaken the framework and lead to fracture.

5- Finish lines.

a. Staggered (offset) finish lines. In order to maintain framework

strength, the internal and external finish lines should not be superimposed.

b. The internal line angles of external and internal finish lines should

be less than 90 degrees to provide mechanical retention for the denture

base resin.

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C - Radiographic evaluation; it shows the invisible porosity and the size of the

partially visible one.

1. Porosity not visually detectable. Radiographs may demonstrate internal

porosity.

2. Porosity visually detectable. Radiographs may indicate the size of a

porosity which is only partially visible.

3. Technique.

a. 10 MA - 100 KVP - 15/60 seconds.

b. 15 MA - 70 KVP -15/60 seconds.

B] Intraoral evaluation of the Framework

1-Seating the framework (Checking fit):

The framework should be positioned correctly over the standing natural

teeth and gentle seating pressure applied along the path of insertion selected when

the study cast was surveyed. It should be found to slide easily into the fully seated

position, only moderate resistance being encountered corresponding to the

retentive value of any clasps which are present. If any undue resistance to

movement is encountered in the seating process,

Excessive force should not be applied as this may cause discomfort or make

it difficult to remove the framework subsequently without overstressing the

periodontal attachment of the tooth.

A near fit of the framework is not sufficient; an accurate fit is essential for

success. The framework may fit the cast but does not fit in the mouth, due to:

� A distorted impression,

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Mostafa fayad 10

� An improperly poured cast,

� An abraded cast, and/or

� Shifting teeth.

In the latter two instances, if the interferences are minor and can be located,

one may be able to, with care, adjust the framework into place.

One should avoid over reducing contacts on guide planes, rests, and

retentive tips. Contacts between the framework and the teeth gingival to the survey

line should not be arbitrarily removed, because these contacts can help guide the

framework into place and provide some degree of retention and stability.

The most common areas that interfere with seating are:

1. under rests

2. rigid portions of direct retainers (e.g. above the survey line)

3. interproximal portions oflinguoplate major connectors

4. interproximal minor connectors

5. shoulder areas of embrasure clasps

To locate small areas of the framework that are interfering with the fit,

a) By visual and tactile examination, an attempt should be made to

determine where resistance to further movement is occurring. Location of the

exact site of resistance can be assisted by the use of the disclosing wax. The

resistance area will be revealed as the area where the wax has thinned to display

the underlying metal.

b) A probe may also be used to check the closeness of fit of any elements

contacting the teeth. Clasp arms should be checked for non traumatic placement

Try-in of RPD

Mostafa fayad 11

relative to the gingival margins of the teeth. The various component elements

should also be checked for correct positioning relative to the soft tissues. For

example, gingivally approaching clasp arms should not enter soft tissue

undercuts. Palatal connectors on an upper framework should be in contact with the

underlying tissues. Where a lingual bar has been used in the design of a lower

framework, it should be correctly positioned relative to the gingival margins of the

standing teeth and the functional level of the lingual sulcus.

c) The patient should be questioned as to whether or not they feel any

discomfort when the framework has been inserted. Where the patient can detect a

pressure area, particularly in relation to covered soft tissues, it may be necessary to

relieve pressure in the area concerned by grinding the fitting surface of the

framework.

d) Some type of disclosing medium is needed. See later

The fitting of the framework to the mouth should be done in three phases:

(a) Fitting the framework to the abutment teeth,

(b) Fitting the framework to the soft tissue, and

(c) Adjusting the framework to the opposing occlusion.

a. Fit the framework to the abutment teeth:

i. Seat the framework in place carefully with minimal force:

Use gentle pressure over the rests as the framework is seated along the path of

insertion. Areas of interference must be relieved.

The most common areas that will interfere are: the junction between rests and

minor connectors, periphery of rests, guide planes, undercut areas, and clasp arms.

Try-in of RPD

Mostafa fayad 12

Failure to relieve even the smallest amount of interference can cause slight but

continuous pressure on abutment teeth, which may cause pain and discomfort.

Repeat the adjustment steps until the framework is seated in place uniformly and

completely.

ii. Check for rocking of the framework in both anteroposterior and

buccolingual direction:

Place fingers on the rests and rock the framework. The rests should stay in place

and not lift out of the rest seats as pressure is applied to one side and then the

other.

iii. Check for close adaptation of rests, clasp arms, and lingual plates:

After the framework has been seated, it is evaluated for fit . All rests should

seat completely in their prepared seats. Clasps, indirect retainers and minor

connectors should be in intimate contact with the abutment teeth. The adaptation

of the framework to the teeth may be confirmed by rouge and chloroform or

disclosing wax.

A sharp explorer is the instrument of choice to determine whether margins are

open or closed.

Excess saliva and bubbles should be blown of the teeth. All metal structures

designed to contact tooth structure should be adapted closely to the teeth, which

will ensure a precise fit.

iv. Cheek for physiologic relief on distal extension frameworks:

Place pressure on the retentive meshwork areas and observe:

� The movement of the clasp arms and guide planes.

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Mostafa fayad 13

� Disengagement of the retentive tips and guide planes as the framework rotates

around the rest seats.

� Proximal contact areas between abutments and adjacent teeth to ensure that the

abutments are not being torqued during rotation of the framework. Make sure

there is enough clearance between the proximal plate and gingiva to allow some

movement of the framework without tissue impingement.

Care should be taken when the framework is adjusted along the occlusal edge of

guide planes, rests, and major connectors. Do not accidentally open the

tooth/metal contact and create an area for food impaction.

b. Fitting the framework to the soft tissue (Check soft tissue contact or relief):

Make sure there is adequate space between the meshwork and the soft

tissue to allow a sufficient amount of acrylic resin material under the retentive

meshwork.

The tissue stop must be in contact with the edentulous ridge. The retentive

arm of a bar-type clasp should not impinge on soft tissue. There should not be an

excessive amount of relief that could result in a food trap.

The same can be said for minor connectors that cross soft tissue. Lingual

plates or bars should not impinge on soft tissue in the lingual vestibule area.

Additional relief may be necessary if tori are present.

c. Adjusting the framework to the opposing occlusion: see checking occlusion

2- Checking for clicking or tilting during insertion:

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Mostafa fayad 14

A – There should be no clicking during insertion , which occurs when a rigid

portion of the framework is being forced into an undercut .

B- Tilting during seating from the intended path of insertion , results when clasp

arm in one side is more rigid or extended into a deeper undercut than the other side

. To equalize force during seating and prevent tilting , the resisting clasp is

reduced in diameter , or its taper is increased .

3- Verifying retention and reciprocation:

The resistance by the framework to vertical dislodging force should be

evaluated. While seating and removing the framework slowly, the relationship

between the clasp arms and the abutments is observed.

After the framework is properly seated, remove and replace the framework several

times to evaluate retention. If there is too little or too much retention, the clasps

can be carefully adjusted.

The instruments of choice are orthodontic contouring pliers, which have smooth

beaks.

After adjustment, the clasp should have the desired retention and still be intimately

adapted to the tooth surface.

Avoid over bending the clasps, which may change the characteristics of the metal

through work hardening.

An over retentive framework can be detected by a snap or click as the

framework seats. The clasp should be in passive contact with the tooth when the

framework is completely seated. With over retentive clasps, tipping forces will

cause a destructive effect on the periodontal support tissues.

Try-in of RPD

Mostafa fayad 15

The amount of retention can be reduced by adjusting the clasp to engage a

smaller amount of undercut or by reducing the degree of adaptation to the tooth

surface.

As long as the forces are limited and do not exceed the elasticity of the periodontal

fibers, there should not be any damage to the teeth.

Each reciprocal arm should contact the abutment just prior, or at the same

time as the retentive arm. This will brace the abutment against the force applied by

the flexible retentive arm.

4- Checking stability

Stability of the framework should be checked by applying pressure on

various elements - rests, saddles and palatal connectors in particular – and noting

whether any rotational displacement occurs.

Special attention is necessary when checking the stability of a framework

carrying one or two free-end saddles. It is usual for the free-end saddle portion of

a metal framework to have been relieved from tissue contact in the constructional

procedure, to enable the saddle to be relined where this is subsequently required.

Before testing the stability of the free-end saddle element of a metal framework

which has been relieved from tissue contact, it is advisable that a wax baseplate be

positioned to bridge the gap between the metalwork and the underlying tissues.

Where the design of the partial denture includes the use of a stress-

breaker, especially where this is of Type 1, an appreciable degree of rotational

displacement should be observable when pressure is applied to the metalwork of

the free-end saddle. Where no stress breaker has been used, and yet an appreciable

degree of rotational displacement of the free-end saddle occurs when this check is

applied, there is a need for subsequent action to be taken to overcome this

Try-in of RPD

Mostafa fayad 16

instability. This will usually involve relining of the free-end saddle at the insertion

stage of treatment.

5 – Checking for deformed clasp :

A clasp may have been deformed during finishing and polishing . A clasp

under tension may force the frame to assume wrong or tilted position . This

condition is mostly seen with wrought wire clasps . Deformed clasp should be

corrected and should be passive when fully seated .

6- Checking aesthetics

The framework should be inserted and its appearance noted when the

patients lips are at rest and when the patient is smiling. If any elements of the

metalwork are visible when the patient smiles, it is advisable to point this out to

the patient and show them what is involved with the aid of a hand mirror.

If proper care has been applied in the stages of treatment planning and

denture design, objections to the aesthetics of a metal framework should be rarely

encountered. Where objections do arise, they usually relate to an unaesthetic

display of clasp arms or incisal rests. Where this is due to an unnecessary

thickening having occured in the construction of the framework, it may be

possible to overcome the objections by reducing the thickness of the element

concerned by grinding.

7- Checking occlusion:

Vertical dimension should remain unchanged by a removable partial

denture in almost all instances. The framework should not interfere with normal

centric and eccentric contacts

If both maxillary and mandibular frameworks are being constructed, only

one at a time should be corrected. Then, they should be tried in the mouth

Try-in of RPD

Mostafa fayad 17

together. Any interference noted now will be between the metal of the opposing

frameworks.

The patient should be guided into centric, protrusive and lateral

positions, with articulating paper is placed over the teeth, to locate the interference

in these positions. Mark occlusal contacts with thin articulating paper and remove

the framework for adjustment.

The highly polished metal surfaces do not mark well with articulating

paper so that the opposing occlusion should be checked for heavy contacts.

Diamond burs, heatless stones, Shofucoral stones or cross cut Brasseler lab burs

will most readily remove interferences. DO NOT FORGET TO LOCATE AND

ADJUST EXCURSNE INTERFERENCES.

Heatless stones or diamond instruments in the high speed hand piece are

used to reduce the interference, first in centric occlusion, then eccentric positions.

The framework must not keep the natural teeth from making normal

occlusal contact in either centric or eccentric closures. Since most frameworks are

be fabricated on unmounted casts there are usually occlusal interferences present

on rests and indirect retainers. These should be adjusted at this time.

-- Occlusal rests or indirect retainers that have inadequate thickness ( 1.5

mm) after adjustment will be subject to fatigue and possible fracture.

The inadequate thickness may occur due to inadequate preparation (i.e.

not considering opposing occlusion) or subsequent extrusion of teeth. If the teeth

have extruded, the entire framework will most likely not fit.

If occlusal interferences exist that will excessively thin the rests, the rest

seat preparation may have to be deepened and a new impression taken, or an

opposing cusp or framework

Try-in of RPD

Mostafa fayad 18

element may have to be reduced. Reduction of opposing cusps should be

performed as a last resort to save an otherwise acceptable framework.

-- Occlusal interferences should not normally occur on retentive clasp arms

if proper treatment planning has been followed. However, if the opposing

occlusion is not considered at the time of mouth preparations, it is possible that

occlusal contact may occur on a retentive arm. If this contact is minor, the

opposing cusp may be reduced. Again, reduction of opposing cusps should be

performed as a last resort to save an otherwise acceptable framework. If the

interference is gross, the tooth surface should be recontoured (i.e. lower height of

contour) and a new impression taken. IN NO INSTANCE SHOULD A

RETENTIVE ARM BE RELIEVED, since this will affect its flexibility and

resistance to fracture.

When occlusal discrepancies framework are corrected, care must be used

not to cut excessively and thus weaken the occlusal rests or clasp arms . If the

occlusal clearance is insufficient , in preference to weakening the framework by

too much metal reduction , the opposing tooth may be relieved to obtain the

necessary clearance .

Where the natural dentition does not contact at the required occlusal

vertical dimension and the design of the framework includes onlays, a check

should be made that with the framework inserted the opposing natural teeth and

the metalwork contact evenly at a vertical dimension providing an acceptable

freeway space.

Adjusting the framework to the opposing occlusion:

i. Identify natural tooth contacts in the centric occlusion (C0) or

maximum intercuspation positions (MIP):

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Mostafa fayad 19

The framework should not prevent the natural dentition from contacting in

the CO/MIP or during normal functional movements.

Start by removing the framework, and identify CO/MIP and eccentric

contacts between the natural dentition. These contacts will be the reference points

for judging the amount of occlusal adjustment needed.

ii. Adjust the framework in the C0 /MIP position:

� Place the framework in the mouth, and determine whether the-natural

dentition is able to reproduce the CO/MIP contacts. If not adjust the framework

until the teeth reproduce the desired occlusal contacts.

� Roughen up the surface by sandblasting with aluminum oxide or lightly

grinding with a fine carborundum stone, since highly polished framework metal

does not mark well with articulating paper.

� Place two articulating paper strips simultaneously on both sides of the

mouth, and have the patient close into the Co/MIP position. Two strips are

necessary because patients will tend to bite to one side it only one strip of

articulating paper is used.

� Adjust the framework without over thinning and weakening the metal

components. Rests and clasp arms are usually at risk of being excessively adjusted

and subsequently weakened. However, sometimes tooth migration can reduce the

desired occlusal clearance.

� If there is a risk that, the metal framework might be weakened,

adjustment of the opposing natural teeth may be necessary. Avoid exposing

dentin, and polish and fluoridate the teeth after the adjustment.

iii. Adjust the framework during eccentric movements:

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During mandibular eccentric movements the patient should reproduce

movements representative of normal masticatory function and not wide excursions

into lateral and protrusive positions. Instruct the patient to use relatively moderate

to heavy biting force.

iv. Occlusal adjustment of two frameworks:

If there are two frameworks, adjust the occlusion of each framework

independently.

Once each framework is in occlusal harmony with the opposing natural

dentition, place both frameworks in the mouth and adjust the frameworks to

occlude with each other.

Any interference detected should be between frameworks. If adjustment

procedures are carried out correctly, the patient's occlusion should be the same

with and without the frameworks in the mouth.

8- Finishing and polishing ground surfaces :

After the framework has been fit and occlusal adjustments have been made,

the surfaces of the ground metal must be finished and polished. Carborundum

points and wheels are used to restore smooth finish to all ground surfaces.

Dedco green knife edge wheels for chrome cobalt alloys will remove

scratches and bring the adjusted surface to a high shine quickly. Additionally,

Dedco blue clasp polishers or any other carborundum impregnated points can be

used to finish the chrome cobalt alloy. A final polish can be placed using a tripoli

on a bristle brush and rouge on a small diameter cloth wheel. Use care not to snag

the cloth wheel on sharp edges of the framework (to prevent injury to yourself).

Remove traces of the polishing compounds with soap and water and a toothbrush.

Adjusting and polishing tools:

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The framework can be adjusted with various burs, coarse Carborundum

stones, or both. All adjusted areas should be repolished with rubber points and

wheels.

For final polishing use a rag wheel and polishing compound.

When relieving or polishing, avoid staying in one spot for extended periods

of time to prevent the generation of localized areas of high temperature, which can

run the risk of changing the temper of the framework metal.

Special Adjustments for Distal Extension Cases:

In most cases distal extension cases will be designed with relatively short

occluso-gingival guiding planes to allow for release of the abutments during

tissueward movement of the denture base. However, there are some cases where

teeth are tipped and a long guiding plane is the only type of guiding plane that can

be placed. In these instances, "physiologic relief' of the framework should be used

to provide release. With this technique the distal guiding planes, minor connectors

and linguoplates are coated with alcohol and rouge (not wax or silicone). The

framework is placed intraorally and placed under hyperfunction by pressing over

the distal extension gridwork. The framework is removed and the guideplanes and

other rigid metal contacts, which could torque the tooth, are relieved in areas of

burn-through. Relief should be provided so that marks remain in only the occlusal

one third of the guiding planes.

It should be noted that it is inadvisable to attempt to rectify any faults

which are present in a framework (for example, inadequate retention in clasp

arms) by bending the framework. It is virtually impossible to apply bending

without disrupting the essential passive placement of the elements relative to the

oral tissues. A bent framework may well give rise to appreciable tissue damage.

.

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TRIAL PARTIAL DENTURE BASE TRY-IN

Indications:

A. Evaluation of Esthetic, and phonetic characteristics of the prosthesis. If

anterior teeth are being replaced, an esthetic try-in is essential.

B. Evaluation of the accuracy of the jaw relationship when all posterior teeth

in one or both arches are being replaced.

EXTRAORAL EXAMINATION:

Each denture should first be examined on the articulated casts.

INTRAORAL EXAMINATION

A. Checking extension, retention and stability: as in complete denture

B.Esthetic try-in:

• It is better if the dentist examines the teeth in the mouth before the patient

has an opportunity to observe them. Corrections can be made without

upsetting the mental attitude of the patient.

• Attention should be given to:

a) The anteroposterior position of the anterior teeth for adequate lip

support. Evaluate the positions of anterior teeth and assess lip support.

b) Tooth length in relation to lip length and length of the remaining

natural teeth.

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c) Mesiodistal width of the replacement anterior teeth (decreased or

increased).

d) Horizontal and vertical overlap of the anterior teeth.

e) Vertical alignment of the teeth.

f) The maxillary first premolar. (Considered anterior tooth in many

patients)

g) Shade, size and shape.

Facial support affected by:

! Position of the incisal edge

! Thickness and contour of the labial flange

Procedures

1) The patient should be seated in a quite, relaxed atmosphere. This

which helps him to alleviate the tension since he views the tooth

arrangement for the first time.

2) The denture base should be clean, and resistant to tooth

displacement.

3) Carefully insertion of the RPD and tell the patient to avoid

application of biting forces.

4) Then the patient is directed to close lightly to ensure that no

interference is present.

5) The dentist should evaluate the position of anterior teeth and assess

lip support.

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6) Tooth length should be carefully evaluated.

7) If an anterior edentulous space has been decreased by drifting of the

teeth, decreasing number of teeth should be avoided, instead,

attempts should be made to rotate or overlap the denture teeth in

order to give an acceptable esthetic result.

8) If the anterior edentulous space is relatively large, diastema may be

incorporated into the tooth arrangement.

9) Checking of the horizontal and vertical overlap of the anterior teeth.

10)Examination of the maxillary midline, for its (vertical alignment, and

for its mid face position).

11) Checking of the teeth shade specially if there are natural teeth is

present, which makes shade selection and patient acceptance a

critical point.

Once the technical and mechanical requirements are satisfied, the patient should

be allowed to view his new RPD and comment on the results. The patient's

remarks should be noted, and required changes should be made.

1- Abnormal fullness

If anterior teeth have been missing for 6 months or more, the patient may

report a sensation of abnormal fullness at the upper lip.

A short period of accommodation usually will eliminate this problem.

2-Teeth length

If all anterior teeth are being replaced and the upper lip is of normal length,

the edges of the central incisors should be visible when the lip is relaxed.

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Mostafa fayad 25

When the lip is drawn upward, the gingival contours of the denture base

should be minimally evident.

3- Short space

If an anterior edentulous space has been decreased by drifting of the teeth, a

decreased number of teeth should not be placed.

Attempts should be made to rotate or overlap the denture teeth in order to

achieve an acceptable esthetic result.

4-Large space

If the anterior edentulous space is relatively large, diastemata may be

incorporated into the tooth arrangement.

If this is to be accomplished, the patient should be informed of potential

difficulties associated with interdental spacing.

Spacing complicates oral hygiene procedures, increases the likelihood of

food impaction, and may create difficulties with phonetics.

5- Overlap of the anterior teeth.

If some anterior teeth remain, the overlap should be duplicated.

If no natural teeth remain, care should be taken to avoid excessive vertical

overlap without accompanying horizontal overlap.

This could result in the application of undesirable forces to the artificial

teeth and associated soft tissues.

6-Vertical alignment of the teeth also should be evaluated.

A slight deviation from the vertical can produce an acceptable esthetic

result, but a significant deviation can create esthetic difficulties.

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The practitioner should pay particular attention to the maxillary midline.

This midline must be examined for its vertical alignment and for its

midface position.

Any error in the position of the maxillary midline can be extremely

distracting.

7- Tooth shade.

The presence of natural teeth makes shade selection and patient

acceptance a critical component of removable partial denture therapy.

To ensure selection of an appropriate shade, the prosthesis should be

viewed using a variety of light sources.

8- The patient evaluation.

The patient should stand several feet from a wall mirror to examine the

teeth critically.

The use of a hand mirror should be discouraged because the patient’s

attention will be focused on individual teeth and not on the overall effect of

the prosthesis.

The patient’s remarks should be noted, and required changes should be

made.

Arrival at mutual acceptance by the patient and dentist frequently demands

a high level of communicative skill combined with psychological insight.

Treatment should not proceed until patient approval has been gained.

Many practitioners insist upon written approval by the patient.

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C. Jaw relation try-in (VERIFICATION OF JAW RELATION) :

The jaw relation need be verified specially in certain cases:

1. If doubt exists as to whether the recorded jaw relationship is accurate.

2. If the partial denture is opposed by complete denture

3. If all posterior teeth in both arches are being replaced.

4. If there an: no opposing natural teeth in contact.

The jaw relation only needs to be verified in limited steps:

12) Checking of the accuracy of the articulator mounting should be

performed, especially if problems were present during jaw relation

procedures.

13)Evaluation of the vertical dimension is necessary.

14)Checking the horizontal jaw relationship

In many cases, visual evaluation may be sufficient for checking of the contact of

the opposing natural teeth, and for checking the occlusion in centric and eccentric

positions.

D. Checking phonetics

Maxillary incisors should make fricative “f” and “v” sounds at the wet/dry line of

the lower lip . “s” sound is most important

Closest speaking space of 1 – 1.5 mm

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Difficult for edentulous patients that have not worn dentures

Thickness of palate is important

Arch form must be compatible with Neutral Zone

Whistling usually means too little room for the tongue

Lisping indicates too much room

E. Verification of waxing up

- assess proper shaping and contour of polished surface

- checking peripheral extension

- proper labial fullness

F. patient approval

PRESCRIPTION WRITING

When a trial denture is returned to the laboratory for finishing, the following

information should be provided:

1. The colour and nature of the denture-base material to be used.

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Mostafa fayad 29

2. Details of position and depth of anyperipheral seal lines required at the borders

of palatal connectors in an upper denture.

3. Details of any areas which require relief. Information on the site and depth of

relief areas should be given in the written prescription, supplemented by the

mapping out of the required extent of relief areas on the casts. Sites which

frequently require relief include a torus palatinus which is to be covered by an

upper denture base and the gingival areas of standing teeth, where these are to be

covered by connectors.

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Disclosing media

Ideal requirements of disclosing media

� Easy to apply � Not require mixing

� Easy to manipulate intraorally � Work will in a wet environment

� Not need time to set � Shows the degree of interference

� Easy to read � No potential for false positive results

� Easy to remove from the framework � Not carcinogenic

� Not expensive � Provides 3-D representation of framework adaptation

For effective Use of a disclosing media:

i. Dry off the framework.

ii. Apply the disclosing medium,

iii. Gently seat the framework, and remove.

iv. Areas that exhibit metal showing through should be adjusted.

v. The old disclosing medium should be cleaned off.

vi. New medium applied, and the framework tried in again.

Types of disclosing media

There are numerous acceptable disclosing media on the market:

Occlude (Pascal), Accufilm (Parkell), disclosing wax (Kerr/Division

of Sybron), pressure-indicating paste (Mizzy Inc.), Fit Checker (GC

Dental Industrial Corp), and chloroform and rouge.

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Several media can be used for this purpose:

1. Rouge and alcohol: A small amount of alcohol

is placed in a dappen dish and a paint brush is wetted

in chloroform and then brushed against the rouge stick

until it picks up the pigment. The pigment is then

brushed in an even continuous layer over ALL tooth-

contacting portions of the framework. The advantage

of this medium is that it is thin and accurate and is not easily displaced from the

framework. A disadvantage of this technique is that it provides only two-

dimensional assessment of fit. The technique was originally described with

chloroform instead of alcohol. Chloroform dries more quickly, but should not be

used as it has been shown to be potentially carcinogenic. An alternative to alcohol

and rouge is pre-packaged spray type pigments (e.g. Occlude'P'). These can be

applied more quickly, and are non-carcinogenic. However, it is difficult to obtain a

thin layer.

Advantages: i. It is easy to apply ii. Identifies interferences well.

Disadvantages: i. It is difficult to remove ii. It has carcinogenic potential.

2. Disclosing wax: A small amount of wax is

removed from the jar and placed on a mixing pad. A

warmed instrument (#7 wax spatula, PKT waxing

instrument, etc.) is used to pick up and melt a portion

of the wax. The melted wax is applied in an even coat

over ALL tooth-contacting portions of the framework. The wax is allowed to gel

prior to placement in the mouth. The advantage of this medium is that it provides

Try-in of RPD

Mostafa fayad 32

three-dimensional assessment of fit. Areas of burn-through indicate possible areas

of binding, and the thickness of the remaining wax indicates how far the rest of the

framework is from contact with the teeth. A disadvantage of wax is that it can

stick to teeth or be wiped away easily if the framework is seated improperly.

Advantages :

i. It provides three dimensional representation of framework adaptation

ii. It shows the degree of interference.

Disadvantages:

i. It requires a flame source.

ii. It is relatively difficult to remove.

3. Silicone impression materials or indicating medium (e.g. Fit Checker™):

These materials can also be used as three-dimensional

indicators. A disadvantage of elastic materials is that they can

tear or pull off the framework. In addition, time is required for

set of the materials. In this regard the silicone fit-checking

media are more useful since they have shorter working times.

Advantages

i. They are easy to read, ii. Easy to remove from the framework,

iii. Provide a three-dimensional model

Disadvantages

i. They are expensive, ii. Require mixing, and

iii. Need time for the material to set.

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4. Spray type Powders (Occlude): A small amount is sprayed in an even

continuous layer over ALL tooth-contacting portions of the framework. The

advantage of this medium is that it is thin and accurate and is not easily displaced

from the framework. The material can get quite thick if over-sprayed. Teeth,

tissues and the framework must be dry to prevent the pigment bleeding and

making reading of the indicator difficult. A disadvantage of this technique is that it

provides only two-dimensional assessment of fit.

Advantages

i. It marks areas of interference well ii. Is easy to clean off.

Disadvantages

i. It is expensive,

ii. There is potential for applying too thick a layer of material, and

iii. It is difficult to work with in a wet environment

5. Accufilm disclosing film:

AccuFilm is a unique liquid that lets you mark anything

including highly glazed porcelain or interproximal walls

or the inner surfaces of a casting.

Advantages

i. It marks interferences well and

ii. It is not as messy as some of the other media

Disadvantages

i. It is relatively difficult to manipulate intraorally and

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Mostafa fayad 34

ii. There is the potential for false positive results.

6. Air abrasion with 50 m aluminum oxide:

Advantages

i. It identifies areas of interference well and

ii. It is a clean method of disclosing.

Disadvantages

i. It requires access to air-abrading equipment, and

ii. Extended use of air abrasion may affect adaptation of the framework by

abrading the intaglio surface of the framework.

Clinical Adjustment

Binding against one or more of the abutment teeth can cause inadequate seating of

a framework. The area(s) of binding cannot be located without the use of an

indicating medium.

Pressure indicating paste , rouge dissolved in chloroform or

disclosing waxes are used as follows :

a-The disclosing material is placed on all framework surfaces that will

contact the teeth .

b- The framework should be aligned over the abutment teeth and finger

pressure applied in the direction of the planned path of insertion .

c- The framework should be carefully removed from the mouth and then

examined under magnification . The most common points of metal show

through or high spots that interfere with seating occur above the survey line

on the teeth . These usually occur under rests , shoulder of circumferential

Try-in of RPD

Mostafa fayad 35

clasp, under embrasure clasp and in interproximal extensions of lingual

plating .

d- The located areas of interference , should be relieved by grinding .

e- The entire procedure is repeated until the framework is seated .

Use of Indicating Media (technique described for wax but applicable for

all media)

1. Attempt to place framework intraorally. If gross resistance to placement is

felt, remove and coat with indicating medium. If the framework seats, ask the

patient if they feel the framework pulling on any teeth. The latter sensation will be

caused by active engagement of abutment teeth. Inquire as to the overall comfort

of the framework.

2. Remove the framework and coat it with indicating medium. Align the

framework over the abutment teeth and use finger pressure over rest seats along

the path of insertion. DO NOT PLACE PRESSURE OVER GRIDWORK OF

DISTAL EXTENSIONS as this will fulcrum the framework. If gross resistance to

seating is encountered, remove and inspect for areas of burn-through. Have an

instructor inspect the framework. Relieve areas of binding as indicated. Repeat

until seating is achieved. The master cast can be inspected for areas of abrasion

that may indicate areas of gross binding as well.

3. Once the denture can be seated, coat with wax and seat along the path of

insertion again. Use firm even pressure over the rest seats and or indirect retainers.

A mirror handle can be used for seating purposes. Use care in removing the

framework, as removal along the wrong path of insertion will change the markings

in the wax.

Try-in of RPD

Mostafa fayad 36

4. Use caution in adjusting the framework. The clinician must differentiate

between normal and abnormal contacts. Guiding planes normally will exhibit long

vertical areas of contact, but broad areas of complete burn-through may indicate a

binding contact on the guiding plane. Similarly, the retentive tip of direct retainers

will normally exhibit burn-through, but active clasp retention must be eliminated

after the framework is fully seated. Therefore, the first step in adjustment is to

ensure complete seating.

Experience is required to differentiate between normal and excessive

marking of the indicator medium. Adjustments can be made with small round

carbide burs, white stones or rubber abrasive points, depending on the position and

extent of binding. Do not use excessive force or the framework may be bent. Heat

generation is one of the reasons major adjustments are made prior to acrylic

placement (i.e. the heat would melt the acrylic).

5. Completely remove the wax contaminated with metal grindings and place

fresh wax. Repeat this procedure until full seating is achieved. At this point a thin,

even film of wax should be observed under rests and indirect retainers. The wax

will have a greyish hue from the underlying metal. The feel of the denture upon

seating will change from a grating or snapping sensation to one of a gliding

sensation. Normal adjustment of a framework should take no longer than 20

minutes.

6. Check for soft tissue impingements using pressure-indicating paste.

Remove a small portion from the jar, and place it on a mixing pad. Use a stiff-

bristled brush to spread a thin layer over the tissue surfaces of the major

connector, and infrabulge clasps. Leave streaks in the paste. Place intraorally with

moderate pressure and remove. Relieve any areas of marked burn-through. If

streaks are left in the paste, this indicates no contact with the tissues. Adjust or

Try-in of RPD

Mostafa fayad 37

leave accordingly. Maxillary palatal connectors should exhibit broad even contact

with the palate.

7. If the framework cannot be adequately adjusted, it should be remade. In

some cases this decision may be made at the pre-clinical inspection stage. Make

this determination early, so that time will allow for a new impression to be made.

Determine if the casting fits similarly on the cast and in the mouth. If it does not,

the final impression was most likely inaccurate and should be remade. If the

casting does fit similarly, the discrepancy may be due to laboratory errors. In

many cases abrasion of the master cast will require re-making of the final

impression as well. If the pre-clinical inspection leads the dentist to believe a

remake is a possibility, a new custom tray should be made prior to the patient

appointment in anticipation of the need for a new impression.

Delivery of RPD

Mostafa Fayad 1

Delivery of the Removable Partial Denture

I- Extraoral (visual) examination of the denture

II. Intraoral examination:

A. Objectives:

a. Correcting the acrylic denture base.

b. Correcting occlusal discrepancies

c. Adjusting retentive clasps.

B. Checking of:

a) Fit of the Denture Base:

b) Checking up the denture stability:

c) Checking denture retention

d) Soft tissue adaptation.

e) Abutment tooth adaptation.

III- Patient instructions:

� Post insertion review

IV - Maintenance

V - Post placement adjustments

-----------------

Delivery of RPD

Mostafa Fayad 2

I- Extraoral (visual) examination of the denture

To ensure that:

a. The borders should be rounded and not sharp.

b . The impression surface should not have any sharp

edges.

c. The polished surface is smooth and highly polished.

d. Any acrylic ‘pearls’ should also be removed.

e. Elimination of acrylic resin entered the gingival sulcus adjacent to the natural

teeth.

f. The duplicate casts (If present) should be examined for signs of abrasion

produced by forcing rigid portions of the denture into place. Such abraded areas

indicate parts of the denture, which may require adjustment.

II. Intraoral examination:

A. Objectives:





Objective:

1. Identify and elimination "show through" that would prevent the denture from

seating properly.

2. Adjusting the peripheral extensions: No border over extensions, especially in

the posterior palatal area, buccal shelf area, and the frenum areas.

Delivery of RPD

Mostafa Fayad 3

Identify and elimination "show through"

The denture is seated in the mouth.

If acrylic resin has entered the gingival sulcus adjacent to the

natural teeth, the resultant sharp ridge of acrylic should be

eliminated. Care must be taken not to remove excess material,

since the soft tissues are liable to proliferate into the space so

created.

Along the planned path of insertion and withdrawal. If it does not

seat, it is likely to be due to acrylic having entered undercuts

related to the natural teeth or the alveolar ridges.

The area of acrylic involved may be detected by visual inspection

or by the use of pressure indicating past.

If the interference with insertion is related to a flange, blanching of

the mucosa as attempts are made to pass the acrylic flange over the

most prominent part of the alveolar ridge may indicate the area

responsible.

The acrylic resin, which hinders insertion of the denture, is

removed, taking care to preserve the contact between denture and

hard and soft tissues in the non-undercut areas.

Once the denture is seated and is comfortable the fit of all its

components is checked.

Modifying the Peripheral Extension of the Denture Base:

Checking of the correct extension of the periphery should be

performed visually, and digitally.

The cheek is held between the thumb and index fingers, and moved

downward, outward and upward (for lower denture) or moved

upward, outward and downward (for upper denture).

Delivery of RPD

Mostafa Fayad 4

As the buccal tissue adjacent to the denture border during this

movement is observed, any tissue trapped by the denture base is

identified.

To check the lingual extension of the lower distal extension base,

the patient is instructed to thrust tongue forward and into the cheek

of the opposite side of the mouth tested, while the operator placing

the index finger on the occlusal surface.

If there is any overextension it should be corrected by grinding.


1. Maximum intercuspation. Posterior teeth should demonstrate bilateral,

simultaneous contact. Anterior teeth should demonstrate the appropriate

relationship to opposing teeth.

2. Occlusal vertical dimension. The partial denture should demonstrate occlusal

contacts at the correct occlusal vertical dimension. Verify that the RPD is not

increasing the vertical dimension.

3. Articulation. The partial denture components should demonstrate appropriate

occlusal contacts with the opposing dentition or restorations during excursive

mandibular movements.

4. Adjustments.

a. Tooth borne partial dentures. The occlusion and articulation can usually

be evaluated and adjusted intra orally.

b. Tooth-mucosa borne partial dentures. The evaluation and adjustment of

the occlusion and articulation usually require a clinical remount procedure.

The displaceability of the muco-osseous segment allows the extension base

to move tissue-ward during occlusal loading forces. Deflective occlusal

contacts usually cannot be evaluated intraorally.

Delivery of RPD

Mostafa Fayad 5

Materials of locating occlusal interferences:

a. The use of articulating paper.

b. The use of occlusal indicator wax. It may be obtained as a special item that is

supplied with one surface of the wax treated with an adhesive so that it adapts

firmly to the teeth being studied.

c. Thin sheets of regular casting wax, 28or 32-gauge.

Intraoral method:

Articulating paper or occlusal

indicator wax may be used as a mean

of identifying occlusal contacts.

This Intraoral technique can be used

only when the partial denture being corrected are stable in the

mouth (e.g. class III RPD).

Technique:

With the partial denture out of the mouth, a two opposing

natural teeth that are contact in centric occlusion are selected

(as index).

Insert one partial denture into the mouth and get the patient

closing in centric occlusion, and note the selected index teeth,

if they are not contacting, articulating paper is used to locate

interference, which must be relieved until the index teeth

getting in contact.

Then interference in centric relation and protrusive and lateral

excursions must be corrected.

For patients receiving two removable partial dentures, after

adjustment of one partial denture, the same procedures are

followed with the opposing partial denture.

Delivery of RPD

Mostafa Fayad 6

After each denture has been corrected individually, correction

for interference with both dentures seated in the mouth is

performed.

The artificial teeth must be carefully adjusted until the natural

teeth meet in precisely the same way with or without the

denture in place.

Where natural teeth do not indicate the desired jaw

relationships, the artificial teeth must be adjusted to provide

even occlusal contact at the optimal occlusal vertical

dimension in the retruded jaw relationship. Further adjustment

should be undertaken to permit even contact to be maintained

in an intercuspal position slightly anterior to the retruded

contact position. In lateral and protrusive excursion the

denture teeth should normally be adjusted so that they do not

disturb the guidance offered by the remaining natural teeth.

The articulating paper should be applied bilaterally in order to

discourage deviation on closure of the mandible. Heavy tooth

contact is indicated by ‘target’ markings, having a light centre

surrounded by a ring of ink transferred from the paper. Other

marks, simply produced by the paper taking up the space

between the teeth, are generally less distinct and lack the

lighter centre. The paper is relatively thick, and care must be

taken to grind only those marks that indicate actual tooth

contact.

In those cases, where the partial denture saddles are extensive

and the guidance in excursion from the remaining natural teeth

allows the maintenance of bilateral balancing contacts, the

following method of occlusal adjustment should be adopted:

Delivery of RPD

Mostafa Fayad 7

In intercuspal position The upper palatal cusps and lower

buccal cusps (supporting) cusps contacting the fossae of their

opposing teeth maintain the occlusal vertical dimension:

If one of these cusps contacts prematurely when the patient

attempts to reach intercuspal position and is also premature in

lateral excursions, the cusp is reduced in height.

If the cusp contacts prematurely on closure as before, but is

not premature in lateral excursions, the fossa is deepened.

Once even occlusal contact is achieved at the desired static

jaw relationship, further adjustment of the supporting cusps

should be avoided if possible.

• In lateral excursion, if a premature contact occurs between

a buccal upper cusp and a lower buccal cusp on the working

side, only the buccal upper (BU) cusp is adjusted. If contact

occurs between the upper palatal and lingual lower cusps, the

lingual lower (LL) cusp is reduced. This method of adjusting

tooth contact on the working side is thus called the BULL

rule. If premature contacts on the balancing side occur

between supporting cusps, such prematurities should be

eliminated, wherever possible, by adjusting the height of

supporting cusps.

• In protrusive excursion, grinding the distal facing inclines

of upper teeth and mesial facing inclines of lower teeth

eliminates premature contacts.

• As a final step, the occlusal anatomy of the posterior

artificial teeth must be restored to re-establish the functional

efficiency of the occlusion. Sluiceways and supplemental

grooves should be added to occlusal surfaces to create escape

Delivery of RPD

Mostafa Fayad 8

ways for food and to act ascutting blades to increase the

Chewing efficiency.

• The patient is invited to check the appearance of the dentures

so that any further minor modification can be carried out.

After adjustments to the dentures have been completed, all

areas that have been ground are repolished.

Occlusal Correction by Remounting:

In a small percentage of patients when stability is a problem as:

1. When all or nearly all the posterior occlusion is being restored and

locating discrepancies intraorally would be difficult if not impossible

(stability of the prosthesis is questionable).

2. When a complete denture is being constructed simultaneously with a

removable partial denture (so much of the occlusal scheme is being

restored).

An irreversible hydrocolloid impression in a stock tray is made

while the partial denture is seated.

The impression is poured into dental stone after blocking of the

denture undercuts with wax.

By using the face-bow transfer, the maxillary cast is mounted on

the articulator.

Then centric jaw relation records must be made to mount the

mandibular cast.

Articulating paper is used to locate interfering cusps and to help

determine evenness of occlusal contacts.

Delivery of RPD

Mostafa Fayad 9


The denture should be retentive and stable. If free-end saddles rock

about their most distal occlusal rests, this should be corrected by relining

the saddles.

B. Checking of the following

a) Fit of the Denture Base:

Painting the tissue surface of the base evenly with a thin coating of

pressure indicating paste.

The paste over the areas which preventing the partial denture from

seating correctly will be displaced.

This area or areas should be relieved.

b) Checking up the denture stability:

The framework components should be properly related to the

abatement teeth.

Checking of the stability by applying pressure anteriorly and

posteriorly alternatively.

The denture is stable when exhibit no movement under this test.

c) Checking denture retention:

The resistance to vertical dislodging force should be evaluated.

Modification of retentive components may be made to obtain

optimum retention, if needed.

The amount .of retention required is subjective as determined by

the dentist and patient.

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d) Soft tissue adaptation

1. Evaluate the relationship of the components to the underlying soft

tissues.

a. Components which should contact the soft tissues.

i. Denture base.

ii. Maxillary major connector, except where crossing the gingival

margins.

b. Components that require relief from the soft tissues.

1- Mandibular major connectors.

Ii. Minor connectors and proximal plates. iii. Bar clasps.

2. Procedure for tissue surface adjustment.

a. Visually and digitally inspect the finished partial denture. Examine

closely for rough or sharp areas.

b. Apply a pressure indicating paste to the tissue surface.

c. Place the partial denture in the mouth and verify its complete seating.

Remove the partial denture and inspect the tissue surface for regions

of paste displacement.

d. Relieve the pressure areas where the paste has been displaced, using

an appropriate bur. Repeat the process until the areas of unfavorable

pressure have been removed.

e. The denture base areas of tooth-mucosa borne partial dentures should

also be examined while simulating occlusal loading forces under

finger pressure.

f. The tooth-mucosa borne partial denture should demonstrate the

required mucoosseous support. Simulated loading forces applied to

the extension base area usually should not cause the third point of

Delivery of RPD

Mostafa Fayad 11

reference to be elevated from its tooth contact. When movement of

the third point of reference is noted, a relining of the base is usually

indicated.

3. Evaluate the relationship of the components to the adjacent movable soft

tissues. The partial denture should not impinge on movable soft tissues.

a. Denture base.

b. Major connectors.

c. Bar clasps.

4. Procedure for periphery adjustment.

a. Visually inspect the peripheral components of the seated partial denture

in the mouth.

b. Manually activate or instruct the patient to move the lips, tongue, cheeks

and jaw through simulated functional movement.

c. Where the periphery cannot be adequately observed and a question of

peripheral extension exists, a disclosing wax may be utilized.

d. Modify the periphery as indicated by the visual or disclosing wax

evaluation.

e) Abutment tooth adaptation.

The framework components should be properly related to the abutment teeth.

1. The rests should demonstrate a complete and stable seating in their rest seats.

2. The clasps, minor connectors, and proximal plates should demonstrate the

required contact with the abutment teeth.

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III- Patient instructions:

A. MAINTENANCE OF THE PARTIAL DENTURE.

Describe and demonstrate proper maintenance procedures. Written instructions may

supplement the verbal communication.

1. Brushing technique.

a. Use of a proper brush for the RPD.

b. Brush over a sink with water or a towel in it. This minimizes the

potential for damage if the RPD is dropped.

c. Do not squeeze or bend RPD while brushing.

2. Cleaning agents.

a. Hand soap.

b. Denture pastes or creams.

c. Soak cleaners may be used where stain accumulation is not controlled by

brushing alone. Advise the patient to brush the RPD before and after soaking

to maximize plaque and stain removal. Patients should be cautioned not to

soak the RPD in a sodium hypochlorite (bleach) solution.

d. Ultrasonic baths may be useful for patients who have difficulty brushing or

as an adjunct cleaning procedure.

e. Patients should be advised not to use toothpaste or abrasive cleaners.

3. Adjustments. The patient should be advised not to adjust their RPD. If any

difficulties with the fit or retention develop, they should contact their dentist.

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Mostafa Fayad 13

B. CARE OF THE ORAL TISSUES.

1. Tooth brushing technique. Demonstrate the proper technique of sulcular

brushing with a soft toothbrush.

2. Flossing technique. Demonstrate the proper flossing technique.

3. Adjunct devices. Where indicated, other devices may be recommended to

improve plaque control.

a. Floss holders.

b. Tooth picks.

c. Interproximal brushes

d. Mechanized tooth brushes.

4. Brushing of mucosal tissues adjacent to or covered by the RPD with a soft

toothbrush.

5. Plaque reducing rinses. Over-the-counter or prescription solutions may be

beneficial for patients who demonstrate less than optimal plaque control.

6. Fluoride may be useful for patients who demonstrate an increased risk for

caries.

a. Rinses.

b. Gels.

c. Stents. Where patients demonstrate a high caries activity, stents may be

used to carry a fluoride gel to the tooth surfaces.

d. Fluoride on RPD. RPD framework may be used to carry a fluoride gel to

the tooth surfaces.

7. The use of disclosing tablets is excellent way to disclose areas that are

susceptible to plaque accumulation.

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Mostafa Fayad 14

8. Brushing of the denture with denture and clasp brushes

and regular toothpaste or soap should be a routine. Abrasive

agents should be avoided.

9. Removing of the accumulated calculus by scraping with hand instruments, or

by soaking the RPD in a full strength vinegar solution for at least 12 hours. (Using of

cleansing solutions containing chlorine should be completely avoided).

10. The patient should be instructed to remove the prosthesis all over the night.

(Only in rare instances RPD should be worn at night).

C. PLACEMENT AND REMOVAL OF THE PARTIAL DENTURE.

The proper placement and removal of the RPD should be demonstrated. The

patient should be able to accomplish these procedures before leaving the office.

1. Finger pressure should be used to completely seat the RPD.

2. The patient should be cautioned not to seat the RPD with occlusal force (not

"bite" into place).

3. Devices or modifications in the RPD may be required for patients who have

difficulty removing the RPD with their fingers.

a. Devices. Small smooth hooks placed in a toothbrush handle or modified

dental hand instruments may aid the patient in removing the RPD.

b. Modifications. Grooves or slots placed in the denture base or artificial

teeth may improve the patient's ability to engage the partial denture.

4. The patient should be positioned in front of a wall-mounted mirror while the

dentist inserts the prosthesis. After the patient has observed insertion of the removable

partial denture, its removal also should be demonstrated. Before the patient being

dismissed, he should be asked to demonstrate the proper methods of RPD insertion and

removal for the dentist.

Delivery of RPD

Mostafa Fayad 15

5. Weak components must be pointed out; thus clasps should not be used as

fingernail holds during removal.

D. WEARING THE PARTIAL DENTURE.

1. Initial accommodation period. Patients should be given specific instructions to

facilitate adaptation to their new prosthesis.

a. Bulk. It may take several days to several weeks before the patient

accepts the presence of the partial denture, especially for the inexperienced

patient.

b. Speech. If the RPD alters enunciation, the patient should be instructed to

practice reading aloud.

c. Mastication. The patient should initially masticate smaller portions of

softer foods.

d. Saliva. A transient increase in salivary flow may be noticed initially.

e. Explanation of any expected difficulties and limitations of the dentures

should be reinforced at the beginning of treatment.

f. Patient should be advised that muscular control takes time to develop; so

small quantities of non-sticky food should be chewed on both sides of the

mouth initially.

2. Prosthesis should be removed from the mouth several hours daily to facilitate

tissue health. Several exceptions may be noted:

a. RPD that splints hypermobile teeth. Where the patient experiences

difficulty or discomfort in placing RPD at the morning.

b. RPD that maintains the occlusal vertical dimension. When RPD prevents

trauma to remaining natural teeth or mucosa, a splint may be used at night as a

substitute for the RPD.

Delivery of RPD

Mostafa Fayad 16

c. When the RPD is worn at night, the patient should clean the oral tissues

and prosthesis before retiring and again in the morning.

Written instructions:

It is impractical to expect that all patients will remember all of the instructions

provided in the insertion visit, so providing the patient with written instructions will

permit him to review the instructions at home.

Post insertion review:

Post insertion difficulties should be expected by both the dentist and the patient;

however attention to details during the fitting and insertion visit will minimize, but not

eliminate all possible complications. Therefore the patient should return to his dentist

within 24 hours of partial denture insertion. This period is sufficient to allow detection

of initial signs of post insertion complications.

Methods of managing the complications depend upon the type of that complication.

IV - MAINTENANCE

A. PERIODONTAL.

1. Recall intervals.

a. Shorter intervals for patients with active periodontal disease. (Two to

four months).

b. Longer intervals for patients without active periodontal disease. (Six to

twelve months).

c .. Consider shorter interval s initially after RPD delivery.

2. Plaque control instructions at each appointment.

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Mostafa Fayad 17

a. Intraoral hygiene procedures.

b. RPD maintenance procedures.

3. Evaluate periodontal health, especially RPD abutments.

4. Periodontal treatment as required.

B. RESTORATIVE.

1. Tooth examination.

a. Caries.

b. Defective restorations.

2. Soft tissue examination. Examine all oral soft tissues, especially those adjacent

to or supporting the R

3. RPD Examination.

a. Extraoral.

i. Fracture of components. ii. Wear of artificial teeth.

b. Intraoral."

1. Muco-osseous support. Apply pressure to extension base areas of tooth

mucosa borne RPDs. Examine for movement of third point of reference

indicating a need to reline the base.

2. Retention and Stability.

3. Occlusion and articulation.

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Mostafa Fayad 18

• The patient should be given an appointment for review in approximately

seven days’ time.

• The patient should be advised that if significant discomfort is experienced

during the first week the dentures should be removed and should not be worn

again until a few hours before the review appointment. This short period of

wear often aids the location of the cause of the pain.

• The need for regular review of the mouth and denture should be emphasized.

Not only may the natural teeth and periodontal tissues require treatment, but

also it is necessary to prevent damage from the denture, which, in the initial

stages, may be painless. For instance, free-end saddles may need to be relined in

order to eliminate the rocking movement that could loosen abutment teeth and

hasten loss of alveolar bone in the edentulous area. It must also be made clear

that dentures have a limited life and therefore replacements will need to be

constructed as appropriate.

V - POST PLACEMENT ADJUSTMENTS

A. SOFT TISSUE ADAPTATION.

1. Patient's subjective evaluation.

2. Clinical examination of soft tissues.

3. Adjustment.

a. Apply a pressure indicating paste to the involved tissue surface of the

prosthesis.

b. Place the partial denture into the mouth and verify complete seating of

the partial denture.

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Mostafa Fayad 19

c. An indelible pencil may be used to mark the mucosa in the pressure area.

The mark transferred to the prosthesis may be used to confirm the area to be

adjusted.

B. OCCLUSION.

1. Patient's subjective evaluation.

2. Clinical examination.

a. Visual.

b. Articulating paper.

c. Wax.

d. Shim stock.

3. Adjustment.

C. FRAMEWORK.

1. Clasps. The retention may be modified as necessary,

2. Minor connectors and proximal plates. The amount and location

of tooth contact may be modified.

REPAIRS AND ADDITIONS!!

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MAINTENANCE AND REPAIRE OF RPD

Relining

Definition:

Relining is the resurfacing of the tissue surface of a denture base

with new material to make it fit the underlying tissues more accurately,

Indications:

1. Loss of tissue support that cause rotation of the distal extension

base.

NB; in the bounded saddles loss of tissue contact leads to unpleasant

appearance, food traps, and/or patient’s discomfort.

2. Loss of occlusal contact.

Diagnosis:

In order to diagnose if the distal extension partial denture is n need

of relining,

1- A pressure or force is applied on the extreme distal end of the

denture base and watching, if the anterior indirect retainer (rest seat) lift

off its rest preparation as the denture rotates around the fulcrum line; this

indicates that there is a tissue loss occurred, and a relining is required.

2- Another method for diagnosis by using alginate impression as

indicating paste for the area needed for relining, Areas loaded with

alginate.


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RELINING TOOTH-SUPPORTED DENTURE BASES

A- NEED FOR RELINING

Support for that restoration is derived entirely from the abutment

teeth at each end of each edentulous span. This support may be effective

through the use of occlusal rests, boxlike internal rests, internal

attachments, or supporting ledges on abutment restorations.

Tissue changes that occur beneath tooth-supported denture bases

do not affect the support of the denture, and therefore relining or rebasing

is usually done for reasons that include

(1) Unhygienic conditions and the trapping of debris between the

denture and the residual ridge;

(2) An unsightly condition that results from the space that has

developed; or

(3) Patient discomfort associated with lack of tissue contact that

arises from open spaces between the denture base and the tissues.

(4) Anteriorly, loss of support beneath a denture base may lead to

some denture movement, despite occlusal support and direct retainers

located posteriorly.

Rebasing would be the treatment of choice if the artificial teeth are

to be replaced or rearranged, or if the denture base needs to be replaced

for esthetic reasons or because it has become defective.

B- PROCSDURES OF RELINING

Before relining or rebasing is undertaken, the oral tissues must be

returned to an acceptable state of health by conditioning abused and

irritated tissues.

a- Resin base

Methods of relining:


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A) Direct reline, intraoral reline (chair-side):

It is entirely acceptable for most tooth supported partial denture

bases made of an acrylic resin material, except when some tissue support

may be obtained for long spans between abutment teeth. In the latter

situation, a reline impression in tissue-conditioning material or other

suitable elastic impression material may be accomplished.

Advantages:

1. Saving time.

2. The patient does not leave his denture.

3. The direct reline materials are constantly improved with greater

predictability and color stability. The possibility that the original denture

base will become crazed or distorted by the action of the activated

monomer is minimal when the base is made of modern cross-linked

acrylic resin. However, caution should be exercised to be sure that the

older types of acrylic resin bases are compatible when relining with direct

reline acrylic resins.

The vertical dimension of occlusion may be increased and that the

denture may be distorted during laboratory procedure

Disadvantages of intra-oral reline:

It may results in porous and non-hygienic base.

Procedure:

Materials:

1. Special auto polymerizing resins that are intended to be cured in

the mouth.

2. Visible light cured resin as a hard chair side relining.


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3. Resilient relining can be used in case of severe atrophic ridge,

irradiated and diabetic patients, and in presence of hyperplasic

tissues.

Technique

1. Relieve the tissue side of the denture base. Lightly relieve the

borders. This not only provides space for an adequate thickness of new

material but also eliminates the possibility of tissue impingement because

of confinement of the material.

2. Apply lubricant or tape over the polished surfaces from the

relieved border to the occlusal surfaces of the teeth to prevent new resin

from adhering to bases and teeth.

3. Mix the powder and liquid in a suitable container according to

the proportions recommended by the manufacturer.

4. While the material is reaching the desired consistency, have the

patient rinse the mouth with cold water. At the same time, wipe the

fresh surfaces of the dried denture base with a cotton pellet or small brush

saturated with some of the reline acrylic resin monomer. This facilitates

bonding and ensures that the surface is free of any contamination.

5. When the material has first begun to thicken, but while it is still

quite fluid, apply it to the tissue side of the denture base and over the

borders. Immediately place the denture in the mouth in its terminal

position, and have the patient close into occlusion. Be sure no material

flows over the occlusal surfaces or altering the established vertical

dimension of occlusion. Then, with the patient's mouth open, manipulate

the cheeks to turn the excess at the border and establish harmony with

bordering attachments.

If a mandibular partial denture is being relined, have the patient

move the tongue into each cheek and then against the anterior teeth to

establish the functional lingual border.


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It is necessary that the direct retainers be effective to prevent

displacement of the denture while molding of the borders is

accomplished. Otherwise the denture must be held in its terminal position

with finger pressure on the occlusal surfaces while border molding is in

progress.

6. Immediately remove the denture from the mouth and with fine

curved iris scissors, trim away gross excess material and any material that

has flowed onto proximal tooth surfaces and other components of the

denture framework. While doing this, have the patient again rinse the

mouth with cold water. Then replace the denture in its terminal position

to bring the teeth into occlusion. Then repeat the border movements with

the patient' s mouth open. By this time, or soon thereafter, the material

will have become firm enough to maintain its form out of the mouth.

7. Remove the denture, quickly rinse it in water, and dry the relined

surface with compressed air. Apply a generous coat of glycerin with a

brush or cotton pellet to prevent frosting of the surface caused by

evaporation of monomer

8. Allow the material to bench cure in a container of cold water

this will eliminate any patient discomfort and tissue damage that could

have resulted from exothermic heat or prolonged contact of the tissues

with raw monomer.

Although it is preferable that 20 to 30 minutes elapse before

trimming and polishing, it may be done as soon as the material hardens-

Polymerization may be expedited and condensed by placing the denture

in warm water in a pressure pot for 15 minutes at 20 psi.

The masking tape must be removed before trimming is done but

should be replaced over the teeth and polished surfaces below the

junction of the new and old materials to protect those surfaces during

final polishing


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Metal base

A metal base is not used in a tooth supported area in which early

tissue changes are anticipated. A metal base should not be used after

recent extractions or other surgery or for a long span when relining to

provide secondary tissue support is anticipated.

Commonly, tooth supported partial denture bases are made of

metal as part of the cast framework. These generally cannot be

satisfactorily relined, although they may sometimes be altered by

1- Drastic grinding to provide mechanical retention for the attach-

ment of an entirely new acrylic resin base.

2- Using some of the new acrylic resin bonding agents, such as

Four-meta, Silicoating, or Rocatec.

B) Laboratory relining:

Procedure:

• Removing a uniform amount of denture base resin from the tissue

side of the base as well as all undercuts.

• Sufficient space is allowed beneath the denture base to permit the

excess material to flow to the borders, where it is either turned by

the bordering tissues or, as in the palate, allowed to escape through

venting holes without unduly displacing the underlying tissues.

• Impression material which used that will record the anatomic form

of the oral tissues.

• A closed mouth impression technique is performed (because the

tooth-supported denture base cannot be depressed beyond its

terminal position with the occlusal rests seated and the teeth in

occlusion, and because it cannot rotate about fulcrum) by asking


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the patient to close in centric occlusion until complete setting of the

impression material.

. RELINING DISTAL EXTENTION DENTURE BASES

A- NEED FOR RELINING

The need for relining a distal extension base is determined by

evaluating the stability and occlusion at reasonable intervals after initial

placement of the denture.

There arc two indications of the need for relining a distal

extension partial denture base.

1- A loss of occlusal contact between opposing dentures or between

the denture and opposing natural dentition:

This is determined by having the patient close on two strips of 28

gauge soft green or blue (casting) wax or Mylar matrix strips.

If occlusal contact between artificial dentition is weak or lacking while

the remaining natural teeth in opposition are making firm contact, the

distal extension denture needs to have occlusion reestablished on the

present base by

• Altering the occlusion

• Reestablishing the original position of the framework and base

• Sometimes both.

In most instances, reestablishing the original relationship of the

denture is necessary, and the occlusion will automatically be

reestablished.

2- A loss of tissue support that causes rotation and settling of the distal

extension base or bases

It is obvious when alternate finger pressure is applied on either side of

the fulcrum line.


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Although checking for occlusal contact alone may be misleading, such

rotation is positive proof that relining is necessary.

If occlusal inadequacy is detected without any evidence of denture

rotation toward the residual ridge, all that needs to be done is to

reestablish occlusal contact by

• Rearranging the teeth or

• Adding to the occlusal surfaces with resin or cast gold onlays.

If denture rotation can be demonstrated, but occlusal contact is

adequate, it is usually a result of migration or extrusion of opposing teeth

or shift in position of an opposing maxillary denture, thus maintaining

occlusal contact at the expense of the stability and tissue support of that

denture.

This is often the situation when a partial denture is opposed by a

maxillary complete denture. It is not unusual for a patient to complain of

looseness of the maxillary complete denture and request relining of that

denture when actually it is the partial denture that needs relining. Relining

and thus repositioning the partial denture results in repositioning of the

maxillary complete denture with a return of stability and retention in that

denture.

Therefore evidence of rotation of a distal extension partial denture

about the fulcrum line must be the deciding factor as to whether relining

needs to be done.

B- PROCSDURES OF RELINING

Laboratory relining

• As in bounded saddle relining except some differences


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• Open mouth impression technique is used, and the dentist must

hold the framework against the abutment teeth until the impression

material sets.

• Dentist’s three fingers placed on the two principal occlusal rests

and at a third point between, preferably at an indirect retainer

farthest from the axis of rotation.

• The completed partial denture reline impression is presented to the

laboratory for processing.

Re-establishing occlusion on a relined partial denture:

A loss of occlusal contact of a distal extension partial denture and

opposing teeth may be automatically established when performing a

relining. But re-establishing of the occlusion may be indicated due to:

1. Migration or extrusion of opposing natural teeth.

2. Shifting in position of an opposing complete denture and occlusal

disharmony.

3. Wearing of the occlusal surface over a period of time. This tooth is

restored by chemical-curing resin.

If the artificial teeth to be corrected arc acrylic resin, the occlusion

can be reestablished either by

1- Adding auto polymerizing or light-activated acrylic resin to

occlusal surfaces or by fabricating gold occlusal surfaces, which can be

attached to the original replaced teeth.

2- The original teeth may also be removed from the denture base

and replaced by new teeth arranged to harmonize with the opposing

occlusal surfaces.


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Rebasing

Definition:

Rebasing is the replacement of the entire denture base with new

material while preserving the occlusal relationship. The artificial teeth

may need to be replaced in a rebase procedure.

Indications:

• When the denture borders do not extend to cover all the supporting

tissue.

• When the denture is fractured in the denture base.

• When the denture is stained or discolored.

Technique:

First Technique

The tissue side denture base is relieved as in relining.

Modeling plastic is then added in small increments for border

molding.

Covering of the base with the suitable impression material for

making the final impression.

The rebase impression is flasked directly without pouring a cast.

After opening the flask the traces of the impression material and

wax are removed and the old resin is removed.

Packing of acrylic resin, curing, deflasking, finishing and polishing

is carried out.


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Second Technique

1- The tissue surface of the denture base is relieved and trimmed to provide

space for re adaptation of borders with modelling plastic.

2- Border moulding is done.

3- After border moulding, a final impression is made using the framework.

4- A cast is poured against the rebase impression.

5- The modelling plastic and the final impression material is scrapped away

from the denture base.

6- The denture base extending over the area to be rebased should be trimmed

leaving just about 2-3 mm adjacent to the base of the teeth.

7- When the anterior teeth are involved, the junction of the new resin and the

existing denture base should be kept in an area that is not visible. A faint line

will always exist at this junction and it may be visible when the patient smiles.

8- This observable line is reduced when the borders of the resin are at 90º to the

external surface. If aesthetics is not important, the junction should be rounded

to reduce the stress concentration and to increase the strength. 9- Now the

framework with the trimmed denture base will not contact the edentulous ridge.

10 - The contour of the denture base is re-established by adding small amounts

of base plate wax. This gives a finished contour to the processed rebase and

reduces the finishing time.

11- Flasking is done.

12- A boil-out procedure is done to soften the wax and modelling plastic.

13- The tissue surface of the denture resin is trimmed to provide space for the

new resin. This trimmirtg should stop short of the denture teeth.

14- Acrylization and processing is done as usual.

15- The denture is de-flasked using a lab knife or pneumatic blade and a shell

blaster.

16- Finishing and polishing is done.


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REPAIRS AND ADDITIONS TO RPD

Accidents or careless handling of the denture by the patient might result

in a need for denture repair. The following are some of the repair procedures

which might be necessary in these cases.

A] Broken clasp arms

The most common type of repair is the replacement of a broken

retentive clasp arm,

causes:

- 1- Repeated flexure into and out of a deep undercut. This can be

avoided by placing retentive tips of clasp arms in undercuts where

an acceptable minimum retention is gained as determined by an

accurate survey of the master cast.

- 2- Structural failure of the clasp arm: This occurs when the clasp

arm is not uniformly tapered. it can be prevented by providing the

appropriate taper to flexible retentive clasp arms and uniform bulk

to all rigid non retentive clasp arms.

- 3- Careless handling by the patient.

- It can be prevented by cautioning the patient against removal of P.d.

by sliding the clasp arm away from the tooth with fingernails

- 4- Accidental dropping of the denture.

- 5- Re crystallization of wrought wire clasp resulted from

overheating so it is better to solder the wrought wire clasp to the

frame work electrically.

A broken retentive clasp arm, regardless of its type, may be

replaced with a wrought-wire retentive arm embedded in the resin

base or attached to a metal base by electric soldering.

Repair is done in the following manner

- The remaining part of the original clasp arm is first cut off flush

with the point of origin of the clasp.


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- A hole is then drilled just below the adjacent denture tooth. From

this hole a groove is cut in the resin base long enough to

accommodate sufficient length of the wrought wire.

-A piece of 18-gauge wrought wire is shaped and adapted to fit the

groove.

- A right angle bend is made at the end of the wire.

- A straight portion is left emerging from the resin base at the point of

origin of the new clasp arm.

- The projecting wire is then cut off to the required length and

adapted to the abutment tooth on the master cast to serve as a new

retentive clasp arm. The wire is fixed to the base with chemically

activated resin.

Because of the flexibility of the wrought wire, it cannot be used to

replace a rigid stabilizing clasp arm. In such case, it is better to entirely

cast a new clasp assembly and attach it to the framework by soldering. The

resin base must to be protected with wet asbestos during soldering. Gold

solder is used for soldering both gold and chrome-cobalt alloys. A colour-

matching white gold solder is preferred for the chromium-cobalt alloys.

B] Broken Occlusal Rests

Causes

Breakage of an occlusal rest almost always occurs at the point

where it crosses the marginal ridge due to weakness at this point.

Breakage may be due to improperly prepared occlusal rest seat or

reduction of occlusal rest to adjust occlusal interference from the

opposing dentition. it rarely occurs due to structural defect of alloy used.

Treatment:

Repairing a broken occlusal rest may first require alteration of the

occlusal rest seat preparation and/or relieving an opposing occlusal

interference.

Broken occlusal rests may be repaired by soldering a new rest in

the following manner:

-The partial denture is adequately seated in the mouth.


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-An alginate impression is made. After setting, the impression is removed with

the denture inside it.

-Dental stone is poured into the impression to form a cast.

-The denture is removed from the cast.

-Platinum foil is adapted to the rest seat and over the reduced marginal ridge.

-The partial denture is returned to the cast and a gold solder is used to fuse the

platinum foil to the minor connector.

N.B.: In case of broken occlusal rest it is always best to replace the

whole clasp assembly.

C] Distortion of Major or Minor Connectors

Causes:

Although major and minor connectors are constructed with

sufficient bulk, breakage may result due to abuse by the patient or

excessive adjustment and grinding during denture insertion in order to

avoid tissue impingement.

Treatment:

The distorted connector usually looses rigidity. It can no longer

function effectively. Hence it is preferable to make a new restoration.

D] Loss of an additional natural toothIf a natural tooth is to be extracted the procedure of adding such

tooth is simple when the partial denture base is made of acrylic resin.

However when the denture base is made of metal the procedure

will be more complex.

If the lost tooth is not abutment ,it necessitates either casting a

new component and soldering it to the denture base or creating retentive

elements as perforation or soldered wire is created for the attachment of

an acrylic resin extension to place the missed tooth.

If the abutment tooth which supporting the clasp arm is lost. The

clasp arm is cut off the framework. The next adjacent tooth is modified

by preparing an occlusal; rest seat and guiding planes. A new clasp

assembly is cast for the new abutment and soldered to the framework.


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Denture Base Repair

• If the broken segments are available and can be accurately re-positioned,

the section are held together and luted with sticky wax along the fracture

line.

• Dental stone is poured against the tissue side of the denture base. When

the stone sets, the denture is removed and the sticky wax is cleaned.

• The denture is separated along the fracture line.

• The fractured margins are dovetailed.

• The separating medium is applied over the cast.

• The pieces of denture are assembled and held in position.

• Auto-polymerizing resin is added along the fracture line by sprinkle-on

method.

• It is placed in a heated pressure pot to complete the curing.

If the broken segments are lost or cannot be re-positioned, they are

discarded. In such cases, the modelling plastic is added and contoured in the

defective area. The impression is made without displacing soft tissues. The

repair is done as a rebase procedure.

Replacement of Denture Teeth

• An accurate opposing cast and a jaw relation record is necessary.

• The tooth of the same mould and shade is selected and set in the space

produced by the missing tooth.

• Access should be gained by opening through the lingual surface. The

labial or buccal denture base should be preserved.

• The ridge-lap area should be relieved to allow at least 2 mm of repair

resin to bind the tooth to the base.

• The tooth is luted to the framework with sticky wax.

• Auto-polymerizing resin is added with a fine brush If multiple teeth are

to be replaced, a mounting cast is poured against the tissue-surface of

the RPD.


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• This cast is articulated with the opposing cast.

• Teeth to be replaced are positioned and finally the denture base is

relieved.

• Gingival contours are waxed and the denture is flasked, packed and

processed.

RECONSTRUCTION OF RPD

The partial denture is reconstructed by removing the resin and denture

teeth from the framework The existing framework can be re-used if it has a

clinically acceptable fit.

Indications

When the denture base is damaged beyond repair.

When the fit of the denture is not satisfactory .

Loss of aesthetics, function, etc.

Procedure

• The resin is removed from the tissue side while holding the framework in a cotton

forceps or haemostat (artery forceps).

• The framework is sandblasted to remove the residue and re-polished.

• The framework is seated in the mouth and an alginate impression is made over it.

• The framework should come out along with the impression. If it remains in the

mouth (separated from alginate), the retentive clasp arms should be adjusted to

reduce retention and the impression is remade.

• In order to accurately record the tissues in the retentive meshwork area, the

impression material must be forced into the mesh by applying finger pressure.

• Cast is poured with dental stone.

• The framework is carefully separated from the stone cast by lifting it along the

inferior border of the major connector.

• Force should not be applied as it can distort the retentive clasp arm.

• dual impression can be made (if needed)

• Then the RPD is articulated and fabricated as usual.


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Restorations under Existing RPDs

The two or three surface alloy restoration that fractures at the isthmus is

difficult to place under an existing partial and maintain positive contact with

the rest. In these instances, the tooth usually requires re preparation of the box

form to widen or deepen or some combination of the two, to ensure that an

adequate bulk or amalgam is present.

These restorations may also be made in composite. Since the composite

filling can be layered into the cavity; the final contact with the rest or other

component of the partial cam be made, after the removal of the rubber dam and

matrix. Light activation or the composite is usually possible in a two stage

process where the material is first activated with the partial in place. This will

usually set the material sufficiently to allow removal of the partial denture

without distorting the restoration. Additional light curing with the partial out of

the mouth completes the restoration .

For those situations in which a complete composite restoration is not

indicated, a combination of alloy and composite can be used to support an

occlusal rest. After the additional mouth preparation, the alloy is packed in the

usual manner and then a dovetailed box in the area of the rest is formed.

Chemically curing composite is placed in the box and the partial is fully seated

in the mouth until completely cured. This combination of restorative materials

will allow the creation of a positive rest.

Crowns under Existing RPDs

The impression is made by removing the retraction cord and injecting the

low viscosity impression material of choice completely around the margin of

the preparation. A small amount of Impression material can be injected onto

the remainder of the prepared tooth. An excess of material might restrict the

full seating of the partial.

The impression must he made with the partial denture in its proper

relationship tot he supporting abutment teeth. This requires a sectional


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impression with the clinician holding the partial in position while the assistant

seats the sectional tray.

The partial denture is seated in the mouth, and additional material is

syringed onto the prepared tooth and into the space between the tooth and the

partial. Once the space is filled with the low-viscosity material, the sectional

tray can be seated. This tray must extend on either side of the repair area so that

there will be sufficient impression material to lock the partial into the

impression.

The master cast is then poured. It is critical that the stone is poured

directly against all parts of the partial denture with the exception of clasp arms,

precision attachments, and undercut s in the resin areas.

The technician marginates the die and wax the crown to fit the

framework. This is usually done by first waxing a thin coping to the margins.

The casting is then seated on the cast. and molten wax is flowed in the space

between the coping and the casting using a glass eye dropper that have been

warmed in the flame to prevent the wax from cooling too quickly.

The most difficult part of the repair is waxing the area where the clasp,

should there be one, will lie. not only will the wax need to flow against the

internal area of the clasp arm , but a retentive contour will have to be built into

the wax-up.

If the crown is to have a porcelain veneer

The task becomes even more difficult; since the porcelain must he

overbuilt originally. As a result, the frame can’t be removed from the crown

without fracturing off the dry porcelain. The solution to these problems is to

sacrifice the retentive clasp arm and make the facial contour to ideal

dimensions. Alter the porcelain veneering is complete. With appropriate

undercut in place, a repair clasp is added to the partial

Documents

40047675 Partial Denture FAYAD