SDS – 321 McCracken’s Removable Partial Prosthodontics. Chapter 10 & 19

SDS – 321SDS – 321

McCracken’s Removable Partial Prosthodontics. Chapter 10 & 19

‘‘Our objective should be the perpetual preservation of what remains Our objective should be the perpetual preservation of what remains rather than the meticulous restoration of what is missing’.rather than the meticulous restoration of what is missing’.

Preserving what remainsPreserving what remains

Designing RPDDesigning RPD

‘‘On the On the basis of information gathered from the clinical examination of information gathered from the clinical examination and the analysis of the study casts, … and the analysis of the study casts, …

Designing RPDDesigning RPD

… the components of an RPD framework are so selected that the resulting design is esthetically pleasant and is least harmful to the remaining tissues’.

As a result of the examination and diagnosis, the design of an RPD must originate on the diagnostic cast so that all the mouth preparation are carried out with a specific design in mind. This could be influenced by the following factors,

Factors influencing the RPD Design

1. One arch is to be restored or both

a. Orientation of the occlusal plane.

b. Space available for restoring missing teeth.


c. Occlusal relationship of the remaining teeth.

d. Arch integrity and tooth morphology.

Overlay restOverlay rest

Over-denture

Long rest

Over-denture

Vertical spaceVertical space

Retentive area


2. Remaining abutment support / periodontal health / need for splinting or future additions.


3. Tooth or Tooth & tissue supported prosthesis.


4. Need for abutment modification – clasp design.


5. Type of major connector indicated – e.g., a torus.

6. Materials to be used for framework, bases, & teeth.


7. Patient’s past experience, i.e., patient’s inability to accept lingual bar or palatal bar major connector.


8. Replacing a single tooth or anterior teeth – RPD or FPD.

Difference Difference between between two two types of RPDstypes of RPDs

Tooth Supported Tooth & tissue Supported class III & IV class I & II

1. Support Abutment teeth Combination of abutment teeth and soft tissues.

Difference Difference between between twotwo types of RPDs types of RPDs

Tooth Supported Tooth & tissue Supported class III & IV class I & II

2. Impression Anatomic form Anatomic and functional forms (altered cast technique).


Tooth Supported Tooth & tissue Supported

class III & IV class I & II

3. Indirect No denture rotation Needed to resist any denture base

Retention hence, not needed lifting away from the tissues.

Difference Difference between between two two types of RPDstypes of RPDs



4. Base type Metal base – no future Acrylic base – future reline is reline is required. anticipated due to bone loss.




5. Clasp design Circlet/Embrasure/Ring Stress release design – RPI / ‘No stress release’ RPC, - wrought wire clasp.

Components of an RPD FrameworkComponents of an RPD Framework(Review)(Review)

Circumferential ClaspsCircumferential Clasps

Circlet / conventional / C claspCirclet / conventional / C clasp Embrasure claspEmbrasure clasp Reverse action / Hairpin claspReverse action / Hairpin clasp Ring claspRing clasp Multiple claspMultiple clasp Half & half claspHalf & half clasp Combination claspCombination clasp


Infra Bulge or Bar type ClaspsInfra Bulge or Bar type Clasps

1. T – bar1. T – bar

2. Y – bar2. Y – bar

3. L – bar3. L – bar

4. I – bar4. I – bar

systemsystem

Factors Factors for thefor the Choice Choice of aof a Direct Retainer Direct Retainer

1. The type of an RPD:1. The type of an RPD:

a. tooth supported:- any type of clasp can be used.a. tooth supported:- any type of clasp can be used.

b. tooth-tissue supported:- stress releasing (I bar) is used.b. tooth-tissue supported:- stress releasing (I bar) is used.

2. The location of the undercut on the abutment tooth in relation to 2. The location of the undercut on the abutment tooth in relation to the saddle area (circlet / ring / hairpin).the saddle area (circlet / ring / hairpin).

3. The periodontal health of abutment (cast / wrought clasp).3. The periodontal health of abutment (cast / wrought clasp).

4. The size of an abutment tooth (cast / wrought clasp).4. The size of an abutment tooth (cast / wrought clasp).

5. The presence of a tissue undercut – combination clasp.5. The presence of a tissue undercut – combination clasp.

6. Esthetic considerations – I bar clasp in the distal undercut or 6. Esthetic considerations – I bar clasp in the distal undercut or circlet clasp in the mesial undercut on anterior abutment.circlet clasp in the mesial undercut on anterior abutment.


Maxillary Major ConnectorsMaxillary Major Connectors

1. Single Palatal Bar

2. Single Palatal Strap

3. U – shaped Palatal Connector

4. Anterior & Posterior Palatal Straps / Bars

5. Palatal Plate

Factors Factors for thefor the Choice Choice of aof a Maxillary MaxillaryMajor ConnectorMajor Connector

The rigidity and location in relation to the gingivae and the The rigidity and location in relation to the gingivae and the vibrating line posteriorly is critical.vibrating line posteriorly is critical.

1. Its design depends on the number and location of the saddle 1. Its design depends on the number and location of the saddle areas and emerges finally after connecting them together, e.g., areas and emerges finally after connecting them together, e.g., modified palatal strap or anterior – posterior palatal straps major modified palatal strap or anterior – posterior palatal straps major connectors.connectors.

2. Single palatal bar and U – shaped connectors are seldom used. 2. Single palatal bar and U – shaped connectors are seldom used. The later design may be used in the presence of a large palatal The later design may be used in the presence of a large palatal torus.torus.

Components Components of anof an RPD RPD FrameworkFramework(Review)(Review)

Mandibular Major ConnectorsMandibular Major Connectors

1. Lingual Bar1. Lingual Bar

2. Lingual Plate2. Lingual Plate

2b.Interrupted Lingual Plate2b.Interrupted Lingual Plate

3. Double Lingual Bar3. Double Lingual Bar

4. Labial Bar4. Labial Bar

Factors Factors for thefor the Choice Choice of aof a Mandibular MandibularMajor ConnectorMajor Connector

It must be rigid and properly located in relation to the It must be rigid and properly located in relation to the gingivae and movable oral tissues.gingivae and movable oral tissues.

1. Depth of anterior lingual sulcus (8 mm or less).1. Depth of anterior lingual sulcus (8 mm or less).

2. Periodontal health of the anterior teeth (bar or plate).2. Periodontal health of the anterior teeth (bar or plate).

3. Class I edentulous arch may necessitate lingual plate3. Class I edentulous arch may necessitate lingual plate

for additional resistance to horizontal rotation.for additional resistance to horizontal rotation.

4. Anterior spacing (interrupted plate or Continuous bar).4. Anterior spacing (interrupted plate or Continuous bar).


Posterior Rest Seats

1. Occlusal rest.

2. Long occlusal rest.

3. Embrasure rest.

4. Onlay/overlay rest.


Anterior rest seats

1. Cingulum / inverted V rest.

2. Ledge rest.

3. Ball rest.

4. Incisal rest.

Selection of a Denture BaseSelection of a Denture Base

Types:Types:

1. Metal base (class III & IV).1. Metal base (class III & IV).

2. Acrylic resin base (class I & II)2. Acrylic resin base (class I & II)

The single important factor in the design of a saddle area The single important factor in the design of a saddle area and for the choice of a denture base material is the anticipated and for the choice of a denture base material is the anticipated need need for future relinefor future reline.. As class I & II RPDs may require future reline of the As class I & II RPDs may require future reline of the saddle areas saddle areas (to compensate for the bone loss due to the rotational (to compensate for the bone loss due to the rotational movement occurring under occlusal load),movement occurring under occlusal load), an acrylic resin denture an acrylic resin denture base in indicated.base in indicated.

Step by Step Procedure to Design

As a start, guiding planes should be marked on the proximal surfaces of the abutment teeth adjacent to the saddle areas, according to the selected path of insertion.

Step 1: Plan Tooth SupportFor bounded saddles, place the

prepared rest seats on the occlusal,

cingulum, or incisal surfaces of the

abutment teeth, near the edentulous

areas.

For distal extension saddle areas,

the rest seats are placed on the mesial

side of the abutment, i.e., away from the saddle areas.


Step 2: Design & Locate the Connectors.The final shape and form of the palatal major connector

develops after connecting the tooth supported and tooth-tissue supported units of the arch together.

The choice of a mandibular major

connector, however, depends on the

depth of the anterior lingual sulcus.

The minor connectors will then be

placed to connect other parts of the

RPD (rests, retainers, artificial

teeth, etc..) to the major connector.


Step 3: Plan Retention:

Ideally, a direct retainer should be placed on either side of the saddle area. Its location on the tooth is dependent on the presence of a suitable undercut – 0.01”. A bracing or

reciprocal arm should also be included.

For a distal extension saddle, an I-bar

retainer is preferred, as a part of RPI.

This design should also include an

indirect retainer to minimize rotation

of the denture base away from the

tissues.


Step 4: Connect retainers to the support units:

Supra-bulge clasp is connected to the occlusal rest or the guiding plate. Infra bulge clasp is connected to the mesh work minor connector in the denture base.

Step 5: Outline and join the saddle areas

(denture base) to these selected or

drawn components of the RPD

framework.

Designing Mandibular Framework

Check List Locate Guide planes – POI. Plan Support. Select the major connector. Place the minor connectors for

occlusal rests, clasps, artificial teeth.

Plan retention (direct & Indirect). Connect the retainers to the

framework components. Outline and connect the saddle

areas to the major connector.

Documents

SDS – 321 McCracken’s Removable Partial Prosthodontics. Chapter 10 & 19