Choice of Retainer

7/28/2019 Choice of Retainer

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CHOICE OF RETAINER IN FIXED PARTIAL

DENTURES

Introduction

In fixed prosthodontics it is the retainer which provide retention and

resistance against horizontal oblique and vertical dislodging forces.

The selection of retainer plays on important role in success of fix partial

denture and so it becomes very important to select suitable retainer for the

existing situation by keeping physiologic, mechanical hygienic and esthetic

factors in mind.

According to Glossary of prosthodontics (1994) fixed partial denture

retainer is defined as the part of fixed partial denture that units the abutments to

the remainder of the restoration.

Requirements of retainer(Physiologic, mechanical hygienic and esthetics)

1. It should with stand the masticatory forces (Mechanical).

2. It should restore the anatomy of the tooth (Physiologic).

3. It should not be harmful to the pulp (Physiologic).

4. It should improve the aesthetics (aesthetics).

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Uses of retainer

1. To improve the masticatory efficiency.

2. To establish the contact point to prevent food lodgement.

3. To be useful in correcting malalignment.

4. To close diastema in anterior teeth.

5. To prevent drifting of teeth.

Selection of retainer: It is dictated by following factors.1. Age

2. D.M.F. Rate

3. Edentulous space

4. Periodontal support

5. Arch position of tooth

6. Skeletal relationship

7. Interocclusal conditions such as crown length

8. Oral hygiene status

9. Vitality of abutments

Classification of retainers

I. Based on type of preparation

A. Intra coronal retainers.

B. Extra coronal retainers.

C. Radicular retainers.

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II. Based on type of materials used in the construction of

retainers.

D. Metals

e.g. Nickel chrome, Titanium, Cobalt chrome.

A. Porcelain

B. Acrylic resins

C. Composite resins

E. Combination of any metal with porcelain or acrylic resin

or composite resin.

I) A. Intra coronal retainer

Modified class II inlay and MOD

onlays.

Pinledge retainers.

I) B.Extra coronal retainers

Full veneer crown.

Partial veneer crowns.

I) C.Radicular retainers

Dowel crowns

Richmond crowns

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Extra coronal retainers

Partial veneer crown

A partial veneer crown is a restoration covering two or more surfaces at

tooth.

The surfaces usually covered are the lingual, proximal, occlusal or

incisal except buccal or labial.

Types of partial veneer crowns

a) For posterior teeth

1. Three quarter crown / Posterior 4/3 crown.

2. Modified three quarter crown / mesial half, mesial hood / Kennedy

carmichal crown.

3. Seven eighths crown

b) For anterior teeth

1. Three quarter crown

2. crown with pinledges

The crown covers 3/4 th of the gingival circumferences of tooth

leaving one surface intact the facial surface remains untouched.

To ensure tooth structure however lingual surface of mandibular

posterior tooth is occasionally preserved and is reffered as a reverse three

quarter crown.

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Reverse three quarter crowns are indicated on mandibular molars

with severe lingual inclination.

The seven-eighths partial crown covers seven eighths of gingival

circumference of tooth.

It is generally indicated for maxillary molars and premolars that

are sound mesially but have extensive carious involvement or a previous

restoration on the distal surfaces.

The seven eighths crown preparation extends the distal finish line

to the mid facial surface avoiding an unnecessary display of metal on the

mesial surface.

The mesial half crown is actually a three quarter crown rotated so

degrees preserving the distal surface of the tooth while veneering theremaining surface.

It is indicated for distally tilted molar abutment.

Indications:

1. Coronal tooth structure is intact or minimally restored teeth.

2. Sturdy clinical crown of average length or longer.

3. Teeth with normal anatomic crown form i.e. without excessive cervical

constriction.

4. Anterior teeth with adequate labiolingual thickness.

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5. Abutment teeth are in reasonable axial ligament.

6. Short edentulous span.

7. There are average or below average occlusal forces.

Contra indications:

1. High caries index

2. Teeth with extensive core restorations before a partial veneer restoration

can be placed the unveneered tooth surface must be sound.

3. Deep cervical abrasion

If the unveneered surface has deep cervical abrasion it is difficult to

establish a finish line.

4. Short teeth

Teeth with short clinical crowns are not suitable for partial veneer crown.

The difficulty is in establishing adequate retention and resistance form.

5. Bell shape or Bulbous teeth

Teeth severely constricted at the cervical area require more axial reduction

to provide adequate groove length. The additional depth required to place

proximal grooves or boxes can jeopardize pulpal health.

6. Thin teeth

It is difficult to prepare groove of suitable length in teeth with insufficient

buccolingual width without undermining the facial enamel.

7. Poor alignment with path of placement of F.P.D.

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Advantages:

Partial veneer crowns have several advantages over complete crowns.

1. Less tooth reduction conservation of tooth structure.

2. Having fever margins in the intra cervicular space increases

biocompatibility with supportive tissue less gingival involvement than

with complete cost crowns.

3. Easy margin accessibility for finishing and cleaning is improved.

4. Complete seating of casting is more easily verified with at least one

margin visible.

5. Complete seating of casting during cementation is enhanced by

diminished hydraulic pressure.

6. Electric pulp testing can be conveniently accomplished on the intact

enamel surface.

Disadvantages:

Partial veneer crowns have the following disadvantages.

1. It is less retentive than complete cast crown.

2. Limited adjustment of path of withdrawal / placement.

3. There is limited display of metal with partial veneer crowns.

4. The partial veneer crown preparation is limited to fairly intact teeth with

normally shaped average length clinical crown.

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Full veneer crowns

They are of three types

1. Complete metal veneer crowns

2. Metal ceramic crowns

3. All ceramic crowns

General indications:

1. It should be used on teeth which demands maximum retention.

2. It should be used when abutment tooth is small or when the edentulous

span is long.

3. Porclian Jacket crown or porcelain fused to metal crowns are used

where high esthetics is required.

4. When all axial surfaces of the teeth have been affected by

decalcification or caries and are restored, a full veneer crown should be

used.

Contra indication:

Poor oral hygiene

Complete metal veneer crown

Indications:

1. Any posterior tooth in nonesthetic zone with existing restoration unable

to withstand normal occlusal forces.

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2. An fixed partial denture retainer requiring maximum retention.

3. Short clinical crowns ditating complete coverage for artificial crown.

4. Presence of extensive caries.

5. Fracture of tooth.

6. Long edentulous span.

7. Occlusal forces greater than average.

8. Abutment tooth alignment that requires full coverage preparation to

achieve adequate retention.

Advantages:

1. Strength imparted to tooth.

2. Contact areas can be conveniently developed.

3. Protects the coronal integrity of a natural tooth compromised by

extensive caries involvement or restoration.

4. Provides maximum retention, favourable contours and guide planes for

retainer.

Disadvantages:

1. Unaesthetic

2. Restricted to posterior teeth

3. Belated supportive tissue response

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4. Post cementation caries is difficult to detect

5. Vitality test are unreliable

Porcelain fused to metal crown

Indications:

1. Single and multiple restorations for both anterior and posterior teeth.

2. Mandibular anterior teeth where full shoulder preparations are

prohibitive.

3. Peg shaped laterals or teeth with similar morphologic deviations.

4. Patients with reduced interocclusal clearance.

5. Extensive tooth destruction as a result of caries trauma or existing

previous restorations that precludes the use of a more conservative

restoration.

6. Need for superior retention and strength.

7. An endodontically treated tooth in conjunction with a suitable

supporting structure.

8. Need to recontour axial surfaces or correct minor malocclusions.

9. Esthetics

10. If porcelain jacket crown is contraindicated.

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Contraindications:

1. Large pulp chamber because of high risk of pulp exposure.

2. Intact facial wall

3. When more conservative retainer is technically feasible.

Advantages:

1. Superior esthetics as compared to complete cast crowns.

2. Strength imported to tooth is superior as compared to partial veneer.

Disadvantages:

1. Removal of substantial tooth structure.

2. Subject to fracture because porcelain is brittle.

3. Difficult to obtain accurate occlusion in glazed porcelain.

4. Inferior esthetics compared to porcelain jacket crown.

5. Expensive.

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All ceramic crowns

Indications:

1. High esthetic requirement

2. Considerable proximal caries

3. Incisal edge reasonably intact

4. Endodontically treated teeth with post and cores

5. Favourable distribution of occlusal load

Contraindications:

1. When superior strength is warranted because of absence of reinforcing

metal substructure.

2. Significant caries with insufficient coronal tooth structure for support.

3. Thin teeth faciolingually.

4. Unfavourable distribution of occlusal load.

Advantages:

1. Superior esthetics.

2. Good tissue response even for subgingival margins.

3. Slightly more conservative of facial wall.

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Disadvantages:

1. Reduced strength compared to metal ceramic crown.

2. Proper preparation extremely critical to ensure mechanical success.

3. Least conservative.

4. Brittle nature of material.

5. Causes wear on the functional surfaces of natural teeth that opposeporcelain restorations.

Intra coronal retainers

Intra coronal retainers obtain their retention and resistance to

displacement from their intimate fit to the restoration within the confines of the

coronal portion of the tooth.

Inlay (Class II) metal

Indications:

1. Small caries lesion in otherwise sound tooth.

2. Adequate dentinal support the abutment tooth should be bulky, well

supported periodontally.

3. Low caries index.

4. Tooth replacement should not exceed a single tooth, preferably a

maxillary second molar.

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5. The occlusal stresses should be minimal or normal.

6. Abutment should be in good alignment.

Contraindications:

1. High caries index.

2. Poor plaque control.

3. Small teeth.

4. Adolescents

5. Poor dentinal support requiring wide preparation.

6. Heavy occlusal stresses.

Advantages:

1. Superior material properties.

2. Longevity.

3. No discoloration from corrosion.

Disadvantages:

1. May display metal.

2. Gingival extension beyond ideal.

3. Wedge retention.

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MOD onlay metal

Indications:

1. Worn or carious teeth with intact buccal wall and lingual cusps.

2. Low caries index.

3. Bell shaped teeth.

4. Span not exceeding replacement of two teeth and in good alignment.

Contraindications:

1. High caries index.

2. Poor plaque control.

3. Short clinical crown.

4. Caries lesions extending beyond transitional line angles.

Advantages:

1. Supports cusps.

2. High strength imparted to the abutment tooth.

3. Longevity.

Disadvantages:

1. Lacks retention.

2. May display metal.

3. Gingival extension beyond ideal.

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Ceramic inlay and onlay

Indications:

1. Demand for esthetics

2. Low caries rate

3. Intact buccal and lingual enamel

Contraindications


2. Poor plaque control

3. Bruxism

Advantages:

1. Superior esthetics

2. Conservative

3. Durable

Disadvantages:

1. Abrasion of opposing natural tooth.

2. Occlusion difficult to adjust.

3. Wear of luting agent.

4. Expensive.

5. Longivity questionable or unpredictable.

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Pin ledges

Indications:

1. Undamaged anterior teeth in caries free mouth.

2. A high esthetic requirement.

3. Where proximal grooves are impossible to prepare.

4. To alter lingual contour of maxillary anterior teeth or to alter occlusion.

5. Anterior splinting.

6. Anterior coronal form is present.

7. The crown of tooth is of average length or longer.

8. The tooth with average or greater labiolingual thickness in the incisal

one half of the crown.

Contraindications:

1. Large pulp

2. Thin teeth

3. Non vital teeth


5. Problems with proposed path of placment / withdrawal of fixed partial

denture.

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Advantages:

1. Minimal tooth reduction

2. Minimal margin length

3. Minimal gingival involvement

4. Optimum access for margin finishing and hygiene

5. Adequate retention

6. Excellent esthetics

Disadvantages:

1. Less retentive than complete coverage crowns.

2. Alignments can prove difficult.

3. Not usable on non vital teeth.

4. Technically demanding.

Radicular retainer

Radicular retained posthesis consist of a post or dowel with an

attached core that obtains its retention and resistance to displacement fromthe prepared root portion of an endodontically treated teeth.

While the root preparation retains the post the core establishes

retention and resistance for a complete veneer crown that restores the

pulpless tooth to normal form and function.

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The post or dowel and core may be custom cast, where the

radicular retainer is fabricated to fit the root preparation or prefabricated

where the root preparation is designed to fit a stock post and core is build

up with silver amalgam or composite resin.

Posts

1. Custom made

2. Prefabricated - Tapered smooth sided posts- Tapered serrated posts

- Tapered threaded posts

- Parallel threaded posts

- Parallel serrated posts

- Parallel smooth side posts

Complete crowns with Dowels

Types of crowns

1. All metal with a dowel .

2. All porcelain with a dowel .

a. Detached Post crown without a cast base.

e.g. Davis crown

b. Detached post crown with a cast base

e.g. Davis crown

c. Attached post crown

e.g. Logan crown

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3. Combination of metal and porcelain

A cast core for a jacket.

e.g. Richmond crown

4. All plastic dowel processed in acrylic material.

5. Combination of metal and plastic core replacement

Detached dowel crown (Davis)

All porcelain crown with a post that is detached and can be placed on a

prepared root end by cementation of both the post in the root and the

cementation of crown on the post.

Indications:

1. When impossible to restore crown by other means so that vitality can be

maintained.

2. Mostly on anterior teeth, occasionally on posterior teet.

3. When there is normal occlusal relationship.

4. Sufficiently long and thick root structure.

5. Only when periapical and periodontal conditions are favourable.

Contraindications:

1. Heavy and close bite cases.

2. Poor oral hygiene.

3. Patients with parafunctional habbits.

4. Thin narrow roots.

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Advantages:

1. Esthetics.

2. Adequetely strong.

3. Permits alignment with other teeth.

4. Good tissue adaptability.

5. Easily removed for treatment of required.

Disadvantages:

1. Tooth must be non vital.

2. Weakening of root face and canal by enlarging.

Detached post crown with a cast base

When the coronal portion of the remaining tooth is missing to a

point below gingiva and it is impossible to adapt the crown and root face, a

cast metal base is interposed between the base of the crown and root face.

This cast base is rigidly attached to the dowel.

Indications:

1. Tooth broken or destroyed by caries to a point subgingivally.

2. Mostly anterior teeth, occasionally bicuspids.

3. In cases with heavy bite.

4. Sufficiently long or thick roots.

5. All periodontal factors favourable.

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Contraindications:

1. Poor oral hygiene.

2. Thin and narrow roots.

3. If possible to design other variety, such as core and jacket restoration.

Advantages:

1. Quite strong and lasting.

2. Strengthens remaining tooth structures.

3. Esthetics.

Disadvantages:

1. Tooth must be non vital.

2. Difficult to construct in comparison to the restoration without a cast

base.

Richmond crown: By Richmond (1835 1902)

A dowel retained crown made for an endodontically treated tooth using

porcelain facing.

Resin bonded retainers

Types : 1) Rochette.

2) Maryland

3) Sockwall

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The restoration consists of one or more pontics supported by thin metal

retainer placed lingually and proximally on the abutment teeth.

These prosthesis rely in part on adhesive bonding between etched

enamel and the metal casting.

They are held in place by resin which locks mechanically into

chemically etched enamel and into microscopic undercuts in castings.

1. The Rochette type Uses small perforation in the retainer sections for

restoration and is best suited for anterior bridges.

2. Maryland bridge, reported to have improved bonding strength. Instead

of perforations, the tooth side of framework is electrolytically etched

which produces microscopic undercuts. It can be used for both anterior

and posterior bridges.

3. The Sockwell type suggested design incorporating both perforations and

etching of metal.

This perforated type (Rochette) can be etched on the tooth side of metal

retainer to provide microscopic undercuts for added retention. This is

especially important in areas where perforations cannot be placed such

as proximal surface. The etched metal type (Maryland) can be improved

by adding perforations to provide both types of retention.

Indications:

1. Retainer of fixed partial denture for abutments with sufficient enamel to

etch for retention.

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2. Splinting of periodontally compromised teeh.

3. Stabilizing dentitions after orthodontic treatment.

4. In young patients for replacement of anterior teeth.

5. In medically compromised, indigent and adolescent patients.

Contraindications:

1. Patients with parafunctional habbits e.g. Bruxisum.

2. Long endentulous spans, replacing multiple missing teeth.

3. When the facial esthetics of abutment require improvement.

4. Insufficient occlusal clearance to provide 2 to 3mm vertical retention

e.g. abraded teeth.

5. Inadequate enamel surfaces to bond e.g. caries, existing restorations.

6. Incisors with extremely thin Faciolingual dimensions.

Advantages:

1. More conservation over conventional fixed prosthodontics.

2. Preparation confined to tooth enamel only the potential for trauma topulp is minimized.

3. Tissue tolarance because of supragingival margins.

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Disadvantages:

1. Longevity of prosthesis is questionable Debonding rate increases with

time.

2. Higher dislodgement rate with posterior resin retained fixed partial

dentures.

Indications for multiple retainers

1. Abutment teeth with short roots.

2. Lack of sufficient bone support.

3. Density of alveolar bone.

4. Excessive length span.

5. Excessive lever arm action because of shape of anterior arch.

6. Distal extension of pontic for increased function.

7. Replacement of a missing cuspid.

Summary and Conclusion

The objective in selection of retainer whether it involves a single tooth,

several teeth or complete restoration of masticatory mechanism, it should

restore and maintain function of dental arch. It should be therefore both

restorative and preventive.

To accomplish this objective preventive as well as theraputic measures

should be utilized. The efficiency in selecting the retainer depends on the

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intelligent application of mechanical, physiological, hygienic and esthetic

principles within the limits of the supporting tissues.

As it is the critical component of fixed partial denture we have to give

atmost care in selection of retainer to achieve the goal in the success of fixed

partial denture.

References:

1. A.E. Kahn : Partial versus full coverage.J. Prosthet. Dent. 10:167-178,

1960.

2. Edger Kopp: Partial veneer retainers.J. Prosthet. Dent. 23(4): 412-419,

1970.

3. Johnstons Modern Practice in fixed Prosthodontics 4th edition 1986.

4. Joseph E. Ewings Fixed Partial Prosthesis 2nd edition 1959.

5. Lowerence Weinberg: Vertical non parallel pininlay fixed partial

prosthesis.J. Prosthet. Dent. 23: 420-433, 1970.

6. Stephen F. Rosenstial, Martin F. Land. Junhei Fujimoto:

Contemporary fixed prosthodontics 2nd edition 1995 Indian edition 1959.

7. Schelling burg: Fundamentals of Fixed Prosthodontics. Second edition.

8. Sturdevent: The Art and Science of Operative Dentistry. Second

edition.

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9. Someul E. Guyer: Multiple preparation for fixed prosthodontics. J.

Prosthet. Dent. 23: 529-553, 1970.

10. W.F. Malone, D.L. Koth, E. Carazos: Tylmans theory and practice of

fixed prosthodontics. 8th edition, Indian edition 1997.

11. Weinberg: A new design for posterior porcelain fused to metal

prosthesis.J. Prosthet. Dent. 17: 178-194, 1967.

12. W.H. Wilson and R.L. Lang: Practical crown and Bridge

prosthodontics.

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Choice of Retainer