FAILURES IN FIXED PARTIAL DENTURES

CLASSIFICATION

Bennard G. N. Smith

1. Loss of retention2. Mechanical failure of crowns or Fixed partial denture

componentsa. Porcelain fractureb. Failure of solder jointsc. Distortiond. Occlusal wear and perforatione. Lost facings

3. Changes in the abutment tootha. Periodontal diseaseb. Problems with the pulpc. Cariesd. Fracture of the prepared natural crown or roote. Movement of the tooth

4. Design failuresa. Under-prescribed FPDsb. Over-prescribed FPDs

5. Inadequate clinical or laboratory techniquea. Positive ledgeb. Negative ledgec. Defectd. Poor shape and color

6. Occlusal problems

PresentationPresentation• PainPain• Loss of retentionLoss of retention• Inability to functionInability to function• Dissatisfaction with aestheticsDissatisfaction with aesthetics• Broken teeth or restorationBroken teeth or restoration• Inflammatory swellingInflammatory swelling• Bad tasteBad taste• HalitosisHalitosis• Bleeding gumsBleeding gums• AnxietyAnxiety• Symptom freeSymptom free

TYPES OF FAILURES IN FPD

I. Cementation failureII. Mechanical failureIII. Gingival and periodontal breakdownIV. CariesV. Necrosis of pulpVI. Biomechanical failureVII.Esthetic failure

I. CEMENTATION FAILURE

Can be broadly divided into:

1. CEMENT FAILURE2. RETENTION FAILURE3. OCCLUSAL PROBLEMS4. DISTORTION OF FPD

Causes of cement failure1) Cement selection2) Old cement3) Prolonged mixing time4) Thin mix5) Cement setting prior to seating6) Inadequate isolation7) Incomplete removal of temporary cement8) Thick cement space9) Inclusion of cotton fibers10) Insufficient pressure

Selection of luting agent: The primary function of the luting agent is to provide a seal preventing marginal leakage and pulp irritation. The luting agent should not be used to provide significant retentive and resistive forces.

An ideal luting agent would have the following properties:1. Adequate working time2. Adhere well to both tooth structure and metal surface3. Provides a good seal4. Non toxic to the pulp5. Have adequate strength properties6. Be compressible into thin layers7. Have low viscosity and solubility8. Exhibit good working time and setting properties

Cement failureCement failure- Complete decementationComplete decementation- Partial decementationPartial decementation

carious attackcarious attack

Patient feeling: Patient feeling: movement of the bridgemovement of the bridge

bad tastebad taste

sensitivitysensitivity

Clinically: Clinically: applying displacing pressure to the applying displacing pressure to the restoration will cause bubbles at the cervical marginrestoration will cause bubbles at the cervical margin

Management:Management:- Restoration must be removedRestoration must be removed- Abutment should be evaluatedAbutment should be evaluated- Recementation if abutments and restoration are Recementation if abutments and restoration are

satisfactory or new restoration should be madesatisfactory or new restoration should be made

2. RETENTION FAILUREFor a restoration to accomplish its purpose, it must

stay in place on the tooth. The geometric configuration of the tooth preparation must place the cement in compression to provide the necessary retention and resistance.

CAUSES FOR RETENTION FAILURE1) Excessive taper2) Short clinical crowns3) Mis-fit4) Misalignment

Excessive taper : As a cast metal or ceramic restoration is placed on or in the preparation after the restoration has been fabricated in its final form, the axial walls of the preparation must taper slightly to permit the restoration to seat

Theoretically, the more nearly parallel the opposing walls of the preparation are, the greater should be the retention.

Recommendations for optimal axial wall taper of tooth preparations for cast restorations ranged from 10 to 12 degrees.

Short clinical crown : Cement creates a weak bond largely by mechanical interlocks between the inner surface of the restoration and the axial wall of the preparation. Therefore, the greater the surface area of the preparation the greater is its retention. The preparations on large teeth are more retentive than preparations on small teeth. A short, over-tapered or short clinical crown would be without retention as there would be many paths of removal. A shorter wall cannot afford this resistance. The walls of short preparations should have as little taper as possible.

Clinical conditions with excessive taper and short clinical crowns should be treated with :-

1. In case of excessive taper:a. Incorporation of proximal grooves. b. Additional retentive grooves (should be along with the path

of insertion).c. Additional pins

2. In case of short crowns:a. Crown lengthening procedureb. Modification of supra-gingival margin to sub-gingival

marginc. Additional retentive grooves and proximal boxd. Incorporation of pinse. Addition of extra abutments

Misfit : The fit of casting can be defined best in terms of the “misfit” measured at various points between the casting surface and the tooth.

The measurement of misfit at different locations and geometrically related to each other and defined as :

1. Internal gap2. Marginal gap3. Vertical marginal discrepancy 4. Horizontal marginal discrepancy 5. Over-extended margin6. Under-extended margin

Causes for misfit : a. Defective castingb. Porcelain flowed inside the retainerc. Excessive oxide layer formation in inner side of the retainer (due

to contaminated metal or repeated firing of porcelain)d. Tight contact points with abutment teethe. Incorrect manipulation of luting agentsf. Insufficient pressure during cementation procedure

Misalignment : it is more difficult to differentiate whether a FPD is not seating because of a faulty fit, or the alignment of the retainers relative to each other is incorrect. The only difference which may sometimes be apparent is that, in the case of misalignment the FPD will have some ‘spring’ in it and tend to seat further on pressure due to the abutment teeth moving slightly, whereas in the case of a defective fit, the resistance felt will be solid.

Causes for misalignmenta. Abutment displacement due to improper temporization.b. Distortion of wax pattern while sprueing and investing.c. Casting defects. d. Distortion of metal frameworks in porcelain firing.e. Porcelain flow inside the retainers.f. Misalignment of soldering points.g. Insufficient pressure in cementation.h. Thick cement film.i. Excessive metal or porcelain in tissue surface (ridge lap) of

pontic prevents the proper seating of FPD and open margin (can be detected by observing the blanching of the tissue or patient may complain of pressure on the pontic region).

3. OCCLUSAL PROBLEMSFollowing the placement of a dental restoration, a patient

might report discomfort ranging from a feeling of ‘lameness’ to ‘severe and constant pain’. Sensitivity, in most cases, is due to pulp irritation from traumatic contact or greater leverages. When the occlusion has been adjusted, each type of discomfort may be relieved almost instantly and should disappear shortly.

Causes in occlusal problems1. Immediate problems

Occlusal interference Marginal ridges at different levels Supra eruption of the opposing tooth Parafunctional habits

2. Delayed problems Wearing of occlusal surface Loss of occlusal contacts Perforation of occlusal surface due to

• Porcelain Vs resin• Porcelain Vs gold

Food lodgment due to plunger cusp Fracture of facing due to defective occlusal contact Periodontal or gingival breakdown due to improper occlusal contacts Tenderness due to food lodgement

4. DISTORTION OF FPD

The completed restoration should go into place without binding of its internal aspect against the occlusal surface or the axial walls of the tooth preparation. In other words, the best adaptation should be at the margins. If the indirect procedure is handled properly, there should be no noticeable difference between the fit of a restoration on the die and that in the mouth.

Causes of distortion: Casting defects- distorted margin, rough castings, banding of

the FPD due to improper care taken during wax pattern making, investing and casting procedures.

Bending of long span FPDs due to Thin crown, Soft metal, Heat treatment not being done, Porosity in the metal

Distortion of the metal substructure during the porcelain firing

II MECHANICAL FAILURES

Classification of mechanical failure1. Retainer failure2. Pontic failure3. Connector failure

1. RETAINER FAILURE

1) Perforation2) Marginal discrepancy3) Facing failure

FractureWearingDiscoloration

1) Perforation

Causesa) Insufficient occlusal reductionb) Insufficient occlusal materialc) High points in opposing dentition (plunger cusp)d) Premature contactse) Contaminated metalf) Porosity in metal work (subsurface, back pressure, suck

back)g) Due to improper melting temperatureh) Improper pattern positioni) Improper sprue (too thin)j) Improper locationk) Parafunctional habits

2) Marginal discrepancy

Causesa) Selection of marginb) Improper preparation and failure to establish the margin

properlyc) Failure to do gingival retraction prevents definite margin

location and subsequently in impressiond) Selection of the impression material

i. Shrinkage in material (condensation silicon)ii. Distortion of material (alginate)

e) Improper impression proceduresf) Voids in the impressiong) Variation in pressure application in wash techniqueh) Delayed pouring of die materiali) Distortion of wax patterns at margins

j) Insufficient flow of metalk) Shrinkage of metall) Nodules in margins and inner side of coping

i. Due to inadequate vacuum during investingii. Improper brushing techniqueiii. No surfactant

m) Excessive sand blastingn) Distortion due to degassing procedureo) Open margins due to porcelain shrinkage (opaque porcelain)p) Thick mixing of luting agentq) Cement setting prior to seatingr) Insufficient pressure application during cementation

3. Facing failure

Types of veneer failuresa) Fracture b) Wearing of facing (resin veneers)c) Discoloration

Porcelain failurePorcelain failureFull ceramic restorations:Full ceramic restorations:

Fracture indicate that full ceramic restoration is not Fracture indicate that full ceramic restoration is not suitable for the situation in regard to occlusal suitable for the situation in regard to occlusal forcesforces

Metal ceramic restorations:Metal ceramic restorations:- Chipping: Chipping: failure in porcelain buildupfailure in porcelain buildup- Debonding: Debonding: failure in the bond between failure in the bond between

metal and porcelainmetal and porcelain

Mechanical Failure

Causes:Causes:- Technical failure in opaque layer applicationTechnical failure in opaque layer application- Inadequate framework designInadequate framework design- Placing porcelain margin at highly stressed areasPlacing porcelain margin at highly stressed areas- Thin metal framework for long span FPDsThin metal framework for long span FPDsManagement:Management:- Small fractures can be repaired with composite kitSmall fractures can be repaired with composite kit- Large fractures: replace restoration avoiding the Large fractures: replace restoration avoiding the

cause of failurecause of failure

2. PONTIC FAILURE

Factors affecting selection and failure of pontics1) Pontic space2) Residual ridge contour3) Biological consideration

a. Ridge relationb. Dental plaquec. Gingival surface of pontic (Contact with mucosa)

i. Mucosal contactii. Non mucosal contact

4) Pontic ridge relationship5) Pontic material6) Biocompatibility7) Occlusal forces8) Metal substructure support

3. CONNECTOR FAILUREThe connector is that part of the FPD or splint that joins the individual components (retainers and pontics) together.

Causes for connector failureImproper selection of connectorThin metal at the connectorIncorrect selection of solderSolder gap – narrow or widePorosityInsufficient metal aroundDefective occlusal contacts over thin connectors

III GINGIVAL AND PERIODONTAL PROBLEMS

Margins are one of the most important and weakest links in the success of FPD restorations. One of the prime goals of restorative therapy is to establish a physiologic periodontal health.

A successful prosthesis depends on a healthy periodontal environment and periodontal health depends on the continued integrity of the prosthodontic restoration.

The margin is one of the components of the cast restoration most susceptible to failure, both biologically and mechanically. Most of the investigative proof shows that supragingival margins are kinder to the gingiva than are subgingival margins. However, practicality dictates that supragingival margins are not always usable

Failure to produce the margin of the preparation in the impression lead to reproducing the marginal integrity of the restoration. Using of gingival retraction technique in case of sub gingival preparation is mandatory.

However, all displacement techniques have the potential damage gingiva, attachment apparatus and bone, especially if anatomic forms are weak or if disease is present.

In healthy patients, properly used cord displacement or copper band methods have proved to be atraumatic.

IV CARIES

CAUSESIatrogenic (dentists role)

Failure to identify caries Incomplete removal of caries Marginal discrepancy with subsequent plaque accumulation and microleakageSubgingival marginal placement in inaccessible areas or regions Burning of root dentin or cementum in electro surgical technique (leads to damage or rough surface and causes plaque retention)Over contouring of the cervical thirds of crowns or bridges prevents the physiologic too cleaning by tongue or muscles Thick cement space in margins leads to cement dissolution. Narrow embrasures (inaccessibility to maintain hygiene) Wide connector

Patient role Systemic factors

Xerostomia Due to radiation therapy Drug induced Endocrine disorders

Epilepsy (difficult to maintain the oral hygiene) Rheumatoid arthritis

Local factors Improper brushing and flossing Dietary habits Failure to understand importance of oral hygiene.

Management

-Limited at margin: remove caries and restore-Extended under retainer: remove restoration, restore the teeth and reassess the need for new restoration

V PULP DEGENERATION

Pulp reactions to various procedures

Each step in full crown preparation presents hazards, which may injure the pulp. In general, heat desiccation and / or chemical injury cause the insult. The result may be pulpitis or even necrosis. Among the many essential procedures that may cause pulp injury are:Tooth preparation: excessive heat generation, over preparation with less than 1mm of reaming dentinImpression making: irritation from the impression materialsPulp infection: from microbial infiltration due to poor oral health and faulty temporization and cementation.

VI BIOMECHANICAL FAILURE

Causes:- Failure in selection of right abutment- Lack of retention and resistance form- Incorrect design of FPD- Wrong material selection

VII. ESTHETIC FAILURES

REASONS FOR ESTHETIC FAILURE Failure to identify patient expectations regarding esthetics Improper shade selection Excessive metal thickness at incisal and cervical regions Thick opaque layer application Surface blistering (chalky appearance) Over glazing or too smooth a surface Metal exposure in connector, cervical and incisal regions (anteriors)

Failure to produce incisal and proximal translucency Improper contouring Failure to harmonize contra lateral tooth morphology

Contour Color Position Angulation

Dark space in cervical third due to improper pontic selection Discoloration of facing

Post and core failurePost and core failure

1- loss of retention1- loss of retention- Short postsShort posts- Over tapered postsOver tapered posts- No anti-rotation lockNo anti-rotation lock

ManagementManagement

New post with adequate designNew post with adequate design

Post and core failurePost and core failure

2- lateral perforation of the root2- lateral perforation of the root

- Misalignment of root canal preparation- Misalignment of root canal preparation- Thin root or over preparationThin root or over preparation

ManagementManagement- surgically by raising a flab and sealing the surgically by raising a flab and sealing the

perforationperforation- Extraction if access is dificultExtraction if access is dificult

Post and core failurePost and core failure

3- Root fracture3- Root fracture- Over tapered postsOver tapered posts- Short postsShort posts- Wide postsWide posts- Threaded postsThreaded posts

ManagementManagement

ExtractionExtraction

Removal of Crowns and FPDsRemoval of Crowns and FPDs

Attempts can be made to remove the Attempts can be made to remove the prosthesis intact using crown removers prosthesis intact using crown removers “caution”“caution”

*Sectioning of the prosthesis might be *Sectioning of the prosthesis might be necessary if the retainers are firmly necessary if the retainers are firmly cementedcemented

Before removing old restoration we Before removing old restoration we should ask:should ask:

- How long has this restoration been in How long has this restoration been in place?place?

- Why has it failed?Why has it failed?- How can further failure be prevented?How can further failure be prevented?

That’s it!!That’s it!!