Failures in FPD

                       Failures in fpd

 

Bridge Failures

         “Technology in the hands of a skilled operator makes it possible to do more work of an even higher quality.  But in the hands of one who has not mastered the skills of his or her profession, that technology merely enables one to do tremendous damage.”

                                                       -      Herbert T. Shillingburg

Excellence in dental care is achieved through the dentist’s ability to  assess the patient, determine needs, design an appropriate treatment plan and execute the plan with proficiency.

CLASSIFICATIONS

The causes of FPD failures were summarized as early as in 1920 when Tinker wrote

“Chief among the causes for such disappointing results has been:

First: Faulty, and in some cases, no attempt at diagnosis and prognosis.

Second: Failure to remove foci of infection in attention to treatment and care of the investing tissues and mouth sanitation.

Third: Disregard for tooth form

Fourth: Absence of proper embrasures

Fifth: Inter proximal spaces

Sixth: Faulty occlusion and articulation

Other classification given by Bennard G. N. Smith

1. Loss of retention

2. Mechanical failure of crowns or bridge components

    a. Porcelain fracture

    b. Failure of solder joints

    c. Distortion

    d. Occlusal wear and perforation

    e. Lost facings

3. Changes in the abutment tooth

    a. Periodontal disease

    b. Problems with the pulp

    c. Caries

    d. Fracture of the prepared natural crown or root

    e. Movement of the tooth

4. Design failures

   a. Under-prescribed FPDs

   b. Over-prescribed FPDs

5. Inadequate clinical or laboratory technique

   a. Positive ledge

   b. Negative ledge

  c. Defect

  d. Poor shape and color

6. Occlusal problems

Failures of FPD

Failures of fixed partial dentures occur based on:

•         Patient complaints

•         Duration of time

Patient complaints

•         Pain

•         Sensitivity

•         Looseness of bridge

•         Pain in soft tissue (gingiva)

•         Esthetics

•         Fracture

•         Swelling

•         Speech

•         Mastication

Duration of time

•         Immediate

•         Delayed

TYPES OF BRIDGE FAILURES

I.        Cementation failure

II.        Mechanical failure

III.        Gingival and periodontal breakdown

IV.        Caries

V.        Necrosis of pulp

VI.        Esthetic failure

I.CEMENTATION FAILURE

•  Cement failure

•  Retention failure

•  Occlusal problems

•  Distortion of the bridge

Cement Failure

•  Cement selection

•  Old cement

•  Prolonged mixing time

•  Thin mix

•   Thick mix

•  Cement setting prior to seating

•  Inadequate isolation

•  Incomplete removal of temporary cement

•  Thick cement space

•  Inclusion of cotton fibers

•  Insufficient pressure while cementation

Cement Selection

•  FPD Multiretainers - GIC

•  Non Vital Teeth/Advanced Pulp Recession -   ZINC PHOSPHATE

•  Temporary Cementation - ZINC OXIDE EUGENOL

•  Fixation of Facings- DIMETHACRYLATE COMPOSITES

•  Abutment with Minimal Dentin / Exposure - CALCIUM HYDRO OXIDE + ZINC OXIDE EUGENOL

 

Thick Cement Space

•  Convergence below 6º

•  Excessive application of die spacer

•  Thick cement mix

•  Grinding metal inside retainers

•  Cement setting prior to seating

 

How to Confirm Cement Failure

ØPull the crown margin and see for movement of the crown

ØCrown margins which were subgingivally placed will be visible when we pull the crown margin

ØBubbles come out of the margin or through perforation of the crown    (if present) when the crown margin is pushed by applying pressure occlusally

Retention failure

•  Excessive taper

•  Short clinical crown

•  Mis-fit

•  Mis-alignment

Retention

•  Retention prevents the removal of the restoration along the path of insertion or the long axis of the tooth.

•  Resistance prevents dislodgement of the restoration by forces directed in apical or oblique direction

Improving Retention

•  Additional retentive grooves/ proximal grooves.

•  Additional pins- drill the retainer & tooth .5 to .7 mm with round bur in buccal & lingual aspects, cut the excessive length & smoothen the area.

•  Crown lengthening

•  Sub gingival margins

•  Additional abutments

Excessive Taper

•  The relationship of one wall of preparation to the long axis of that preparation is the inclination of that wall.

•  Sum of the inclination of two opposing walls give the taper of the preparation.

•    Minimum 12º taper is necessary to ensure the absence of undercuts

    & also the restoration is placed on the preparation after being   

    fabricated in final form.

•  Conscious effort to incorporate taper usually results in over tapered, non retentive preparation.

 

Short Clinical Crown

•  Cement creates a weak bond, largely by mechanical interlocks, between the inner surface of the restoration & the axial wall of the preparation. So, greater the surface area of preparation, greater wills the retention.

•  A short, over tapered crown would have minimal retention because the restoration can be removed along infinite paths.

•  Because the length of axial wall occlusal to finish line interferes with the displacement, the length & inclination become important factors.

Misfit

Causes

•  Expansion of metal substructure because of

    -Improper water /powder ratio of investment

    -Improper mixing time

    -Improper burn out temperature

•  Distortion of the margins

•  Distortion of metal substructure

•  Metal bubbles in occlusal or margin regions because of

    - Inadequate vacuum during investing

    - Improper brush technique

   - No surfactant

•  Porcelain inside retainer

•  Excessive oxide layer in inner side of retainer

•  Tight contact points

•  Thick cement space

•  Insufficient pressure during cementation

Misalignment

•  In case of misalignment the bridge will +ve  spring in it & tend to seat further on pressure due to abutment teeth moving slightly

•  In misfit the resistance felt is solid.

Causes

•  Abutment displacement due to improper temporization.

•  Distortion of wax pattern

•  Casting defects

•  Distortion of metal framework in porcelain firing.

•  Porcelain flow inside the retainers

•  Mal alignment of solder joints

•  Excessive metal or porcelain in tissue   surface of pontic.

Remedy

•  If the bridge seats fully under pressure- leave it in place for 30 min to 1 hr asking the patient to exert gentle pressure.

•  If it does not work, temporarily cement to one of the retainers for 1 to 2 days.

•  Then, the bridge is unsoldered, separate components tried. If they seat, take location impression & resolder.

Occlusal problems

 Problems in occlusion are basically

     Immediate problems

1.      Occlusal interferences

2.     Marginal ridges at different levels

3.     Supra eruption of opposing tooth

4.     Para functional habits

    Delayed problems

1.     Wearing of occlusal surfaces

2.     Loss of occlusal contacts

3.     Cementation failure due to lateral forces

4.     Periodontal and gingival breakdown

5.     Tenderness

Torque

•  From a cusp extended too far bucally or lingually.

•  Pre mature contact on lateral excursion extremity.

•  Results in cementation failure.

   Reduce bucco lingual width of  occlusal surface

Indications

•  Mobility of teeth

•  Tenderness on mastication

•  Hyperemia of soft tissues

•  Sensitivity to heat, cold & sweet

•  Burnished metal in area of premature contact

Checking occlusion

                                 

·     Touch

·     Tin articulating paper

·     Occlusal indicator wax

  Occlusion should be adjusted both in centric and eccentric

Distortion

•  Distortion of wax patterns

•  Incomplete casting

•  Long span bridges

Wax Patterns

•  Removal from the die

•  Spruing stage

•  Investing stage because of the thick investment material.

Incomplete Casting

•  Too thin wax patterns

•  Incomplete wax elimination

•  Cool mold or melt

•  Insufficient metal

Long Span Bridges

•  Thin crown

•  Soft metal

•  Heat treatment not being done

•  Porosity in the metal

•  Distortion of margins.

MECHANICAL FAILURE

1.   Retainer failure

2.   Pontic failure

3.   Connector failure

Retainer Failure

Perforation

•  Insufficient occlusal reduction

•  High points in opposing dentition

•  Premature contacts

•  Soft metal

•  Porosity

•  Para functional habits

Marginal Discrepancy

       The more accurately the restoration is adapted to tooth, the less will be chances of cementation failure, recurrent caries or periodontal disease. 50μ to 100μ discrepancy is acceptable.

•  Rough margins reduce adaptation

•  Open margins encourage entry of saliva and cariogenic organisms

•  Over extended margins cannot be adapted to converging convexity of tooth at cervical margin

Causes

•  Selection of margin

•  Improper preparation

•  No gingival retraction

•  Improper selection of impression material

•  Distortion of wax patterns

•  Nodules at margin or inside casting

•  Thick cement

•  Prior setting of cement

Facing Failure

·     Fracture

·     Too little retention

·     Spot contact at porcelain metal junction

·     Malocclusion

·     Microleakage.

Wearing

                                                       

•  Deep bite

•  Acrylic veneering opposing porcelain teeth

•  Faulty brushing & flossing

•  Parafunctional habits

Discoloration

•  Absorption of oral fluids

•  Absorption of artificial food colouring agents through the microcracks or microleakage in metal & facing

•  Tarnish of underlying metal & facing

Pontic failure

Requirements

·     Form & shape of gingival surface must not irritate residual ridge

·     Design must incorporate mechanical principles for strength & longevity

·     Esthetics

Residual Ridge Contour

•  Ideal - smooth, easy to clean

•  Irregular hyperplastic tissue (commonly because of an ill fitting rpd) must be surgically removed

•  Severe bone resorption (particularly because of trauma) - surgical ridge augmentation

Ridge Contact

•  Pressure free contact without blanching.

•  In esthetic zone, the pontic should contact on the labial/ buccal aspect.

•  In mandibular posteriors hygienic pontic can be given.

 

Metal Sub Structure is compromised due to

•  Limited edentulous space in Occluso gingival direction due to supra eruption of opposing tooth.

•  Limited space mesiodistally due to drifting of adjacent teeth

•  Framework must provide uniform thickness for porcelain- cut back wax uniformly

Metal ceramic junction should be 1.5 mm away from junction.

 

GINGIVAL AND PERIODONTAL BREAKDOWN

-         Margins placement

-         Integrity of contacts and margins

-         Occlusion

Reasons for gingival breakdown

•         Plaque retention

•         Improper design

•         Faulty margins

•         Incorrect occlusal anatomy

•         Over contoured retainer

•         Inadequate embrasure

Treatment options:

•         Give proper oral hygiene instructions

•         Remake the bridge

Reasons for periodontal breakdown:

•         General periodontal problems

•         Local periodontal problems like

         - Poor bridge design

         - Incorrect assessment of abutment strength

         - Insufficient abutment selected

         - Traumatic occlusion

Treatment options:

•         Remake the bridge

Supra Gingival Margins

Advantages

•  Can be easily finished

•  Easily cleanable

•  Impressions easily recordable

•  Easy evaluation at recall

Disadvantages

•  Esthetically inferior

•  Not indicated for short clinical crowns

•  Not indicated in case of root sensitivity

Sub Gingival Margins

Indications

•  Esthetic demands

•  Caries removal

•  Existing sub gingival restorations

•  Crown lengthening.

Disadvantages

•  Difficult to prepare

•  Soft tissue prone to trauma

•  Causes gingival & periodontal pathosis

•  Difficult oral hygiene

•  Metal margins seen through gingival.

 

 

 

 

CARIES

•  Caries occouring on the margin of the retainer,

•  Caries affecting indirectly by starting elsewhere on the tooth and spreading.

•  Caries due to cementation failure.

Reasons for caries:

•         Poor oral hygiene

•         Open margins

•         Faulty contacts

Treatment options:

•         Use conventional filling materials

•         Correction of crowns and bridges if possible

•         Remake the bridge

NECROSIS OF PULP

                                                           

Can occour at three stages

     - Prior to preparation

     - During preparation

     - After preparation

Reasons for pulp necrosis:

•         Increased occlusal trauma

•         Increased heat during preparation

•         No pulp protection

Other reasons for pulp necrosis:

•         Speed, size, and type of the rotating instrument

•         The amount of pressure used

•         Depth of remaining dentin

•         Vibration

•         Coolants

•         Desiccation

•         Chemical injury

Treatment options:

•      For anterior teeth – apicectomy and retrograde filling

•      For posterior teeth – endodontic therapy

•      Remake the bridge

 

ESTHETIC FAILURES

Requirements for Esthetic Restorations

·     Proper shade selection

·     Correct tooth preparation

·        Avoidance of grey margins

·        Prevention of metal exposure

·     Final impression

 

 

Reasons for Esthetic Failure

•  Failure to identify patient expectations regarding esthetics

•  Improper shade selection

•  Failure to transfer shade selection to laboratory

•  Excessive metal thickness at incisal and cervical regions

•  Over glaze or too much smooth surface

•  Metal exposure in connector, cervical, and incisal region

•  Dark space in cervical third due to improper pontic selection            (anteriors)

•  Failed to produce incisal and proximal translucency

•  Improper contouring

•  Failure to harmonize contra-lateral tooth morphology- contour, colour, position, angulations

•  Discoloration of facing

Shade Selection

•  Walls and surroundings should be in neutral colour or blue

•  Never select under direct sunlight

•  Upright position of the patient

•  Use squint test

•  Teeth should be clean and unstained

•  Shade selection should be done before teeth preparation

•  Don’t dry the tooth while selecting the shade

•  Canine is the darkest tooth

•  Premolars lighter shade than canine

•  Maxillary anteriors are missing, shade of the mandibular anteriors is considered

•  In case of a non-vital tooth, cover it and select the shade of the adjacent tooth.

Other Biologic bridge failure are

Fracture of tooth

Reasons for fracture:

•         Improper abutment selection

•         Wear of tooth

•         Increased occlusal forces

Treatment options:

•         Remake the bridge using more abutment teeth.

Temporo-mandibular joint problems

                                   

Reasons for TMJ problems:

•      Improper occlusal scheme

Treatment options:

•      Remake the bridge using proper occlusal scheme

Caries… the frequent culprit

Caries – 38%

Periapical involvement – 15%

Perforated occlusal surface – 10%

Fracture post &core – 8%

Defective margins – 8%

Fracture teeth – 7%

Porcelian failures – 8%

                          JPD, Vol 78, Issue 2, pg 127-131, Aug 1997

 

Conclusion

Failures most often occur because of violation of principles either collectively or individually and for the most part are due to attempted short-cuts or positive indifference and inexcusable ignorance on the part of those concerned. Whatever said and done, at last it is only the ability of a Prosthodontist which determines the success or failure of a fixed partial denture.

Bibliography

•         Shillingburg HT, Hobo S, Whitsett LD, Jacobe R, and Brackett SE:  Fundamentals of fixed prosthodontics, ed. 3, Chicago, 2001, Quintessence, Inc.

•         Tylman’s theory and practice of fixed Prosthodontics,8th edi,1989,William F.P.Malone, David .L.Koth     

•         Roberts DH: Fixed bridge prosthesis, ed. 1, Bristol, 1973, John Wright & Sons.

•         Rosenstiel SF, Land MF and Fujimoto J: Contemporary fixed prosthodontics, 2001, ed. 3, N.Delhi, Harcourt.

•         Longevity of fixed partial dentures,JPD,Vol 78,Issue 2,Pg 127-131,Aug 1997.

•         Failures related to crown and fixed partial dentures fabricated in Nigerian dental school, Journal of contemporary dental practise, Vol 6, No 4,Nov 15,2005.

•         Clinical complications in fixed Prosthodontics, JPD,2003,90 Vol,   pg 31-41