Saturday, July 27, 2013

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

 


 






























                      

                  

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