CLINICAL FAILURES IN FPD

- CAUSES AND MANAGEMENT

CONTENTS

• Introduction

• Causes of failure

• Biologic failures

• Mechanical failures

• Esthetic failures

• Facing failures

• Removal of restorations

• Conclusion

INTRODUCTION

A realistic approach to fixed prosthodontics is that “total”

success or “total” failure is seldom achieved. Because of many

complexities of treatment, a level somewhere between the two

extremes will be experienced.

All fixed prostheses are subject to damage that will require

repair or remake. Both patient and dentist should be aware,

however, that repairs may not carry as long a life expectancy as the

original or as a remake.

CAUSES OF FAILURE A. Biologic failures

1) Caries 2) Pulp degeneration 3) Periodontal breakdown 4) Occlusal problems 5) Tooth perforation

B. Mechanical failures 1) Loss of retention 2) Connector failure 3) Occlusal wear 4) Tooth fracture 5) Acrylic veneer wear / loss 6) Porcelain fracture

C. Esthetic failures D. Facing failures

A survey of crown and fixed partial denture failure : Length of

service and reasons for replacement.

Joanne N. Walton, F. Michael Gardner and John R. Agar.

JPD 1986; 56(4): 415-421.

They conducted a survey of crown and fixed partial denture

failures, length of service and reasons for replacement.

They presented their observations which is follows.

Table 1 : Reasons for replacement, by frequency

Reasons for replacement

No. of units

failed

No. of units requiring

replacement

Units failed (%)

Units requiring

replacement (%)

Mean length of service

(yr)

Caries 99 211 22.0 24.3 10.9

Uncemented restoration 68 150 15.1 17.2 5.8

Poor esthetics 51 52 11.3 6.0 9.6

Worn/lost resin veneer 59 63 10.8 7.2 13.1

Fractured tooth / root 18 38 3.9 4.4 10.2

Periapical involvement 12 27 2.7 3.1 10.0

Fractured connector 9 36 2.0 4.1 2.3

Miscellaneous (all other causes)

9 11 2.0 1.3 -

Total 451 870 100 100 8.3 yr (mean)

Table 2 : Crowns : Length of service and most common reason(s) for replacement

Type of crown Most common reason(s) Mean length of service (yr)

Ceramic-metal Porcelain failure, poor esthetics

6.5

Complete veneer metal Caries, defective margins 6.1

Resin veneer metal Worn / lost veneer 13.9

Porcelain jacket Defective margins, fractured porcelain

8.2

Partial veneer Caries, defective margins 11.0

Mean 9.1yr

Table 3 : Retainers : Length of service, by type Retainer type No. of

retainers No. of retainers requiring

replacement Mean length of

service (yr)

Ceramic-metal 85 165 6.3

Complete veneer metal 30 53 7.1

Resin veneer metal 24 30 14.7

Partial veneer 32 48 14.3

Inlay / onlay 10 13 11.2

Table 4 : length of service by prosthesis span

No. of units Mean years of service No. of FPDs requiring replacement

Single crown 9.1 193

2-Unit cantilever FPD 3.7 9

3-,4-unit FPD 9.6 28

5-, 6-unit FPD 6.6 13

6 unit canine to canine 10.4 9

Greater than 6 units 6.8 6

Mean for all FPDs 7.7 yr 258 (total)

BIOLOGIC FAILURES

Caries :

• One of the most common biologic failures.

• Early detection possible mainly through comprehensive probing of the margins of the prosthesis and tooth surfaces with a sharp explorer.

• Radiographs are helpful to detect caries on proximal surfaces.

Management :

Small lesions :

• Gold foil – filling material of choice for restoring marginal caries.

• Amalgam – best alterative to gold foil filling.

• Composite – indicated for restoration of caries in esthetic zone.

– Less desirable

• Glass ionomer cement.

Proximal lesions :

• Removal of prosthesis is required to obtain access to caries. If

the lesion is small, the tooth preparation can be extended to

eliminate the caries and a new prosthesis can be fabricated.

• When the lesion is large, an amalgam restoration is often required.

• The abutment preparation is extended to cover the filling, and a new restoration is fabricated.

• An extensive lesion may require endodontic treatment when pulp has been encroached.

• A grossly destroyed teeth by caries that cannot be restored must be extracted.

Pulp degeneration :

Causes :• Extensive preparation • Excess heat generation during preparation • Post-insertion pulpal sensitivity. May

manifest as sensitivity which does not subside with time

Intense pain Periapical pathology

Management :

Endodontic intervention

Procedure :

Access preparation – a hole is drilled in the prosthesis through

which the biomechanical preparation (BMP) is completed.

The access cavity is restored with

• Gold foil

• Amalgam

• Cast metal inlay

If the retainer come loose during access opening or if the

porcelain fractures, then remaking of the prosthesis may be

necessary. A post and core restoration should be considered if

little sound tooth structure is remaining.

Periodontal breakdown :

It can be localized around the prosthesis, as a result of inadequate instruction in prosthesis hygiene or a restoration that hinders good oral hygiene.

Aspects of the prosthesis that interfere with effective plaque removal include

• Poor marginal adaptation

• Overcontouring of the axial surfaces of the retainers

• Excessively large connectors that restrict cervical embrasure space

• A pontic that contacts too large an area on the edentulous ridge.

• A prosthesis with rough surfaces which promote plaque accumulation.

Management :

• Recontour to eliminate the defects

• Remake to correct the defects

OCCLUSAL PROBLEMS

Interfering centric and eccentric

occlusal contacts can cause

• Excessive tooth mobility

• Irreversible pulpal damage

Management :

• When detected early occlusal adjustment should be done to

eliminate these interferences without permanent damage.

• Occasionally, a combination of excessive mobility and reduced

bone support require extraction of abutment teeth

• Irreversible pulpal damage requires endodontic treatment.

Tooth perforation :

Improperly located pinholes or pins used in conjunction with pin-retained restorations may perforate the tooth laterally.

Management : depends on the location of the perforation. • Occlusal to periodontal ligament

• Extend the preparation to cover the defect. • Extends into periodontal ligament

• Perform periodontal surgery • Smoothening of the projecting pin • Place a restoration into perforated area

• Furcation region • Surgically inaccessible • Severe periodontal problems may ultimately lead to

extraction of the tooth. • Pulp chamber

• Endodontic treatment

MECHANICAL FAILURES

Loss of retention :

A prosthesis can come loose from an abutment tooth and if this occurrence is not detected early, extensive caries often develops.

The loss of retention can be detected by several ways

1. Patients awareness of looseness or sensitivity to temperature or sweets.

He may experience bad taste or odor.

2. Periodic clinical examinations that includes attempts to unseat existing prosthesis by lifting the retainers up and down (occlusocervically) while they are held between the fingers and a curved explorer placed under the connector.

If a casting is loose, the occlusal motion causes fluids to be drawn under the casting and when it is reseated with a cervical force the fluid is expressed, producing bubbles as the air and liquid are simultaneously displaced.

Management :

• Removal of the prosthesis

• Evaluation of the abutment

Caries restoration

Preparation form modify the preparation poor

• Fabricate new restoration

If the span length is excessive or occlusal forces heavy then a

removable partial denture may be the only satisfactory solution.

CONNECTOR FAILURE

A connector between an abutment retainer and a pontic or between two pontics can occur.

• Under occlusal forces

• Internal porosity is the cast or soldered connectors

When fracture occurs, pontics are placed in a cantilevered relationship with the retainer casting and this can allow excessive forces to be developed on the abutment tooth.

Management :

• Prosthesis should be removed and remade as soon as possible.

• An inlay like dovetailed preparation can be developed in the metal to span the fracture site and a casting can be cemented to stabilize the prosthesis.

• Pontics can be removed by cutting through the intact connectors and a temporary removable partial denture can then be inserted to maintain the existing space and satisfy esthetic requirements.

OCCLUSAL WEAR

An accelerated occlusal wear of a prosthesis can be produced due to

• Heavy chewing forces

• Clenching or bruxing

After several years, a casting perforation may develop, thus allowing leakage and caries to occur, which ultimately lead to prosthesis failure.

• If the perforation is detected early, a gold or amalgam restoration can be placed to seal the area and provides additional years of service.

• If the metal surrounding the perforation is extremely thin, a new prosthesis should be fabricated

• When porcelain occlusal surfaces opposes a natural tooth,

dramatic wear of enamel may occur with eventual perforation

into the dentin.

This problem is exacerbated by heavy chewing forces,

clenching or bruxing and often requires the restoration of the

abraded teeth.

• Same problem occurs when porcelain opposes metallic

restorations. So, in mouths in which occlusal wear is

anticipated, it is better to place metal over occluding surfaces

when natural teeth or metallic restorations are present in the

opposing arch.

TOOTH FRACTURE

Causes :

Coronal fractures :

1. Excessive tooth preparation – leaving insufficient tooth structure to resist occlusal forces.

2. Use of restorative material which was not retained in sound dentin with pins.

3. Presence of interfering centric of eccentric occlusal contacts

4. Heavy occlusal forces on a properly adjusted restoration.

5. Attempting to forcefully seat on improperly fitting prosthesis.

6. Incorrect unseating of a cemented bridge.

7. Around inlays and partial veneer crowns, as a result of increasing brittleness, of tooth structure with age.

Radicular fractures :

• Trauma

• Forceful seating of a post and core.

• Attempting to seat an improperly fitting post and core.

• Fractures occurring during endodontic treatment.

• Coronal tooth fracture can be dramatic, resulting in considerable loss of tooth structure, or it can be minor with little significant damage.

• If the surrounding tooth structure can be adequately prepared and still possess sufficient strength, then gold foil, amalgam, or resin can be used to restore the area.

• If there is question regarding the integrity of the remaining tooth

structure or restoration, a new prosthesis should be fabricated so

that it encompasses the fractured area.

• When fracture occurs under a full coverage retainers, it is usually

horizontal, at the level of the finish line.

• This necessitates removal of prosthesis, endodontic therapy, a post

and core, and a new prosthesis.

• Certain single restorations can be salvaged if the finish line and a

little coronal tooth structure remain intact after the fracture. A post

and core fabricated can be made to fit both the restoration and the

prepared tooth.

ACRYLIC VENEER WEAR OR LOSS

• Abrasion can result in loss of severe amounts of acrylic on acrylic veneer crowns and pontics.

Cause

• Functional loading or abrasive foods and habits.

• Tooth brush abrasion

Repair

• Replacing lost contours with autopolymerizing resin.

• Composites

- Mechanical retention is required

- More resistant to wear and

-Maintain function and appearance longer than acrylic resin repairs.

PORCELAIN FRACTURE

• Porcelain fractures occur with both metal – ceramic and all –

ceramic crown restorations.

Metal – ceramic porcelain failures :

Frame work design :

• Sharp angles or extremely

rough and irregular areas over

the veneering area serve as

points of stress concentration

that cause crack propagation

and ceramic fracture.

• Perforations in the metal can also cause failure for the same

reason.

Sharp angles

Rough surfaces

Perforations

Stress concentrations

Crack propagation

Ceramic fracture

• An overly thin metal casting does not adequately support porcelain, so that flexure and porcelain fracture may result

0.2 mm over large areas of the veneering surface, the potential for failure is greater.

• Also, when the angle between the veneering surface and the non-veneered aspect of the casting is less than 90 degrees, it allows occlusal forces to cause localized burnishing of the metal and distortion, which leads to premature porcelain fracture.

• With facially veered restorations, porcelain fracture results from a framework design that allows centric occlusal contact on, or immediately next to, the metal ceramic junction.

Occlusion :

• The presence of heavy occlusal forces or habits such as clenching and bruxism can cause failure.

• Centric or centric occlusal interferences and uncorrected occlusal sides which create deflective contact of the opposing teeth can cause fracture of porcelain.

Metal handling procedures :

• Metal contamination due to improper handling during casting, finishing or application of the porcelain can lead to formation of bubbles at the metal ceramic junction when porcelain is applied, creating stress and possibly cracks.

• Separation of the porcelain from the metal has been observed in cases of severe contamination.

• Excessive oxide formation on the alloy surface can also cause separation of porcelain from the metal.

Preparation, impression and Insertion :

• A tooth preparation with a slight undercut can cause binding of the prosthesis as it is seated, which initiates a crack in the porcelain.

An impression that is slightly distorted can also lead to the same problem.

• Teeth prepared with feather edge finish lines or impressions that donot record all of the finish line can lead to an extension of metal beyond the actual termination of tooth reduction, because the technician cannot determine from the die or impression where to terminate the wax pattern.

o The thin metal may bind against the tooth and initiate a crack in the overlying porcelain.

o Definite finish lines and impressions record detail are prerequisites to acceptable ceramics.

• Attempts to achieve complete seating of a ceramic restoration by using a mallet and wooden stick during trial insertion or cementation can also produce porcelain fracture.

Metal and Porcelain Incompatibility :

• In rare instances, an alloy and porcelain are found to be truly incompatible, and successful bonding without loss of the veneer or cracking is impossible. However, failure resulting from improper handling of the material is often erroneously attributed to porcelain, metal incompatibility.

Repair of Fractured Metal – Ceramic Restorations :

• The best method of repairing a fractured metal ceramic fixed partial denture is the fabrication of a new prosthesis.

• some of the procedures available for repair can at least serve as the interim until a new prosthesis is fabricated.

Material for repair :

1) Composite resins :

• Adequate to good color matches can routinely be achieved.

Porcelain-to-composite bond strengths using four organosilane materials.

JH Bailey.

Compared the flexural strengths of porcelain bonded to composite resin specimens using four organosilane materials.

1) 3M porcelain repair kit (Scotch bond) (Dental products division / 3M)

2) Fusion repair material (George Taub products, Jersey city NJ)

3) Ultrafine (Sybron / Kerr) porcelain repair bonding system.

4) Den Mat ultrabond restorative kit product.

He concluded that there was no significant difference in the bond strength of these materials. It is noted that the organosilane coupling agent did not bond to a metal surface as it did with the porcelain. Therefore it is advisable to create mechanical retention by using a coarse diamond when a repair involves a large surface of metal (Jochen DG, Caputo AA. JPD 1977; 28: 673-9).

• Lack of longevity is the main drawback because true chemical bonding does not occur between the current resins and either metal or porcelain, pinholes or groves must be made for mechanical interlocking.

2) A more permanent repair is possible when adequate metal framework thickness is available.

• This techniques works best with facially veneered restorations and involves the following steps.

Procedure :

1) Removal of the remaining porcelain on the fractured until to expose the underlying metal.

2) Drilling of several pinholes (4 or 5) into the framework to a depth of at least 2 mm.

3) Making of an impression.

4) Creation of a pin – retained metal casing 0.2 to 0.3 mm thick out of a metal – ceramic alloy to fit over the exposed metal framework.

5) Fusion of porcelain to the pin – retained.

6) Cementation of the casting in position.

• With full porcelain coverage prosthesis failures, the fractured until can be prepared with an incisal or occlusal path of insertion, and a staple like casting can be fabricated and veneered.

• The preparation should include grooves and pinholes, or both, in the underlying framework to provide retention and stability. A metal ceramic restoration is then fabricated and cemented in position.

Porcelain jacket crown failures :

• With good tooth preparations, long term success has been achieved on incisors, whereas fractures are more frequently observed when these restorations are placed on posterior teeth and on canines because of the occlusal forces on these teeth.

• All ceramic restorations are more likely to fail in the presence of heavy occlusal forces, clenching, or bruxism.

Vertical fracture :

• The marginal area of jacket crowns is often more closely adapted to the prepared tooth than are other areas of restoration.

• If a tapered finish line (such as a chamfer) is used, the restoration may contact the tooth on a sloping surface, so that forces are produced that attempt to expand the restoration and that are not well resisted by porcelain. A vertical fracture may occur.

• Vertical fractures have been observed when a large portion of the

proximal preparation form is missing and is not restored prior to

the impression procedure.

• When occlusal forces to the marginal ridge in which the missing

tooth form is located, greater leverage is developed because of

the distance from the point of force application to the underlying

prepared tooth.

• Sharp areas on the preparation

such as the line angles or the

incisal edge, produce areas of

high stress in the restoration –

causing fracture.

The occlusal forces attempt to rotate the restoration, causing expansive forces.

• A round preparation form that does not provide adequate resistance to rotational forces can also cause vertical fracture.

Facial cervical fracture :

• Fracture of the facial cervical porcelain, which often assumes a semilunar form, generally occurs, with a short preparation.

• The incisocervical length of the preparation should be two – thirds to three quarters that of the final restoration.

• When the preparation is short, forces applied at the incisal edge attempt to tip the restoration facially and cause cervical porcelain fracture.

Lingual fracture :

• Semilunar lingual fractures are observed when the occlusion is located cervically to the cingulum of the preparation, where forces on the porcelain are more shear in nature and not well resisted.

• Other lingual fractures, not necessarily semilunar in form are the result of inadequate lingual tooth reduction in which less than 1 mm of porcelain is present.

• Exceptionally heavy occlusal forces also can cause lingual fractures even when adequate porcelain thickness is present.

Dealing with failures of all ceramic crowns :

• There are no satisfactory methods of repairing fractures of all

ceramic restorations. A new restoration must be fabricated.

• In early failures, in the absence of clinical or laboratory defects,

occlusal forces are likely to be present that exceed the strength of

the restoration.

• In such case, a metal – ceramic restoration should be seriously

considered for the new restoration.

• If many years of good service occurred prior to failure and

optimal esthetics is still required, a new all ceramic restoration

should be considered

ESTHETIC FAILURES

• Ceramic restorations more often fail esthetically than mechanically or biologically. Poor color match is the frequent reason for most of the remakes of the restorations.

Causes : For unacceptable color match.

1) Inability to match the patients natural teeth with available porcelain colors.

2) Inadequate shade selection.

3) Metamerism.

4) Insufficient tooth reduction.

5) Failure to properly apply and fire the porcelain – creating a restoration that does not match the shade guide itself or the surrounding teeth.

6. Incorrect form or a framework design that displays metal.

7. Age changes in the natural tooth over the years.

8. Partial veneer restorations can be esthetically unacceptable

because of over extension of the finish line facially. This

displays excessive amount of metal.

9. When thin incisors are prepared, the metallic color of the partial

coverage casting may be visible through the remaining tooth

structure (grayness).

10.The marginal fit or cervical form of a prosthesis can promote

plaque accumulation, causing gingival inflammation, which

produces an unnatural soft tissue color or form that is

esthetically unacceptable.

FACING FAILURES

• Recementation of a loose facing is a simple process, but when

fracture has occurred, a facing repair may be indicated if the

prosthesis is otherwise satisfactory.

• A new facing (manufactured facing – if still available) can be

ground to fit the prosthesis on trial and error basis and cemented.

• Another repair process is to rebuild the desired form with a resin.

• Pins can be cemented or threaded into the casting if additional

retention is required.

• Another technique is to prepare the remaining metal casting so

that a new pin – retained casting can be fabricated and cemented

in place.

Removal of a prosthesis :

• Many well retained restorations cannot be removed intact and to prevent abutment tooth damage, must be cut off the prepared tooth and thereby destroyed.

• Attempts should be made for intact removal of restorations without damaging the abutments.

• The forces applied for removal should be sharp and in an occlusal direction.

1) Straight chisel and mallet technique :

• The chisel is kept as nearly parallel as possible to the path of withdrawal and mallet is used to tap with sharp blows, not so intense to cause tooth fracture or extreme pain.

2) Reverse mallet technique

3) Crown removers :

• These can be placed around retainers or under pontics and connectors so that occlusally directed forces can be applied

Amurol or Richwil technique :

• If the restoration cannot be removed with a crown remover the addition of the use of an Amurol sugarless fruit drop or a Richwil crown remover can be used.

• It is based on the principles of adhesion and depends on equal and opposing force being applied to opposing teeth.

• Patients co-operation is essential as it is largely dependent on the patient.

• The material [Amurol sugarless fruit drop) (Amurol Products

Eo. Box 300. Naperville, IL 60566)] is tempered in water at

1450 F for 1-2 min. Then the material is placed on the opposite

to the restoration being removed.

• The patient should close into the material compressing it to

2/3rd its original height, holding steady for about 10 seconds.

• The patient should then open the mouth with a quick

movement. This exerts a constant negative load on the

restoration in a completely vertical direction instead of the

torquing action from the crown remover.

Advantage :

• Effective and highly successful in highly retentive restorations.

• Eliminates any marginal damage that could occur with metal

instrument.

Modification techniques :

1) Typing of ligature wire around contacts.

2) Application of a grappling hook to improve the direction of

unseating forces.

3) Ultrasonic instrumentation

Effect of prolonged ultrasonic instrumentation on the retention

of cemented cast crowns.

Paul S. Olin. JPD 1990 Vol 64(5) p. 563-565.

He studied the effect of ultrasonic instrumentation on the

retention for both zinc phosphate and glass ionomer cemented cast

crowns. A 12 minutes vibrations showed a significant decrease in

retention for both the cements.

He concluded that when it is desirable to try removal and

recementation of a cast restoration instead of refabrication,

vibration used for the specified length of time can be a valuable aid,

used in conjunction with other removal devices.

4) Copper band and stainless steel wire soldering technique

Removing crowns with minimal damage : Nicholas Naffah, JPD, 2003; 89:522.

A copper band is prepared by adapting it to the crown to be removed and soldering a 0.9mm metallic SS wire on the buccal and lingual sides to form a handle.

Several holes are made in the band body and abraded with air borne particles on the inner surface.

Band is placed on the crown and autopolymerising acrylic resins is added on the entire crown and allowed to set.

Once set the crown is removed and the copper band is

separated using a disk.

• If the restoration is not removed intact a variety of crown removal kits are available.

1) Golden west crown remover :

• This uses a sized hole cut in the occlusal of posterior units. A hollow core tap, threaded both inside and outside is tapped into the sized opening and against tooth structure. A pin is inserted into the core of the tap, which engages tooth structure. A small bolt is threaded into the inside of the tap to engage the pin at which point a strong and effective unseating force may be exerted.

• This is much less traumatic than the blow imparted by the crown remover but care must be taken not to drive the pin through foundation or tooth structure into the pulp.

2) Sectioning and prying method :

• The safest but most destructive method of removing cemented units is by cutting a channel through the restoration to prepared tooth structure on the facial or lingual and occlusal or incisal aspects and gently expanding the casting with a large spoon excavator to break the cement joint.

• When this removal technique is used it is advantageous to use a round bur for cutting the metal. The curved cutting leaves of the round bur remain intact and sharper for a much longer time than the angular leaves of a fissure or an inverted cone bur.

This results in more efficient cutting and a major saving of time.

CONCLUSION

• The first consideration when confronted with any failure or

repair situation is to ascertain the cause or suspected cause.

Sometimes this is easy and obvious. If there is a cause that is

correctable it should be taken care of first. Care should be taken

not to become involved in repairs that should have been

remakes. Repairs are usually second best to the original in one

or more ways.

• Imagination and innovation are key factors in successful

repairs. Most failures are unique and present varying challenges

to the dentist. Great satisfaction can be achieved in meeting a

situation and solving it in an effective and economical manner.