Failures of Fixed Partial Dentures

7/11/2019 Failures of Fixed Partial Dentures

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INTRODUCTION :

It is important to be aware of obvious and subtle indications of

prosthesis failure and to have a working knowledge of the procedures that

are necessary to remedy the situation. It is natural that dramatic mechanical

failures, such as fracture attract attention, but it must be remembered that

failures can also be esthetic and biologic in nature. Some failures are the

result of poor patient care, while others occur as a result of defective design

or inadequate execution of the clinical or laboratory procedures. Other

failures like unacceptable colour match with age are normal because

changes in the oral environment that are not related to prosthesis necessitate

its removal and reconstruction. Also, a restoration may simply wear out.

After all, prosthesis cannot routinely be expected to last a lifetime.

BIOLOGIC FAILURES :

1) CARIES :

Caries is one of the most common biologic failures, it may affect a bridge in several ways, either directly at the margins of the retainer,

indirectly by starting elsewhere on the tooth and spreading to the fit surface

of the castings or it may follow cementation failure.

A study was conducted to evaluate the causes of failure and length of

service of fixed restorations. They concluded that caries was the most

common cause of failure and resin veneer metal crowns provided the

longest services of all crown types observed (13.9 years) and failed most

frequently because of worn or lost veneers. (Joanne N.W. et al 1998)

Its detection can be very difficult particularly when complete

coverage is used. At each appointment, the teeth should be thoroughly dried

and visually inspected.

Careful use must be made of explorer when assessing early enamel

lesions because “heavy-handed” examination may damage the fragile

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demineralized enamel matrix. Radiographs are also helpful, particularly

interproximally.

Conventional operative dentistry procedures can generally be used torestore small carious lesions without the need to fabricate a new prosthesis.

Marginal caries can be restored by using amalgam, composite resin, or gold

foil. Carious lesions in certain locations, such as proximal surfaces, may

require removal of the prosthesis to obtain access to the caries. Extensive

lesions may encroach on the pulp, making endodontic treatment necessary,

or the tooth may be so much destroyed by caries that it cannot be restored

and must be extracted. Meticulous oral hygiene must be a routine procedure

for patients with a high caries index and particularly for those who have a

past history of developing carious lesions around restorations. Other

preventive measures should include the use of fluoride containing

dentrifices, home mouth rinses containing fluoride and professionally

applied topical fluoride.

If the caries is secondary to cementation failure, then the bridge must

always be removed and the sooner the better.

2) ROOT CARIES :

Caries of exposed root surfaces can be a severe problem in the age

group commonly seeking fixed prosthodontic care. Root surface caries

seems to be initiated by a plaque of different composition containing more

anaerobic and gram negative organisms than that causing coronal caries.

The presence of Actinomyces viscous is thought to be of special

significance. These organisms seen to proliferate among the filiform

papillae of the tongue.

Tongue brushing twice daily may be an effective means of preventing

the root caries. (Massler M 1980)

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Similarly, xerostomia as a consequence of aging or caused by

medication or irradiation has been implicated as contributing to the etiology

of rampant caries. Only a most vigorous effort on the part of the dentist and patient will lead to restoration of the problem.

Often this requires the placement of large cervical amalgam or glass

ionomer restorations that wrap around the periphery of previously placed

cast restorations. Such restorations are difficult to place, yet, in view of the

constraints, they are a preferred alternative to comprehensive retreatment

with elaborate fixed prosthesis.

The reasons for failure of 142 bridges in 130 patients were assessed.

The results showed that the mean age of the bridges at failure was 6.2 years.

The main single reasons for failure were secondary caries or apical

pathology, but many bridges failed as a result of factors related to design

and structure. Eighteen percent of the bridges were repaired, recemented or

rescued by endodontics alone, 61% were replaced by a new bridge, and the

remainder required a removable prosthesis. (L.V. Foster 1990)

3) PERIODONTAL DISEASE :

It is unfortunate that periodontal disease often occurs following

placement of fixed prosthesis. In some situations, the disease process may

be present in both restored and non restored areas of the mouth but with no

relationship to the prosthesis. It also can be localized around the prosthesis,

as a result of inadequate instruction in prosthesis hygiene, poor

implementation of proper hygiene procedures, or a restoration that hinders

good oral hygiene. Aspects of a prosthesis that interfere with effective

plaque removal include poor marginal adaptation, placing the cavosurface

margin subgingivally, overcontouring of the axial surfaces of the retainers,

excessively large connectors that restrict the cervical embrasure space, a

pontic that contacts too large an area on the edentulous ridge, or a prosthesis

with rough surfaces which promotes plaque accumulation.

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Periodontal disease can produce extensive bone loss that in time

results in the loss of abutment teeth and attached prosthesis. Less severe

breakdown can be treated without fear of loss of the teeth, but treatmentoften involves surgery, which may produce an unacceptable relationship

between the prosthesis and the soft tissue. At recall appointments particular

attention is given to sulcular hemorrhage, furcation involvement, and

calculus formation as early signs of periodontal disease.

A prosthesis that hinders effective plaque removal must be

reconstructed or remade to correct such defects. If mobility of bridge

abutments is noticed, it may be due to periodontal overloading. This may be

result of faulty design, for instance incorporating too few abutment teeth in

the prosthesis or due to incorrect occlusion. If former is the case, remake

will be necessary, but if latter, occlusal equilibration should be done.

4) OCCLUSAL PROBLEMS :

Interfering centric or eccentric occlusal contacts can cause excessive

tooth mobility. If this is detected early, the interferences can be eliminated

by occlusal adjustment without permanent damage. However, traumatic

occlusion on teeth previously weakened by periodontal disease or the long

term presence of occlusal interferences on teeth with normal bone support

can lead to mobility, which cannot be reduced or eliminated through

adjustment of the interfering areas. The prosthesis may have to be removed

and the teeth bilaterally braced with a removable partial denture.

The patient is examined for signs of occlusal dysfunction at each

appointment. An examination of the occlusal surfaces may reveal abnormal

wear facts. The canines, in particularly should be inspected because wear

here will soon lead to excursive interfering contacts on the posterior teeth.

Articulated diagnostic casts should be periodically remade and compared

with previous records, so any occlusal changes can be monitored and

corrective treatment initiated.

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Occasionally the combination of excessive mobility and reduced bone

support require extraction of abutment teeth. The presence of interfering

occlusal contacts can also cause irreversible pulpal damage requiringendodontic treatment. Neuromuscular discomfort related to improper

occlusion can result in prosthesis failure, since occlusal adjustments that are

required to allow the mandible to be properly positioned may cause

perforation of the prosthesis or make the restoration esthetically

unacceptable.

5) GINGIVAL IRRITATION :

The commonest cause of gingival irritation around a prosthesis is

plaque retention because of patient’s poor oral hygiene, because of lack of

care or because of the design of the bridge makes this difficult. Other

factors may be faulty margins of the retainers, incorrect occlusal anatomy,

over contouring of buccal and lingual surfaces, and inadequate

interproximal embrasures.

Irritation of the mucosa by the pontic may also be due to the wrong

choice of material for its fit surface. Acrylic is a particularly bad offender in

this respect and the gingival irritation it causes may be further aggravated by

the deposition of calculus on it. In some cases local gingivectomy has to be

done for satisfactory maintenance of gingiva in region of bridge especially

in case of sanitary pontic where gingival proliferation is likely to occur.

6) GINGIVAL RECESSION :

This may be local or general. If the former, the reason should be

assessed and if possible eliminated. If the latter and there are no aesthetic

considerations, such as the exposed, discoloured root of a non-vital tooth,

the situation may be acceptable as it stands. However, generalized

periodontal therapy may be indicated.

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7) PULP AND PERIAPICAL HEALTH :

At the recall appointment, the patient may reveal having experienced

one or more episodes of pain during the previous months. This couldindicate the loss of vitality of an abutment tooth and should be investigated.

Appropriate corrective measures can then be taken. Post insertion pulpal

sensitivity on abutment teeth that does not subside with time, intense pain,

or periapical abnormalities that are detected radiographically often indicate

the need for endodontic intervention.

One advantage of partial coverage restoration is that pulp health can

be monitored with an electric pulp tester, although the vitality of any tooth

with a complete crown can still be assessed by thermal means. Access to

pulp requires preparation of a hole in the prosthesis through which the

necessary treatment is completed. Frequently, the perforation can be

restored with gold foil, amalgam, or a cast metal inlay without

compromising the prosthesis. The retainer casting may come loose during

preparation of the access opening or the porcelain may fracture,

necessitating remaking of the prosthesis.

During endodontic treatment, an assessment should be made of the

quantity and quality of tooth structure remaining for support and retention

of the restoration. When little healthy tooth structure remains, it may be

necessary to place a post and core and to fabricate a new restoration. It is

recommended that endodontically treated teeth be reviewed radiographically

every few years.

8) TOOTH PERFORATION :

Pinholes or pins used in conjunction with pin-retained restorations

can be improperly located and may perforate the tooth laterally. If the

perforation is located occlusal to the periodontal ligament, it is often

possible to extend the tooth preparation to cover the defect. When the

perforation extends in to periodontal ligament, it may be possible to perform

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periodontal surgery and to smoothen off the projecting pin or place a

restoration in to the perforated area. Certain locations (such as furcations)

may not be surgically accessible and perforation can lead to extraction of the tooth. Lateral perforations may not be detected initially, becoming

apparent only after insertion of prosthesis. Occasionally these perforations

are accessible and can be restored with amalgam, but more often the tooth is

lost. Endodontic treatment is required when pinholes or pins perforate in to

pulp chamber.

MECHANICAL FAILURES :

1) LOSS OF RETENTION :

A prosthesis can come loose from an abutment tooth, and if this

occurrence is not detected early, extensive caries often develops. This loss

of retention can be detected in several ways.

The patient may be aware of looseness or sensitivity to temperature or

sweets. Also, there may be a recurring bad taste or odour, which must be

differentiated from similar symptoms caused by poor oral hygiene or

periodontal problems.

Periodic clinical examinations should include attempts to unseat

existing prostheses by lifting the retainers up and down (occlusocervically)

while they are held between the fingers and a curved explorer placed under

the connector. If the casting is loose, the occlusal motion causes fluids to be

drawn under the casting, and when the casting is reseated with a cervical

force, the fluid is expressed, generally producing bubbles as the air and

liquid are simultaneously displaced. When more than two abutment teeth

are involved in a prosthesis, it is much more difficult, and sometimes

impossible, to detect a single loose retainers.

Removing the prosthesis intact for recementation is often difficult or

impossible. Sometimes judicious malleting or the use of a crown remover is

successful. Other times a direct pull with hemostat forceps succeeds. (metal-

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ceramic crowns should first be coated with autopolymerizing acrylic resin

so they do not chip or crack). Even by the use of prolonged ultrasonic

vibration, crown retention can be decreased.The effect of prolonged ultrasonic instrumentation on the retention of

cemented cast restoration was examined. He concluded that the use of

vibration is considered an advantageous adjunct to other cast restoration

removal devices (Paul S. Olin 1990).

When trying to remove a permanently cemented prosthesis, the

dentist must use great caution. Unless force is applied in the path of

withdrawl, an abutment tooth may fracture.

A loose retainer is usually a sign of inadequate tooth preparation,

poor cementation technique, or caries. In this case the tooth requires

repreparation and a new prosthesis. Some fixed partial dentures come loose

even when maximally retentive preparations have been developed. This

problem is generally caused by excessive span length or heavy occlusal

forces, and a removable partial denture may be the only satisfactory

solution.

2) CONNECTOR FAILURE :

An improperly fabricated connector may fracture under functional

loading. Failures of both cast and soldered connectors have been observed

and are generally caused by internal porosity that has weakened the metal.

Depending on the design and location of the FPD, the patient may complain

of varying degree of pain. When fracture occurs, pontics are placed in a

cantilevered relationship with the retainer casting, and this can allow

excessive forces to be developed on abutment tooth. For this reason, the

prosthesis should be removed and remade as soon as possible. Wedges can

sometimes be positioned to separate the individual FPD components enough

to permit the correct diagnosis. In some cases if a solder joint fails,

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porcelain facings can be detached by boiling in acid and components are

cleaned and relocated in the mouth before they are resoldered.

It is sometimes desirable to repair a broken joint in fixed prosthesesor to replace one loose crown in a multiple unit splint by using a parallel pin

repair rather than to attempt to remove the prosthesis and risk the possibility

of destroying the entire restoration or damaging abutment teeth (T.H. Miller

and K.E. Thayer 1971).

.

3) OCCLUSAL WEAR :

Heavy chewing forces, clenching, or bruxism can produce accelerated

occlusal wear of a prosthesis. When the occluding surfaces are restored with

metal, a casting perforation may develop after several years which allow

leakage and caries to occur, which ultimately leads to prosthesis failure.

If the perforation is detected early, a gold or amalgam restoration can

be placed that seals the area. However, if the metal surrounding the

perforation is extremely thin, a new prosthesis should be fabricated.

When occlusal surfaces are covered with porcelain, dramatic wear of

enamel of opposing natural teeth or the opposing metallic restoration can

occur. This problem is exacerbated by heavy chewing forces, or bruxism.

So, in mouths where 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.

4) TOOTH FRACTURE :

Coronal tooth fracture can be minor or considerable loss of tooth

structure. Small coronal tooth fractures occurs primarily around inlays and

partial coverage crowns as a result of wear and apparent increasing

brittleness of tooth structure with age. If the restoration and tooth structure

surrounding defect can be adequately prepared and still possess sufficient

strength; gold foil, amalgam or resin can be used to restore the area. Large

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coronal fractures generally requires a full coverage restoration to be made.

However, the tooth may require a separate pin-retained restoration to serve

as a core and provide support and retention for a new prosthesis. If thefracture causes a pulp exposure, endodontic treatment followed by

placement of a post and core is necessary prior to fabrication of a new

prosthesis. Abutment tooth fractures under full coverage retainers usually

occur horizontally at the level of the finish line, so that little or no coronal

tooth structure is left. This condition necessitates removal of the prosthesis,

endodontic therapy, a post and core, and a new prosthesis.

Several conditions known to promote extensive coronal fractures of

abutment teeth are :

a) Excessive tooth preparation leaving insufficient tooth structure to

resist occlusal forces.

b) Presence of interfering centric or eccentric occlusal contacts, or

simply heavy occlusal forces on a properly adjusted restoration.

c) Attempting to forcibly seat an improperly fitting prosthesis.

d) Attempting to unseat a cemented bridge incorrectly.

Root fractures are often located well below the alveolar bone crests so

that the tooth must be extracted and a new prosthesis fabricated. However,

ocasionally the fracture terminates at or just below the alveolar bone. In

such cases, it may be possible to perform periodontal surgery, remove bone,

and expose the fracture site so it can be encompassed by a new prosthesis.

Root fractures are most often caused by trauma. They can also occur

during endodontic treatment, forceful seating of a post and core, or the

attempt to fully seat an improperly fitting post and core.

5) PONTIC FRACTURE :

Mechanical failures of pontic may occur because of inadequate

strength. Thus an all-porcelain occlusal pontic should never be used unless

the occlusion is favourable. Similarly the gold framework must always be of

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adequate rigidity. Even slight flexion will cause cementation failure or the

fracture of the porcelain facing.

6) FLEXION, TEARING OR FRACTURE OF THE GOLD :These may of themselves result in failures of the bridge. They may

also result in cementation failures of the retainers or loss of facing.

Most of these disasters may be avoided by providing gold of adequate

thickness, using a proper casting technique to ensure freedom from porosity,

carrying out heat treatment, and making certain that the occlusion is correct.

It is also necessary to remember that the longer the span, the stronger and

thus the thicker the gold will have to be.

7) CEMENTATION FAILURE :

It may be either partial or complete, and is normally the result of

retainers which are inadequate for the bridge in question. With fixed-fixed

designs if there is any doubt regarding the adequacy of retention and

particularly if clinical crowns are short, full crowns showed be employed.

The sides of the preparation should be as near parallel to each other as

possible.

Another important factor is the rigidity of the casting. Even slight

flexion will cause cementation failure and this can only be prevented by

using a hard gold and making certain that it has been correctly heat-treated

and is of sufficient thickness. Besides an inadequate retainer, failure can

also occur because of a poor cementation technique. This may be due to the

wrong choice of material, failure to observe manufacturer’s mixing

instructions, the use of old or contaminated stock, an inadequate powder /

liquid ratio, or the insertion of prosthesis when the cement has started to set.

This latter may result in a weak cement and a casting which is incompletely

seated. Likewise if the teeth are not dried off carefully before cementation,

the bond will be weakened. Where full crowns are being employed, venting

is usually indicated.

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Study of 703 resin-bonded fixed partial dentures, the success rates of

two study groups were analysed where rebonding or renewals were

necessary. Results revealed that rebonding often leads to repeated failureswhere as renewals showed a failure rate similar to the whole of the

investigated failures (C.P. Marinello et al 1990).

Evaluation of 137 cantilevered fixed partial dentures made between

1974 and 1990 clinically and radiographically. The results showed that

failures occurred more when endodontically treated abutments were used

and overall success rate of cantilever fixed prostheses was 70% over a

period of 18 years (Veerle Decock et al 1996).

Eighty-five patients with a total of 103 resin bonded bridges placed

between 1982 and 1989 were evaluated. The results showed that debonding

occurred most frequently in the mandibular arch. Failures occurred more

frequently in men than in women, and prosthesis with more than two

retainers had twice the probability for problems (Paul S. Olin et al 1991).

8) ACRYLIC VENEER WEAR OR LOSS :

Abrasion can result in loss of severe amounts of acrylic on acrylic

veneer crowns and pontics. Abrasion can be caused by functional loading or

abrasive foods and habits, but probably tooth brush abrasion is the most

common cause. Repairs may be effected by replacing lost contours with

autopolymerising resin. This can be done without removing remaining resin.

It may or may not be necessary to add mechanical retention in the form of

undercuts or threaded posts. The composites are now becoming more

popular for these repairs. They are more resistant to wear and maintain

function and appearance longer than acrylic resin repairs.

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9) PORCELAIN FRACTURE :

A) METAL –CERAMIC PORCELAIN FAILURES :

1) FRAMEWORK DESIGN :Sharp angles or extremely rough and irregular areas over the

veneering area serve as points of stress concentration that can cause crack

propagation and ceramic fracture. Perforations in the metal can also cause

failure for the same reason. When the framework thickness is less than

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

much greater regardless of the type of casting alloy. Porcelain fracture may

also occur if the framework design allows centric occlusal contact on, or

immediately next to, the metal-ceramic junction or the angle between the

veneering and nonveneered aspect is less than 90 degrees. These designs

allow occlusal forces to cause localized burnishing of the metal and

distortion, which leads to premature porcelain fracture.

2) OCCLUSION :

The presence of heavy occlusal forces or habits such as clenching and

bruxism and centric or eccentric occlusal interferences can cause failure.

3) METAL HANDLING PROCEDURES :

Improper handling of the alloy during casting, finishing, or

application of porcelain can lead to metal contamination which can create

stress and possibly cracks. Excessive oxide formation on the alloy surface

can also cause separation of the porcelain from the metal. This is most

frequently caused by improper conditioning of the alloys.

4) 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 some problem.

Teeth prepared with a feather edge finish lines or impressions that do

not record all of the finish line can lead to an extension of metal beyond the

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actual termination of tooth reduction and this thin metal may bind against

tooth and initiate a crack in the overlying porcelain. Definite finish lines and

impressions that record proper detail are prerequisites to acceptableceramics.

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.

5) METAL AND PORCELAIN INCOMPATIBILITY :

In rare instances, an alloy and porcelain are found to be truly

incompatibly and successful bonding without loss of the veneer or cracking

is impossible.

PORCELAIN JACKET CROWN FAILURES :

All ceramic restorations are more likely to fail in the presence of

heavy occlusal forces, clenching or bruxism. The preparation from must be

ideal to optimize success.

1) VERTICAL FRACTURE :

The reasons for this are :

a) If tapered finish line is used (such as chamfer), the restoration may

contact on a sloping surface, so that the forces attempt to expand the

prosthesis and leading to vertical fracture.

b) Sharp line angles or incisal edge which acts as area of stress

concentration.

c) When a large portion of the proximal preparation form is missing and

is not restored prior to the impression procedure. When occlusal

forces are applied to the marginal ridge, greater leverage is developed

because of the distance from the point of force application to the

underlying prepared tooth which can cause rotation of prosthesis and

leading to expansive forces and vertical fracture.

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2) FACIAL CERVICAL FRACTURE :

It often assumes a semilunar from and generally occurs with a short

tooth preparation. The inciso-cervical length of the preparation should betwo-thirds to three-quarters that of the final restoration. When the

preparation is short, forces applied at the incisal edge attempt to tip the

prosthesis facially and cause cervical porcelain fracture.

When opposing tooth contact is located incisally to the prepared

tooth, tipping forces are more frequently developed, with the restoration

having a fulcrum on the cervically located incisal edge. This occlusal

relationship can also lead to facial cervical porcelain failures.

3) 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 as well resisted.

Other lingual fractures, not necessarily semilunar in form, are the

result of inadequate lingual tooth reduction in which less than 1mm of

porcelain is present. Exceptionally heavy occlusal forces can also cause

lingual fractures even when adequate porcelain thickness is present.

REPAIR OF FRACTURED PORCELAIN VENEER :

If the porcelain has fractured on an otherwise satisfactory multi-unit

prosthesis, to save the patient from additional discomfort, time and expense,

an attempt at repair rather than a remake may be justified. When the

fractured porcelain is not missing and there is little or no functional loading

on fractured site, it can sometimes be bonded in place with a porcelain

repair system using silane coupling agents or 4-META to promote bonding

with acrylic or composite resin. These repairs appear to have reasonable

strength. Unfortunately, however-the strength of joints diminish with

changes in temperature and with prolonged water storage. Such repair is

considered to have only temporary benefit.

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The flexural strength of porcelain bonded to composite resin

specimens using four organosilane materials were compared. The results

showed that unhydrated specimens had significantly higher bond strengththan the hydrated specimens with all products (J. H. Bailey 1989).

The effectiveness of two new porcelain repair systems which use

coupling agents were compared. The results showed that the repair system

using a bonding agent with acrylic resin is significantly stronger than repair

system using a specific composite resin (R.M. Highton et al 1979).

The bond strength of 4-META (etch free primer with C and B

metabond) to porcelain was evaluated. The mean bond strengths were : 24

hours 17. 4 MPa (± 4.8), thermocycled 19.1 MPa (± 7). These bond

strengths were comparable with or exceed those of other porcelain repair

systems tested (Robert L. Cooley et al 1991).

The bond strength of three commercial composite resins advocated

for repairing dental porcelain was evaluated. They concluded than mean

strength of repaired samples was only 18% of the original strength which

indicates that their use is a temporary clinical procedure (Thomas P. Nowlin

et al 1981).

The bond strengths of porcelain / composite resin repair samples was

evaluated. They concluded that the mean bond strengths were significantly

less after storage in water for 28 days and fractures of all specimens were

caused by adhesive failures occurring at the interface (William A. Gregory

et al 1988).

In either circumstances, the factures area may be repaired with

composite resin retained by means of mechanical undercut and use of silane

coupling agent.

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A technique for repairing fractured porcelain fused-to metal

restoration has been presented. Mechanical retention on the coping must be

created. The porcelain is beveled and etched and treated with silane. Themetal is masked with a mix of unfilled resin and the corresponding shade of

porcelain opaque powder. Then the surface is rebuilt with a microfilled resin

and finished by conventional methods (M.T. Barreto, B.F. Bottaro 1982).

A more permanent repair can sometimes be effected by making a

metal ceramic restoration to fit over the fractured original and it is

appropriate where pontic has fractured. The most commonest difficulty in

this is weakening of connectors during preparation with associated risk of

subsequent fracture of the prosthesis.

There are no satisfactory methods for repairing fractures of all-

ceramic restorations, a new restoration must be fabricated, and if it is due to

excessive occlusal forces which exceed the strength of the restoration, a

metal – ceramic restoration should be considered.

ESTHETIC FAILURES :

Ceramic restorations more often fail esthetically than mechanically or

biologically. Remakes occur more frequently because of poor colour match

than for any other reason. It may be due to :

a) Inability to match the patients natural teeth with available porcelain

colours.

b) Inadequate shade selection.

c) Metamerism may contribute to poor colour matching

d) Insufficient tooth reduction

e) Failure to apply and fire porcelain

f) Incorrect form of framework design that displays metal.

g) Natural teeth undergo colour changes that do not occur in porcelain,

so an unacceptable colour match is caused over the years.

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h) Partial veneer crowns can be esthetically unacceptable because of

overextension of the finish line facially.

i) Visibility of metallic colour of partial coverage casting if thin incisorsare prepared.

j) Marginal fit or cervical form of a prosthesis can promote plaque

accumulation, causing gingival inflammation, which produces

unnatural soft tissue colour or form that is esthetically unacceptable.

FACING FAILURES :

Recementation of a loose facing is indicated if the prosthesis is

otherwise satisfactory. A new facing can be ground to fit the prosthesis

which is done on a trial and error basis and often does not yield ideal fit.

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

be cemented or threaded into the casting if necessary to facilitate retention

of resin.

REMOVAL OF THE PROSTHESIS :

It can be done by four different methods. It is essential that forces be

applied in the correct direction, if the fracture of the abutment teeth is to be

avoided.

1) CROWN REMOVER :

It is the best method because it is relatively easy to see that the force

is being exerted in correct direction.

Initially after placement of the hook at the cervical margin, a few

light blows are given to provide a surface on to which the hook can engage.

Then jerks are given on the end of handle, thus applying a sudden blow to

the retainer and simultaneously second retainer should be held firmly in

place by a assistant. Sometimes, it may also be used below the pontic.

2) USE OF A STRAIGHT CHIESEL :

This is generally used as a means of applying force to a retainer on

which one cannot use a crown remover. Initially, the chisel is placed either

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mesially or distally, at an angle of 450 and tapped sufficiently to create a

facet. Then it is positioned paralled to the line of withdrawl of retainer and

sudden fairly hard blow, of which the patient should have warning, is thenapplied.

3) USE OF A BRASS LIGATURE WIRE :

A 4 feet length of wire is threaded between the pontic and retainer so-

that a loop is created. A metal bar is put through this loop, one end of it held

firmly, and a sudden blow applied to the other end. Great care must be taken

so that the wire does not cut the patient lips.

4) USE OF A SCREW THREAD :

When the retainer has a gold occlusal surface, a small hole may be

drilled in this and then tapped. A threaded bolt is now inserted into the hole

until it reaches the bottom. If the bolt continues to be turned, its base will

then press on the tooth tissue, and with a little good fortune, will elevate the

casting from the tooth.

Should all the above methods fail, the retainer must be weakened, in

the case of full crown by cutting up its side and in case of three-quarter

crown by cutting across the occlusal surface. It will then be possible to

apply an instrument which will spread the crown slightly and break the

cement seal.

CONCLUSION:

The first consideration when confronted with any failure or repair

situation is to ascertain the cause or suspected cause. 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 the second best to the original in one or more ways. Imagination and

innovation are key factors in successful repairs. Great satisfaction can be

achieved in meeting a situation and solving it in an effective and economical

manner.

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BIBLIOGRAPHY :

1) Contemporary fixed prosthodontics, Stephen F. Rosenstiel 3

rd

edition2) Modern practice in fixed prosthdontics, Johnsion, 4th edition.

3) Fixed prosthodontics, Keith E. Thayer

4) Fixed bridge prostheses, D.H. Roberts, 2nd edition.

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and fixed partial denture failures”. Length of service and reasons for

replacement”, JPD 1986, 56(4), 416-21.

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1980, 44, 147.

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retention of cemented cast crowns”, JPD 1990; 64, 563-5.

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dentures; JPD 1971; 25(4), 382-388.

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516-518.

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14) William A. Gregory, Charles. A. Hagen, John. M Powers,

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1) INTRODUCTION

2) BIOLOGIC FAILURES

a) Caries b) Root caries

c) Periodontal disease

d) Occlusal problems

e) Gingival irritation

f) Gingival recession

g) Pulp and periapical health

h) Tooth perforation

3) MECHANICAL FAILURES

a) Loss of retention

b) Connector failure

c) Occlusal wear

d) Tooth fracture

e) Pontic fracture

f) Flexion, tearing or fractures of the gold

g) Cementation failure

h) Acrylic veneer wear or loss

i) Porcelain fracture

- Metal-ceramic porcelain failures

- Porcelain jacket crown failures

4) ESTHETIC FAILURES

5) REMOVAL OF THE PROSTHESIS

6) CONCLUSION

7) BIBLIOGRAPHY

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DEPARTMENT OF PROSTHODONTICS

INCLUDING CROWN AND BRIDGE

COLLEGE OF DENTAL SCIENCES

DAVANGERE

SEMINAR ON

Presented By

DR. NITIN GAUTAM

(2001-2002)

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COMPLAINTS AND

FAILURES OF FIXEDPARTIAL DENTURES

Failures of Fixed Partial Dentures

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Transcript of Failures of Fixed Partial Dentures