05 Clinical Failures and Its Management in Fixed Partial Denture

CLINICAL FAILURES IN FIXED PARTIAL DENTURE AND ITS MANAGEMENT

INTRODUCTION: A compli complicat catio ion n has been been define defined d as ‘A secon secondar dary y dis diseas ease e or condition developing in the course of a primary disease or condition’. Although complications may be an indication that clinical failure has occu occurr rred ed,, this this is typi typica call lly y not not the the case case.. It is also also poss possib ible le that that compl complica icati tions ons may may reflec reflectt subst substand andard ard care. care. But But once once again again this this is usually not true. Most of the time, complications are conditions that occur during or after an appropriately performed fixed prosthodontic treatment procedures. An objective evaluation of an existing restoration is necessary before coming to a conclusion that it is defective and requires either replacement or repair. What constitutes a failure? Are failures absolute or are there degrees of failures?  There are of course minor failures, which are a matter of opinion and could be possibly left without immediate repair or replacement, and there are obvious failures where repair or replacement is essential to avoid further damage to the dentition. Failure may occur at any time. Hence it is important to be aware of obvio obvious us and subtle subtle indica indicati tions ons of prost prosthes hesis is failur failure e and have have a working knowledge of the procedures that are necessary to remember the situation. 1

It is natural that dramatic mechanical failure such as fracture attracts attention, but it must be remembered that failures can be biologic and esthetic in nature. I.

Biologic failure

II.

Mechanical fa failure

III.

Aesthetic failure

I. BIOLOGIC FAILURE: 1. Caries: It is the most common biologic biologic failure. Caries may affect a bridge in seve severa rall ways ways,, eith either er dire direct ctly ly at the the marg margin ins s of the the reta retain iner er,, or indirectly by starting elsewhere on the tooth and spreading to the fit surfaces of the casting or it may follow cementation failure. Detection: -

Visua Visuall inspe inspecti ction on (Disc (Discol olor orati ation on aroun around d margin margins) s)

-

Probi Probing ng marg margins ins of of restor restorati ations ons wit with h a sharp sharp expl explore orerr

-

Radi Radiog ogra raph phs s for for inte interp rpro roxi xima mall cari caries es

Causes: -

Defective Defective margins margins (supragi (supragingiv ngival al preferred preferred over subgingi subgingival) val)

-

Loose Loose reta retain iners ers that that allow allow gross gross leak leakage age to occu occurr

-

Incom Incompl plete ete remo removal val of cari caries es pri prior or to to resto restorat ratio ion n

-

Poor Poor des desig ign n lead leadin ing g to foo food d accu accumu mula lati tion on

-

Chan Change ge in the the die diett of of pat patie ient nt

2

It is natural that dramatic mechanical failure such as fracture attracts attention, but it must be remembered that failures can be biologic and esthetic in nature. I.

Biologic failure

II.

Mechanical fa failure

III.

Aesthetic failure

I. BIOLOGIC FAILURE: 1. Caries: It is the most common biologic biologic failure. Caries may affect a bridge in seve severa rall ways ways,, eith either er dire direct ctly ly at the the marg margin ins s of the the reta retain iner er,, or indirectly by starting elsewhere on the tooth and spreading to the fit surfaces of the casting or it may follow cementation failure. Detection: -

Visua Visuall inspe inspecti ction on (Disc (Discol olor orati ation on aroun around d margin margins) s)

-

Probi Probing ng marg margins ins of of restor restorati ations ons wit with h a sharp sharp expl explore orerr

-

Radi Radiog ogra raph phs s for for inte interp rpro roxi xima mall cari caries es

Causes: -

Defective Defective margins margins (supragi (supragingiv ngival al preferred preferred over subgingi subgingival) val)

-

Loose Loose reta retain iners ers that that allow allow gross gross leak leakage age to occu occurr

-

Incom Incompl plete ete remo removal val of cari caries es pri prior or to to resto restorat ratio ion n

-

Poor Poor des desig ign n lead leadin ing g to foo food d accu accumu mula lati tion on

-

Chan Change ge in the the die diett of of pat patie ient nt

2

Prevention: -

Meticu Meticulo lous us oral oral hygie hygiene ne must must be a rout routin ine e procedu procedure re for for patien patients ts with a high caries index and particularly for those who have a history of developing carious lesions around restorations.

-

Fluor Fluoride ide contai containi ning ng dent dentifr ifrice ices s and and mout mouthwa hwashe shes s

Management: 1) If carious lesion is small



conservative operative procedures

can be performed -

Good Good foil foil is is the the mater material ial of choic choice e for for margi marginal nal caries caries

-

Amalgam is preferred over gold because of its long term marginal seal and into areas of limited accessibility

-

In aest aesthet hetic ic area areas s – Resi Resin n mater material ials s or GIC GIC may may be used. used.

2) If caries is on the proximal surfaces, prosthesis has to be removed to gain access. If the lesion is small the preparation can be extended if  a large amalgam restoration may be required before fabrication of a prosthesis. 2. Pulp Degeneration: Clinical Clinical features: features: - Postinser Postinsertion tion pulpal pulpal sensitiv sensitivity ity in the abutment abutment teet teeth h that that does does not not su subs bsid ide e with with time time;; inte intens nse e pain pain or peri periap apic ical al abnormality abnormality that are detected radiographically. radiographically. Causes:-

Excess Excess heat heat genera generati tion on during during prepar preparati ation on

-

Exces xcess s to tooth redu educti ction

-

Pin Pin poin pointt expo exposu sure re whi which ch may may go go unno unnoti tice ced d

-

Occlusal trauma

-

Cement involved 3

Prevention: - Use of varnish or dentin bonding agent form an effective barrier and prevents underlying pulp from toxic effects of cement and core materials. Management:-

Acce Ac cess ss to the the pulp pulp requi require res s a hole hole in the the pros prosth thes esis is thro throug ugh h

which the necessary treatment is completed. -

Perfor Perforati ation on creat created ed can be be restor restored ed with with gold gold foil foil or ama amalga lgam. m.

-

If the the retain retainer er castin casting g become becomes s loose loose or porce porcelai lain n fractur fracture e occurs occurs

during access cavity preparation  remake of prosthesis. -

Duri During ng endodo endodonti ntic c treatme treatment nt an asses assessm sment ent shou should ld be made made of  of 

the quality and quantity of tooth structure remaining for support and retention of restoration. If it is decreased reinforcement with post and core may be required. -

Teeth eeth that that wer were sati atisfac sfacto torrily root oot fil filled when the cro crown or

brid bridge ge were were made ade may late laterr give give trou troubl ble. e. In su such ch situ situat atio ions ns apicectomy is the solution. Care must be taken not to shorten the root of the abutment tooth more than absolutely necessary so that maximum support for the bridge can be maintained. Note: - Indirect pulp capping is not recommended as its failure may  jeopardize the existing prosthesis. 3. Periodontal Breakdown: Clinical Clinical Features: Features: - Gingival Gingival recession recession,, furcation furcation,, pocket pocket formatio formation, n, mobility mobility of abutment.

4

  This can be either a generalized periodontal breakdown of the whole mouth which may be associated with the drifting of teeth or may be localized to the bridge abutment. Causes:-

Inadequate

instructions

in

prosthesis

hygiene

or

its

poor

implementation by the patient. -

Prosthesis that hinders good oral hygiene o

Poor marginal adaptation

o

Overcontouring of axial surfaces

o

Large connectors that restrict cervical embrasures

o

Pontics that contact too large an area on the edentulous ridge

o

Prosthesis with rough surfaces which promote plaque accumulation

-

Traumatic occlusion

-

Insufficient number of abutment selected

Prevention: - Proper oral hygiene instructions Review appointments Preparation design: - Proper axial contours



flat axial contour are

better than overcontouring as they are easy to maintain and avoid plaque accumulation.  Treatment:-

If less severe scaling and proper plaque control

-

Increased severity – flap surgery, bone graft etc.

-

Correct occlusion 5

-

If prognosis of abutment teeth has decreased than the crown or bridge and the tooth may have to be removed.

4. Occlusal Problems: Clinical Features: - Large wear facets, mobility, tender on percussion, open

contacts,

perforation,

cusp

fracture,

tenderness

of

the

masticatory muscles involved. Radiographically-widened periodontal ligament is seen. Interfering centric or eccentric occlusal contact can cause excessive tooth mobility. If this is detected early, the interferences can be eliminated by occlusal adjustments without permanent damage. However, traumatic occlusion on teeth previously weakened by periodontal disease or 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 area. The prosthesis may have to be removed and teeth bilaterally braced with RPD. Many a times it requires extraction of abutment teeth. In patients with bruxism night guards or occlusal splints may be given. A slightly flatter anterior ramp is preferred in clenchers than ordinarily given. Neuromuscular discomfort related to improper occlusion can result in prosthesis failure, hence selective reshaping of defective contacts and restoring or replacing teeth in more favorable position should be done to accommodate occlusal forces.

6

5. Tooth Perforations: Pin

holes or pins used in

conjunction

with pin retained

restorations can be improperly located and may perforate the tooth laterally. •

If perforation is located occlusal to PDL – it is often possible

to extend the tooth preparation to cover the defect. •

If perforation extends into the PDL – perform periodontal

surgery to smooth off the projecting pin or place a restoration into the perforated area. •

If area is not accessible – lead to extraction of tooth.

•

Perforations may not be detected initially, becoming

apparent only after insertion of the prosthesis. Endodontic treatment is required when pinholes or pins perforate into pulp chamber. II. Mechanical Failure: 1. Loss of Retention:  This occurs mainly due to leverage and unequal occlusal loads on

different

parts of

the

bridge.

Loose

retainers

cause

rapid

destruction of the abutment tooth. Saliva and plaque and pumping action of loose retainer are responsible for caries leading to rapid destruction of abutment teeth. Clinical Features: - 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. 7

Detection:-

Sometimes the patient is aware of movement developing in the

bridge. -

Diagnostic test is to examine the bridge carefully without drying

the teeth, pressing the bridge up and down (occlusocervically) and with a curved explorer – looking for small bubbles in the saliva at the margins of the retainer. -

When more than 2 abutment teeth are involved in prosthesis, it

is difficult or impossible to detect a single loose retainer. Management:-

If retainer becomes loose prosthesis must be removed so that

the abutment teeth can be evaluated. -

If the restoration can be dislodged from the prepared teeth

without damage and no caries is present, it is possible to recement the

prosthesis.

Improper

cementation

procedures,

such

as

contamination with moisture or increased cement space may have caused the problem. -

If the prosthesis reveals loss of adequate retention, teeth should

be modified to improve the retention

and resistance form.

Additional

grooves,

retention

by

cross

pinning,

boxes

etc.

Alternatively it may be necessary to include additional abutment to increase overall retention or change the design in some other way (i.e. use of full coverage instead of partial coverage). In case of  grossly destructed teeth, core build up may be done to support the

8

retainer or surgical exposure of crown can also be done. After all this a new prosthesis is fabricated. -

Sometimes FPD come loose even when maximally retentive

preparation have been developed. This problem is caused by excessive span length or heavy occlusal forces – A RPD may be the only satisfactory solution. -

“It is better for teeth to have no cover than loose cover”.

-

Because there is usually less permanent damage or plaque is not

retained against the surface of preparation and the patient is obviously aware of the problem and seeks treatment quickly. 2. Connector Failure/ Solder Joint Failure:  There are several points to watch if a breakdown of the solder  joint is to be avoided. i)

Adequate width and depth to resist occlusal stress

ii)

A sufficient bulk of gold

Causes:-

Connector failure can occur under occlusal load. When fracture occurs pontic is placed in an cantilever relationship with the retainer casting which may lead to excessive forces on abutment teeth. Hence prosthesis should be removed and remade.

-

A flaw / inclusion in solder itself (porosity)

-

Failure to bond to surface of metal

-

Joint not be sufficiently large for the condition in which it is placed.

9

-

Improper flow of metal due to decreased width between joining parts. Minimum width for solder to flow properly is 0.25mm.

 Treatment:-

Fracture connectors are difficult to detect in an abutment teeth with no mobility. Wedges are placed beneath the connector to separate the FPD components to confirm diagnosis. Occasionally an inlay like dovetail preparation can be developed in metal to span the fracture site and casting can be cemented to stabilize the prosthesis.

-

If this is not possible, and a remake cannot be rapidly accomplished, the pontics should be removed by cutting through the intact connectors. A temporary RPD can be inserted to maintain the existing space and satisfy esthetic requirements.

-

It is better whenever possible to join multiple unit bridges by solder joint in the middle of pontics before porcelain is added.  This gives much larger surface area for the solder joint and it is also strengthed by porcelain covering.

Effect of connector design on the fracture resistance of all ceramic FPD. JDP 2002; 87 -

The results of this study

showed that the occlusal embrasure

can be designed as sharp as is practical for the aesthetics of an all ceramic 3 unit FPD; provided that the gingival embrasure has a increased ratio of curvature to increase the fracture resistance. 3. Occlusal Wear and Perforation: 10

Heavy chewing forces, clenching or bruxism can produce accelerate occlusal wear of a prosthesis. Clinical Features:- Attrition of opposing teeth, polished facets on the retainers/ pontics, gingival recession or inflammation. Causes:-

Faulty

preparation

were

occlusal

clearance

for

metal

is

inadequate. -

Even with normal attrition, occlusal surfaces of posterior teeth wear down substantially over a period of time.

-

Gold crowns made with 0.5mm or so of gold occlusally may wear through a period of 2-3 years.

-

There perforations allow leakage and caries to occur which leads to prosthesis failure.

Management:- If perforation is detected early, a gold or amalgam restoration can be placed. Other materials – resin, composite and GIC o

If perforation is over amalgam core, leave it untreated and

check it periodically. o

If metal surrounding perforation is extremely thin a new

prosthesis should be fabricated. o

If occlusal surfaces are covered with porcelain, wear of 

ceramic is not a problem, instead the opposing natural teeth shows dramatic wear of enamel. This problem is exacerbated by heavy chewing forces, clenching or bruxism and often requires the

11

restoration of abraded teeth. The same occurs when porcelain opposes metallic restoration. So, in mouths in which occlusal wear is anticipated, it is better to place metal over occluding surfaces to minimize wear and maintain the integrity of natural teeth.

12

4) Tooth Fracture: a) Coronal fracture: Coronal tooth fracture can be dramatic, resulting in considerable loss of tooth structure, or it can be minor with little significant damage. Causes:-

Caries of abutment teeth

-

Excessive tooth preparation which may leave insufficient tooth structure to resist occlusal forces.

-

Preparation may have been composed mainly of restorative material which was not retained in sound dentin with pins.

-

Presence of interfering centric and eccentric occlusal contacts or even heavy occlusal loads.

-

Fracture can also occur when attempts to forcibly seat an improperly

fitting

prosthesis/

unseat

a

cemented

bridge

incorrectly. Management:-

If defect is small it is restored with amalgam, gold foil or resin to provide additional years of service.

-

If there is a question regarding the integrity of the remaining tooth structure or restoration, a new prosthesis should be fabricated so that it encompasses the fractured area.

-

Large coronal fracture around partial coverage retainers, then full coverage restorations may be fabricated. Tooth may require separate pin retained restoration to serve as core and provide support and retention.

13

-

If fracture causes exposure of pulp, endodontic treatment along with post and core; abutment preparation should involve placement of bevels to increase resistance form.

-

Abutment tooth fracture under full coverage restoration usually occur horizontally at the level of finish line. This necessitates removal of prosthesis. Endodontic treatment



post and core



new prosthesis. b) Root Fracture:Causes:- Most often due to trauma -

During endodontic treatment, forceful seating of post

-

Attempts to fully seat an improperly fitting post Fracture may not be immediately apparent and only become

detectable with time. Root fracture are located well below the alveolar bone, so it must be extracted and new prosthesis fabricated. Occasionally 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 that it can be encompassed by new prosthesis. c) Pontic fracture/ failure:Mechanical

failure

of

the

pontic

may

occur

because

of 

inadequate strength. Thus an all porcelain occlusal pontic should never be used unless the occlusion is favorable.

14

Similarly the gold framework must always be of adequate rigidity. Even slight flexion will cause cementation failure or fracture of  the porcelain facing. Probably one of the commonest cause of pontic failure is a faulty occlusion particularly in lateral excursions, which was not corrected when the bridge was placed. An acrylic facing will wear and discolour quite rapidly. Tissue contact of pontic – extensive area of tissue contact is cited as major cause of failure. Area of contact should be small and convex. Mesial, distal, lingual and gingival embrasure should be wide open to allow easy cleaning. 5) Porcelain Fracture: Porcelain fracture occur with both metal ceramic an all ceramic crown restoration. The majority of PFM fracture can be attributed to improper design characteristics of the metal framework or to problem related to occlusion. All ceramic restorations commonly fail because of deficiencies in tooth preparation or presence of heavy occlusal forces. a) Metal-Ceramic Porcelain Failure: Framework 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 same reason.

15

•

An overly thin metal casting does not adequately support

porcelain, so that flexure and porcelain fracture are allowed. •

Overbuilt porcelain unsupported by metal in PFM may

fracture because of cohesive failure within the porcelain. •

In PFM restoration porcelain fracture result from framework

design that allows centric occlusal contact, on or immediately next to the metal ceramic junction. •

When angle between veneering surface and non-veneered

aspect of the casting is less than 90°. These designs allow occlusal forces to cause localized burnishing of metal and distortion, which leads to premature porcelain fracture. Occlusion:•

Heavy occlusal forces or habits such as clenching and

bruxism •

Centric or eccentric occlusal interferences can lead to

failure, or failure may also be due to uncorrected occlusal slides, 16

which create deflective contact of

opposing teeth with

the

prosthesis. Metal Handling Procedures:Improper handling of alloy during casting, finishing or

•

application of the porcelain can lead to metal contamination. Bubbles may form at metal ceramic junction, when

•

porcelain is applied, creating stress or possibly cracks. •

Severe contamination

•

Excessive

oxide

layer

on

metal,

due

to

improper

conditioning of base metal alloys can lead to separation of porcelain from metal. Preparation, Impression and Insertion: Preparation with slight undercut can cause binding of the prosthesis as it is seated, which initiates crack in the prosthesis. This may go unnoticed until premature postinsertion failure occurs. An impression that is slightly distorted can lead to same problem.   Teeth with feather edge finish line or impression which do not record all finish lines can lead to extension of metal beyond the actual termination of tooth reduction. The thin metal may bind against the tooth and initiate a crack in overlying porcelain. Good preparation with definite line and impression that record proper detail are prerequisites to acceptable ceramics. Metal and Porcelain Incompatibility:

17

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.

18

Repair of fractured metal ceramic restorations:•

Best method is fabrication of a new prosthesis

•

Resin materials are often used to rebuild the porcelain

form in area where fracture has occurred, adequate to good colour matching can be achieved. Drawback is lack of longevity and discolouration. Even light cure composites can be used. Retention

of

these

materials

is

mainly

due

to

mechanical

interlocking so if used in areas of heavy occlusal forces repair often fails shortly after insertion. •

If fracture is due to heavy occlusal forces the contact

should be avoided at the metal ceramic junction, and it should be at least 1.5mm away from the junction. •

A more permanent repair is possible if adequate thickness

of metal available. Steps – -

Removal of remaining porcelain

-

Drill several pin hours (4-5) to depth of 2mm and make impression

-

Creating pin retained metal casting 0.2 – 0.3mm thickness out of  a metal ceramic alloy to fit over exposed metal framework.

-

Fusion of porcelain to the pin retained casting and establish normal form

-

Cementation of casting in position

-

If there is any risk of pontic area flexing, porcelain should be carried on to the lingual side of the pontic to stiffen them further.

19

Sleeve Crown:When a considerable portion of porcelain is lost from labial/ incisal surface of a retainer or pontic it is often possible to repair that replace the entire unit. The porcelain facing is removed with some of  the underlying metal from the labial surface. Porcelain as well as metal are removed from incisal third of the palatal surface. This is a simple procedure when damaged unit is pontic, but when the damaged unit is a retainer and underlying pulp has to be considered. Common mistake is removal of too little porcelain and metal. An impression is made of this and the two adjacent units. The technician is then asked to make metal ceramic crown that will have 2 surfaces instead of usual four. This sleeve crown is then cemented in usual way. If too little porcelain is removed from original unit, the new sleeve crown will fill slightly bulky.

20

b) Porcelain Jacket Crown Failures:Since porcelain jacket crown have been in use for rarely a century, considerable clinical experience related to their failure is available. With good preparation considerable success has been achieved on incisors, whereas fracture are more frequently observed when restorations are placed on posterior teeth and on canines because of  occlusal force on these teeth. Cause:- Quality of tooth preparation and magnitude of occlusal load are the main factors that determine clinical success or failure. They are more likely to fail in presence of heavy occlusal forces clenching/ bruxism. Prevention:- Tooth preparation should be adequate but not excessive.  Tooth reduction must be designed to support the restoration since no metal is present to provide support. Management:-

Short term repair can be done with GIC, resin and light cure

composites. -

Severely

chipped

all porcelain

crowns

must

therefore

be

replaced by a new crown. -

If an early failure occurs without any clinical/lab defects heavy

occlusal forces are likely to be present that exceed strength of  restoration. Metal ceramics should be seriously considered for the new restoration.

21

-

If failure occurs after many years of service and optimal esthetics

is still required a new all-ceramic should be considered. -

If fracture is due to trauma it should be replaced by another all

ceramic restoration particularly when old restoration has served successfully for sometime. Types of Ceramic Fracture:a) Vertical Fracture:-

Marginal area of jacket crown is often more closely adapted to

prepared tooth than other areas. If tapered finish line is used, restoration contacts the tooth on a sloping surface resulting in forces that attempt to expand the restoration which are not well resisted by porcelain, leading to vertical fracture. -

Sharp areas on tooth such as line angles and incisal angles

produce areas of high stress in restoration, leading to vertical fractures. -

A round preparation form that does not provides adequate

resistance to rotational forces can also cause vertical fracture. b) Facial Cervical Fracture: Often assumes a semilunar form (Half moon fracture), generally occurs with a short tooth preparation. Inciso cervical length of the preparation should be 2/3rd to 3/4th that of the final restoration. When opposing tooth contact is located incisally to prepared tooth, tipping forces are more frequently developed, with the restoration having a fulcrum on the cervically located incisal edges, leading to facial cervical fracture. 22

Prevention:- Give 45° level

23

c) Lingual Fracture: Cause:-

When occlusion is located cervically to the cingulum of the

preparation, when forces on the porcelain are more shear in nature and not as well resisted. -

Inadequate lingual tooth reduction, in which