CLINICAL FAILURES IN FIXED PARTIAL DENTURE AND ITS
MANAGEMENTINTRODUCTION: A complication has been defined as A
secondary disease or condition developing in the course of a
primary disease or condition. Although complications may be an
indication that clinical failure has occurred, this is typically
not the case. It is also possible that complications may reflect
substandard care. But once again 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 obvious and subtle
indications of prosthesis failure and 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. II. III. Biologic failure
Mechanical failure Aesthetic failure
I. BIOLOGIC FAILURE: 1. Caries: It is the most common biologic
failure. Caries may affect a bridge in several ways, either
directly at the margins of the retainer, or indirectly by starting
elsewhere on the tooth and spreading to the fit surfaces of the
casting or it may follow cementation failure. Detection: Visual
inspection (Discoloration around margins) Probing margins of
restorations with a sharp explorer Radiographs for interproximal
caries
Causes: Defective margins (supragingival preferred over
subgingival) Loose retainers that allow gross leakage to occur
Incomplete removal of caries prior to restoration Poor design
leading to food accumulation Change in the diet of patient
2
Prevention: Meticulous oral hygiene must be a routine procedure
for patients with a high caries index and particularly for those
who have a history of developing carious lesions around
restorations. Fluoride containing dentifrices and mouthwashes
Management: 1) If carious lesion is small conservative operative
procedures can be performed Good foil is the material of choice for
marginal caries Amalgam is preferred over gold because of its long
term marginal seal and into areas of limited accessibility In
aesthetic areas Resin materials or GIC may be 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
features: - Postinsertion pulpal sensitivity in the abutment teeth
that does not subside with time; intense pain or periapical
abnormality that are detected radiographically. Causes:Excess heat
generation during preparation Excess tooth reduction Pin point
exposure which may go unnoticed 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:Access to the pulp
requires a hole in the prosthesis through
which the necessary treatment is completed. Perforation created
can be restored with gold foil or amalgam. If the retainer casting
becomes loose or porcelain fracture occurs
during access cavity preparation remake of prosthesis. During
endodontic treatment an assessment should be made 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 that were
satisfactorily root filled when the crown or
bridge were made may later give trouble. In such situations
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 Features: -
Gingival recession, furcation, pocket formation, 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 retention by cross pinning, grooves, 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)
ii) 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. Adequate width and depth to resist occlusal stress A
sufficient bulk of gold
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 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. fitting prosthesis/ unseat a cemented bridge
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:
bruxism Centric or eccentric occlusal interferences can lead to
Heavy occlusal forces or habits such as clenching and
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
