failures of restorations / orthodontic courses by indian dental academy
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Contents Introduction
Ways in which restorations fail
Failure rates of common restorations
Causes of failures
Evaluation system for restorations
Failures common to all restorations & causes
Failures of specific restorations
(A) Failures of amalgam restorations
(B) Failures of pin-retained restorations
(C) Failures of glass ionomer restorations
(D) Failures of composite restorations
(E) Failures of inlays
Conclusion
References
1
INTRODUCTION
Failure may be defined as the inability to meet the desired outcome. On
specifications that have been established by national bureau of standards and other
institutions of standardization and specifications, little chances exist of
manufacturers selling inferior quality restorative materials.
Majority of restorative failures in dentistry can be attributed to the
hindrances of the operator himself.
Everything done from the time of cavity preparation, until the restoration is
polished has a definite affect on the success and failure of a restoration.
Being critical about your work is good but being too critical about them aint
so good either.
It is salutary to replace a restoration that has been condemned as , only to
produce a new restoration with just as many, if not ‘more’ faults, When the
manikin turns into a real life person with fears, aspirations, and a small wet
wriggling mouth, the difficulties become compounded.
Combined efforts of meticulously done work, and maintenance by the
patient is bound to yield fruitful results.
Ways in which restorations fail (Acc. to wilson & fuzzi)
Failure
New Disease Technical Failure
Caries & Tooth wear Fractured restoration
Periodontal disease Marginal breakdown
Pulpal problems Tooth fracture
Trauma Defective contours
Failure of retention2
(ACC TO JENDERASON & RONING )
Failures of restorations can be characterized as.
Secondary caries
Marginal deterioration
Tooth fractures
Loss of anatomy
Loss of aesthetics
Restoration fractures
(Acc to mount et al)Failure of tooth structure Failure of restorative material
Failure of enamel margin failure of margins
Failure of dentin margin # or collapse of material
Bulk loss of tooth structure Total loss of restoration
Split root
Loss of vitality
Failure rate of common restorations
(Wilson, roulet, Fuzzi)
Annual Failure % Restoration Type All
Studies Studies 73 yr
Longitudinal studies
Cross-sect studies
Amalgam Restoration Direct post composites GIC restorations Cast gold inlays & onlays composite inlays onlays Ceramic inlays & onlays Anterior Restoration (III & IV) Cervical restorations (Class V)
0-70.7-90-14.40-5.90-100-7.10-11.60-26
0-70.7-90-14.30-5.91.5-9.80-4.30.5-11.60.3-7.2
0-70.7-5.90-14.40-2.60-100-7.10-11.60-26
1-6.33.3-9--0.5-5.9---0.8-41-31.6-5.9
3
Principle problems of individual restoration
Amalgam - Secondary caries, High incidence of bulk &
tooth
Cervical overhang,
Marginal deterioration
Composites - Wear Of restoration,
Discoloration, Marginal Deterioration,
Secondary caries
GIC Bulk fracture Due to low Mechanical strength,
(Ironically) Secondary caries.
Inlays :- Cast Gold :- Tooth fracture Marginal defects,
Retention
ceramic Marginal & Bulk fracture,
Marginal discoloration & degradation
Failures in General occur due to :-
Material used Operator
A) Faulty production (Inferior Products) A) Improper diagnosis & wrong
treatment modality suggested
B) Improper storing & handling, B) lack of knowledge about use
packaging of restorative material
C) Impurities incorporated C) Lack of skill
D) Technique sensitivity of material D) casual attitude & manipulative
techniques
E) Inhibitions of the material itself
patient
4
A) Not following post-operative instructions & maintenance
B) Improper Oral hygiene protocol c)deleterious habit
Any shortcomings occurring during following stages cause adverse effects to
restoration
Operative stage
Handling storage & dispensing of material
Manipulation stage
Insertion stage
Finishing & polishing
Post-Insertion & maintenance stage
Patient maintenance
Common Phenomenon Leading to Failure Microleakage
Def :- ‘The clinically indetectable passage of bacteria and bacterial
products, fluids, molecules or ions from oral environment along various gaps
present in cavity restoration interface’.
Three Possible routes :-
1) Within or VIA smear layer
2) B/W smear layer & cavity varnish/cement
3) B/W varnish/cement & restoration
A minimum of 10 um space definitely exists between a restoration and
tooth surface which is not clinically perceivable but large enough to allow
ingress of bacteria and their products.
Properties of restorative materials promoting microleakage
Major contributors :-
1) Coefficient of thermal expansion (CTE) change in length per unit
length of material per degree change in temperature
More deviation of CTE
5
Of material from Higher rate of
CTE of tooth microleakage
Material CTE (x 10-6 %)
Tooth
Crown enamel
Dentin
Amalgam
Composite
GIC
Pure Gold
Aluminous Porcelain Inlay wax
11.4
8.3
25.0
20.0-25.0
11.0
14.0
6.6
400.0
2) Polymerization shrinkage :-
Seen with resin restorations , occurs when monomer chains are
polymerised to form polymer chains
This shrinkage pulls material away from walls of cavity
Type Value
Conventional Comp
Organic Comp
Microfilmed
Hybrid
1.5-2.0%
2.5-3.5%
1.3-1.5%
2.2-2.5%
3) Property of adhesion
Adhesion is attraction of molecules of two different substances to each
other when brought in close contact.
Influenced by :
Wetting capability
Surface energy6
Presence of water & smear layer
Surface roughness etc.
Better adhesion – lesser gap – lesser Microleakage
e.g Leaving margins of inlay unfurnished exposes cement more to leakage
Improper isolation of composites
Surface contaminants More Leakage
Inadequate bond
Minor contributors :
Creep
Elasticity
Resistance to fatigue
Solubility
Role of smear layer :-
Generally 1-2 mm thick consists of :
Blood saliva, bacteria’s enamel & dentin particles smear layer may be
pushed to 1-5 um in tubules forming ‘Smear plugs’
2 Schools of thought for smear plugs
1) Prevent permeability of dentin by blockage
2) Smear itself source of bacteria’s
Best way :- Fixing smear layer by 25% tannic acid, polyacrylic acid 10%
Partial removal of layer
Leaves smear plug intact
Makes sterile, inert, non-toxic synthetic smear layer.
Secondary cariesThese are caries around a restoration, also known as ‘Recurrent caries’
Etiological Factors 7
Marginal leakage – around restoration
When width of marginal defect is than 50 um risk is lower
Ditching of restoration
Marginal fractures
Rough restoration surface
Poor hygiene maintenance
Improper cavity preparation
Microbiology :-
Resemble pit & tissue caries type
S. Mutans & lactobacilli
Found in increased number in secondary caries
(Fonta na t al 1996, 12)
Fitzgerald et al (1994)
stated role of 3 major organisms
S. Mutans – 35 %
S. Sanguis – 24 %
S- Salivarius – 14% in samples
Other isolates,
S. gordonii
S. milleri
S. oralis
S. mitis
Actinomyces found in 46% samples though in less numbers.
Studies :-
I) Pimento et al (1995) 47
Study on amalgam restoration (1497 samples)
47.16% - non-ditched surfaces
52.94% - non-ditched surfaces without caries
58.82 – ditched with caries8
41.18 – ditched without caries
II) Espelid and tveit (1991)10
Classified secondary caries.
S1 initial carious lesion characterized by discoloration only
S2 lesions characterized by softness and/or cavitation on root surface
S3 Lesions cavitation on root surface only.
S1 73.3 %, S2- 58.5%, S3 – 89.7%
didn’t specify status of occlusal caries
Major (1998) 44
3.8 % - Secondary caries with class I amalgam
0.4 % class I composite
4.3 % GIC
2.3 % unspecified
Class II restorations
Amalgam
composite GIC
Gingival
90%
75%
60.5 %
Occlusal
5%
8%
10%
Other surf
10%
15%
10%
Histopathology :-
Process :
Penetration of hydrogen ions-key role in demineralization
Penetration occurs along
Microspaces – capillary forces, diffusion difference in electrical potential b/w
tooth & restoration.
Defects in restoration
Fracture lines in tooth or restoration9
Studies show,
Both wall and outer surface lesions 60%
Outer lesion and no wall lesion 20%
Wall lesion and no outer lesion – 11.9%
Diagnosis
Visual and tactile method
Transillumination
Anterior portion of oral cavity
Radiographs
Especially bitewing
Inhibition – incipient lesions
Latest
Tuned Aperture computer topography (Tact)
Offers 3-dimensional images of synthesized image slices, by tuning number of
projections at angular disparity b/w projections
Advantage :- Can be added to digital system without added costs.
Loss of anatomy(Faulty contacts)
I) Too broad a contact c(buccolingually or occlusogingivaly)
Change in anatomy of co1 and tooth increased degree of food impaction due to
improper shunting of food
II) Too narrow a contact
Food impaction vertically, plaque accumulation. Inaccessibility to hygiene
measures
III) Loose contact
Continuity created b/w co1 & embrasure leads to periodontal destruction &
Secondary caries
IV) Contact too occlusally
Flattened marginal ridge leads to fracture of restoration10
V) Contact too gingival
increased Depth of occlusal – embrasure
Impingement of food
VI) Contact placed too buccally or lingually
Flattened restoration on expense of buccal or lingual proximal wall
Decreased Strength prone to fracture
Failures of specific restorationsFailures of amalgam
Introduction
Silver amalgam is indoubtly the most commonly used restorative material.
It correctly used and compared with any other restorative material the advantages
of silver amalgam always surpass the disadvantages.
The average life span of an amalgam restoration is upto 8-10 yrs if
manipulated correctly. Though failures occur. They are mostly due to faulty cavity
preparation or faulty manipulation.
Healy and Philips (1949) evaluated 1521 defected amalgam restorations and
reported
56 % Failures :- Due to improper cavity preparation
42 % Failures :- Due to faulty manipulation
Types of Amalgam Failures
At Visual Level:
Secondary caries
Marginal fractures
Buck fractures
Tooth fractures
Dimensional change
11
At Microstructural Level
Corrosion and tarnish
Stresses associated with masticatory forces
Pain following restoration
Pulpal and periodontal involvement
Amalgam Failures Can Be Attributed To following Causes
Failures due to faulty cavity preparation.
Failures due to poor matrix adaptation.
Due to faulty amalgam manipulation.
Due to improper condensation.
Failures due to contamination.
Improper finishing and polishing procedures.
Post-operative pain.
Microleakage of amalgam.
Tarnish and corrosion
Role of creep
Role of faulty contacts
Effects of bleaching.
Faulty Cavity Preparation :
Improper cavity preparation leading to recurrence of caries and fracture of
restorations is greatest single factor responsible for failures in amalgam.
Different causes that can occur at various steps while preparing cavities are:-
Inadequate occlusal extension:-Inadequate extensions into pits and fissures increases the chances of
recurrent caries particularly in patients with high caries index. Thus all
12
susceptible pits and fissures should be included while terminating margins in
areas that can be finished.
Inadequate extension of proximal box:-Embrasures if not involved adequately are not amneable to brushing and
cleaning. These result in secondary caries affecting the life of the restoration.
However radical extension of the proximal box will weaken the tooth structure
leading to fracture of restoration.
Special attention in this category should be given to lower bicuspid and
distal embrasures of maxillary and mandibular 1st molars where frail walls can
be formed easily.
Over extensions of cavity prepared walls:-
One fourth of inter-cuspal distance facio-lingually is the ideal requirement
for amalgam restoration to possess adequate strength for functioning.
Caries Involvement Suggested protocol
1. 1/4th of Facio-lingual distance
2. ½ of facio-lingual distance
3. 2/3rd of facio-lingual distance
Simple preperation
Considering cuspal capping
Cuspal capping mandatory
This is because amalgam acts as a wedge between the opposite cusps and
tries to split them apart thickness of amalgam required for capping :
Functional cusps-2 mm
Non-Functional cusps-1.5mm
If thickness required is not provided fractures result inadverently.
It has been calculated that 1.5mm of minimal amalgam bulk is necessary to
resist fractures
13
It pulpal floor is not smooth or is curved the restoration causes a wedging
effect and increases chances of tractor of tooth.
Butt joints especially where occlusal stresses are to be encountered are
essential. Thus the cavo-surface angle has been suggested to be 90o or
preferably 110o.
Cavosurface angle
More acute :- Fractures of tooth margins
More obtuse :- Marginal amalgam fracture
under occlusal tresses.
Cavity margins are to be finished so as to remove unsupported enamel rods
susceptible to fractures and resulting secondary caries failure to round off axio-
pulpal line angle as well as internal line-angles and point angles results in
concentration of forces at these places resulting in fractures of the material or
worse the tooth itself.
By rounding axio-pulpal line angle increase bulk of amalgam for strength is
also obtained. Very narrow isthmus related to rest of the cavity preparation and
co-positioning of the isthmus and axio-pulpal line angle results in fracture of
proximo-occlusal restoration due vulnerability of these areas to be the weakest
points of cavity preparation.
Such phenomenon can also occur due to inadequate proximal retention
form. Undermining of mesial and distal walls of preparations can result in fracture
of mescal or distal marginal ridge due to these areas being unsupported. Thus it is
always advised to keep mesial and distal walls straighter.
The retentive element of the cavity should be in dentine without undermining
enamel so as to give proper support to the restoration or it lead to fractures.
Incomplete caries removal:-
Incomplete caries removal:-14
Incomplete caries removal can lead to failures either by:-
1. FURTHER INVOLVEMENT AND PULPAL INSULT.
2. FRACTURE OF RESTORATION DUE TO UNSUPPORTED
MATERIAL.
If pulpal floor is not flat there will be inability of the restoration to resist forces
directed along long axis of tooth.
This leads to stress concentration and as a result fracture of restoration.
Poor Matrix Adaptation :-
Proper matrix selection is mandatory for a proximal restoration to be
successful. A Minimal thickness of 0.03-0.05mm is required for a matrix to be
burnishable and allow condensation of amalgam without deformation.
Also an extension of 0.5-1mm beyond cavo-gingival line angle of cavity
and similarly above level of marginal ridge is required for proper condensation of
amalgam.
The band should also be stable after application because if not so it can lead
to distorted restoration, gross marginal excess, uncondensed mass of amalgam,
leading to failure. The use of a wedge is justified and mandatory. Also, if band
width is too large it will lead to creations of an open contact or a contact too
occlusally.
If Band width is less it will allow amalgam to escape and form an overhang
resulting in tissue irritation & destruction or incorporation of amalgam in tissues.
Faulty Amalgam Manipulation:-
Mercury – Alloy Ratio :-
Serious loss of structure was reported when residual mercury is in an excess
of 55% in a restoration.
Higher mercury content used during mixing results in higher residual
mercury which cannot be effectively removed by squeezing or condensation.
This high mercury results in :-15
Decrease in crushing strength.
increase in flow and increased susceptibility to tarnish and corrosion .
One should prefer minimal mercury technique which gives proper mixes with
use of dispensers for correct proportioning or amalgamation.
Mulling with bare hands causes incorporation of contaminants esp moisture
into the mix which is deleterious.
esp in zinc containing alloys.
Hardened set amalgam if not removed from the mortars will act as points of
weakness in the matrix of the mix, rendering the restoration prone to failure as
stress concentration occurs at these points.
Undertriturated and over triturated mixes and their effects:-
Undertriturated - Soft-Powdery, Non-coherent mass
Overtriturated Mix - May break already forming matrix
Effective removal of residual mercury is possible only within 4 mins of triturating.
Replastiasing mix by adding mercury seriously decreases strength and
rendering the restoration weak.
Improper Condensation :-
Condensation is a very important step in amalgam restorative procedures as
it reduces the residual mercury contents, and ensures amalgam reaches to all parts
of preparation to obtain a homogenous mix.
Due to improper condensation if voids occur these serve as areas of least strength
in the restoration very susceptible to fracture.
Thus proper condensation is a “Stepping” motion to drive away anyvoids is
advice.
Contamination:-
By Moisture :-16
Bare hand mulling leads to decreased strength esp in Zinc containing alloys
Moisture contamination in oral cavity by saliva and blood:-
Leads to delayed expansion, resulting in marginal flaws, tarnish, pitting
corrosion and pain.
By Materials :-
Any impurities incorporated during the procedure.
e.g. Bare hand manipulation of material to add impurities
Using mix kept on unclean apparatus leads to incorporation of flaws into the
matrix rendering the mix weak and susceptible to degradation.
Improper carving, finishing & polishing
Caries may recur in stagnation areas formed marginal gaps, excess of
amalgam, or in crevices resulting from fracture of excess amalgam.
The main carving should be delayed until the surface offers resistance to
instrumentation.
The correct time is indicated by a particular “Squeaking” sound deviated
from surface “Cry of tin”. The instruments used should be sharp and proper
otherwise defects can be produced in the carvings occasionally excess amalgam at
margins is dressed down to thin flakes or “SPUR” like overhangs which get #ed
away from restoration resulting in areas susceptible to secondary caries.
A rough pitted and corroded surface leads to increased susceptibility for furnish
and corrosion and increased failure rate.
Overcarving :-
Leads to decreased thickness of restoration with increased chances of
fracture.
Undercarving :-
Leads to production of high points causing increased forces on tooth
resulting in post operative pain and potential source for fractures. When carving 17
marginal ridges the instrument should be directed into bulk of restoration,
otherwise the ridge amalgam remains relatively unsupported & may fracture.
Polishing :-
Should not be initiated less than 24 hrs after condensation and carving and
should be done adequately and sufficiently.
If rough surfaces exist they act as sources of plaque adhesion and
subsequent caries progression. These spots also promote corrosion of the material.
If polishing temperature increases more than 65% mercury is released from
amalgam leading to failure by rendering the matrix weak.
Inadvertently this heat may also irritate the pulp and cause deleterious
effects.
Marginal degradation (Ditching)
The “Ditching” around amalgam restorations misthought to be due to
amalgam contraction is mainly due to stress/corrosion dependent defect occuring
in areas subjected to occlusal loading. Magnitude of extent of ditching is directly
related to creep properties so
Increased Creep Increased Ditching
Role of Creep :-
Creep is a critical factor leading to fracture of restoration or teeth. e.g. The
mere fact that incidence of fracture of lingual cusps in mandibular teeth and
buccal cusps in maxilla explains the phenomenon of creep High copper alloys
have low creep rates and are thus more stable.
Material type % CU % Creep Comp Str at 24 HRS(Mpa)
Amalcap Lathecut 6 2.5 410
Dispersalloy Admixed 12 0.25 44018
Sybralloy Spherical 30 0.05 500
Other Factors Responsible for Marginal Deterioration :-
1. Improper Marginal preparation
Poorly supported enamel rods may fracture resulting in crevice
formation.
2. Improper Carving and finishing
“Flashes” around margins may fracture.
3. Excess Mercury
Excess mercury induces weak gamma – 2 phase resulting in weaker
amalgam.
4. Low copper amalgams
Low copper alloys have hi8gh corrosion rates, making margins
porous and # prone.
5. Amalgam Expansion
Material expands – Protrudes- Margins unsupported.
Post – operative pain
Caused due to :-
Hyperocclusion due to undrcarving
Cracks in teeth
Galvanism
Delayed expansion
- Zinc containing alloys on contamination with water.
Microleakage in amalgam :-
Amalgam when freshly condensed does not adapt closely to walls of
prepared cavity.19
Generally a gap of 10-15 mm exists around a restoration and is justified.
Though amalgam later becomes a self-sealing material by virtue of products
of corrosion.
e.g. – Different oxides and chlorides, but if spherical particles of alloy are used or
faulty manipulation done chances of increased Microleakage.
Amalgam “Blues” and “Tattoo” :-
Penetration of amalgam products into dentinal tubules leads to very
anaesthetic condition called “Amalgam Blues” needing re-restoration as desired
by the patient caused by not adhering to proper lining systems. Penetration of
amalgam residuals during restoration in marginal gingiva and when not removed
results in “Tattooing” of gingiva which discolors the mucosa and irritates the
attachment apparatus.
Effects of bleaching :-
These can also have deleterious effects on amalgam
6 % H2O2 Gels – Do not alter surface texture
10-16% carbamide Peroxide - On non-polished surfaces causes corrosion and
increases corrosion susceptibility on polished amalgams too.
Caused due to active oxidation.
Bleaching also Greens the tooth – amalgam interface.
Failures of Pin Retained Restoration Failures may occur in 5 areas :-
1. Within Restoration
2. At Interface B/W Pin & Restorative Material
3. Within pin (Pin Fracture)
4. At interface B/W pin & dentin (Pin-dentin separation)
5. Within dentin (Dentin Fracture)
Within Restoration -
20
Due to :-
1. Improperly retained matrix
2. Movement of matrix
3. Improper condensation
4. Premature removal of matrix
5. High points in restoration
Solution :- Repair or Re-restoration
2) At Pin –Restoration Interface
Due to :- Corrosion products at interface resulting in # of restoration
Solution :- Use of titanium pins or Re-restoration
3) Within Pin (Pin #)
Due to :- Wrongs placement, leading to inadvertent force concentration on body
of pin
Solution :- Removal of restoration & pin drilling another hole 1.5-2 mm away
from original site
Re-Restoration
4) At pin –Dentin Interface
Due to :- Loose pins that do not properly engage dentin, as hole size too large.
Solution :- Preparing pin hole for next pin size or drilling hole at another site.
5) Within Dentin
Due to :- Preparation kept rough on floor uneven direction of forces
stress concentration
dentin fracture
Solution :- Reduce to Hat surface & redrill pin hole
Pulpal damage or exposure, biologic space invasion
1) Heat generation while drilling
Solution :- Pulp capping with calcium hydroxide, redrilling hole 1.5-2 mm away.
21
As most of teeth receiving such restoration have/had extensive restorations /caries
health of pulp already compromised so ideal treatment is ENDODONTIC
THERAPY.
Failures of glass ionomer cements.
Introduction :-
Glass ionomers are one of the most versatile of the acid-base cement and
have many application, used as Restoratives, liners, bases and luting cement.
Outside profession used as bone cement, model material etc. With so, many uses
and implications, criticisms are bound to be associated with the material. Though
failures are to be encountered but most of them still remain within confines of the
operator only.
Disadvantages of the material :-
* Sensitivity to moisture at placement leads to expansion
* Technique sensitive esp in powder : liquid
* Susceptible to dehydration over time
* Less colour stable
* Poor abrasion resistance * Poor acid resistance
* Average esthetics
* Less strength thus contraindicated in stress bearing areas.
* Less tensile strength than composite
Failures of Gic can be visualized as :-
1) Fractures
2) Dislodgment of restoration (By swelling D.T. hydration)
3) Microleakage
4) Gic Sensitivity
5) Porosities
22
6) Colour instability
Failures can be attributed to following reasons. :-
Altering powder liquid ratio :-
Altering powder : liquid – alteration of physical properties
It more than Required powder is incorporated physical properties are altered by
1. Increase in no. of voids & faults
decrease in translucency
2. Marked decrease in strength
Improper Dispensing :-
Bottle of powder it not shaken and fluffed up properly before dispensing
improper mix with weak matrix. occurs
It liquid left to lie on slab or pad takes up moisture and renders restoration weak.
So liquid should be dispensed immediately before mixing.
Altering mixing time, working time :-
Working time of 2 mins from completion of mixing can be achieved with a
mixing time of 7-10 secs.
Decreased Mixing Time :- Leaves unreacted liquid visible in cement
Increased Mixing Time :-Increased Viscosity, decreased Working Time
By 25 secs (30 secs Max) Mixing should be complete any continuation of mixing
will begin to break up newly formed polyacrylate chains & weaken material.
Improper Storage :-
As Gic is a water based material the lids should always be replaced at earliest as
there is increase in viscosity and deleterious effects on physical properties.
Contamination :-
Use of metal instruments for manipulation-corrosion of metal surface –
Incorporation into mix
Colour instability23
Decreases Strength by weakening matrix
Contamination by saliva, blood, pellicle, plaque decrease in strength of GIC
tooth interface bond , leads to adhesive fracture of restoration
Improper or non-removal of smear layer :-
Essential for formation of bond with tooth surface.
Failure to remove smear layer Adhesive # of restoration
10 % Polyacrylic acid conditioning for 10-15 secs (Aboesh & Jenkins 1987)
To dissolve smear layer. It left for more than 20 secs – Demineralization of
dentin. Another alternative, Fixing smear layer by mineralizing solution of 25%
tannic acid or ferric chloride. Unites smear layer to dentin and seals tubules.
Improper tooth support :-
GIC is a tooth supported material at least 2-3 mm of tooth structure required. If
placed at stress bearing areas like cups tips or marginal Ridges
- Restoration likely to #
- Due to Poor Tensile Strength
Porosity :-
Some degree of Porosity is inevitable as two part material mixing.done
Main hazard with Porosity
Compressive strength
Tensile strength
Promotion of crack propagation
Porosity Increased by
Improper dispensing
Improper mixing
Porosity Decreased by
Mixing at low atmospheric pressure 38 % increase in strength achieved (Ngo et
al, 1997a)
Using capsulated materials machine mixed. 24
Dehydration :-
GIC Prone to dehydration, even varnishes seen not to provide significant results.
Leads to Crack propagation
Leads to Bulk fractures
Resin – modified (Light – activated) least prone to dehydration.
Hydration :-
Prone to water uptake during placement and first 24 hrs.
Swelling of restoration - Displacement
Requiring :- Repolishing or replacement
GIC sensitivity :-Caused by dessication
Attributed to washout and open margins from early saliva contamination.
Removal of smear layer by conditioning followed by early cement loss
Permits access to bacteria to open tubules.
Sol :- A hydration period of 2-10 mins prior to restoration es post – op sensitivity.
Improper Finishing :- Dry finishing has deleterious effects.
Marginal Leakage :- Esp in cervical third of tooth prone to leakage more.
Though less critical than other materials.
If occurs leads to
Secondary caries
Pulpal irritation
Failures of direct filling gold :-Due to material
Impurities in material added during production- even small amounts of
impurities in material have pronounced effects on mechanical properties e.g. 0.2%
lead makes gold brittle and thus creation of a non-uniform restoration.
Other Contaminants :- Bismuth
Mercury
25
Impurities incorporated during procedures :-
1. Contaminated gases like SO2 , Ammonia and water vapours during annealing.
2. If flame used is not of Methanol or Ethanol without additives contaminants
are bound to be incorporated.
3. Overheating done during annealing leads to carbon contamination by flame,
tray or instrument making physical properties inferior.
Due to faulty procedures :-
A) Improper caries removal
B) Large cavities :- Inability to take masticatory stress, role of creep and thus
leading to # of tooth though malleable and ductile.
C) Contamination :- A totally dry cavity is mandatory for cohesive condensation,
contamination by blood, saliva etc lead to lack of strength of restoration.
D) Improper Annealing :-
Improper removal of surface contaminants cohesive form.
Overheating makes gold stiller, difficult to condense and ductility.
Contaminants may get incorporated by over heating, use of faulty flame
etc.
Temp below 315O (600f) were inadequate to attain optimum hardness of gold
during annealing.
Improper condensation :-
It restoration not condensed in a proper “Stepping” motion VOIDS can be
incorporated - decreasing cohesive form when in the bulk .
When on surface called “Pits”
These lead to Corrosion, marginal leakage, secondary caries d.t.
Plaque accumulation
High force concentration by hand can damage tooth and insult pulp.
Also high thermal conductivity of gold causes thermal insult to pulp,
Galvanism.26
Failures of composite restorationsComposites have become one of the most preferred esthetic restorations in
modern times. But as they say ............ “All that looks gold is not gold, even these
restorations have their own hindrances,
failures that can be seen in a composite restoration are as follows :-
Discolorations esp at margins
Marginal fractures
Recurrent Caries
Gross fractures of restorations
Lack of contact maintenance
Post-operative sensitivity
Pulpal irritation or damage
Microleakage around composites
Failures caused by the following factors :-
Limitations of operator and process:-
Improper caries removal
Faulty preparation
Faulty handling, manipulation of material
Improper isolation
Contamination
Improper Etching and bonding
Inadequate curing
Bulk placements
Improper finishing & polishing
Limitations of material composite:-27
Polymerization shrinkage
Weak bond strength when cavosurface margin in dentin
Water sorption
Penetration in tissues to irritate pulp
Inadequate polymerization in deep inter proximal areas
Incomplete caries excavation :-
If incomplete caries excavation is done, the left over caries hinders the
bonding mechanism. As studies suggest that the weakest bonding of composite is
to carious tooth structure and early failures are to be expected.
Also if Zinc Oxide Eugenol is not removed fully in any case it hinders the
methacrylate group of resins making the bonding weaker .
Incomplete etching or failure to remove residual acid from enamel tags:-
Proper concentration of etchant and etching time has to be adhered to -
total etching time should not be more than 60 secs (30-60 Secs range). Though
15 Secs etching sufficient for enamel, washing 20-30 Secs (Gels) 10-15 Secs
(Liquids)
Avoid 3-way syringe for drying – Contamination by machine oils etc.
Role of exit angles :-
90 degree - Conservative - Doesn’t expose ends of rods
45 degree - Most common - Superior seal –decreased Microleakage
exposes rods
Concave exit - Most retentive - Least conservative (used in cl IV cases)
Joining convex exit -
Least practical clinically but illustrated rounded ends provide excellent exits used
for stiff composites provide excellent exits
used for stiff composites only
Sem studies – 90 exit – Poorest seal
28
Improper bonding :-Bonding agent is to be applied gently and uniformly all around cavity
walls. Double Coats are to be avoided as these lead to marginal leakage non-
uniform bonding hinders the bond strength to bonding agent.
Also if one has to shift from microfilled resin to a layer of macrofilled, an
unfilled bonding agent if not place weakens the bond and causes fracture at that
point.
Role of evaporation
Lack of isolation
Isolation is mandatory in a composite restoration ideally rubber dam
should be used, otherwise cotton rolls should be kept ready and changed evenly.
Any contact with gingival fluid, saliva or blood
Potential source of contamination
reduces resin to resin bond strength.
Sol – Etching and bonding to be repeated.
Other contaminants :-
Touching the material with hands or fingers
Picking material from tongue etc and placing back
Using unclean instruments
These add impurities to the material rendering it weak and less
colour stable, changing shade characteristics. Always teflon coated instruments to
be used.
Bulk placements
29
Material is to be cured in increaments and each increament should
be as small as possible as gaps may occur after shrinkage of material at tooth
restoration interface.
These lead to post-operative sensitivity, marginal leakage & secondary caries.
Also due to gaps and voids, material is rendered weak and stress
points – source of #
Improper curing
Curing if not done from all sides and for a stipulated period results
in a restoration with marked decreased strength and prone to marginal leakage.
If first curing is not done gingivally the material due to its property
to shrink towards source of light creates a gap between pulpal floor and bulk of
material in occlusal cavities and also leads to gap formation in gingival seat area
in proximal restorations which are prone to leakage’s and fractures.
Improper angle &Path of light :-
As angle deviates from perpendicular, the penetration and intensity
of light is afflicted & reduced.
e.g. Marginal ridge of adjacent tooth blocks light placed at an angle.
Thickness of resin :-
Optimum polymerization occurs at depth of just 0.5-1mm owing to
air inhibition at surface and difficulty of light penetration.
Study showed:-
7 days after 40 sec curing cycle
1mm deep composite – 68-84% Optimum hardness
At 2 mm same composite – 40-60%
At 3mm – only 34%
Air Inhibition :-30
Oxygen in air competes with polymerization and inhibits setting of
resin.
Extent of surface inhibition is inversely related to filler loading.
Undercured layer can vary from 50-500mm or more, depending on
reactivity of photoinitiator used .
Unfilled resins should be cured, covered with air inhibiting gel
(Oxyguard-Commercial Preparation )
Petroleum jelly glycerin & then recured This reduces air inhibition.
Improper light intensity:-
Optimum curing intensity – 468 + 20nm
Blue light – 400mv/cm2
Causes of decreased intensity :-
Age of bulb
Increased Age – Decreased Intensity
Voltage
- Voltage drops decrease intensity
Sterilization of curing tips reduces light transmission
Filters to increase blue light transmission degrades intensity.
Curing distance :-
Distance of 1 mm from occlusal surface- ideal
increase in distance - Decreased intensity
- Decreased strength
Exposure :-
Minimum exposure of 20-40 secs under continuous light is mandatory.
Any deviations in lesser range results m partially cured, inferior
restorations.
Temperature :-
Light cure composites cure less effectively if they are cold during
application (Freshly taken out of refrigerator )
They cure move rapidly & completely at room temp.31
Also most curing lamps produce heat which speeds curing process.
However excess heat by undue application can result in pulpal irritation and
inflammation.
Improper finishing & polishing :
Meticulous finishing and polishing is to be done, As all rough surfaces act
as a nidus for microorganisms (Plaque accumulation)
Special attention in interproximal area as sharp projections – irritate &
inflame gingiva by impingement
Dry Polishing & Finishing is detrimental as it can open dentin margins at
dentin – restoration interface.
Exception- Microfilled composites
Effect of number of flutes of finishing & polishing bur – more the number of
flutes lesser the damage
Pulp irritation or damage :-
It is difficult to differentiate the effect of components of composite resin
itself, the trauma of cavity preparation, and sequelae such as microleakage at
margins
Cytotoxicity Studies State :-
Cured polymerized resin as far as possible causes minimum irritation. but
incompletely cured resin because of presence of uncured resins or surface active
complexes formed b/w low molecular wt. components of light initiator systems.
One potent component is Hema (Hydroxlethyl Mehacrylate )
an essential component of light cured composites,
Highly Hydrophillic
Allergenic
Studies show that it can transverse in tubules appear in pulp & Cause
deleterious effects.
Composite Discoloration :-32
Composite may undergo extensive surface staining intrinsic colour change
or both.
Extrinsic surface staining
Max. water sorption in first 7-10 days
Strong staining agents (Tea, Coffee, cola) penetrate to
depth of 3.0-5.0 mm (Mount & Hume)
Problems accentuate with wear and incomplete curing .
Intrinsic discoloration
Seen in both chemically activated & light activated
Chemically activated – Substantial yellowing in 1-3 yrs due to oxidation of excess
amine from initiator system
Visible light cured systems :-
Lighten in colour & become more translucent during curing e further in 24-
48 hrs. by decomposition of camphoroquinone.
Degradation in oral environment :-
Unreacted methacrylate groups degrade more rapidly. May be leached from
resins
Hydrolytic degradation of barium & strontium
Glass fillers – Pressure build up at resin –filler
interface – crack formation
Type of composite used -
Microfilled less susceptible to hydrolytic degradation
Chemical attack – Breakdown of silane coating
Weakening of tiller- resin bond
Rapid thermal changes – Breakdown of silane coating
In Microfilled :-
Bond b/w prepolymerised particles & Matrix – potential site for
hydrolytic degradation failures.
Role of water sorption :-33
Limited amount may be beneficial
More sorption – Restoration dimensionally unstable
Aesthetically unpleasant
More Water sorption – More Creep rate
Microfilled Resin – 1.5-2.0 mg/cm2
Hybrid & Macrofilled – 0.61.1 mg/cm2
Water sorption increases when
Filler content less, resin content more
reduced curing time – Increased Water sorption
e.g 25% reduction in curing time
2fold increase in sorption
– 6 fold increase in solubility
Seriously affects – Durability & colour stability.
Microleakage of composites :-
Considerable evidence - Etching itself not a culprit of pulpal inflammation
As acids get buffered in dentin
However etching opens tubules , allowing positive dentinal flow
Should marginal leakage occur & presence of partially or uncured monomers
occurs – Pathway to pulp open.
Adviced – not to etch dentin in vital teeth or a strong GIC base completely
covering all dentine before etching enamel walls.
In vitro study (Haggesmon, Mason – 2001)
Resin Mod GIC Has lesser Microleakage
than (A) Bonding agents
(B) Flow able composites
(C) by dunn’s test.
34
Marginal Defects :-
1. Surface fracture of excess material
2. Crevice formation CD itching, Marginal
3. Porosity or void (incorporation of air b/w restoration & Tooth during
placement)
4. Wear of restoration (Progressive exposure of axially directed cavity wall)
Role of type of composite used :-
Macrofilled – More of wearing type of defects
Hybrides – Tend to chip (Crevice formation) & wearing too
Microfilled – Chipping & Surface fractures
Due to – Fracture toughness, tensile strength elastic modules,
polymerization shrink coeff. of thermal contraction.35
Role of composite fatigue :-
Under certain loading conditions, composites begin to tire, losing strength
over a period of time. Results in cohesive microcracks & external chipping.
Role of bleaching :-
Results in colour instability by changing shade.
10-16% carbamide peroxide, may lead to slight deterioration by statistically
causing Surface roughness & amount of parasites esp in microfilled &
hybrid resins result in increased plaque adhesion & staining
25-35% hydrogen peroxide uniformly showed shear-bond & tensile bond
strength of all composites.
37% carbide peroxide or pastes c 30% H2O2 and Na perorate, lead to
microleakage.
These concentrations after affecting marginal seal may penetrate to pulp and
cause deleterious effects.
Failures of inlays Important failures include :-
Secondary caries
Surface discoloration
Marginal fractures (Esp porcelain inlays)
Restoration dislodgements
Marginal leakage
Tooth fractures
Failures caused due to
(A) Faulty preparation :
Angle of divergence of walls :-
Buccal and lingual walls divergence should be at an angle b/w 5o & 10 0
If Angle < 5o – Remaining structure under undue stresses during cementing
& force loading in function
If Angle > 10o – Compromised retention
36
Structure of walls :-
After inlay seated in mouth, maintenance of retention depends on
Strength and integrity of both lingual & buccal walls.
It is virtually impossible to gain strength and retention from opposite
remaining cusp which is already weak (Extracoronal coverage)
Improper Margins :-
30-40o Marginal metal desirable
angle of 140-150o (Cavosurface angle)
desirable while cutting
Cavosurface angle > 150o – Metal too thin and weak
< 140o – Metal too bulky and difficult to burnish
Gingival bevel of 30o desirable
No mesial tilt of INST – Too steep cutting Metal thin & weak
Not connecting & blending with Sec flares
Distofacial & distolingual
areas exposed for cement dissolution.
Secondary flares :-
If not given results in proximal surfaces in – accessible to surface cleaning
action – leading to plaque accumulation & periodontal problems.
Luting cement dissolution.
Luting cements are prone to dissolution in oral environment
More the gap in restoration- tooth interface
More cement exposed
More dissolution
more marginal leakage
Also in proximal areas any excess cement remaining after cementation,
unchecked-
Becomes an area of continuous periodontal irritation.
Post-insertion sensitivity :-
Seen c both GIC and Zinc phosphate 37
Occurs mostly due to removal of smear layer
Fixing of smear layer advised thus,
Through reinforced Zoe has been advised
But tends to hydrolyze washings around margins
more prone to leakage
Marginal leakage & percolation
Leakage occurs- Teeth subjected to alternative cooling and warming.
Due to – diff in coeff of thermal expansion of tooth and material.
Resulting ingress & egress of fluids – percolation
As a result bacteria’s can gain access & cause deleterious effects
Another cause – increased taper – continuing loads – restoration gives away by
rotating on walls - fractured thin metal margins.
Considerations in porcelain inlays :-
Bevels
If given – Thin sections of porcelain at cavosurface
Highly brittle, prone to fracture
FracturesA strain of only 8-10 mm/cm in dental porcelain is required before it
fractures
Most fractures start from inner surfaces esp- at or near gingival margins
Role of surface flaws :-
Porcelains are brittle materials but not synonymous with weakness.
Because of structure of Si-O2 bonds & absence of grain boundaries, the vitreous
matrices of porcelain have intrinsic strength.
As material perfectly elastic – Measured strength strongly dependent on presence
or absence of surface flaws.
38
Fracture Propagation :-
Caused by stress concentration at tip of surface How. Once initiated , the
extension of crack is ensured by applied stresses & increasing stress
concentration factor of growing crack.
Exposure to water strength of porcelain attributed to stress enhanced B/w
glass & H2O occurs primarily at tips of such cracks water reacts with glass –
destruction of Si-O network –hydroxyl ions attack siloxane bonds.
39
CONCLUSION
As a wise man has said…….
In the wide arena of world failure and success are not accidents as we suppose but
strict justice of nature. If you do your work sincerely you are certain to get
rewarded .
A person who has not seen his or her work fail over the years is myopic,
peripatetic, or simply very young.
It is good to be critical about work but being unfairly critical about work of others
is not done for us we do not know about the circumstances in which the
restoration was done.
40
REFERENCES
A) Studervant – Textbook of operative dentistry
B) Marzovk – Textbook of operative dentistry
C) Vimal sikrj – Textbook of operative dentistry
D) Tooth coloured restorations – albers
E) Mount- Preservation & restoration of tooth strvcture
F) Leinfelders & Lemons – clinical restorative materials & techniques
G) Advanced operative dentistry - Wilson, fuzzi, Voli, vol II
H) Plckards Manual of dentistry
I) Skinners & Philips – dental material science
J) JR. of academy of dental materials
-20 (9) Nov 2004
-20(1) Jan 2004
-20(2) Feb 2004
-20(3) Mar 2004
K) JR of conservative dentistry
-7 (3) Jul – Sep 04
-7 (4) Oct – Dec 04s
-7 (1) Jan –Mar 04
41
SEMINAR
FAILURES OF
RESTORATIONS
: SEMINAR BY :
DR. SHANTUN MALHOTRAP.G. STUDENT
DEPT. OF CONSERVATIVE
DENTISTRY & ENDODONTICS
S.P.D.C. SAWANGI
: GUIDED BY :
DR. W. N. GHONMODE
DR. MANOJ CHANDAK
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