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FAILURES OF AMALGAM

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Fracture of the restoration Tarnish and Corrosion
Fracture of the tooth Gingivitis and Periodontitis
Inadequate retention Lack of functional efficiency
Marginal leakage Pain after restoration
Porous and Weak restoration Discolouration of the tooth

Back to the topFRACTURE OF THE RESTORATION

CAUSE
EFFECT
Too shallow cavity Amalgam thin
Too thick cavity liner
Too thick cement base
Inadequate cuspal reduction Amalgam thin (over the cusp)
Giving cavosurface bevel
Sharp axio-pulpal line angle Stress concentration (fracture thro' isthmus)
Sharp angles in occlusal outline form of Class II
Sloping gingival step No resistance form (fracture thro' isthmus)
Too narrow gingival step
Insufficient Hg Amalgam weak
Excess Hg
Undertrituration
Moisture contamination (Zn having alloys) Delayed expansion (flow over margins)
Insufficient condensation pressure Increased residual Hg
Not squeezing out excess Hg
Mix squeezed too dry Lack of cohesion (amalgam weak)
Condensation of partially crystallized amalgam
Overfilling Thin amalgam over margins
Failure to warn patient not to chew on the restoration for first few hours Early strength not high enough
Failure to support proximal part of the restoration while removing matrix band

Back to the topFRACTURE OF THE TOOTH

CAUSE
EFFECT
Sharp angles in occlusal outline of Class II Stress concentration
Excess removal of tooth structure Enamel undermined and tooth weakened

Back to the topINADEQUATE RETENTION

CAUSE
EFFECT
Absence of undercuts No retention form
Dovetail with only one cornu No resistance to dislodgement
Too thick liner that is lost subsequently Lack of adaptation to cavity walls
Using large condensers initially Undercuts and margins not filled - No retention

Back to the topMARGINAL LEAKAGE

CAUSE
EFFECT
Excess Sn (tin) in the alloy Too much shrinkage
Overtrituration Shrinkage on setting
Excessive pestle pressure Slow setting with shrinkage
Failure to condense towards margins Marginal gaps
Using large condensers initially Deficient margins and undercuts
Carving from amalgam to tooth Marginal defects and gaps
Excess amalgam left beyond cavosurface angles Breaks away leaving deficient margins

Back to the topPOROUS AND WEAK AMALGAM

CAUSE
EFFECT
Increased γ2 Phase (low Cu alloys) Weak phase
Irregularly shaped particles in the alloy Porosities and voids; less coherence of phases
Too less Hg Same as above (Incomplete amalgamation; non-plastic)
Too much Hg Increased residual Hg (Increased γ2 Phase , decreased γ1 Phase phases)
Undertrituration Porosities & voids
Trituration beyond limits Decreased coherence (due to cracking of crystals)
Delayed insertion after trituration Porosities and voids
Insertion of too large increments
Decreased condensation pressure Porosities and voids (increased residual Hg)
Moisture contamination Porous amalgam
Mix squeezed too dry Decreased coherence
Mix not squeezed (with high Hg:Alloy ratio) Porosities and voids (increased residual Hg)
Condensation of partially crystallized amalgam Porous amalgam
Condensing with serrated pluggers with set amalgam in the serrations Old amalgam contaminates restoration and weakens it
Overheating while polishing 'Burns' amalgam and releases Hg resulting in porosity
Burnishing set amalgam Breaks up superficial crystalline structure releasing Hg causing porosity

Back to the topTARNISH AND CORROSION

CAUSE
EFFECT
Alloy with excess γ2 Phase Has least resistance to corrosion
Fissures carved too deep Food stagnation leading to tarnish and corrosion
Failure to polish Rough surface causing crevicular corrosion
Contact with dissimilar metallic restoration Galvanic corrosion

Back to the topGINGIVITIS AND PERIODONTITIS

CAUSE
EFFECT
No wedge used Gross overhang; Contact area deficiency
Surface left high in bite High point causing periodontitis
Failure to polish proximal surface Food stagnation resulting in gingivitis and periodonitis
Lack of proximal contact

Back to the topLACK OF FUNCTIONAL EFFICIENCY

CAUSE
EFFECT
Fissures carved too deep Reduced masticatory efficiency
Underfilling
Failure to carve Decreased masticatory efficiency (Tooth anatomy not simulated).

Back to the topPAIN AFTER PLACING RESTORATION

CAUSE
EFFECT
Failure to use liner and base Thermal conduction
Overfilling High point causing periodontitis resulting in pain
Moisture contamination Delayed expansion with pressure on pulp
Increased Hg: alloy ratio Mercuroscopic expansion with pressure on pulp
Failure to squeeze out excess Hg Mercuroscopic expansion (increased residual Hg)
Inadequate condensation pressure
Cavity preparation without water coolant Pulpitis resulting in pain
Microscopic pulp exposure

Back to the topTOOTH DISCOLOURATION

Sometimes excess Hg within the restoration may seep through the dentinal tubules, discolour dentin and result in blackish or greyish staining of teeth. Since enamel is semi-translucent, this discolouration is not inconspicuous.


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These web pages created and maintained by
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Dr R. V. Subramanyam
Professor, Dept. of Oral Pathology
College of Dental Sciences, Davangere 577 004
Karnataka, India.

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