Failures of Amalgam

FAILURES OF AMALGAM

Would you like to give a feedback about these notes?
Please click here.

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

FRACTURE 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	Amalgam thin (over the cusp)
Sharp axio-pulpal line angle	Stress concentration (fracture thro' isthmus)
Sharp angles in occlusal outline form of Class II	Stress concentration (fracture thro' isthmus)
Sloping gingival step	No resistance form (fracture thro' isthmus)
Too narrow gingival step	No resistance form (fracture thro' isthmus)
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	Increased residual Hg
Mix squeezed too dry	Lack of cohesion (amalgam weak)
Condensation of partially crystallized amalgam	Lack of cohesion (amalgam weak)
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	Early strength not high enough

FRACTURE 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

INADEQUATE 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

MARGINAL 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

POROUS 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	Porosities and voids
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

TARNISH 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

GINGIVITIS 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	Food stagnation resulting in gingivitis and periodonitis

LACK OF FUNCTIONAL EFFICIENCY

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

PAIN 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	Mercuroscopic expansion (increased residual Hg)
Cavity preparation without water coolant	Pulpitis resulting in pain
Microscopic pulp exposure	Pulpitis resulting in pain

TOOTH 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.

These web pages created and maintained by

Dr R. V. Subramanyam
Professor, Dept. of Oral Pathology
College of Dental Sciences, Davangere 577 004
Karnataka, India.