Amalgam Flashcards
amalgam is
an alloy formed by the reaction of mercury [liquid] and silver/tin/copper and other metals [powder]
amalgam composition
powder - 50%
liquid - 50%
amalgam powder composition
silver-tin intermetalli compound
copper increases strength and hardness
Zn - during production, oxidises and slag formed/removed
Hg - reacts faster
amalgam liquid composition
mercury
very pure, triple distilled
slag
by-product of industrial processes where metals are extracted from ores
how is amalgam matrix formed
silver/tin powder reacts with mercury
some powder remains
silver mercury and tin mercury forms amalgam matrix
sets with small amount of contraction
effect of zinc
interactions with saliva/blood
H2 bubbles formed, pressure build up, expansion, downward pressure, pulpal pain
AVOID
properties of amalgam
good - abrasion resistance, thermal expansion, low failure rate, compressive strength
bad - biocompatibility concern of mercury toxicity, high thermal conductivity [liner], thermal diffusity high, doesnt bond to tooth, poor aesthetics
creep
when a material experiences low-level stress levels [below elastic limit stress] which are applied repeatedly over a prolonged time period, it may FLOW, resulting in PERMANENT DEFORMATION
corrosion in amalgam
electronegative, tin and mercury, weakens enamel at margins
reduce this by cooper enriched, polishing margins
copper rich amalgam effects
high early strength, less creep, higher corrosion resistance, incrased durability of margins
cavity design in amalgam
retention, resitance, self-retentive box, proximo-occlusal, moisture contmaination
retentive form
features which prevent loss of any restoration in any direction
undercuts
resistance form
features that prevent loss of material due to distortion or fracture by masticatory forces
cavity floor parallel to occlusal surface, depth 1.5-2mm, interproximal box 90 degrees to axial wall
self-retentive box, minimal
less tooth tissue removed, less amalgam used, more technically demanding
