Amalgam Flashcards
What is amalgamation?
Process of combining alloy materials with mercury
Composition of amalgam
Silver, tin, copper, zinc, other materials, Mercury
What does silver contribute to?
Strength of amalgam, long term brightness, decreases corrosion, decreases creep and setting time.
Too much silver causes excessive expansion during setting. Alloys with 70%+ silver not stronger than 70%-
What does tin do? (Food and bad)
Promotes amalgamation with mercury, reduces expansion.
Excess of tin = contraction, decreases strength, increased setting time, corrosion, plasticity.
What does copper do?
Improves strength, decreases setting time, decreases corrosion and creep, increases setting expansion, decreases plasticity.
Excess= tarnish, discolouration
Properties of zinc
Removes unwanted oxides during manufacturing, “cleaner” amalgam, improves corrosion resistance, shiny, if contaminated with water will expand excessively.
Properties, advantages and disadvantages of mercury
Is a matrix material=temporary liquid stage.
Ad- gives plasticity and softness, binds the particle of the alloy together, necessary for the setting reaction and hardening.
Dis- if in excess= low strength, high creep.
Lathe cut and spherical cut alloy % and properties
Lathe cut = 50% - irregular shaped, fine, micro cut or course. Require high condensation pressure
Spherical cut = 42% - atomised, round, require less mercury and give more early strength but more micro leakage
Admix- provides best qualities of both
Advantages of high copper alloys
Physical properties are improved, better corrosion resistance, less creep, better marginal integrity, easier polishing, superior clinical performance, elimination of gamma 2 phase in set amalgam
What is corrosion?
Breakdown of restoration. To minimise, use high copper alloy, use correct trituration, condensation and avoid moisture contamination
What is creep
Slow deformation over time. To minimise, use high copper alloy
Reasons for excessive expansion/contraction.
Contraction - over trituration
Expansion - under trituration, poor condensation, moisture contamination
Amalgam phases
Gamma (Ag+Sn) Gamma 1 (ag+hg) happens in mixing Gamma 2 (an+hg) happens in mixing Epsilon (cu+sn) happens/sets in the mouth Eta (cu+sn) happens after 24hrs
Which is the weakest phase?
Gamma 2. Corrodes easily.
Properties of amalgam
Expansion Contraction Strength Tarnish and corrosion Creep
To maximise strength of amalgam you must:
Use high copper alloy, pre weighted Triturate for correct time Appropriate condensation pressure Maintain dry field Use small increments
After condensation amalgam does….
Slight contraction may be observed
Then a slower expansion (gamma 1 crystals grow)
Steps in amalgam placement
Trituration
Condensation
Adaptation
Carving, finishing, polishing
Why place a liner at the base of your filling
To protect pulp or to aid in pulp recovery
Protect pulp from heat (thermal conductivity)
Ingredients of most filling materials are not biocompatible with pulp
Protect dentine and pulp from occlusal forces
Inhibits noxious products and bacteria through microleakage
(If filling leaks, base is protected)
Advantages and disadvantages of amalgam
Ad- high strength, longevity, wear resistant, easy to use, maintains anatomical form, cheap, clinical proven success,
Dis- invasive, not bonded, expansion/contraction, electro galvanism and corrosion, mercury toxicity, aesthetics.
