Metals in dentistry (Ch 10) Flashcards
what is a metal
- is any substance that is good conductor of electricity and heat
what is an alloy
- any mixture of two or more metals
what is mercury
- is a metallic element that is liquid at ordinary temperatures
what is amalgamation
- is the reaction that occurs when a silver-based alloy is mixed with mercury
what is dental amalgam
- a mixture of alloy and mercury
- safe, affordable and durable material used predominantly to restore premolars and molars
what are indications for using amalgam
- in individuals of all ages
- in stress-bearing areas of the mouth
- when there is severe destruction of tooth structure
- as a foundation for a crown
- when oral hygiene is poor
- when moisture control is problematic
- when cost is an overriding factor
what are indications for not using amalgam
- aesthetics is important
- a history of allergy to mercury or other amalgam components
- the cost of other restorative materials or treatment options is not a factor
what is the composition of amalgam
- mercury (43% to 54%)
- alloy powder (57% to 46%)
- silver - strength
- tin - workability
- copper - strength and corrosion resistance
- zinc - suppresses oxidation
what are the 3 types/shapes of alloy particles
- lathe-cut alloy
- spherical alloy
- admix alloy: lathe cut and spherical
what are some advantages of spherical alloys
- less mercury to wet the particles
2. less time to set
what is the setting transformation process
- chemical reaction
- working time
- initial set
- final set
what are the 3 phases of chemical reactions in the setting transformation
- gamma phase
- gamma-1 phase
- gamma-2 phase
why does tarnish occur
- oxidation: oxygen, chlorides, sulfides in the oral cavity
- rough surfaces
other facts
- dark dull appearance
- not destructive to amalgam
what can cause a reduction for tarnish
- palladium
- finishing
- high copper
what causes corrosion
chemical reaction: oxidation, galvanism
where does corrosion takes place
- between the metals within the amalgam
what is creep
- the gradual change in shape of the restoration
- compression
- pressure
what is dimensional change (excessive contraction and excessive expansion)
- excessive contraction: opens gaps at the margins and contributes to leakage of fluids bacteria
- excessive expansion: pressure on the cusps, pain with biting pressure, could result in the fracture of cusps
what are some issues concerning amalgam
- harm to patients: essentially harmless, the exception is with patients who have many amalgam restorations or a high sensitivity to metals
- harm to dental personnel: health concerns with high exposure to mercury, not amalgam
what are some signs of high mercury exposure
- tremors
- kidney disfunction
- depression
- nervous system disorders
what are some guidelines for hygienists using mercury
- do not contact mercury with your skin
- protect against spillage during trituration
- do not discard scrap amalgam into waste containers
- collect all scrap and store in a closed containers
- suction scrap amalgam
what is involved in preparation of amalgam
- capsules: 600 mg of alloy for small or single-surface restorations; 800 mg of alloy for larger restorations
- activator: used to break the separating membrane in the capsule
- trituration: the process by which the mercury and alloy are mixed together to form the mass of amalgam
what is the process of direct application of amalgam
- mixed amalgam placed
- amalgam carried to the prepared tooth
- amalgam placed in increments in the prepared tooth
- each increment is condensed immediately
- carvers are used to carve anatomy into the amalgam
- a burnisher is used to smooth the amalgam
- the new restoration’s occlusion is checked
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