amalgam Flashcards
advantages of dental amalgam
- long lasting
- low cost (inexpensive)
- doesnt require very specific conditions (humidity, saliva)
- fast (compared to CR eg)
- resin free, prevents allergy tp CR (however, this cannot be the main reason to choose amalgam)
definition of amalgam
an alloy of mercury with another metal
constituents of amalgam
basic: silver, tin, copper, mercury
other: zinc, indium, palladium
properties of silver
ONLY GOOD THINGS :)
- major element
-increases strength
- increases expansion (balanced by tin)
- decreases CREEP
properties of tin
good
- decreases setting expansion
bad
-decreases strength
- increases setting time and corrosion
is corrosion on amalgam desirable (by tin)
products of corrosion seal the margins (late shrinkage)
- therefore, corrosion on margins are desirable
however, corrosion on occlusal is not desired as lose electrons, material degrades
what is creep
-time dependent deformation in response to a constant load
-a kind of viscoelastic behaviour where the material experiences stress/strain characteristics (chewing) that are time dependent
- it is the tendency of a solid material to move slowly or deform permanently under the influence of persistent mechanical stresses
properties of copper
- ties up tin, reducing gamma-2 formation
- increases strength
- reduces tarnish and corrosion (LOW Cu)
-reduces creep and marginal deterioration
through what process does amalgam harden
crystalisation
properties of zinc
- scavenger *** (main reason why zinc is used)–> decreases oxidation of other elements
- provides better clinical performance –> less marginal breakdown
HOWEVER: - causes delayed expansion with low Cu alloys , creates H2 gas when it reacts with water –> gas expands and amalgam cracks
properties of palladium
-reduced corrosion
- greater luster
however: expensive
