DENTAL MATERIALS Flashcards
describe dental amalgam
it is made up as an alloy along with mercury - metals are silver, tin, copper and zinc - the deoxidiser!
what is the setting reaction of amalgam
gamma phase - strongest, least corrosion
gamma-1-phase - still strong, not as resistant (silver)
gamma-2-phase - weak easily erodes (tin)
describe the effect on metal if we have low Cu
we would have more CORROSION, this is due to the fact that Cu reacts with tin to keep it from gamma-2-phase! - easily eroding phase
what are the effects on metal if we have high Cu
dont have gamma -2 - phase meaning STRONGER!
how long does it take for amalgam to have functional compressive strength
15-20 mins (final strength is achieved by 24 hrs)
name the different forms of GI
powder + liquid , powder + water, encapsulated - degree of constancy
describe the acid/base reaction with GI
unreacted glass cores - reflect the colour of the tooth and transmit light , the glass releases FLUORIDE
describe some properties of GI
brittle, increase adhesion with citric acid (removes debris), takes up F+ and releases to tooth, poor ABRASION resistance…..
what composes resin composites
a resin matrix and glass filler particles
what is the setting reaction for resin composties
polymerisation reaction by chemicals and the UV light - an EXOTHERMIC reaction
what does the resin matrix do in a composite material
it controls the viscosity and handling of the material
what do the glass filler particles do in resin comps - quartz, silica, glass
they reduce shrinkage BUT weaken
what do the coupling agents do in resin comps (silane)
they improve adherance to tooth
some problems with resin comps
thermal diffusivity matches dentine, may stain, wear problems, polymerisation shrinkage may occur when setting!
what is nucleation within metals
when metals crystalise (heterogenous - many sites of nucleation, homogenous - one site of nucleation)
