DMT Flashcards
definition of working time
from start of mix till can’t be used
measure at room temp
definition of setting time
from start of mix to setting
measured in mouth
what is a pseudoplastic material
viscosity decreases with pressure
what is elastic and plastic strain
elastic = recovered plastic = permanent - occurs when yield stress applied
definition of hardness
resistance to indentation under load
definition of strength
maximum stress that can be withstood
what are added during polymerisation to reduce shrinkage
fillers
advantages of alloys compared to pure metal
harder
stronger
melting range
cheaper
strength properties of amalgam
develops over 24hrs
high compressive strength
low tensile/flexural strength
weak in this sections, unsupported edges
cavity design for amalgam
undercut for mechanical retention rounded internal angles to reduce stress keys/grooves for retention remove unsupported enamel flat floor
thermal disadvantages of amalgam
high thermal diffusivity - use liner to insualte
high coefficient of thermal expansion - more expansion/contraction than tooth = microleakage or fracture
what must be removed before bonding to dentine
remove smear layer
2 types of elastic impression material
alginate, silicone
3 types of non-elastic impression material
Zinc oxide
plaster
compound
2 uses of impression wax
correct airblows in impressions
produce mucocompressive impression of lower free ed saddles
