CR principles Flashcards
what is CR
a mixture of highly cross linked polymeric materials
reinforced by dispersion of glass, crystalline or resin filler particles
bound to matrix by silane coupling agents
what are the properties of bis gma
high molecular weight
low volatility
high viscosity
low polymerisation shrinkage(5-6%)
radiolucent
how to reduce viscosity of bisgma
add low viscosity liquids, tegdma decrease viscosity of resin matrix
whats an example of thermochemical inititators
benzoyl peroxide, rxt w amine and result in free radicals
what are some inhibitor of CR
hydroquinone, delays premature polymerisation
what does coupling agent do
promote wettability and dispersion, decrease viscosity between filler and liquid resin component, improve physical and mechanical properties
what does filler particles do
improve physical and mechanical properties
decrease polymerisation shrinkage
decrease water sorption
decrease coefficient of thermal expansion, decrease marginal leakage
improves translucency and handling
what does an increase in vol percentage of filler particle mean for the shrinkage of cr
decreases shrinkage as amount of matrix decrease
why does fillers increase mechanical properties
more fillers means lesser matrix, fillers are harder, stornger , denser, does not shrink and absorb less water than matrix
what is camphorquinone
it is a yellow component and absorbs blue light (469nm)
what happens when there is underpolymerisation
inferior physical and mechanical properties, higher solubility, loss of retention, excessive wear, poor colour stability, more susceptible to staining
what are the disadvantage of CR
variable degree of polymerisation, different degree of conversion, technique sensitivity, decreased longevity compared to amalgam
what is the direction of polymerisation shrinkage
towards centre of mass for autocured/chemical cure, also shrinks towards most retentive wall
what is C factor
bonded: unbonded surfaces
what does a high c factor do to stress
increase in stress caused by shrinkage
