L13: prosthetic polymer and resins Flashcards
denture base materials are available as ___
powder (polymer)
liquid (monomer )
colorless material used in fabrication of denture :
polymethyl methacrylate
how does polymethyl methacrylate polymerize?
under heat and pressure
curing of denture base polymer :
type I class I :
type II class I:
type IV:
type I class I : heat cured powder/liquid
type II class I: chemical/self polymerized powder liquid
type IV:light cured
list the polymer powder and monomer liquid present in heat cured polymethyl methacrylate :
polymer powder : polymethylmethacrylate beads
monomer liquid : methyl meth acrylate
what is the most commonly used denture base?
heat activated (type 1 class 1) polymethyl methacrylate
how are heat activated PMMA shaped?
compression modeling
molds of heat activated PMMA are prepared by :
dental gypsum in dental flask
denture base is made with :
wax, missing teeth are also positioned in wax
what is the ratio of polymer to monomer in heat cured acrylic resin?
3:1. using this ratio , volumetric shrinkage can be limited to 2.3%
5 distinct stages that occur after mixing of powder and liquid of PMMA :
sandy stage : little or no interaction occurs immediately after mixing
stringy stage : monomer liquid is absorbed into beads, causing swelling . polymer chains now uncoil and increase viscosity of mix ( stringiness or stickiness)
dough-like stage : ideal consistency for compression molding , pliable dough no longer stringly or sticky . packing is done in this stage
rubbery stage : no longer flows freely , initial setting
stiff or hard stage : dry mixture resistant to mechanical deformation
controlled heating process used for polymerization of heat activated acrylic is termed ____
polymerization cycles or curing cycles
when does benzyl peroxide decompose ?
65C to form free radicals
resin is processed :
at 74 C For 2 hours and increasing the temperature of the water bath to 100C for 1 hour
boiling point of liquid MMA monomer ?
100.8C
What happens if you over heat the monomer ?
gaseous porosity
insufficient monomer produces :
dry mix and granular porosity
insufficient dough and inappropriate pressure causes :
contraction porosity
initiator used in chemically activated denture base resin is activated by ____
tertiary amine such as dimethyl para-toludine added to liquid monomer
what happens when liquid and powder of chemically activated denture base resin are mixed?
tertiary amine causes decomposition of benzoyl peroxide which results in free radical production and polymerization occurs similarly to the way it does in heat activated PMMA
Residual monomer in which type of denture material is higher ?
chemically activated ( high residual monomer figures decrease the strength and serve as a potential tissue irritant (compromises biocompatibility )
which denture base material has slightly less shrinkage
chemically activated , they have greater dimentional accuracy
which denture base material has better color stability ?
heat activated
which denture base material has smaller polymer beads which disolve quicker ?
chemically activated resins
light activated denture base polymers are supplied in __
pre mixed sheets or bars
what’s the major pro of light activated denture base polymers?
reduced working time by eleminating need for flasks, wax , boiled out , packing
which denture base polymer is very useful for production of the hallow denture bases for obturators ?
light cured denture base polymer
density ____ with polymerization
increases
change in density results in ___
volumetric shrinkage of 21%
volumetric shrinkage exhibited by polymerized mass___
7%
linear shrinkage within a denture base rarely exceeds :
1%
production flaws , micro leakage due to internal stress is termed ___
crazing
