Acrylic Resin Flashcards
ideal properties
dimensionally accurate, high softening temperature [no distort in heat/cleaning], unaffected by oral fluids
high YMs, high proportional limit, thermal expansion, high thermal conductivity [feel hot food on mucosa], low density [aid upper retention], colour to match natural tissue, non-toxic
acrylic resin uses
denture creation
stress-strain diagram
as increase stress, increase strain
elastic limit is where it can be stretched and return to original shape, past this point it will relax but not to its original shape or configuration
proportional limit - stress applied before inelastically
setting reaction of acrylic resin
free radical addition polymerisation - adding 2 molecules to form larger molecules without elimination of smaller[ breaking C=C bonds]
acrylic polymerisation stages
activation - of initiator to provide free radicals
initiation - free radicals break C=C bond in monomer and transfer free radicals
propagation - growing polymer chain
termination - of polymerisation
heat cured acrylic compositon
powder - initiator, PMMA particles, plasticiser, pigments
liquid - methacrylate monomer [dissolves PMMA], inhibtor [prolongs shelf life], copolymers [improves mchanical properties]
why heat cured acrylic
produces dough-like material that can be handled easily and cutomised to desired shape
minimised polymerisation shribkage
efficient polymerisation, increased moleculer weight = better mechanical properties
problems with acrylic curing
undercuring - free monomer [irritant], low molecular weight [poor mechanical properties]
overcuring - gaseous porosity [voids], polymerisation shrinkage [20% shrinks]
acrylic properties
good - non-toxic/irriant, unaffected by oral fluids, colour, low density, high softening temperature, dimensionally accurate, stable
bad - thermal expansion only ok if acrylic teeth used, thermal conductivity poor, poor mechanical properties
