Acrylic Flashcards
What type of material is acrylic?
polymer
requirements for a denture base?
- dentist and lab point of view
adequate strength to withstand occlusal loading
easy to manipulate and process
not produce toxic fumes or dust during processing
remain unstained and unaffected by fluids and temperature changes in oral cavity
simple to repair when necessary
maintain its shape, form and aesthetics in normal function
biocompatible
radiopaque
requirements for the denture - from a pt point of view?
fit well and b compatible in use
not traumatise the tissues
easy to clean
aesthetically pleasing both immediately on placement and in the linger term
allow good heat diffusion to retain normal perception
permits food to be tasted normally so that food can remain appealing
PPMA?
poly methylmethacrylayte
what forms is PMMA available in?
gel
sheet
blank
powder/liquid
powder?
polymer
liquid?
methylmecarylate
initiator in PMMA?
benzoyl peroxide
what is the carcinogenic component?
phthalates as the plasticiser can be hazardous at high concentrations
MMA monomer boiling point?
100 dc
can boil out
MMA toxic?
yes, toxic if inhaled for prolonger period
what is in inhibitor of MMA?
HYDROQUINONE
role of hydroquinone?
inhibitor - prevents monomer polymerizing during storage
preferentially react with any random free radicals to prevent premature reaction
stop polymerisation procoess
What needs to happen before polymerisation can occur?
all the hydroquinone must be use up before the polymerisation reaction may take place
the role of plasticisers in acrylics?
prevent interaction between polymer molecules
what cold affect the biocompatbility of PMMA?
phthalates and carcinogenic
methacrylate will polymerise - less likely to leach out over time
failure of methacrylate to polymerise could lead to subsequent hardening of the denture base over time
setting reaction of PMMA?
Initiated by an organic peroxide such as benzoyl peroxide
free radicals produced wither by heating (heat cured) or by reacting with chemical accelerator such as an organic amine
highly exothermic reaction
heat is slow to displace as processing is carried out on a plaster mould
why does polymerisartion shrinkage occur?
shrinkage of the material occurs on setting reaction is a plymerisation reaction
processing regime look t reduce the heat production
mechanical propertis of PMMA?
low tensile strength and low elastic modulus
flexes in use
will result in fracture of the denture base over time
due to cyclical loading aka fatigue fracture
midline fracture
what does fracture toughness mean?
behaves as a brittle material on impact
advise to pt when cleaning denture to prevent fracture?
clean over sink half full with water
properties of PMMA?
- Brittle (EASILY BREAK)
- low tensile strength (fracture)
- high coefficient on thermal expansion (may lose ceramic teeth due to contraction of material)
- low thermal conductivity
- high dimensional stability
- polymerisation shrinkage (dont let it dry out - shrinkage and crazing)
- low density
- relatively lightweight
- easy to wear
- no taste
- relatively cheap
- easy to process
problems of low thermal conductivity of PMMA?
- pt sensation of hot and cold food is reduced
- oral mucosa may become less keratinised … if denture lost or replaced by fixed restoration, oral mucosa is sensitive to hot temps
lab
- during processing the het produced form the exothermic reaction cannot escape - gaseous porosity
how to prevent polymerisation shrinkage of denture?
keep wet, overnight etc
PMMA absorbs fluid - water sorption
drying out cause shrinkage and crazing
what does long-term water sorption cause?
discolour and stain - aesthetics
Problems of residual monomer?
denture base weaker and more flexible
fracture may result
polymer may creep under load over the long term and deform the denture base
more marked with cold-cure acrylic and can create problems
crosslinking agents may b added in an attempt to minimize this effete
loss of material due to water solubility low
presence of organic solvents such as alcohols and chloroform has an adverse effect on methacrylates
crazing?
fine cracks in surface of acrylic
can no longer support stress
lead to fracture
what can minimise crazing?
Keeping denture moist
what can cause crazing?
not kept moist
heat
problems of PMMA being radiolucent?
not ideal if swallowed, cant find n xray
