PMMA

3 point loading (flexural). acrylic is being flexed and pivot point is palate so when forces either side are applied this can potentially cause fracture at pivot point

chemical union of 2 molecules either the same or different to form a larger molecule without the elimination of a smaller molecule. involves molecules with C=C double bonds

activation - of initiator to provide free radicals initiation - free radicals break C=C in monomer and transfer free radical propagation - growing polymer chain termination - of polymerisation

• initiator = benzoyl peroxide 0.2-0.5% • PMMA particles = pre-polymerised beads • plasticiser = allows quick dissolving in monomer liquid e.g. dibutyl phthalate • pigments = to give natural colour • co-polymers = to improve mechanical e.g. ethylene glycol dimethacrylate

• methacrylate monomer = dissolves PMMA particles; polymerises • inhibitor = hydroquinone 0.006%; prolongs shelf life reacts with any free radicals produced by heat, UV light • co-polymers = improve mechanical properties, particularly cross linking of polymers

need efficient polymerisation i.e. lots of crosslinking of MMA monomers to produce a high molecular weight polymer with good mechanical properties hence high temp but this has gaseous porosity limits

• non toxic • non irritant - if no monomer released, few patients are allergic • unaffected by oral fluids - water absorption, virtually insoluble in fluids taken orally • mechanical properties - poor so increase bulk to compensate

impact strength - reasonable high hardness / abrasion resistance TEC - ok if acrylic teeth used thermal conductivity - low density - low which is good but increase in bulk to overcome poor mechanical properties high softening temp dimensional accuracy & stable in use

ability to resist repeated application of low level stress e.g. mastication on denture base

self cure has similar composition to heat cure except benzoyl peroxide is activated by a promoter (a tertiary amine) e.g. dimethyl-para-toluidine, not heat

polymerisation stage requires no heating stage so little thermal contraction would be experienced leading to a better fitting and more dimensionally accurate denture

chemical activation yields less efficient polymerisation hence a lower molecular weight so poorer mechanical properties and Tg also leaves unreacted monomer which acts as a plasticiser softening denture base and reducing transverse strength; this can potentially be an irritant thus compromising biocompatibility

HC - higher molecular weight; stronger, curing process may cause porosity SC - higher monomer levels; may be irritant, fits cast better but water absorption in mouth makes it over sized, poorer colour stability; tertiary amines more susceptible to oxidation, other properties same as HC

it incorporates high impact resistance materials but has long term fatigue problems or difficult processing to incorporate fibres

high impact heat cure acrylic resin which has better flexural strength + ductility which helps mitigate effect of microcracks - used in GDHS

similar to SC but smaller powder particles, fluid mix pour into mould so good fitting but poor mechanical properties

urethane dimethacrylate matrix plus acrylic copolymers, microfine silica fillers and photo initiator systems. adapted to cast and cured in light chamber but used mostly as customised impression tray material and for repair of fracture dentures

• nylons - water absorbing which can lead to swelling/softening • vinyl polymers - polyvinyl acetate / polyvinylchloride / styrene go through injecting moulding (expensive) and Tg = 60 degrees which leads to softening in use • polycarbonates - injection moulding also but develop internal stresses during use causing distortion, good impact strength otherwise