What are the ideal properties of denture base materials?
- dimensionally accurate & stable
- high softening temperature
- unaffected by oral fluids
- low density
- high thermal conductivity
- radiopaque
- non toxic
- inexpensive
- easy to repair
What are the steps involved in acrylic polymerisation?
Activation = of initiator to provide free radicals
Initiation = free radicals break C=C bond in monomer and transfer free radical
Propagation = growing polymer chain
Termination = of polymerisation
What are the constituents of the powder part of heat cured acrylic?
- Initator = benzoyl peroxide
- PMMA particles
- Plasticiser
- Pigments
- Co-polymers
What are the constituents of the liquid portion of heat cured acrylic material?
- Methacrylate monomer
- Inhibitor = Hydroquinone 0.006%
- Co-polymers
What is the function of plasticisers in heat cured acrylic material?
allows quicker dissolving in monomer liquid
What is the function of pigments in heat cured acrylic material?
to give ‘natural’ colour
What is the function of co-polymers in heat cured acrylic material?
to improve mechanical properties
What is the function of methacrylate monomer in heat cured acrylic material?
dissolves pmma particles
What is the function of inhibitor in heat cured acrylic material?
prolongs shelf life
- reacts with any free radicals produced by heat/UV light
What are the mechanical properties of denture base materials like generally?
Poor
- increase in bulk to componsate
The thermal conductivity of pmma is low, is this good or bad?
POOR
- does not feel natural in mouth
How does self-curing acrylic differ in composition/polymerisation to heat cured acrylic?
As heat cured except benzoyl peroxide is activated by promoter (tertiary amine) in liquid
Why are self-cure acrylics used?
Cure at a lower temperature –> less thermal contraction –> better dimensional accuracy
How much unreacted monomer is left in self cure vs heat cute?
self cure = 3-5%
heat cure = 0.2-0.5% so MUCH BETTER
Why is heat cured acrylic superior to self cured acrylic?
- less unreacted monomer present
- undersized originally so better tolerated once water absorbed
- stronger
- better colour stability
If a patient has a known allergy to acrylic, what can be used instead?
- nylons
- vinyl polymers
- polycarbonates
