Polymethylmethacrylate

Question 1

what are all the ideal properties needed for PMMA?

Answer 1

• goes in mouth (safe, non toxic, irritant)
• good value for money
• dimensionally accurate and stable
• unaffected by oral fluids
• thermal expansion, low density, high thermal conducitivity
• radiopaque
• colour/translucency
• easy & inexpensive to manufacture
• easy to repair

Question 2

what are the mechanical properties of PMMA?

Answer 2

HIGH:
- Young’s elastic modulus (needs high force to bend)
- proportional limit
- fatigue strength
- impact strength
- hardness/abrasion resistance

Question 3

what are the 4 stages of acrylic polymerisation (and what happens in each)?

Answer 3

ACTIVATION: initiator activated to provide free radicals

INITIATION: free radicals break C=C in monomer and transfer radical

PROPAGATION: reactions occur growing the polymer chain

TERMINATION: polymerisation is then terminated

Question 4

what are the differences between heat cured and self cured acrylic?

Answer 4

self cured:
- chemically cured
- weaker
- prone to discoloration
- more monomer (irritant)

Heat cured:
- Heat cured
- higher molecular weight - [STRONGER]
- Thermal contraction (tighter fit)
- COLOUR STABLE