PMMA

Question 1

What are the ideal properties of a denture base material?

Answer 1

• dimensional stability
• high softening temperature
• unaffected by oral fluids
• thermal expansion
• low density
• high thermal conductivity
• radiopaque
• non toxic, non irritant
• easy to repair
• inexpensive and easy to manufacture

Question 2

What are the ideal mechanical properties of a denture base material?

Answer 2

• high elastic modulus
• high proportional limit
• high transverse strength
• high fatigue strength
• high impact strength
• high hardness/resistant to abrasion

Question 3

outline the steps of acrylic polymerisation

Answer 3

Activation - initiator activated to provide free radicals
Initiation - free radicals break C=C bond in monomer
Propagation - growing polymer chain
termination - of polymerisation

Question 4

how is self cured acrylic formed?

Answer 4

Same as heat cured except benzoyl peroxide is activated by a promoter in liquid

Question 5

What kind of promoter is used to activate benzoyl peroxide in self cured acrylic?

Answer 5

A tertiary amine

Question 6

how do the properties of self cured acrylic differ from heat cured?

Answer 6

chemical activation = less efficient
hence
- lower molecular weight
- poorer mechanical properties
- more unreacted monomer - potential tissue irritant

But - fits cast better than heat cured
- water absorption give expansion
self cure = over sizeed
- heta cured - undersized and better tolerated

Question 7

What percentage of acrylic dentures fraction within 3 years?

Answer 7

10%

Question 8

alternative polymers when there is a proven allergy to acrylic

Answer 8

• nylons
• vinyl polymers
• polycarbonates