Dental Base materials

Question 1

ideal properties of denture base acrylics

Answer 1

• high softening temp.
• unaffected by oral fluids
• high elastic modulus
• high proportional limit
• high thermal conductivity
• low density (less gravity to dislodge upper)
• non-toxic/irritant

Question 2

what is the acrylic material called that is used for denture bases

Answer 2

• PMMA 1 (polymethyl methacrylate)

Question 3

reaction to create acrylic denture base PMMA 1

Answer 3

• free radical addition polymerisation
  1. activation (of free radicals via heating or self curing)
  2. initiation (free radicals break C=C bond of monomer)
  3. propagation (growing polymer chain)
  4. termination (of polymerisation = PMMA)

Question 4

types of acrylic PMMA denture base material creation (two methods)

Answer 4

via:

i. heating (liquid or powdered method)
ii. curing

Question 5

issues with denture base PMMA if under cured

Answer 5

• irritant (uncured monomer)
• low molecular. weight
• poor mechanical properties (porosity):

Question 6

issues with porosity in PMMA denture bases and two ways can occur

Answer 6

• affects strength, aesthetics, roughness and bad hygiene as can absorb saliva
• caused by:
  i. boiling monomer
  ii. contraction porosity (if too much monomer and not packed correctly as powder and monomer have different polymerisation shrinkages

Question 7

properties of concern surrounding PMMA 1 denture bases

Answer 7

• thermal expansion (significantly higher than porcelain teeth - okay if acrylic teeth)
• poor thermal conductivity
• low density (actually good but cancelled out by bellow)
• mechanical properties (poor so need to bulk to make up for)
• softening temperature bellow boiling water so cant clean with