PMMA
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What are the ideal properties of PMMA/acrylic
-replaces function of natural teeth -non toxic/irritant -colour/translucency -easy and inexpensive to manufacture -easy to repair -Dimensionally accurate and stable in use -High Softening Temperature (Tg) -Unaffected by Oral Fluids -Thermal Expansion -Low Density -High Thermal Conductivity -Radiopaque
What are the ideal mechanical properties of a denture material
High Young’s (Elastic) Modulus High Proportional Limit High Transverse Strength* High Fatigue Strength High Impact Strength High Hardness / Abrasion Resistance
What is free radical addition polymerisation
Chemical union of two molecules either the same or different to form a larger molecule WITHOUT the elimination of a smaller molecule
What are the steps to 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 properties of acrylic
Fatigue strength - fairly resistant High hardness Thermal expansion - ok High thermal conductivity Low density High softening temp - dont use boiling water to clean
What is the benefit to self cure acrylics
Lower temp - less thermal contraction Hence, better dimensonal accuracy
What are the downsides to self cure acrylic
Chemical activation - less efficient Lower molecular weight Poorer mechanical properties
What does unreacted monomer within self caure acrylic do
Acts as a plasticiser, softening denture base, reducing transverse strength Potential tissue irritant
What percentage of unreacted monomer is left in self and heat cure acrylic
Self - 3-5% Heat - 0.2 - 0.5%
Heat cured vs Self cured
Heat -higher molecular weight (stronger) -Curing process may cause porosity Self -higher monomer levels -fits cast better but water absorption makes it oversized -poorer colour stability
What is Ultra-Hi
A High Impact heat cure acrylic resin - that exudes quality and gives the technician confidence -exceptional flexural strength -superior fracture toughness
If a patient has an allergy to acrylic what can be used
Nylons Vinyl polymers Polycarbonates