Processing

Question 1

High impact resin

Answer 1

Styrene-butadiene
-Incorporating a rubber phase in the beads during polymerization
-Increasing impact strength and fatigue resistance

Question 2

Composition and fxn of PMMA

Answer 2

Monomer
-MMA-
-Hydroquinone-Inhibitor
-Dimethyl-p-toluidine(tertiary amine)-Accelerator
-Dibutyl pthalate-Plasticizer

Polymer
-Pre-polymerized spheres of PMMA - reduces shrinkage
-Benzoyl peroxide- Initiator
-Butadiene-styrene-strength
-Titanium dioxide-opacifier
-Dibutyl pthalate-Plasticizer

Question 3

Heat cure vs Cold cure PMMA

Answer 3

Heat
-Heat is activator-decomposes benzoyl peroxide after 60C to initiate polymerization
-LESS residual monomer (0.2-0.5%)
-MORE shrinkage
-MORE strength
-MORE color stability
-MORE biocompatibility

Cold
-Tertiary amine is activator
-MORE residual monomer(3%)
-LESS shrinkage
-LESS strength
-LESS color stability
-LESS biocompatible

Question 4

Linear and Volumetric Shrinkage of PMMA during polymerization

Answer 4

Linear shrinkage
-More clinically significant
-Results in loss of fit/seal/occlusal contacts
-Greatest in heat cured compression molding

Volumetric
-Produces changes in density

Initial PMMA formation experiences 21% volumetric and 7% linear shrinkage

1. PMMA beads are pre-polymerized
2. 3:1 powder:liquid ratio

Decreases shrinkage to 6% volumetric and 0.5% for heat cured (0.25% for cold cure)