Distortion of acrylic resin

By Dr.Swathi Pai on Wednesday, January 7, 2009 with 0 comments

What were Johnson’s findings as to the distortional opening of the posterior palatal seal?

In test groups of small flat and large V-shaped palate, the distortional opening of the postpalatal periphery decreased as the size and thickness of thew denture base was increased. Distortional openings along the posterior palatal border of U-shaped and V-shaped palates were greatest at the midline and extended laterally two thirds of the distance from the midline to the hamular notch.

What did he recommend?

That the postpalatal seal should be deeper in the central part of the palate and extend to the hamular notch to compensate for acrylic distortion

During processing of the denture what may contribute the most to acrylic distortion?

Heat activation and cooling. It is assumed that the gypsum materials, the metal flask and the positive pressure all combine to compensate for polymerization shrinkage. The magnitude of the remaining linear shrinkage is attributed to thermal changes, which occur after the plastic assumes the physical properties of a solid. Linear shrinkage is estimated about 0.44% and by volume has been stated to be up to 8%. (varies according to author)

Cure Cycle: 165 F for 8 hrs. 2nd stage at 212 F for 1hr. bench cool 1 hr. soak room temp water ½ hr.

Monomer boils at 213.4F = porosity. If temperature rises too quickly what may occur to the thin areas of the denture base? Denture syllabus

( Stone acts as a heat sink by pulling the heat away from the thin denture base areas. The thin areas of the denture base never reach activation temperature of 157 F.

Category: Prosthodontics Notes



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