Temperature Effect on the Hardness of Different types of Resin Denture Base Materials

Abstract

The cold cured acrylic resin is inferior to heat cured acrylic resin from stand pointof strength and degree of polymerization. Many attempts have been made to improvethese properties. Because heat affects maturity of the chemical reaction of acrylicresin therefore its maintenance during polymerization will affect the properties ofcured resin.The purpose of this study was to evaluate the effect of increase curing temperatureon the hardness of two commercially available cold cured acrylic resin material(Holland and Germany type) in comparison to heat cure resin and to those(cold cure)curing by conventional methods in air at 23°C ± 5°C.Ninety specimens,10 specimens from heat cure resin curing by water bath(shortcycle) and eighty specimens from cold cured acrylic [forty from cold curedacrylic(Holland Type) and forty from cold cured acrylic(Germany type)] wereprepared , flasking and packing procedure were done according to manufacturerdirection and divided according to processing as follow:20 specimens(10 fromHolland type and 10 from Germany type) were processed in air for two hours at 23°C± 5°C under press (bench curing) as a control, and 60 specimens(30 from Hollandtype and 30 from Germany type) were processed by ivomat curing device containingwater under air pressure 30 Pascal for 15 minutes at different temperature: 40°C,60°C, and 80°C(10 specimens for each groups) .All specimens were tested forhardness test by shore D device (adigital model) for measuring the indentationhardness of the specimens the test load was set to 50 Newton for shore (( D ))which issuitable for acrylic resin material .Result showed that heat cure resin show the maximum value of hardness(88.8),followed by cold cured acrylic type Germany( polymerized by elevatedtemperature 80˚C) (88.696) followed by cold cured acrylic type Holland polymerizedat 60˚C(88.471). While control group type Germany (polymerized at air bench)recorded the minimum value of hardness (81.83). All groups that polymerized at hightemperature: 40°C, 60°C, and 80°C show the higher value of hardness in comparisonto those processed by conventional methods (at air bench at 23°C ± 5°C) withsignificant and highly significant differences. There were highly significantdifferences between heat cure acrylic and cold cure (both types) processed byconventional methods and with cold cure Holland type processed at 40˚C, but therewere no significant differences between heat cure acrylic and cold cure (both types)processed at high temperatures.