ABSTRACT
This article was conducted to examine and compare the effect of thermocycling on some important properties of two types of denture base materials, which were conventional and high impact strength resins. High impact strength resin was prepared by dissolving different proportion of butadiene-styrene rubber [BSR] in MMA monomer, the prepared monomer was then polymerized with ordinary PMMA by conventional means. So, graft copolymers were obtained. Three groups were prepared according to the concentration of BSR in MMA, i.e. 10%, 20% and 30% by weight. The test specimens of each group were classified into three subgroups depending on the degree of thermocycling, i.e. 500, 1000 and 1500 thermal cycles, respectively, between 60C and 5C, with immersion time 30 seconds per cycle. In addition, one group of uncycled samples was tested [control group]. Multifactorial experiments were carried out on the different groups and evaluated with respect to impact strength, flexural strength, young's modulus and tensile tooth-base bond strength. From the results obtained, it could be concluded that both impact and flexural strength of high impact strength resin are superior to the conventional heat-cured acrylic resin, while the young's modulus values for the two types are considered within the clinical and technical limits of use as denture base materials. Thermocycling used in this study did not affect the impact, transverse, young's modulus and tensile tooth-base bond strength values of high impact strength resin, while a significant effect was reported for conventional heat- cured acrylic resin. The tooth-base bond strength of high impact strength resin is inferior to heat-cured resin. Further investigations are required to increase the bond strength by mechanical or chemical means of retention