Thermal and dynamic mechanical properties of microwave and heat-cured poly(methyl methacrylate) used as dental base material

In this study, the particle size distribution, molecular weight, thermal analysis (TGA) differential scanning calorimetry (DSC) and thermogravimetric analysis, and dynamic mechanical analysis (DMA) of poly(methyl methacrylate) used as dental base material were investigated. The commercial raw material used were prepared for microwave curing, and they were cured by microwave and conventional heat methods. The average particle size of the powder studied (103.1 mu m) were much larger than that of the commercial powders (50-78 mu m) for conventional curing. The particle size dietribution were almost symmetrical and narrow. The viscosity-average molecular weight were larger for microwave curing and increased with curing time. The glass transition temperature T-g measured (about 110 degrees C) by DSC increased with curing period in microwave oven. The values of T-g were close: to each other for both curing techniques. The degradation temperature range observed by TGA were 200-377 degrees C. The movements of molecular chains in their conformations were studied by DMA in the form of changes in different mechanical properties with temperature. It was shown that crosslinking increased with increase of curing time. The changes were more noticeable in microwave curing compared to conventional heat curing. (C) 1999 John Wiley & Sons, Inc.