The Experimental Study Of Effect Of Varied Curing Methods On Surface Roughness And Water Absorption Of PMMA Denture Base Material

IntroductionHeating-curing PMMA is still the most commonly materials for denture base widely because of its excellent properties, easiness to be processed and so on. There is some affinity between the heat curing methods and procedure and the properties of denture base resins.This study compares the difference of surface roughness and water absorption of 2 PMMA resins respectively polymerized by water bath, microwave energy with long cycle, microwave energy with short cycle and electrothermal treatment, therefore reflects the effect of varied curing methods on surface roughness and water absorption of denture base resins. Some evidence can be provided to choice the fitting curing method which would process resins in possession of better properties for the clinical work.Material and Methods1. 64 wax patterns which were 30×30×2 mm were made and randomly divided into eight groups and each group has 8 samples. All the wax patterns were preserved in the water at the room temperature. The casts with wax patterns were invested in different flasks using routine method. After different deceration, 2 factories' denture base resins were respectively packed, pressed and fixed. Each material was singly cured by water bath, microwave energy with long cycle, microwave energy with short cycle and electrothermal processing. After cooling. and desflasking, one side of the sample was ground and polished with the principle of "from coarse to refined". Surface roughness (Ra) of the resin specimens was measured and using a handy profilometer (TR200, TIME GROUP INC. Beijing, China).2. The specimens were immersed in black ink for 30min, then scoured by floating water and dried. Each surface was selected 1 cm~2 area and observed under a microscope, and photographed with the microscopical camera.3. 64 columned wax patterns were made by a metal mold with 50 mm diameter and 2.5 mm thick and randomly divided into 8 groups. Each group has 8 samples and all the wax patterns were preserved in the water at the room temperature. All samples were processed using before-mentioned method and procedure, including flasking, eliminating wax, packing, heat curing, cooling and desflasking. After finishing and polishing, specimens were dried periodically in desiccators until constant quality. Then specimens were immersed in constant temperature water for 7 days and weighed. Whereafter samples were dried again until constant quality and weighed. The water absorption value was calculated according volume.4. All results were subjected to two factors ANVOA(Repeated Measures) and multiple comparison with SPSS13.0 software. The effect of varied curing methods and varied factories' material on surface roughness and water absorption was analyzed.Results1. The surface roughness Ra means of all groups were lower than 0.2μm. No statistically difference was found among the Ra means of specimens cured by varied heat processing methods (p > 0.05); no statistically difference was found among the effect of varied materials on the Ra (p > 0.05); there was no interaction between the heat processing methods and materials (p > 0.05).2. Some black pores and scotches on the specimen surface were observed using a x40 magnified microscope, which could not be found while macrography. The orientations of scotches were basically consistent and pores were dispersed. These pores were found on lays of different depth inside the specimens. Several pindling pores were massed. The pores were basically global, the larger were about 500μm diameter and the smaller were about 10μm diameter.3. The water absorption mean of specimens cured by microwave energy with long cycle was the smallest, but the absorption mean of water bath group was the biggest. Statistically difference was found among water absorption means of varied curing groups. After multiple comparisons, remarkable difference was found between the microwave curing with long cycle group and the other groups, but there was no difference between the other groups. No statistically difference was found among the effect of varied factories' materials on the water absorption(p > 0.05); there was no interaction between the heat processing methods and materials (p > 0.05).Conclusion1. Surface roughness of PMMA base materials cured by microwave processing and by electrothermal processing is consistent with those cured by water bath processing, and they all can satisfy the clinical request.2. Water absorption of denture base resins cured by microwave with long cycle is lower than those cured by the other methods, but no difference can be found between the other groups.3. Varied factories' heating-curing PMMA materials have the same capability to water bath curing ,microwave curing and electrothermal processing. Varied materials have no effect on the varied curing methods.