Effect of water temperature during polymerization on strength of autopolymerizing resin

Statement of problem. Breakage is a potential problem of provisional resin restorations. A method that effectively increases the strength of the resin is desirable. Purpose. This study examined the effects of the curing environment, air or water, and water temperature during polymerization on the mechanical properties of autopolymerizing resin. Material and methods. After mixing the autopolymerizing methyl methacrylate resin for 10 seconds, it was placed in a stainless steel mold (2 x 2 x 25 mm). One minute and 50 seconds after the start of mixing, the mold containing the resin was placed under the following conditions: in air at 23°C; or in water at 10°C, 23°C, 30°C, 40°C, 60°C, and 80°C. Six minutes after mixing began, the resin specimen was removed from the mold and the transverse test (3-point flexural test) was performed. Results. Alteration of conditions during polymerization revealed a significant effect on both the transverse strength and modulus of the resin (P<.0001). Both increased with an increase in water temperature. Water conditions of 60°C to 80°C produced more than 2 times greater transverse strength and modulus of the resin compared with polymerization in 23°C air (P<.0001). Conclusion. Polymerization of the resin in hot water greatly increased its mechanical properties. The method of placing resin restorations in hot water during polymerization may be useful for improving mechanical requirements and obtaining long-lasting performance.