Objective:The objective of this study is the effect of different heat polymerization conditions on the strength of polymethyl methacrylate (PMMA) resin base is unknown. Distinguishing one method that provides improved mechanical properties may be beneficial to the clinical success of complete and partial dentures and overdentures. The purpose of this study was to evaluate the effect of different polymerization methods on the flexural strength of a dental PMMA resin.Materials and Methods:Forty PMMA specimens (64 mm × 10 mm × 4 mm) were prepared with 4 different polymerization methods (n = 10); heat polymerization at 74°C for 9 h, at 100°C for 40 min, and with 620 kPa pressure at 100°C for 20 min. The remaining group of specimens was microwave polymerized at 180 W for 6 min. All specimens were thermocycled at 5°C and 55°C for 5000 times. Three-point flexure test was used to measure the flexural strength of specimens. One-way ANOVA and Tukey Honestly Significant Difference were applied to analyze the differences in flexural strengths (α = 0.05).Results:The flexural strength of heat-polymerized groups was similar. The flexural strength of microwave polymerized group was significantly different and lower than the other groups (P < 0.05).Conclusion:Polymerizing conventional heat-polymerizing PMMA resin with microwave energy resulted in a significant decrease in flexural strength. The results of this study suggest that clinicians may benefit from using heat polymerization when processing PMMA denture bases instead of microvawe polymerization when tested brand is used.

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There is limited knowledge about the effects of ultrashort pulsed laser on zirconia ceramic surfaces. The aim of this study was to evaluate the effects of ytterbium (Yb)-doped fiber laser and other surface treatment methods -namely, sandblasting with 110 µm aluminum oxide or 30 µm silica-coated alumina on shear bond strength (SBS) of zirconia to tooth surface. A total of 128 zirconium oxide disks were made by using CAD-CAM technology. Disk surfaces were sandblasted with Al2O3 particles or silica-coated alumina or irradiated with Yb-doped fiber based nanosecond pulsed laser at 85W output power at 25 kHz. Disks were luted to dentin using two different resin cement. SBS of each specimen was measured. Results were statistically analyzed using two-way analysis of variance (ANOVA) and Bonferroni and Dunnett tests (p<0.005). Highest bond strength was obtained when zirconia surface was pretreated with Yb-doped fiber-based nanosecond pulsed laser regardless of the resin cement used.

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