The effects of adding various ratios of zirconium oxide nanoparticles to poly(methyl methacrylate) on physical and mechanical properties.

The aim of the present study is to evaluate the transverse strength, modulus of elasticity, surface roughness, hardness, and water sorption/solubility of nanoparticle zirconium oxide (nano-ZrO2) added to heat-cured poly(methyl methacrylate) (PMMA) after thermocycling. The specimens were divided into four groups according to the ratio of nano-ZrO2 addition to heat-cured PMMA; group 1: 5% nano-ZrO2; group 2: 10% nano-ZrO2; group 3: 20% nano-ZrO2, and group 4 (control): PMMA without nano-ZrO2. A statistically significant decrease in transverse strength was observed by all additional rates of nano-ZrO2 compared with group 4 (control; P < 0.025). When hardness results were evaluated, groups 1 and 2 showed statistically higher values compared with groups 3 and 4 (P < 0.025). The surface roughness of group 3 was statistically higher than the other groups (P < 0.025), but it was within the clinically acceptable limits. As the nano-ZrO2 addition rate increased, water sorption/solubility values of the specimens also increased. Although nano-ZrO2 addition had an adverse effect on some mechanical and physical properties of heat-cured PMMA, it increased hardness values, implying that the addition of nano-ZrO2 would contribute positively to some mechanical properties of PMMA denture base material when nano-ZrO2 was homogeneously distributed in PMMA.