The wear of acrylic denture teeth is a serious problem that can change the vertical dimensions of dentures. This study evaluates the effect of adding salinized nano ZrO2 particles on the microstructure, hardness, and wear resistance of acrylic denture teeth. Heat polymerizing polymethyl methacrylate resin was mixed with salinized ZrO2 at concentrations of 5 wt% and 10 wt%. Acrylic resin specimens without filler addition were used as a control group. SEM/EDS analyses were performed and the Vickers’ hardness was evaluated. Two-body wear testing was performed using a chewing simulator with a human enamel antagonist. After subjecting the samples to 37,500 cycles, both height loss and weight loss were used to evaluate the wear behavior. The microstructural investigation of the reinforced-denture teeth indicates sound nanocomposite preparation using the applied regime without porosity or macro defects. The addition of zirconium oxide nanofillers to PMMA at both 5% and 10% increased the microhardness, with values of up to 49.7 HV. The wear mechanism in the acrylic base material without nanoparticle addition was found to be fatigue wear; a high density of microcracks were found. The addition of 5 wt% ZrO2 improved the wear resistance. Increasing the nanoparticles to 10 wt% ZrO2 further improved the wear resistance, with no microcracks found.

Statement of problem: Addition of zirconium oxide nanofillers to PMMA had improved the mechanical properties of heat polymerized acrylic resin, but it's effect on bond strength to acrylic teeth hadn't been evaluated yet. Purpose: The purpose of the study was to evaluate the effect of Zirconium oxide (ZrO 2) nanofillers powder with different concentrations (1.5%, 3%, 5%) on bond strength of resin denture base to acrylic teeth before and after thermocycling. Material and methods: Zirconium oxide nanoparticles powder were added to heat cured (PMMA) with different concentrations (0, 1.5% ,3%, 5%). The base surfaces of 16 molar acrylic teeth were flattened, and zirconia reinforced heat-polymerized acrylic resin was applied to them. Thereafter, bar specimens were produced for the microtensile bond strength testing either before or after thermocycling. Results: The results showed that 5% ZrO 2 conc. recorded the highest value of microtensile bond strength. The lowest value was recorded in 1.5%, followed by 3%. Regarding thermocyling, the non-thermocycled groups always recorded higher values of microtensile bond strength either significant (1.5% & 5%) or insignificant (0% & 3%) than thermocycled ones at p < 0.05. Conclusions: Within the limitation of this study, it was concluded that reinforcement of acrylic denture base with zirconia nanofillers had significantly decreased bond strength with acrylic denture teeth in 1.5 % and 3% concentration; however, 5% had increased the bond strength values insignificantly. Thermocycling had reduced the bond strength in all concentrations.

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