The Effect of Nano- ZrO2 and nano-Al2O3 Reinforcement on Flexural and Impact Strength of Repaired Acrylic Denture Base

Purpose: This study was conducted to evaluate the effect of reinforcement
of different concentrations of nano-ZrO2 and nano-Al2O3 on the flexural strength and impact strength of repaired acrylic resin denture bases. Materials and Methods: A total of 100 specimens were prepared from heat-polymerized acrylic resin and then they were equally divided for the flexural and impact strength tests. 50 specimens were assigned for each testing group. For the flexural strength testing, metallic rectangular molds with rectangular-shaped (65 mm length x10 mm width x 2.5 mm thickness) were prepared. While specimens for the impact strength testing were prepared using rectangular-shaped molds with dimensions of (50 mm length x6mm width x4mm thickness). The prepared intact specimens were cut vertically in two halves along their long axis. For the flexural and impact strength testing, a repair gap was done. Specimens for each strength test were divided into one control group (specimen repaired with autopolymerizing acrylic resin with no fillers) and two repair groups with 2 concentrations (2% and 5%) of nano-ZrO2 fillers and two repair groups with 2 concentrations (2% and 5%) of nano-Al2O3 fillers. Flexural strength was measured using an Instron mechanical testing machine and impact strength was measured by Izod impact tester. Results: For the flexural strength results, the highest flexural strength was recorded with the 5% nano-ZrO2 fillers repair group followed by the 2% nano-ZrO2 group which also recorded higher significant mean value than the control group. In both nano-Al2O3 groups, there was a highly significant reduction in the flexural strength for both concentrations. For the impact strength results, the highest impact strength was recorded for the 2% nanoZrO2 fillers repair group followed by the 5% nano-ZrO2 group which also recorded higher significant mean values than the control group. In the 2% nano-Al2O3 repair group, there was a non-significant difference in the impact strength mean values compared with the control group. While the repair group reinforced with 5% nano-Al2O3 showed significant reduction in impact strength.
Conclusions: The incorporation
of nano-ZrO2 into repair resins may improve the flexural and impact strength of the repaired denture base whereas nano-Al2O3 caused reduction of both strengths.