Surface Roughness of Monolithic Zirconia and Gold Alloy After Wear Simulation Against Human Enamel

Purpose: To evaluate the effect of simulated wear against human enamel on the surface roughness of monolithic zirconia and gold alloy under different occlusal loads.
Materials and Methods: Forty rectangular plate specimens (6×6×2) mm, were prepared from monolithic zirconia (Bruxzir, n=20) and type IV gold (Begostar, n=20) forming two experimental groups. Forty premolar teeth freshly extracted for orthodontic purpose were sectioned mesio-distally and only the cusp tips of the buccal halves were used as antagonists in the wear simulation testing procedure. All of the specimens were mounted to chewing simulator with the cusp antagonists, half of them were subjected to (50000 chewing cycles under 50N load), the other half subjected to (50000 chewing cycles under 150N load) cyclic loading. Data were submitted to two-way ANOVA, and statistical significance was set at p < 0.05.
Results: With low load (50 N), it was found that gold alloy group recorded statistically significant higher roughness change mean value (0.00085±0.001 Ra) than Bruxzir group mean value (-0.00079±0.0023 Ra). The difference between groups was statistically significant as indicated by student t-test (t=2.08, p=0.0492 < 0.05). While, enamel cusp antagonist of gold alloy group recorded non-statistically significant higher roughness change mean value (0.01867±0.024 Ra) than enamel cusp antagonist of Bruxzir group mean value (0.016567±0.0013 Ra). The difference between groups was statistically non-significant as indicated by student t-test (t=1.7, p=0.1043> 0.05). With high load (150 N), it was found that gold alloy group recorded statistically non-significant higher roughness change mean value (0.00135±0.0017 Ra) than Bruxzir group mean value (-0.00052±0.003 Ra). The difference between groups was statistically non-significant as indicated by student t-test (t=1.648, p=0.1135 > 0.05). While, enamel cusp antagonist of gold alloy group recorded statistically non-significant higher roughness loss mean value (0.00219±0.005 Ra) than enamel cusp antagonist of Bruxzir group mean value (-0.00021±0.005 Ra). The difference between groups was statistically non-significant as indicated by student t-test (t=1.15, p=0.2615> 0.05).
Conclusions: 1. Monolithic zirconia do not become as rough as type IV gold when subjected to simulated mastication cycles at low (50 N) load, although they were not significantly different from each other at high (150 N) load. 2. Although being non-significant, there was a correlation between roughness change of both monolithic zirconia and gold substrates, and that of their enamel antagonists.