Effects of wear on hardness and stiffness of restorative dental materials

The aim of this research was to evaluate the effects of mechanical wear on surface mechanical properties (hardness and elastic moduli) of commonly used restorative materials. For this purpose, the materials were characterized before and after wear mechanical cycles and compared with tooth tissues. Dental restorative materials were evaluated for the effect of wear on surface mechanical properties. All samples were characterized for nanoindentation before and after mechanical wear using Hysitron [TI 725 Ubi] testing instrument. Data was analyzed using the SPSS software (version 20) and t-test was used to calculate the statistical significance. The wear mainly affected the direct restorative materials and increasing their elastic moduli significantly (p=0.05).The elastic moduli of PMMA jumped from 3.93±0.57 GPa to 4.85±0.4, GIC from 9.57±2.00 GPa to 20.87±3.56, resin composites from 11.16±3.08 GPa to 19.41±2.61 and for amalgam from 60.44±5.98GPa to 108.63±7.37 (p=0.05). Similar trend has been observed for nanohardness of these materials. Wear increases the hardness and elastic modulus of direct restorative materials (acrylic resins, glass ionomers, resin composites and silver amalgam). However it did not affect properties of indirect restorative materials including dental porcelain, nickel chrome and cobalt chrome casting alloys.