Effects of surface finish on indentation modulus and hardness of dental composite restoratives

Objectives The depth-sensing micro-indentation testing was recently introduced for the characterization of dental composites. One of the critical issues raised was the possible influence of surface finish on material properties. The aim of this study was to investigate the effects of surface finish on the indentation modulus and micro-hardness of resin-based dental composite materials. Methods The materials used included minifill (Z100, 3M ESPE), microfill (A110, 3M ESPE) and poly-acid modified (F2000, 3M ESPE) composites. The specimens were polished successively using SiC grinding papers of different grit size and diamond suspensions to achieve varying surface roughness. The arithmetic mean of the roughness (Ra) was measured using profilometry. In the depth-sensing micro-indentation test, specimens (n=7) were indented to 10 N with Vickers indenter and the load-displacement (P–h) data was obtained using a universal testing system. The indentation modulus (Ein) and hardness (H) were then computed using the developed analytical solutions. Data was analyzed using ANOVA/post-hoc Scheffeʹs test at significance level 0.05. Results The polished specimens had surface roughness ranging from 0.02 to 0.81 μm. The roughness of F2000 was significantly higher than A110 and Z100. The Ein and H for Z100 ranged from 14.02 to 14.83 GPa and 1.18 to 1.27 GPa, respectively. Ein for F2000 and A110 ranged from 12.25 to 13.82 GPa and 5.26 to 5.52 GPa and hardness ranged from 0.89 to 0.98 GPa and 0.52 to 0.55 GPa, respectively. Significance The indentation modulus and hardness of dental composite restoratives were independent of the surface finish provided indenter penetration is sufficiently deep (hmax/Ra>30).