Effect of amount of grinding on flexural strength of dental ceramics.

The aim of this study was to determine a suitable amount of grinding of a flexural test specimen for clinical evaluation of dental ceramics. Three dental ceramics (Crys-Cera, OCC and IPS Empress Cosmo) were selected. Five types of bar-shaped patterns were prepared for a three-point bending test, and four types of disk-shaped patterns for a biaxial flexural test. Ceramic specimens were fabricated using these patterns in accordance with the manufacturers' instructions. All specimens were ground with diamond polishing pads to yield either bar or disk specimens with the same final geometry. The surface roughness and X-ray diffraction (XRD) patterns of the specimens were examined. The flexural strength values of Crys-Cera and Empress decreased with increasing amounts of grinding, while that of OCC increased with increased grinding. The surfaces of all specimens were smoother when the amount of grinding was deeper. The XRD patterns of Crys-Cera and Empress changed with increased grinding; however, that of OCC did not change regardless of the extent of grinding. The flexural strengths of three dental ceramics differed with the amount of grinding probably because of changes of surface roughness and crystalline component composition. Unground specimens provided important insight into clinical failure modes.