Does Diamond Stone Grinding Change the Surface Characteristics and Flexural Strength of Monolithic Zirconia?

The present study evaluated the effect of grinding on the surface morphology, mean roughness, crystalline phase, flexural strength, and Weibull modulus of monolithic (MZ) and conventional (CZ) zirconias.

CZ and MZ bars and square-shaped specimens were distributed into three subgroups, combining grinding (G) and irrigation (W) with distilled water: Ctrl (Control: no grinding, 20 × 4 × 1.2 mm and 12 × 1.2 mm), DG (dry grinding, 20 × 4 × 1.5 mm and 12 × 1.5 mm), and WG (grinding with irrigation, 20 × 4 × 1.5 mm and 12 × 1.5 mm). The grinding (0.3 mm) was performed on a standardized device using a low-rotation wheel-shaped diamond stone. The four-point flexural strength test was performed on the EMIC 2000 machine (5 KN, 0.5 mm/min). Scanning electron microscopy (SEM) was used to evaluate the surface morphology. An X-ray diffractometer (XRD) was used to obtain the crystalline structures that were analyzed by the Rietveld method. Flexural strength (FS) values were subjected to the Shapiro-Wilk test and two-way analysis of variance followed by the Tukey's test (for all tests, α=0.05).

Grinding, either with or without irrigation, did not change the FS of the MZ but increased the FS of the CZ. Both MZ and CZ showed similar morphologic patterns after grinding, and in the WG groups, the grinding was more aggressive. The MZ had greater monoclinic content in all groups; grinding without irrigation caused the smallest t→m transformation.

The grinding, when necessary, should be carried out without irrigation for conventional and monolithic zirconias.