Surface morphology and fracture in handpiece adjusting of a leucite-reinforced glass ceramic with coarse diamond burs

The aim of this paper was to understand surface morphology and fracture occurring on leucite-reinforced glass ceramic surfaces adjusted with coarse diamond burs. The surface roughness was quantitatively assessed using stylus profilometry and was analyzed statistically. The surface morphology was viewed using scanning electron microscopy. Surface phase transformations were preliminarily studied using Raman spectrometry. The results show that the surface roughness did not significantly depend on either depth of cut (p > 0.05) or feed rate (p > 0.05). However, when decreasing the depth of cut and the feed rate, a tendency for brittle-to-ductile transition existed. The surface morphology consisted of microfracture, chipping, ductile removal scratches, smear areas and debris. Brittle fracture was the primary mechanism for material removal. Lateral and radial cracks due to the mechanical impact of diamond burs were the major cause of surface fracture in the leucite-reinforced glass ceramic. The maximum adjusting temperatures on the adjusted surfaces were estimated based on heat transfer analysis. The Raman spectra of the adjusted and unadjusted surfaces show a strong temperature-dependence of Raman shifts near 525–529 cm−1. This indicates the occurrence of temperature-induced cubic-tetragonal phase transformations in the adjusted leucite glass ceramic surfaces. These phase transformations are considered to contribute crack initiation and propagation on the adjusted surfaces