A Machining Science Approach to Dental Cutting of Glass Ceramics Using an Electric Handpiece and Diamond Burs

Dental cutting using handpieces has been the art of dentists in restorative dentistry. This paper reports on the scientific approach of dental cutting of two dental ceramics using a high-speed electric handpiece and coarse diamond burs in simulated clinical conditions. Cutting characteristics (forces, force ratios, specific removal energy, surface roughness, and morphology) of feldspar and leucite glass ceramics were investigated as functions of the specific material removal rate, Q(w) and the maximum undeformed chip thickness, h(max). The results show that up and down cutting remarkably affected cutting forces, force ratios, and specific cutting energy but did not affect surface roughness and morphology. Down cutting resulted in much lower tangential and normal forces, and specific cutting energy, but higher force ratios. The cutting forces increased with the Q(w) and h(max) while the specific cutting energy decreased with the Q(w) and h(max). The force ratios and surface roughness showed no correlations with the Q(w) and h(max). Surface morphology indicates that the machined surfaces contained plastically flowed and brittle fracture regions at any Q(w) and h(max). Better surface quality was achieved at the lower Q(w) and the smaller hmax. These results provide fundamental data and a scientific understanding of ceramic cutting using electric dental handpieces in dental practice.