In vitro study on high rotation deep removal of ceramic prostheses in dental surgery

In vitro study on high rotation (up to over 300,000 rpm) deep removal (up to 150 microm) of ceramic prostheses, made of a machinable ceramic, Vita Mark II, was performed in dental surgery using a high-speed dental handpiece. Dental clinical removal relevance, including tangential and normal grinding forces, specific grinding energy, and surface roughness, was investigated to establish the relationships among the surgery parameters, chip geometry, and fracture mechanism. The results show that both the tangential and normal grinding forces increased with increases in both depth of cut and maximum undeformed chip thickness, but decreased with an increase in grinding speed. Specific grinding energy decreased with increase in the depth of cut and the maximum undeformed chip thickness, but increased with an increase in grinding speed. Surface roughness and morphology appeared to be independent of the increases in depth of cut, grinding speed, and maximum chip thickness. The limitation for deep removal using the dental handpiece was found that the operation at the depth of cut of 150 microm or beyond resulted in a huge normal force exertion of 3 N with a great variation. The microfracture, the lateral fracture, and the ductile microcutting were found to occur simultaneously in dental surgery to remove the ceramic prostheses.