Abrasive machining of glass-ceramics with a dental handpiece

Dental restorations are commonly prepared from machinable glass-ceramics using modern dental CAD/CAM systems. Unfortunately, little is understood about the influence of machining parameters on material removal rates and any damage which could be introduced into the restoration during the abrasive machining processes employed with these systems. These effects are investigated for three experimental machinable glass-ceramics with varying microstructure and one closely related commercial material. Abrasive machining is performed with dental burs containing coarse and fine diamond particles. The results show that the microstructure of the glass-ceramic, the size of diamond grit in the burs, and the load applied to the burs during machining have significant effects on the machining behavior. By increasing the size of the mica platelets within the glass-ceramics or by increasing the load on the burs, material removal rate increases. However, chipping damage at groove edges increases as either the load is increased or as the size of the mica platelets is decreased. The use of coarse burs does not necessarily result in high material removal rates but increases the extent of chipping damage. Surface roughness is found to be relatively independent of the microstructure or applied load but is strongly dependent upon coarseness of the diamond particles in the burs.