Abrasive machining of glass-ceramics with a dental handpiece

Dental restorations are commonly prepared from machinable glass-ceramics us ing modern dental CAD/CAM systems. Unfortunately, little is understood abou t the influence of machining parameters on material removal rates and any d amage which could be introduced into the restoration during the abrasive ma chining processes employed with these systems. These effects are investigat ed for three experimental machinable glass-ceramics with varying microstruc ture and one closely related commercial material. Abrasive machining is per formed with dental burs containing coarse and fine diamond particles. The r esults show that the microstructure of the glass-ceramic, the size of diamo nd 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 t he mica platelets within the glass-ceramics or by increasing the load on th e 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 microstruc ture or applied load but is strongly dependent upon coarseness of the diamo nd particles in the burs.