Abrasive machining of glass-infiltrated alumina with diamond burs

The abrasive machining characteristics of a glass-infiltrated alumina used for fabrication of all-ceramic dental crowns were investigated using a high -speed dental handpiece and diamond burs with different grit sizes. The mat erial removal rate, surface roughness, and extent of edge chipping were mea sured as a function of grit size. The removal rate decreased substantially with decreasing bur grit size from supercoarse (180 mum) to fine (40 mum) a nd ultrafine (10 I-lm) The removal rate with the supercoarse burs was appro ximately twice that achieved with the fine burs and four times the removal rate with the ultrafine burs. Both surface roughness and edge chipping dama ge were sensitive to diamond grit size. Chipping damage was severe and the surface roughness substantial with the supercoarse burs, while negligible e dge chipping and smooth surfaces were obtained with the ultrafine burs. The removal rate also decreased with continued machining for all grit sizes. T he observed reduction in removal rate was found to be primarily due to wear of the diamond grit and accumulation of debris on the bur (i.e., bur loadi ng). After prolonged use, a significant loss of diamond grit was observed t hat led to a substantial loss of cutting efficiency. It is concluded that, with respect to material removal rate and surface integrity, diamond machin ing is a feasible machining process for glass-infiltrated alumina in the fi nal infiltrated state. However, caution should be exercised in the use of d iamond grit larger than 40 mum. Such burs may result in excessively rough s urfaces, chipped edges, and strength limiting surface and subsurface microc racks.