Study On In Vitro Intra-Oral Dental Abrasive Finishing Mechanism Of A Feldspar Porcelain

With the consideration of the machining damage of dental ceramics induced in dental abrasive finishing processes, abrasive fininshing behavior of a feldspar porcelain was investigated using a novel computer controlled in-vitro apparatus which was developed for simulation of two-degrees-of-freedom restorative operation with a dental handpiece and a coarse diamond bur of grit size of 106-126μm. The following work and conclusions are drawn:Both the tangential and normal forces were measured using a piezoelectric dynamometer and a data processing system to increase with increasing either the depth of cut or the feed rate of dental handpiece.The normal grinding forces per grit were analysed based on the indenting fracture theory. The results showed that at any finishing conditions, the minimum normal grinding forces per grit were much smaller than the critical threshold load, but the maximum normal forces per grit were larger than the critical load. Furthermore, the maximum normal forces per grit increased with increases in feed rate, but the depth of cut did not affect the maximum normal forces per grit.Surface roughness and morphology were independent of the increase in either depth of cut or feed rate.The finished surfaces were observed with a scanning electron microscopy (SEM) to consist of irregular fracture and chipping areas, ductile removal areas, microcracks and debris. Microfracture and chipping were found to take the extension of lateral/median cracks, and ductile microcuting was attributed to the plastic deformation with companies of the distributed microcracks. A combination of microfracure and ductile maching was determined as the primary mechanism for material removal.The above research results are significative to guide the dental finishing of a feldspar porcelain in dental surgery using a dental handpiece and a coarse diamond bur for dentists.