Surface integrity and removal mechanism in simulated dental finishing of a feldspathic porcelain.

Dental abrasive finishing of a fine-grained feldspathic porcelain was performed on a computer-assisted apparatus for simulation of a 2-degrees-of-freedom restorative operation with a dental handpiece and a coarse diamond bur of grit size of 106-125 mum. Finishing forces, surface roughness, and morphology were investigated as functions of finishing conditions. The tangential and normal forces were measured using a piezoelectric dynamometer and a data processing system. The results indicated that these forces increased with either the depth of cut or with the feed rate, in the ranges of 0.12-0.31 N and 0.45-1.09 N, respectively. However, an increase in either depth of cut or feed rate affected neither the surface roughness measured using a stylus profilometer nor the morphology observed under a scanning electron microscope. The finished porcelain surfaces were found to consist of the microfracture and chipping areas, ductile removal areas, smeared areas, and debris. Irregular fracture and chipping resulted from the extension of lateral/median cracks; ductile micromachining was attributed to the plastic deformation accompanied by distributed microcracks. It was determined that a combination of the microfracture and ductile micromachining was the primary mechanism for material removal.

Performance evaluation of a dental handpiece in simulation of clinical finishing using a novel 2DOF in vitro apparatus.

This paper reports on the performance evaluation of a dental handpiece in simulation of clinical finishing using a novel two-degrees-of-freedom (2DOF) in vitro apparatus. The instrumented apparatus consisted of a two-dimensional computer-controlled coordinate worktable carrying a dental handpiece, a piezoelectric force dynamometer, and a high-speed data acquisition and signal conditioning system for simulating the clinical operations and monitoring the dental finishing processes. The performance of the dental handpiece was experimentally evaluated with respect to rotational speed, torque, and specific finishing energy under the applied clinical finishing conditions. The results show that the rotational speeds of the dental handpiece decreased by increasing either the depth of cut or the feed rate at a constant clinically applied air pressure and water flowrate. They also decreased when increasing both the tangential and normal finishing forces. The specific finishing energy decreased with an increase in either depth of cut or feed rate, while the finishing torque increased as either the depth of cut or the feed rate was increased. Implications of these results were to provide guidance for proper applications of dental handpieces in clinical practice.