Ultrasonic assisted high rotational speed diamond machining of dental glass ceramics

Subsurface damage and edge chipping remain a persistent technical challenge for the abrasive machining of dental restorations made from glass ceramics, and they impede the fabrication of long-lasting dental restorations. This paper reports on an integration of ultrasonic assistance to dental high-speed rotary abrasive machining for improvement of the surface quality of glass ceramics. An ultrasonic assisted computer-controlled high-speed rotary cutting apparatus was designed and fabricated with functions of ultrasonic vibration, automatic cutting, and force measurement. A multi-phase feldspar glass ceramic with the highest brittleness among glass ceramics was selected for the study. Machining forces, surface roughnesses, and edge chipping damage were evaluated for a range of cutting conditions with and without ultrasonic vibrations. Our most significant finding is that ultrasonic assisted machining led to a clear and consistent reduction of edge chipping and thus subsurface damage. Ultrasonic machining also achieved significant reductions in normal and tangential forces, and surface roughness at higher removal rates (p < 0.05). Our results suggest that ultrasonic assisted dental machining may be a way to improve quality and lifetime of ceramic dental restorations, whose failures are rooted in chipping damage and surface flaws using current machining techniques.