Cracking of Porcelain Surfaces Arising from Abrasive Grinding with a Dental Air Turbine

Purpose: The purpose of this in vitro study was to evaluate porcelain cracking induced by abrasive grinding with a conventional dental air turbine and abrasive diamond burs. Materials and Methods: Four commercially available porcelains were examinedWieland ALLUX, Wieland ZIROX, IPS e. max Ceram, and IPS Empress Esthetic Veneering porcelain. Sixty discs of each porcelain type were fabricated according to manufacturer instructions, followed by an auto-glaze cycle. Abrasive grinding using fine, extra-fine, and ultra-fine diamond burswas carried out, using a conventional dental air turbine. The grinding parameters were standardized with regard to the magnitude of the force applied, rotational speed of the diamond bur, and flow rate of the water coolant. A testing apparatus was used to control the magnitude of force applied during the grinding procedure. The ground surfaces were then examined under scanning electron microscope. Results: Cracking was seen for all porcelain types when ground with the fine bur. Cracking was not seen for specimens ground with the extra-fine or the ultra-fine bur. Conclusion: Wet abrasive grinding with a conventional dental air turbine and fine grit diamond burs has the potential to cause cracking in the four porcelain types tested. Similar abrasive grinding with smaller grit size particles does not cause similar observable cracking.