Burs with guide pins for standardized tooth preparation

Objective: The aim of this study was to develop and test self-limiting diamond burs to ease precise chamfer preparation and to fulfill the special requirements of computer-aided design/computer-aided manufacturing and all-ceramic restorations. Method and materials: Rounded cylinder (based on ISO 881) and torpedo (based on ISO 879) diamond burs with a polished guide pin, 0.5 mm in length and 0.15 mm in radius, at the front end were developed in cooperation with an industrial partner. The in vitro testing involved a total of 140 human teeth. Experimental variables were the quality of the finish line, the microhardness of the enamel, and the thermal alteration of the dentin. Conventional diamonds served as a control. Results: No mechanical or thermal damage related to the bur design was found in the hard tissues that had potentially been in contact with or in close proximity to the guide pin. Microhardness of the enamel at the finish line was significantly higher when prepared with burs with a guide pin compared to conventional burs. The results of using the guide pin might indicate the beneficial effect of reduced vibration. Conclusion: The guide pins of the self-limiting diamond burs reduce, rather than increase, the risk of hard tissue damage at the preparation margin. No adverse effects were found. Clinical use is justified.