Influence of different cutting instruments and rotational speeds on heat generation and cutting efficiency when sectioning different types of zirconia.

Purpose: The purpose of this study was to evaluate the temperature generated on the intaglio surface and efficiency when cutting different types of zirconia with different rotary instruments and rotational speeds.

Methods: A conventional diamond rotary instrument (Brasseler, grit size 107 μm) and special diamond rotary instrument marketed to cut zirconia (4 ZR, Brasseler, grit size 126 μm) were tested on 3Y-TZP and 4Y-TZP zirconia with a rotation speed of 100,000 rpm and 200,000 rpm. Zirconia specimens were cut under water cooling (110 mL/min) in a custom-made holder attached to a universal testing machine. The temperature was recorded with infrared sensors pointing at the intaglio surface of the zirconia specimens.

Results: A rotation speed of 200,000 rpm resulted in significantly shorter cutting times, but also in significantly higher temperatures at the intaglio surface of the zirconia specimens compared with a rotation speed of 100,000 rpm. Significantly shorter cutting times were observed for the conventional diamond rotary instrument than for the special rotary instrument marketed to cut zirconia. Using the special rotary instrument, significantly longer cutting times were recorded for 3Y-TZP than for 4Y-TZP.

Conclusions: A conventional diamond rotary instrument was more efficient than a special rotary instrument. However, to avoid high temperatures when cutting zirconia clinically, a rotation speed of 100,000 rpm is recommended.