Evaluation of diamond rotary instruments marketed for removing zirconia restorations

The high strength of zirconia makes the removal of zirconia restorations challenging and time consuming. Whether diamond rotary instruments marketed for removing zirconia restorations are more efficient is unclear. The purpose of this in vitro study was to compare the efficiency of diamond rotary instruments specifically marketed to cut zirconia with the efficiency of a conventional diamond rotary instrument. Two diamond rotary instruments marketed to cut zirconia (JOTA Zirkon Cut Z838L [JOT] and Intensiv ZirconCut Zr02/10 [IZC]) and a conventional diamond rotary instrument (Intensiv FG 334/6 [IFG]) were tested on 2 zirconia materials: 3Y-TZP (IPS ZirCAD LT) and a multilayered 4Y-TZP (IPS ZirCAD MT Multi). Zirconia specimens (2 mm) were cut under water cooling using a force of 2 N or 6 N. Cutting times and maximum temperatures at the tip of the diamond rotary instruments were recorded. The surface roughness before and after use was measured, and the elemental composition was analyzed. Overall, cutting times were shorter for IFG (85 seconds) and IZC (100 seconds) than for the JOT (182 seconds). Cutting times were shorter for MT zirconia than for LT zirconia. Higher temperatures (2 N: 24.6 °C, 6 N: 36.7 °C) and lower surface roughness occurred with higher cutting loads. Impurities of diamond particles were seen for JOT. The diamond particle embedding materials were either nickel alloys (IFG and JOT) or a resin material (IZC). Diamond rotary instruments marketed for cutting zirconia did not perform better or generate less heat compared with a conventional diamond rotary instrument. A load of 2 N with sufficient water cooling is recommended for cutting zirconia to avoid an extensive temperature increase.