Thermal advantages of zirconia drills in bone drilling.

Heat production during surgical bone drilling is a serious risk factor for osteonecrosis, and cortical bone damage is observed at temperatures exceeding approximately 47°C for 1 min. Traditional stainless steel (SS316L) drills have high thermal conductivity, which can cause rapid heat transfer, whereas zirconia (ZrO2) has lower thermal conductivity and may result in lower thermal injury. This research comparatively studied SS316L and ZrO2 drills under dry-drilling conditions in terms of diameter (2.5, 3.0, 3.5 mm), drill speed (900, 1100, 1300 rpm), and feed rate (30 & 40 mm/min) using standardised bone blocks with thermocouple temperature monitoring. Findings proved that the two dominant factors were drill diameter and spindle speed. In the case of SS316L, a high temperature of 61 °C was observed at 3 mm dia, 1100 rpm, and 40 mm/min, which is above the necrosis temperature, whereas at the same conditions ZrO2 remained at low temperatures below 46 °C. An increase in feed rate (30-40 mm/min) decreased the Tmax of 2.5 mm SS316L drills (48.0 -39.3 °C) and raised it at 3.5 mm (48.5 -53.5 C). In all the parameters, ΔTmax (SS316L - ZrO2) was positive (15 - 23 °C) with increased diameter and with increased speed, which demonstrates the consistent thermal merit of zirconia. In clinical practice, zirconia drills are better in mid-diameter osteotomies and high-speed operations, whereas SS316L drills have to be irrigated or have parameter changes to reduce the chances of thermal risk.