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 T_max 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, ΔT_max (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.