Experimental evaluation of heat generation in bone drilling using SS316L and ZrO 2 drill bits across multiple speeds and drill diameters

Abstract

Overheating of the bone during drilling may raise intraosseous temperature to more than 47°C, leading to osteonecrosis and compromising implant stability. Tool material, geometry and operating conditions play an important role in heat generation. Stainless steel (SS316L) is commonly used, but ZrO₂ has become a possible alternative due to its biocompatibility and lower thermal impact. Custom drill bits (2.5, 3.0 and 3.5 mm diameter; two flutes; 90° point angle; 25° helix angle) were manufactured. A five-axis CNC machine was used to perform drilling experiments on standardized polyurethane bone blocks. A feed rate of 30 mm/min and spindle speeds of 900, 1100 and 1300 r/min were used. Temperatures T_max and T_avg were measured using thermocouples and recorded in two trials per condition. For T_max and T_avg, the temperature values obtained in two repeated trials were reported as mean ± standard deviation. SS316L drills produced greater, more fluctuating thermal profiles, reaching a T_max of ∼37°C at 900 r/min (2.5 mm) to 58.75°C at 1300 r/min (3.0 mm), exceeding the osteonecrosis threshold. The T_avg reached up to 39°C at 1300 r/min. On the contrary, ZrO₂ drills generated lower temperatures with a T_max of 31–46°C and a T_avg of 29–35°C irrespective of the diameter and speed. It is worth noting that ZrO₂ drills did not surpass 47°C. Thermal response is highly dependent on drill diameter and spindle speed, but material properties are the decisive factor. ZrO₂ drills operated at lower T_max and T_avg than SS316L and exhibited greater thermal control, minimizing the risk of thermal osteonecrosis. Results suggest that ZrO₂ may provide a safer thermal response during the test dry-bone drilling process.