An experimental comparative study of drilling efficiency and temperature elevation with unmodified and modified medical drills in pig tibia bone

BACKGROUND: There are no medical drill specifications capable of achieving bone drilling in a short time under low-thrust and low-speed drilling. Gekkou-drill® is an industrial drill that enables drilling with low cutting resistance by its characteristic point design. Our aims were to develop Gekkou-modified drills by processing to the points of currently available medical drills and to verify whether these modified drills enable less invasive drilling procedure for bone tissue in thermal exposure compared with unmodified medical drills. MATERIALS AND METHODS: Two commercially available 3.2-mm drills were compared before and after Gekkou modification. Drilling of pig tibias was performed at speeds of 300, 800, and 1,500 rpm and a uniform thrust force of 10 N. Temperature at the entry point for bone drilling was measured using a digital thermometer system. The feed rates were calculated using cortical thickness and monitoring data of the digital force gauge. RESULTS: Two unmodified drills could not penetrate the cortical bone on the near side at 300 rpm, even after 5 min of drilling. The maximum temperatures with modified drills were 54.6 °C and 46.2 °C at 300 rpm. At medium to high speeds, those were statistically significantly lower than with unmodified drills (58.5 °C vs. 90.5 °C at 800 rpm, 62.6 °C vs. 80.8 °C and 73.9 °C vs. 104.6 °C at 1,500 rpm). The feed rates for modified drills were 4.9–6.9 times as high as unmodified drills at 800 rpm, and 3.4 to 4.5 times at 1,500 rpm. On the other hand, the feed rates of modified drills at 300 rpm were equal to or higher than those of unmodified drills at 1500 rpm. CONCLUSION: Gekkou-modified drills clearly suppressed the temperature rise and increased the feed rate compared with conventional drills. Furthermore, it was notable that these modified drills had higher performance even at conditions of low thrust and low speed.