Thermological study of drilling bone tissue with a high-speed drill

OBJECTIVE: To perform a detailed quantitative analysis of the effect of intermittent drilling and irrigation to lower the temperature during high- speed drilling. METHODS: We examined the thermal changes for 15 bone flaps while drilling a 7- x 7-mm area for 18 seconds and a specific point for 9 seconds, under the following conditions: continuous or intermittent drilling; with a fluted steel or a diamond ball cutter; without or with irrigation, with room temperature or cold (8°C) Ringer solution. RESULTS: The maximum temperature during continuous drilling with a diamond cutter (or steel cutter) was 82.4 ± 1.3°C (55.2 ± 1.0°C) without irrigation, 42.5 ± 1.2°C (35.4 ± 0.9°C) with room temperature Ringer irrigation, and 22.5 ± 1.4°C (21.6 ± 0.3°C) with cold Ringer irrigation, whereas that during intermittent drilling was 66.1 ± 1.2°C (35.6 ± 0.8°C), 35.0 ± 0.8°C (25.4 ± 0.7°C), and 21.5 ± 0.6°C (21.8 ± 0.4°C), respectively. During continuous drilling of a specific point, the radius of the concentric isothermal line for 43°C (thermal threshold for neurons) was 3.6 ± 0.8 mm with a steel cutter, and it was 8.1 ± 0.3 mm with a diamond cutter. The radius was 4.2 ± 0.8 mm during intermittent drilling with a diamond cutter, and it was 4.0 ± 0.1 mm during continuous drilling with room temperature Ringer irrigation. Intermittent drilling with cold Ringer irrigation kept the temperature, even at the center of the drilled area, below 20°C. CONCLUSION: Intentional intermittent drilling with irrigation reduces temperature elevation and its expansion. These procedures are necessary for safe drilling, especially with a diamond burr. Although cold irrigation can minimize temperature elevation, its substantial effect on nerves or other structures needs to be elucidated.