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 degrees C) Ringer solution. RESULTS: The maximum temperature during continuous drilling with a diamond cutter (or steel cutter) was 82.4 +/- 1.3 degrees C (55.2 +/- 1.0 degrees C) without irrigation, 42.5 +/- 1.2 degrees C (35.4 +/- 0.9 degrees C) with room temperature Ringer irrigation, and 22.5 +/- 1.4 degrees C (21.6 +/- 0.3 degrees C) with cold Ringer irrigation, whereas that during intermittent drilling was 66.1 +/- 1.2 degrees C (35.6 +/- 0.8 degrees C), 35.0 +/- 0.8 degrees C (25.4 +/- 0.7 degrees C), and 21.5 +/- 0.6 degrees C (21.8 +/- 0.4 degrees C), respectively. During continuous drilling of a specific point, the radius of the concentric isothermal line for 43 degrees 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 degrees 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.