Influence of bone density and implant drill diameter on the resulting axial force and temperature development in implant burs and artificial bone: an in vitro study.

PURPOSE: The aim of this study was to determine how the bone density affects the temperature development in artificial bone and drill. METHODS: Ten single drills with diameters of 2.2, 2.8, 3.5, and 4.2 mm were used on four artificial bone blocks (density I-IV), with constant speed and external irrigation. Temperature measurement in blocks and drills was done by infrared camera. The resultant axial force was measured, and light microscopic examinations of the drills were performed before and after preparation. RESULTS: The block density has a greater influence on resulting axial force than the drill diameter (D1 = 2.2 mm, 4.11 +/- 0.64 N; 4.2 mm, 9.69 +/- 0.78 N vs. D4 = 2.2 mm, 0.5 +/- 0.18 N; 4.2 mm, 1.23 +/- 0.08 N). For the narrowest drill, a decrease in bone density caused a significant temperature increase in the bone and drill. However, for the thickest drill, no thermal differences were found in the bone but were seen in the drill itself (D1 = 2.8 mm vs. D4 = 2.8 mm; bone p < 0.0001, drill p < 0.0001; D1 = 4.2 mm vs. D4 = 4.2 mm; bone p = 0.5366, drill p = 0.0411). An increase in the drill diameter in the highest bone density led to a significant thermal increase in the bone and drill. However, for the lowest bone density, thermal changes were observed only in the bone (D1 = 2.8 mm vs. D1 = 4.2 mm; bone p < 0.0001, drill p < 0.0001; D4 = 2.8 mm vs. D4 = 4.2 mm; bone p < 0.0102, drill p = 0.1784). CONCLUSIONS: Thermal development depends on bone density with increasing density causing a temperature rise. However, this effect is reduced with increasing drill diameter. This may be important with regard to bone reactions and also in terms of tool wear.