Temperature rise during drilling through bone

Temperature was measured during drilling in bovine cortical bone specimens. A surgical drill fitted with a custom-designed speedometer and mounted on a drill press was used to drill holes at one speed, 49,000 rpm, and at forces in the range of 1.5 to 9.0 N. The resulting temperatures were recorded by thermocouples placed at various locations. The distribution of maximum local temperature rise (delta T) was best fitted by the function delta T = aR-b, where R is the distance from the center of the drilled hole and a and b are constants that were found by regression analysis. It was also found that the temperature increased with force, up to about 4.0 N, and then decreased at forces greater than that because of decreased drilling time. A separate series of tests revealed that temperatures were higher in the longitudinal direction than in the circumferential direction; this difference was attributed to the anisotropic thermal properties of bone.