[Damaging temperature during the machining of bone]

Yet one of the major problems with tools of bone machining is the possible thermal damage to the bone caused by the cutting action. Thermal damage to bone is the combined result of the temperature and the period of time that the bone tissue is at the elevated temperature. The effect of heat on bone tissue can result in the denaturation of the enzymic and membrane proteins and cellular death. That results in disorder capability of regeneration of bone tissue and in advantage of resorption. This paper described the research to study the thermal response of drilling of bone. Results are judging with temperature, cutting time as a normed comparison time and damaging temperature, which is the combined result of temperature and the period of time. Decrease of cutting time and temperature can avoid thermal damage, that be achieved with optimal drill bit geometry and conditions for drilling. A helix angle of 12 to 14 degrees, a point angle of 70 degrees and a clerance angle of 18 to 24 degrees are very appropriate for an optimized geometry. The borings should be executed by a medium cutting speed of 9 to 16 m/min (n = 600 to 1100 rpm at d = 4.5 mm). Concerning the thrust, one should not drill timidly but also avoid excessive forces. Thrust should be in the range of about 10 N/mmd. After 20 to 30 borings executed the drill bit must be repointed.