Title: Experimental observation of temperature variations in the bone due to certain physical parameters during bone drilling process

Abstract

During bone drilling, the cyclic use of the same drill bit causes progressive wear of the cutting edges. The resulting high frictional forces can lead to a significant temperature variation around the drilling site. Above 55°C, irreversible damage to the bone tissue occurs. An experimental study was conducted on a test rig, measuring the temperatures during bone drilling as a function of rotational speed, feed rate and cycle of use of drill bit. Bovine tibia cortices were used because of their mechanical properties similar to those of human bone. Six thermocouples were placed around the drill focus in 0.5mm increments, in order to determine the heat flow during drilling. The same drill bit of 3.2mm diameter was used 3 times and temperatures were measured on each trial without any irrigation. The risk of having temperatures above the critical threshold of 55°C was greater at the 30mm/min feed rate than at the 60mm/min feed rate. The temperature increased with both the speed of rotation and the number of drillings regardless of the other cutting conditions. The best cutting conditions were found at a rotational speed of 200 rpm and a feed rate of 60 mm/min and at a rotational speed of 100 rpm and a feed rate of 30 mm/min. When the rotation speed exceeded 200 rpm, the temperature appeared to be very high. The temperature gradients were calculated for the drilling conditions where the maximum temperatures measured at the closest point to the drilling focus were less than 55°C. The equations were used to calculate the projected temperatures at the bone-drill bit interface. It was observed that in the majority of cases the temperatures are above 55°C. It became clear that the thermal conductivity of the bone is low. The heat remains concentrated around the drilling point.