Effects of repeated drill use on temperature of bone during preparation for osteosynthesis self-tapping screws.

Drills used during preparation for osteosynthesis with self-tapping screws are often used repeatedly until they become blunt and ineffective. Because the sharpness of the drill is one of the most important factors in its cutting efficiency, blunt drills may require the application of extra force, which in turn may contribute to excessive frictional heat produced during preparation of screw holes. Large rises in temperature can impair bony regeneration around screws and contribute to failure of internal fixation. In an attempt to quantify the potential increase in temperature produced by blunt drills, we devised an in vitro experiment to simulate preparation for osteosynthesis by using drills with different degrees of wear. Three drills were used: one was new, one had drilled 600 holes, and the third drill had been in use in theatre for several months. The mean (range) rise in temperature for the three drills were: new drill 7.5 degrees C (0.6-20.5 degrees C); drill after 600 holes 13.4 degrees C (5.7-28.3 degrees C); and drill from theatre 25.4 degrees C (12.4-41.3 degrees C). There was a highly significant difference in the temperatures generated by the three drills, and the changes in temperature were related to the amount of wear. The cost of drills is low, and as their repeated use can compromise the results of the operation they must be discarded after single use.