The effect of tip geometry on the mechanical performance of unused and reprocessed orthopaedic drill bits.

Although reprocessed drill bits have been in clinical use as a cost-saving measure, their performance has not been critically evaluated in comparison with the performance of unused drill bits. The effect of three commonly used reprocessing methods on the geometry and mechanical performance of 2.5 mm orthopaedic drill bits was investigated and compared with that for unused drill bits. Four mechanically significant drill parameters including chisel edge, chisel edge angle, point angle, and lip length of 36 drill bits in four groups were measured and compared. Group A included unused drill bits. Group B included drill bits reprocessed once by one company whereas group C included those reprocessed twice by the same method. Group D included drill bits reprocessed once by another company. For mechanical performance, a test set-up was developed in which the time of travel of the drill bits through layers of cortical and trabecular synthetic bone materials under constant compressive force were measured. The geometrical parameters were found to be significantly altered as a result of the reprocessing methods. A linear relationship was derived to relate the chisel edge to the drill time through cortical and trabecular bones. The mechanical performance of drill bits is correlated largely to the chisel edge length. A larger chisel edge is correlated to a reduced drill time, particularly in the cortical bone.