Objective To investigate the effects of noises generated by drilling on the cochlear function of operated ear during middle ear surgeries.Methods A TES-1351 Sound Level Meter was used to measure noise levels from drills with different specifications of bits during the middle ear surgeries.Bone-conduction hearing thresholds of the operated ear and non-operated ear were measured before and two weeks and three months after operation.Results Noise levels generated by different drills used in operations ranged f...