Variables affecting the drill-generated noise levels in ear surgery.

The manner in which the variables rotation speed, type of burr, burr size and site of drilling influence bone-conducted, drill-generated noise levels in ear surgery, has been investigated. From the results obtained, the following conclusions can be drawn. 1. The noise levels were primarily influenced by the size of the burr. The 6 mm cutting burrs gave a noise level of 88-108 dB, the use of a 4 mm one resulted in a reduction of 1-6 dB and the use of a 2 mm one, 5-16 dB. The mean noise levels of the diamond burrs were 5-11 dB lower than the mean noise levels of the cutting ones. 2. Variations in rotation speed had only a slight influence on the noise levels produced (0-5 dB). 3. Three different types of cutting burr were tested. All gave noise levels of about the same order of magnitude. 4. The noise levels around the cochlea were only slightly influenced by the localization of the drilling within the ear (less than 1.8 dB). 5. Drill-induced noise levels in ear surgery cannot be reduced to any great extent. Possible noise traumas to the inner ear can only be avoided by minimizing the duration of drilling and thus, the duration of harmful noise exposure to the cochlea.