Large band spectral analysis and harmful risks of dental turbines.

Previous studies have attributed harmful effects to ultrasonic frequencies and recently many have addressed the problem of early deafness among dentists caused by high-speed air turbines. In this study, we measured the spectra of the sounds generated by high-speed air turbines, ranging from audible to ultrasonic frequencies (0-70 kHz). The hypothesis advanced is that the ultrasound spectrum of high-speed air turbines reaches amplitudes that may be noxious. We performed continuous analyses of the spectra of three bands of turbines (n = 17). Measurements of frontal incidence were made using a Bruel & Kjaer microphone and sonometer. For spectral analysis we used the autoregressive parametric method. Using Akaike's criteria the model weights were fixed at 12. The method used in the present work led to an accuracy in the results of 10(-2) kHz within the same brand of turbine. Results show, in terms of frequencies, the presence of four main peaks: 5.6 kHz +/- 0.73 in the audible range, and 20.1 kHz +/- 2.16, 35.7 kHz +/- 2.56 and 46.5 kHz +/- 0.71 in the ultrasonic range. In a normalized spectrum, the amplitude of the ultrasonic component reaches 115 dBspl for 46.5 kHz and is 76% greater than that of the audible component. Such values, both in terms of frequencies and amplitude, reach levels which may provoke short- or long-term negative physiological disturbances and hearing-damage risk. Further research should be directed to determine to what extent they might induce noxious effects for the dental team.