Workplace noise exposure and audiometric thresholds in dental technicians

Noise is a well-known risk factor in occupational medicine. Several studies have been performed in workplaces with noise sources, especially in the industrial field; on the contrary, only a few studies have been carried to evaluate the noise exposure effects in non-industrial workplaces such as small factories, handicraft laboratories, and dental laboratories. The aims of this study were to evaluate workplace noise exposure and hearing thresholds in dental technicians. Four laboratories and 51 dental technicians were included in the study. Noise exposure levels during a nominal eight-hour working day (LEX, 8 h) were assessed in the included laboratories. Audiometric thresholds with pure tone audiometry were performed in 51 dental technicians, and results were compared with those expected in subjects not exposed to noise. The environmental noise measures showed moderate differences of the LEX, 8 h among the four laboratories (range 71.4 to 76.2); average LEX, 8 h was 73.9 ± 2.2 dB(A). The audiometric results showed a progressive increase of hearing threshold values at the frequencies mostly involved in noise-induced hearing loss (3, 4 and 6 kHz) and a correlation with age and working seniority especially in males (p<0.005). Nevertheless, in the 92.1% of subjects the threshold increases were in line with those expected in subjects of the same age and sex not exposed to noise and in the remaining 7.8% were not statistically significant (p>0.05). In 3.9% of the cases the increases were bilateral, typical of noise-induced hearing loss, and only 1.9% showed involvement of several frequencies with worsening of expected thresholds >25 dB. In conclusion, our study showed that exposure to noise in dental laboratories was not sufficient to represent a hazard to hearing, as demonstrated by the LEX, 8 h, which were below 80 dB(A) and therefore below the European exposure limit values and exposure action values for workers.