Dentists' hearing and exposure to high speed turbine dental drill noise.

Effect of high speed turbine dental drill noise (DDN) on dentists' hearing at present and during the era of noisier drills was investigated. Hearing of two generations of dentists, power spectral density (PSD) functions of DDN from various drills and the equivalent level (LAeq) of a modern dental operatory were studied. The LAeq was 65 dB with 1 and 50% probability distribution levels of 74 and 57 dB, respectively. DDN was tonal with the spectrum peak always above 6 kHz, containing within 128 Hz frequency band 28-85% of the total noise energy in the PSD function. A cartridge type ball bearing drill from early 1960's was found noisier than an air bearing drill or a modern sealed head ball bearing drill by 8.5 and 5 dB, respectively. Sound pressure levels of DDN ranged from 68 to 79 dBA, being within safe limits. The high values earlier reported for cartridge type or worn drills could not be verified. Hearing of dentists free from clear ear pathology was found good and very similar to the reference, representing a population with no exposure to noise. There was no difference in hearing of 46 dentists 33-42 years of age, examined in 1973 and among whom there had been exposure to early and noisier drill, as compared to hearing of 56 dentists of similar age and years in dentistry, examined in 1988 and who had only been exposed to quieter drills of the 1970's. Noise dose and audiometric measurements were in agreement and indicated that DDN is not and has never been a risk to dentists' hearing.