Introduction:
Instruments and equipments used in dentistry field produce sounds with wide spectrum, so dentists and other personnel are exposed to these sounds continuously. The purpose of this study was measuring the received noise level of  personnel working in clinics of Mashhad dental school and frequency analysis of sounds at 20-20000 Hz frequency range.
Materials and Methods:
In this study, the noise level in operational dentistry, endodontics, prosthodontics, oral surgery, periodontics, pediatric dentistry and orthodontics of Mashhad dental school were assessed in 2004. Sound level  measuring device and their establishment and set up were selected in which according to acquired data, the received noise level of dentist and average received noise level of personnel could be calculated.
Results:
Equivalent noise level (L_Aeq) measured surrounding central unit of each clinic, was less than 73.2 dB and noise level inside each clinic was less than 69.9dB. The dentists received noise level during work and presence at the studied clinics was measured  to be 67.2-83.7 dB.
The equivalent maximum noise level in all clinics was related to frequency band of 630 Hz and sounds of operational dentistry, endodontics and periodontics clinics had strong components in high frequency.
Conclusion:
According to permitted exposure noise level, the received noise level of dentists and personnel in studied clinics were not hazardous, but because of high frequency sounds, it is suggested to repeat the study with systems which can assess analysis of higher frequencies.