# Evaluation of Noise Levels in a University Dental Clinic
## 2 Background  
Due to the auditory and non-auditory consequences of noise exposure and the sensitivity in terms of continuous noise levels in dental settings, noise reduction has recently become a topic of research. Legislation suggests monitoring, which includes noise assessments, regular audiometric testing, and protective equipment for doctors and dentists [43; 44]. However, the available evidence for the associations between occupational noise exposure and hearing loss is complex as there is a lack of appropriate non-exposed control samples and longitudinal studies. It is further suggested that there should be better quality prevention programs in susceptible professional environments, higher quality research in these environments, and massive implementation of the relevant legislation [45]. It is also reported that, in most working environments, efforts to control the problem focus on hearing protection rather than on noise control using improved equipment design and different programming of functions of this equipment or better noise-proof construction materials. Thus, various regulatory agencies have made recommendations on noise exposure limits, notably on exposure to noise in the workplace. The choice of an exposure limit usually depends on setting a maximum acceptable hearing loss for a lifetime and determining the percentage of the population exposed to noise for which the maximum acceptable hearing loss is tolerated [46; 47]. According to the Directive 2003/10/EC of the European Parliament [48] and the consequent Greek Presidential Decree No. 149/2006 [49], which were followed to take measurements in this study, the exposure limit values and exposure action values for daily noise exposure levels and peak sound pressure values are established as shown in Table 1 (abbreviations are discussed in the relevant section at the end of the paper). Additionally, in the US, three organizations have issued recommendations on exposure limits to dangerous noise levels, including the Occupational Safety and Health Administration (OSHA) [50], the National Institute for Occupational Safety and Health (NIOSH) [51], and the Environmental Protection Agency (EPA) [52]. The exposure limits issued by each of these organizations consider three parameters related to exposure: level (\"how loud\"), frequency (\"how often\"), and duration (\"how long\"). Typically, the OSHA \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Values** & **LEX, 8 h** & **Peak** & **Ppeak** \\ \hline Exposure limit values & 87 dB(A) & 140 dB(c) & 200 Pa \\ Upper exposure action values & 85 dB(A) & 137(C) & 140 Pa \\ Lower exposure action values & 80 dB(A) & 135 dB(C) & 112 Pa \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Exposure limit values and exposure action values according to the Directive 2003/10/EC and Presidential Decree No. 149/2006 used in the present study. and NIOSH recommendations are applied in a professional environment based on what happens on an 8 h workday during a 40-year working life. OSHA's permissible exposure limit is 90 dB(A) with an exchange ratio of 5 dB (e.g., 90 dB(A) for 8 h, 95 dB(A) for 4 h, etc.). Meeting OSHA limits could lead to hearing problems in 25% of the working population over a 40-year working period [50]. The recommended exposure limit (REL) of NIOSH is more conservative at 85 dB(A) with an exchange ratio of 3 dB (e.g., 85 dB(A) for 8 h, 88 dB(A) for 4 h, etc.). NIOSH estimates that meeting these limits could lead to hearing problems in 8% of the working population [51]. Finally, the EPA sets a recommended exposure limit of 70 dB(A) for the whole year (not limited to working hours). Adherence to the EPA limit is intended to protect the entire population [52] and is considered a safe level of protection against hearing loss [53; 54]. Noise levels are calculated in dBs. A dB(decibel) is the ratio between two noise quantities that have been reported on a logarithmic scale. Although dB is commonly used when referring to measuring sound, humans do not hear all frequencies equally.