# Evaluation of Noise Levels in a University Dental Clinic
## 3 Materials and Methods
### Equipment and Validation for Measurements  
The noise measurement equipment (sound level meter, noise dosimeter, and acoustic calibrator) was calibrated using an external accredited laboratory to ISO/IEC 17,025 standards and issued calibration certificates. The Solo 01 dB-Metravib (Acoeum, France) was used as a sound level meter, and both the CAL02 01 dB-Stell (Tokyo, Japan) and the Bruel and Kjaer 4231 were used as sound level calibrators. Two Bruel and Kjaer Noise Dose Meters (Type 4436) were used to measure and store the data. Each was calibrated using a Bruel and Kjaer Sound Level Calibrator (Type 4231) prior to testing (Figure 3).  
Figure 2: Students wearing personal sound measurement equipment (arrows show position of atomic measurement equipment).  
For the estimation of noise levels, we followed the measurement methodology defined by P.D. 149/2006. The sound level meters, and noise dosimeters followed the specifications of IEC 804--IEC 651 for the work-related noise measurements. The sound level meters operated in fast mode (time weighting) using A and C weighting filters and recorded noise statistics every minute. From the logged parameters, Leq was analyzed (the equivalent continuous sound level represents the total noise exposure for the period of interest or an energy average noise level). Simultaneously, the spectrum analysis was recorded.  
The noise exposure level in each section (fixed workstations at the center of the clinic and two randomly selected workstations in the left and right parts of the clinic (Figure 2) to assess work noise per clinic/laboratory area) was measured by a researcher holding the noise instrument by facing the microphone toward the noise source and viewing the measurement on the liquid crystal display (LCD). Personal noise measurements using dosimeters worn by selected students were performed in the dental clinics and laboratories.  
For the analysis and evaluation of the data, we referred to Presidential Decree No. 149/2006 [49], which describes the \"Minimum requirements regarding the exposure of workers to risks arising from physical agents (noise) in accordance with Directive 2003/10/EC\" [48] and established the daily exposure values (Leq in dB(A) and Ppeak in dB(C)) for 8 h occupational exposure, as described in Table 1.  
In both personal noise monitoring (chairside) and static measurement (area monitoring), all necessary information was collected in relation to the clinical training (specialty description and use of suction and/or different handpieces), the duration of the measurement, the weighting circuits used, and any hearing protection devices used by students. Sound level meters and noise dosimeters were randomly used by students during their performance, according to their willingness to participate and their position in the setting of the clinic to be at least 5 m away from the position of the static measurements in the area to avoid bias in different measurements.  
Average noise levels were calculated and compared between various positions and methods of measurement using an Analysis of Variance (ANOVA). Furthermore, [PERSON]'s test was applied to perform a pairwise comparison between groups. Intra-setting measurements comparing the differences between various times were analyzed using [PERSON]'s Signed Sum Rank Test. Comparisons between the postgraduate and undergraduate clinics were made using the Mann-Whitney U test. The level of significance was set at \(p<0.05\).