Noise Levels in University Dental Clinic: History
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Contributor:
Maria Antoniadou
,
Panagiota Tziovara
,
Sophia Konstantopoulou

Noise levels in a dental office can be produced by different specialty instruments. Exposure to high levels of noise (unwanted sounds) may cause auditory and non-auditory health problems in dentists.

  • occupational noise
  • occupational dentistry
  • dental public health
  • dental cutting equipment

1. Introduction

Sound is a multidimensional concept that is characterized by measurable and audible changes in air pressure, perceived in both positive and negative ways. It can either be understood as noise (e.g., a nuisance) or present itself as noise, particularly when it transforms into it. People tend to habituate to noise exposure in different ways [1]. Among the different types of noise exposure, occupational noise is the one that has been investigated the most [2], followed by entertainment noise (e.g., music festivals, concerts, and bars) and headphone use with PMPs (personal music players) [3], and environmental noise (e.g., noise from road, rail, and air traffic, and industrial construction) [4]. If exposure to noise is chronic and exceeds certain levels, it can lead to negative health consequences, such as auditory and non-auditory health problems [5].
Auditory problems due to noise include various levels of hearing loss. Noise-induced hearing loss can be caused by an intense impulse sound occurring once (such as a gunfire or explosion) [6], or by steady long-term exposure to noise levels higher than LA 75–85 dB—e.g., in industrial settings, including healthcare [7] and dental units [8]. World Health Organization (WHO) reports that 10% of the world’s population is exposed to sound pressure levels that could potentially cause noise-induced hearing loss [9]. Hearing loss is the 13th most important contributor (2–6% of the total number) to the global years lived with disability [1][10][11]. In about half of these people, auditory damage can be attributed to exposure to intense noise [12][13]. Accidents and falls are consequently associated with undiagnosed hearing loss, especially in the elderly, with increased mortality [14]. Changes in sound perception that cannot be attributed to an external source, such as in hearing ringing, called tinnitus, often follow acute and chronic noise exposure and persist for extended periods [15]. Tinnitus affects the quality of life through sleep disturbances, depression, and inability to sustain attention [15]. The characteristic pathological feature of noise-induced hearing loss is the loss of auditory sensory cells in the cochlea [1]. Because these hair cells cannot regenerate in mammals, no remission can occur [16]. So, the prevention of noise-induced hearing loss is the only option to preserve hearing and avoid social discomfort [17].
Additionally, noise exposure has been linked to non-auditory health effects, including annoyance [18] and sleep disturbance, with consequent daytime sleepiness [19], which further leads to patient fear [20] and stress-related outcomes in healthcare settings [21], increases the occurrence of hypertension and cardiovascular diseases [22][23], elevates cholesterol [24] and impairs cognitive performance [25]. It also leads to extreme stress responses [26], communication and concentration difficulties, mental fatigue, and a decline in efficiency/effectiveness [27]. Finally, noise annoyance in the workplace might be accompanied by negative responses, such as anger, displeasure, exhaustion, and burnout [28][29].
Healthcare units are considered noise-sensitive facilities [5]. Since the 1960s, hospital noise levels have increased by about LAeq 10 dB [30]. Noise levels in hospitals are now typically more than LAeq 15–20 dB higher than those recommended by WHO [31], leading to noise-induced stress linked to burnout, diminished well-being, and reduced work performance for employees [32][33]. Annoyance, irritation, fatigue, and tension headaches are also assigned to noisy healthcare workplace environments [34]. Noise also affects speech intelligibility and could, therefore, lead to misunderstandings that result in clinical errors [5][32].
Among healthcare professionals, dentists are exposed to sounds from a variety of sources within the office, mainly from equipment and tools in use. Additionally, there are verbal interactions with assistants and patients that may be at a louder level than ordinary conversation. Further, there may be music playing in the practice. Exogenous sources include noise from the external environment (e.g., vehicle traffic from outside and work in construction areas). It is also widely accepted that noise during clinical dental practice creates negative emotions in the clinicians and dental staff, such as nervousness, loss of concentration, and restlessness, but at the same time exacerbates anxiety in phobic patients [5]. Previous studies have shown that the noise levels produced in a dental office in dB(A) are less than 80dB(A), which is within the permissible limits set by the WHO. WHO recommends that noise exposure levels should not exceed 70 dB over a 24 h period and 85 dB over a 1 h period to avoid hearing impairment [35]. However, there are variations in the measurements in different dental environments, resulting in different factors that determine the noise levels that can be recorded. These variations can be attributed to the different methods used. For example, in a study conducted by Songkla University [36], the personal noise dose in the hearing zone was estimated using a decibel meter attached to participants, instead of the noise level in the working areas. The second method involved recording the noise in each minute by obtaining a mean period, in contrast to the method described in the study by da Cunha et al. [37], where only the peak of noise every 5 min was recorded. In a study by Kadanakuppe et al. [38], conducted at the Oxford Hospital and Oxford School of Dentistry, Bangalore, Karntaka, the level of noise of the cutting devices was measured using a microphone placed near the operator’s ear, close to the main noise source. The minimal intensity and the maximal intensity of noise were assessed for 30 s using the dental devices triggered only during the cutting moments when the intensity of noise ranged from 64 to 97 dB. In some studies, the environment was also assessed [36], reporting that the level of noise was slightly higher than that recorded in the hearing zone. The common part of all relevant studies is that the level of noise that really damaged the hearing of students could be a little lower than that registered in the dental clinic, but at times very high in frequencies temporarily surpassing the control limits [36][37][38]. Other relevant studies report on the differences in equipment used for the measurements of noise levels [39][40][41][42]. So far, there has not been enough evidence of the differences in noise levels between different university clinics or laboratories due to years of use of dental equipment, settings, and tasks performed. Further, no noise spectra during dental clinical work have been reported so far.

2. Noise Levels in University Dental Clinic 

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, 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.
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.
Values LEX, 8 h Peak Ppeak
Exposure limit values 87 dB(A) 140 dB© 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
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 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. For this reason, sound levels at the low-frequency end of the spectrum are reduced as the human ear is less sensitive at low audio frequencies than at high audio frequencies. On the decibel scale, audible sounds range from 0 dB, which is the threshold of hearing, to over 130 dB, which is the threshold of pain. Although doubling the sound pressure corresponds to an increase of 6 dB, it takes about a 10 dB increase for the sound to subjectively appear twice as loud. The smallest change that humans can hear is about 3 dB. The sound pressure level (SPL) can be described subjectively based on the decibel (dB) scale. A range of 0 to 40 dB is considered quiet to very quiet, whereas 60 to 80 dB is generally described as noisy. A sound pressure level of 100 dB is perceived as very noisy, whereas anything greater than 120 dB is intolerable. Further, A, C, and Z are frequency weightings used in noise level meters to adjust the measured sound pressure level (SPL) to better match the human perception of sound. The A-weighting curve shows how the human ear reacts to different sound pressure levels, and it is often used to measure noise in the environment and in industry. The A-weighting curve attenuates low- and high-frequency sound pressure levels, giving more weight to frequencies between 500 Hz and 10 kHz, where human hearing is most sensitive. dB(A) is then a weighted scale for judging the loudness that corresponds to the hearing threshold of the human ear [47][55]. Noise levels given in dBA or dB(A), as they are sometimes written (A-weighted sound levels) instead of dB, are usually found in the relevant literature and are also used in the present study. The main effect of this adjustment is that low and very high frequencies are given less weight compared to the standard decibel scale. Compared to dB, A-weighted measurements underestimate the perceived loudness, annoyance factor, and stress-inducing capability of noises with low-frequency components, especially at moderate and high volumes of noise [48][49][50]. The C-weighting curve measures the overall sound pressure level across all frequencies without attenuation. It is used for measuring sound in high-level noise environments, such as rock concerts or airport runways. The Z-weighting curve is also known as “linear” or “flat” weighting and does not apply any frequency weighting to the SPL measurement. It measures the sound pressure level across all frequencies and is used for scientific measurements or calibrating instruments [51][52][53].
The aim was to (a) measure the noise levels within different clinics and laboratories of the Department of Dentistry, School of Health Sciences of the National and Kapodistrian University of Athens, (b) promote information sharing on this serious health issue among stakeholders, and (c) collect data to organize preventive measures for students and personnel (faculty members, collaborators, administrative, and technical staff). Since the study did not apply to acoustics and acoustic measurements, a digital sound level meter and noise-integrating dosimeters with an analogue electronic transducer were used to collect data from certain postgraduate (PG) and undergraduate (UG) clinics and laboratories (LAB) during peak working periods and with a duration of 1 h per clinic/lab. Both personal (dosimeters) and static (area monitoring) noise exposure assessments were evaluated, resulting in various teaching-related activities in dental clinics. At all locations, the maximum exposure limit value of 87 dB(A) was not exceeded. However, chairside personal measurements during ultrasonic work revealed that the lower exposure action value of 80 dB(A) was exceeded. PG clinics were noisier than UG. LAB training settings, even with the new equipment, were close to the upper exposure limit due to the simultaneous use of airotors. In this context, targeted research and investigations into measures are proposed to safeguard the health and safety of students during their duties at the dental school.

This entry is adapted from the peer-reviewed paper 10.3390/app131910869

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