ORIGINAL RESEARCH |
https://doi.org/10.5005/jp-journals-10015-2364 |
Occupational Noise-induced Hearing Loss among Dental Professionals: An In Vivo Study
1–6Department of Conservative Dentistry and Endodontics, Malla Reddy Dental College for Women (MRDCW), Hyderabad, Telangana, India
Corresponding Author: Ramachandruni Nimeshika, Department of Conservative Dentistry and Endodontics, Malla Reddy Dental College for Women (MRDCW), Hyderabad, Telangana, India, Phone: +91 9701205874, e-mail: nimeshikaram@gmail.com
Received: 01 December 2023; Accepted: 03 January 2024; Published on: 20 February 2024
ABSTRACT
Aim: The aim of this study was to evaluate sound levels generated in the Departments of Conservative Dentistry and Endodontics, Prosthodontics, and Periodontics and to find out if the continuous high-frequency noise generated by dental armamentarium could damage the dental professionals hearing efficiency.
Materials and methods: A total of 30 randomly selected dental practitioners from different specialties and 30 individuals in a control group who had no history of noise exposure were evaluated for their hearing capacity. The sound levels generated in the various departments were evaluated by decibel (dB) meter and the participant’s hearing capacity was evaluated using an otoscopic examination, pure tone audiometry, and brainstem evoked response audiometry (BERA) test. Wilcoxon test was used to assess the significant difference between the dentists and the control group.
Results: Sound levels generated in the department of periodontics were higher than in other departments. Around 20% of the study sample, or six dental practitioners, exhibited signs of hearing impairment; however, the qualitative analysis showed that the dentist’s group had a greater percentage of hearing loss than their control groups in the pure tone audiometry test.
Conclusion: The study shows that when dental professionals are exposed to noise in the workplace, the suddenness and frequency of noise occurrence, produce a significant influence on dental professionals.
Clinical significance: As dental professionals are exposed to constant noise generated by the various dental equipment there might be an occupational hazard of these continuous exposure to long duration of high frequency sounds. So, the usage of protective equipment will help in preventing noise-induced hearing loss (NIHL).
How to cite this article: Madhamshetty V, Aravelli S, Nimeshika R, et al. Occupational Noise-induced Hearing Loss among Dental Professionals: An In Vivo Study. World J Dent 2024;15(1):64–67.
Source of support: Nil
Conflict of interest: None
Keywords: Dental professionals, Hearing loss, Noise
INTRODUCTION
Since the introduction of high-speed handpieces in the field of dentistry, concerns have been raised by dental professionals regarding the potential impact of these devices on their hearing capacity. In response to these concerns, the United States Occupational Safety and Health Administration implemented safety standards aimed at mitigating the risk of noise-induced hearing loss (NIHL) among workers.1 The established standard dictates that the maximum permissible exposure limit during an 8-hour workday should not exceed a sound pressure level of 90 dB, as measured on a preweighted scale.1
Numerous studies have been conducted to quantify the sound intensities generated by dental equipment,2,5 with authors such as Barek et al. specifically reporting on the audible (<20000 Hz) and ultrasonic (>20000 Hz) frequency ranges of high-speed dental handpieces.6 It has been observed that exposure to noise frequencies within the range of 2000–4000 Hz can lead to the occurrence of NIHL.7 Given that the normal hearing frequency range for individuals is 20–2000 Hz, continuous exposure to high-frequency noise may result in the loss of high-frequency pitch first, followed by low-frequency pitch.8
Furthermore, long-term exposure to noise has been found to induce both auditory and nonauditory effects.9,10 Dental devices have been identified as sources of sounds ranging from 66–91 dB. Ahmed et al. conducted a study on noise exposure through audiometric analysis, revealing that prolonged exposure to a tone of ≥85 dB for about 8 hours daily could lead to permanent hearing loss.11
The aim of the study is to assess the sound levels generated in the various dental departments. And also, to determine whether the continuous high-frequency noise produced by dental instruments could adversely affect the hearing efficiency of dental professionals and whether there might be an occupational hazard from this continuous exposure to long-duration high-frequency sounds.
MATERIALS AND METHODS
In May 2020, following institutional approval, a noise evaluation was conducted within the Departments of Conservative Dentistry and Endodontics, Periodontics, and Prosthodontics at Malla Reddy Dental College for Women in Hyderabad over the course of 1 week. The sound levels in various departments were measured using a dB meter at 3-minute intervals. Maximum and minimum values were recorded and documented in a tabular format. Recordings were taken at the chairside with the meter positioned near the operator’s ear (6 inches away) during the use of suction and aerator handpiece. Additionally, recordings were made at the clinic’s center with a minimum of five operators working.
To assess NIHL, 30 controls (individuals aged between 35 and 50 years, whose jobs don’t involve working in a noisy environment and are not dental professionals) and 30 dental practitioners (including professors and readers, 10 from each department of periodontics, prosthodontics, conservative dentistry, and endodontics) were randomly selected. Eligible participants had a minimum of 5 years of dental experience, were aged between 35 and 50 years, and did not have conditions compromising hearing (such as recent cough/cold or ear blockages). A questionnaire covering age, sex, past medical history, and dental practice experience was administered. An otoscopic examination by an audiology specialist at Malla Reddy Narayana Hospital, Hyderabad, was conducted after obtaining informed consent.
Following the otoscopic examination, an audiometric examination using pure tone audiograms was performed by an audiologist specialist in a soundproof room to evaluate the hearing capacity of both ears of dentists and the control group.
Different frequencies ranging from 100 to 15600 Hz were checked, and the audiologists noted dentists’ responses, creating audiograms representing sound waves from the audiometry system.
The sound was then delivered to participants through a headset, and the obtained sound data was presented in audiogram charts indicating frequency and amplitudes. Hearing ranges and areas of reduced hearing capacity were calculated. The results were categorized into three groups using discriminant analysis—≤ 31% amplitude (good hearing), 32–79% amplitude (significant hearing damage), and 80–100% amplitude (severe hearing impairment) for all tested frequencies.
The minimum frequency in the right and left ear (LE) represented the hearing quality of participants. Additionally, the brainstem evoked response audiometry (BERA) test, conducted by an audiology specialist at Malla Reddy Narayana Hospital, utilized BERA testing to evaluate hearing thresholds and diagnose retrocochlear lesions and outer hair cell function. It is a noninvasive and objective technique for assessing hearing. It detects the electrical activity generated from the inner ear to the inferior colliculus. Recordings were conducted using an Intelligent Hearing SmartEP two-channel device equipped with four disposable electrodes. Two electrodes were positioned on the frontal area (serving as ground and positive electrodes), while one was placed on each mastoid (serving as negative electrodes). An acoustic stimulus in the form of alternate polarity clicks, delivered at a rate of 19 clicks per second through monaural insertion earphones at 80 dB normal hearing level, a total of 2,048 stimuli. Absolute values (measured in milliseconds) of absolute latencies and waves I, III, and V interpeak intervals were examined for each ear. Mean measurements from the exams were computer-based on the sex, side (right or left), and age of patients to explore potential variations in absolute wave latency period values.
The data were statistically analyzed using Statistical Packages for the Social Sciences 23 (IBM), employing the Wilcoxon test to compare pure tone audiometry results between dentists and the control group, with a significance level set at p < 0.05.
RESULTS
Results of Decibel Meter Test
As per the data, at the chair side, the sound levels recorded by the dB meter in the periodontics department with a mean of 84.2583 surpassed those in the conservative dentistry and endodontics department with a mean of 82.3167, with prosthodontics following closely with a mean of 80.5000.
At the center of the clinic, the sound levels recorded by the dB meter in the periodontics department with a mean of 75.1833 surpassed those in the conservative dentistry and endodontics department with a mean of 68.2000, with prosthodontics following closely with a mean of 66.5000 (Table 1 and Fig. 1).
| Department | Groups | n | Mean | Standard deviation (SD) |
|---|---|---|---|---|
| Conservative and endodontics | Chairside | 10 | 82.3167 | 2.69538 |
| Center of clinic | 10 | 68.2000 | 2.71292 | |
| Prosthodontics | Chairside | 10 | 80.5000 | 2.66289 |
| Center of clinic | 10 | 66.5000 | 1.79566 | |
| Periodontics | Chairside | 10 | 84.2583 | 3.12658 |
| Center of clinic | 10 | 75.1833 | 1.40478 |
Fig. 1: Bar graph representation of sound levels in various departments
Results of Audiometry Test by Pure Tone Audiogram
Examining the impact of persistent high-frequency sounds from dental equipment yielded results detailed in Tables 2 and 3. Notably, 20% of the study sample, or six dental practitioners, exhibited signs of hearing impairment.
| Dentist (n = 30) | Pure tone audiometry | Control group (n = 30) | Pure tone audiometry | |
|---|---|---|---|---|
| Ear of participant | Low frequency | High frequency | Low frequency | High frequency |
| Right | 9.94 ± 5.01 | 10.67 ± 6.92 | 9.40 ± 5.02 | 10.42 ± 4.86 |
| Left | 10.29 ± 6.29 | 11.64 ± 8.22 | 8.50 ± 5.47 | 9.21 ± 7.11 |
| Both ears | 11.61 ± 6.23 | 11.60 ± 7.43 | 10.43 ± 5.27 | 9.62 ± 6.06 |
| Pure tone audiometry | ||||
|---|---|---|---|---|
| Low frequency | High frequency | |||
| Right | 30 | 30 | 0.293 | 0.217 |
| Left | 30 | 30 | 0.387 | 0.321 |
| Both ears | 30 | 30 | 0.173 | 0.132 |
In the pure tone audiometry results of the dentist group, the hearing threshold levels for different frequencies were as follows, 250 Hz to 10 dB, 500 Hz to 15 dB, 1 kHz to 15 dB, 2 kHz to 10 dB, 4 kHz to 20 dB, 6 kHz to 35 dB, and 8 kHz to 45 dB.
Similarly, for the control group, the hearing threshold levels for different frequencies were as follows, 250 Hz to 15 dB, 500 Hz to 15 dB, 1 kHz to 20 dB, 2 kHz to 20 dB, 4 kHz to 15 dB, 6 kHz to 15 dB, and 8 kHz to 20 dB.
Results of the BERA Test
Comparing dental professional and control groups according to the ear [right ear (RE); LE], statistically significant differences were found only in wave V and interval I–V in the RE (Table 4).
| Empty Cell | Dentists RE | Controls RE | p-value | Dentists LE | Controls LE | p-value |
|---|---|---|---|---|---|---|
| Wave I | 1.70 ± 0.13 | 1.68 ± 0.13 | 0.843 | 1.76 ± 0.16 | 1.7 ± 0.12 | 0.79 |
| Wave III | 3.87 ± 0.16 | 3.76 ± 0.15 | 0.983 | 3.87 ± 0.16 | 3.79 ± 0.16 | 0.991 |
| Wave V | 5.68 ± 0.25 | 5.51 ± 0.17 | 0.051 | 5.67 ± 0.21 | 5.56 ± 0.18 | 0.540 |
| Wave I–III | 2.20 ± 0.15 | 2.11 ± 0.16 | 0.719 | 2.17 ± 0.13 | 2.12 ± 0.18 | 0.578 |
| Wave III–V | 1.89 ± 0.19 | 1.73 ± 0.17 | 0.446 | 1.83 ± 0.15 | 1.74 ± 0.15 | 0.935 |
| Onda I–V | 4.05 ± 0.29 | 3.82 ± 0.15 | 0.008 | 3.98 ± 0.22 | 3.89 ± 0.19 | 0.567 |
Based on the findings from the pure tone audiogram, it was observed that 20% of dental practitioners manifested signs of impairment, a conclusion supported by the results of the BERA test.
DISCUSSION
Occupational NIHL is defined as bilateral sensorineural hearing loss that occurs bilaterally in an individual who was exposed to intermittent or continuous loud noises generated over a period of several years. Environmental noise is responsible for hearing loss when workers endure continuous exposure to noise for 8 hours and noise levels above 85 dB.12 The noise generated in the department of periodontics was higher because of the usage of high-speed suction devices and ultrasonics for scaling and root planing continuously. The earliest sign of hearing loss from continuous noise exposure shows a “notching” of the audiogram at 3000, 4000, or 6000 Hz, greater than 25 dB, and recovery at 8000 Hz.13,14 Due to concerns raised by several authors regarding potential influences of physiological factors, such as age and sex, on brainstem auditory evoked potential recordings, there arose a necessity for a study to evaluate these variables in individuals with normal hearing and to compare them with dentists. The results of the study present data on absolute latency values for waves I, III, and V, along with interpeak intervals I–III, III–V, and I–V means. The information was gathered from a diverse sample of 30 dentists and 30 control groups aged 35–50 years. According to the studies conducted by Krishnamurti and Dube et al., the occurrence of noise-induced hearing impairment among dental practitioners has been reported to range from 7 to 16% in the biography14,15 which is in accordance with the current study results with the prevalence of hearing loss in dental personnel to be 20% when compared to the control group. Studies conducted by Bali on assessment of the effect of sound produced in a dental clinic on the hearing of dentists state that high-speed air turbines were the main cause of early hearing impairment among dental practitioners which is like our current study.16 It has been proven that noise-induced auditory impairment will decrease the function of tinnitus and outer hair cell function. Dental practitioners and their staff encounter various sources of sound in their daily practice, including high- and low-speed turbine handpieces, ultrasonic scalers, and stone mixers. Research conducted by Kilpatrick reveals the noise levels produced by different dental equipment—high-speed turbine (70–92 dB), ultrasonic cleaner (90 dB), ultrasonic scaler (86 dB), stone mixers (84 dB), and low-speed handpiece (74 dB)3 which is in accordance with the current study. Aged and worn-out equipment can generate noise exceeding 100 dB. Although noise exposure for dental professionals is intermittent, the risk of NIHL exists due to prolonged exposure. The study indicates a decrease in hearing threshold levels at 3000 Hz and 4000 Hz, particularly pronounced in the LE, influenced by the right-handedness of most dental professionals. Consequently, this study emphasizes the importance of health education for dental professionals to raise awareness and provide strategies to reduce noise exposure in their practice. To prevent and control noise exposure in dental offices, several measures can be implemented. Firstly, it is advisable to avoid using aged and worn-out equipment, as they tend to produce more noise. Regular maintenance of devices is crucial to ensure optimal performance and reduce noise levels. Additionally, proper acoustic treatment of the dental office, including walls, ceilings, and floors, can help minimize sound transmission. The use of earplugs and muffs is recommended for individuals working in noisy environments. Maintaining a distance of 35 cm between devices and the ear is another effective measure. Equipment should only be activated during procedures to minimize unnecessary noise. Placing compressors outside the dental office or in isolated areas can further isolate noise sources. Lastly, periodic audiometric evaluations are essential for the early detection of potential hearing issues among dental professionals. The noise generated from the dental workplace should never be underestimated, with the primary sources being very high-speed handpieces and high-vacuum suction devices, ranging from 55 to 80 dB. Long-term exposure to noise levels above 80–85 dB imparts an increased risk of hearing loss.18,19 So the high-risk from the high-frequency noises generated from the dental workplace could cause hearing impairment among dental practitioners which suggests the use of additional tests like high-frequency threshold detecting audiometry, that might help in early recognition of NIHL among dental practitioners and also the usage of protective equipment in noisy environments, including ear plugs, ear muffs, and canal caps will help in preventing NIHL.20
Limitations
As the results obtained from the pure tone audiometry are completely based on the patient’s response, there might be a subjective bias and the graphs are drawn by the audiology specialist, so the complete dependency is on the specialist. Long-term follow-up is necessary to obtain accurate results and to assess the side effects of the noises generated at the dental workplace.
CONCLUSION
This study assesses the sound levels within a dental clinic environment and compares the prevalence of sensorineural hearing loss in dental practitioners to that of nondental individuals. A positive correlation was identified between the years of experience and diminished hearing capacity among dental practitioners. Due to their exposure to workplace noise, the suddenness and frequency of these occurrences significantly affect the hearing of dental professionals. Hence, it is essential for them to use protective equipment in noisy environments to prevent NIHL.
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