Occupational noise induced hearing loss among dental professionals

Occupational noise induced hearing loss among dental professionals

MENA Dental Science

6. November 2019

Natheer H. Al-Rawi, Ansia Sadiqi, Elaf Azaiah, Dunia Ezzeddine, Qoot Ghunaim , Zeyad Abbas , Ahmed S. Al Nuaimi

Objective: The purpose of this study was to determine whether the persistent high-frequency noise produced by dental equipment could cause hearing impairment among the dental professionals in the United Arab Emirates (UAE).

Method and materials: This cross-sectional study was conducted to evaluate the hearing capacity of 90 randomly selected dental practitioners from different specialties working in the UAE. The participants were approached in their workplace and their hearing capacity was evaluated using the pure tone audiometer.

Results: Twenty dental practitioners suffered from hearing impairment, which constitutes 22.2% of the studied sample. At high frequencies, left ears were more affected than right ears, but this was not statistically significant. There was a direct relationship between working hours per week and the hearing capacity, but this did not reach a statistically significant level. The lowest hearing capacity was detected in males at a significantly lower value compared to females.

Conclusions: Positive correlation was found between years of experience and reduced hearing capacity among dental practitioners. In addition, males had a significantly higher median count of severely affected hearing frequencies compared to females. Online pure tone audiometric testing is an easy, costeffective tool that can be used to selfassess the hearing capacity of dental professionals, and it is recommended to perform this test annually. (Quintessence Int 2019;50:245–250; doi: 10.3290/j.qi.a41907)

Introduction

Since the development of the handpiece, there has been concern regarding their impact on hearing capacity. The US National Institute of Occupational Safety and Health states that “dentistry is one of the occupations that exposes individuals to harmful levels of noise which increase their risk of developing noise induced hearing loss.” Noise-induced hearing loss (NIHL) is the most common occupational hazard,1 and occurs at about 2,000 to 4,000 Hz. Individuals with excellent hearing can distinguish sounds from 20 Hz. Human speech ranges from 20 to 2,000 Hz, so as hearing impairment begins, the high frequency pitches are often lost first followed by the lower frequencies. Permanent NIHL is due to destruction of cochlear hair cells.2

NIHL among dental practitioners could be due to various sources, such as high-/low-speed handpieces, high-/low-volume suction devices, and ultrasonic scalers. Several studies have tested the noise produced in dental practice that could exceed the Occupational Safety and Health Act (OSHA) standards. Dental devices can produce sounds between 66 and 91 dB; however, these devices differ. It is reported that air turbines can produce noise that reaches 100 dB.3 In their study on audiometric analysis, Ahmed et al3 stated that “Noise exposure to a loudness of ≥ 85 dB for about 8 hours on daily basis can produce permanent hearing loss.”3 Noise in a dental office together with other 24-hour noise exposure may have an additive effect and this could explain why hearing loss is experienced by a significant number of dentists.4 A study in Saudi Arabia revealed that 16.6% of dental practitioners suffered from tinnitus, 14.7% experienced difficulty in speech discrimination, and 63% had difficulty with speech discrimination in background noise.5 The present investigation aims to identify the hearing capacity in a sample of dental professionals in the UAE who practice where noise-generating instruments are frequently used.

Method and materials

This cross-sectional study comprised 90 dental practitioners who were randomly selected from private clinics and governmental dental hospitals across UAE during the period of January to March 2017. Only dental practitioners with at least 5 years of experience who did not suffer from any conditions that could compromise hearing and had no preexisting hearing impairment were recruited.

The potential participants were approached in their clinics to explain the objective of this cross-sectional study and were asked to take part. After provision of the informed consent, the data were collected during a personal interview using a structured questionnaire that included questions about their age, gender, duration of experience, and specialty. Following the questionnaire, an audiometric examination using a calibrated online pure tone audiometric test set up on different frequencies (100 to 15,600 Hz) was done at the comfort of their workplace. The software generates data representing sound waves that are sent to the computer’s audio system. Sound is then emitted out of a connected headset. Data points in the form of frequency and amplitude (ie, volume) are depicted in a table and drawn on a chart called an audiogram. Hearing range and areas of reduced sensitivity can be easily depicted using the audiogram. The right and left ears were tested separately in a soundproof room outside the clinic.

The test gives a result for hearing capacity at selected frequencies by amplitudes ranging between 1 and 100. Lower values were associated with better hearing, indicating that the tested subject heard the emitted sound at a lower amplitude, where as a value of 100 indicates inability to detect the test sound at the highest possible amplitude for the specific frequency. Discriminant analysis was used to classify the resulting amplitudes for being able to detect the tested frequencies into three distinct categories. Those with amplitude of ≤31% belong to the first category, with the best hearing for all tested frequencies. The second category had amplitude of between 32% and 79% for all tested frequencies. This category was labeled as having significant hearing impairment. The third category had amplitude ranging between 80% and 100% for all tested frequencies and was labeled as having severe hearing impairment. These two cut-off values for amplitude were used to define significant and severe levels of hearing loss at each tested frequency. As hearing amplitude decreases, more frequency intervals in the high end of hearing frequencies spectrum become affected. The lowest frequency associated with the first sign of affected hearing is one of the outcome measures of hearing quality being adversely affected. The lowest frequency in both ears was used to represent the hearing quality of a study subject. In addition, another measure used in the current study was the count of sound frequencies (out of the total 32 frequencies tested for each individual), with a hearing amplitude less than each of two cut-off values suggested by discriminant analysis. The more hearing frequencies showing evidence of low hearing amplitude, the worse the hearing quality. The sum of affected frequencies in both ears was used to represent each study subject. The collected data were analyzed using SPSS-23 (IBM). Frequency, median, range, paired t test, and correlation coefficient were analyzed. A significance level of P < .05 was chosen.

Results

The results presented in this section were based on the analysis of a random sample of 90 dental practitioners with an age ranging between 25 and 55 years. About half (47.8%) of the study sample was young adults with an age range of 25 to 35 years, and only a fifth (22.2%) were in the older age group (46 years and above). Males constituted 54.5%, and more than one third had more than 15 years of work experience in the dental profession, while 16.7% had worked for less than 5 years.

Regarding dental specialties, about half of dental practitioners (46.6%) were general practitioners and the other half were dental practitioners with different specialties. Twenty dental practitioners suffered from hearing impairment, which constitutes about 22.2% of the studied sample. The median lowest frequency for severe and significant hearing impairment showed no statistically significant differences between left and right ears. In addition, no significant paired differences were shown between the two ears in median count of severely and significantly affected hearing frequencies (Table 1).

Table 1 The difference between right and left ear

Parameter Right ear Left ear Difference between right and left ear P
Lowest frequency for a detectable hearing impairment (Hz) Severe hearing impairment (> 79%) Range 9,100–16,100 4,100–16,100 -6,000–5,000 0.44 [NS]
Median 16,100 16,100 500
Interquartile range 14,100–16,100 14,100–16,100 -1,000–2,000
N 90 90 0
Significant hearing impairment (> 31%) Range 7,100–16,100 4,100–16,100 -5,500–5,000 0.46 [NS]
Median 15,350 16,100 500
Interquartile range 13,100–16,100 14,100–16,100 -1,000–2,000
N 90 90 0
Count of affected frequencies Severely affected hearing frequencies (> 79%) Range 0–12 0–23 -11–12 0.33 [NS]
Median 0 0 0
Interquartile range 0–4 0–4 0–0
N 90 90 90
Significantly affected hearing frequencies (> 31%) Range 0–14 0–24 -11–12 0.26 [NS]
Median 1 2 0
Interquartile range 0–6 0–5 -1–0
N 90 90 90
NS, not significant.

Both age and years of experience had a moderately strong negative (inverse) linear correlation with the lowest frequency for severe hearing impairment (r = −0.425 and −0.39, respec- tively) (Table 2). The lowest hearing capacity was detected earlier in males at a significantly lower value compared to females (13,600 Hz for males vs 15,600 Hz for females). A similar pattern was observed for the lowest frequency for significant hearing impairment (Table 2).

Table 2 The median lowest frequency in any tested ear for severe and significant hearing impairment by selected explanatory variables

Parameter Range Median Inter-quartile range N Mean rank P
Lowest frequency for severe hearing impairment (amplitude > 79%): any ear (Hz) Age group (y) (r = −0.425, P < .001) 25–35 12,100-16,100 16,1 15,100–16,100 43 56.2 <.001
25–35 10,100-16,100 15,1 12,100–16,100 27 38.1
≥ 46 4,100-16,100 16,6 15,100–16,100 20 32.5
Gender Female 11,100-16,100 16,1 15,100–16,100 37 39.2 .003
Male 12,100-16,100 15,1 13,100–16,100 53 54.5
Experience (y) (r = −0.39, P < .001) < 5 11,100-16,100 16,1 15,100–16,100 15 58.0 .002
5–10 11,100-16,100 16,1 15,100–16,100 22 56.8
11–15 10,100-16,100 15,1 13,100–16,100 21 40.2
> 15 4,100-16,100 13,85 11,600-16,100 32 35.3
Overall 4,100-16,100 15,85 13,100–16,100 90 NA
Lowest frequency for significant hearing impairment (amplitude > 31%) Age group (y) (r = −0.465, P < .001) 25–35 11,600-16,100 16,6 15,100–16,100 43 57.6 <.001
25–35 9,100-16,100 13,6 11,600-15,100 27 37.6
≥ 46 4,100-16,100 12,6 10,600-14,600 20 30.0
Gender Female 10,100-16,100 15,6 14,100–16,100 37 55.7 .002
Male 4,100-16,100 13,6 11,600-15,100 53 38.4
Experience (y) (r = −0.41, P < .001) < 5 12,100-16,100 16,1 14,100–16,100 15 57.8 <.001
5–10 10,100-16,100 15,6 15,100–16,100 22 58.5
11–15 9,100-16,100 13,6 12,100-16,100 21 41.1
> 15 4,100-16,100 13,1 11,600-15,100 32 33.7
Overall 4,100-16,100 15,1 13,100–16,100 90 NA
NA, not applicable; r, linear correlation coefficient.

Both age and years of experience had a moderately strong positive (direct) linear correlation with count of severely affected hearing frequencies (amplitude > 79%) (r = 0.423 and 0.318, respectively). In addition, males had a significantly higher median count of severely affected hearing frequencies (4) compared to females (0). A similar pattern was observed for count of significantly affected hearing frequencies (amplitude >31%), with six males affected compared with only one affected female (Table 3).

Table 3 The median count of severely and significantly affected hearing frequencies in both ears (out of 32 tested frequencies in each ear)

The median count of severely and significantly affected hearing frequencies in both ears (out of 32 tested frequencies in each ear)

Parameter Range Median Inter-quartile range N Mean rank P
Count of severely and significantly affected hearing frequencies (amplitude > 79%) Age group (y) (r = 0.423, P < .001) 5-35 0-14 0 0-3 43 34.9 <.001
36-45 0-18 4 0-12 27 52.2
≥ 46 0-35 6 0-14,5 20 59.1
Gender Female 0-14 0 0-2 37 35.9 .002
Male 0-35 4 0-9 53 52.2
Experience (y) (r = 0.398, P < .001) < 5 0-14 0 0-1 15 31.9 .002
5-10 0-13 0 0-2 22 34.8
11-15 0-13 3 0-8 21 51.0
> 15 0-35 4 0-12 32 55.6
Overall 0-35 1 0-8 90 NA
Count of at least significantly affected hearing frequencies (amplitude > 31%) in both ears Age group (y) (r = 0.425, P < .001) 25-35 0-16 1 0-4 43 34.5 <.001
36-45 0-19 5 1-13 27 52.4
≥ 46 0-38 9 3-18,5 20 59.9
Gender Female 0-19 1 0-4 37 34.6 <.001
Male 0-38 6 2-13 53 53.1
Experience (y) (r = 0.393, P < .001) < 5 0-16 0 0-4 15 32.7 .002
5-10 0-19 1 0-4 22 34.1
11-15 0-18 5 0-11 21 49.7
> 15 0-38 7 2-16 32 56.6
Overall 0-38 4 0-9 90 NA
NA, not applicable; r, linear correlation coefficient.

The high-frequency end of the hearing spectrum and the first evidence of affected hearing (whether significant or severe hearing loss) starts at 4,100 Hz sound frequency, with 0.6% of tested study subjects showing evidence of hearing loss at this frequency. This proportion increased to 41.1% at 15,600 Hz sound frequency for severe hearing loss, and 51.7% of subjects showed evidence of significant hearing loss at this extreme tested frequency.

Discussion

The dental office is a noise-polluted environment. Oral health care workers are constantly subjected to both intermittent and continuous noise from high-speed handpieces, ultrasonic scalers, suction devices, automated mixers, ultrasonic instrument cleaners, entertainment systems, and heating and air-conditioning units. The prevalence of NIHL among dental professionals has been reported to range from 7% to 16%.6 Bali et al7 found shifts of hearing thresholds at frequencies between 4 and 6 kHz in a group of dental practitioners.7 Other studies also confirmed that high-speed air turbines are the main cause of early hearing loss problems among dental practitioners.8 It has been shown that noise-induced auditory damage increases tinnitus. The severity of tinnitus is in direct relation with age and duration of noise exposure.9 Previous studies in Saudi Arabia found that 16.6% of dental practitioners suffered from tinnitus and 14.7% had speech discrimination difficulties. The incidences of symptoms were similar because all dental personnel are exposed to similar noise levels.5 The increased availability and the constant usage of many high-frequency dental devices can increase the noise levels so that they can reach the limits of the risk for hearing loss. Hearing loss has been reported in dental practitioners who have practiced for 10 or more years,10,11 and those over the age of 40.11,12 This is in accordance with the present study where both age and years of experience had a moderately strong negative correlation with the lowest frequency for severe hearing impairment. Some studies stated that both male and female dental practitioners in the same age range develop hearing impairment.12,13 This finding is not in accordance with the present findings, which demonstrated that males develop hearing loss at lower frequencies than females. The differences could be attributed to the lesser working hours of females in the tested sample. The range where a person loses the ability to hear high-pitched sounds is 3 to 6 kHz.12,13 Hearing impairment among dental practitioners is being reported at these frequencies.12-14 The first evidence of hearing impairment in the present study started at 4.1 kHz. The noise generated in dental clinics should not be underestimated. The main source is the high-speed handpieces and the high-volume suction devices, which ranged in this study from 55 to 80 dB. Nevertheless, the prevalence rate is about 22.2%, which is slightly higher than that reported in other studies.4,5 In the present study, the hearing loss of the left ear was more profound than in the right ear, which is in accordance with other studies.6 The increased risk for high-frequency hearing loss among dental professionals necessitates the use of additional tests such as high-frequency threshold audiometry, which could help the early detection of NIHL.14 To the present authors’ knowledge, this study was the first of its kind in the UAE to assess the hearing capacity among dental professionals.

Conclusion

Occupational NIHL in adults is considered untreatable and the best approach is to provide optimal protection. In this study, a positive correlation was found between years of experience and reduced hearing capacity among dental practitioners. In addition, males had a significantly higher median count of severely affected hearing frequencies compared to females. Online pure tone audiometric testing is an easy, cost effective tool that can be used to self-assess hearing capacity among dental professionals, and it is recommended to perform testing annually.

Declaration

The study was approved by the Research and Ethics Committee of the University of Sharjah, under Protocol no. REC-16-10-06- 06-S. The dataset used and/or analyzed during the current study are available from the corresponding author on reason- able request.

The authors declare that they have no competing interest regarding the publication of this paper. The project was selffunded.

 

 

 

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Natheer H. Al-Rawi
Natheer H. Al-Rawi
Associate Professor

College of Dental Medicine, University of Sharjah, UAE.

Ansia Sadiqi
Senior Dental Student

College of Dental Medicine, University of Sharjah, UAE.

Elaf Azaiah
Senior Dental Student

College of Dental Medicine, University of Sharjah, UAE.

Dunia Ezzeddine
enior Dental Student

College of Dental Medicine, University of Sharjah, UAE.

Qoot Ghunaim
Senior Dental Student

College of Dental Medicine, University of Sharjah, UAE.

Zeyad Abbas
Senior Dental Student

College of Dental Medicine, University of Sharjah, UAE.

Ahmed S. Al Nuaimi
Assistant Professor

College of Medicine, University of Baghdad, Iraq.