Assessment of occupational noise‐related hearing impairment among dental health personnel

Background and introduction

Dental professionals are exposed to either a high level of noise or a continuous noise source that often becomes annoying over a period of time. These types of noise are often due to their work-related sources like aspirators, ultrasound scalers, high and low speed handpieces, turbines, etc to name a few.¹ These compressor-based, predominantly rotary instruments are kept too close by the dentist for easy accessibility, ease of work, and increased cognition. Because of the work protocol of chair-side dental assistants, an extra noise source is often created in the form of low- and high-volume suction, spittoon water, glass/tumbler filling water set, etc., which are not in direct control of the dentist. There are few studies that also highlight the plight of the extended care dental assistant related to the high noise levels in the dental office and often related to them working longer hours in the clinics compared to dentists.^2,3 There are various other risks highlighted in the literature that cause detrimental effects related to the dental profession, including infectious and communicable diseases, musculoskeletal pathologies, and ionizing radiation.^4,5 These effects have shown an early physical and mental effect; hence, more studies have been conducted to highlight the cause of remedial measures. Exposure to high noise was initially disregarded as the initial dental treatment was mostly biomechanical in which the dentists themselves used semi-automated foot controlled instruments, but since the advent of compressor-based instruments, although the treatment time is reduced and so may be physical fatigue, it has led to a more blaring reality of effects expressed both at the atrial level and at the extra-auricular level (sleep disorders, cardiovascular disorders, stress, etc.). Apart from these, there are other reasons for hearing impairment like social noise exposure largely related to recreational activities, and the increasing age of an individual. The effects of noise can be both auditory which causes fatigue and temporary impairment while non auditory effects can interference with speech, annoyance and reduction inefficiency with psychologic damage.^6,7 It was noticed that left ear of a right handed person showed a greater loss of hearing ostensibly related to proximity to the noise source.⁷ Acoustic environment of educational and teaching activities for the faculty of dentistry makes them more vulnerable to high noise levels compared with other areas of education, as it require the use of various equipment that emit different decibels of noise by many students at the same time.^4,8 The educational institutes have laboratory areas where noise levels were recorded to be as high as 93dB, while in preclinical areas the sound levels are 78.8dB. In the clinical areas the ultrasonic scalers had maximum noise levels recorded as 83.3dB, and since these equipment’s run for a longer duration of time since there may be many clinics performing similar tasks hence the faculties and auxiliaries working in this environment are more vulnerable, even though the noise levels are within the acceptable range. There is also effect seen between new and old instrument which is roughly a 2 decibel less noise in new equipment compared to the old ones.⁸ Noise levels has been roughly divided into distracting and destructive noise.^3,9 Recently, Occupational Safety and Health administration in the year 2011¹⁰ has incorporated enforcement guidance for personal protective equipment which is in continuation to the original occupational noise exposure code of federal regulation number 29 1910.95 which was originally given in 1981, in order to highlight the working hours with the maximum permissible dose and has considered it as a highly important fields of study in the upcoming century. In addition there are studies which has reported that a prolong high exposure to noise can lead to other risk areas such as vibration and hand neuropathy, it might help to determine whether these problems are related to practicing dentistry, as the recommendations of ADA council suggest that dental practitioners concerned about the potential hearing impairment should go for otologic examination and audiometric evaluation. It is also recommended to use ear protective devices in order to avoid hearing impairment in a long run.¹¹ To reduce workers’ risk of developing noise-induced hearing loss (NIHL), the exposure levels of contemporary dental equipment are generally within the limits set by the National Institute for Occupational Safety and Health (NIOSH), which recommends limiting noise exposure to 85 dBA at 40 h per week.^12,13 The maximum permitted exposure limit (PEL) in an 8-hour day should not surpass 90 dBA SPL (decibel; sound pressure level using an A-weighted scale), according to the 2001 decibel levels standard. This is roughly in accordance to OSHA’s standard, which employs a 5 dB exchange rate. The maximal permissible exposure limit (PEL) of 95 dB noise should cut down the working time to 4 hours. Similarly, the PEL for a 100 dB sound is permitted for a working time of 2 h, and so on. Besides its effects on hearing, loud noise may also impair other organic systems, such as in behavioral, neurological, psychological, vestibular, digestive, and cardiovascular disorders, among others. Excessive noise increases stress levels, which increases blood pressure and hormone release, such as adrenaline and cortisol. The effects of noise on hearing (Noise-Induced Hearing Loss [NIHL]) and general health may affect dentists, hinder communication, and negatively impact their quality of life.¹³ Dentistry demands knowledge, skills, and focus as part of a profession, and hence, a good quality of life is in turn affected by destructive noise or long-time exposure to distracting noise. Owing to modern equipment, manufacturing companies have done a great deal of work in keeping the sound decibels low, mostly hovering around 85 decibels,¹⁴ but apart from the noise levels, it is the time duration for which the dentist has been working that can itself affect his overall hearing ability. In this regard, there are several studies in dental literature examining hearing loss among dental professionals that warrant discussion.^6,7,13 Certain studies have gone farther by using noise dosimeters to record the noise and has been able to show a positive correlation between the length of service and the degree of hearing impairment among dental practitioners.¹³ There are studies which has tried to correlate the years of practicing dentistry to associated hearing impairment, as was discussed in a study that dental professionals with more than 10 years of experience working 8 hours a day are at the highest risk of developing hearing impairment, and it was also commented that the worse the hearing status of dental professionals, the more their health status is adversely affected.^13,15,16 Among different dental professionals, a comparative difference among the hearing thresholds of three dental professional groups (dentists, dental nurses, and prosthodontists) using a high-frequency audiometric testing method reported that general dentists were the most affected group followed by the prosthodontists at the mean frequencies of 500-2000 Hz and 3000-6000 Hz, while dental nurses were the most affected group at the mean high frequencies of 9000 and 16000 Hz.^17–19 As highlighted before, dental university clinics have different levels of noise exposure, probably due to a greater number of clinics and different clinics performing various clinical activities simultaneously, which has not been discussed much in the literature. We performed this study with an aim to examine the occupational noise related hearing impairment among dentists and to know the need for efforts to reduce its impact on young dentists; hence, our objectives were to determine the hearing impairment in dentists before entering the clinical procedure, during the clinical procedure and to post-clinical procedures; to explore the methods used by the dentist to reduce noise exposure depending on their awareness of hearing impairment in their day today life and also the methods that can be used to reduce the impact of hearing impairment.

Methods

The study was carried out at the Dar Al Uloom University Dental Clinic, which has 45 fully equipped dental cubicles separated by a partition of heat proof walls of 7 feet height. Since it involved the participation of the concerned dentists, ethical clearance was taken bearing, from scientific research and ethics committee of college of dentistry belonging to dar al uloom university. This committee follows the Helsinki ethical principles of medical research involving human subjects while giving ethical approval. During this study approximately 10 cubicles of equal size, shape, appearance with dental chair standardized in the center of the cubicle and dentist chair at the head rest position of the dental chair are working at a time when this study is performed, each cubicle may perform separate dental procedures, such as prosthodontics, oral surgery, and periodontics. However, the pedodontics clinical schedules are maintained in the late afternoons when the other specialties are not high and/or are operated in a separate clinical corridor within the same clinics. The study group comprised final-year dental students, interns, and board students of family dentistry, endodontics, and prosthodontics. A total of 102 dentists were enrolled, with 53 males and 49 females between the ages of 22 and 33 years having a mean of 25.60 years as shown in Table 1. After explaining the procedure and obtaining signed consent from the concerned dentist and their supervisors wherever necessary, the sound level meter was switched on to determine the baseline noise level in the clinics before the start of the procedure. The hearing ability of the dentist was recorded by placing the sound level meter at the ear level of the dentist and approximately 1 meter away from the ear. A pre-recorded verbal communication of 3 minutes duration, among three people, two male and one female through the speaker which is kept on the same side and same height of the sound level meter, but at 2 meters away from the ear of the dentist was used as a verbal sound source. The selection of location, of both the sound level meter and speaker was decided based on the preliminary study where we found that the sound level meter was able to record the correct decibels of the speaker and was clearly audible by the dentists. The volume was adjusted to a comfortable level of the concerned dentist. This recorded value is considered the basic hearing ability of the dentist. When the dentist starts the procedure, the same verbal communication is re-introduced to understand the hearing ability of the dentist. Based on his reaction, this sound level is increased to a point when he can understand the verbal communication, and this change in noise decibel level is recorded. After the procedure, the dentist was exposed to the same verbal communication set at the decibel level before the start of procedure and gradually increased until he could clearly hear the same voice note. Hence, always, the dentist is semi-concentrated on the voice note and conveys the hearing response as he can hear the voice clearly. The dentist will be asked the following questions before the start of the procedure, which is their awareness of hearing impairment among the dentists, was it ever experienced by the dentist that there was hearing impairment, was their specific modification carried out to reduce the ill effects of it. The device used in this study is manufactured by Wintact professional instrument, model WT 1357, version WT 1357 – EN - 00 that has the ability to record the noise level in digital units of decibels. The unit can be switched off with a single click and has memory of five recent readings. Each reading was recorded each time; however, a memory function was used to correlate the readings later or in cases where it was not possible to record immediately. There are 3 researchers available in the clinic to record the values at different stages to avoid conflicting results.

Results

The research comprised both male and female young dentists within the age range of 22 to 33 years, with 52 males and 49 females. It also shows that this group is also divided into less than or equal to 25 years which are 67 individuals while those who are above 25 years are 35 as described in Figure 1, and the mean age with standard deviation is shown in Table 1.

Figure 1. Explaining the demographic data.

The data were assessed using a T-test because it is a comparative hearing assessment study within the same individual, as described in Table 2. It shows the mean comparison sound level in the dental clinic apart from the total number of males and female participants. It shows the t-value to be negative before the procedure and during the procedure period, while it turns positive after the procedure readings, suggesting that there is an eminent change in the hearing ability of the dentists. We found a small variation in the overall noise level in the male and female clinics and hence we measured the values independently for both and furthermore there is a variation in the hearing ability of both the genders. The obtained data show a marked increase in the overall clinical cubicle sound level when the procedure is performed, as seen in the mean value, which can be attributed to the commonly used rotary instruments and suction. Each dentist worked for a minimum of two hours, operating on more than one patient depending on the appointment, and then there was a break for 30 minutes.

The study also described the general change in hearing ability between males and females, which was obtained using the ANOVA test, as both genders are involved. Before the procedure started, there was a neglibile difference in the hearing ability of the males and females subjects in which males had a mean of 58.37dB while females had a higher mean of 58.60dB which is 0.33dB higher than the males, this further increased during the procedure (Table 3). It also revealed that after the procedure, hearing showed a difference of 0.88dB more in females as their mean is 61.03dB while that in males is 61.91dB.

Since the research involved individuals between 22 and 33 years of age, and our study has more participants who are less than 25 years, and was also targeted to the young dentists, another correlation between the ages was performed as described in Table 4 using ANOVA test, in which they were divided into those less than 25 years and more than 25 years. We found that subjects under 25 years of age had better hearing ability, even when the procedure was in progress, compared to those above 25 years of age.

Irrespective of sex and age, there is a constant change seen in hearing ability, which decreases during the procedure and immediately after the procedure up to a minimum of 30 minutes duration, suggesting that during the procedure, since there are other clinical sounds added like rotary instruments and suction, but even when the procedure is completed and the dentist has sent the patient, his hearing ability is reduced, and this can be related to the stress post clinical procedure. A decrease in hearing ability means that the dentist must spoken to in a louder tone to make the same conversation comfortably audible to them during and after the procedure. It can be further seen that individuals with more than 25 years of age has an overall hearing impairment when compared to those with less than 25 years.

Discussion

Our study included final-year students, dental interns, and board students of family, endodontics, and prosthodontic dental specialties. Care was taken to avoid pedodontics clinics for dental interns, and there were no pediatric clinics running at the time of the study. We have a greater number of subjects below the age of 25 compared to above 25 years, suggesting that the enthusiasm to join dentistry and continue it further as board dental specialties is continuous, thereby highlighting the awareness among the young population. It is further seen that there are a greater number of male students than females; however, this difference is very low and hence can be considered insignificant and largely related to the time and availability of respective genders during the study period. However, it highlights the willingness of either gender to participate in the study, thus disproving the theory as an orthodox population. This finding goes close to various studies conducted in this region^3,20,21 and few studies had more of female population compared to the males.^22,23 The consent form was filled by all the participants, and we found that the questions in the consent form added no value to the study results as all the participants said that they have only heard about the hearing impairment among the dentists, and they have not experienced it on themselves and so have not used any methods to reduce it. Hence, we have not included the findings of the consent form in the results. It is a known fact that dental rotary instruments^2,4 cause sudden increase in the sound level within the clinics and there are reports of it causing tinnitus ^20,21,24 initially and on long exposure leading to permanent hearing impairment.^5,6 Even after the procedure has been completed, there is still loss of hearing ability, which was prominently seen in our study and continued for a considerable period, thereby suggesting that it has an impact as a stress factor among them, which has been reported in other studies.^21,25 We want to highlight a review study conducted by Hartland²⁵ and published in the year 2023 discussing various articles highlighting the amount of noise induced by different equipment during the procedure, the awareness of the dentists to the same, to the articles highlighting a permanent hearing impairment, and there are few studies that suggest different guidelines that should be implemented to reduce the amount of hearing impairment,²⁶ ranging from reducing the usage of different turbines whenever possible to wear ear plug muffs as a compulsion. It is not like the early dentists did not consider noise as a detrimental factor in their profession, as was discussed by Kaymak et al. in 2007,²⁷ who classified the noise reduction methods into active noise reduction, adaptive filtering, and passive noise reduction. The study highlighted the use of earphones to be worn by the dentist and the patient, and these headphones must have adaptive filtering, thereby reducing the handpiece sound and allowing the dentist voice to be heard more clearly by the patient. This was further explored by the same researchers,²⁸ who concluded that modifications in the headphones can reduce the noise to a great level, but their work was concentrated more towards handpieces, and there are various restrictions in real-time dentistry to apply larger headphones to all individuals in the operating room, as some might find its use itself annoying. A study²⁹ was conducted using smaller headphones with noise cancellation technology involving airpods, QC30, and Quieton Dental, which are commercially available headphone devices. The authors concluded that Quieton Dental is a device that can effectively block the noise induced from dental equipment’s since it blocks noise above 3 kHz without disrupting normal conversations by maintaining or amplifying sound at 3 kHz. However the findings are not in decibels. The authors concluded that Active noise control (ANC) equipment that can effectively match with dental clinical setup noise characteristics more precisely should be developed. To improve the quality of dental treatment and provide comfort to people in the clinic. A similar conclusion was seen in another study,³⁰ which was published in 2023, who tested antinoise ear plugs (Quiton), which found it to have limited use in the dental treatment setting.

Conclusion

Our study highlights that there is a definitive change in hearing among young dentists from before starting the procedure to during and after the procedure; hence, there is an urgent need to address this health hazard among them and related dental auxiliaries. Although there are few noise cancellation devices in the market, dental professionals need something that is specific to their requirements, because commercially available products are built and developed for other purposes. Furthermore, most noise reduction studies are performed in a simulated dental setup using an ear and cheek simulator to be placed on the phantom heads and hand piece operated on typodonts. Our study was not able to highlight which procedures have a greater noise impact to suggest specific recommendations. We conclude with a proverb: the deaf believes there is nothing wrong, the hearing believes something needs to be fixed.

Ethical approval and consent

Scientific Research Ethics and Innovation Committee Number 04 – 08 – 2021.

Ethics approval number: 04 – 08 – 2021, obtained from scientific research and ethics committee of college of dentistry belonging to dar al uloom university This committee follows the Helsinki ethical principles of medical research involving human subjects while giving ethical approval. The ethical approval was received on 10 – 09 – 2021.