Should Dentists Mandatorily Wear Ear Protection Device to Prevent Occupational Noise-induced Hearing Loss? A Randomized Case–Control Study

Abstract

INTRODUCTION Noise is defined as an unwanted and undesirable sound in the environment.[1] Noise is one of the leading causes of work-related diseases or injuries, especially affecting the auditory system.[1] The hearing loss that arises from prolonged noise exposure at the workplace is known as occupational noise-induced hearing loss or boilermakers notch (ONIHL or NIHL). According to the Occupational Safety and Health Administration (OSHA), around 30 million people suffer from ONIHL due to harmful levels of noise at their workplace.[2] Among all the occupations, dentists and dental auxiliaries are at an increased risk of developing ONIHL due to prolonged and continuous exposure to high-frequency noise in their workplace.[3456] The prevalence of hearing loss among dentists is 5–20%.[78910111213] Other dental professionals that use various noise-inducing dental equipments noise-inducing dental equipments include dental nurses, dental technicians, clinical dental technicians, orthodontic therapists, and dental hygienists. Dentists are exposed to 70–120 dB of high-frequency noise for more than 8 h in a day, which is around 8% of their 24 h noise exposure.[678910111213] The most common dental instruments and equipment that emit high-frequency noise include high-speed turbine handpiece (airotor or micromotors); high-velocity suctions; stone mixers and grinders; sonic and ultrasonic scalers, ultrasonic cleaners, and vibrators; model trimmers; and other mixing devices.[67891011121314] Among all these instruments, ultrasonic scalers are one of the most common instruments known to emit high-frequency noise in a dental setup. Ultrasonic scalers produce noise levels between 87.1 dBA to 107 dB, at the one-third octave band of 25,000 Hz.[789151617] Although the measurement of 107 dB is above the recommended 87 dB, human ears are insensitive to this ultra-high frequency.[1718] Previous studies have shown that ultrasonic scalers can cause a temporary threshold shift (TTS), whereby an individual requires a louder stimulus than usual to hear the same frequency.[19] This temporary condition was found to last between 16 h to 48 h, but the researchers have also cautioned that a certain degree of permanent damage can occur.[19] A continuous exposure to more than 100 dB for more than 8 h increases the risk of permanent hearing loss from 94.5% to 99.5%.[678910151617181920212223242526272829303132333435363738] Previous studies have shown that approximately 7–20% of the dental hygienists, dental assistants, and dentists report problems such as difficulty in communication, annoyance, conversation interference, concentration difficulty, hearing loss even at speech frequencies.[14151617323334353637] Although the presence of ONIHL among dentists is well established, preventive measures and use of hearing protection device (HPD) or ear protection device (EPD) among dentists are not widely advocated and used. Many dentists are unaware about the immediate and long-term side effects of work place noise and its effects on the auditory and non-auditory systems. Dentists are even reluctant to use are unaware about the importance of EPDs in a dental setup. Hence, it is crucial to generate evidence on the efficacy of using EPDs in a dental set up. No study has yet compared the immediate changes in hearing acuity of dentists who use EPDs when compared with those who work without EPDs. Hence, the present study aims to evaluate and compare the efficacy of using an EPD in preventing the TTS among dentists while performing ultrasonic scaler. The study is of global significance as it lays the foundation and highlights the importance of using EPDs by dental professionals to protect their ears while working in a noisy workplace. MATERIALS AND METHODS STUDY DESIGN AND SETTINGS The study was conducted at the Department of Periodontology, Manipal College of Dental Sciences, Manipal, Karnataka, India, in collaboration with the Department of Speech and Hearing, Manipal College of Health Professions, Manipal Academy of Higher Education, India, between September 2017 and December 2018 in accordance with the Helsinki Declaration of 1975, as revised in 2000. Before the data collection, the ethical permission was obtained from the Institutional Review Committee IEC no.: 323/2017 and registered at the Clinical Trial registry with No. CTRI/2017/07/009031 registered on 12/07/2017. The following instruments, test, and methodology were adopted for the study. SAMPLE SIZE AND PARTICIPANTS The sample size was calculated on the basis of the formula with 95% confidence interval, 80% power, ratio of cases to controls=1, and standard deviation between cases and controls: 0.5, Z-beta=0.84, Z-alpha/2= 1.96. A total of 64 participants were required for the study. A total of 70 dental practitioners aged 20–35 years of age (both males and females) were initially screened in the study after taking written and oral informed consent. All participants were screened for the presence of any previous or existing ear and hearing problem with the following inclusion criteria: (a) hearing sensitivity below 15 dBHL (hearing loss in decibel) in both the ears; (b) no previous history of any ear infection; (c) no history of any trauma to the head and neck region; (d) no systemic illness or history of any drug intake; and (e) no history of any nerve injury or trauma involving the central or peripheral nervous system. Exclusion criteria were as follows: hearing threshold above 15 dBHL in both the ears; those with a history of previous ear infection; head and neck injury; nerve injury, sinusitis, tonsillitis; and pregnant or lactating mothers. OUTCOME MEASURES The hearing sensitivity was checked for all the participants by performing audiometric testing. All tests were repeated three times for both the ears for all the participants: Pure tone audiometry (PTA): PTA is the standard behavioral assessment of an individual’s hearing sensitivity.[2833,34] A calibrated inter-acoustics AC-40 clinical audiometer with standard accessories (TDH-50 Headphone and Read Ear B-71 Bone Vibrator) was used to estimate hearing thresholds. PTA provides information about the peripheral hearing acuity across human audible frequencies and allows clinicians to compare the hearing sensitivity between both the ears.[39404142434445464748495051] PTA was performed by a duly calibrated (ANSI S3.43–1996) Inter-acoustics AC-40 Double-Channel Clinical Audiometer coupled with standard accessories [Telephonics Dynamic Headphone (TDH-50P) and Radio Ear B71 Bone Vibrator]. The threshold estimation was done using a modified Hughson–Westleke procedure for the air conduction (250 Hz to 8 kHz) and bone conduction (250 Hz to 4 kHz) 36. The subjects were instructed to indicate by raising their finger if any sound was heard. The changes in the overall hearing sensitivity was evaluated based on the change in the response for each frequency (250, 500, 1000, 2000, 4000, 8000 Hz). Tympanometric test was performed for both the ears using a calibrated (ANSI 3-39-1987) Immittance audiometer (GSI-Tympstar). The tympanometric test indirectly reflected the middle ear status by assessing changes in the ear canal volume, middle ear pressure, and static compliance.[33] Further, the stapedial acoustic reflex was elicited for the frequencies 500, 1000, 2000, and 4000 Hz with presentation levels starting at 85 dBHL. The presence of reflex is considered when the deflection is 0.03 mL in compliance. Otoacoustic emission (OAE) test: A transient evoked OAE from the inner ear was measured for five frequencies (1000, 1414, 2000, 2828, and 4000 Hz) using a calibrated ILO-OAE system (Version 6.38.25.0). The amplitude of OAE was recorded for all the five frequencies for both the right and left ears. Any signal-to-noise (SNR) ratio above 6 dB in amplitude was considered as a sign of the presence of OAE. Any change in the number of OAE received before and after exposure to noise was recorded to evaluate the state of the inner ear.[33] After the evaluation of initial hearing acuity, six participants were excluded because of the loss of hearing acuity (hearing sensitivity below 15d BHL in both the ears) and the presence of ear infection. Thus, a total of 64 participants were recruited for the study. Age (in years), gender (M/F), duration of scaling (min), hours spent in the dental clinics (in min), total work experience (in years), and baseline noise in the workplace (Hz) were recorded. Noise measurement of the dental workplace was done to measure the maximum and minimum noise levels available. The minimum noise measurement corresponded to the sound level meter reading when dental instruments are being used. Similarly, the maximum noise corresponds to the sound level meter reading when all the dental types of instruments and equipment are working. A minimum of three readings were taken, one at the center of the workplace and four at the corners of the room, to evaluate the overall distribution of noise in the workplace. Successively, noise measurements were taken for a single ultrasonic scaler. The average of all the three readings and the difference between the maximum and minimum readings were noted. GROUPING, BLINDING, AND INTERVENTION After the baseline audiometric testing and noise measurements, the participants were randomly divided into two groups (group 1 and group 2) using the coin toss method. All participants in group 1 were asked to use the ultrasonic scaler (Parkell Auto/Manual Tuned Ultrasonic Scaler) at 25,000 Hz and medium power settings; power 110 V, 50/60 Hz, 100 VA for removing the hard and soft deposits from the surface of teeth for 45–60 min without wearing any EPDs. The participants in group 2 were asked to perform ultrasonic scaling by using an ultrasonic scaler (Parkell Auto/Manual Tuned Ultrasonic Scaler) for only 45–60 min after wearing the same type of EPD (Foam Plugs Classic Soft, Eggar, India) with noise attenuation properties (SNR: 36, H-value: 36 dB, M-value: 33 dB, L-value: 29 dB) [Figures 1 and 2].Figure 1: Schematic representation of research question and methodology. PTA= pure tone audiometry; OAE = otoacoustics emissionFigure 2: CONSORT flow diagramThe participants were demonstrated and trained to wear the EDPs as follows: the participants were requested to first roll the earplug into a small and thin shape with their fingers (single or both hand) and pull the top of the ear in an upward and backward direction with their opposite hand to straighten out their ear canal. The rolled-up earplug should then be carefully put inside the ears. The participants should hold the earplug with the finger until it expands to fill the ear canal. The voice should sound muffled when the plug has made a good seal. Once the ear plugs are fitted in both the right and ear ears, the participants were also requested to follow the ergonomically correct operatory position and to perform ultrasonic scaling. All participants were requested to maintain a distance of 35–40 cm from the ultrasonic scalar tip and performed ultrasonic scaling for 45–60 min. Once the scaling was completed, all three audiometric tests were repeated for all the participants for both the left and right ears. The clinicians were also questioned regarding any non-auditory symptoms such as irritation, headache, fatigue, pain in hands, fingers, wrist, or back, dizziness or ringing sensations in the ears, and difficulty in wearing the EDPs. All investigators who performed the audiometric evaluations and statisticians who analyzed the data were blinded about the group assignment. STATISTICAL ANALYSIS All data were checked for entry errors and manually entered in a spreadsheet and analyzed with a statistical package, IBM SPSS version 15 (IBM Co., Armonk, NY, USA). Continuous variables [age, gender, duration of scaling, hours spent in the dental clinics, total work experience, and baseline noise in the workplace (Hz)] recorded were summarized by the mean and standard deviation. For intergroup and intragroup comparison of outcome measures from pre- and post-scaling across the ears, groups, and frequency in both the groups, mixed-effects of was used. overall for comparison of mean outcome measures from pre- to post-scaling across the groups for the of both the ears and frequency was A of than was considered to be The mean age of all the participants was years in the group and in the were 30 males and (group and group 15 and in the study. The average noise recorded on the when one scaler was for three were and more than one dental was the average noise dB 1: data and of the The mean TTS across all the octave frequencies was found to be dBHL in group 1 and dBHL in group The pre- and post-scaling for the PTA test a difference between group 1 and group with a of than and The PTA for and Hz were increased in group 1 when compared with group 2 in which a was of for both the The average in the hearing threshold for group 1 from to dBHL and from to dBHL The difference in scaling for group 1 was more when compared with group 2 with a mean in right ear from a minimum of dBHL to a maximum of dBHL. The maximum difference in the hearing threshold was found to be dBHL for the left The left ear was more than the right ear and 2].Figure of the post-scaling pure tone audiometry readings of the left ear and right ear in groups 1 and 2 compared with baseline mixed-effects at group 1: without ear protection device group 2: with 2: Pure tone audiometer readings of the left and right ears in both the groups mixed-effects at (group group with no ear protection group group with ear protection The of the stapedial acoustic also the of an in threshold in group 1 and a or threshold shift in group 2 4 and The left ear more threshold shift with maximum shift in the 1 the of with the mean in the stapedial reflex threshold found to be dB sound level and dB compared with group group 2 a in the stapedial reflex threshold with a mean of dB and dB both the groups, the left ear was found to be more when compared with the right ear with a of than of the average post-scaling readings of the left ear and right ear in both the groups compared with baseline using mixed-effects group 1: without ear protection device group 2: with reading in the right and left ears in both the groups mixed-effects (group group with no ear protection group 2 = group with ear protection The of the OAE the effects of high-frequency noise exposure following scaling on the inner was a in the hearing acuity that from dB to dB for group compared with group the difference in the OAE readings was not in group The minimum difference in OAE was found to be dB in group The OAE for both right and left ears in both the groups was done using at a confidence and 4 and Otoacoustic reading of both right and left ears in both the and groups at confidence and (group group with no ear protection group group with ear protection of the average post-scaling otoacoustics emission (OAE) readings of the left ear and right ear in both the groups compared with baseline at confidence and group 1: with no ear protection device (EPD) and group 2: with hearing loss among dentists is one of the most yet occupational to high-frequency noise in a dental has with and changes in the and inner these changes in the hearing threshold are for are not or by the dentists until the permanent hearing loss A study in dentists that is a of and among dentists and the to the of the of among a between the duration of dental and the degree of hearing loss among dental Dental professionals with more than years of experience and more than 8 h of work have the risk of developing hearing loss at frequencies from to Hz and compared the hearing of and dental using a high-frequency audiometric testing and found that are the most were the at the mean frequencies of and Hz, the dental were the most group at the mean frequencies of and also a between the degree of hearing among dental and the duration of exposure to dental occupational by The also recommended and hearing protection for dental dental and most dental professionals work for more than 6 h in dental and are exposed to from various dental to any measures or to the harmful effects of noise at Many and the Occupational Safety and Health Administration of the Department of have regarding occupational noise exposure and when are exposed to noise to or 85 dB for more than 8 working The also the to and and use noise at the dental A of 15 that use of as of a hearing loss is with hearing also compared the audiometric data from who were exposed to noise and that is a in the risk for high-frequency threshold shift without the use of can the noise by dB when in a A of dB is to a as even a dB attenuation the noise levels to the in more than of the exposed of noise and use of EPDs among dentists and are not well adopted across the This that dentists are about the harmful effects of or not to it is that dentists the presence of evaluate their hearing acuity and use or EPDs while Although the of hearing protection for dental is the use of EPDs is not widely the present study aims to generate evidence and to evaluate EPDs are in the TTS exposure to noise from the ultrasonic The of the study that the noise by the ultrasonic scalers can the hearing acuity, especially for threshold in the acoustic reflex and OAE the changes in the hearing This also that exposure to ultrasonic scaler even for a duration can the overall hearing The change in the TTS exposure to high-frequency noise is to the of the and in the This of the ear in response to high-frequency sound is known as an acoustic reflex or stapedial The in the acoustic reflex and middle ear is reflected by the increased PTA and The of acoustic reflex the of ears to the noisy and the of hearing loss by dentists is a OAE after scaling is the most and that that a exposure to frequency after using the ultrasonic scalers can damage the of the inner that dentists should wear EPDs while working with instruments that emit high-frequency noise to the TTS and of The use of EPDs the of which in long-term the risk of permanent hearing EPDs can also the risk of non-auditory effects of high-frequency noise such as fatigue, irritation, and even of wearing an the work and work Thus, it is to and the among dentists regarding the importance of using EPDs and risk of from the dental workplace. and should be conducted to dentists regarding the importance of hearing protection and risk of ONIHL among The overall in is also with increased hearing and an distance of from the noise is the use of for noise is recommended for dentists and dental as have acoustic that can the noise more and dentists to maintain with and it is to that the of noise on the of the the of the dentists to use the and of the correct the duration of and overall noise level of the working are two types of EPDs that can be noise and sound noise such as and ear canal plugs work as to are to be into a thin and in the ear canal to the ear these EPDs not be the for dental practitioners as these the sound of their but the of the to with their for and The sound in are as can sound unwanted noise of use hearing and hearing protection from while other and with the the can be and to than the A among dentists found that is most to its of of and the to with the have shown that the of hearing protection is to 8 dB following on the use of when compared with no or is also shown that the EPD to a ear canal in of the the and of EPD the protection from these noise are not a with a such as can be into the ear dentists should a working to the of For the duration of each dental procedure should be and a good between noise should be to of the Dentists should their work and set their duration of exposure on the maximum frequency of noise According to the the maximum duration of exposure to noise with a frequency of dB is 8 For noise above the exposure be by for dB dB is 4 dB is 2 dB is 1 dB is 30 dB is 15 This in the noise exposure is to as the dB or dB as the left ear is more with when compared with the right dentists to maintain minimum of 30 while The handpiece should also be well as and equipment sound of to the prevalence of hearing loss among dental the noise levels by the high-speed should be below and should the noise levels by dental equipment are below 85 it be that aged or dental equipment produce noise levels 85 from the and of dental a common on the prevalence of hearing loss is to the use of studies that was or no hearing loss among if were is also that dentists of their overall noise exposure and audiometric testing to the presence of temporary hearing loss at an The threshold shift measured audiometric testing is the most of the of noise exposure on the on these should dental professionals to wear EPDs and of noise exposure and hearing This the of hearing and permanent ear damage from harmful effects of noise in the dental research with and should be conducted for dentists to regarding the importance of EPDs and of of research should evaluate and compare the effects of types of EPDs on among dentists to the type of EPD that can be by dentists and dental to and should be by various dental to the among dental practitioners regarding the risk of and to the importance of EPD and it can be used to protect their hearing ONIHL is an and occupational among The noise in the dental workplace can TTS and hearing acuity, with left ear more than the right Hence, noise device or EPDs should be by all dental practitioners to the harmful of noise on the auditory and non-auditory EPDs can shift in the hearing threshold and changes in the stapedial reflex and the from the inner ears. the use of the use of EPDs should a dental to the harmful and of noise in the dental workplace and of ONIHL among AND are no of AND The study was conducted by the College and with Institutional Review Committee IEC no.: 323/2017 and registered at the Clinical registry with No. CTRI/2017/07/009031 registered on 12/07/2017. The data set used in the study is on from of the of of the reading the of the of of and the reading the of and the reading the of the of of and the reading the of and the the reading the

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