Are We at Risk for Noise Induced Hearing Loss in the Dental Office?
July 1, 2024
By Lisa Germain, DDS, MScD
It is not something we think about every day, but it is a fact that the whir of a hand-piece and high-pitched buzz of an ultrasonic have the potential to affect our hearing. According to the National Institute for Occupational Safety and Health, noise induced hearing loss is the most common occupational injury seen in dentists.
The level of risk and type of noise can determine whether specific noise is hazardous to your hearing. The 3 properties of noise that can be examined to determine the level of risk is intensity, duration, and spectrum of sound. Included in this are time characteristics and the physical make-up of the noise.
The intensity of sound is measured in decibels (dB). The greater the intensity of sound (higher decibel level), the greater the risk of hearing damage. The level of sound and the impact it makes are influenced greatly by the temporal patterns of exposure. There are 4 temporal patterns of sound. “Steady state” is when the sound is continuous and does not vary. “Fluctuating” is continuous but varies over time. “Intermittent” noise may be hazardous for some amount of time but is combined with time periods of non-hazardous sound levels. “Impulse,” is intense and short. Dental professionals will likely be exposed to “intermittent” noise more frequently than the other types.
Duration of the sound is measured in time. The longer the period during which an individual is exposed to a sound, the greater the risk of developing hearing loss.
The final element of noise is the spectrum. Studies have shown that most noise exposures are due to complex, variable, broadband signals.
The effects of noise on hearing have been reported to fit into three general categories: acoustic trauma, temporary threshold shift, and permanent threshold shift. Acoustic trauma describes the effect of one or few exposures to very intense sound levels such as an explosion. Typically, the loss of hearing with an acoustic trauma is noted immediately. The second category, temporary threshold shift, refers to a temporary change in hearing thresholds that follows an exposure to noise. The symptoms of a noise-induced temporary threshold shift may be a reduction in hearing sensitivity, tinnitus, or a possible feeling of subjective fullness in the ears. The amount of the hearing threshold shift and the recovery time are related to the intensity and duration of exposure to the noise. Permanent threshold shifts, the third category, refer to a change in hearing that, once it occurs, is permanent and irreversible. This may be a common occurrence as small amounts of permanent damage often result from many noise-induced temporary threshold shifts. It is the accumulation of repeated noise exposure over many years. It is this category that puts dental professionals at risk for hearing loss.
Various types of equipment in a dental office emit different noise levels and frequencies. Some of the ubiquitous types that can cause hearing loss include angled-design turbine hand-pieces, low-speed angled design hand-pieces, lab electromotor hand-pieces, high-speed turbine hand-pieces, low-speed hand-pieces, stone mixers, lab machines, ultrasonic scalers, and ultrasonic cleaners. These pieces of equipment can emit sounds ranging from 66-100 dB(decibels), with the air turbines being the worst offenders.
Anyone may be at risk for hearing loss if exposed to noise. All noise, regardless of its source, will cause hearing loss if it is loud enough or if exposure is long enough. Once noise-induced hearing loss becomes permanent, recovery of hearing is impossible. Initially, the affected individual may not perceive a change in their hearing. Eventually, however, the small changes in hearing sensitivity accumulate, causing a greater degree of hearing loss. As the hearing loss progresses, one may unknowingly develop compensatory strategies to help with communication. As a result, the hearing loss may go unnoticed until significant difficulties are experienced. This could be since it is gradual, progressive and painless.
Since noise-induced hearing loss typically affects high frequencies first, individuals who experience this kind of hearing loss may have very little difficulty hearing in quiet, face-to-face situations but may begin to have trouble hearing women and children’s voices. Other factors, such as age of the individual and genetics add to noise-induced hearing loss, and other frequencies will be affected. As the hearing loss progresses, an individual may experience added difficulties hearing in the presence of background noise, when sounds are at a distance, or in rooms with poor acoustics.
The noises to which dental professionals are exposed are intermittent. The amount of noise to which the dental professional is exposed depends on the type of treatments that are scheduled and the type of equipment used. Older equipment has the potential to create an increased exposure to noise. Older drills may produce the louder sounds of 100 dB. The higher intensity reduces the allowable exposure time to two hours per day. While a typical dental office does not appear to exceed the limits set by OSHA and proposed by NIOSH, damage to hearing may still occur.
Tinnitus is often a comorbidity associated with hearing loss. This low grade buzzing, or ringing sound is heard only by the afflicted person, may be constant or intermittent, and varies in intensity. Individuals suffering from tinnitus may experience annoyance, anxiety, difficulty with concentration, sleep disturbances, depression, and/or difficulty with spoken communication. As many as 90 percent of people who experience tinnitus have had some noise-induced hearing loss, although it has been observed that an individual may notice the tinnitus before he or she notices any hearing difficulties. As a result, tinnitus is often the precipitating cause for an individual to pursue a hearing evaluation.
Since noise-induced hearing loss is not medically treatable, preventing the effects of noise is important. Methods to reduce noise exposure in the dental office, and to protect hearing, can be implemented to prevent noise induced hearing loss. The work environment can be modified to decrease the effects of noise. Methods used to reduce noise exposure can include having the dental professional maintain good posture while a hand-piece is being run which will keep an appropriate maximum distance between the dental professional and the noise. Maintaining dental equipment appropriately is critical— insufficient lubrication contributes to noise, together with the resultant bearing wear and turbine failure. These are associated with an increased level of noise production from air turbine hand-pieces. While these modifications are helpful, they are not sufficient in themselves, and dental professionals should consider wearing hearing protective devices. It has been found that if you cannot or will not avoid hazardous noise, the use of ear protectors is a simple, effective, and under-utilized way to reduce noise exposure. There are several types of hearing protection devices that can be worn over the ears as a headset or in the ear as an earplug. Hearing protection devices can be disposable or custom made. The amount of protection a hearing protection device offers depends on its design. There are advantages and disadvantages to each design, and these should be considered when choosing which type of devices to use in a dental office.
The hearing requirements of dental professionals are unique. Hearing protection devices, if used, must protect the dental professional from potential noise damage induced by hand-pieces as well as other equipment. At the same time, the dental professional must be able to hear sufficiently to communicate with the patient and team members. One option is to purchase custom earplugs, the same type of hearing protection device used by many musicians for protection from occupationally induced hearing loss. The musician’s style earplug is perfectly suited to the dental environment and is an affordable and comfortable solution — voices sound softer but are still audible. A definite decrease in the noise from dental equipment will be observed. If custom products are not used, other hearing protection devices such as generic insert earplugs (foam plugs or flanged plastic plugs) and headsets are possible alternatives.
Since correlation does not necessarily imply causation, it can be said that noise induced hearing loss in the dental office is a theory based on anecdotal evidence. However, even if noise exposure in the office is minimal there seems to be a strong argument that practicing dentistry increases your risk for noise induced heating loss more than a quiet desk job.