One day you might have a hearing aid implanted in your mouth. Researchers tested the efficiency of natural teeth and dental implants to conduct sound as an alternative to traditional hearing aids.
Bone-anchored hearing aids (BAHA) are surgically implanted devices that treat hearing loss through bone conduction of sound vibrations to the inner ear, while traditional hearing aids amplify acoustic sounds that enter the ear canal. Bone conduction (BC) is the conduction of sound to the inner ear through vibrations of bone, usually in the skull, which allows a person to perceive auditory content by stimulating the cochlea. This type of technology has become popular recently with the widespread sale of bone conduction headphones.
Recent studies have shown that BC stimulation of teeth could initiate auditory sensations, and in fact, teeth are comparable to the mastoid – a bone in the skull behind the ear, traditionally used for BAHA – in terms of audio sensitivity in BC. Thus, in-the-mouth hearing assistive devices have been developed that take advantage of this fact (SoundBite Hearing System, Sonitus Medical, San Mateo, CA).
People are likely to have natural teeth replaced with dental implants as they age. Therefore, a team of scientists at the Stomatological Hospital and Dental School of Tongji University in Shanghai, China wanted to test the feasibility of this technology by seeing how effective BC could be for dental implants compared to natural teeth as a means of carrying sound for in-the-mouth hearing assistive devices.
The researchers quantified the pure tone auditory thresholds of normal teeth, dental implants, and mastoids by comparing their BC thresholds. The team determined the BC thresholds by having participants listen to a signal transmitted by a vibrator on natural teeth, dental implants, and the mastoid bone. The signals varied in frequency and volume; the BC threshold for a given frequency was defined as the lowest volume at which the signal was still detected by the participant.
The team found that overall, dental implants had a much lower BC sensitivity threshold than natural teeth and even mastoids, meaning that dental implants are a much more efficient medium for sound conduction. Consequently, dental implants could be used as effective BC hearing assistive devices in the mouth.
The superior BC thresholds for dental implants may be a consequence of how they are installed, which results in different interfaces with the bone for dental implants vs. natural teeth. Natural teeth are connected to the alveolar bone through the periodontium, a thin layer of dense connective tissue, whereas dental implants are connected to the alveolar bone by osseointegration, or direct bony contact. This implies that sound travels more efficiently through dense bone than through soft connective tissue.
Hearing assistive devices could be contained within the superstructures of dental implants. In addition to their excellent BC properties, dental implant hearing aids boast numerous advantages in practical applications. These devices could improve a person’s quality of life by improving the quality of sound and providing a more comfortable option for a hearing aid, all while providing excellent concealment, which could increase equity. Hence, widespread use of dental implant hearing aids is expected as technology continues to improve.