Biting Into Sound

INTRODUCTION
It is no secret that technology drives the field of medicine. Through this drive, new bonds have been formed among different fields of medicine. A team of George Washington hospital doctors has been united around a new innovation expected to revolutionize a treatment for millions of patients suffering from a hearing disorder.

The Ear
The ear is a highly complex organ that captures, filters, and processes sound. Sound can be heard through 2 mediums: through the air (air conduction) and through the bone (bone conduction), with both working via the principle of sound waves. To fully understand the transmission of sound to the brain, a brief review of the ear anatomy is in order. The ear consists of an inner, middle, and outer section (Figure 1). The ability to hear occurs when sound waves go into the ear canal, causing the tympanic membrane to vibrate. This sets off the malleus, incus, and stapes, ie the inner ear bones, which amplify the sound waves and cause the fluid inside the scala vestibuli to move. The fluid movement, alongside the cochlear ducts, triggers the nerve impulses that are processed by the brain as sounds via the cochlear nerve. Due to the intricacy and fragile nature of the ear, its functionality may easily become compromised.

Figure 1. Anatomy of the ear.

One common deficiency is single-sided deafness. Single-sided deafness (SSD) af­fects an estimated 9 million people in the United States.1 SSD is the absolute or substantial loss of hearing in one ear. The causes for SSD are sometimes congenital or un­known, but frequently occur because of physical damage to the ear, pressure on the nerve involved in hearing, infections, diseases, tumors, and trauma. SSD is detrimental in that it causes the inability to recognize the direction of sound. The failure to recognize the direction of sound can make everyday tasks, such as walking across the street or even talking to friends, difficult. Two tasks that are particularly difficult include locating the source of sound and hearing in a noisy environment. The sufferers of SSD vary in age and often chose to live their whole life without medical intervention. Until now, if patients chose to opt for treatment, they were limited to having a bone-anchorage implant.

Bone Anchor Implants
A bone-anchored hearing system is surgically implanted to help SSD disabilities that are conductive, mixed, or unilateral. A bone-anchored implant trans­mits sound vibrations to the inner ear where it differentiates sounds. There are 2 common systems for SSD. The first system is the Baha (Cochlear) system; this involves surgically placing an implant behind the ear. This device consists of 3 parts: a titanium implant, an external abutment, and a sound processor (Figure 2). The Baha works by utilizing natural bone transmissions as a passage for sound to travel to the inner ear. The second system is the Ponto (Oticon Medical) system, which is also a surgically implanted device behind the deaf ear. Ponto also consists of 3 parts: a (3- or 4-mm) titanium implant, an external abutment and a sound processor. Although both systems can address SSD, many patients find having a screw implanted in the side of the skull, and a bulky apparatus that is visibly at­tached to the side of the head, objectionable. Suffers of SSD have been looking for a new solution that does not involve surgery.

A New Solution
A new device approaches SSD by addressing the limitations of the existing SSD devices. The new system, called the SoundBite (Sonitus Med­ical) hearing system, is a nonsurgical intraoral prosthetic device consisting of 2 components; a behind-the-ear (BTE) microphone (Figures 3 and 4a) and a removable in-the-mouth (ITM) hearing device (Figure 4b). SoundBite is meant to restore hearing without surgery for patients who have SSD, conductive, or mixed hearing. The BTE microphone unit is optimized specifically to improve spatial hearing, while the ITM delivers a bone conduction signal directly to the skull via high frequency outputs through the teeth. The BTE microphone unit is a wireless transmitter with a tiny microphone sitting in an open fit dome in the canal of the impaired ear. Placing the microphone in the canal is intended to emphasize on the “natural acoustics” provided by the patient’s pinna (also called the auricle; the visible part of the ear that resides outside of the head).

Unlike conventional hearing aids, SoundBite uses bone conduction and does not need a working middle or outer ear. By contrast, conventional hearing aids use air conduction to turn up the volume of sound traveling into the ear and require a working middle or outer ear to have any effect.

Figure 2. The Baha (Cochlear), the alternative to the SoundBite system (Sonitus Medical).	Figure 3. A look at how unnoticeable the behind-the-ear (BTE) device is.
Figure 4a. This is the BTE device.	Figure 4b. This is the in-the-mouth (ITM) device.

Figure 5. This shows how seamless the ITM device is. This does not affect the bite at all and is basically unnoticeable.

Comparing Hearing Systems
Overall, the comparisons between the devices are significant. (The capabilities of SoundBite as compared to the Baha and Ponto systems are shown in the Table). With SoundBite, bone conduction signals are delivered by the ITM component via the surfaces of the teeth with an embedded transducer that delivers signals to 12,000 Hz; this is a much broader frequency bandwidth than with existing SSD devices. In comparison, the frequencies for systems like the Baha are only 6,000 to 7,000 Hz.

To determine the speech recognition of words in sentences, a hearing in noise test (HINT) is used. In a traditional audiologic HINT test, a one-decibel increase results in a 10% increase in sound perceived by the patient. In a HINT test conducted by SoundBite, the increase was 2.6-decibels, compared to the Baha, which was only a 2.0-decibel increase. Sound­Bite’s end result was a 26% increase compared to the common system of Baha, which was only a 20% increase.

SoundBite in the Marketplace
There are currently 12 providers nationwide of the SoundBite prepilot implementations. By the end of 2011, Sonitus Medical will have a maximum of 45 providers for the SoundBite system. These groups will have exclusive prescribing authority during the prepilot launch. An otolaryngologist, who works closely with an audiologist, will refer the patient to the partner dentist. First, the otolaryngologist diagnoses the issues of the ear. Then, the patient is referred to an audiologist who performs a number of tests to determine the exact hearing frequencies. If the patient is a possible candidate for Sound­Bite, the audiologist will then refer the patient to the associated dentist, who evaluates the teeth and oral tissues for suitability.

Partner dentists help designate the best site based on health of available teeth; this can be done to any 2 contiguous teeth. The dentist will then take an impression of the maxillary arch and send it to Sonitus Medical for device fabrication. After Sonitus medical evaluates the impression and the patient’s condition, the company will return a custom-fitted BTE and an ITM to the audiologist. The audiologist will then program the BTE device to the correct frequencies for the patient’s needs.

Safety Issues
Safety and possible health risks in­volved in using the SoundBite device can be of concern to many patients. As a result, whenever foreign devices are introduced, it is advantageous to take a critical look at the short- and long-term safety of any products.

The issue of radio wave transmissions interfering with the transmission between the BTE and the ITM are negligible. SoundBite uses a system called near field magnetic induction, which transmits the frequency of the BTE to the ITM. SoundBite only gives off 1/10,000 of the power of a cell phone, and is equal to or less than the radiation emitted by a household power outlet. The ITM piece will not affect the teeth in any harmful ways; the vibrations given off by the ITM are less disruptive to the teeth than brushing/chewing food. Additionally, SoundBite uses a safe and effective alkaline polymer that will not harm tooth enamel or otherwise compromise the integrity of healthy teeth.

Dental Aspect
The ITM component in the teeth is comparable to a maxillary retainer. The ITM is placed on the buccal and palatal areas (unilaterally), with an arm that extends around the back of the second molar (or most distal tooth). Before this retainer can be put on the teeth, the dentist must do a complete examination on the patient. The examination should include radiographs and a periodontal evaluation. The clinician should check for any decay or pulpal pathology, examining the teeth for undercuts and available retention as part of the evaluation/examination procedure. Finally, the dentist needs to evaluate the occulsion of the patient to ensure that it is stable and healthy. If any of the aforementioned dental problems are noted, dental work may be necessary before SoundBite can be used. It should be noted here that SoundBite will work if the patient has fillings, crowns, or even implants, but good oral health is an essential prerequisite.

SoundBite will have the same effect on a person as a retainer will. The gingiva may be slightly irritated and sore for the first few days, but the teeth will slowly adjust to the device. To clean the ITM device, the patient should brush it with a toothbrush and toothpaste.

Overall, the ITM is more comfortable than retainers or most orthodontic appliances. In addition, the size of the ITM is small enough that it will not impinge on the speech of the patient. The SoundBite microphone is located on the BTE device, not in the intraoral device (Figure 5), so the chewing and biting of food does not affect the quality of sound perception.

The ITM device can be worn on either side of the molars. If the dentist deems fit to put the ITM device on a certain side, there will be no feedback from the system. The physician will recommend a certain side, but the dentist can determine the placement by the stability of the teeth in the mouth.

CLOSING COMMENTS
The development of new nonsurgical hearing systems allow the otolaryngologist, audiologist, and dentist to help patients with SSD regain hearing and to enhance their quality of life. The innovation has helped doctors transcend divides between their individual specializations, to offer patients convenient and comprehensive care. Collaborative treatment, such as this, is a sign of a new and evolving trend; we are likely to see more professionals from across the health spectrum joining forces to solve many of the world’s medical dilemmas.

Reference

1. Wazen JJ, Spitzer JB, Ghossaini SN, et al. Transcranial contralateral cochlear stimulation in unilateral deafness. Otolaryngol Head Neck Surg. 2003;129:248-254.

Suggested Readings
Miller RJ. It’s time we listened to our teeth: The SoundBite hearing system. American Journal of Orthodontics & Dentofacial Orthopedics. 2010;138(5):666-669.

Popelka GR. SoundBite hearing system by sonitus medical: a new approach to single-sided deafness. Seminars in Hearing. 2010;31:393-409.

Dr. Singer earned his bachelor of science in human development from Vanderbilt University, and his doctor of medical dentistry from the University of Pennsylvania School of Dental Medicine. Dr. Singer holds the title of assistant clinical professor of surgery at the George Washington University Hospital, where he is responsible for emergency facial trauma, and performs surgeries and procedures for special needs patients. Dr. Singer owns DC Smiles in Washington, DC, and NOVA Smiles in Alexandria, Va. He can be reached at novasmiles@yahoo.com.

Disclosure: Dr. Singer reports no disclosures.