Good vibrations: Bone conduction is key to innovation in hearing aids

DETROIT — Sara McGowen sat in a chair at Henry Ford Hospital in West Bloomfield, Mich., as a team of doctors and technicians put a hearing aid in her mouth, positioning it on her teeth. McGowen, 34, of Grand Blanc, Mich., had been deaf in her left ear for more than five years; the hearing loss came after surgery to remove a tumor on her acoustic nerve. It was early February and a doctor whispered in McGowen’s left ear: “What did you eat for breakfast?” McGowen was stunned. She thought she heard something, but she wasn’t sure. “Can I hear you?” she asked. “Yes,” she was told. The doctor whispered again. “It was crazy,” McGowen said. “All of a sudden, you can hear again.” McGowen can hear while wearing the SoundBite prosthetic device, a nonsurgical, removable hearing aid that transmits sound through the patient’s teeth and bone. “It’s freaky,” McGowen said. “But it works. I don’t understand the technology. It blows my mind that they can do something like this.” The primary way that most people hear is through air conduction. “Sound waves enter the ear and wiggle the ear drum,” said Dr. Brad Stach, the division head of the audiology department at Henry Ford Hospital. “That sets the middle ear bones into motion and they talk to our inner ear, the cochlea. Through that, we hear sounds.” The second way people can hear is through bone conduction, which happens when sound waves travel through teeth and bone into the inner ear. “In bone conduction, we kind of bypass the outer ear, the floppy part of the outer ear,” Stach said. “We bypass the middle ear, and we stimulate the inner ear directly by vibrating the skull and hearing that vibration through the fluids of the inner ear.” Stach said bone conduction is why a dentist’s drill seems to sound so loud and why it is hard to hear while you chew hard candy. “Your teeth are great conductors of vibration,” Stach said. “Once you vibrate your skull, your ear is set up to hear those vibrations.” The SoundBite system consists of two small devices — one is placed in the mouth and the other is worn on the deaf ear. The device in the mouth looks like a retainer and fits over teeth. It contains a wireless receiver, a small vibrator and a rechargeable battery that lasts six to nine hours. The device worn on the deaf ear looks like a tiny hearing aid with a microphone that is placed in the ear canal. This device transmits information to the vibrator on the teeth, which changes the audio sounds into imperceptible vibrations. “The device translates acoustic information to vibratory information and delivers it to the teeth,” Stach said. “We have known about bone conduction hearing forever. Putting a hearing instrument in the mouth is a new idea. It’s very clever.” It has been approved by the Food and Drug Administration for patients with single-sided deafness. It is also approved for use by people with conductive hearing loss, which can be caused by chronic middle ear infections. “The quality of the sound is excellent,” Stach said. “The teeth are very good conductors. It sounds pretty darn good.” Amir Abolfathi, 47, of Petaluma, Calif., who founded the company that makes the SoundBite system, said that 1.5 million Americans could benefit from this technology. The product is available now in 35 centers across the United States, Abolfathi said, including at Henry Ford. “Next year,” he said, “we expect to be at 100 centers and then kind of ramp up from there.” Abolfathi said the device is still in the pilot launch stage. He said several hundred people have been fitted with the device across the country. The device is not worn during sleep and can be removed so the battery can be charged. No surgery or dental work or modifications to the teeth are required. Stach said the SoundBite system is an example of several advances in hearing-aid technology. “If you haven’t seen a hearing aid in two years, you haven’t seen a hearing aid,” Stach said. “We have everything from fully implantable hearing aids to partially implantable hearing aids to extended-wear hearing aids to open-fit hearing aids, which are tiny, great amplifiers for some of the young-old people who need a little boost, but not too much.” McGowen is one of six patients who have been fitted with the device at Henry Ford. She said the device cost about $6,000 and it was covered by her insurance company, although not all insurance plans do. “Looking at me, you can’t tell I’m deaf,” McGowen said. “If I’m in a meeting, or at church, at a convention, I have to constantly look around to see if somebody is talking to me.” She used to position herself at church so nobody could sit on her left side. But those problems are gone now that she is wearing the device. And she said it has helped her at work at Creative Foam in Fenton, Mich. She works in customer service. “I’m on the phone constantly,” she said. “I go to trade shows, lunches with my customers. You kind of have to hear.” McGowen said the sound is crystal clear. “It is the weirdest thing,” McGowen said. “It has changed my life.”