in oral surgery, where implants were used for retention of dentures. Brånemark sought an acoustic way to evaluate osseointegration. A patient with implants in the jaws was fitted with a bone vibrator on one of his implants. When tested, the patient experienced very loud sound even at low stimulation levels, indicating sound could propagate very well in the bone. It has later been shown by Håkansson that the sound transmission in bone is linear, indicating low distortion of the sound. The implant in the bone is made of titanium and will osseointegrate. The hearing instrument is impedance-matched. Osseointegration has been defined as the direct contact between living bone and an implant that can take a load, with no soft tissue at the interface. Models There are several models of bone-anchored hearing aids available. Most common are the BAHA from Australian company Cochlear, and the Ponto from Danish manufacturers Oticon Medical. There are also other types of bone conduction hearing aids, such as implants and non-surgical devices. Costs In the US, the cost of the Baha device is about $4,000. In the Netherlands, the cost of the device is around €3000 (in 2008). The cost of the titanium implant, surgery, and aftercare from surgeon and audiologist must also be considered. References Hearing aids Otorhinolaryngology