Hearing thresholds with direct bone conduction versus conventional bone conduction

Some patients who need hearing aids are unable to use an aid which transmits the sound via the external ear canal but have to use a bone-conduction hearing aid. The pressure needed to apply the transducer often gives the patient discomfort, and the attenuating effect of the skin gives poor electroacoustical function of the aid. A permanent skin penetration has made it possible to develop a bone-anchored hearing aid with all components in one housing. Ten patients have been equipped with such an aid. This paper deals with a comparative hearing threshold measurement on 10 patients. Békésy audiometry was performed and a conventional Oticon (A-type) transducer was used. In the frequency range 600 to 6 000 Hz, there was a lowering of 10-20 dB in thresholds when skin penetration was performed. This lowering in thresholds means lower transducer distortion, lower electrical gain, and lower power consumption to produce a given sensation level.