gms | German Medical Science

TACHAS is the abbreviation for transcutaneous air conduction hearing aid system, a new category of semi-implantable hearing aids, established by the Food and Drug Administration in the US. The only representative is the RetroX from auric hearing system, Germany. A part of this system is a titanium tube, which has to be implanted in the soft tissue retroauricularly.

First the histology of the native retroauricular tissue was clarified as far as it was relevant for an implantation. By forming the implantation channel the following biopsies were taken: retroauricularly at the entrance of the designated implantation channel, in the meatus acusticus externus at the exit and between these two locations. The biopsies at the entrance and the exit of the designated channel showed keratinocytes in 5 layers with various densities, followed by a Str. granulosum with scattered granula only, a normal developed Str. spinosum and a two-layered Str. Basale. The subepidermal differences in the biopsies were evident but got in touch to our questions indirectly. In comparison to this a 15 months old blend implantation channel was investigated. At first, impressions and swabs were taken of the channel and investigated in the scanning electron microscope. Subsequently biopsies were taken retroauricularly from the entrance, from the exit in the meatus acusticus externus and in the middle of the channel. All the biopsies showed a complete epithelialization. In the biopsy of the middle of the channel the cellular keratinization and number of keratinocyte layers are clearly lesser than in the other biopsies. The other strata showed in comparison to the biopsies of the entrance and the channel exit a minor height of the epithelial layers. The results show the evident reduced epithelialization within the channel and allows the interpretation that this is the reason why the keratinocytogenesis in the vicinity of titanium-implants does not cause any injuring reactions of the tissue.