Biofilm formation on bone-anchored hearing aids

To investigate microbiological biofilm contamination of retrieved bone-anchored hearing aids.

Nine failed, retrieved bone-anchored hearing aids and 16 internal screws were examined by scanning electron microscopy. A fixture from a failing implant, which had been removed and disassembled under aseptic conditions, was cultured. Finally, an internal screw from a new, unimplanted fixture was examined by scanning electron microscopy.

Debris was seen on the fixture and abutment of all bone-anchored hearing aids, and on the heads of the 16 internal screws. On eight screws, biofilm extended down the shaft to the threads, where it was several micrometres thick. Culture of a failing fixture yielded staphylococcus. The new, unimplanted fixture internal screw showed evidence of scratching and metallic debris on the threads, which may interfere with close fitting of the screw and subsequently facilitate microleakage.

There may be a link between internal microbial contamination and failure of bone-anchored hearing aids.