Investigating the race for the surface and skin integration in clinically retrieved abutments with two-photon microscopy.

Bone conduction hearing implants can rehabilitate some types of hearing loss. A hydroxyapatite (HA)-coated skin-penetrating abutment was developed to allow for soft tissue preservation and increased skin-abutment adherence. Inflammation is thought to relate to bacterial infection of pockets around the abutment. Upon integration, the host's ability to cover the abutment surface ("race for the surface"), and thus control and prevent competitive bacteria from colonizing it, is improved. However, the attachment mechanisms behind it are not clear. In this study, we applied two-photon microscopy to visualize tissue attachment on abutments retrieved from patients. Skin integration markers were validated and applied to four HA-coated abutments. Evidence of skin integration was found, including the presence of hemidesmosomes, a basement membrane, dermal collagen and vascularization. Cases with clinical signs of severe inflammation and evident biofilm formation showed limited skin integration based on these indicators, confirming the applicability of the "race for the surface" model.