Histologic Evaluation of Soft Tissue Integration of Experimental Abutments for Bone Anchored Hearing Implants Using Surgery Without Soft Tissue Reduction

Objective: The protocol for bone-anchored hearing implants (e. g., Baha (R)) surgery involves reduction of soft tissues around the abutment to minimize the risk of skin-related complications. It is hypothesized that good soft tissue outcomes may be achieved without performing skin reduction if improved abutment designs and/or materials are used that provide enhanced integration with surrounding soft tissues. The aim of the study was to investigate soft tissue response to different abutment designs/materials. Methods: Thirty-six Baha implants and abutments were inserted in the skull of six sheep without performing soft tissue reduction. Four different abutments were used: 1) standard Baha abutments, 2) hydroxyapatite-coated standard Baha abutments, 3) concave titanium abutments, and 4) hydroxyapatite-coated concave abutments. Healing times of 1, 2, and 4 weeks were used (2 animals per time point). Samples were analyzed using descriptive histology and morphometric measurements, and results were compared using Wilcoxon's signed-ranked test. Results: Histologic assessment showed healthy soft tissues around the abutments with limited or no signs of inflammation. Hydroxyapatite-coated abutments showed tight adherence with dermis and limited epidermal downgrowth and pocket formation. Weaker adherence, often associated with significant epidermal downgrowth and pocket formation, was noted for noncoated titanium abutments. The mean pocket depth for abutment types A, B, C, and D was 1.38, 0.42, 1.51, and 0.24 mm, respectively. The difference between C and D was statistically significant (p = 0.031). Conclusion: The results showed enhanced dermal adherence and reduced epidermal downgrowth and pocket formation for hydroxyapatite-coated abutments, with the most significant effect recorded for the hydroxyapatite-coated abutments with a concave shape.