THE ROLE OF CONNECTIVE-TISSUE IN INHIBITING EPITHELIAL DOWNGROWTH ON TITANIUM-COATED PERCUTANEOUS IMPLANTS

Ideally, the surface of epithelium-penetrating implants should impede apical epithelial migration. Previous studies have shown that micromachined grooved surfaces can produce connective-tissue ingrowth, which inhibits epithelial downgrowth on percutaneous implants [Chehroudi et al., J. Biomed. Mater. Res., 24, 9, (1990)]. However, in those studies, connective tissue and epithelium interacted with the same surface so that the effects of the surfaces on each population could not be determined separately. The objectives of this study were (a) to examine cell behavior on implants in which connective tissue contacted surfaces of various topographies and epithelium encountered only a smooth surface, and (b) to compare one-stage and two-stage surgical techniques. Implants had a base component (BC) which was either smooth or had a surface with 19-mu-m- or 30-mu-m-deep grooves or 120-mu-m-deep tapered pits, and a skin-penetrating component (SPC) which was smooth. In the two-stage technique, the BC was implanted subcutaneously for 8 weeks, which permitted the healing of the peri-implant connective tissue. In the second stage the SPC was connected to the BC. For one-stage implants, BC & SPC were connected and implanted percutaneously. Implants (BC & SPC) were removed 1, 2, or 3 weeks after percutaneous implantation and histological sections were measured for recession, connective tissue and epithelial attachment as well as capsule thickness. Light microscopy indicated that both grooved and tapered pitted surfaces encouraged connective tissue ingrowth. On the grooved surfaces, the orientation of fibroblasts changed from an oblique to a more complex pattern which included cells having round nuclei within the grooves, as well as cells oriented oblique or perpendicular to the grooves. In the tapered pits a hammock-like arrangement of fibroblasts was observed. In some cases, foci of mineralization and formation of bonelike tissue were found on the grooved and pitted surfaces. The apical migration of the epithelium was significantly (p < 0.05) inhibited by those micromachined surfaces which produced connective tissue ingrowth to the BC. This study found that placing the implants in two stages improved the performance of percutaneous devices, and that a further improvement was achieved if the implant had a surface promoting connective tissue ingrowth.