HYDROXYAPATITE ORBITAL IMPLANT - A LIGHT-MICROSCOPIC AND ELECTRON-MICROSCOPIC AND IMMUNOHISTOCHEMICAL STUDY

Objective: This study aimed to characterize the constituents of the in grown host tissue in explanted orbital coral spheres by means of light electron microscopy and immunohistochemistry and to compare findings at different intervals after implantation, Design and Methods: A micro scopic retrospective laboratory study of three explanted coral spheres from three different patients was undertaken. The first specimen was an infected hydroxyapatite orbital implant, which was removed after 18 .5 months and processed for standard light microscopy and transmission electron microscopy. Immunohistochemistry was performed using vimenti n, actin, CD-68, and CD-34 marker, Two other explanted spheres (after 3 weeks and 2.5 months) were examined by light microscopy only, becaus e no fibrovascular ingrowth could be detected, Results: On light micro scopy, the pores of the first coral were filled entirely with the fibr ovascular tissue, A basophilic line reminiscent of calcium deposition was seen along hydroxyapatite spicules, where it often was associated with newly formed bony lamellae, Similar lines were seen partially in the 2.5-month specimen but not in the 3-week specimen, Immunohistochem istry of the first specimen enhanced visualization of the capillary ne twork when the CD-34 marker was used. The fibrovascular tissue was uni formly vimentin-positive and partially actin-positive. On transmission electron microscopy, typical fibroblasts and myofibroblasts were obse rved, The latter were separated by thin sheets of banded collagen and formed pseudoepithelial structures, Proliferating vessels often showed high endothelial cells, Conclusions: The fibrovascular ingrowth conta ins not only vimentin-positive regular fibroblasts but also actin-posi tive myofibroblasts. Interaction between the invading tissue and hydro xyapatite structures leads to long-term ossification.