Peri-implant soft tissue and bone from 12 patients undergoing removal of stainless steel miniplates and screws after healing of jaw fractures were studied with regard to histomorphology and metal content. Three patients with titanium plates were also included. Light microscopy and scanning electron microscopy with energy-dispersive X-ray microanalysis were used. Non-osseous tissue adjacent to devices of both materials showed fibrosis, including areas of mild chronic inflammation. The cellular picture was dominated by fibroblasts with small aggregates of lymphocytes and scattered macrophages. A connective tissue collar was found between the bone tissue and the screws of both stainless steel and titanium. Bone formation was also evident adjacent to screws of both materials. Stainless steel or titanium particles 5-50 microns in diameter were found in both soft tissue and bone next to implants of their corresponding bulk material. The amount of metal impregnation varied between individual sections, and fewer particles were found in the bone specimens than in soft tissue. The mild inflammatory changes were not restricted to areas of metal impregnation.

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Subepithelial soft tissue and bone obtained from the implant bed in the vicinity of stainless steel and titanium miniplates and screws were evaluated with respect to the presence of immunocompetent cells. The study included tissue specimens from 19 patients, in whom the implants (14 stainless steel and 5 titanium) had been in situ for more than 6 months. The ABC (avidin-biotin-complex) immunoperoxidase staining technique using monoclonal antibodies defining T lymphocytes (CD3+), macrophages (CD11c+) and Class II MHC (HLA-DR) was performed on EDTA demineralized, frozen bone tissue, and on fresh frozen soft tissue specimens. The results showed scattered T lymphocyte clusters, small numbers of macrophages and abundant expression of HLA-DR in the soft tissue adjacent to both stainless steel and titanium implants. There was no substantial difference in tissue reactions between implants of the two materials. The demineralized bone sections disclosed presence of immunocompetent cells in the connective tissue lining the periphery of the screw holes. Metal particles were seen in both the soft tissue and the bone specimens. We conclude that a mild tissue reaction takes place in the vicinity of miniplates and screws of stainless steel and titanium, and that the intensity of the reaction indicates that the implants are well tolerated by the host tissue.

The surfaces of 43 stainless steel miniplates and 19 titanium miniplates with matching screws of the same materials were studied after retrieval with respect to surface degradation. Stereomicroscopic and scanning electron microscopic (SEM) examinations were performed, and surface roughness and hardness of the plates were measured. Defects of mechanical nature which could be traced back to handling procedures were found in all stainless steel and titanium devices. Metal tongues and splinters were occasionally found associated with screw threads and in the periphery of plate screw holes. Corrosion defects were observed in about 1/5 of the stainless steel plates, restricted to the countersink area. Corrosion defects were also found on the chamfer of the underside of stainless steel screw heads. None of the titanium devices showed evidence of corrosion. The surface roughness of the titanium plates was higher than for the stainless steel plates. The retrieved plates were rougher than the new plates.