Histological Research of Soft Tissue and Auditory Bulla Bone, and Microstructural Analyses of synthetic Auditory Ossicle in Rats

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The synthetic auditory ossicle alumina oxide (AlィイD22ィエD2OィイD23ィエD2, Bioceram) and hydroxyapatite [HA : CaィイD210ィエD2(POィイD24ィエD2)ィイD26ィエD2(OH)ィイD22ィエD2] are currently used widely in reconstructive middle ear surgery.To evaluate biocompatibility to tissue in long-term implantation, Bioceram disks were implanted subcutaneously in rats for 20 months. Light microscopy of H&E specimens differentiated cell types. Histological response included some macrophages and lymphocytes at six month which gradually disappeared by 16 months. The findings indicate that, from the viewpoint of long-term tissue response, Bioceram is a satisfactory biocompatlble material for reconstructive surgery.To investigate the long-term microstructure of Apaceram (Ap), a synthetic auditory ossicle composed of dense HA, thin Ap disks were implanted subcutaneaously in rats for 20 months. Implanted surfaces observed using stereoscopic microscopy and scanning elecron microscopy indicated progressive degradation on disk sur … More faces of the implants and later, progressive redeposition. Raman spectra analysis demonstrated that demineralization occurred on disk surfaces of implants, followed by progressive remineralization. Our histological study showed that, with increase in time after implantation, fibrous capsule thickness (FCT) increased and fibrous capsules surrounding Ap disks became denser. Increase of FCT and high density of collagen fibers could have restricted diffusion of ions passing through dense fibrous capsules located in the interface regions (body fluid phase) between Ap and capsules. The balance between demineralization and remineralization would then have been maintained under a restricted condition for ion diffusion. These histopathological findings supported our earlier hypothesis of Apaceram model (Cell mol Biol, 1995), that remineratization is accompanied by environmental change in the soft tissue. Apaceram seems useful for reconstructive surgery, since remineralization allows implanted Apaceram to maintain almost its original size in vivo.To investigate the bicompatibility of synthetic auditory ossicle (Ap) to host bone, small Ap disks contacting on the auditory bulla bone in rats were implanted for 270 days. The experiment showed : 1) no evidence of inflammatory reaction caused by implants from 90 days after implantation, 2) no evidence of osteolysis caused by implants, and 3) direct contact of bone to implants on the bone-disk interfaces at 180 and 270 days after implantation. The findings suggest that Ap has a high degree of implant biacompatibility, making it a satisfactory substitute biomaterial for otological reconstructive surgeries. Less