[Biological value of various bone substitutes in the treatment of bone defects. Animal experiment studies]

In clinical practice, biologic and synthetic substances have been used more and more as bone substitutes during the last few years. Different properties of the implant material are required according to the various fields of application. This implies a precise investigation of the biologic value by adequate experimentations on animals. It has been demonstrated in a bioassay with several synthetic implant materials, especially ceramics made of calcium phosphate, powders and granulated materials of tricalcium phosphate, and hydroxylapatite with different pore sizes and numbers, that there is only poor or even not any biologic activity in these substances which would produce an orthotopic stimulation of osseous formation. The application of these substances as bone substitutes can only be recommended in an adequate transplantation bed. However, all implant materials tested by different experimentations on animals showed an incomplete absorption in the histomorphological investigation even after twelve months. The various biologic bone substitutes (autologous and homologous spongiosa, demineralized homologous spongiosa, different forms of bone gelatin) show different degrees of biologic activity. Hitherto an inducing heterotopic effect could be demonstrated for bone gelatin in rats, dogs, and sheep. The inducing effect of bone gelatin combined with soluble calcium phosphate ceramics in rats was increased as compared with autologous spongiosa. Regarding our own results as well as various communications in literature, we consider it absolutely necessary to give more attention to the objectifying criteria when describing the biologic activity of "biologic and synthetic bone substitutes".