Potential lack of "standardized" processing techniques for production of allogeneic and xenogeneic bone blocks for application in humans.

In the present study, the structure of two allogeneic and three xenogeneic bone blocks, which are used in dental and orthopedic surgery, were histologically analyzed. The ultimate goal was to assess whether the components postulated by the manufacturer can be identified after applying conventional histological and histochemical staining techniques. Three samples of each material, i.e. allogeneic material-1 and -2 as well as xenogeneic material-1, -2 and -3, were obtained commercially. After decalcification and standardized embedding processes, conventional histological staining was performed in order to detect inorganic matrix, cellular or organic matrix components. Allogeneic material-1 showed trabecular bone-like structures, which were free of cellular components as well as of organic matrix. The allogeneic material-2 showed trabecular bone structures, in which connective tissue and cellular remnants were embedded. Additionally, some connective tissue, which resembled fat-like tissue, was found within this material. The xenogeneic material-1 showed trabecular bone-like structures and contained organic components comparable to that demonstrated for the allogeneic material-2. The xenogeneic material-2 showed trabecular bone structures with single cells located in lacunae. The xenogeneic material-3 also showed trabecular structures. Neither cellular nor organic matrix components were found within this material. According to the data of the present study, the allogeneic material-1 and the xenogeneic material-3 were the only investigated materials for which the obtained histological data were in accordance with the manufactureŕs advertised information. The remaining three materials showed discrepancies-although the manufacturers of all five bone substitute materials stated that their blocks were free of organic/cellular remnants. These data are of great clinical and material science interest. It seems that even patented processing techniques are not always able to deliver reproducible materials. Although the manufacturers of all five bone blocks stated that their blocks were free of organic/cellular remnants, our histological analysis revealed that three out of five bone blocks did contain such remnants. Such specimens might be able to induce an immune response within the recipient.