CAST TITANIUM AS IMPLANT MATERIAL

The tissue response in rats to implants made of machined and cast tita nium was evaluated after 1 and 12 weeks; The implants consisted of a c ircular plate portion, located in the abdominal wall, and a cylindrica l rod portion protruding into the peritoneal cavity. The chemical and topographical surface properties of the two types of implants differed considerably. The implants with surrounding tissue were processed en bloc for light and electron microscopy. The bulk metal was removed by an electrochemical procedure which permitted the sectioning and evalua tion of the intact implant-tissue interface. The general distribution of macrophages and fibroblasts was the same around the plate portion o f both types of implants. Macrophages constituted the predominating ce ll type with the highest concentration in the innermost cell zone clos est to the implant. The number of macrophages per section area was sig nificantly higher around machined implants. Multinuclear giant cells, always located at the implant surface, were more frequent around cast implants. The majority of the intraperitoneal rod portions were partia lly (1 week) or completely (12 weeks) covered by tissue; partial or co mplete overgrowth of tissue was rare for machined rod portions. Imagin g electron energy loss;spectroscopy demonstrated the presence of titan ium in macrophages in the peripheral part of the tissue capsule around cast, but not machined implants. We conclude that the tissue response s to the two types of titanium implants differed considerably in the t wo biological environments (soft tissue in abdominal wall; peritoneal cavity) examined and that the response in one environment does not pre dict the response in the other. We also believe that improvements have to be made in the casting procedure in order to reduce surface roughn ess and contamination before cast implants can be used in clinical app lications.