Commercially pure 5-mm-diameter titanium (cpTi) discs received droplet inoculations of cells derived from rat bone marrow and were maintained in supplemented culture medium for 2-3 weeks. The cells and extracellular matrix (ECM) were processed for observation by light (LM), scanning (SEM), and transmission electron (TEM) microscopy. The latter was achieved by freeze-fracturing the solid metal from the resin-embedded tissue using a method which preserved the interface. Surface staining of whole discs revealed cells separated from the metal substratum by areas of ECM which stained positively using von Kossa's method to identify mineralization. At SEM, the ECM comprised dense interwoven collagen fiber networks which were partially obscured by globular masses (GMs). Individual GMs were associated with collagen fibers, especially at fiber intersections. EDAX line scan analysis confirmed the presence of Ca and P in these areas which were assumed to be spheritic foci of calcification since the Ca and P peaks diminished in areas which demonstrated only collagen fibers or the underlying cpTi. TEM examination confirmed the presence of globular mineralization and also revealed the presence of an interfacial zone between the metal substratum and the mineralized ECM elaborated by osteoblasts during the culture period. The interfacial zone comprised two layers, a bonding zone containing few collagen fragments and a ruthenium red positive layer containing more densely packed collagen fibers. We believe that this is the first report of both the formation of bonelike tissue on solid titanium substrata in vitro and demonstration of an interface which bears close morphological similarities to that known to develop in vivo.

Cells obtained from calvariae of fetal rats, human gingival connective tissue and periodontal ligament of rat molars were each co‐cultured in vitro with non‐demineralized and partly demineralized root slices in nutrient medium containing 50 μGg/ml ascorbic acid and 10 mM B‐glyeerophosphate, in order to determine whether the root slices could affect the phenotype expressed by the cells. The cultures were examined by light and transmission electron microscopy. Nodules of bone‐like tissue, resembling those previously described by others, were observed in the multilayers of cells obtained from rat calvariae. but not in the multilayers of gingival and periodontal ligament cells, after 30 days of culture. Calvaria cells associated with the root slices produced tissues exhibiting ultrastructure that resembled that of bone or cellular cementum. acellular cemenlum and afibrillar cementum in vivo when examined after the same length of time. The tissues were never found in cultures of gingival fibroblasts or periodontal ligament cells. These observations suggest, first, that cells derived from bone can express in vitro the phenotype for the cementums; second, that cells obtained from human gingival and rat periodontal ligament do not do so when cultured under similar conditions; and third, the possibility that the osteoblasts, cementoblasts and their progenitors that are found in the periodontal ligament could, at least in part, have their origin and migrate there from the endosteal spaces of the alveolar process.

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The purpose of this study was to assess the importance of the phagocytic mechanism of collagen resorption in the normal turnover and remodelling of soft connective tissues. Collagen phagocytosis by fibroblasts in rat skin, attached gingiva, and periodontal ligament was quantitated using the methodology of electron microscopic stereology. Periodontal ligament contained five and 15 times as much phagocytosed collagen as attached gingiva and skin respectively. Also, for each tissue examined, a positive correlation was observed between the amount of collagen phagocytosed and the known rate of mature collagen turnover.

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