Bone induction in vitro. I. Human gingival fibroblast cell lines versus tooth matrix

Cells with osteoblastic phenotypes can be explanted from human gingiva and periodontal ligament

Considerable phenotypic heterogeneity has been reported in gingival fibroblasts. Similarly, cells from the periodontal ligament (PDL) can be isolated with different phenotypes. Although it has been suggested that cells from the gingiva do not contribute to the formation of hard tissue, it is theoretically possible that under appropriate stimuli, immature mesenchymal cells in gingiva could differentiate along an osteoblastic pathway. Differentiation of immature mesenchymal cells into osteoblasts following stimulation with osteoinductive factors has been demonstrated in muscle. We undertook experiments to establish whether cells with osteoblastic characteristics could be identified from human gingiva as well as from human periodontal ligament. Some cell populations from each of these tissues were found to have high basal alkaline phosphatase activity, to release osteocalcin in response to 1,25(OH)2 VitD3, and to form a mineralized matrix. Thus, cells can be isolated from the gingiva and PDL that exhibit phenotypic markers, which taken together are characteristic of osteoblastic cells. Other cell populations derived from the PDL and gingival connective tissue were isolated that had fibroblastic characteristics. These studies support the concept that gingival tissue can give rise to cells which may differentiate along either a fibroblastic or an osteoblastic pathway.

Citric acid demineralization of cementum and dentin: the effect of the storage medium

The purpose of this study was to see if the root surface topography of teeth, stored in saline and subsequently treated with citric acid, differred from the root surface topography of teeth that were treated immediately upon extraction, 12 freshly extracted adult human permanent teeth, with proximal surfaces free of caries and periodontal disease, were treated in succession. The crowns were removed at the level of periodontal attachment, the teeth sectioned buccal-lingually and a treatment area deligniated on each proximal section. The treatment area of 6 teeth was root planed to expose dentin (D) and scaled to remove adherent tissue and leave a cementum surfaces (C) on the other 6 teeth. A coronal-apical groove down the middle of the treatment area divided it into approximately equal parts or experimental regions. One proximal section of each tooth was placed in physiologic saline (S) and treated after 6 weeks of storage while the other proximal section was freshly treated (F). Treatment consisted of applying a 30% citric acid (CA) solution (pH = 1.60) for 5 min. Cotton pellets soaked in the citric acid solution were placed (P) on one half of the experimental area and heavily burnished (B) on the other half. Treatment areas were subsequently prepared for scanning electron microscopy analysis. Assessment was made of (i) the % of surface area tufted, (ii) fibril tufting depth (0.3) and (iii) fibril tufting density (1.3). Similarities were found in the data for both storage methods (F and S) across each application technique (P or B) and each tooth surface (D or C) with respect to the (i) % area tufted and (ii) frequency distribution of tufting depth scores. As for the application techniques, the data for burnishing was greater than placed across each storage method (F or S) and each tooth surface (D or C) for the same two parameters. The results of the study indicated that 6-week physiologic saline storage does not affect root surface demineralization by citric acid, as assessed by SEM.

Surface energies and the bone induction principle

The macroscopic and histologic sequence of events in the induction of ectopic bone formation by porous demineralized bone and by synthetic porous sponges of poly-hydroxyethylmethacrylate (poly-HEMA) is described and reviewed. The observed relationship between the yield of new bone generated, and in vitro calcification, with the zeta potential, seems to parallel the connection between general adhesion in biologic systems and the critical surface tension. Consistent with experimental findings over the years, the bone induction principle (BIP) is probably associated with porous, mechanically suitable, hydrophilic materials with a high polar surface energy. It can be inferred that such surfaces are exposed when bone is suitably demineralized and treated, as has been reported. The discovery of noncollagenous proteins that are important to the BIP may be viewed in this light. Local heterogeneities on cellular surfaces are known to be important but are not detected by macroscopic techniques. It is suggested, following Lerchental, that induced stresses in the cell membranes cause a redistribution of surface charges that increases the local surface energy. This may lead therefore to an agglomeration and alignment of cells, as a response to the stress, accompanied by differentiation, as well.

An electron microscopic demonstration of induction of chondrogenesis in neonatal rat muscle outgrowth cells in monolayer cultures

Second passage fibroblast-like cells grown from explants of neonatal rat muscle continue to demonstrate fibroblast-like properties for many days when cultured on plastic surfaces. Such cells can be induced to change to a chondrocyte-like mode of expression by the addition of effector materials prepared from bovine cortical bone decalcified with 0.6 N HCl. Other studies show that similar demineralized bone particles and extracts from them have, in vivo, osteoinductive properties. Optimum conditions for this differentiation in monolayer culture were found in the use of 2% fetal calf serum with Dulbecco's modified Eagles medium. At 10% fetal calf serum the chondrogenic changes could not be detected. Light microscopy showed a sequence of morphological changes, after 36 h in culture, which resembled those seen at the beginning of osteogenesis in vivo. Induced cultures showed abundant extracellular proteoglycan production. Isotope incorporation studies showed stimulation of glycosaminoglycan synthesis in response to effector materials in soluble form. Type II collagen could be detected after three days. Electron microscopic analysis of induced and control cultures showed unequivocal evidence for marked production of an extensive extracellular matrix in the region of effector particles. The cells themselves change shape and develop an abundant system of lysosome-like vesicles and a very active, highly engorged endoplasmic reticulum and Golgi apparatus. After nine days in culture, evidence for the formation of a ruthenium red stained structure on the surface of the cells in contact with inductive particles, was observed. The simple monolayer culture system described provides a direct means by which the presence of active chondrogenic fractions may be assessed, and in which the mechanism of action of the effectors can be studied.

Connective tissue regeneration to periodontally diseased roots, planed and conditioned with citric acid and implanted into the oral mucosa

This investigation used autogenous submucosal implants of root sections to study the connective tissue healing to periodontally diseased roots which had previously been planed and demineralized with citric acid. Eighteen implants were performed, with each being removed 2 to 24 weeks after implantation. The results showed new connective tissue attachment to the old cementum and to the dentin. After 18 weeks, in all specimens new cementum had formed on the dentin, with collagen fibers attached to it. No deposition of new cementum on the old cementum was noted. The formation of new cementum on roots placed in an environment without periodontal ligament cells might be ascribed to the inductive principle of demineralized dentin. The results suggest that a diseased root which has been planed and conditioned with citric acid is likely to form a new connective tissue attachment, even if it is placed in an environment without periodontal ligament cells. They also suggest that the factor inhibiting potential new connective tissue attachment is the condition of the root surface, rather than the lack of an adjacent progenitor cell population.