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Stem cell biology, an emerging field of research, provides promising methods in vitro as well as in vivo in animal models which make speculation about a future application in human dentistry reasonable. The objective of this study was to review the literature of stem cell research concerning fields relevant for dentistry. In dentistry, different stem cells are discussed. Adult dental ectomesenchymal stem cells seem promising for future therapy. Human stem cells have been isolated from the dental pulp, exfoliated deciduous teeth, the periodontal ligament, the dental follicle and the dental papilla. Stem cell markers such as STRO-1 were used for the characterization and isolation of stem cells. Adult dental stem cells can differentiate into many dental components, such as dentin, periodontal ligament, cement and dental pulp tissue, but not into enamel.

This review article arranges the current results of stem cell biology for their use in dentistry. There are different types of stem cells, which are applicable for dental treatments. The use of embryonic stem cells, whose possibilities for breeding an artificial tooth were hardly evaluated, is however ethically precarious. On the other side the ethically harmless adult stem cells, which were isolated for example from bone marrow, were little examined for their capability of differentiation into dental tissues. Therefore their forthcoming use in dentistry is rather improbable. However, dental ectomesenchymal stem cells are more promising for dentistry in future. For example dental pulp stem cells (DPSCs) are capable to differentiate into dentin under in vitro conditions. Moreover it is possible to use periodontal ligament (PDL) stem cells and dental follicle precursors for periodontal tissue differentiations in vitro. Recently new populations of stem cells were isolated from the dental pulp and the PDL. These cells distinguish from the initially isolated DPSCs and PDL stem cells in growth and cell differentiation. Therefore stem cell markers are very important for the characterization of dental stem cells. A significant marker for dental stem cells is STRO-1, which is also a marker for bone marrow derived mesenchymal stem cells. Nonetheless dental stem cells are CD45 negative and they express rarely hematopoietic stem cell markers. These research results plead for the participation of dental stem cells in dental practice in future.

The fine tissue structure of ovine odontoblasts was studied in various developmental and maturational stages. Odontoblasts differentiate from the peripherally-located mesenchymal cells of the dental papilla. On the basis of cytological parameters, it was possible to divide the odontoblasts into the following groups: pre-odontoblasts, juvenile (light) odontoblasts and mature (dark) odontoblasts. The three maturational stages of odontoblasts exhibit substantial differences with respect to their form and to the number and arrangement of their cytoplasmatic organelles. Structural differences in the three cell types appear to be closely correlated to the level of cellular activity.

The purpose of our study was the culture of cellular elements of the pulp. Migration and proliferation of fibroblast-like cells can be observed during the in vitro culture of pulpal tissue. However, no mitotic acticity of the odontoblasts could be induced by nutritive variations of the culture medium. The proliferation of the fibroblastlike cells varied during the primary culture and the first subculture. By contrast, during the second subculture there is a homogeneous process of growth. The growth rate of the second subcultures is therefore suitable for a biological evaluation of dental materials.

As compared with mesenchyme no genuine defense cells are developed in the tissue of the dental pulp and the nervous tissue. This is a further hint for the common development from ectoderm. The three dimensional meshwork of pulpa fibroblasts ("mesectoderm") is structured by elongated cell processes connected with each other by a variety of special cell junctions ("electronic cell coupling"). Metabolites from the microcirculation and neuropeptides from vegetative axons influence the activity of fibroblasts synthetizing groundsubstance. The meshwork of the groundsubstance has exclusion effects concerning molecules with a distinct molecular weight and charge. Thus a primitive defense system is established. With this the role of a newly described cell type of the dental pulp, the "lymphocytic pericyte" is discussed. Because of the poor capacity of the pulpa tissue for immunological reactions pathologically disorders may easily become chronically spreading their antigenic components throughout the body.

The generation time and the division rate were measured with routine methods of cell culturing. The conditions contributing to the stagnation of growth were examined; the synchrony of the growth process was investigated. The biochemical composition of the cells was assessed via colorimetry and then compared with other cell systems. The cell culture examined may be used to test capping materials; only cells up through the eighth generation however should be utilized.