Regional odontodysplasia (RO) is a rare dental anomaly involving both dentitions, mostly teeth of one quadrant. The characteristic findings are discolored soft teeth accompanied by gingivitis, swelling or abscess. Enamel and dentin are hypomineralised and hypoplastic, so that the 'ghost teeth' appear shadowy in radiographs with wide pulp chambers. The etiology is unknown. Epidemiological data is rare; 138 cases of RO have been published to date and reports on ultrastructure are few. An analysis of published cases of RO in the international literature is presented. The sex ratio of females to males was 1.7:1. The age at the time of diagnosis ranged between 4 and 23 years. The maxilla was more often affected (maxilla to mandible ratio 1.6:1). In 67 patients the deciduous and permanent dentitions were affected (47.1%). In 129 cases, affected teeth lay side by side. Missing tooth development was observed in 10.7%. Failure of tooth eruption of RO teeth occurred in 39.7%. In addition, four cases with RO which were collected over a period of more than 25 years are presented. Ultrastructural findings of one specimen are demonstrated.

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Pluripotent cells from the periosteal layer adjacent to cortical bone attain an osteoblast-like phenotype in culture when reaching confluence in monolayer. It is unknown whether such newly differentiated osteoblast-like cells preserve the chondrogenic potential characteristics for stem cells derived from the periosteum. Primary osteoprogenitor cells derived from bovine metacarpal periosteum were differentiated into alkaline phosphatase-positive osteoblast-like cells by an established monolayer culture protocol. After transfer into suspension culture in agarose gels, the cells differentiated into chondrocytes demonstrated by the production of collagen II, but not of collagen I, as well as alkaline phosphatase activity was abated. Contrarily, with continuation of monolayer culture, the cells maintained their osteoblast-like phenotype and secreted large amounts of collagen I and a minor quantity of collagen III and V. The alkaline phosphatase activity steadily increased during the entire culture period of 2 weeks. Thus, our culture techniques can serve as useful tools to study mechanisms of differentiation by modulating the phenotypic potential of osteogenic cells. The results presented here support the notion that the extracellular environment strongly influences the cell type and its metabolism.