Vitamin D receptor deficiency and postnatal tooth formation

by M.S. Zhang, Xueming

The reduction of caries is one of the major objectives of Healthy People 2010 (USDHHS, 2000). For individuals at risk for caries, early identification and interception before the occurrence of the disease are crucial to preventing the cariogenesis. However, host genetic variants that compromise the mineralization of dental enamel and dentin are unclear. The vdr mutation has been reported to be associated with bone loss. Therefore, it is likely that vitamin D resistance may affect dental enamel and dentin formation. The objective of this study was to investigate the effects of VDR deficiency on postnatal tooth formation in a vdr knockout (vdr-/-) mouse model. Materials and methods: Mandibles from 70.5-day-old wild type (vdr+/+) and vdr-/- mice were used for observation. Three regions were studied along the length of each mandibular incisor: the eruptive region, the region underlying the molars, and the region behind the third molar. Histochemistry and immunohistochemistry were used to determine the morphological changes and the expression of biglycan and decorin in different regions of the mouse incisor. SEM was used to determine the ultrastructural changes in dental enamel and dentin. Micro-CT was applied to compare the morphometry and mineralization density (MD). Results: In vdr-/mice, rickets-like phenotypes in bone were clearly observed. Dentin was the most affected tissue in teeth, with an enlarged pulp chamber and thinner dentin wall in the eruptive region and the region underlying the molars. Predentin was thickened, with diffused expressions of biglycan and decorin. Lower MD and pore-like defects were ii observed in the dentin with the use of micro-CT. No significant decrease of enamel MD was found in the eruptive region; however, early mineralization and a transient transition stage in the enamel were observed in the regions behind the third molar. Micro-CT also revealed less thickness and volume in the enamel and dentin. SEM showed fewer tubules in the dentin and thinner surface enamel in the eruptive region. In the region behind the third molar, early maturation in the enamel was observed, along with a decreased volume of interprismatic enamel. Conclusion: Vitamin D deficiency plays different role in the enamel mineralization and dentin mineralization. The resulting compromised mineralization in the enamel and dentin may cause a highly susceptibility to cariogenesis. iii