Objective: To evaluate the morphological and radiological changes on lower incisor of vitamin D receptor knock out mice. Materials and methods: Vdr+/- mice were mated; puppies were grouped based on genotyping. vdr +/+ mice and vdr-/- mice were sacrificed at 45.5 days of life. X-rays were taken for comparison of mineral density. The mandibles and femurs were fixed, dehydrated and infiltrated by PMMA, then cured by UV light overnight. The blocks were cut as 75um sections. The orientation and distance were exactly matched between vdr-/- and vdr +/+ siblings. Sections were polished and stained with Toluene blue. The Images were then taken on matched locations. Results: In vdr-/- mice, the femur was much shorter than the wild type littermate. The distal epiphyseal part showed hypertrophy. The sizes of lower incisors were almost same between the siblings. In the ground section, the pulp chambers in all the levels of maturation zone and transition zone of the lower incisor of vdr-/- mice were much bigger than the wild type mice. The dentin wall adjacent to pulp was much thinner in vdr-/- mice. The porosity was clearly observed in the cross section of the femur in vdr-/- mice, but it was not clear in the dentin. The mineral density by X-ray analysis showed big difference between the vdr +/+ mice and vdr-/- mice. Conclusion: Vitamin D receptor knockout increases the porosity in bone, but it is not clearly in dentin, although the dentin wall is significantly thinner. It suggests the effect of vdr-/- on the dentinogenesis is on molecular level. (Supported by T35 HL07473 and T32 DE-14300).

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