الفهرس 
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Abstract
This study was carried out to assess the effect of vitamin D3 deficiency and hypervitaminosis D3 on dentinogenesis in rats. This study was conducted on 18 female pregnant rats. They were divided equally into three groups (6 rats in each group). The first group was the control group in which rats received a normal balanced diet and exposed to the normal dark /light cycle till the end of the experiment.The second group was the deficiency group in which the rats deprived from sources of vitamin D (light and diet) for several weeks till developing vitamin D deficiency.The third group was the hypervitaminosis group in which the female rats supplemented with high dose of cholecaciferol (4000IU) till developing hypervitaminosis state.After mating, pregnancy and labor, two pups were taken from the litter of each female rat and sacrificed in the fourth day post-partum. Mandibles were dissected out and prepared for light, histomorphometric and ultrastrucural examination .The newly formed dentin of the mandibular first molar was chosen to be examined.
Histological result
Result of the control group
The odontoblasts were well differentiated tall columnar cells with proximally situated nuclei. The sub-odontoblastic zone was studded with undifferentiated mesenchymal cells. The newly formed dentin exhibited a uniform thickness and a homogenous staining denoting a uniform mineralization without evident inter-globular dentin.Regular mineralization front between dentin and predentin.
Result of the deficiency group
• At the occlusal third of the crown, the odontoblasts appeared disorganized, ill differentiated and poorly arranged in homogenous row. Evident interglobular dentin areas were present in the newly formed dentin.The mineralization front between dentin and predentin appeared erratic and irregular.
• At the middle third of the crown, there was a marked decrease in cellularity in both the odontoblastic and sub-odontoblastic cell layers.Other specimens showed increase in the predentin thickness with interglobular dentin formation.
• At the cervical third of the crown, the odontoblasts were cuboidal in shape not tall columnar.The newly formed dentin was formed totally of numerous globules that failed to fuse together (interglobular dentin). High magnification images showed notable increase in the predentin thickness reaching about the same thickness of the newly formed dentin.
Result of the hypervitaminosis group
• At the occlusal third of the crown, the odontoblasts well differentiated with proximally situated nuclei.The sub-odontoblastic zone was studded with undifferentiated mesenchymal cells.Regular mineralization front line present between dentin and predentin. Interglobular globular dentin could be detected in some areas.
• At the middle third of the crown, some areas of interglobular dentin could be detected. Irregular mineralzation front between dentin and predentin was also evident.
• At the cervical third of the crown, a slight increase in predentin thickness could be seen in some areas with irregular mineralization front between dentin and predentin. Discrete areas of interglobular dentin were present in some specimens.
Histomorphometric results
The mean measurement of dentin and predentin thickness in the occlusal third of the first cusp of the first mandibular molar was calculated by image-J software. The difference in dentin thickness in the three groups posed no significant difference. The difference in predentin thickness between the three groups was statistically significant especially when comparing the increased predentin thickness in deficiency group to the remaining two groups.