BACKGROUND: Vitamin A is present in our food such as meat, dairy products, and vegetables. A control balanced diet maintains our nutritional needs of vitamin A. Over consumption of products as well as supplementations with vitamin A increases the risk of hypervitaminosis A. Hypervitaminosis A has been associated with thinning of the long bones and reducing of bone formation OBJECTIVES: to investigate the effect of over as well as optimum doses of vitamin A on growth of mandibular condyle in Wister albino rats. MATERIALS AND METHODS: Eight healthy (2month old age) male Wister albino rats weighting (274 -375grams) were used in present study. The rats were randomly divided into 2 equal group, study and control group .In the control group; rats fed a standard diet containing an optimum dose of vitamin A (12 IU/g of each pellet). In the study group, rats fed a standard diet supplemented with overdose of vitaminA (1700 IU /g of each pellet). After 2months, all rats were euthanized. Blood samples were collected from all rats the day after administering the last dose of vitamin and the concentration of vitamin A in serum was determined for all samples. The condyles of each rat of all groups were dissected out and processed for histological study and histomorphometric analysis. RESULTS: In the study group, the histological examination revealed marked reduction in thickness of hypertrophic zones and increase in the width of chondroblastic zones of condylar cartilage. Bone trabeculae were thin with irregular outline. The subchondral bone showed marked bone resorption with numerous osteoclasts in Howship's lacunae as compared with the control group. CONCLUSIONS: findings from the present study have indicated that, hypervitaminosis A increases resorption of the bone and diminishes endochondral bone growth.

INTRODUCTION: Several pharmacological agents have been investigated for their ability to reduce orthodontic relapse. OBJECTIVE: The current research was performed to test the short term influence of systemic Co-enzyme Q10 administration on post-orthodontic relapse in rabbits. MATERIALS AND METHODS : Thirty New Zealand rabbits were randomly divided into 2 groups (n=15) : Experimental receiving Co-enzyme Q10 and control receiving control vehicle. Orthodontic tooth movement was performed using NiTi coil spring for 21 days for both groups, then this coil spring was detached, and teeth were allowed to relapse for another 21 days. Amounts and percentages of relapse were assessed on threedimensional models of the experimental and control groups at two time points (T2: 1 week of relapse) and (T3: three weeks of relapse). Animals were sacrificed after 3 weeks of relapse for histological examination using H&E stain. Also, histomorphometric analysis was performed. Statistical analysis was computed. Significance was judged at the 5% level. RESULTS: The amount and percentage of relapse showed insignificant difference among experimental and control groups, although relapse in the experimental group was less. However, the histological analysis showed that Co-enzyme Q10 resulted in significant reduction in osteoclast count with the area of new bone formation being significantly increased. Signs of bone resorption were more evident in the control group. CONCLUSION: From the present results, it could be concluded that Co-enzyme Q10 is capable of altering bone resorption pattern favorably in spite of its short term ineffectiveness in minimizing relapse.