Background: Bone remodeling and metabolism associated with orthodontic tooth movement are regulated by alarge number of local and systemic factors. The widespread useof therapeutic corticosteroids (GCs) today raiseconcerns with regard to their effects on mineralized tissue metabolism. This study aimed to investigate the effect ofMethylprednisolone treatment on alveolar bone remodeling during orthodontic tooth movement.Materials and Methods: A twenty-six 12-weeks old male Wistar albino rats were divided into 2 groups; control group (n= 13) without any drug administration during the study and steroidal group (n = 13) which received 5 mg/kg/day ofmethylprednisolone for 3 weeks. A split- mouth design was used performing orthodontic tooth movement on theupper right 1st molar by applying 20 g of mesial force using superelastic closed-coil spring attached to the incisors for21 days while the upper left side served as the non-appliance side. Orthodontic tooth movement was evaluated onweekly basis using digital caliber. The rats were sacrificed after 3 weeks and alveolar bone remodeling process wasevaluated by counting the number of osteoblast and osteoclast cells at the compression and tension sites at thecoronal and apical levels of the mesiobuccal root of upper 1st molar in both appliance and non-appliance sidesusing digital microscope at 400~ magnification. At day of sacrifice serum measurements for alkaline phosphatase(ALP) and acid phosphatase (ACP) activity were carried out.Results: Showed that in the steroid group there was significantly greater amount of orthodontic tooth movement,greater reduction of bone formation and an increase in bone resorption with the presence of orthodonticappliance, increase in serum ACP activity and reduction of serum ALP activity as compared with the controlgroup,(P . 0.05).Conclusion: The Methylprednisolone therapy in low-medium doses elicits a noticeable change in the bone turnoverrate during orthodontic tooth movement

methylprednisolone --- tooth movement --- bone remodeling