The effect of oral contraceptives on orthodontic tooth movement in rat.

INTRODUCTION: The purpose of this study was to investigate the effect of ethinyl estradiol/norgestrel - used in some oral contraceptives- on orthodontic tooth movement in Wistar rats. MATERIAL AND METHODS: Forty eight female three-month old Wistar rats with an average weight of 250 ± 25 gr were divided into two experimental and control groups. One week prior to appliance insertion and during the appliance therapy period, 100 mcg/kg/day of ethinyl estradiol and 1 mg/kg/days of norgestrel were administered to the experimental group by gavage; meanwhile the control group received an equivalent volume of Sodium Chloride 0.9 % (Saline). Maxillary central incisors were tipped distally by insertion of springs exerting 30 g force. Two, seven and fourteen days after spring insertion animals were sacrificed. The mesioincisal distance between maxillary incisors were measured. Subsequently, histological sections were prepared for histomorphometric studies. RESULTS: 14 days after force application the orthodontic tooth movement was significantly lower in the experimental group (p<0.05). The number of osteoclasts were significantly lower in the experimental group 2, 7 and 14 days after spring insertion (p<0.05). CONCLUSION: Ethinyl estradiol/norgestrel (oral contraceptives) can significantly decrease the amount of tooth movement in the linear phase.