BONE RESPONSE OF INTRAMUSCULAR CONTRACEPTIVES ON ORTHODONTIC TOOTH MOVEMENT IN ADULT RATS

OBJECTIVE: To study the effect of injectable hormonal contraception, with long-acting steroid preparations, during the bone remodeling process caused by the application of orthodontic forces in adult female rats. METHODS: 12 Wistar female rats of 250 g were divided into two groups: treated (TG) and control (CG). Intramuscular injection of estradiol valerate plus norethisterone enanthate (Mesigyna, 1.5 mg/kg BW) to TG was given every 5 days, 15 days prior to placement of orthodontic appliances and until the end of the experimental period. On the left side of the maxilla a force of 25 g was applied between the first molar and incisor using nickel-titanium spring, for 7 days, in both groups. Pre and post orthodontics impressions of the upper jaw of both groups were taken and the models were digitized in order to quantify dental movement. At the end of the experiment and under anesthesia, cone beam computed tomography (CBCT) was performed to determine bone density (Hounsfield Units). In addition, plasma levels of estradiol and phospho-calcium metabolism parameters were measured. The results were expressed as mean ± ES. Student's t test (independent and paired) was used; significant differences were considered with a p <0.05. RESULTS: Estradiol levels were higher in TG in comparison to CG (103.0 ± 9.5 vs. 19.8 ± 4.5 pg/mL, p <0.0001). Alkaline phosphatase was lower in TG in comparison to CG (176.4 ± 18.6 vs. 244.3 ± 29.4 UI/L, p <0.05). No significant differences in calcium and phosphorous plasma levels were found between groups. Bone density was higher in TG in comparison to CG (886.9 ± 22.5 vs 487.5 ± 21,6 UH, p< 0. 0001), although tooth movement values in TG were lower than CG, the difference was not significant. CONCLUSION: The high values of estradiol in TG validated the experimental model. Alkaline phosphatase is a marker of bone turnover and its decreased activity in TG is consistent with the increase in bone mineral density found by CBCT. These changes did not generate significant differences in tooth movement between the two groups. It is important to analyze this parameter at longer times of exposure to orthodontic forces and its relationship with the chronic administration of long-acting steroid preparations