Effects of Hypothyroidism Associated with Dental Trauma on Induced Tooth Movement of Female Rat Molars

Aims: The aim of this study was to evaluate the influence of hypothyroidism associated with dentoalveolar trauma on the induced tooth movement of female rats molars.

Study Design: Experimental research.

Methodology: Forty-eight female Wistar rats were randomly divided into eight experimental groups (n=6 per group): Group 1 – control: animals that were not subjected to any experimental procedure; Group 2: animals that were subjected only to hypothyroidism (HPT); Group 3: animals that were subjected only to dentoalveolar trauma (DT); Group 4: animals that were subjected to HPT+ DT; Group 5: animals that underwent induced tooth movement (ITM); Group 6: animals that underwent DT+ITM; Group 7: animals that underwent HPT+ITM; and Group 8: animals that underwent HPT+DT+ITM. At the end of the experimental period, the animals were weighed and euthanized. The right hemimaxillae were removed, fixed in 10% formalin, decalcified, embedded in Paraplast, cut to 5 µm thickness, and stained with hematoxylin and eosin. the histological slides, and histomorphometric analysis of external root resorption were performed.

Results: The animals that consumed propylthiouracil (0.05% diluted in water) showed lower concentrations of T3 and T4 but higher thyroid-stimulating hormone. The tooth movement rate was significantly higher in the animals of the HPT+DT+ITM group than the other groups (p<0.05). The HPT+ITM group showed greater tooth movement than the ITM and DT+ITM groups (p<0.05). Among the animals in the groups without the tooth movement device, the HPT group had the smallest areas of root resorption when compared to the CTL, DT, and HPT+DT groups (p<0.05). In the analysis of the groups with tooth movement devices, the HPT+ITM group had a smaller root resorption area than the other groups with tooth movement devices (p<0.05). Animals in the HPT+DT+ITM group exhibited the highest root resorption area out of all experimental groups (p<0.001). The animals in the DT, HPT+DT, ITM, HPT+ITM, and DT+ITM groups showed occasional periodontal ligament disorganization, and the animals in the HPT+DT+ITM group had moderate disorganization. In the evaluation of hyaline areas, the groups that underwent DT and/or ITM (DT, HPT+DT, ITM, DT+ITM, HPT+ITM, and HPT+DT+ITM) showed a moderate presence of hyaline areas. Regarding vascular changes in the periodontal ligament, the presence of giant cells, hyperemia, and inflammatory infiltrate were observed in the ITM, DT+ITM, HPT+ITM, and HPT+DT+ITM groups.

Conclusion: We conclude that hypothyroidism associated with dental trauma causes increase in the rate of tooth movement and greater occurrence external root resorption during orthodontic movement in female rats molars.