4 Avaliação dos efeitos da obesidade hipotalâmica associada a movimentação dentária induzida sobre a estrutura do periodonto de ratos

Abstract

Obesity is a chronic multifactorial metabolic disease associated with several comorbidities. Among the various pathologies related to obesity, disturbances in bone metabolism and remodeling play a crucial role in orthodontic movement. This study aimed to evaluate whether hypothalamic obesity associated with induced tooth movement influences the histological structure of periodontal tissues in rats. Forty male Wistar rats, five days old, were obtained from the Central Animal Facility of the State University of Western Paraná. Twenty neonatal rats were administered subcutaneous injections of monosodium glutamate (4g/kg/day) in the cervical region during the first five days of life to induce obesity (MSG group), whereas twenty animals received hyperosmotic saline solution injections (1.25g/kg/day) (non-obese control group - CTL). After this period, the animals were divided into four experimental groups (n=10/group): G1: non-obese control group (CTL), rats that were not subjected to any experimental procedure; G2: CTL rats subjected to induced tooth movement (CTL + ITM); G3: obese rats without induced tooth movement (MSG); G4: obese rats subjected to induced tooth movement (MSG + ITM). At 90 days of age, the ITM device was installed in the CTL+ITM and MSG+ITM groups, and the total ITM period was seven days. This device consisted of a closed-coil nickel- titanium spring (Morelli®; Sorocaba, São Paulo, Brazil) exerting a force of 50 cN. At 97 days, all animals were weighed and euthanized, followed by decapitation. The right hemimaxillae were removed, fixed in 10% buffered formalin for 24 hours, washed in running water for 48 hours, and stored in 70% alcohol. After euthanasia, tooth movement was assessed by measuring the distance between the mesial surface of the first upper molar and the distal surface of the third upper molar on the right (moved) and left (non- moved) sides. For histological analyses, serial longitudinal sections were performed on the mesio-buccal and disto-buccal roots of the right first upper molar, from mesial to distal. The histopathological events investigated included external root resorption, hyalinized areas, acute inflammatory infiltrate, chronic inflammatory infiltrate, presence of multinucleated giant cells, vascular alterations, and periodontal ligament organization. Obese animals from the MSG groups showed increased Lee index and retroperitoneal and 7 perigonadal fat deposits compared to CTL animals. The obese animals in the MSG+ITM group showed a reduction in the rate of induced tooth movement when compared to the non-obese animals in the CTL+ITM group. None of the groups analyzed presented acute or chronic inflammatory processes. The animals in the MSG+ITM group showed an increase in areas of external root resorption, presence of multinucleated giant cells and disorganization of the periodontal ligament when compared to the other groups. The animals with CTL+ITM and MSG+ITM tooth movement presented the highest occurrences of hyalinization, while the obese animals (MSG and MSG+ITM) presented the highest frequencies of vascular alterations. We conclude that induced tooth movement associated with hypothalamic obesity causes a reduction in the orthodontic movement rate and greater occurrences of periodontal changes and external root resorption.