Efeitos do estresse sistêmico no músculo pterigóideo medial de ratos com e sem alteração oclusal

Abstract

Emotional stress is a phenomenon of high incidence at globalized society that has been linked as a possible etiologic factor for many diseases. The effect of adrenergic activity in increased tone of skeletal muscles during episodes of chronic stress suggests the occurrence of others structurals and functionals alterations in the stomatognathic system, but the mechanism by which emotional factors can cause muscle dysfunction is not well understood. The malocclusion by tooth loss also promotes muscle changes that associated with the effects of stress can have a big impact on the etiology and development of orofacial pain and dysfunction. Stress and masticatory hypofunction are factors related to the appearance of temporomandibular disorders (TMD) and have not been evaluated in the medial pterygoid muscle. The aim of this work was to investigate the effects of acute and chronic stress on the medial pterygoid muscle of animals subjected or not to unilateral extraction, through morphological and physiological analyse. Forty male Wistar rats (♂-200g), young adults were randomly divided into two groups: Malocclusion group (M = 20) induced by unilateral upper left molar extraction and Not Malocclusion Group No (S = 20): rats without extractions. Each group (n = 20) was subdivided into four subgroups (n = 5): control group (CG), acute stress (GA), repeated chronic stress (GR) and varied chronic stress (GV). Stress protocols were performed from 14 th day after the extraction. Stress by physical restriction was used in GA (two hours, day 23 th) and GR (day 14 th to 23 th); GV was subjected to five different methodologies (day 14 th to 23 th). Euthanasia and collection of samples were performed on day 23 th. It was evaluated: cell morphology by hematoxylin eosin (HE), metabolic activity and muscle oxidative capacity by staining for succinate dehydrogenase (SDH) and nicotinamide adenine dinucleotide (NADH), production of reactive oxygen species (ROS) and capillary density of muscle by immunohistochemistry for proteins alpha CD-31 and Laminin. Normal distribution of data was observed. A factorial ANOVA test with fixed factors of variation was performed and then Tukey-Kramer test (p <0.05). Stress and malocclusion, isolated or associated, induced morphological and physiological changes in the left medial pterygoid muscle; dimorphism of muscle fibers and nuclei of central localization were induced by both factors; increased oxidative metabolism was observed with stress and antagonistic effect with malocclusion; stress increased muscle capillary density and a tendency to oxidative stress increased was observed. The association of chronic stress and malocclusion had increased the glycolytic metabolism. It was concluded that systemic chronic stress has physiological and morphological effects in the medial pterygoid muscle and associated with masticatory hypofunction, could be a possible cause for the development of TMD.