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Effects of the Umpredictable chronic stress in contralateral medial pterygoid muscle in rat with and without occlusal alteration

Grant number: 12/23003-2
Support Opportunities:Scholarships in Brazil - Scientific Initiation
Effective date (Start): February 01, 2013
Effective date (End): January 31, 2015
Field of knowledge:Biological Sciences - Morphology - Anatomy
Principal Investigator:Mamie Mizusaki Iyomasa
Grantee:Bruno Melo Loyola
Host Institution: Faculdade de Odontologia de Ribeirão Preto (FORP). Universidade de São Paulo (USP). Ribeirão Preto , SP, Brazil


The temporomandibular disorder (TMD) has a high prevalence in our society, a condition characterized by severe pain of the masticatory muscles and/or temporomandibular joint. Despite the indication of multiple factors contributing to the TMD primers, including emotional stress, there is still controversy as to its etiology, and its pathophysiology is poorly understood. Using the rat as experimental animal model, this study aims to investigate the effect of umpredictable chronic stress associated with unilateral exodontia on the contralateral medial pterygoid muscle. Our hypothesis is that umpredictable chronic stress associated with malocclusion induce plastic changes, causing changes in morphology, oxidative stress and oxidative metabolism of muscle fibers. The purpose of this study is to evaluate the contralateral medial pterygoid muscle. Thirty two male young adults Wistar rats, weighing on average 200 g were randomly divided into two groups: Groups Malocclusion (GM): rats exposed to left unilateral exodontia (n = 16) and Group Without Malocclusion (GS): rats without extraction (n = 16). In each group there will be the following subgroups (n = 8) in each: I - no stress, II: umpredictable chronic stress. Animals of group malocclusion (GM) will undergo unilateral extraction of upper left molars under intraperitoneal anesthesia with 4% Xylazine (10mg/kg) and ketamine 10% (80mg/kg) on day zero. In both groups (GM and GS) the rats of subgroups II will undergo different stress protocols, from the 14th day after the extraction. The protocols are different every day for five consecutive days, which will be repeated from the 6th day during five days. The rats will be euthanized on the 24th day after the start of the experiment to obtain the contralateral medial pterygoid muscle, and subsequent morphological and histochemical. (AU)

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