Chronic orofacial pain is a common and debilitating problem that affects at least 10% of the adult population. This term refers to different disorders that have pain, as the main characteristic, such as Temporomandibular Dysfunction (TMD), neuralgias and neurovascular facial pain. Different multidisciplinary and symptomatic therapies have been proposed to control chronic orofacial pain from these disorders. However, due to the constant reports of new mechanisms that integrate the mechanisms of maintenance of chronic orofacial pain, new therapies are constantly being proposed as injections of Botulinum Toxin type A (BoNT-A). Mechanisms of peripheral and central neuronal hyperexcitability and deficiency in the intrinsic modulatory mechanisms are part of these mechanisms and can be determined by means of tests that determine a patient's somatosensory profile (quantitative sensorial tests (QST)). However, the few randomized and double-blind clinical studies in the literature present contradictory results regarding the efficacy of BoNT-A for these disorders; due mainly to the lack of consistent evidence on which specific mechanisms of chronic pain or which somatosensory profiles the botulinum toxin would be most effective. Thus, the present double-blind, randomized clinical trial aims to determine the influence and efficacy of botulinum toxin tipa A on the modulation and perception of pain in the orofacial region in patients refractory to conventional therapies. To this end, 80 adult participants, aged 18-50 years, with musculoskeletal pain and / or neuropathic pain, who have been treated with conservative therapies without success in the last 3 months, will be selected. Participants will be classified according to the somatosensory profile presented after receiving injections of botulinum toxin or saline according to the randomization performed. The somatosensory characteristics related to pain perception and pain modulation will be assessed in the anterior temporal region, masseter and tenar by the mechanical pain threshold (MPT), temporal summation test (WUR), threshold (PPT), thermal pain threshold (TSL), and pain modulation conditioning test (CPM), respectively. The psychosocial characteristics qualified by the Catastrophic Thoughts Scale Questionnaire, Pittsburg Sleep Quality Index, SF-36 generic quality of life assessment questionnaire, and Global Change Perception Scale (PGICS) will also be evaluated. Data will be submitted to statistical analysis using multivariate analysis of variance (ANOVA) and multiple linear regression, with significance level of 95%.
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