Peripheral TMD Pain Mechanisms and the Effect by Botulinum Toxin A

The goal of this clinical trial is to investigate the effect of botulinum toxin on neurons' plasticity in the masseter muscle in humans with and without painful myogenous temporomandibular disorders (TMDM). The main questions it aims to answer are: * does treatment with botulinum toxin alter gene expressions, epigenetic signatures, and cells plasticity in the masseter muscles of TMDM patients? * do any such changes differ between patients with local and regional TMDM? * does treatment with botulinum toxin influence pain characteristics (intensity, frequency, and sensibility) and other variables in patients with TMDM and are there correlations between significantly changed expression of biomarkers and other variables? Participants will be examined with a questionnaire, clinical examination (including quantitative sensory testing; QST), and microbiopsy sampling from one of the masseter (MM) and anterior tibialis (AT) muscles and are then randomized to treatment with botulinum toxin or control (isotonic saline). Follow-ups occur after one and three months for all patients, and six months with questionnaire, clinical examination, and collection of post-treatment microbiopsies to see if botulinum toxin alter peripheral molecular events and clinical variables.