Association between chewing dysfunctions and temporomandibular disorders: A systematic review

Temporomandibular disorder (TMD) is an umbrella condition presenting several signs and symptoms including pain in the temporomandibular joint (TMJ) and masticatory muscles, articular noises, earache, headache, irregular or restricted jaw function, chewing difficulty, and limited mouth opening. Such TMD impairment may cause disorders during the chewing process. Therefore, the purpose of this systematic review was to assess chewing dysfunctions measured by sEMG, and their association with TMD. A combination and variation in the descriptors "temporomandibular joint disorders", "masticatory dysfunctions", and electromyography were used to perform the searches across databases. The databases chosen were: LILACS, PubMed, Science Direct, Scopus, and Web of Science. Additionally, grey literature was assessed using Google Scholar, ProQuest, and OpenGrey. Studies in adults that diagnosed TMD through the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD), Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) or Helkimo Protocol were selected. Furthermore, those studies should have evaluated chewing processes through surface electromyography (sEMG). Risk of bias of the included studies was assessed through the Meta-Analysis of Statistics Assessment and Review Instrument (MAStARI) tool. Eleven included studies shown significant results; however, they evaluated discrepant parameters, presented high inconsistency in the application, and had chosen different tasks to analyse the sEMG and hence, there was no consensus in the results of studies. In conclusion, strength of recommendations was very low due to a series of limitations on studies and it was not possible to made categorical statement about association between TMD and chewing dysfunctions in adults when parameters of sEMG were analysed.