The inhibitory effect of a chewing task on a human jaw reflex

Chew the Pain Away: Oral Habits to Cope with Pain and Stress and to Stimulate Cognition

The acute effects of chewing gum on cognitive performance, stress, and pain have been intensively studied in the last decade. The results have been contradicting, and replication studies proved challenging. Here, we review some of the recent findings of this topic and explore possible explanations for these discrepancies by incorporating knowledge derived from studies into oral habits and bruxism. Both stress and cerebral functional specialization (i.e., the involvement of specific brain structures in distinctive cognitive processes) are hypothesized to play a major role in the underlying physiological mechanisms of the diverse effects of chewing gum on cognition, stress, and pain.

Pesquisa da fadiga nos músculos faciais e mastigatórios: revisão de literatura

O objetivo deste estudo foi aprofundar os conhecimentos acerca da fadiga muscular dos músculos faciais e mastigatórios por meio da análise da literatura científica. A estratégia de pesquisa baseou-se nas indicações da Biblioteca Cochrane. Os artigos foram selecionados por meio da base de dados PubMed, utilizando-se o descritor "muscle fatigue" em conjunto com os seguintes descritores: "speech therapy", "facial muscles", "jaw muscles", "mastication", "chewing", "lip" e "clenching". Foram incluídos artigos dos últimos dez anos, independente de idioma. Os textos foram analisados inicialmente em seu abstract, sendo excluídos os que não se adequavam ao objetivo. Em seguida foram analisados os textos integralmente e considerou-se: objetivo, delineamento do estudo, formação dos grupos, critérios e rigor metodológico, protocolos aplicados, resultados encontrados e a existência de discussão sobre a fadiga nos músculos objetivados. Nesta última etapa, aqueles que não estavam de acordo com o propósito deste estudo também foram excluídos. Assim, foram encontrados 138 artigos, dos quais 54 foram excluídos devido à repetição mediante cruzamento dos termos e 84 foram analisados. Destes, 46 foram excluídos na etapa do abstract e 38 analisados na íntegra. Destes 38, 24 foram mantidos e 14 excluídos por não se adequarem aos critérios do estudo. Embora existam alguns trabalhos referentes à análise da fadiga, a metodologia dos mesmos é muito variada, dificultando a sua comparação e detalhamento. Enquanto alguns estudos observaram, por exemplo, maior fadiga dos músculos masseteres e orbiculares da boca, outros não encontraram os mesmos resultados, o que pode ter sofrido influência da população alvo de cada estudo.

Quantification of jaw reflexes evoked by natural tooth contact in human subjects

Inhibitory jaw reflexes are believed to be important for protecting the teeth and temporo-mandibular structures from damage during sudden or forceful biting or mastication. Accordingly, alterations in these reflexes are sometimes implicated in aetiologies proposed for oro-facial pain syndromes, although the association is not well-established. We now aim to develop a method for quantifying objectively inhibitory jaw reflexes evoked by natural tooth contact. In the longer term, this may provide a new approach to examining the association of altered reflexes and clinical conditions. Eighteen subjects gave their written, informed consent, and were recruited to participate in this study. They were instructed to clench their teeth together in response to visual cues. They performed two such tasks twenty times: from the jaw postural position and from a more open position with the jaws set 10mm apart. Both tasks produced a rapid rise then stabilisation in electromyographic activity in the masseter muscle. This was always interrupted by a large inhibitory reflex starting 11.1±1.5 ms (mean±SD) after tooth contact. The inhibitions produced during the second task were similar but of significantly longer duration (24.3±6.4 vs 18.4±6.5 ms, P=0.0003, paired t-test) and greater magnitude (measured as an integral of the waveform: 1577±478 vs 1279±425%.ms, P=0.007, paired t-test). Interestingly, in a minority (13%) of the tasks, a second inhibition with a longer latency (50.9±0.9 ms) was also observed. Thus reflex responses in the masseter muscle to natural tooth contact usually consist of single inhibitory periods. In this respect they are like those induced by externally applied tooth pushing although occasionally there is a second inhibition, reminiscent of that seen with externally applied tooth taps.