Threshold for detection of incisal forces is increased by jaw movement

PubMed ID: 20200410Current knowledge regarding the sensitivity of the teeth to forces is based on psychophysical experiments that measured touch detection thresholds under static jaw conditions. It is not known whether jaw movements alter the perception of forces applied to the teeth, but, based on limb movement studies, it is hypothesized that the perception of mechanoreceptor outputs will be downwardly modulated by jaw movements. We predicted that, compared with static jaw conditions, rhythmic jaw movements would be associated with significantly higher psychophysical thresholds for the detection of incisally applied forces. In eight participants, mechanical pulses were delivered to an incisor during static jaw holding or during cyclic jaw opening and closing. Analogous to findings in human limbs, the psychophysical salience of periodontal mechanoreceptor feedback was downwardly modulated by physiologically relevant movements; detection thresholds for mechanical pulses applied to a central incisor were significantly higher during jaw-closing movements than during static jaw positioning

Delayed-onset muscle soreness in human masticatory muscles increases inhibitory jaw reflex responses

The effects of masticatory muscles’ overloading on jaw-motor control are not yet fully clarified. Therefore, it was tested whether eccentric and concentric exercises of the human masticatory muscles would influence inhibitory jaw reflex responses. Eleven participants (6 males, 5 females) performed 6, 5-minutes bouts of eccentric-concentric contractions. Before, immediately after, 24 hours, 48 hours and 1 week afterwards, visual analogue scale (VAS) scores for jaw muscle fatigue and pain, maximum voluntary bite force (MVBF) and inhibitory jaw reflexes were recorded. Reflex data were analysed with the cumulative sum control chart error box method. Immediate and delayed masticatory muscle fatigue and pain were provoked. Further, 24 hours after the exercises, MVBF tended to decrease (P =.056), suggesting that delayed-onset muscle soreness (DOMS) was provoked in the masticatory muscles. In addition, the inhibitory jaw reflex showed a delayed increase in size 24 hours after the exercise (P <.05). In conclusion, DOMS provoked in the masticatory muscles alters jaw motor control by inducing a delayed increase in the size of the inhibitory jaw reflex

Is myofascial pain in temporomandibular disorder patients a manifestation of delayed-onset muscle soreness?

Objective: In a study to the possible role of overuse of the jaw muscles in the pathogenesis of jaw muscle pain, we used a protocol involving concentric and eccentric muscle contractions to provoke a state of delayed-onset muscle soreness (DOMS) in the jaw muscles of healthy individuals. We tested whether the accompanying signs and symptoms would yield the temporary diagnosis of myofascial pain according to the research diagnostic criteria for temporomandibular disorders (RDC/TMD) in these individuals. Methods: Forty persons (mean age±SD=27.7±7.5 y) performed six, 5-minute bouts of eccentric and concentric jaw muscle contractions. Before and immediately after the exercise, and 24 hours, 48 hours, and 1 week later, self-reported muscle fatigue and pain, pain-free maximum mouth opening, pressure-pain thresholds, and the number of painful jaw muscle palpation sites were recorded. Results: Significant signs and symptoms of DOMS in the jaw muscles were found, which all had resolved after 1 week. In 31 (77.5%) of the participants, these signs and symptoms also gave rise to a temporary diagnosis of myofascial pain according to the RDC/TMD. Conclusions: The results of this study demonstrate that an experimental protocol involving concentric and eccentric muscle contractions can provoke DOMS in the jaw muscles and the temporary diagnosis of myofascial pain according to the RDC/TMD. The results observed strengthen the supposition that the myofascial pain in TMD patients may be a manifestation of DOMS in the jaw muscles

Two different analyzing methods for inhibitory reflexes: Do they yield comparable outcomes?

Background: For the analysis of inhibitory reflexes, no consensus exists regarding the methodology that should be used. The most commonly used methods are the cumulative sum (CUSUM) error box and the t-test. The aim of this study was to assess the interexaminer reliability of those two analyzing methods and to test whether both methods: yield similar results. Methods: Inhibitory jaw reflexes were recorded from the right masseter muscle of 11 participants (6 males, 5 females). Electrical stimuli were applied at the hairy skin of the upper lip on the right side. In total, 16 stimuli were applied while the participants maintained their clenching level at 10% of their maximum voluntary EMG activity. Two different examiners analyzed the reflex data with two different methods: the CUSUM error box and the t-test. The outcome variables were the number of reflex parts, the reflex area size, and the reflex onset. Comparability between examiners and between the two analyzing methods: was assessed with the use of the intraclass correlation coefficient (ICC). Results The interexaminer reliability was fair-to-good to excellent for both the CUSUM error box and the t-test analyses and for all the variables tested. The comparability of the two analyzing methods: was fair-to-good. Comparison with existing methods/conclusion When analyzing the inhibitory reflex data, both the CUSUM error box and the t-test can be used