Effects of teeth clenching on the soleus H reflex during lower limb muscle fatigue

Effects of remote facilitation on ankle joint movement: Focusing on occlusal strength and balance

Background

Remote facilitation refers to teeth occlusion-activated spinal cord activity resulting in increased trunk and limb muscle strength. Facilitation depends on dentition-related pressure during occlusion and masticatory muscle contraction strength.

Aims

This study aimed to clarify the neurophysiological phenomenon and mechanisms by which occlusal strength and balance affect leg muscle activity and smooth joint movement execution.

Materials & Methods

To examine occlusal strength, three conditions were set: no contact between teeth and Moderate- and Maximum-strength occlusion (No-bite, Moderate, and Max conditions, respectively). To assess occlusal balance, we measured occlusal forces and calculated the left-right force ratio. We designated the sides with higher and lower occlusal pressure as hypertonic and hypotonic, respectively. We assessed ankle dorsiflexion movements with joint movement and isometric tasks.

Results

The rate of joint development and peak ankle dorsiflexion torque were significantly higher under occlusion (moderate and max compared to No-bite conditions), and the joint movement performance time was significantly shorter under Moderate compared to No-bite conditions. The joint movement execution time change rate from No-bite to Moderate condition was significantly lower on the Hypertonic side. Joint movement function was most improved under Moderate conditions.

Discussion

While remote facilitation improves with higher occlusal strength, leading to increased muscle strength, there is optimal occlusion intensity in joint movement. Moreover, an occlusal balance-dependent imbalance exists in remote facilitation between the Hyper- and Hypotonic sides.

Conclusion

Thus, low-intensity occlusion is optimal for smooth joint movement, and unbalanced occlusion results in asymmetrical motor function facilitation.

Effects of Clenching Strength on Exercise Performance: Verification Using Spinal Function Assessments

BACKGROUND

This study aimed to determine the relationship between exercise performance and spinal function based on clenching strength.

HYPOTHESIS

Low-intensity clenching contributes to joint movement, whereas high-intensity clenching contributes to joint fixation.

STUDY DESIGN

Randomized crossover trial.

LEVEL OF EVIDENCE

Level 3.

METHODS

Two experiments were conducted using 2 groups of 20 healthy adults. The 4 clenching conditions in experiment 1 were 0%, 12.5%, 25%, and 50% of the maximum voluntary contraction (MVC) of the masseter muscle. Experiment 2 consisted of 3 conditions: no-bite condition, moderate effort, and maximum effort (max condition). In experiment 1, spinal function and ankle dorsiflexion tasks were measured for each clenching condition, and the ankle dorsiflexion task was measured in experiment 2. Regarding spinal function, we measured spinal reciprocal inhibition (RI) and excitability of spinal anterior horn cells. For the ankle dorsiflexion task, ankle dorsiflexion MVC was performed for 3 seconds under each clenching condition. The items analyzed were reaction time, peak ankle dorsiflexion torque, and soleus (Sol)/tibialis anterior (TA) electromyography (EMG) ratio.

RESULTS

The results of experiment 1 illustrated that RI was significantly attenuated or eliminated with increasing clenching strength (>25% MVC). Spinal anterior horn cell excitability increased significantly with increasing clenching strength. The peak torque was significantly higher at 50% MVC than that at 0% MVC. In experiment 2, the peak torque was significantly higher under moderate and max conditions than no-bite condition, and the Sol/TA EMG ratio was significantly higher under max condition than that under moderate condition.

CONCLUSION/CLINICAL RELEVANCE

The results illustrated that during high-strength clenching (≥50% MVC), antagonist muscles are activated simultaneously to increase muscle strength. High-strength clenching improved kinetic performance (joint fixation), whereas low-strength clenching (<50% MVC) enhanced exercise performance (joint movement).

Occlusal Splints and Exercise Performance: A Systematic Review of Current Evidence

The role of the dento-mandibular apparatus and, in particular, occlusion and jaw position, received increased attention during last years. In the present study, we aimed to systematically review, on the light of the new potential insights, the published literature covering the occlusal splint (OS) applications, and its impact on exercise performance. A structured search was carried out including MEDLINE^®/PubMed and Scopus databases with additional integration from external sources, between March and June 2021. To meet the inclusion criteria, studies published in the English language, involving humans in vivo, published from 2000 to 2021 and that investigated the role of occlusal splints on athletes' performance were selected. Starting from the 587 identified records, 17 items were finally included for the review. Four main aspects were considered and analyzed: (1) occlusal splint characteristics and occlusion experimental conditions, (2) jump performance, (3) maximal and explosive strength, and (4) exercise technique and biomechanics. The results of the systematic literature analysis depicted a wide heterogenicity in the experimental conditions and suggested the application of the OS as a way to improve athletes' or individuals' oral health, and as a potential tool to optimize marginal aspects of exercise performance.

Development of a Wearable Mouth Guard Device for Monitoring Teeth Clenching during Exercise

Teeth clenching during exercise is important for sports performance and health. Recently, several mouth guard (MG)-type wearable devices for exercise were studied because they do not disrupt the exercise. In this study, we developed a wearable MG device with force sensors on both sides of the maxillary first molars to monitor teeth clenching. The force sensor output increased linearly up to 70 N. In four simple occlusion tests, the trends exhibited by the outputs of the MG sensor were consistent with those of an electromyogram (EMG), and the MG device featured sufficient temporal resolution to measure the timing of teeth clenching. When the jaw moved, the MG sensor outputs depended on the sensor position. The MG sensor output from the teeth-grinding test agreed with the video-motion analysis results. It was comparatively difficult to use the EMG because it contained a significant noise level. Finally, the usefulness of the MG sensor was confirmed through an exercise tolerance test. This study indicated that the developed wearable MG device is useful for monitoring clenching timing and duration, and the degree of clenching during exercise, which can contribute to explaining the relationship between teeth clenching and sports performance.

Effect of breathing type on electromyographic activity of respiratory muscles during tooth clenching at different decubitus positions

OBJECTIVE

To compare the effect of breathing type on electromyographic (EMG) activity of respiratory muscles during tooth clenching at different decubitus positions.

METHODS

Forty young men participants were included, 11 with upper costal, 9 with mixed, and 20 with costo-diaphragmatic breathing type. EMG recordings of diaphragm (DIA), external intercostal (EIC), sternocleidomastoid (SCM), and latissimus dorsi (LAT) muscles during tooth clenching in the intercuspal position were performed in dorsal, left lateral, and ventral decubitus positions.

RESULTS

DIA EMG activity was higher in subjects with upper costal or mixed than with costodiaphragmatic breathing type (p = 0.006; 0.021, respectively), whereas it was similar between upper costal and mixed breathing types. EIC, SCM, and LAT activity was similar among breathing types.

CONCLUSION

Higher DIA activity would be a risk factor to exceed the adaptive capability of healthy subjects with upper costal or mixed breathing type.

Standardization of the Jendrassik maneuver in Achilles tendon tap reflex

Objective

For many decades, the Jendrassik maneuver (JM) has been used as a reinforcement for stretch reflexes, although the underlying mechanism of this reinforcement is still not fully understood. Moreover, the term JM has been used for many different muscle contraction strategies as there is no fixed movement for the maneuver in the literature. In this study, we aimed to investigate the effects of clenched hand pull, teeth clenching, and their combined effects to reach standardization.

Methods

Achilles tendon tap reflex responses in the soleus were recorded during rest (R), hand pull (HP), teeth clench (TC), and HP + TC combined, hereafter referred to as the JM.

Results

Reflex response amplitudes significantly increased during JM, HP, and TC in the soleus. HP and JM significantly changed the background activity in the soleus, but TC alone did not.

Conclusion

These results suggest that dominantly presynaptic disinhibitory mechanisms may be responsible for the increase in the tendon tap reflex during HP, TC, and JM.

Significance

Because the findings indicate that HP increases the background activity of the soleus, we suggest that researchers should use only TC during the Jendrassik maneuver to avoid any confounding background activity change.