Effect of jaw clenching on head acceleration during a predictable load impact.

BACKGROUND: Jaw clenching is considered to reduce head acceleration while receiving a strong impact on the body during sport activities. OBJECTIVE: The present study aimed to clarify the effect of jaw clenching on reduction of head acceleration during a predictable load impact to the body. METHODS: Seven healthy participants were exposed to a predictable load impact with and without jaw clenching. We recorded the electromyographic activity of the masseter (MA) and digastricus (DIG) muscles, occlusal pressure and head acceleration throughout the experiment. RESULTS: When participants were not instructed to clench their jaws, they naturally positioned their jaws without occlusal contact at the time of pendulum impact by co-contracting the jaw opener and closer muscles. When participants were instructed to clench their jaws, neither the activity of the jaw opener muscle nor the head acceleration differed at the time of pendulum impact when compared with when participants were not instructed to clench their jaws. CONCLUSIONS: A slightly distanced jaw position (co-contracting the jaw opener and closer muscles without occlusal contact) might serve inherently safety for reduction of head acceleration during predictable body impact, while jaw clenching does not contribute to reduction of head acceleration in response to pendulum impact more than the distanced jaw position does. Notably, DIG activation to minimise the head acceleration in response to pendulum impact was similar in clenching and no clenching positions. This suggests that DIG may play a crucial role in the reduction of head acceleration, regardless of MA muscle activity.

Effect of jaw clenching on postural adjustments to a predictable external perturbation.

This study investigated the effect of jaw clenching on anticipatory postural adjustments (APAs) and reactive postural adjustments (RPAs). Eight healthy adults were exposed to predictable external perturbations with and without submaximal jaw clenching. We recorded the three-dimensional body kinematics, ground reaction forces, and electromyography (EMG) of 12 muscles. EMG onset, integrated EMG, and positions of the center-of-mass (COM) and center-of-pressure (COP) during the anticipatory and reactive phases of postural adjustments were computed and compared for the jaw clenching and control conditions. Jaw clenching resulted in an earlier onset of APAs and a greater amplitude of trunk and lower limb EMG activities in the APAs and RPAs. There were no differences in the COM and COP displacements after the perturbation. Jaw clenching is effective for enhancing APAs and RPAs, although it may not increase postural stability following predictable external perturbation in healthy adults.

Occlusal support and postural stability in children: An observational study.

BACKGROUND: The relationship between uneven occlusal contact and fall risk has been described in elderly participants; however, multiple confounding factors, such as systemic disease or deterioration in vestibular function, have not been well considered. This study aimed to investigate this relationship in pediatric participants at the age of approximately 9-12, where these confounding factors are absent and the replacement of primary molars by permanent ones generally occurs and transiently results in uneven occlusal contact. METHODS: Sixty-five children (36 boys and 29 girls, mean age: 9.5 ± 1.5 years) were enrolled in this study. Participants were asked whether they had experienced at least two falls within the past 1 year. The occlusal contact area ratio was calculated by dividing the greater half (right or left dental arch) by the smaller half (the other half) with U-shaped pressure sensor sheet. The total length and rectangular area of the center of pressure while standing upright for 10 s were measured with a stabilometer and used as postural sway parameters. RESULTS: The occlusal contact area ratio significantly correlated with the postural sway parameters. Comparison between those who had experienced the fall incidences and those who had not after propensity score matching that adjusts their overall physical function revealed that there were no significant differences in the postural sway parameters and occlusal contact area ratio regardless of the history of fall incidence. CONCLUSIONS: Uneven occlusal contact leads to an increase in postural sway in children; however, this may not be associated with fall incidence.

Association between Sports-Related Concussion and Mouthguard Use among College Sports Players: A Case-Control Study Based on Propensity Score Matching.

Sports-related concussion (SRC) is a major public health concern. This study aimed to assess the association between mouthguard use and the incidence of SRC in college students through a case-control study using propensity score matching. In total, 195 of 2185 potential participants volunteered to participate in this study. We used Google Forms online to capture participants' information, including: age; gender; height; weight; sports contact level; level of play; exposure time; frequency of mouthguard use; mouthguard type; and SRC experience. Data for 115 participants who played collision and contact sports were used for the analysis. The difference in the frequency of mouthguard use was assessed between matched pairs and the overall association between SRC and mouthguard use was evaluated. In the matched groups, those who had not experienced SRC wore a mouthguard more frequently than those who had experienced SRC (7/28 vs. 1/28; p = 0.051). Logistic regression analysis showed there was a significant negative association between the frequency of mouthguard use and the incidence of SRC (odds ratio 0.101; p = 0.041). Within the limitations of this study, these results suggest that mouthguard use may offer some benefit in preventing SRC.