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In most sports, mobility of the body's center of mass is as important as muscle strength and posture maintenance. Many dynamic studies have revealed a positive relationship between teeth clenching with a mouthguard (CLMG) and athletic ability. However, the effects of CLMG on mobility remain controversial. Vertical jumping, particularly squat jumping (SJ), can be used to evaluate this ability. During SJ, arm swing and reactionary operation of lower limbs are limited. Therefore, the effects of CLMG can be readily investigated. In the present study, we measured SJ height, biomechanics data and masseter muscle activity under two oral conditions: CLMG, and no mouthguard with no instructions on clenching. The aim of the present study was to clarify whether CLMG improves SJ performance. A total of 10 adult female athletes with an average age of 20.8±1.2 years participated in this study. The study protocol was approved by the Tokyo Dental College Ethics Committee (approval No. 437). The study adhered to the tenets of the Helsinki Declaration on the Ethical Treatment of Human Subjects. A customized EVA MG was used for each subject. Measuring devices included the 3-dimensional motion capture system, ground reaction force meters, and electromyograms. The results indicated that CLMG improved SJ height by enhancing work, work rate of hip joints, steadiness of body balance function during jump preparation, and masseter muscle activity. Within the limitations of this study, the results indicated that CLMG tended to improve SJ performance. [ABSTRACT FROM AUTHOR]

A laminated mouthguard is made by fusing sheets of mouthguard materials together. Adequate adhesive strength is required to use mouthguards in stable condition for a long time. To date, adhesive strengths have been investigated on a flat surface. However, an actual mouthguard is made on a player's model with different inclination. Therefore, in this study, the exfoliation test was applied to determine the adhesive strength during thermoforming using a special simulation model with three different flat surfaces of 0 degree, 45 degrees, and 90 degrees against a pressurizing force. Air pressure type samples were made by EVA blank. Samples were laminated with two pieces of mouthguard material and cut out with an adhesive area of 5 × 5 mm2, the other end was the holding part. Three different heating times of 100, 115 and 130 s were employed. The delamination test was carried out by employing Autograph. Original jigs with screws were used to grip the specimen firmly. Adhesive strength was measured at the center of the 0-degree and 45-degree surfaces, and upper and lower positions on 90-degree surface. The result was measured at the time of breakage of the maximum load, and the form of destruction was examined. At a heating time of 100 seconds, all four surfaces showed interface failures. The 0-degree surface showed the largest failure load, and the greater inclination and lower measuring position of a 90-degree surface reduced the adhesive strength significantly. At a heating time of 115 seconds, the 0-degree surface showed material failures. The other three surfaces showed interface failures and the greater inclination and lower measuring position of a 90-degree surface reduced the adhesive strength significantly. At a heating time of 130 seconds, all four surfaces showed material failures; these failures do not represent adhesive strength, but material thickness after thermoforming. [ABSTRACT FROM AUTHOR]

Background: The purpose of this study was to investigate changes in six segments in the head, jaw, torso, pelvis, and bilateral shanks, the ground reaction force vectors of each foot and the center of mass in the static standing posture induced by an experimental mandibular deviated splint. Methods: Ten healthy adults with no past medical history related to the stomatognathic system or otological disease participated in this study. Measurements were performed by motion capture (Vicon Nexus, Vicon) and tw o ground reaction force meters. We employed a three-dimensional motion analysis software (Visual 3D, c-Motion), and added the jaw model to the musculo-skeletal model disclosed by the International Society of Biomechanics. Results: Compared to those in the mandibular rest position, the center of gravity of the five segments and the center of mass were shifted leftward (mandibular deviated direction) at the mandibular deviated position, confirming that the shift was larger in the upper regions. Additionally, rotations in retroflexion, the left rotation of the jaw segment, and rotation in left lateroflexion at the right shank segment were observed. In the ground reaction forces, vertical components were shifted leftward. Moments in the Y component at the left ankle and right hip were significantly changed. Conclusion: The experimentally deviated mandibular position made the jaw segment itself shift leftward significantly. This mandibular deviation made the head shift significantly followed by larger effects in the more upper segments. Therefore, abnormalities of occlusal position affect the static standing posture. [ABSTRACT FROM AUTHOR]

Purpose: The prefrontal cortex (PFC) regulates the stress response, which affects concentration level, maintenance of muscle tone, and assessment of the situation and is closely related to injury and sports performance. The purpose of this study was to determine the influence of an abnormality in the stomatognathic system on emotion by measuring PFC activity in response to an experimentally deviated mandibular position (EDMP). Fleart rate (FIR) and a visual analog scale (VAS) score of stress were used as an indicator of autonomic nervous system (ANS) function and psychological index, respectively. Methods: Subjects were 14 healthy right-handed volunteers (10 men and 4 women; age, 26.5 ± 2.2 years). Written consent was obtained from all subjects and the study design was approved by the Ethics Committee of Tokyo Dental College. The subjects performed each of the following 4 tasks once, in a random order: (1) control (rest), (2) arithmetic (a mental task often used to evoke stress), (3) EDMP, and (4) arithmetic + EDMP. Prefrontal cortex activity was measured using near-infrared spectroscopy. Results: Activity in the PFC, FIR, and VAS were greater in the arithmetic, EDMP, and arithmetic + EDMP tasks than in the control task, with significant differences observed between the arithmetic, EDMP, and arithmetic + EDMP tasks and the control task in all three variables (p < 0.05), except between arithmetic + EDMP and the control task in FIR. Conclusion: These findings suggest that EDMP-induced elevation of PFC activity was a response to discomfort, suggesting that EDMP affects systemic function, such ANS function, by acting as an unpleasant stressor. [ABSTRACT FROM AUTHOR]

This paper describes a case of root fracture in the maxillary central incisor of a rugby player incurred during touch football training. The tooth was treated with a flexible fixed splint, a removable resin splint (made from pre-laminated soft and hard layers of material) and a high shock absorption Hard & Space mouthguard. We believe that fixation with a flexible fixed splint and a removable resin splint allowed the patient to maintain a normal diet, which may have contributed to his being able to maintain body weight and return to competition earlier than might otherwise have been possible. At approximately 12 months into the rugby season, the player had sustained no further injury in the affected area and experienced no pain or discomfort. This indicates that the Hard & Space mouthguard is also effective in preventing injury. Furthermore, keeping the plaster model which had been used to fabricate a mouthguard for the player allows the dentist to respond promptly to further injuries, something considered important by team doctors. The present results also show the need for not only players, but also trainers and coaches to be aware of the importance of regular use of a mouthguard in all types and levels of sport. This is particularly pertinent right now, as touch football is to be included in the physical education curriculum at both the elementary and junior high school levels. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study was to determine how the intensity of tooth clenching (TC) affected brain activity using functional magnetic resonance imaging (fMRI), focusing on those areas involved in motor function. As a comparison, the effect of finger pinching (FP) on brain activity was also investigated. Method: First, the maximum values of TC and FP were determined using a specially designed force sensor. To ensure uniformity of intensity and speed of TC and FP, feedback was provided by means of simultaneous force values displayed on the monitor and the pace set by a digital metronome while fMRI was conducted. Subjects were required to perform either TC or FP at 50% or 10% of the maximum value at a rate of once per second. Result & Discussion: The results showed that an increase in the intensity of TC increased the area of activity in the sensory, motor, supplementary motor and premotor areas of the brain bilaterally. The same tendency was also observed with FP, but only contralaterally. This indicates that an increase in TC force will elicit greater brain activity. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the effect of a mouthguard on root distortion resulting from an impact force applied by means of a pendulum-type impact testing machine equipped with an accelerometer to a tooth model with strain gauges attached. A two-layer type EVA mouthguard (MG) was employed. Peak impact acceleration with an MG (33.2 g) was significantly smaller than that without a mouthguard (NOMG) (78.8 g). The shock absorption ability of the MG was 57.9%. A paired t-test was used to compare the peak impact distortion at five different measurement points and shock absorption of the MG at total distortion (sum of distortion values at all five points). Distortion at each measurement p o in t was significantly smaller with an MG than with NOMG. Total root distortion with an MG (8319.4 με) was significantly smaller than that with NOMG (3555.8 με). The shock absorption ability of the MG at total distortion was 56.0%. With in the limitations of this study, the results showed that an MG significantly reduced peak impact acceleration (to approximately 58%) and root distortion at each measurement point and total distortion (to approximately 56%). These results indicate that a mouthguard has the potential to prevent root injury. [ABSTRACT FROM AUTHOR]