Masseter Muscle Activity in Track and Field Athletes: A Pilot Study.

Teeth clenching has been shown to improve remote muscle activity (by augmentation of the Hoffmann reflex), and joint fixation (by decreased reciprocal inhibition) in the entire body. Clenching could help maintain balance, improve systemic function, and enhance safety. Teeth clenching from a sports dentistry viewpoint was thought to be important and challenging. Therefore, it is quite important to investigate mastication muscles' activity and function during sports events for clarifying a physiological role of the mastication muscle itself and involvement of mastication muscle function in whole body movement. Running is a basic motion of a lot of sports; however, a mastication muscles activity during this motion was not clarified. Throwing and jumping operation were in a same situation. The purpose of this study was to investigate the presence or absence of masseter muscle activity during track and field events. In total, 28 track and field athletes took part in the study. The Multichannel Telemetry system was used to monitor muscle activity, and the electromyograms obtained were synchronized with digital video imaging. The masseter muscle activity threshold was set 15% of maximum voluntary clenching. As results, with few exceptions, masseter muscle activity were observed during all analyzed phases of the 5 activities, and that phases in which most participants showed masseter muscle activity were characterized by initial acceleration, such as in the short sprint, from the commencement of throwing to release in both the javelin throw and shot put, and at the take-off and landing phases in both jumps.

Influence of Pleasant and Unpleasant Auditory Stimuli on Cerebral Blood Flow and Physiological Changes in Normal Subjects.

The prefrontal cortex (PFC) plays an important role in emotion and emotional regulation. The valence asymmetry hypothesis, proposes that the left/right asymmetry of the PFC activity is correlated with specific emotional responses to stressors. However, this hypothesis still seems to leave room for clarifying neurophysiological mechanisms. The purpose of the present study was to investigate the effects of stimuli with positive and negative valence sounds (hereafter PS, NS) selected from the International Affective Digitized Sounds-2 on physiological and physiological responses, including PFC activity in normal participants. We studied the effect of both stimuli using 12 normal subjects (mean age 26.8 years) on cerebral blood oxygenation in the bilateral PFC by a multi-channel NIRS, alpha wave appearance rate in theta, alpha, beta by EEG, autonomic nervous function by heart rate, and emotional conditions by the State-Trait Anxiety Inventory (STAI) and the visual analogue scale (VAS). PS was selected over 7.00 and NS were fewer than 3.00 in the Pleasure values. Sounds were recorded during 3 s and reproduced at random using software. Every task session was designed in a block manner: seven rests with Brown Noise (30 s) and six tasks (30 s) blocks. All participants performed each session in random order with eyes closed. A paired Student's t-test was used for comparisons (P<0.05). PFC activity showed increases bilaterally during both stimuli with a greater activation of the left side in PS and a tendency of more activation by NS in the right PFC. Significantly greater alpha wave intensity was obtained in PS. Heart rate tended to show smaller values in PS. The STAI level tended to show smaller values in PS, and a significantly greater VAS score was obtained in PS which indicated 'pleasant'. Despite the limitations of this study such as the low numbers of the subjects, the present study indicated that PS provided pleasant psychological and physiological responses and NS unpleasant responses. The PFC was activated bilaterally, implying a valence effect with the possibility of a dominant side.

Relationships Between Gum-Chewing and Stress.

Studies have shown that chewing is thought to affect stress modification in humans. Also, studies in animals have demonstrated that active chewing of a wooden stick during immobilization stress ameliorates the stress-impaired synaptic plasticity and prevents stress-induced noradrenaline release in the amygdala. On the other hand, studies have suggested that the right prefrontal cortex (PFC) dominates the regulation of the stress response system, including the hypothalamic-pituitary-adrenal (HPA) axis. The International Affective Digitized Sounds-2 (IADS) is widely used in the study of emotions and neuropsychological research. Therefore, in this study, the effects of gum-chewing on physiological and psychological (including PFC activity measured by NIRS) responses to a negative stimulus selected from the IADS were measured and analyzed. The study design was approved by the Ethics Committee of Tokyo Dental College (No. 436). We studied 11 normal adults using: cerebral blood oxygenation in the right medial PFC by multi-channel NIRS; alpha wave intensity by EEG; autonomic nervous function by heart rate; and emotional conditions by the State-Trait Anxiety Inventory (STAI) test and the 100-mm visual analogue scale (VAS). Auditory stimuli selected were fewer than 3.00 in Pleasure value. Sounds were recorded in 3 s and reproduced at random using software. Every task session was designed in a block manner; seven rests: Brown Noise (30 s) and six task blocks: auditory stimuli or auditory stimuli with gum-chewing (30 s). During the test, the participants' eyes were closed. Paired Student's t-test was used for the comparison (P<0.05). Gum-chewing showed a significantly greater activation in the PFC, alpha wave appearance rate and HR. Gum-chewing also showed a significantly higher VAS score and a smaller STAI level indicating 'pleasant'. Gum-chewing affected physiological and psychological responses including PFC activity. This PFC activation change might influence the HPA axis and ANS activities. In summary, within the limitations of this study, the findings suggest that gum-chewing reduced stress-related responses. Gum-chewing might have a possible effect on stress coping.

Effect of clenching with a mouthguard on head acceleration during heading of a soccer ball.

Concussions are acceleration-deceleration injuries that occur when biomechanical forces are transmitted to the cerebral tissues. By limiting acceleration of the head, enhanced cervical muscle activity derived from clenching with a mouthguard (MG) may reduce the incidence or severity of concussions following impact. The purpose of this study was to investigate the effect of voluntary clenching with a proper MG on acceleration of the head during "heading" of a soccer ball. Eleven male high school soccer players (mean age, 16.8 years) participated in the study. Each player was given a customized MG. An automated soccer machine was used to project the ball at the participants at a constant speed. The participants headed the ball under 3 different oral conditions: drill 1, heading freely performed without instruction and without the MG; drill 2, heading performed as the subject was instructed to clench the masseter muscles tightly while not wearing the MG; drill 3, heading performed as the subject was instructed to clench tightly while wearing the MG. Each participant repeated each drill 5 times. Linear acceleration of the head was measured with a 3-axis accelerometer. Activity of the masseter and sternocleidomastoid muscles was measured by wireless electromyography. Weak masseter and sternocleidomastoid muscle activity was observed during drill 1. After the soccer players had been instructed to clench their masseter muscles (drills 2 and 3), statistically significant decreases in head acceleration and increases in masseter and sternocleidomastoid muscle activity were observed (P < 0.05; paired t test). The effect was stronger when the players wore the MG. Dentists should encourage soccer players to habitually clench while wearing a proper mouthguard to strengthen cervical muscle resistance as a way to mitigate the damage caused by heading.

Thinning factors influence on custom-made mouthguards thermoforming.

The aim of this study was to clarify and quantify factors influencing thinning during a thermoforming using a special simulation model that has three different flat surfaces such as 0 degree, 45 degree and 90 degree against a pressurizing force. Air pressure type samples were made by EVA and acrylic resin blank. Vacuum type samples were also made by EVA. Thickness gauge was employed to measure the thickness. As results, pressure forming showed significantly larger thinning at 45 and 90 degree surfaces and smaller thinning at 0 degree surface, 36% in thinning rate by vacuum forming and 66% by the pressure forming at 90 degree surface, and 17% and 20% at 45 degree surface, and 11% and 2% at 0 degree surfaces. Thinning was increased with the increase in distance from the centre in 0 degree surface and increased with the decrease in height in the vertical surface significantly. The air pressure, the material thickness in EVA (Drufosoft) and difference in material colour did not affect thinning rate. An acrylic resin material showed approximately 10% smaller thinning than EVA (Drufosoft). To retain enough thickness of 3 mm on 90 degree surface corresponding to an incisal labial aspect for pressure laminate type, over 55% reduction is taken into consideration and at least two 3-mm-thickness materials should be laminated. 0 degree surface showed at most 2 % reduction in pressure lamination; post thermoforming occlusal thickness became almost 6 mm with a usual 3 mm plus 3 mm lamination. Therefore, careful occlusal adjustment in an actual mouthguard fabrication to achieve an appropriate 2 mm thickness on this surface should be requested.

Shock absorption ability of mouthguard against forceful, traumatic mandibular closure.

BACKGROUND: The positive effects of wearing a mouthguard on shock absorption have been indicated in various papers. The ability of a mouthguard to protect against indirect injury, however, is not clear, and the thickness that a mouthguard would require to provide such protection remains to be determined. The primary aim of this study was to clarify the shock absorption potential of a mouthguard against forced, traumatic occlusion. The secondary objective was to compare the shock absorption ability of different thicknesses of mouthguard against this type of trauma. MATERIALS AND METHODS: An artificial skull (ZA20; 3B Scientific International, Co. Ltd, Niigata, Japan) with two-axis strain gages applied to the right buccal aspect of the mandible and the mandibular and maxillary teeth was used to measure shock absorption ability. Three different thicknesses of EVA mouthguard (1, 2, and 3 mm at the first molar) were tested. RESULTS AND CONCLUSIONS: Within the limitations of this laboratory study, the following results were obtained: the results showed that increasing the thickness of the mouthguard improved its shock absorption ability.

Paired maxillary and smaller mandibular mouthguard for rugby player with malalignment.

A rugby player who had frequently experienced soft tissue injuries while playing rugby and wearing a conventional custom-made mouthguard came to the hospital clinic. The patient had suffered traumatic soft tissue injuries such as lip lacerations and bite trauma. Severe crowding due to ectopic maxillary and mandibular canines was observed. In response to the patient's request for better protection, a set of maxillary and mandibular mouthguards was designed: one covering the entire maxillary dentition and the other the mandibular front teeth only. The mouthguards were to be worn simultaneously. In this paper, we describe how these mouthguards were fabricated and discuss the results. The patient has experienced no injury to the stomatognathic system, including the lips, for five seasons since he began wearing this set of mouthguards. This new pairing of mouthguards appears to offer sufficient protection against injury, despite severe malalignment. We believe that this new type of paired maxillary and mandibular mouthguards has the potential to reduce sports-related dental injuries.

Does clenching reduce indirect head acceleration during rugby contact?

BACKGROUND: Concussions are common among athletes, with the potential to cause memory-related, physical, cognitive, emotional, and behavioral damage. A concussion is an acceleration/deceleration injury resulting from direct and indirect biomechanical forces transmitted to the cerebral tissues. From a sports dentistry viewpoint, increased mastication muscle activity or clenching due to the presence of a mouthguard may enhance cervical muscle activity, thereby reducing damage following impact. This relationship has not been previously investigated in the context of rugby. The purpose of this study was to investigate the effect of voluntary clenching on indirect head acceleration during attack- and defense-related drills. MATERIALS AND METHODS: A total of 12 high school rugby players participated in the study. Linear acceleration of the head was measured using an accelerometer that took measurements in three axes. Masseter and sternocleidomastoid muscle activities were measured using wireless electromyography. These data were synchronized using digital video imaging software for analysis. The study protocol was approved by the Tokyo Dental College Ethics Committee. RESULTS AND CONCLUSIONS: Within the limitations of this study, the following results were obtained: the activities performed during rugby practice involved relatively small indirect head acceleration and masseter and sternocleidomastoid muscle activities. After the young male rugby players were instructed to clench their masseter muscles, a marked decrease in head acceleration was observed.

Influence of different post-core systems on impact stress: a pilot study.

UNLABELLED: This pilot study compared impact strain at the core and root surfaces between two different post-core systems. MATERIALS AND METHODS: The form of a bovine mandibular front tooth was modified to resemble that of a human maxillary incisor as a test specimen. A cast post and core (Metal PC) and composite resin and glass fiber-reinforced epoxy resin post (Fiber-Resin PC) system were tested. Four gauges were affixed to the buccal and lingual surfaces of the core and root. The specimens were then embedded in a metal mold using dental stone. A pendulum-type device with a pyramid-shaped metal impact object with a titanium alloy head was used to provide 2 different shock forces. Maximum distortion was measured and analyzed. RESULTS: Distortion at the core at each measurement point and total amount of distortion with Fiber-Resin PC was significantly greater (p<0.05) than that with Metal PC against both impact forces. On the other hand, distortion at the root at the buccal measurement point with Fiber-Resin PC was significantly less than that with Metal PC against both impact forces. Total distortion was significantly less with Fiber-Resin PC than that with Metal PC against the greater impact shock. Acceleration with Fiber-Resin PC was significantly less than that with Metal PC against both impact forces. CONCLUSION: Fiber-Resin PC has the potential to protect remaining root against traumatic force. This suggests that a Fiber-Resin PC is more suitable for non-vital teeth against not only occlusal but also traumatic impact force.

Influence of pre-laminated material on shock absorption ability in specially designed mouthguard with hard insert and space.

PURPOSE: We have developed a new type of laminated mouthguard, the Hard & Space mouthguard, which incorporates a hard material insert and a space to prevent contact between the mouthguard and the buccal surfaces of the teeth. The purpose of this study was to investigate the effect of this new design on shock absorption. METHODS: Three types of mouthguard (a conventional laminated EVA mouthguard and two 3-layer type "Hard & Space" mouthguards made of 1.8-mm or 3.0-mm thick pre-laminated material (Konbiplast) and EVA with a 1.0-mm space) were impacted. Shock absorption was measured by means of a pendulum type steel ball impact testing machine at impact distances of 10, 20, and 30 cm and a dental study model with strain gauges attached to the lingual surfaces and an accelerometer fixed to the maxilla. RESULTS: Distortion of the impacted tooth and acceleration of the model were significantly reduced by all types of mouthguard at all 3 impact distances. The effect of the mouthguard was remarkable in terms of tooth distortion: both thicknesses of Hard & Space mouthguard showed more than 90% shock absorption, compared with only approximately 55-78% with an EVA mouthguard. Furthermore, shock absorption with the thicker 3.0-mm Hard & Space mouthguard reached more than 95% at the highest impact power. CONCLUSION: Within the limitations of this laboratory study, Hard & Space mouthguards showed significantly greater buffer capacity than a conventional EVA mouthguard in terms of tooth distortion at the 3 impact powers tested.