Head injuries caused by contact with teeth during sports and exercise activities in Japanese schools during the period 2012-2018.

BACKGROUND/AIM: During sports activities, teeth-related contact can cause injury to both ally and opponent players, which can lead to potential infections and aesthetic problems. However, the extent of such injuries remains unclear. This study aimed to clarify the frequency and situation of head injuries caused by teeth (HICBT) occurring under the supervision of schools in Japan. MATERIAL AND METHODS: HICBT records were extracted from the Japan Sport Council data on head injuries occurring reported during the 7-year period from 2012 to 2018 under the supervision of schools in Japan. RESULTS: Of the total 463,527 head injury cases during the study period, 4495 cases (approximately 1%) were HICBT. Of the HICBT cases, 3650 (81.20%) were related to sports and athletic activity. Such injuries were reported to occur most often during basketball with a rate of 57.07% and 50.43%; soccer/futsal was the next most common sport with a rate of 13.38% and 24.01% in junior high school and high school students. Tag games were responsible for a similar number of HICBT cases at 22.73% and 39.03% in kindergartens and elementary school students. CONCLUSIONS: A total of 4495 cases of HICBT were identified, accounting for about 1% of all head injuries under the supervision of schools in Japan during the study period. This result reminds us that our teeth could be the weapon against the players during sports events. HICBTs occurring during basketball and soccer/futsal, in which mouthguards are not mandatory, were conspicuous among junior and senior high school students. Active use of mouthguards in various sports will protect players as well as their teammates and opponents. Sports dentists should encourage the revision of rules, such as mandating the use of mouthguards, in popular sports with a high incidence of HICBT, such as basketball and soccer/futsal.

Improving light-cured intermediate resin for hard and space mouthguard using a glass fiber.

BACKGROUND/AIMS: A light-cured intermediate material is useful for fabricating a hard insert and a buffer space mouthguard (H&SMG). However, it requires improvement in its mechanical properties and shock-absorbing capacity. The aim of this study was to evaluate the mechanical properties of two prototype light-cured intermediate materials reinforced with glass fibers, and the impact absorption capacity and durability of H&SMGs made with the prototype intermediate materials. MATERIALS AND METHODS: Two prototype materials containing long and microlength glass fibers in a light-cured intermediate material, Innerframe LC®, for H&SMG, were fabricated and tested. A three-point bending test was performed for evaluation of the mechanical properties. In addition, a shock absorption test was conducted using a customized pendulum impact testing machine to evaluate the H&SMGs' impact absorption capacity and durability. RESULTS: Long and microlength glass fibers significantly improved flexural modulus and strength. H&SMGs made with these two glass fiber-containing materials had high impact absorption capacity against both low and high impact forces, while the mouthguards made with long glass fiber materials had the best results. CONCLUSION: Long and microlength glass fibers with the prototype materials improved the mechanical properties of Innerframe LC® and the impact absorption capacity and durability of H&SMGs. H&SMGs made with the long glass fiber prototype materials had the best performance.

Jaw-Clenching Intensity Effects on Masseter Oxygen Dynamics and Fatigue: A NIRS Oximetry Study.

The purpose of this study was to clarify the effects of jaw-clenching intensity on masseter muscle oxygen dynamics during clenching and recovery and masseter muscle fatigue using the spatially resolved method of near-infrared spectroscopy. Pulse rate, mean power frequency from electromyography in the masseter and visual analogue scale for masseter fatigue were also examined as related items. The 25% and 50% maximum voluntary contractions were determined using electromyography before the experiment and used as visual feedback on the screen. Twenty-three healthy adult male subjects volunteered for this study. Clenching decreased oxygen and oxygenated haemoglobin, and increased deoxygenated haemoglobin in the masseter muscle. The higher the intensity of clenching, the more prominent the effect. The oxygen dynamics tended to return to normal after clenching, but the change was slower with higher clenching intensity. Pulse rate increased with clenching, and the increment was more prominent with higher clenching intensity. Clenching caused a shift of mean power frequency to a lower range, an increase in subjective fatigue, an early appearance of a breakpoint appearance time and a prolongation of a 1/2 recovery time. All of these effects were more evident with increasing clenching intensity. In conclusion, clenching intensity influenced the oxygen dynamics of the masseter muscle and fatigue state during clenching and recovery. The higher the intensity, the greater the impact.

Effect of Vinyl Acetate, Glass Fibers Contents, and Buffer Space on EVA's Mechanical Property and Shock Absorption Ability.

OBJECTIVES: The aim of the study was to evaluate the mechanical properties and impact absorption capacity of prototype materials comprising ethylene vinyl acetate (EVA) of different hardness reinforced using different amounts of glass fibers (GFs), considering a buffer space. MATERIALS AND METHODS: Six prototype materials were made by adding E-GFs (5 and 10 wt%) to EVA with vinyl acetate (VA) contents of 9.4 wt% ("hard" or HA) and 27.5 wt% ("soft" or SO). Durometer hardness and tensile strength tests were performed to evaluate the mechanical properties of the materials. Moreover, an impact test was conducted using a customized pendulum impact tester to assess the impact absorption capacity (with or without a buffer space) of the specimens. RESULTS: The mechanical properties of the prototypes, namely, durometer hardness, Young's modulus, and tensile strength, were significantly higher in the HA group than in the SO group, regardless of the presence or added amount of GFs. The addition of GFs, particularly in a large amount (10 wt%), significantly increased these values. In terms of the impact absorption capacity, the original hardness of the EVA material, that is, its VA content, had a more substantial effect than the presence or absence of GFs and the added amount of GFs. Interestingly, the HA specimens with the buffer space exhibited significantly higher impact absorption capacities than the SO specimens. Meanwhile, the SO specimens without the buffer space exhibited significantly higher impact absorption capacities than the HA specimens. Moreover, regardless of the sample material and impact distance, the buffer space significantly improved impact absorption. In particular, with the buffer space, the impact absorption capacity increased with the added amount of GFs. CONCLUSION: The basic mechanical properties, including durometer hardness, Young's modulus, and tensile strength, of the EVA prototype were significantly increased by reducing the amount of VA regardless of the presence or added amount of GFs. Adding GFs, particularly in large amounts, significantly increased the values of aforementioned mechanical properties. Impact absorption was significantly affected by the hardness of the original EVA material and enhanced by the addition of the buffer space. The HA specimen had a high shock absorption capacity with the buffer space, and the SO specimen had a high shock absorption capacity without the buffer space. With the buffer space, impact absorption improved with the amount of added GFs.

Effects of Mouthguards on Skin Damage In Vitro Study.

OBJECTIVE: Mouthguards can prevent and reduce orofacial sports traumas, which occur to the players themselves. However, the effect of mouthguards on skin damage has not been clarified. The present study's purpose was to examine whether the mouthguard can reduce or prevent skin damage caused by teeth (including the difference in mouthguard thickness). MATERIALS AND METHODS: Pigskins, artificial teeth, and Ethylene-vinyl acetate (EVA) mouthguard blanks with 1.5- and 3.0-mm thickness were employed. Each of the two type mouthguards was produced in 10 replicates. Mouthguard incisal thickness and collision touch angle were measured on a PC using imaging software. A pendulum-type machine was used to apply impact. Strain gauges attached to the tooth and impacted plate were used to measure mouthguards' effect on impact stress. Also, a microscope was used to observe the after impacted skin condition, and the extent of damage was assessed as a score. RESULTS: The pigskin was ruptured in without mouthguard (NOMG) with presenting the highest damage score, whereas the complete rupture was not seen in the 1.5 mm MG, but the damage of the skin (defeat) was observed. No tissue change was found with the 3 mmMG. In both the flat plate and impact tooth strain, no significant difference was observed between NOMG and 1.5 mmMG. However, 3 mmMG had a significantly smaller value than the other two conditions. These results are likely to be strongly influenced by the mouthguard incisal thicknesses and collision touch angles differences. CONCLUSION: The present study results clarified that two different thickness mouthguards reduced the skin damage, and the thicker mouthguard showed more effectiveness. Therefore, mouthguards may prevent the wearer's stomatognathic system's trauma and avoid damage to the skin of other athletes they are playing with. This effect seems to be an essential basis for explaining the necessity of using mouthguards for others besides full-contact sports.