Easy fabrication of a new type of mouthguard incorporating a hard insert and space and offering improved shock absorption ability.

The positive effects of wearing a mouthguard have been indicated in various epidemiological surveys and experiments, and their usage appears to be increasing in many sports. However, many preventable sports-related dental injuries still occur even with the use of a conventional mouthguard. We have developed a mouthguard (the Hard & Space mouthguard) with sufficient injury prevention ability (more than 95% shock absorption ability against impact with a steel ball carrying 15.2 kg m(2) S(-2) potential energy) and ease of clinical application. This mouthguard consists of an outer and an inner EVA layer and a middle layer of acrylic resin (hard insert), with a space to prevent contact between the inner surface of the mouthguard and the buccal surfaces of the maxillary front teeth or teeth already weakened through prior damage or treatment. The purpose of this article is to describe the method by which the Hard & Space mouthguard may easily be fabricated. We believe that this new type of mouthguard has the potential to reduce sports-related dental injuries.

Effect of experimental horizontal mandibular deviation on dynamic balance.

PURPOSE: There are two aspects of human balance: static balance and dynamic balance. However, to the author's knowledge, no studies have investigated how changes in the stomatognathic system influence dynamic balance. This aim of this study was to determine the effect of horizontal mandibular deviation on stability of upright posture on an unstable platform in order to clarify the relationship between the stomatognathic system and the dynamic balance. METHODS: Fifteen healthy adult participants were selected. To determine the effect of changes in the stomatognathic system on dynamic balance, three experimental conditions were established: a resting mandibular position, a position in which experimental horizontal mandibular deviation was maintained by a splint, and a mandibular rest position maintained by a splint. Each participant was instructed to stand in a natural upright posture on an unstable board, and resulting variation in angle of the board was then measured. Measurements were taken 15 times under each condition. RESULTS: Variation in angle of inclination of the board as dynamic balance was the largest in the splint-maintained deviated mandibular position. CONCLUSION: Horizontal deviation in mandibular position interfered with stability of upright posture on an unstable platform, suggesting that changes in the stomatognathic system affect dynamic balance.

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.

Are all mouthguards the same and safe to use? Part 2. The influence of anterior occlusion against a direct impact on maxillary incisors.

The purpose of this study was to clarify the influence anterior occlusion, of mouthguards, has on protecting against a direct collision to the maxillary anterior teeth. In other words, the support mandibular dentition has when wearing a mouthguard. Two types of mouthguards were used for this study, one with an appropriate anterior occlusion or a mouthguard with positive anterior occlusion (MGAO+) and another which was a single-layer mouthguard lacking the same occlusion or a mouthguard with negative anterior occlusion (MGAO-) but with the same thickness on the buccal side. The instruments used for testing were a pendulum-type impact device with two interchangeable impact objects (a steel ball and a baseball), with a plastic jaw model having artificial teeth. Four testing conditions were observed: one with the jaw open without a mouthguard (Open NoMG), the second with the jaw clenching (loaded with 30 kg weight) without a mouthguard (Clench. NoMG), the third with the jaw clenching with MGAO- (Clench. MGAO-) and the last with the jaw clenching with MGAO+ (Clench. MGAO+). The results are as follows: both types of mouthguards showed the effects in reducing the distortion of the teeth. However, the effect was significantly obvious (steel ball = about 57% shock absorption ability, baseball = about 26%) in the mouthguard with anterior occlusion or support by lower dentition through mouthguard (Clench. MGAO+) than Clench. MGAO-. Thus, the influence of anterior occlusion of mouthguards or the support of mandibular dentition through wearing a mouthguard (MGAO+) is indispensable in reducing the impact force and tooth distortion. The results of this research should further contribute to the establishment of guidelines for safer mouthguards.

Expression of myosin heavy-chain mRNA in cultured myoblasts induced by centrifugal force.

Ballistic muscle training leads to hypertrophy of fast type fibers and training for endurance induces that of slow type fibers. Numerous studies have been conducted on electrical, extending and magnetic stimulation of cells, but the effect of centrifugal force on cells remains to be investigated. In this study, we investigated the effect of stimulating cultured myoblasts with centrifugal force at different speeds on cell proliferation and myosin heavy-chain (MyHC) mRNA expression in muscle fiber. Stimulation of myoblasts was carried out at 2 different speeds for 20 min using the Himac CT6D, a desk centrifuge, and cells were observed at 1, 3 and 5 days later. Number of cells 1 and 5 days after centrifugal stimulation was significantly larger in the 62.5 x g and 4,170 x g stimulation groups than in the control group. Expression of MyHC-2b mRNA 1 day after centrifugal stimulation was significantly higher in the 2 stimulation groups than in the control group. Almost no expression of MyHC-2a was observed in any group at 1 and 3 days after centrifugal stimulation. However, 5 days after stimulation, MyHC-2a was strongly expressed in the 2 stimulation groups in comparison to the control group. Three days after centrifugal stimulation, expression of MyHC-1 was significantly higher in the 2 stimulation groups than in the control group. The results of this study clarified the effect of different centrifugal stimulation speeds on muscle fiber characteristics, and suggest that centrifugal stimulation of myoblasts enhances cell proliferation.

Effects of stretching stimulation with different rates on the expression of MyHC mRNA in mouse cultured myoblasts.

In vivo studies have shown that changes in the characteristics of skeletal muscle fiber are determined by type of exercise or training. These earlier studies on mechanical stimulation, however, have all employed stimulation applied at a constant intensity, and no studies appear to have investigated change with variation of intensity of stimulation. In this study, we investigated the characteristics and differentiation of myoblasts stretched at different rates. Myoblasts were stimulated at 3 different rates, and the numbers of cells and nuclei on days 1, 3, and 5 were compared. The myosin heavy chain (MyHC) mRNA expression level was also compared. We investigated expression of MyHC-perinatal to determine speed of differentiation of myoblasts, and expression of MyHC-2b, 2d, and 2a to ascertain muscle cell characteristics. Counting cells and nuclei of myoblasts revealed clear promotion of differentiation with stretching. With rapid stretching, expression of MyHC-perinatal was high at first, but then showed a decrease. In terms of effect on muscle fiber characteristics, MyHC-2b, MyHC-2d, and MyHC-2a were high with rapid, medium, and slow stretching, respectively. This indicated that myoblast differentiation was promoted regardless of difference in stretching speed, with the myoblasts acquiring the muscle-fiber characteristics appropriate to each rate of stretching.

Does hard insertion and space improve shock absorption ability of mouthguard?

Mouthguards are expected to reduce sports-related orofacial injuries. Numerous studies have been conduced to improve the shock absorption ability of mouthguards using air cells, sorbothane, metal wire, or hard material insertion. Most of these were shown to be effective; however, the result of each study has not been applied to clinical use. The aim of this study was to develop mouthguards that have sufficient prevention ability and ease of clinical application with focus on a hard insertion and space. Ethylene vinyl acetate (EVA) mouthguard blank used was Drufosoft and the acrylic resin was Biolon (Dreve-Dentamid GMBH, Unna, Germany). Three types of mouthguard samples tested were constructed by means of a Dreve Drufomat (Type SO, Dreve-Dentamid) air pressure machine: the first was a conventional laminated type of EVA mouthguard material; the second was a three layer type with acrylic resin inner layer (hard-insertion); the third was the same as the second but with space that does not come into contact with tooth surfaces (hard + space). As a control, without any mouthguard condition (NOMG) was measured. A pendulum type impact testing machine with interchangeable impact object (steel ball and baseball) and dental study model (D17FE-NC.7PS, Nissin, Tokyo, Japan) with the strain gages (KFG-1-120-D171-11N30C2: Kyowa, Tokyo, Japan) applied to teeth and the accelerometer to the dentition (AS-A YG-2768 100G, Kyowa) were used to measure transmitted forces. Statistical analysis (anova, P < 0.01) showed significant differences among four conditions of NOMG and three different mouthguards in both objects and sensor. About acceleration: in a steel ball which was a harder impact object, shock absorption ability of about 40% was shown with conventional EVA and hard-insertion and about 50% with hard + space. In a baseball that was softer compared with steel ball, a decrease rate is smaller, reduction (EVA = approximately 4%, hard-insertion = approximately 12%, hard + space = approximately 25%) was admitted in the similar order. A significant difference was found with all the combinations except for between EVA and hard-insertion with steel ball (Tukey test). About distortion: both buccal and lingual, distortions had become small in order of EVA, hard-insertion, and hard + space, too. The decrease rate is larger than acceleration, EVA = approximately 47%, hard-insertion = 80% or more, and hard +space = approximately 98%, in steel ball. EVA = approximately 30%, hard-insertion = approximately 75%, and hard + space = approximately 98% in baseball. And a significant difference was found with all the combinations (Tukey test). Especially, hard + space has decreased the distortion of teeth up to several percentages. Acceleration of the maxilla and distortions of the tooth became significantly smaller when wearing any type of mouthguard, in both impact objects. But the effect of mouthguard was clearer in the distortion of the tooth and with steel ball. Considering the differences of mouthguards, the hard-insertion and the hard + space had significantly greater buffer capacity than conventional EVA. Furthermore, hard + space shows quite high shock absorption ability in the tooth distortion. Namely, hard + space has decreased the distortion of teeth up to several percentages in both impact objects.

[Mouthguard effect of tooth distortion during clenching].

PURPOSE: A mouthguard can protect stomatognathic systems from traumatic damage. However, severe occlusal wear of teeth and loss of teeth have often been found in players clinically. These problems might originate in strong clenching during sports. Although it is thought that a mouthguard may be effective for these types of clenching, the relation between mouthguards and clenching has not been sufficiently examined. In this study, the effect of a mouthguard (Drufosoft 3mm, EVA) on tooth distortion caused by clenching was measured and examined at three different clenching strengths. METHODS: As a test tooth, a lower first molar was selected. A strain gauge applied to the outer surface of the buccal cusp was used to measure the distortion. A muscle balance monitor (GC) was used to regulate clenching strengths (10, 50, and 100%). The maximum-effort clenching without a mouthguard was assumed to be the 100% clenching strength. Measurements were conducted with or without mouthguard. A maximum value during clenching was assumed to be date of distortion by using analytical software AcquKnowledge (BIOPAC System Inc.). Statistical analysis software SPSS (SPSS Japan Inc.) was used for the Mann-Whitney test. RESULTS: 1. The tooth distortion by clenching, regardless of the presence of the mouthguard, increased as clenching power strengthened, from 10, 50 to 100%. 2. The tooth distortion, regardless of strength of clenching, was decreased by wearing the mouthguard in all subjects. At 50 and 100% clenching, it was decreased significantly by the mouthguard in all subjects. CONCLUSIONS: Mouthguards decreaseed the tooth distortion caused by clenching. Therefore, a mouthguard may prevent not only traumatic injuries in contact sports but also damage to teeth and periodontal tissues and so on, which occur due to frequent strong clenching in many sports.