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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.

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 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.

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.

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 (P0.05). 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.

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 (P0.05). 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.

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).

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 HardSpace 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 HardSpace mouthguard may easily be fabricated. We believe that this new type of mouthguard has the potential to reduce sports-related dental injuries.

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.

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.

The aim of this study was to examine the effect of centrifugal force on rat bone marrow osteoblast-like cells (RBM) in vitro. RBM were seeded and cultured for 2 days. Centrifugal forces were added to the cells in the culture dishes using a centrifuge for 20 min either at 600 rpm or 4,800 rpm. The cells without centrifugation were used as control. The expression of HSP27 mRNA of both experimental groups after addition of centrifugal force for 3 hrs was significantly up-regulated compared with the control group. In the 4,800 rpm groups, the cells showed contracted shapes compared to the controls and the 600 rpm groups after treatment with centrifugal force. The maximum height of each cell in the control group was 2.00 ± 0.33 μm. The maximum height of each cell in the 600 rpm group was 1.50 ± 0.23 μm, and in the 4,800 rpm group it was 1.13 ± 0.23 μm. The proliferation ratio in the 4,800 rpm group at day 3 was significantly higher than in the other group. The expression of type I collagen and alkaline phosphatase (ALP) mRNAs in both experimental groups increased at earlier time periods compared to the control groups. ALP activity revealed no significant difference between the experimental groups and the control group. A centrifugal force of 4,800 rpm might promote the proliferation and early differentiation of rat bone marrow cells.

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.

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.

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 (P0.05; 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.

The manufacture of laminated-type mouthguards requires skill in fusing sheets of mouthguard materials together. Adequate adhesive strength is required to use mouthguards in a stable condition for a long time. Therefore, in this study, the exfoliation test was applied and some treating techniques and conditions that improve the adhesive strength on a laminated surface were examined. Samples were laminated with two pieces of mouthguard material (3 mm thickness) having an adhesive area of 5 x 5 mm2, and whose other end was the holding part. The experimental factors used were as follows: heating time, use of solvent, elimination and direct heating of the laminate surface, colour of materials and water sorption. The result was measured at the time of breakage of the maximum load (N) and the form of destruction was examined. At 165 s of heating time, material failure was shown at under a load exceeding 5.0 N when compared to an untreated condition. Material failure was measured when a solvent was used and during the elimination of the laminated surface at a heating time of 150 s, which is 15 s lesser than in an untreated condition. Material failure was also measured by direct heating on the bonding surface of a second sheet of material at a heating time of 135 s, which is 30 s lesser than in an untreated condition. The differences in colour of the materials influence adhesion. Clear and light coloured materials showed higher adhesion ability. One-way analysis of variance confirmed a statistically significant difference in heating time differences, usage of solvent, elimination, direct heating on bonding surface and colour (P < 0.05). The decrease of adhesive strength by water sorption at 23 degrees and 37 degrees C was not observed significantly. Maximal laminated bond strength can be obtained by minimal heating time and proper treatment with the use of solvent, elimination and direct heating on bonding surface. The differences in the colour of the materials influenced adhesion. Clear and light coloured materials showed higher adhesive ability. Water sorption did not affect the adhesive strength. Therefore, if laminated-type mouthguards were manufactured properly, it can be used for a longer time and in a good condition.

Purpose: The purpose of this article is to review the studies related to dentures published by the members of the Japan Prosthodontic Society.Study selection: A total of 6 original articles published in the Journal of Japan Prosthodontic Society were selected. All articles were related to prosthodontic dentures and published in volume 49 of the journal in 2005.Results: The research project covered oral comfort, oral dryness in denture wearers, care management, and oral condition.Conclusion: This report is to advocate the pursuit of comfort in oral function for dentures and the importance of masticatory function to the health care of people.

When using post materials that are more rigid than teeth for abutment construction, tooth root fracture may be caused by stress concentration in the remaining part of the tooth root. Most of the tooth root fractures clinically observed in metal post abutment cases are longitudinal fractures, resulting in tooth extraction in many cases. In cases with sufficient coronal tooth substance, post-less abutment construction has recently been considered. Fiber posts have recently attracted attention as a post material for resin abutment construction due to their flexibility with elastic modulus similar to that of dentine. In Japan, although approval by the Ministry of Health, Labour and Welfare has recently been obtained, there have been few experimental studies and clinical reports on fiber posts. In this study, we performed a break-down test and finite element analysis of fiber posts as in vitro studies, and reviewed overseas references on clinical results. Experimental results show that, the effects on preventing stress concentration are high in all abutment construction methods when sufficient ferrule in the remaining teeth is present, and stress may be concentrated in the cervical area in fiber post abutment cases. Clinical results obtained from references showed that, fiber posts are superior to cast posts and commercially available metal posts, in terms of fracture and dislodgment. However, since issues were revealed in previous clinical studies, further comparison studies are necessary to evaluate the superiority of fiber posts compared with metal posts.

Some sports' accidents are responsible for inflicting traumatic brain injuries and mandibular bone fractures when impacts occur to the chin. It is often thought that mouth guards can prevent many of these injuries. However, such assertions may be insufficient without adequate research. It is therefore necessary to establish a systematic method of investigation to solve this problem. In the present laboratory study, tests were performed using pendulum impact equipment and an artificial skull model connected to strain gages and accelerometers to simulate and measure the surface distortions related to bone deformation or fractures and the acceleration of the head related to concussions. As impacts, direct blows to the mandibular undersurface were applied. As a result, wearing a mouth guard decreased (P < 0.01) the distortion to the mandibular bone and the acceleration of the head significantly compared with not wearing a mouth guard (54.7%: to the mandible -- measured at a total of three different points, 18.5%: to the head measured at a total of three different points). Within the limits of this study, the following conclusions were drawn: The present measuring system in this study was able to evaluate the distortion to the mandibular and the acceleration of the head from the direct blow to the mandibular undersurface. Mouth guards can reduce distortion to the mandibular and the acceleration of the head from the same blow. So mouth guards might have the possibility to prevent mandibular bone fractures and concussions. However, further well-designed and exhaustive studies are vital to show that mouth guards reduce the incidence of concussions and mandibular bone fractures.

The safety benefits of mouthguards have been demonstrated in many studies, with many authors and sports dentists strongly recommending the wearing of mouthguards. However, wearing a mouthguard with incorrect occlusion might cause a variety of problems. It comes as no surprise that a traumatic blow to the chin, while wearing an insufficient mouthguard lacking anterior contact, can result in severe distortions to the mandibular bone, and bone fractures. The aim of this study was to clarify how ineffective insufficient occlusal supporting mouthguards are and how dangerous they can be to use. Consequently, in this study, occlusal supportive areas were varied and accelerations of head and distortions of the mandible were measured using an artificial skull model and a pendulum impact device. As a result, the distortions of the mandible tended to increase as the supported area decreased. On the contrary, accelerations of the head decreased as the occlusion part decreased. Thus, a lot of impact energy was consumed in the distortion of the mandible; accordingly, it seemed that only a little destructive energy was transferred to the head. From this study, it would seem that wearing a mouthguard, which is insufficient in the occlusion, has the potential of causing a bone fracture of the mandible. Consequently, mouthguards should have proper occlusion.

Most impact force and impact energy absorption tests for mouthguards have used a steel ball in a drop-ball or the pendulum device. However, in reality most sports-related trauma is caused by objects other than the steel ball, e.g. various sized balls, hockey puck, or bat or stick. Also, the elasticity, the velocity and the mass of the object could change the degree and the extent of injuries. In this study, we attempted to measure the impact force from actual sports equipment in order to clarify the exact mechanism of dental-related sports injuries and the protective effects of mouthguards. The present study was conducted using the pendulum impact device and load cell. Impact objects were removable. Seven mobile impact objects were selected for testing: a steel ball, baseball, softball, field hockey ball, ice hockey puck, cricket ball, and wooden baseball bat. The mouthguard material used in this study was a 3-mm-thick Drufosoft (Dreve-Dentamid GmbH, Unna, Germany), and test samples were made of the one-layer type. The peak transmitted forces without mouthguard ranged from the smallest (ice hockey stick, 46.9 kgf) to the biggest (steel ball, 481.6 kgf). The peak transmitted forces were smaller when the mouthguard was attached than without it for all impact materials but the effect was significantly influenced by the object type. The steel ball showed the biggest (62.1%) absorption ability while the wooden bat showed the second biggest (38.3%). The other balls or the puck showed from 0.6 to 6.0% absorbency. These results show that it is important to test the effectiveness of mouthguards on specific types of sports equipment. In future, we may select different materials and mouthguard designs suitable for specific sports.

The purpose of this study was to examine the effect of a continuous compressive force on rat bone marrow osteoblast-like cells in vitro. Approximately 5.0 × 104 cells were seeded into 35 mm dishes and cultured for 24 h. Thereafter a 2.5 × 2.5 × 0.5 cm glass (which would load the cells with approximately 0.9 g/cm2) was placed on the cell layer for 12 h, and then a glass was removed and continued culturing up to 3 days. Cells cultured without loading were used as a control. The cells were observed using both phase contrast microscopy through the transparent glass and scanning electron microscopy after fixing the cells. Quantitative RT-PCR assays for osteopontin mRNA and osteocalcin mRNA were conducted, and alkaline phosphatase activity was also evaluated. The compressed cells were oriented in mesh-like patterns, and were polygonal and flattened in shape. The compressed cells had a significant down-regulation of osteocalcin mRNA, while there were no significant differences in alkaline phosphatase activity or in osteopontin mRNA between the control and the experimental groups. These results suggest that continuous compression of the cells delays the final cell differentiation of the rat bone marrow cells to active osteoblasts.

The aim of the study was to investigate the mechanical properties and energy absorption behavior of mouth-guard materials. Interpretation of indentation force-displacement data has been used to determine these properties.An ultra micro-indentation system (UMIS) was used to determine near surface properties of mouth-guard materials with nanometer and micro-Newton displacement and force resolution. The measurement procedure was conducted with a small spherical steel indenter (R=500 microm), with impressions that were equally spaced (250 microm). Measurements of force-displacement response of surfaces at maximum forces of 10, 40 or 50 mN, 10 indentations were made at each of these forces. Tests were undertaken in two different modes to determine the mechanical properties, namely: (a) continuous load to the maximum force and then unload, (b) multiple loading and partially unloading sequence to the maximum load.The force-displacement results were analysed to determine the elastic modulus and contact pressure versus depth of penetration as well as the energy loss. Energy absorption for each material was determined from the ratio of the hysteresis energy loss to the total energy at maximum load and ranged from 10 to 24% among different mouth-guard materials. Energy absorption ratio, elastic modulus and contact pressure were significantly different between different materials with same thickness (FC, GC and C3) (p0.01) and significantly different between materials with different thickness (C1 and C3) (p0.01).The present approach provides a simple and efficient method to readily measure the elastic-plastic (hysteretic) response of mouth-guard materials. The indentation technique lends itself to investigate the influence of ageing, heat treatment, sterilisation, moisture etc in a simple systematic manner.

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.

The balance adjustments play an important role in orthostatic and dynamic postural control, influencing the ability to perform daily living and sports activities in preventing injuries and improving performances. And a stomatognathic system thought to be involved in postural control. However, the relation between stomatognathic system and the equilibrium function has not been made sufficiently explicit. The purpose of this study was to investigate an effect of an experimentally altering mandibular position on equilibrium using a planar inclination of body and fluctuation in centerof- foot pressure in orthostatic postureanda stepping test. Twelve healthy males (32.45 ± 9.2 years of age) participated as subjects. Rotation angle, transfer angle and transfer distance during the stepping test, and planar inclinations of the body and path length in center-of-foot pressure were determined at before stepping test, using force plates and the VICON motion capture system. Deviation and rest splints were fabricated using soft-and-hard double-layer sheets pressure formed on maxillary and mandibular models: the former was positioned at the edge of the upper and lower canines where they came into contact on the non-habitual chewing side; the latter was positioned at the mandibular rest position. Significantly greater inclination of the cranial, shoulder and pelvic planes and path length in center-of-foot pressure were observed with the deviation splint. And significant increases were observed in rotation angle, transfer distance, and transfer angle with the deviation splint compared with the rest position or with the rest splint. Within the limitations of this study, these results suggest that even the alteration in mandibular position affects equilibrium function.

A full-balanced occlusion is essential for mouthguards. It has been reported that a balanced occlusion for upper and lower anterior teeth is essential for prevention of injuries occurring to the maxillary anterior teeth and alveolar bone caused by horizontal direct impact. The support of the mandibular teeth through the mouthguard is critical to prevent maxillary front tooth injury from a direct impact force. However, some vacuum mouthguard designs may not achieve a full-balanced occlusion. For example, when a player has a malocclusion, an elongated molar or premolar tooth, an open bite, a large over jet or a maxillary protrusion. An improved vacuum fabrication method is necessary to obtain full balanced occlusion in these cases as opposed to conventional vacuum type single-layer mouthguard technique. Language: en

The condition of contact and the distribution of occlusal force is important in the decision of the treatment method and the judgment of the effect of treatment in occlusal examination.This study was performed to investigate the influence of the insertion area of Prescale on the occlusal contact area, occlusal pressure average, and occlusal force for each tooth in normal persons, and the results were as follows:1. The occlusal contact area in forward teeth tended to increase when the insertion area of Prescale was moved forward.2. It was not more prominent than occlusal contact area though occlusal pressure average of forward teeth was increased when the insertion area of Prescale was moved forward.3. When the insertion area of Prescale was moved forward, the occlusal force of forward teeth tended to increase in the prominence compared with the occlusal contact area and occlusal pressure average.4. Due to the results, it was suggested that Dental Prescale is a more effective system to analyze occlusal force than occlusal contact area and occlusal pressure average.

Various attempts have been made to investigate what effects the constitutional elements of a partial denture have on the abutment teeth and how the difference in its design, retention and supporting method affects the abutment teeth. However, no analysis seems to have been reported as to the difference in the capacity of load that the abutment teeth have and the force on the periodontal tissues, which have different dental root shapes.Therefore, the strain in the periodontal membrane of the straight root and curving root shapes were investigated by using the 3-dimensional strain gauge system. The results were as follows:1. In both root shapes, the greater the load, the greater the strain on the periodontal membrane.2. There was a difference in the value and direction of strain between straight root and curving root shapes. Furthermore, the strain on the curving root shape was greater than that on the straight one.

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. Language: en

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.

In order to verify the relation between the body function and occlusion, the gravity function, electronystagmography, and auditory brainstem response of TMD patients, edentulous patients and healthy subjects with 500 μm thick experimental occlusal interference were analyzed, and it was confirmed that occlusal problems impede the auditory system, body's posture adjusting system and vestibule system. Further, when the relation between the occlusal contact and the bodily motor function were compared between healthy subjects and patients whose occlusion had been treated, it was confirmed that there was close relation between the two.Furthermore, from the analysis of human body phenomena of healthy subjects with 100 μm thick experimental occlusal interference, it was confirmed that occlusal problems induced bruxism or continuously aggravated the problem and eventually entailed TMD, as well as changed the function of the autonomic nervous system and provoked emotional stress and sleep disorders.From these results, it was verified that occlusal problems affected the function of the middle ear transmission system, equilibrium sense, auditory brainstem response, function of autonomic nervous system, emotion and sleep and that the occlusal function was closely related to the bodily motor function.

Self-curing resin for tooth crowns is widely used in clinical practice. It has been applied to temporary restoration for reconstruction of occlusion, resin splint in splint therapy, which is a method for temporomandibular disorder, and formation on the occlusal plane to maintain and restore the occlusal relation of the plate denture.However, since the durability of self-curing resin is lower than other dental materials, it is inadequate to maintain and keep stability of the occlusal relation, vertical dimension, durability against attrition and resistance to abrasion due to mechanical friction.Properties is needed. To improve the hardness and abrasion resistance, cyclophosphazene monomer was combined with 4 commercially available self-curing resin monomers and physical properties were compared.1. Hardness increased as the amount of the cyclophosphazene monomer was increased.2. Abrasion resistance improved as the amount of the cyclophosphazene monomer was increased.3. These results show that the combination of the cyclophosphazene monomer with commercially available self-curing resin monomers improves hardness and abrasion resistance.

The basic study of the “Dental Prescale System” was performed using male persons and a plastic study model. We also studied the clinical value of appllying a thin layer of bite-silicone material (BM) to “Dental prescale” Fuji Photo Film Co.(DP). Although the data of occlusal contact area (OCA) with BM was smaller than that without, it was very easy to identify OCA when apllying BM on DP. And as there was no significant difference between the range of fluctation of OCA, the reliability of the data displayed on “Occluser” was attested in this study.

This study was designed to investigate the effects of pulp and different matters in pulp chambers such as core, posts, and artificial coloring cements on teeth color. Namely, we chromatically measured crowns and roots in 20 newly extracted maxillary anterior teeth. Using a spectroradiometer under the following 4 different conditions:(1) free from artificial matters (2) inserting red wax (3) inserting metal core (12% Pd alloy)(4) setting metal core with opaque cement. Further, extracted teeth were compared with natural teeth for crowns.The results were as follows:1. Extracted teeth have higher values of L*, Hab°, and lower a* than natural teeth. It is supposed that these results depend on the lack of hemoglobin in soft tissues.2. Inserting metal core and red wax caused the decrease in L*. And red wax influenced in a* and Hab°.As for color difference, metal core greatly influenced both crowns and roots.3. Effects of opaque cement appears more clearly in crowns than in roots.4. These results revealed that, in both crowns and roots, teeth coloring had affected the pulp and matters in pulp chambers because of its transparency.Therefore, it is important to consider the pulp's condition when treating an esthetic problem.

The effects of artificial occlusal disharmony (AOD) on working memory function and prefrontal cortex (PFC) activity in the elderly were examined. We evaluated working memory function using the modified Sternberg test (ST). We measured activity in the bilateral PFC during ST using near-infrared spectroscopy (NIRS) before and after AOD: the mandibular position was displaced by a splint for 10 min. AOD caused a gradual increase of oxyhemoglobin (oxy-Hb) in the bilateral PFC. The response time of ST (six digits) after AOD was longer than that before AOD. The oxy-Hb increase during ST after AOD was smaller than that before AOD. These results indicate that short-term physical stress caused by AOD decreased working memory function in elderly subjects, associated with a decrease of the evoked PFC activity during working memory function.

The purpose of this study was to investigate the effects of stress on -prefrontal cortex (PFC), emotion (using visual analogue scale, VAS, and State-Trait Anxiety Inventory, STAI), and the autonomic nervous system (ANS). Two types of stress were applied: (1) malocclusion-induced physical stress and (2) mental stress induced by an arithmetic task. Malocclusion was induced using an experimentally deviated mandibular device (EDMD) to obtain an experimentally deviated mandibular position (EDMP). A total of 11 healthy volunteers participated in the study. On day 1 they performed a pretrial arithmetic task followed by a 10-min rest, after which they performed a posttrial EDMD + arithmetic task or rest device + arithmetic task. These two tasks were selected at random and assigned at the rate of one per day. Activity in the PFC tended to show an increase in the pretrial arithmetic tasks and rest device + arithmetic task, but a decrease in the EDMD + arithmetic task compared with the rest device + arithmetic task. Heart rate significantly increased during the rest device + arithmetic task, whereas no significant difference was observed during the EDMD + arithmetic task. The EDMD + arithmetic task significantly increased STAI scores (p = 0.0047), and the significant decrease in VAS indicated "unpleasant" (p = 0.035). These findings suggest that EDMP-induced reduction in the level of PFC activity was a response to discomfort, indicating that EDMP affects systemic function such as that of the ANS as an unpleasant stressor.

The effects of artificial occlusal disharmony (AOD) on working memory function and prefrontal cortex (PFC) activity in the elderly were examined. We evaluated working memory function using the modified Sternberg test (ST). We measured activity in the bilateral PFC during ST using near-infrared spectroscopy (NIRS) before and after AOD: the mandibular position was displaced by a splint for 10 min. AOD caused a gradual increase of oxyhemoglobin (oxy-Hb) in the bilateral PFC. The response time of ST (six digits) after AOD was longer than that before AOD. The oxy-Hb increase during ST after AOD was smaller than that before AOD. These results indicate that short-term physical stress caused by AOD decreased working memory function in elderly subjects, associated with a decrease of the evoked PFC activity during working memory function.

The purpose of this study was to investigate the effects of stress on ­prefrontal cortex (PFC), emotion (using visual analogue scale, VAS, and State-Trait Anxiety Inventory, STAI), and the autonomic nervous system (ANS). Two types of stress were applied: (1) malocclusion-induced physical stress and (2) mental stress induced by an arithmetic task. Malocclusion was induced using an experimentally deviated mandibular device (EDMD) to obtain an experimentally deviated mandibular position (EDMP). A total of 11 healthy volunteers participated in the study. On day 1 they performed a pretrial arithmetic task followed by a 10-min rest, after which they performed a posttrial EDMD + arithmetic task or rest device + arithmetic task. These two tasks were selected at random and assigned at the rate of one per day. Activity in the PFC tended to show an increase in the pretrial arithmetic tasks and rest device + arithmetic task, but a decrease in the EDMD + arithmetic task compared with the rest device + arithmetic task. Heart rate significantly increased during the rest device + arithmetic task, whereas no significant difference was observed during the EDMD + arithmetic task. The EDMD + arithmetic task significantly increased STAI scores (p = 0.0047), and the significant decrease in VAS indicated “unpleasant” (p = 0.035). These findings suggest that EDMP-induced reduction in the level of PFC activity was a response to discomfort, indicating that EDMP affects systemic function such as that of the ANS as an unpleasant stressor.

Various attempts have been made to investigate what effects the constitutional elements of a partial denture have on the abutment teeth: how the difference in its design, retention and supporting method affects the abutment teeth. No analysis, however, seems to have been reported as to the difference in the capacity of load that the abutment teeth have and the force against the periodontal tissues, having different dental root shapes.When examining, under a condition related to clinical cases, what effect the design of the partial denture has on various dental root shapes of abutment teeth, we tried to measure the values of movement under a given load, having different supporting alveolar bone levels and different dental root shapes. Lower second premolar teeth were chosen as comparison teeth and the Sirognathograph analyzing system was employed as a measuring system.The obtained results are as follows:1. As the supporting alveolar bone level became lower, the value of the movement had a tendency to increase.2. In comparison of the partial denture with the vertical tooth root, the one with the curved tooth root under a given load showed lower values in both the mesial and distal movement and the vertical movement.We can conclude, from the above results, that in designing a free-end saddle denture not only the screening of the condition of periodontal tissues is necessary but due consideration should be given to the shape and the curvature of the dental root.

抄録顎口腔系は咀嚼筋を始めとする頭頸部諸筋群, 歯, 顎関節および周辺組織ならびにこれらを支配している神経系などにより成り立っておりこれらが調和することにより, 顎口腔系の機能が営まれる.顎関節症は主に咬合に起因する様々な原因により, これらの調和が崩れることにより起こるとされている.このような顎関節症患者の中には顎口腔系のみでなく全身症状を含む種々の不定愁訴を持つ者も多くみられることから顎口腔系の不調和がそれのみにとどまらず, 全身状態にまで影響が及んでいるのではないかと推測され, 近年この顎口腔系と全身状態との関連についての報告も多くみられるようになってきた.著者らも, これらの関連を探求することを目的とした一連の報告の中で顎口腔系の変化が, 全身状態に与える影響について重心動揺分析システム, 聴性脳幹反応, 眼振図および指尖容積脈波などを用い, 検討を行ってきた.これらの研究の一つとして, これまでに水平的下顎位保持装置を用い, 健: 常者における水平的下顎位の変化が重心動揺および抗重力筋筋活動量に影響を与えることを報告した.そこで今回は水平的下顎位の変化が, 顎関節症患者の直立姿勢にどのような影響を及ぼすかについて検討を行ったところ, 重心動揺, 抗重力筋筋活動量のいずれについてもアペックスに比べ, いずれの水平的下顎位においても, その値は日間変動範囲を越え増加傾向にあるとともに左右側差の大きい者が多く見られる傾向であった.よって, 水平的下顎位の変化は, 重心動揺および筋活動量に影響を与えることから, 顎口腔系の変化は全身状態に影響を及ぼすこと, また, 顎関節症患者においてはすでに全身状態に影響が及んでいるだけでなく, 負荷を加えることによりその影響がより著明に現れる可能性が示唆された.

The purpose of this study was to compare the influence of biting and finger clenching intensity on the concentration of oxygenated hemoglobin (OxyHb) in regional cerebral blood flow (rCBF) as an indicator of brain activity in the primary motor (MI) and somatosensory (SI) cortices. Functional near-infrared spectroscopy (fNIRS) was used in 8 healthy subjects. Subjects were required to do biting (bite) and finger clenching (fclench) at 20, 50 and 80% of maximum force. To minimize the effect of temporal muscle activity on the working side of the jaw, the fNIRS probes were positioned contralaterally, in the left temporal region. Activation of MI and SI cortices with bite and fclench was noted in all subjects, irrespective of the intensity of bite and fclench. A significant increase was observed in OxyHb in MI and SI between 20% and both 50 and 80% intensity. In MI cortex, OxyHb showed a significant increase between 80% and both 20 and 50% fclench intensity. The results suggest that intensity of bite and fclench influences activation levels in MI and SI. Further, an activation was more obvious with bite than fclench.