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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.

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.

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 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

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.

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.

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.

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 elucidate the influence of bite force control on oxygenated hemoglobin (OxyHb) levels in regional cerebral blood flow as an indicator of brain activity in the premotor area. Healthy right-handed volunteers with no subjective or objective symptoms of problems of the stomatognathic system or cervicofacial region were included. Functional near-infrared spectroscopy (fNIRS) was used to determine OxyHb levels in the premotor area during bite force control. A bite block equipped with an occlusal force sensor was prepared to measure clenching at the position where the right upper and lower canine cusps come into contact. Intensity of clenching was shown on a display and feedback was provided to the subjects. Intensity was set at 20, 50 and 80% of maximum voluntary teeth clenching force. To minimize the effect of the temporal muscle on the working side of the jaw, the fNIRS probes were positioned contralaterally, in the left region. The findings of this study are: activation of the premotor area with bite force control was noted in all subjects, and in the group analysis OxyHb in the premotor cortex was significantly increased as the clenching strengthened at 20, 50 and 80% of maximum voluntary clenching force. These results suggest there is a possibility that the premotor area is involved in bite force control.

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.

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.

Heat-curing resin is mainly used as denture base materials. But, recently, visible light curing resin and its curing unit have been developed by Dentsply Co. to be on the market.According to this method, resin in the dough form directly put on the stone cast, is irradiated with visible light for a short time, while being formed to be polymerized. By applying this method, troublesome management process which is required in the conventional heat-curing method can be omitted. Furthermore, the polymerization time can be shortened.Then, the authors, in the present study, purposing to make use this visible light curing denture base resin of clinical application, examined its mechanical properties.It proved that visible light curing resin, compared with heat-curing resin, was small in transverse deflection, transverse strength, tensile strength and water sorption, large in Rockwell hardness and nearly equall in Els. modulus and solubility.

The purpose of this study is to reveal the relation between condition ofstomatognathic system and condition of whole body.First of all, in this study taking notice of human posture especially about right standing posture, so we have examined influence of occlusal interference on right standing posture by using analyzing system of the locus of the body's gravity center.The subjects were consist of nine normal adult men and measured with eye closed, closed feet position for 20 minutes.As a result, Occlusal interference has made the diameter, the total length and the area ofthe locus followed by the body's gravity center tend to large value of it's late.

Recently, Visible light curing resin has been on the market. This type of resin has advantage that troublesome technical process can be omitted and polymerization time can be greatly shortened in comparison with the conventional heat curing resin. But, there are few research reports related to this resin. Then, in this study, we examined its physical properties and fitness. As the results, it could be noted that hardness was changed by the visible light irradiation time. Furthermore, in the case of resin was separated and irradiated, gap between resin and mold was very small.

In the present study, the authors examined the junctional strength of visible light-curing denture base resin and resin teeth in comparison with that of conventional heat-curing resin. The results obtained were as follows : 1) When visible light-curing resin was used as the resin block on which resin teeth were implanted, the fracture strength for resin teeth having retention holes in the basal planes, was approximately 1.5 times as large as that for teeth with no retention holes. Also, samples in which the resin tooth surface was treated with dichloromethane had a value approximately twice as large.2) When heat-curing resin was used as the resin block on which resin teeth were implanted, employing visible light-curing resin for repair, the fracture strength was small in comparison with the values obtained for specimens described in 1).