Tomotaka Takeda

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 authors 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.

Does clenching reduce indirect head acceleration during rugby contact

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

Instrumented indentation characterisation of mouth-guard materials

OBJECTIVES 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. METHODS 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. RESULTS 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) (p<0.01) and significantly different between materials with different thickness (C1 and C3) (p<0.01). SIGNIFICANCE 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.

A vacuum technique to increase anterior thickness of athletic mouthguards to achieve a full-balanced occlusion.

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.

Functional Near-Infrared Spectroscopy Study on Primary Motor and Somatosensory Cortex Response to Biting and Finger Clenching

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.

Effects of Occlusal Disharmony on Working Memory Performance and Prefrontal Cortex Activity Induced by Working Memory Tasks Measured by NIRS

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.

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

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

Effects of Experimental Horizontal Mandibular Deviation on Stepping Test of Equilibrium Function

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.

Paired maxillary and smaller mandibular mouthguard for rugby player with malalignment

A rugby player who had frequently experienced soft tissue injuries while playing rugby and wearing a conventional custom-made mouthguard came to the hospital clinic. The patient had suffered traumatic soft tissue injuries such as lip lacerations and bite trauma. Severe crowding due to ectopic maxillary and mandibular canines was observed. In response to the patients 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.

Crystallization and hardening of poly(ethylene-co-vinyl acetate) mouthguards during routine use

Mouthguards (MGs) made from poly(ethylene-co-vinyl acetate) (EVA) are widely used in contact sports to prevent injuries such as breaking teeth and lip lacerations and to reduce brain concussion. However, the changes in morphology and the molecular mobility of EVA, which can affect its physical properties during practical usage, have not been precisely examined. Therefore, we attempted to determine the main factors which lead to changes in MG performance after one season of practical use by high school rugby players. Solid-state nuclear magnetic resonance (NMR) and pulse NMR measurements showed the hardening of MGs, which was associated with an increased crystallinity of the EVA resulting from prolonged usage. Furthermore, our data indicated that the increase in the relative amount of the crystalline phase may be primarily attributed to temperature fluctuations and repeated changes in pressure, which could cause the hardening of EVA and eventually diminish the protective ability of MGs.