Objectives : In this explanatory article, we describe some disorders of the teeth and the stomatognathic system that are considered to be caused by bruxism. We also explain the methods for coping with these conditions based on previous evidence-based research, our clinical experience, and the results of our quantitative research on bruxism.
Methods: Sleep and awake bruxism were recorded and analyzed quantitatively with GrindCare^®. Recorded Rhythmic Masticatory Muscle Activity （RMMA） was compared with subjective evaluation and the clinical signs of bruxism.
Results and conclusions: Several systematic reviews have suggested a potential relationship between bruxism and temporomandibular disorders （TMD）, but the reliability is not enough to prove the existence of a direct relationship.
Our quantitative research on bruxism showed an inconsistency between the subjective evaluation of the patient and the objective evaluation of the device. We also found that sleep bruxism increased in many subjects even if their subjective evaluation showed awake bruxism. Moreover, an examination of the relationship among each evaluation factor showed that sleep bruxism increased clinical signs such as tooth wear, but decreased masticatory muscle tenderness. These results do not support the hypothesis that increased sleep bruxism leads to TMD.
There are two methods to cope with bruxism: 1） active control, i.e., reducing bruxism directly; and 2） passive control, i.e., enduring bruxism by constructing a suitable occlusion to counter it. We believe that a combination of these two methods is necessary to prevent the onset of any stomatognathic disorder caused by bruxism. However, because the relationship between bruxism and specific stomatognathic disorders is not clear, the most effective way has not been established. Therefore, further continuous research on bruxism is needed to clarify this topic.

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Sleep bruxism is classified as a sleep-related movement disorder in the International Classification of Sleep Disorders. It is characterized by frequent occurrence of rhythmic masticatory muscle activity （RMMA） during sleep and often causes clenching and RMMA in combination. There are innumerable and wide-ranging harmful effects due to excessive occlusal force, e.g., attrition, root fracture, destruction of prostheses, severe periodontal disease, and temporomandibular disorders. Therefore, when performing dental treatment, it is important to accurately diagnose sleep bruxism and to provide rational care in accordance with a proper diagnosis. In dental practice, conducting a chairside interview and visual/palpation test of the stomatognathic system are important. Sleep bruxism can be classified as primary, in which there is no apparent cause, and secondary, in which a medical etiology is present; a careful review of the patient’s medical history is necessary to differentiate between primary and secondary sleep bruxism. However, the obtained findings comprise only an indirect diagnosis because jaw movement of the patient has not been assessed accurately. The gold standard for diagnosing sleep bruxism is polysomnography （PSG）. By not only measuring the amount of activity of the masticatory muscles during sleep, but also by performing electroencephalography, electrocardiography, measurement of respiration, oxygen saturation, body position, etc., it is possible to understand the physiological status of each patient. In order to perform these measurements, it is necessary for the patient to stay overnight at a sleep lab, which not only imposes a heavy burden on the patient, but also necessitates measurement under an altered living rhythm/sleeping environment. Therefore, it is possible that sleep bruxism may not be accurately detected in the patient. In recent years, a small simple sleep test apparatus utilizing a device capable of accurately measuring sleep bruxism has been developed by putting a pressure-sensitive film in an intraoral splint, allowing the home monitoring of patients. This article reports on the clinical diagnostic methods, management methods and assessment of sleep bruxism and reviews future methodologies.

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Nightguard （NG） is currently used not as a definitive therapy for sleep bruxism （SB）, but as a symptomatic therapy for the purpose of rationally distributing force by occlusal stabilization and protection of the stomatognathic system. It is safe, easy, and has a positive preventive effect. However, there are some reports on the side effects on NG. Dentists should determine whether the patient has SB or not, primary or secondary, or whether it is affected by other factors. Then, we should systematically aim for a definitive therapy of SB. If SB still does not improve, finally NG should be applied. Various types of NG are used according to the area of application, form, jaw position, and material （e.g. stabilization splint, night denture, soft splint, nociceptive trigeminal inhibition tension suppression system, palatal splint, oral appliances for sleep apnea, repositioning splints）. Each of them has different effects and side effects, which must be considered when making a selection. The most commonly used NG is the upper jaw stabilization splint. Despite weak scientific evidence about the occlusion that NG provides, NG should be formed in consideration of the currently known jaw movements of SB and the ideal occlusion in natural dentition. In addition, after wearing the NG, it is necessary to plan how to use it and to check it regularly.

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Objectives: Pharyngeal airway dilator muscles are very important for maintaining upper airway patency. The purpose of this study was to improve our understanding of the physical characteristics of patients with obstructive sleep apnea （OSA） by measuring muscle stiffness in the submental region in healthy persons as a first step.
Methods: Eleven normal dentulous persons （6 males, 5 females; mean age 26.9±1.58 years） without stomatognathic dysfunction were enrolled in this study. Muscle stiffness of the submental region was measured at the habitual occlusal position （HOP）, the maximum mandibular protrusive position （MPP）, and the tongue protrusive position （TPP） at random. All study protocols were in full accordance with the Declaration of Helsinki and approved by the ethics committee at Kyushu Dental University （approval number: 18-28）. All subjects provided written, informed consent.
Results: Muscle stiffness of the submental region was significantly higher at the MPP and at the TPP than at the HOP in all subjects and in male subjects. There was a significant difference between the HOP and the MPP in female subjects. There were no significant differences between the genders.
Conclusion: These results suggest that the suprahyoid and genioglossus muscles play a role in maintaining protrusion of both the mandible and tongue.

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