Nocturnal grinding refers to an oromaxillary facial movement that occurs at night characterized by repetitive (staged, more than 3 times, more than 0.5 s each) or persistent (tonic, more than 2 s) contractions (greater than 20% of the EMG value during strong occlusion) of the ascending jaw muscles (chewing muscles, temporalis muscles, etc.) [1]. Nocturnal teeth grinding is characterized by grinding or knocking of teeth during sleep, sometimes accompanied by sound. Clinical examination of patients with chronic teeth grinding may reveal abnormal wear planes on the teeth. Patients who grind their teeth at night may also have accompanying symptoms such as headache, facial muscle pain and fatigue, temporomandibular joint symptoms, dental hypersensitivity, and chewing muscle hypertrophy. The place it plays in the occurrence of orofacial pain and temporomandibular joint disorders is receiving increasing attention. Patients with nocturnal teeth grinding have a prevalence of up to 8% in the population [2] and is one of the common diseases in dentistry. Although nocturnal grinding itself does not cause serious health disorders, it can significantly affect the sleep and even the quality of life of nocturnal teeth grinding patients and their cohabitants. Patients with severe nocturnal teeth grinding should take active treatment measures. For a long time, the cause of nocturnal teeth grinding has not been fully understood, and there is no specific and scientifically proven treatment method. The traditional etiology believes that due to abnormal disturbance or daytime mental tension, the center is overexcited, resulting in abnormal contraction of the masticatory muscles at the end of the overexcited center during the night when there is no conscious control. In the last decade, this view has changed. There is a tendency to believe that occlusal factors are not the cause and that tension is only part of the pathogenesis [3]. Many studies suggest that nocturnal teeth grinding is a manifestation of sleep disorders [4,5,7,8]. Its appearance is associated with abnormalities of mild arousal during sleep, and abnormalities of central nervous system messaging mediators such as dopamine and norepinephrine are also involved in the occurrence of nocturnal teeth grinding. The symptoms of nocturnal teeth grinding can be reduced or disappeared after administration of botulinum toxin or the β-adrenergic blocking agent tretinoin. We review the results of studies on the neuromuscular system and sleep aspects of nocturnal teeth grinding in the past 10 years, and show the possible treatments that have been applied in clinical practice. 1.Study on the occurrence of nocturnal teeth grinding during sleep: observation of sleep state is the basic method to study nocturnal teeth grinding. In a study by Sjoholm et al [4], the total contraction time of the chewing muscles was 11.6 min per night in night grinders compared to 6.6 min per night in healthy subjects, and the average number of contractions, contractions and rhythmic jaw movements of the chewing muscles were about two to three times higher in grinders than in healthy subjects. et al [5] showed that patients with teeth grinding disorder tend to have maxillofacial and body pain, some with autonomic nervous system symptoms and headache on rising in the morning. On average, the molar-like chewing muscles contracted 79 times per night, and the symptoms of teeth grinding started after an average of 18 min into sleep. Keren Wang [6] observed a shortened stage 2 sleep period, prolonged rapid eye movement (REM) phase, and a higher proportion of REM phase in nocturnal teeth grinding than in controls. Teeth grinding occurs in different sleep periods. deep sleep and REM periods were delayed in nocturnal teeth grinders in Sjoholm’s experiment. tachibana et al [7] found that teeth grinding occurred only in the REM period and was often synchronized with hand movements and vocalizations. The patients had normal non-REM and REM cycles, but the frequency of REM was increased. Bader et al [5] investigated that teeth grinding mostly occurs during sleep stage 2 and REM sleep. One third of sleep phase transitions occurred in the first minute of the onset of teeth grinding. 15% of teeth grinding occurred after sleep phase transitions. He believes that arousal occurs as a small alert response to internal and external stimuli and is often accompanied by teeth-grinding-like movements and an increase in heart rate. Macaluso et al [8] also emphasized that nocturnal teeth grinding is a phenomenon related to wakefulness. They compared the sleep structure of teeth grinders and non-teeth grinders and showed that the number of transient awakenings was significantly higher in teeth grinders compared to the control group. The occurrence of teeth grinding was evenly distributed between non-REM and REM periods, but occurred more frequently in stages 1 and 2 than in slow-wave sleep. Eighty-eight percent of the teeth grinding in non-REM periods was related to the interaction cycle pattern and occurred during the transient awakening period. Most of the above experiments show that teeth grinding occurs more often in stage 2 sleep and is associated with the transition between deep and light sleep during the sleep period. The number of rapid eye movement and light awakening period is significantly increased in those who grind their teeth at night than in those who do not grind their teeth. 2, the central nervous system neurochemical research: the neurochemical mechanism affecting the sleep state of teeth grinders is still not fully understood. There are many studies suggesting that the central dopamine and adrenaline system may be related to the pathophysiology of nocturnal teeth grinding. The areas of the central nervous system associated with sleep and wakefulness are mainly in the basal forebrain area and the limbic system. These systems can activate or decrease the excitability of cortical neurons by stimulating or inhibiting the neuronal up-activation system of the midbrain reticular formation. Neurotransmitters are involved in the transmission of neural impulses at chemical synapses. Currently, a number of studies have investigated the functional state of neurotransmitters and receptors associated with sleep. Among neurotransmitters, catecholamines (including acetylcholine, dopamine, norepinephrine and epinephrine) and 5hydroxytryptamine have physiological functions related to wakefulness and sleep [9]. Acetylcholine has the effect of inhibiting slow-wave sleep, promoting fast-wave sleep, and maintaining wakefulness. Central adrenaline plays a role in maintaining the wake and sleep cycle. The central action of norepinephrine is excitatory in nature. Stimulation of the blue spot where norepinephrinergic neurons are concentrated induces fast-wave sleep and rapid eye movements. Lobbezoo et al [10] investigated the function of dopamine D2 receptors in the brain by single photon emission CT (SPECT) after intravenous administration of specific dopamine D2 receptors that antagonize radioligands to teeth grinding and healthy controls. The results showed that there was no significant difference in the intra-striatal D2 receptor bundle potential between the molar group and the control group. However, the difference between the left and right sides of the molar group was significantly larger than that of the control group, suggesting that the imbalance between the two sides of D2 receptors may be related to the occurrence of nocturnal molar. Areso et al [11] gave plastic crowns to the lower anterior teeth of experimental rabbits to cause occlusal imbalance. 14 d later, changes in neurochemical indicators such as dopaminergic and noradrenergic agonistic activity in the striatum, anterior cortical lobes, and subthalamus were observed. 1 d later there was a significant increase in dopa accumulation. The dopamine level in the hypothalamus and the amount of dopamine and noradrenaline in the precortical lobes also increased simultaneously. 14 d later, the dopamine accumulation in areas other than the left striatum normalized, but there was an imbalance between the two hemispheres. This suggests that the imbalance of occlusion can cause a modulatory response of central catecholamine neurotransmission. All of the above experiments suggest that the function of the left and right side of the brain dopa system is in an unbalanced state when teeth grinding occurs. 3, psychosocial research: teeth grinding disorder is thought to be related to the psychosocial characteristics of patients and their ability to withstand. Most studies support this view, but some investigations have concluded that there is no significant difference between patients with and without teeth grinding.DaSilva et al [12] showed that the group with pathological wear of teeth had significant specific anxiety than the control group.JorgicSrdjak et al [13] studied the temperament and personality characteristics of patients with teeth grinding disorder according to Cloninger’s 7-factor model. They were found to have a tendency to be exploratory, impulsive, impatient, pessimistic, fearful, easily fatigued, and dissociated. The combined characteristics were judged to have an impression of immaturity.Pierce et al [14] investigated the relationship between EMG, self-conscious tension, and certain personality traits in 100 nocturnal teeth grinders for 15 consecutive d. There was no significant relationship between EMG results and personality and mental tension, but those who believed that there was an association between mental stress and teeth grinding had higher mental stress.Fischer and O′toole [15] examined the personality characteristics of molar patients and non-grinding controls using a questionnaire to determine chronic teeth grinding based on tooth wear surfaces. The examination revealed that the molar group was shy, cautious, aloof, stubborn, susceptible to internal sensations, had difficulty expressing themselves, were restless, and were anxious than the control group. 4, the relationship between bruxism and other muscle movements: Watts et al [16] investigated 59 patients with head and neck muscle dystonia, in which involuntary jaw movements and eyelid spasms were the most common symptoms of onset, and 78.5% of them had bruxism. Weideman et al [17] conducted a questionnaire survey of 152 parents of children with nocturnal conditions. The results showed that the five items of nocturnal muscle spasms, bedwetting, colic, salivation during sleep, and sleep talking differed significantly between children who grind their teeth and those who do not. It showed the presence of common sleep disorder under idiosyncratic paradoxical sleep disorder.Okeson et al [18] observed increased heart rate during teeth grinding in nocturnal molar patients. There was no significant relationship between nocturnal teeth grinding and foot movements during sleep. Major et al [19] suggested that increased mental and physical alertness may be a characteristic of nocturnal teeth grinders. However, examination of the reaction time, response error rate, ECG, and EMG of teeth grinders did not reveal significant differences from controls. Recently, some studies have analyzed the muscle characteristics of teeth grinders by examining muscle biochemistry and metabolism. marcel et al [20] examined the chewing muscle status of teeth grinders and non-grinders using spectral MRI. The mean inorganic phosphorus and creatine phosphate and 5′ triphosphate triadenosine peaks were collected during resting and repeated chewing. Total phosphorus and creatine phosphate amounts were significantly lower in teeth grinding patients compared to non-bruisers. This suggests that compared to non-grinders, teeth grinders have altered phosphorus metabolism at rest and show a different pattern of phosphorus metabolism during mastication. 5, treatment of teeth grinding disorder: there is no specific treatment method that can completely stop teeth grinding, clinical treatment of night grinding is mainly to reduce the damage brought by teeth grinding to the oral and maxillofacial system, reduce the symptoms of muscles and joints for the purpose of treatment in the following ways: (1) reduce brain excitement: Zarcone [21] advocated rest and relaxation before bedtime, do appropriate gymnastics, avoid excitatory Zarcone [21] advocated resting and relaxing before bedtime, doing appropriate gymnastics, avoiding excitatory foods and smoking, and improving the sleep environment to reduce the excitement of the brain. Mobilization of the patient’s self-control of the psychological role to reduce the occurrence of teeth grinding. (2) muscle relaxation training: muscle relaxation training is an allopathic treatment. Some people have tried to use myoelectric biofeedback of chewing muscle to make patients control muscle contraction can effectively reduce the degree of teeth grinding. Transcutaneous electrical neuromuscular stimulation (TENS) is commonly used in the treatment of masticatory muscle dysfunction.Frucht et al [22] administered this stimulation to the temporalis and masticatory muscles of patients with teeth grinding and healthy controls, and performed EMG spectral and harmonic analysis. Treacy [23] used muscle aware relaxation training (MART) to treat nocturnal teeth grinding. Patients sat straight for relaxation training of body muscles and breathing habits during various postures. Quinn [24] reported that Isokinetic and stretching exercises could help correct or prevent the pathological and functional changes caused by teeth grinding. (3) Arousal stimulation during sleep: This method uses biofeedback to cause the patient to be awakened by an electrical signal such as sound when teeth grinding occurs, thereby temporarily stopping it. clark et al [25] performed temporary afferent electrical stimulation of the lips, which was effective in controlling teeth grinding. watson [26] tried the effect of arousal and past correction on nocturnal teeth grinding. However, this method disturbed the sleep of the patient and co-inhabitants, and the effect was not long-term. (4) Use of occlusal pads: In order to protect the teeth and reduce wear, patients are often asked to wear a monomandibular all-dentition flat stable occlusal pad or a pressure-formed soft elastic occlusal pad while sleeping. There are many different reports on the effect of wearing occlusal pads, and there are also different experimental results on the effect of increasing or decreasing muscle activity. Domestic scholars have used a maxillary occlusal pad with a vertical wing to restrict mandibular lateral movement compulsively, which is effective in the control of bruxism. Keren Wang observed a significant reduction in the time and number of teeth grinding after the stable occlusal pad was worn. However, the investigation by Holmgren et al [27] showed that occlusal pads did not stop nocturnal teeth grinding. All patients had small abrasive surfaces in the same position and shape on the occlusal pads. Although the question of whether occlusal pads can reduce nocturnal grinding has not been fully proven, the effect of reducing tooth wear and maxillofacial pain is relatively clear. (5) Medication: Medication is gradually reported in recent years. The main focus is to try to adjust the oromaxillofacial dyskinesia and muscle dystonia. Topical botulinum toxin (BTX) has been effective in the treatment of dyskinesia.Tan and Jankovic [28] injected BTX type A into both chewing muscles of patients with perennial teeth grinding, and most stopped grinding immediately to 4 weeks after the injection. Only one case developed dysphagia. Ivanhoe et al [29] reported a case of complete cure in a patient with severe teeth grinding after treatment with BTXA. There are also studies that attempt to directly affect the levels of the central and dopa systems.Amir et al [30] reported cases in which acute nocturnal grinding symptoms that appeared as a side effect of antipsychotics were relieved after the use of the beta-adrenergic blocker,心得安. It is suggested that in addition to dopamine, epinephrine and the central nervous system are also involved in the development of pathological teeth grinding. The effective response of medically induced teeth grinding to the use of benztropine suggests the potential of benztropine as a therapeutic agent for nocturnal teeth grinding.Sjoholm et al [31] reported that the use of benztropine controlled chewing muscle mobility during nocturnal teeth grinding.Lobbezoo et al [32] studied the role of the dopamine system in nocturnal teeth grinding through the use of low short-term doses of L dopa and benserazide.L dopa significantly reduced the number of teeth grinding in teeth grinders and also resulted in L dopa significantly reduced the number of teeth grinding in teeth grinders and also resulted in a significant decrease in electromyographic levels during teeth grinding. In addition, relief of pharmacological molarity has been reported with the smart-improving drug buspirone and serotonin reuptake inhibitors [33]. It has also been reported that teeth grinding can occur secondary to long-term use of antidopamine or antidepressant drugs, and that teeth grinding disappears with anxiolytics plus bupropion [34,35]. Levodopa, for example, can cause schizophrenia-like manifestations or exacerbate schizophrenia symptoms. Therefore, pharmacological treatment requires special caution and should be considered only when other treatments are ineffective.