The action of teeth grinding is caused by the continuous contraction of the masticatory muscles. The masticatory muscles are innervated by the 3rd, motor branch of the trigeminal nerve. 1, mental factors. The patient’s emotions such as fear, anger, resistance and especially anxiety, which cannot be expressed for some reason, will try to be relieved by grinding the teeth. 2, central nervous mechanism. Nocturnal teeth grinding is an involuntary subconscious action like sleepwalking, enuresis, and nightmares, and is a symptom of partial arousal of the brain during sleep, which is a central source of sleep disturbance related to daytime emotions, triggered by internal or external, psychological or physiological sleep-disturbing stimuli. If children are overly excited during the day, or those who work too much during the day and are too busy and tired at night before bedtime, although most of the cerebral cortex is in a state of inhibition after falling asleep, a part of the brain (e.g., the trigeminal nerve in the pons) will be in a state of arousal. Thus, it will send a “signal” to order the chewing muscles of the face to make a short sustained contraction. So the sleeping person will be manifested as involuntary jaw up and down, left and right back and forth movement, which issued a “squeak” sound of teeth grinding. 3, dental factors. Nervous individuals, any dental (occlusal) interference may be the trigger factor of teeth grinding disorder; teeth changing period of the relationship between the wrong, resulting in masticatory muscle movement disorders, spasm and contraction. 4, other factors of the whole body. Gastrointestinal disorders related to parasites, children’s nutritional deficiencies, blood glucose and calcium concentrations, endocrine disorders, perverse reactions and other factors may become the pathogenesis of nocturnal bruxism. In some cases there is a genetic component. In addition, uric acidosis, hyperthyroidism, allergy, bladder stress disorder may be related to nocturnal teething disorder. 5, occupational factors. Automobile drivers, athletes, demanding high precision work such as clockwork, all have a tendency to nocturnal grinding of teeth.