Clinically, it is common to see patients who grind their teeth at night; in life, there are also friends who have the symptoms of grinding their teeth. “Why do you grind your teeth at night?” “How to treat night grinding teeth to be effective?” Are two questions that are often asked by patients or friends. When it comes to night grinding, we have to talk about the oral parafunction. We all know that the main functions of the oral cavity are chewing, speech, pronunciation and maintaining facial appearance. So what is oral parafunction? Some research points out that oral parafunction is the unconscious state of human sleep, temporomandibular junction, teeth, teeth and other anatomical structures occurring non-physiological jaw movement, manifested in the clinical is grinding teeth syndrome. Under normal circumstances, the occlusion of the upper and lower teeth occurs in the waking state, and due to the protective neuromuscular reflexes, the person can clearly perceive how much force he or she is using and should bite in that one position. Teeth grinding is a phenomenon in which the teeth are subjected to a certain intensity of occlusal force in an unconscious state, while the jaw moves in a certain rhythm or shows a tendency to move more. It is characterized by intermittent isotonic contractions of the jaw muscles and is accompanied by regular chewing-like movements. Teeth grinding can occur in people of any age, with children and young adults being the most common. It can be divided into three types, one is the grinding type, often grinding teeth at night after sleep, also known as night grinding. The second is the clenching type, often unconsciously clenching the teeth during the day when concentrating, but there is no upper and lower teeth grinding phenomenon. The third is a mixed type, both night grinding and daytime clenching of teeth. So “why does the phenomenon of night grinding occur?” There is no exact cause, but it may be related to the following factors. (1) Dental occlusal factors Incongruent occlusion is considered a major factor in teeth grinding, including malocclusion, missing teeth, missing or overgrown teeth, and unilateral chewing. Orthodontic or lateralized early contact is the most common initiating factor for bruxism. During the period of teething, most children have an uncoordinated occlusal relationship, and the high point of contact causes the upper and lower teeth to not match well, so the patient often has a subconscious intention to make most of the teeth close contact, and this daytime intention becomes a spasm and contraction of the masticatory muscles during sleep and triggers nighttime teeth grinding. ②Neurological factors Some experts believe that night grinding is a manifestation of sleep disorder, and its appearance is related to the mild awakening abnormalities in sleep. Research on the central nervous system and neurochemistry shows that the occurrence of teeth grinding is related to abnormal changes in dopamine and norepinephrine of the central nervous system messaging. ③ Psychosomatic factors Mental stress is also considered to be one of the causes of teeth grinding disorder. At present, the pace of society is accelerating, people are under more and more pressure, some people are emotionally tense, overworked or children play too excited or overstressed during the day will also cause the night can not calm sleep, even after sleep there is still a part of the cerebral cortex in an excited state, resulting in the contraction of the chewing muscle and the occurrence of teeth grinding. Tooth grinding patients often have anxiety, tension, depression and other psychological immaturity and other characteristics, and the higher the degree of anxiety, the higher the frequency of tooth grinding. ④ Systemic factors Intestinal parasitic infections, gastrointestinal dysfunction, endocrine imbalance, allergic disorders, vitamin D deficiency rickets, uric acidosis, hyperthyroidism, bladder stress, etc. may cause teeth grinding disorder. When children accumulate food, poor digestion, so that the absorption of toxins secreted by bacteria in the gastrointestinal tract stimulate the cerebral cortex, so that its excitation or inhibition process is dysfunctional, resulting in night grinding teeth. ⑤ Genetic factors Some studies have shown that childhood teething disorder often persists, may be related to genetic factors, the elder parents suffer from teething disorder, the chances of children suffering from teething disorder will have increased. In conclusion, teeth grinding is a “multifactorial” oral parafunction. It is associated with dental, psychosocial, gastrointestinal, psychiatric and genetic factors.