Just brushing your teeth before going to bed is not enough. Because brushing cleans the front part of the mouth, which is important to prevent tooth decay. However, after eating food, many residues are left in the back part of the mouth as well as the pharynx and epiglottis. In addition, the content of lysozyme in saliva at night is less than that in daytime, and the bactericidal ability is reduced, and the blood flow becomes slow at night, which decreases the local resistance and so on, so that the bacteria in the mouth can “multiply” and infect the surrounding organs through some mutual channels in the deep part of the mouth. In addition to the fact that the bacteria in the oral cavity can “multiply” and infect the surrounding organs through some mutual channels deep in the mouth, pharyngitis, laryngitis and paranasal sinusitis can occur. So after eating snacks, in addition to brush your teeth, but also drink some plain water to rinse the deep part of the mouth. For children, the most harmful is finger sucking, licking teeth, licking upper lip, biting pencil, biting nails, mouth breathing, etc., which can cause tooth crowding, displacement, open lips and teeth and “envelope”, etc.; eating sweet and greasy food can cause tooth decay. In daily life, adults need to master the 5 aspects of self oral health care: master the scientific brushing essentials; use fluoride appropriately; limit the consumption of sugar and sweets appropriately; conduct oral examination regularly; quit smoking and drinking bad habits. Not brushing teeth or improper brushing method can cause periodontitis and periodontal atrophy; tobacco and bad eating habits such as strong wine, too hot and too spicy diet, eating too fast can cause oral mucous membrane white spots, mucous membrane blood blisters, oral cancer; lateral brushing can cause wedge-shaped defect of teeth; unilateral chewing can cause temporomandibular joint disease as well as dysfunction of contralateral tooth and jaw system and dental caries.