Both brushing and flossing are means to maintain oral hygiene, and there is no difference between who comes first and who comes second. Brushing is mainly used to remove plaque and food debris from the surface of teeth, while flossing is mainly used to remove food debris and bacteria contained in the gap between two teeth. Usually brushing is done once in the morning and once in the evening, which can effectively reduce the accumulation of plaque on the surface of the teeth in the mouth and reduce the formation of tartar, and can also prevent caries. Flossing is usually used after meal, which can clean the food residue between teeth more deeply than toothbrush, and can effectively avoid the formation of tartar between two teeth, and can prevent the caries on the adjacent surface of teeth. However, it should be said that neither brushing nor flossing can prevent the formation of plaque 100%, and it is still recommended to clean teeth regularly every six months to a year.