It is a method recommended by the World Health Organization (WHO) to protect the newly erupted teeth (molar teeth), which simply means to clean the tooth surface without removing any dental tissues, and use a special coating (gutter sealant) to fill the gaps on the tooth surface (mainly the occlusal surface), so that the original uneven tooth surface becomes flat and smooth. On the one hand, this is good for the cleaning of teeth, on the other hand, it also eliminates the accumulation of bacteria and food residues, and is very effective for the prevention of molar sulcus caries. It can only prevent the caries on the occlusal surface of teeth and sulcus, but can not help to prevent the caries on the smooth surface and adjacent surface of teeth; secondly, the sulcus closure will have a certain rate of falling off, and once it falls off, it loses its protective effect. Once it falls off, it loses its protective effect. Therefore, we should not think that we can rest easy after we have done the gutter closure, but we should insist on the good eating habit and oral hygiene habit, and take our children to have oral examination regularly.