The first permanent molars behind the milk molars are also called “six-year-old teeth” because they erupt around the age of six. The newly erupted “sixth-aged teeth” are not very strong, and the unpolished occlusal surface is uneven, the sulcus is deep, easy to accumulate food residues and plaque, and not easy to clean, so they are eroded by the acid produced by bacteria, and are easy to develop caries. The “sixth age tooth” is a very critical tooth in the mouth, which has a great influence on the position of other permanent teeth that will erupt later, and plays an important role in maintaining the beauty of facial shape. If parents mistakenly think that this tooth is a milk tooth and will be replaced sooner or later, and do not treat the caries in time, so that finally it has to be extracted, the whole mouth teeth are like losing a “pillar”, which not only affects the chewing function, but also can cause the front and back teeth to be misaligned, forming malocclusion, and can affect the facial appearance. We can use the method of sulcus closure to level the deep sulcus of the occlusal surface before the occurrence of dental caries, so that the food residue and plaque are not easy to accumulate and achieve the effect of preventing dental caries. In addition, because the “six-age teeth” erupt early and grow quietly behind the last milk molar, they are often mistaken as milk teeth, and the caries is not treated in time at the early stage, and when it becomes painful, it has been destroyed quite seriously, and even has to be extracted in the teenage, which is regrettable for the whole life. In order to avoid this situation, you should take your child to the hospital for dental examination regularly. When you can’t tell whether the problem is with the baby teeth or permanent teeth, you should go to the hospital and ask the doctor to help solve the problem.