Milk teeth and permanent teeth are the two sets of teeth in human’s life, and there are 20 milk teeth, which are the teeth that start to erupt from the age of 6 months to 2 years old. But the milk teeth will be replaced by permanent teeth, about 6 years old, the first permanent teeth begin to erupt, at the age of 6 to 12 or 13 years old, the permanent teeth gradually erupted, the milk teeth are gradually replaced, at this time all the teeth in the mouth for permanent teeth, a total of 28-32 permanent teeth. The permanent teeth will be used throughout the whole life of a person’s teeth, so we should take care of the teeth, so that the teeth do not suffer from caries, pulpitis and other interference, and we should often take care of the oral cavity and brush the teeth carefully every day.