For children during the tooth replacement period the six-year-old teeth and the second permanent molars erupt directly behind the milk molars and will not be replaced, while the milk molars will be replaced. 1. Children will start tooth replacement around the age of six. At the age of six, the first permanent molar will erupt directly behind the second milk molar and will not be replaced. When the first permanent molar erupts, it is easy to confuse it with the second milk molar, and clinical attention is needed. 2. The first and second molar will be replaced by permanent teeth at around ten years of age. Generally speaking, X-rays show that there is a permanent tooth germ underneath the molar. Whether or not the big teeth will be replaced by new ones needs to be determined after checking the oral and dental conditions and X-ray films in the hospital.