Generally, children start to change their teeth gradually at the age of 5 and a half to 6 years old, and the fact that they haven’t lost their teeth at the age of 8 years old may be due to developmental delay, hardness of the milk teeth, and malposition of the permanent embryos. 1. Developmental delay: some children may develop slowly, delayed, if the early speech is late, late eruption of milk teeth, etc., may affect the time of tooth replacement, resulting in the replacement of delayed, lagging and so on. 2. The milk teeth are too hard: If it is because the root of the milk teeth is too hard, it grows more stably in the dental bed and hinders the eruption of the permanent teeth, thus making it difficult for the permanent teeth to grow and leading to non-loss of teeth. 3. The position of permanent teeth embryo is not correct: If the position of permanent teeth embryo is not correct, there is no way to stimulate or press the root of milk teeth, which leads to the milk teeth are not easy to fall off and the permanent teeth are not easy to erupt, or it may be due to congenital lack of permanent teeth embryo, which leads to the delay of tooth replacement. If you are 8 years old and have not lost your teeth, it is recommended that you go to the hospital for an examination to find out the cause.