It is possible that when a child reaches the period of tooth replacement and new teeth are late, there are individual differences. The average age for a child to change teeth is until about 6-7 years old, but there are relatively large individual differences in the timing of tooth replacement, with some children starting to change teeth at 7-8 years old. Therefore, if a child is more than two years behind the normal age and no new teeth have erupted, it is recommended to go to the hospital for a clinical examination and, if necessary, to take pictures to see if there is a congenital absence of permanent teeth, etc. Generally speaking, if the whole tooth is not replaced at the age of 7-8 years, it is possible that the tooth replacement is late and there is nothing to worry about. If there are individual teeth that have not been replaced, but symmetrical teeth have been replaced and new teeth have erupted, this situation should be examined by radiographs because there may be individual differences in the overall age of tooth replacement. However, there is more clinical value in the sequence of tooth replacement, especially in the pattern of symmetry of the eruption of new teeth.