Whether the retained milk teeth must be extracted or not can be decided according to the specific situation, sometimes they need to be extracted, sometimes they can be temporarily retained, and sometimes they can always be retained, as follows: 1. Extraction: If chronic periapical inflammation occurs in the milk teeth and adhesions are formed with the surrounding tissues, such as the slow resorption of the roots of the milk molars, and the crowns of permanent teeth are located below the root bifurcation, they can be extracted as early as possible to prevent them from obstructing the eruption of permanent teeth and causing 2.Temporary retention: If the permanent teeth have erupted in the wrong position and are far away from the milk teeth, and the X-rays also show that the milk teeth have long roots, the milk teeth can be temporarily retained to maintain the arch length, while wearing movable orthodontic appliances, traction permanent teeth to move to the jaw plane, and then extract the milk teeth. 3.Reservation: If the other teeth in the whole mouth have been replaced, and the milk teeth in individual positions are not yet loose, and the X-rays show that there is no If the permanent tooth germ is not present, the baby teeth can be retained until the baby teeth fall out on their own in adulthood.