Secondary orthodontics is generally harmless. However, if there is improper oral care during the orthodontic period, there may be gingivitis, calcification of teeth, loose teeth and other hazards. 1. Gingivitis: In the process of orthodontic treatment, plaque and soft tartar are easy to adhere to the aligners, and if they are not removed in time, they will produce a certain amount of stimulation of the gums, which may lead to the occurrence of gingivitis. 2. Tooth sensitivity: wearing aligners for a long time without regular cleaning may lead to tooth demineralization, and some of the teeth will have cold and acid sensitivity. 3. Loose teeth: Since orthodontic treatment is mainly through the pull of external forces, there may be loose teeth in the process of orthodontic treatment. Orthodontic treatment is completed through the alveolar bone shaping, appropriate loosening is normal, it is recommended to eat less hard and sticky food. The loosening will usually resolve on its own after the orthodontic treatment is completed. If the loosening is excessive, medical attention is recommended. In orthodontic treatment, whether it is the first orthodontic treatment or the second orthodontic treatment, it is necessary to choose a regular hospital to visit, pay attention to a light diet during orthodontic treatment, do not chew too hard food, in order to prevent damage to the teeth or gums.