Before orthodontic treatment, two x-rays are usually taken: 1. Full jaw surface tomography: It can provide a comprehensive understanding of the position relationship of teeth, number of teeth, root development, and jaw joint situation. 2.Lateral cephalometric film: From the analysis of X-ray film, we can understand the mechanism and etiology of malocclusion and formulate a reasonable orthodontic treatment plan. There are two types of models: 1. Memory model: record the size and position of the teeth before and after orthodontic treatment, and the occlusal relationship of the alveolar bone. The analysis of the model can help to develop a treatment plan. 2. Working model: used to make orthodontic appliances, retainers, etc. on it.