Abstract: Objective: To correct the dentition midline position of the terminal state on the patient's oral scanning image in invisible appliance, to solve the problems of poor stability, low efficiency, and limitation of orthodontist experience in determining dentition midline in orthodontic clinics, and to provide more accurate reference for the orthodontic treatment. Methods: 12 malocclusion patients treated with invisible orthodontic treatment were selected according with the standard conditions. The CBCT images of each patient were matched with the oral scanning images before orthodontic treatment to determine the median sagittal reference plane by combining the three-dimensional digital reconstruction model of skull on the three views of the CBCT image. The plane was mapped to the oral scanning model to determine the midline adjustment, and the midline adjustment value of the dentition obtained from the study was compared with the midline adjustment of the dentition value initially designed by the expert orthodontists. Results: The maximum deviation of the adjusted value for the dentition midline obtained in this study was 0.46 mm and the minimum deviation was 0.05 mm compared with the adjusted value designed by the expert orthodontists (P>0.05). The consistency was good. Conclusions: The method can effectively determine the dentition midline position of the terminal state in the oral scanner image, and it helps the junior orthodontists to determine the dentition midline and arrange the teeth by using invisible appliance.

Key words: invisible treatment, dental midline, median sagittal reference plane, oral scanning image, CBCT image