Abstract: BACKGROUND: When invisible appliances are used in tooth extraction, canine distal movement is a retraction pattern that is beneficial to save the anchorage of posterior teeth and resist the arch effect of braces. However, canine distal movement changes the wrapping of braces around the teeth and the vacuole elasticity due to tooth extraction using the appliance, and relieves the constraint to the movement of adjacent teeth, which may have an impact on anterior tooth intrusion.
OBJECTIVE: To study the effect of canine distal movement on anterior tooth intrusion in invisible orthodontic treatment by using finite element method 
METHODS: The mandibular finite element model of the subtractive first premolar was established, including teeth, periodontal ligament, alveolar bone, invisible appliance, and accessories. Step-by-step intrusion of the anterior teeth was conducted through simulation of clinical canine distal movement. In control group, the canines did not move. In experimental group 1, the canines moved 1 mm away, while in experimental group 2, the canines moved 1/3 of the extraction space. The effect of canine distal movement on anterior tooth intrusion was analyzed. 
RESULTS AND CONCLUSION: The maximum anterior tooth intrusion occurred in the experimental group 1, with the vertical displacement of the canine incisal edge by 0.017 867 0 mm, the vertical displacement of the central incisor by 0.009 647 0 mm, and the vertical displacement of the lateral incisor by 0.007 777 5 mm. The minimum anterior tooth intrusion occurred in the control group, with the vertical displacement of the canine incisal edge by 0.008 195 3 mm, the vertical displacement of the central incisor by 0.005 238 0 mm, and the vertical displacement of the lateral incisor by 0.005 689 2 mm. In the experimental group 2, the canine incisal edge moved 0.014 463 0 mm vertically, the central incisor moved 0.009 294 7 mm vertically, and the lateral incisor moved 0.007 013 9 mm vertically. In all cases, the von Mises stress of anchorage molars was smallest, the displacement of the incisor edge was greater than that of the root apex, and the stress appeared differently between the labial and lingual sides of the periodontal ligament. To conclude, canine distal movement can improve intrusion in the anterior teeth by appliance. However, different distal displacement has different effects on anterior tooth movement. The closer the anchor tooth is to the target tooth, the greater the force is, and vice versa. Invisible orthodontic treatment is mainly for inclined and intruded anterior teeth. 

Key words: orthodontic treatment, clear aligner, orthodontic extraction, anterior tooth intrusion, canine distal movement, finite element analysis