Abstract:

Objective The expression rates and the side effect movements of teeth were analyzed after the mandibular molar distalization treated by the invisible aligner. Methods A total of 24 patients who accepted the mandibular molar distalization by the invisible aligner were selected. A three-dimensional coordinate system was established, and the landmarks of crowns and roots of the molars and incisors were located using the pre-treatment and post-treatment CBCT. The coordinates of crowns and roots, the inclinations and torques of the teeth were obtained. The expression rates of tooth movements were calculated by comparing the actual movement and the preset movement. The side effect movements of teeth were studied by paired t-test by comparing the changes in coordinates of incisors and molars in the unplanned movement direction and the inclinations and torques of the teeth. Results The moving expression rate of the crown of mandibular first molar was the highest, which was up to 71%. The side effect movements like the depression and buccal tilt of the molars could happen during the process of mandibular molar distalization by the invisible aligner(P<0.05), but the side effect movements of incisors were not significant(P>0.05). Conclusion The invisible aligner has a high expression rate of tooth movement in mandibular molar distalization, and the expression rate of crown is larger than root. However, attentions should be paid to reduce depression and buccal tilt of the molars during tooth movement.

Key words: mandibular molar distalization, invisible aligner, expression rate of tooth movement