Abstract:

Objective Three-dimensional finite element analysis was used to compare the mechanical effects of double rectangular attachments on the molar mesial movement with clear aligner. Methods Four groups of the three-dimensional finite element model on the molar mesial movement with clear aligner was derived from a cone-beam CT(CBCT)scan data and then built in the software of Mimics, Geomagic Wrap, Unigraphics Nx and Ansys Workbench: Model A with a horizontal rectangular attachment of 5 mm long on mesiobuccal side, model B with double horizontal rectangular attachments of 3 mm long on mesiobuccal and mesiolingual side, model C with double horizontal rectangular attachment of 3 mm long on mesiobuccal and distobuccal side, model D with double vertical rectangular attachments of 3 mm long on mesiobuccal and distobuccal side. Four models were used to analyze the initial tooth displacement, tension-compression pattern at the periodontal ligament and Von Mises stress in mesial alveolar fossa. Results ①In the four models, the mandibular first molars achieved mesial tipping movement. The total displacement and inclination of mandibular first molars were as follows: Model B>model C>model D>model A. The retention force of the attachment and the displacement of the molars were proportional to the inclination of molars. The differences among the three groups of model A, C and D were small. ②The maximum values of periodontal ligament stress on the mesiodistal surface of the mandibular first molar and the maximum Von Mises stress on the mesial surface of the alveolar fossa were as follows: Model B>model C>model D>model A, which was confirmed by the displacement of mandibular first molars. Conclusion ①Only rectangular attachments have mesial tipping movement on the molar mesial movement with clear aligner; ②The attachment can increase the retention force of the molars in the clear aligner. The retention force of the attachment and the displacement of molars are proportional to the inclination of molars; ③The retention force of a horizontal rectangular attachment of 5 mm long on mesiobuccal side, double horizontal rectangular attachments of 3 mm long on mesiobuccal and distobuccal side and double vertical rectangular attachments of 3 mm long on mesiobuccal and distobuccal side are moderate, and the displacement and inclination of molars are moderate. The actual molar movement is more in line with the expected design of the clear aligner, and the aligner is less likely to fall off. It is suggested that when the molars move mesially in clear aligner, the above three attachments should be designed on the molars.

Key words: clear aligner, rectangular attachment, mesial movement, stress, finite element analysis