Abstract:

 Objective  To investigate the effect of en-masse retraction of maxillary anterior teeth by rocking-chair archwire（RCA） in sliding mechanics. Methods  The three dimensional finite element model of maxillary teeth was created based on spiral CT data of a patient by ANSYS software. The forces on each tooth and the torques on the six center of resistance（CR） of the anterior teeth induced by the deformation of RCA with different depth and anterior retraction hook（ARH） with different height were calculated when retracted from a mini-implant between the first molar and the second premolar. The movements of anterior teeth were observed combining different depth of RCA with different height of ARH. Results  The clockwise torque in sliding mechanics to realize en-masse retraction of the anterior teeth could be counterbalanced by RCA of certain depth. The combination of 7.2 mm ARH and 2 mm RCA can be used to intrude and retract maxillary anterior teeth under the condition of applying mini-implant. Conclusion  The excessive retraction that usually exists in traditional treatments can be avoided by RCA in sliding mechanics and intru- sion and torque control during anterior segment retraction can also be achieved by this method.

Key words: rocking-chair archwire, sliding mechanics, en-masse retraction, three dimensional finite element