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Abstract

Introduction: Controversy about the relationship among masticatory muscles, craniofacial morphology and the orthodontic anchorage preparation has not yet been clarified in the literatures. The purpose of this study was to evaluate whether the vertical facial patterns and masticatory surface electromyography (sEMG) influence the molar anchorage and characteristic orthodontic tooth movement. Methods: Subjects for this study comprised 18 patients with a mean age of 23.7 years who had completed orthodontic treatment with therapeutic symmetric extraction. The sEMG data were acquired at the time of bracket debond. The sEMG of anterior temporalis and masseter muscles were recorded during the rest position and in functional positions. Lateral cephalograms were taken before and after treatment, and the tracings were superimposed to assess orthodontic tooth movement and changes in cephalometric variables. Results: The horizontal movement of upper first molar was 1.77± 1.68 mm, the vertical movement of upper first molar was 0.29 ± 1.06 mm, the horizontal movement of lower first molar was 1.27 ± 0.88 mm, and the vertical movement of lower first molar was 2.10± 1.88 mm. Vertical movement of all upper and lower incisors and first molars were positively correlated to change in facial height. The vertical movement of upper first molar was also positively correlated to initial occlusal angle, and the vertical movement of lower incisor is positively correlated to the change of occlusal plane angle. The sEMG activity in masseter muscles was higher in more vertical and sagittal movements of molars, except greater temporalis sEMG activity at habitual intercuspitation had less vertical movement in upper molars. Conclusion: The sEMG activity in masseter muscles was higher in patients with more vertical and sagittal anchorage loss, whereas greater temporalis Semg activity at habitual intercuspitation related with better vertical control in upper molar. Patients with moderate sEMG activity in masticatory muscles had better control in molar anchorage. Vertical control of upper molars is the key factor related to facial height.

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