J Shanghai Jiaotong Univ Sci ›› 2021, Vol. 26 ›› Issue (3): 377-382.doi: 10.1007/s12204-021-2308-2

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Effects of Mandibular Extractions with Clear Aligners: A Finite Element Analysis

FENG Qiping (冯齐平), CHU Fengting (储沨婷), CHEN Rongjing (陈荣敬), PAN Xiaogang  (潘晓岗)   

  1. (Department of Orthodontics, Shanghai Ninth Peoples’ Hospital, College of Stomatology, Shanghai Jiao Tong University
    School of Medicine, National Clinical Research Center for Oral Diseases, Shanghai Key Laboratory of Stomatology &
    Shanghai Research Institute of Stomatology, Shanghai 200011, China)
  • 出版日期:2021-06-28 发布日期:2021-06-02
  • 通讯作者: PAN Xiaogang (潘晓岗) E-mail:xgpan70@126.com
  • 基金资助:
    the Clinical Research Program of Ninth
    People’s Hospital affiliated to Shanghai Jiao Tong University
    School of Medicine (No. JYLJ-10)

Effects of Mandibular Extractions with Clear Aligners: A Finite Element Analysis

FENG Qiping (冯齐平), CHU Fengting (储沨婷), CHEN Rongjing (陈荣敬), PAN Xiaogang  (潘晓岗)   

  1. (Department of Orthodontics, Shanghai Ninth Peoples’ Hospital, College of Stomatology, Shanghai Jiao Tong University
    School of Medicine, National Clinical Research Center for Oral Diseases, Shanghai Key Laboratory of Stomatology &
    Shanghai Research Institute of Stomatology, Shanghai 200011, China)
  • Online:2021-06-28 Published:2021-06-02
  • Contact: PAN Xiaogang (潘晓岗) E-mail:xgpan70@126.com
  • Supported by:
    the Clinical Research Program of Ninth
    People’s Hospital affiliated to Shanghai Jiao Tong University
    School of Medicine (No. JYLJ-10)

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摘要： This study was aimed at analysing the mechanical characteristics of different mandibular extraction  modes using a clear aligner. Three experimental schemes of different extraction patterns were designed to treat  mandibular crowding, including extraction of one mandibular central incisor, bilateral first premolars, and bilateral  second premolars. The stress distribution during the space closing was analysed using the finite element method.  When a central incisor was extracted, a significant retraction force was found in the anterior region, in line  with the design expectation. The posterior teeth, which were designed to move mesially, acted as anchorage for  anterior retraction, and were subjected to a mesial force. The anterior teeth were retracted when the bilateral  first premolars were extracted. The lateral incisors and canines were subjected to a significant distal force and  moment, while the central incisors and canines were subjected to lingual forces and moments. Additionally, the  canines were subjected to a non-designated intruding force. The molars were designed to move mesially when the  bilateral second premolars were extracted. All molars were subjected to a significant mesial force, while the lingual  force on the front teeth was slight. The bilateral second molars were subjected to non-design mesial moment and  extrusive force. The bilateral first molars were subjected to a non-designated mesial moment, and the bilateral  first premolars on both sides were subjected to non-designated intrusive force and distal moment. When one  incisor was extracted, attachments on the anterior teeth had a controlling effect on the tooth axis, but the anterior  teeth still tended to tilt. When the bilateral first premolars were extracted, the anterior teeth showed a tendency  for lingual inclination. The risk of distal inclination of the canines and lingual inclination of the central incisor  increased. When the bilateral second premolars were extracted and the posterior teeth were designed to move  mesially, the teeth on both sides of the extraction sites showed an obvious bowing effect. 

Abstract: This study was aimed at analysing the mechanical characteristics of different mandibular extraction  modes using a clear aligner. Three experimental schemes of different extraction patterns were designed to treat  mandibular crowding, including extraction of one mandibular central incisor, bilateral first premolars, and bilateral  second premolars. The stress distribution during the space closing was analysed using the finite element method.  When a central incisor was extracted, a significant retraction force was found in the anterior region, in line  with the design expectation. The posterior teeth, which were designed to move mesially, acted as anchorage for  anterior retraction, and were subjected to a mesial force. The anterior teeth were retracted when the bilateral  first premolars were extracted. The lateral incisors and canines were subjected to a significant distal force and  moment, while the central incisors and canines were subjected to lingual forces and moments. Additionally, the  canines were subjected to a non-designated intruding force. The molars were designed to move mesially when the  bilateral second premolars were extracted. All molars were subjected to a significant mesial force, while the lingual  force on the front teeth was slight. The bilateral second molars were subjected to non-design mesial moment and  extrusive force. The bilateral first molars were subjected to a non-designated mesial moment, and the bilateral  first premolars on both sides were subjected to non-designated intrusive force and distal moment. When one  incisor was extracted, attachments on the anterior teeth had a controlling effect on the tooth axis, but the anterior  teeth still tended to tilt. When the bilateral first premolars were extracted, the anterior teeth showed a tendency  for lingual inclination. The risk of distal inclination of the canines and lingual inclination of the central incisor  increased. When the bilateral second premolars were extracted and the posterior teeth were designed to move  mesially, the teeth on both sides of the extraction sites showed an obvious bowing effect. 

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