American journal of orthodontics and dentofacial orthopedics : official publication of the American Association of Orthodontists, its constituent societies, and the American Board of Orthodontics · 2022
The effects of aligner overtreatment on torque control and intrusion of incisors for anterior retraction with clear aligners: A finite-element study.
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Liu Lu, Song Qinxuan, Zhou Jing, Kuang Qianyun, Yan Xinyu, Zhang Xiaoqi, Shan Yue, Li Xiaolong, Long Hu, Lai Wenli
Аннотация
INTRODUCTION: The objective of this study was to analyze the effects of aligner overtreatment on torque control and intrusion of incisors for anterior retraction with clear aligners.
METHODS: Models including a maxillary dentition without first premolars, maxilla, periodontal ligaments, attachments, and aligners were constructed and imported to finite-element software. Two groups of models were created: (1) without canine attachment and (2) with canine attachment. Overtreatment degrees (0°, 1°, 2°, 3°, 4°, and 5°) were applied for both groups.
RESULTS: Clear aligner therapy caused lingual tipping and extrusion of incisors, distal tipping and extrusion of canines, and mesial tipping and intrusion of posterior teeth, which was more significant with canine attachments except for second premolars. Aligner overtreatment produced palatal root torquing and intrusion of incisors, distal tipping of canines, and mesial tipping of second premolars, with more significant in the condition with canine attachments. With canine attachments, 1.2° overtreatment could cause bodily retraction of central incisors. Without overtreatment, stress was concentrated on apical and cervical area of both labial and lingual surfaces of periodontal ligaments. The stress value was higher with canine attachments. However, when overtreatment was added, the stress was distributed more evenly.
CONCLUSIONS: Clear aligner therapy produced lingual tipping and extrusion of incisors during anterior retraction. Overtreatment can achieve incisor intrusion and palatal root torquing, and the effect could be augmented by adding attachments on canines, which required more anchorage from posterior teeth. Appropriate overtreatment with placing attachments on canines should be designed to ensure bodily retraction and the least root resorption.
METHODS: Models including a maxillary dentition without first premolars, maxilla, periodontal ligaments, attachments, and aligners were constructed and imported to finite-element software. Two groups of models were created: (1) without canine attachment and (2) with canine attachment. Overtreatment degrees (0°, 1°, 2°, 3°, 4°, and 5°) were applied for both groups.
RESULTS: Clear aligner therapy caused lingual tipping and extrusion of incisors, distal tipping and extrusion of canines, and mesial tipping and intrusion of posterior teeth, which was more significant with canine attachments except for second premolars. Aligner overtreatment produced palatal root torquing and intrusion of incisors, distal tipping of canines, and mesial tipping of second premolars, with more significant in the condition with canine attachments. With canine attachments, 1.2° overtreatment could cause bodily retraction of central incisors. Without overtreatment, stress was concentrated on apical and cervical area of both labial and lingual surfaces of periodontal ligaments. The stress value was higher with canine attachments. However, when overtreatment was added, the stress was distributed more evenly.
CONCLUSIONS: Clear aligner therapy produced lingual tipping and extrusion of incisors during anterior retraction. Overtreatment can achieve incisor intrusion and palatal root torquing, and the effect could be augmented by adding attachments on canines, which required more anchorage from posterior teeth. Appropriate overtreatment with placing attachments on canines should be designed to ensure bodily retraction and the least root resorption.