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Am J Orthod Dentofacial Orthop. 2019 Aug;156(2):178-185. doi: 10.1016/j.ajodo.2018.08.024.

Factors associated with spontaneous angular changes of impacted mandibular third molars as a result of second molar protraction.

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Private practice, Seoul, Korea.
Latin American Research Center, Asunción, Paraguay; Department of Orthodontics, Seoul Saint Mary's Hospital, Catholic University of Korea, Seoul, Korea.
Department of Orthodontics, Faculty of Dentistry, Ain Shams University, Cairo, Egypt.
Postgraduate Orthodontic Program, Arizona School of Dentistry and Oral Health, A. T. Still University, Mesa, Ariz.
Department of Oral and Maxillofacial Surgery, Chung-Ang University Hospital, Seoul, Korea.
Department of Orthodontics, Korea University Anam Hospital, Seoul, Korea. Electronic address:



This study aimed to identify significant factors affecting the spontaneous angular changes of impacted mandibular third molars as a result of second molar protraction. Temporary skeletal anchorage devices in the missing mandibular first molar (ML-6) or missing deciduous mandibular second molar (ML-E) with missing succedaneous premolar spaces provided traction.


Forty-one mandibular third molars of 34 patients (10 male and 24 female; mean age 18.3 ± 3.7 years) that erupted after second molar protraction were included in this study. They were classified into upright (U) and tilted (T) groups. Linear and angular measurements were performed at the time of treatment initiation (T1) and of ML-6 or ML-E space closure (T2). Regression analyses were used to identify significant factors related to third molar uprighting.


Nolla stage (odds ratio [OR] 4.1), sex (OR 0.003 for male), third molar angulation at T1 (OR 1.1), missing tooth space (OR 0.006), rate of third molar eruption (OR 23.3), and rate of second molar protraction (OR 0.2) significantly affected third molar uprighting. Age, third molar angulation at T1, rate of third molar eruption, and rate of second molar protraction were significant factors for predicting third molar angulation at T2.


Available space for third molar eruption before and after second molar protraction is not associated with uprighting of erupting third molars. Older patients whose third molars are in greater Nolla stage, are in a more upright position at T1, and have a greater eruption rate have a greater chance for third molar uprighting. Alternatively, an increase in second molar protraction rate results in mesial tipping of the third molars.

[Indexed for MEDLINE]

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