The korean journal of orthodontics (대한치과교정학회지)

The Korean Association Of Orthodontists (대한치과교정학회)
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Key factors for successful eruption of the mandibular third molar after extraction of the mandibular second molar

  • Jung Jin Park (Department of Orthodontics, Kyung Hee University Hospital at Gangdong) ;
  • Yoonjeong Noh (Department of Orthodontics, Gangnam Severance Dental Hospital, College of Dentistry, Yonsei University) ;
  • Yoon Jeong Choi (Department of Orthodontics, The Institute of Craniofacial Deformity, College of Dentistry, Yonsei University) ;
  • Jae Hyun Park (Arizona School of Dentistry & Oral Health, A.T. Still University) ;
  • Ji Hyun Lee (Department of Orthodontics, Gangnam Severance Dental Hospital, College of Dentistry, Yonsei University) ;
  • Chooryung Judi Chung (Department of Orthodontics, Gangnam Severance Dental Hospital, College of Dentistry, Yonsei University) ;
  • Kyung-Ho Kim (Department of Orthodontics, Gangnam Severance Dental Hospital, College of Dentistry, Yonsei University)
  • Received : 2024.09.26
  • Accepted : 2025.01.07
  • Published : 2025.03.25
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Abstract

Objective: Extraction of the mandibular second molar (L7) and substitution by the mandibular third molar (L8) is an effective treatment option. This study aimed to evaluate spontaneously erupted L8 occlusion after L7 extraction, and identify the influencing factors. Methods: This study assessed 46 L8 from 28 patients using dental study models, panoramic radiographs, and lateral cephalograms obtained during L7 extraction (T1) and completion of L8 eruption (T2). At T2, samples were categorized as acceptable (A-group) or unacceptable (U-group) based on the American Board of Orthodontics index. L8 angulation and position, retromolar space, distance between the Xi point and mandibular first molar (L6), and Nolla stage were compared between the groups to identify the predictive factors for successful eruption. Results: At T2, 58.7% of L8 exhibited acceptable occlusion. Age at T1 was significantly higher in the U-group than that in the A-group. Angles ∠6-MnP and ∠8-MnP differed significantly between the groups at T2. Xi-L6 distance was considerably longer in the A-group than that in the U-group at T1 and T2. Younger age at extraction and Xi-L6 distance at T1 affected the acceptable occlusion. Conclusions: Younger age at L7 extraction and adequate eruption space (Xi-L6 distance) appear to be the key factors for achieving acceptable L8 occlusion.

Keywords

Acknowledgement

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (Grant no. 2023R1A2C100735011).

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