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Korean J Orthod
Copyright © The Korean Association of Orthodontists.
*Jung Jin Park, Clinical assistant professor (DDS, MSD, PhD), Department of Orthodontics, Kyung Hee University Hospital at Gangdong, Seoul, Korea.
First Author, jpie01@naver.com, jjpark@khnmc.or.kr
*Yoonjeong Noh, Postgraduate student, Department of Orthodontics, Gangnam Severance Dental Hospital, College of Dentistry, Yonsei University, Seoul, Korea.
First Author, noyunjeong@naver.com
Yoon Jeong Choi, Associate professor (DDS, MSD, PhD), Department of Orthodontics, The Institute of Craniofacial Deformity, College of Dentistry, Yonsei University, Seoul, Korea.
Second Author, YOONJCHOI@yuhs.ac
Jae Hyun Park, Professor and chair (DMD, MSD, MS, PhD), Postgraduate Orthodontic Program, Arizona School of Dentistry & Oral Health, A.T. Still University, Mesa, USA International Scholar (DMD, MSD, MS, PhD), Graduate School of Dentistry, Kyung Hee University, Seoul, Republic of Korea.
Third Author, jpark@atsu.edu
Ji Hyun Lee, Clinical associate professor (DDS, MSD, PhD), Department of Orthodontics, Gangnam Severance Dental Hospital, Institute of Craniofacial Deformity, College of Dentistry, Yonsei University, Seoul, Korea
Fourth Author, therii@yuhs.ac
Correspondence to:Chooryung Judi Chung, Professor (DDS, PhD), Department of Orthodontics, Gangnam Severance Dental Hospital, Institute of Craniofacial Deformity, College of Dentistry, Yonsei University, Seoul, Korea
Fifth Author, CRCHUNG@yuhs.ac
Kyung-Ho Kim, Professor (DDS, MS, PhD), Department of Orthodontics, Gangnam Severance Dental Hospital, Institute of Craniofacial Deformity, College of Dentistry, Yonsei University, Seoul, Korea.
Corresponding Author, khkim@yuhs.ac
* Contributed equally as first authors
Objective: Extraction of the mandibular second molar (L7) and substitution by the mandibular third molar (L8) is an effective treatment option. This study evaluated spontaneously erupted L8 occlusions after L7 extraction and identified the influencing factors. Methods: The study assessed 46 L8s from 28 patients using dental study models, panoramic radiographs, and lateral cephalograms taken at 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, position, retromolar space, distance between the Xi point and the mandibular first molar (L6), and Nolla stage were compared between the groups to identify predictive factors for successful eruption. Results: At T2, 58.7% of L8s exhibited acceptable occlusion. The age at T1 was significantly higher in the U-group than in the A-group. The angles ∠6-MnP and ∠8-MnP differed significantly between groups at T2. The Xi-L6 distance was considerably longer in the A-group than in the U-group at T1 and T2. Younger age at extraction and the 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 key factors for achieving acceptable L8 occlusion.
Keywords: Mandibular third molar, mandibular second molar extraction, occlusion, tooth eruption
Korean J Orthod
First Published Date January 9, 2025
Copyright © The Korean Association of Orthodontists.
*Jung Jin Park, Clinical assistant professor (DDS, MSD, PhD), Department of Orthodontics, Kyung Hee University Hospital at Gangdong, Seoul, Korea.
First Author, jpie01@naver.com, jjpark@khnmc.or.kr
*Yoonjeong Noh, Postgraduate student, Department of Orthodontics, Gangnam Severance Dental Hospital, College of Dentistry, Yonsei University, Seoul, Korea.
First Author, noyunjeong@naver.com
Yoon Jeong Choi, Associate professor (DDS, MSD, PhD), Department of Orthodontics, The Institute of Craniofacial Deformity, College of Dentistry, Yonsei University, Seoul, Korea.
Second Author, YOONJCHOI@yuhs.ac
Jae Hyun Park, Professor and chair (DMD, MSD, MS, PhD), Postgraduate Orthodontic Program, Arizona School of Dentistry & Oral Health, A.T. Still University, Mesa, USA International Scholar (DMD, MSD, MS, PhD), Graduate School of Dentistry, Kyung Hee University, Seoul, Republic of Korea.
Third Author, jpark@atsu.edu
Ji Hyun Lee, Clinical associate professor (DDS, MSD, PhD), Department of Orthodontics, Gangnam Severance Dental Hospital, Institute of Craniofacial Deformity, College of Dentistry, Yonsei University, Seoul, Korea
Fourth Author, therii@yuhs.ac
Correspondence to:Chooryung Judi Chung, Professor (DDS, PhD), Department of Orthodontics, Gangnam Severance Dental Hospital, Institute of Craniofacial Deformity, College of Dentistry, Yonsei University, Seoul, Korea
Fifth Author, CRCHUNG@yuhs.ac
Kyung-Ho Kim, Professor (DDS, MS, PhD), Department of Orthodontics, Gangnam Severance Dental Hospital, Institute of Craniofacial Deformity, College of Dentistry, Yonsei University, Seoul, Korea.
Corresponding Author, khkim@yuhs.ac
* Contributed equally as first authors
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Objective: Extraction of the mandibular second molar (L7) and substitution by the mandibular third molar (L8) is an effective treatment option. This study evaluated spontaneously erupted L8 occlusions after L7 extraction and identified the influencing factors. Methods: The study assessed 46 L8s from 28 patients using dental study models, panoramic radiographs, and lateral cephalograms taken at 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, position, retromolar space, distance between the Xi point and the mandibular first molar (L6), and Nolla stage were compared between the groups to identify predictive factors for successful eruption. Results: At T2, 58.7% of L8s exhibited acceptable occlusion. The age at T1 was significantly higher in the U-group than in the A-group. The angles ∠6-MnP and ∠8-MnP differed significantly between groups at T2. The Xi-L6 distance was considerably longer in the A-group than in the U-group at T1 and T2. Younger age at extraction and the 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 key factors for achieving acceptable L8 occlusion.
Keywords: Mandibular third molar, mandibular second molar extraction, occlusion, tooth eruption
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