Anatomical Analysis of Root Fragment Extraction in Impacted Mandibular Third Molars Based on CBCT

doi:10.13701/j.cnki.kqyxyj.2026.06.005

Abstract

Abstract: Objective: To investigate the anatomical factors associated with root fragment displacement during the extraction of impacted mandibular third molars (IMTM) using CBCT. Methods: This retrospective study included 52 patients (52 IMTMs) who were referred to the Department of Oral Surgery, School of Stomatology, The Fourth Military Medical University, due to incomplete IMTM extraction over the past five years. These cases were divided into the displaced group (16 root fragments displaced into the lingual space) and the non-displaced group (36 root fragments with no significant displacement, remaining in the alveolar socket). Preoperative and postoperative CBCT were used to assess the thickness and integrity of the lingual cortical bone wall, the anatomical morphology of the lingual side of mandible, the axial positional relationship of IMTMs, the positional relationship between the mandibular canal and tooth roots, and the degree of alveolar bone resorption in the distal aspect of adjacent teeth in both groups. The displaced and non-displaced groups were compared to analyze the anatomical factors contributing to root fragment displacement. Results: Those with missing lingual cortical bone were more prone to root fragment displacement during extraction (P<0.001). IMTMs with alveolar bone anatomical morphologies showing "undercut type" or "inclined narrowing type" on CBCT coronal sections were susceptible to root fragment displacement. IMTMs with non-vertical axial positions and type Ⅲ alveolar bone resorption in the distal aspect of adjacent teeth were more likely to have root fragment displacement during extraction (P<0.05). The average thickness of the lingual bone wall in the displaced group and the non-displaced group was (0.81±0.58) mm and (1.41±1.02) mm, respectively (P<0.05). Conclusion: Alveolar bone anatomical morphologies of "undercut type" and "inclined narrowing type" on CBCT coronal sections, an average lingual bone wall thickness ≤0.81 mm, type Ⅲ alveolar bone resorption in the distal aspect of adjacent teeth, and non-vertical impaction of IMTMs are all significant anatomical factors contributing to lingual displacement of root fragments.

Key words: impacted mandibular third molar, lingual bone wall, root fragment, CBCT

TENG Teng, GONG Kun, LUAN Baiting, WANG Yichen, LIANG Xiaolei, WANG Yiming, ZHANG Wuyang, XUE Yang, HU Kaijin, DENG Tiange. Anatomical Analysis of Root Fragment Extraction in Impacted Mandibular Third Molars Based on CBCT[J]. Journal of Oral Science Research, 2026, 42(6): 487-492.

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