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Association between impacted third molars and external root resorption on adjacent second molars based on cone-beam
Wenxuan Liu1,2,3, Ailin Liang4, Yanling Zhou1,2,3
1Hospital of Stomatology, Guanghua School of Stomatology, Sun Yat-sen University, No. 56, Lingyuan West Road, Guangzhou, 510055, China.
BMC Oral Health
|June 19, 2026
Summary
External root resorption (ERR) on second molars is linked to adjacent impacted third molars (iM3s). Cone-beam computed tomography (CBCT) revealed a 31% prevalence of iM3-associated ERR, particularly with specific iM3 inclinations.
Area of Science:
- Dentistry
- Oral and Maxillofacial Surgery
- Radiology
Background:
- External root resorption (ERR) on second molars (M2s) is a pathological damage associated with adjacent impacted third molars (iM3s).
- Conventional radiographs have limited detectability of ERR, potentially leading to delayed diagnosis and irreversible damage.
- This systematic review focuses on iM3s and their association with ERR on M2s.
Purpose of the Study:
- To quantitatively evaluate the association between impacted third molars (iM3s) and external root resorption (ERR) on second molars (M2s).
- To assess the prevalence of iM3-associated ERR on M2s using cone-beam computed tomography (CBCT).
- To identify risk factors contributing to ERR on M2s from iM3s.
Main Methods:
- A systematic review and meta-analysis of human studies using CBCT.
- Searched six major databases for relevant articles published before June 2025.
- Assessed methodological quality using the Joanna Briggs Institute Critical Appraisal Checklist and performed meta-analyses using random-effects models.
Main Results:
- Twenty-six articles were included, with 24 having a low risk of bias.
- A 31% prevalence (95% CI: 26%–36%) of iM3-associated ERR on M2s was found.
- Higher ERR prevalence was associated with mesioangular, horizontal, or transverse iM3 inclinations and direct contact with the apical third of M2 roots.
Conclusions:
- External root resorption on M2s is linked to iM3 contact with the apical third of M2 roots.
- Mesioangular, horizontal, or transverse iM3 inclinations significantly increase ERR prevalence on adjacent M2s.
- Identified key factors for ERR provide evidence-based guidance for treating asymptomatic iM3s.
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