Predicting and modulating root migration after mandibular third molar coronectomy: Umbrella review and proposed conceptual risk stratification model

BACKGROUND: Coronectomy is an established nerve sparing approach for mandibular third molars in close proximity to the inferior alveolar nerve. Postoperative migration of retained roots is frequently observed and is often considered favourable due to increasing separation from the nerve. However, its determinants and broader clinical implications remain unclear. OBJECTIVE: To synthesise evidence from systematic reviews on the prevalence, magnitude, determinants, and clinical significance of root migration following coronectomy and to explore potential strategies influencing postoperative root behaviour. METHODS: An umbrella review was conducted in accordance with PRISMA guidelines. Databases were searched for systematic reviews reporting root migration after coronectomy of mandibular third molars. Data on migration prevalence, magnitude, timing, associated factors, and clinical outcomes were extracted. RESULTS: Thirteen systematic reviews encompassing 178 primary studies were included. Root migration was common, with prevalence ranging from 6% to nearly 100%. Migration typically began within 3–6 months, progressed most rapidly during the first postoperative year, and stabilised thereafter. Mean migration distances generally ranged from 2–4 mm. Younger age, female sex, and specific root or impaction characteristics were associated with greater migration. Although most migrated roots remained asymptomatic, excessive displacement was occasionally associated with root exposure, pain, and secondary surgical intervention. CONCLUSION: Root migration following coronectomy appears to be a biologically driven yet potentially modifiable process. This umbrella review introduces the concept of controlled root migration and proposes a conceptual risk stratification model integrating key predictors to guide personalised management and minimise secondary interventions.