Association Between Mandibular Ramus Morphometry and Mandibular Third Molar Impaction: A Systematic Review and...

Mandibular third molar impaction is a common clinical condition associated with various functional and pathological complications. Skeletal and morphometric characteristics of the mandible, particularly mandibular ramus dimensions, have been proposed as potential contributors to impaction risk; however, existing evidence remains inconsistent.

To systematically review and quantitatively synthesize the available evidence on the association between mandibular ramus dimensions (height and width) and mandibular third molar impaction.

A systematic review and meta-analysis were conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, with the protocol prospectively registered in PROSPERO (Registration ID: CRD420251238995). PubMed, Embase, Web of Science, Scopus, and Google Scholar were searched from inception to October 16, 2025. Observational studies evaluating the relationship between mandibular ramus height and/or width and mandibular third molar impaction were included. Meta-analyses were performed using random-effects models with restricted maximum-likelihood (REML) estimation and Hartung-Knapp adjustment. Ramus height and width were analyzed separately as mean differences (MDs) with 95% confidence intervals (CIs). Subgroup analyses by study design and sensitivity analyses were conducted to explore heterogeneity. Risk of bias was assessed using the Joanna Briggs Institute (JBI) Critical Appraisal Checklist.

Eleven studies comprising 3570 participants were included, of which nine contributed to the meta-analysis of ramus height and six to ramus width. Meta-analysis demonstrated a significantly smaller mandibular ramus height in individuals with impacted mandibular third molars compared with erupted controls (MD = -1.03 mm; 95% CI: -1.85 to -0.21; p = 0.020), with substantial heterogeneity (I ² = 98.0%). In contrast, no statistically significant difference was observed for ramus width (MD = 0.66 mm; 95% CI: -0.74 to 2.06; p = 0.281). Subgroup analyses by study design did not demonstrate significant subgroup differences for ramus height but indicated significant between-subgroup variability for ramus width. Sensitivity analyses generally supported the robustness of the findings, although statistical significance for ramus height was attenuated after omission of several influential studies. Eight studies were judged to have low risk of bias and three moderate risk.

Reduced mandibular ramus height may be more consistently associated with mandibular third molar impaction than ramus width, although substantial heterogeneity limits definitive conclusions. While sexual dimorphism in ramus morphology is evident, its influence on impaction risk remains unclear. These findings highlight the need for standardized measurement protocols and well-designed longitudinal studies to further clarify the role of mandibular ramus morphology in third molar impaction.