CBCT-Based Analysis of Mandibular Third Molar Impaction and Its Impact on Adjacent Second Molars in a Saudi Cohort: A Retrospective Study

Objectives This study evaluated the impact of mandibular third molar (MTM) impactions on adjacent second molar health in a Saudi population using cone-beam computed tomography (CBCT), focusing on caries prevalence, periodontal bone loss, and associated risk factors. Methods A retrospective analysis of 137 CBCT scans from Saudi adults (≥ 18 years) with impacted MTMs was conducted with post-hoc power analysis confirmed sample adequacy. Scans were assessed for impaction characteristics (Winter's and Pell & Gregory classifications), cementoenamel junction (CEJ) distances, distal caries (ICCMS criteria), and periodontal bone loss (mild/moderate/severe). Statistical analysis included chi-square tests, logistic regression, and non-parametric tests. Results Mesioangular impactions predominated (61.3%), with Class B depth most common (46.7%). Severe distal caries affected 20.4% of second molars, while 52.6% exhibited moderate-to-severe bone loss. Class C impactions showed the highest caries risk (43.6%, p = 0.015). Regression identified younger age (OR = 0.41, p = 0.009), mesial angulation (OR = 2.3), and bone loss (OR = 0.47) as significant predictors. While CEJ distances < 6 mm demonstrated a clinical trend toward greater pathology, this association did not reach statistical significance (p = 0.214). Conclusion Impacted MTMs, particularly mesioangular and Class C impactions, significantly compromise second molar health. Prophylactic extraction should be considered for these high-risk impactions to prevent irreversible damage, supported by CBCT-based assessment. CEJ distance, while clinically relevant, was not an independent predictor of pathology in this cohort.