Assessment of marginal bone loss, distal caries, and external root resorption in second molars adjacent to impacted third molars: a retrospective CBCT and panoramic study.

BACKGROUND: Impacted third molars (M3s) are frequently associated with pathological changes in adjacent second molars (M2s), including marginal bone loss (MBL), distal caries (DCs), and external root resorption (ERR). Accurate radiographic assessment and identification of risk factors are crucial for timely intervention and informed clinical decision-making. This study aimed to investigate the relationship between anatomical and positional risk factors of impacted M3s and pathological changes in adjacent M2s using cone-beam computed tomography (CBCT). Additionally, the diagnostic performance of panoramic radiography (PAN) was compared to CBCT in detecting early and advanced pathological conditions. METHODS: CBCT and PAN radiographs obtained from 129 patients were evaluated, comprising a total of 301 impacted M3s and their adjacent M2s. The presence and severity of MBL, DCs, and ERR in M2s were systematically evaluated in relation to the anatomical characteristics of impacted M3s. Statistical analyses involved chi-square and Cohen’s kappa tests (p < 0.05). RESULTS: Pathological changes were observed in 69.1% of M2s adjacent to impacted M3s. MBL was most common (63.5%), with 31.9% classified as severe. ERR occurred in 21.3% of M2s, mostly mild (53.1%), while DCs was least frequent (4.3%). M3s with mesioangular, horizontal, or transverse angulation, Class C impaction, and a contact point length > 1 mm were significantly associated with higher M2 pathology risk. CBCT demonstrated higher sensitivity compared to PAN, with low agreement between modalities, highlighting PAN’s limitations in detecting early or subtle pathological changes. CONCLUSIONS: These results emphasize the need for thorough radiographic evaluation of impacted M3s, given their potential risks to adjacent M2s. Although the superior diagnostic capability of CBCT over PAN is well-established, this study uniquely correlates specific anatomical risk factors with CBCT-detected pathologies, thereby enhancing risk stratification for clinical decision-making. Furthermore, the proposed risk-based algorithm integrating CBCT findings supports more timely interventions and improved management of impacted M3s.