Effect of Eruption Status of the Mandibular Third Molar on Distal Caries in the Adjacent Second Molar

Abstract

To analyze the effect of the eruption status of the mandibular third molar (MTM) on distal caries in the mandibular secondmolar (MSM) by cone-beam computed tomography (CBCT). Five hundred CBCT images of MTMs from 469 patients were evaluated. Presence of distal caries in MSMs, impaction depths and angulations of MTMs, cementoenamel junction (CEJ) distances between distal MSMs and mesial MTMs, presence of pericoronitis in MTMs, and patient characteristics (age and gender) were assessed. Data were analyzed by χ(2) test, univariate and multivariate logistic regression analyses, and Spearman correlation analysis. Descriptive and bivariate statistics were computed and the P value was set at .05. The overall prevalence of distal caries in the MSM was 52.0%. According to the classification of Pell and Gregory, position A was the impaction depth at which most distal caries in MSMs were present (P= .036). For angulation of the MTM, when mesial angulations were 43° to 73°, MSMs developed more distal caries (P < .0001). For the CEJ distance between the distal MSM and the mesial MTM, when distances ranged from 6 to 15mm, distal caries in MSMs occurred more frequently (6 to 8mm, P < .0001; 8 to 15mm, P= .037). Furthermore, there was a linear correlation between angulation of the MTM and the CEJ distance between the distal MSM and the mesial MTM (P < .0001). Impaction depth and angulation of the MTM are associated with distal caries in the MSM. Angulation of the MTM is more stable and reliable than the CEJ distance between the distal MSM and the mesial MTM for the estimation of risk factors related to the MTM.