Apical anatomy of mandibular second premolars at Nolla stage 8: A cross-sectional CBCT study in Chinese individuals

This study used cone-beam computed tomography (CBCT) to measure the anatomical structures of the apical foramen of mandibular second premolars at Nolla stage 8. A total of 80 mandibular second premolars at Nolla stage 8 with deformed central cusp (DCC) deformity were selected as the observation group, and another 80 normal mandibular second premolars at the same stage were selected as the control group. The mesiodistal diameter (A-B) and buccolingual diameter (C-D) of the apical foramen, as well as the mesiodistal diameter (A1-B1), buccolingual diameter (C1-D1), and superoinferior diameter (E-F) of the periapical radiolucency, were measured using the built-in software of the CBCT system. The data were analyzed using SPSS 26.0 software. Results: In the observation group, the values of A-B, C-D, A1-B1, C1-D1, and E-F were (2.47 ± 0.26) mm, (3.28 ± 0.50) mm, (3.26 ± 0.30) mm, (4.25 ± 0.58) mm, and (3.06 ± 0.27) mm, respectively. In the control group, the corresponding values were (2.43 ± 0.29) mm, (3.27 ± 0.34) mm, (3.26 ± 0.41) mm, (4.24 ± 0.40) mm, and (3.28 ± 0.43) mm, respectively. Within each group, significant differences were found between A-B and C-D, as well as between A1-B1 and C1-D1 (P < .001). In both the observation and control groups, females exhibited significantly lower values than males for A-B, C-D, A1-B1, C1-D1, and E-F (P < .05). A-B and C-D were positively correlated with A1-B1, C1-D1, and E-F, respectively. This study confirmed that in Nolla stage 8 mandibular second premolars, the buccolingual diameters of both the apical foramen and periapical radiolucency were larger than the mesiodistal diameters, and females had smaller values for all parameters. Teeth with DCC but without apical periodontitis showed no significant anatomical differences from normal teeth. As the first CBCT-based comparison of apical anatomy between DCC and normal mandibular second premolars at this developmental stage, these results provide useful imaging references for early diagnosis and therapeutic monitoring of apical periodontitis caused by DCC fracture.