Dental and Skeletal Characteristics According to the Location of Ectopic Eruption of the First Permanent Molar in the Mixed Dentition

This study aimed to evaluate the dentoskeletal characteristics associated with ectopic eruption of the first permanent molars during the mixed dentition. A retrospective analysis was performed on children who visited the Department of Pediatric Dentistry at Pusan National University Dental Hospital between 2013 and 2024. Based on panoramic findings, subjects were classified into a control group with normal eruption and three ectopic eruption groups: maxillary (U6), mandibular (L6), and combined maxillary-mandibular (UL6). Lateral cephalometric radiographs and digital dental models were used to evaluate skeletal parameters, arch dimensions, and anterior tooth size. A total of 178 subjects (Control: n = 64, U6: n = 91, L6: n = 10, and UL6: n = 13) were analyzed. The distribution of skeletal classification did not differ significantly among the ectopic eruption groups (p = 0.055). Among the three ectopic eruption groups, ANB (p = 0.011), APDI (p = 0.007), ODI (p = 0.010), and Wits appraisal (p = 0.001) differed significantly. In post-hoc analysis, the U6 group showed a significantly higher APDI and lower ANB, ODI, and Wits appraisal than the L6 group, consistent with a more Class III–related sagittal pattern. The Mx/Mn incisor ratio was also significantly greater in the U6 group than in the L6 group (p = 0.013). Maxillary arch perimeter differed significantly among the groups (p = 0.035), without significant pairwise differences. These findings suggest possible associations between dentoskeletal patterns and the location of ectopic eruption and may provide preliminary information for early risk assessment in children with ectopic eruption of the first permanent molars.