Three-Dimensional Analysis of the Maxillary Second Premolar in Relation to Ectopic Eruption Types of the Maxillary First Molar Using Cone-Beam Computed Tomography

This study evaluated the 3-dimensional position and angulation of the maxillary second premolar germ according to the type of ectopic eruption of the maxillary first molar using cone beam computed tomography. A total of 105 patients were classified into three groups: Normal (fully erupted first molar without root resorption of the second primary molar), Reversible (ectopic eruption with root resorption that self-corrected), and Irreversible (impacted molar with persistent root resorption). Angulation was measured in the sagittal and coronal planes. Distance and arch ratio were assessed in the axial and coronal views. In the sagittal plane, the mean angulation became progressively more distal from the Normal to the Irreversible group, showing significant differences between the Normal and both ectopic groups (p < 0.0001). In the coronal plane, buccal inclination increased toward the Irreversible group, with significant differences between the Normal and Irreversible groups (p < 0.0001). The coronal distance ratio decreased significantly across all groups, with pairwise differences showing statistical significance (p < 0.0001). In the axial plane, values were significantly lower in both ectopic groups than in the Normal group (p < 0.0001). No significant differences were observed in the arch ratio (p > 0.05). These findings suggest that ectopic eruption of the first molar induces progressive distal and buccal inclination and palatal displacement of the second premolar germ, even after self-correction.