Objectives <p>Impaction of first permanent molars is uncommon but may affect oral function and craniofacial development. Although various etiologic factors have been proposed, three-dimensional imaging features associated with impacted first permanent molars—particularly, furcation area root resorption—have not been well investigated. The objective of this study is to analyze CT imaging features of impacted first permanent molars and determine their correlation with prognosis.</p> Methods <p>This retrospective cohort study reviewed multidetector computed tomography and cone-beam computed tomography scans of 71 patients diagnosed with impaction of first permanent molars. Two oral and maxillofacial radiologists evaluated CT imaging features such as peri-coronal disturbance, root dilaceration, apical closure, ankylosis, and furcation area root resorption. Treatment methods and eruption outcomes were also recorded. Logistic regression analysis was performed to identify imaging features associated with eruption failure of impacted first permanent molars.</p> Results <p>Among 71 impacted first molars, peri-coronal disturbance was observed in 29.6%, root dilaceration in 31.0%, apical closure in 42.3%, ankylosis in 11.3%, and furcation area root resorption in 35.2% of cases. After treatment, furcation area root resorption showed 64.7% (11/17) of eruption failure. Notably, furcation area root resorption was identified as the only significant imaging feature associated with eruption failure (OR 8.32; 95% CI 1.15–60.31; <i>p</i> = 0.036).</p> Conclusions <p>Furcation area root resorption is a relatively common CT imaging feature in impacted first permanent molars and is associated with poor prognosis. Because this feature is often undetectable on plain radiographs, 3D CT evaluation should be considered for accurate diagnosis and appropriate treatment planning.</p>