This report presents the therapeutic approach and results of a case of impacted undeveloped double teeth using 3D simulation in a school-age child. A 10-year-old girl was referred to hospital for the evaluation and treatment of fully impacted premolar double teeth in the left maxillary area. After evaluation, the double teeth were surgically removed, hemisected, and replanted after modification. For accurate surgery, replicas were made of the double teeth using CBCT and a 3D printer, and several mock surgeries were performed. Although remarkable signs for clinical and radiologic pathology were not found at the 5-month follow-up, short root with infraocclusion was found at the 30-month follow-up. This treatment widened the treatment spectrum with modern diagnostic approaches and preparation in large double teeth in children.