Forced eruption of a deeply impacted mandibular second molar after extraction of the mandibular first molar for regeneration of an alveolar bony defect

The presence of a horizontal, deeply impacted mandibular second molar (MM2) is often indicative of a patient with a complex condition. This intricacy is not only linked to the impacted tooth itself but also to the adjacent teeth and alveolar bone. Therefore, when devising the treatment strategy, the orthodontist needs to consider all factors to select the ideal approach with the best prognosis for the patient. This study presents a case of a 15-year-old girl who developed mesially and severely low-impacted right MM2 with a segment of the crown located on the root side of the distal root of the mandibular first molar (MM1). The eruption space was filled by the impacted mandibular third molar (MM3), which was also mesially angulated and accompanied by a large-scale local alveolar bone defect. After fixed orthodontic treatment for the entire dentition, MM3 was uprighted, and MM2 was extruded via closed forced eruption after the extraction of MM1. Finally, MM2 and MM3 were uprighted, restoring the normal occlusal relationship and the deficient alveolar bone after 26 months. Two-year retention cone-beam computed tomography displayed signs of cortical bone regeneration around MM2 and MM3, corroborating that our treatment achieved satisfactory and stable results. This case suggests that MM1 extraction is a candidate option for MM2 impaction, especially when patients are at the appropriate age and develop a complex impacted tooth and challenging MM1 retention.