Osteonecrosis involving the permanent tooth germ in primary dentition is a rare condition that can affect dental and maxillofacial development without correct intervention. This case report presents the successful recovery from drug-induced mandibular osteonecrosis involving the permanent tooth germ in a child. A healthy 4-year-old Chinese girl visited the clinic with an unhealed gingival wound and alveolar bone exposure of the missing primary molar area after 1-day arsenic trioxide sealing during pulp therapy. Radiographic examinations indicated inflammation and sequestrum formation in the jaw. The diagnosis was mandibular osteonecrosis. The treatment plans involved sequestrectomy without extended curettage and removal of the affected permanent tooth germ with systemic antibiotic therapy. A 6-year follow-up revealed no recurrence of the lesion or complications, a gradual increase in bone density of the osteonecrosis area and the development of adjacent permanent tooth germs. A conservative treatment regimen without extended curettage may be an option for young patients with jaw osteonecrosis.