Second Primary Molar Ankylosis With First Permanent Molar Ectopic Eruption

Second primary molar ankylosis occurs when cementum and surrounding alveolar bone are fused, potentially causing ectopic eruption of the adjacent permanent molar. Early diagnosis and intervention are critical. This case underscores the significance of recognizing and managing ankylosis in primary molars. A 7-year-old female patient exhibited an ankylosed second primary molar (tooth 75) with ectopic eruption of tooth 36, confirmed by radiographic examination. The patient presented Angle Class II malocclusion, with dental arch crowding and left posterior teeth crossbite. We found a 5mm space between tooth 74 and 36, with mesially inclination of tooth 36, distal inclination of tooth 74, partial eruption of mesial cusp of tooth 75. The treatment plan consisted of maxillary expansion to address crowding, 2×4 partial fixed appliance to upright tooth 36, and expand space for tooth 75; extraction of tooth 75 upon 35 reaching Nolla Stage 6, followed by space maintenance post-extraction. At the two-year follow-up, the left posterior teeth crossbite was corrected and the dental arch achieved a harmonious shape with relieved crowding .By the three-year follow-up, tooth 35 successfully erupted to the occlusal plane. Individual normal occlusion was achieved. Ankylosis of second primary molar may result in impaction of the successor or ectopic eruption of the permanent molar. The present case highlights how early interventions ensured alignment of first permanent molar and restoration of functional occlusion. It emphasizes the importance of early diagnosis and orthodontic intervention in guiding tooth eruption and reducing long-term complications.