Sequential Treatment For An Ankylosed Primary Molar With Dentigerous Cyst

Primary tooth ankylosis, defined as direct fusion of cementum to alveolar bone, leads to infraocclusion, periodontal ligament loss, and alveolar ridge hypoplasia. Infraoccluded molars may cause adjacent tooth tipping, space loss, and abnormal eruption of successors. The therapeutic goal is to ensure normal eruption of successor permanent teeth. A 7-year-old patient presented with a chief complaint of a missing mandibular right primary second molar (85). Clinical examination revealed mesially tipped permanent first molar (46) and space loss. Radiographs showed subgingivally impacted 85 with root resorption and unerupted premolar (45) within a cystic lesion. Interceptive orthodontics was initiated using a modified cast lingual arch with elastic chains to upright 46, restoring occlusion and surgical access. After 3 months, 46 was aligned, followed by extraction of ankylosed 85 and cyst marsupialization. At 4-month follow-up, cyst regression and 45 root development were observed, and a lingual arch space maintainer was subsequently placed. Primary tooth ankylosis frequently stems from disrupted eruption-related signaling pathways or structural anomalies. In this case, inflammation from the dentigerous cyst likely triggered 85 ankylosis. As succedaneous tooth was at Nolla’s stage 6, early extraction with space maintenance was critical. Severe tipping of 46 necessitated pre-surgical orthodontics to reclaim eruption space, emphasizing interdisciplinary coordination. In complex ankylosed primary molar case accompanied by dentigerous cyst, interceptive orthodontics followed by surgery are expected to achieve minimally invasive cyst management, which preserve alveolar bone and promote physiological development of succedaneous of the ankylosed primary molar.