Eruption Failure Of Primary Molar With Ectopic Permanent Tooth

Eruption failure refers to a tooth's inability to attain its functional position beyond the normal eruption period. It is rare in primary teeth, with the mandibular second primary molar being the most commonly affected. Impaction of primary molars within the jawbone leading to eruption failure is exceptionally uncommon. This report presents a case of a 9-year-old girl with an impacted right mandibular primary molar and ectopic displacement of the successor permanent tooth. The patient’s chief complaint was the absence of eruption of the right lower posterior tooth, with no relevant family history or systemic abnormalities. Clinical examination revealed the absence of tooth 85, reduced alveolar ridge space, and no bony expansion. Cone-beam computed tomography demonstrated impaction of tooth 85, a surrounding dentigerous cyst-like structure, and loss of the periodontal ligament. The successor permanent tooth (45) was ectopically positioned at the lingual side of the 85 crown, displaced distally . Additional findings included insufficient mandibular width and congenital absence of tooth 32. Treatment involved extraction of 85, placement of a loop space maintainer for tooth 46, and regular monitoring of tooth 45 eruption, with orthodontic intervention planned if necessary. Deep impaction of primary molars may lead to ectopic displacement and developmental anomalies of permanent successors. Early extraction of the primary tooth can restore the eruption pathway for the permanent tooth and preserve arch space. Timely diagnosis of primary molar eruption failure reduces treatment complexity, minimizes damage to adjacent tissues, and improves clinical outcomes.