Abstract: Ankylosed tooth is a kind of eruption abnormality of the teeth.It arises more often in primary molars,while it’s rarely that occlusal surface of tooth is lower than proximal gingival clinically.We report a rare case of ankylosed mandibular right second primary molar which is below the gingival has a deep caries in the occlusal surface,and we try to make a detailed introduction about epidemiology,clinical manifestations,diagnosis,and treatment of the disease.

Key words: ankylosed tooth, submerged deciduous teeth, deep caries, malocclusion