Is infraocclusion always caused by ankylosis? Current perspectives on primary molar ankylosis: A systematic review

Ankylosed primary molars are relatively common during the mixed dentition period; however, ankylosis does not always coincide with infraocclusion. This systematic review assessed the clinical evidence regarding ankylosis of primary molars, including its etiology, diagnosis, and management, and discussed whether infraocclusion is primarily caused by ankylosis or instead reflects a broader disturbance of tooth eruption. A literature search was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines across three databases (PubMed, Scopus, and Web of Science) on 25 April 2025 and updated on 3 July 2026. The risk of bias and methodological quality of the included studies were assessed using the Joanna Briggs Institute critical appraisal tools. Fourteen studies met the inclusion criteria. The person-level prevalence of infraoccluded primary molars, used as a surrogate for ankylosis, ranged from 1.3% to 24.8%. Histopathological and clinical studies indicated that not all infraoccluded primary molars exhibited evidence of ankylosis. Treatment strategies varied according to the severity of infraocclusion and the presence or absence of permanent successors. The available evidence remains limited and insufficient to determine the temporal and causal relationship between ankylosis and infraocclusion. Further epidemiological, histopathological, and treatment-related studies are needed.