Root anatomy and canal configuration of primary molars: a systemic review and meta-analysis

Precise knowledge of root and canal morphology in primary teeth is critical for endodontic success, yet existing studies are fragmented and lack synthesis. This systematic review and meta-analysis addresses this gap by investigating the distribution of root numbers, canal configurations, and root lengths in human primary molars, while exploring possible influencing factors.

A literature search was conducted through PubMed, ScienceDirect, Web of Science, the Cochrane Library, and China National Knowledge Infrastructure (CNKI) up to September 2023. Retrospective studies using patients’ cone-beam computed tomography (CBCT) data or cross-sectional studies utilizing computed tomography (CT) or CBCT on extracted primary molars reporting on the root canal morphology of primary molars were included. Study quality was assessed using a modified Newcastle–Ottawa Scale. A meta-analysis was performed to estimate the proportions of root and canal numbers and calculate the mean values of root lengths. Forest plots were used to present the results.

The search strategy identified 799 records. After screening abstracts and full texts, 30 studies met the inclusion criteria. Of these, 2 studies had a high risk of bias, 23 a moderate risk, and 5 a low risk. The meta-analysis revealed that primary maxillary first molars were predominantly three-rooted (80.2%) with three canals (96.9%), while primary maxillary second molars were primarily three-rooted (89.7%) with three or four canals (84.4% and 14.7%, respectively). Primary mandibular first and second molars typically had two roots with M2D2 being the most common canal type, though the former showed high variability in canal configurations. Root lengths were also analyzed. Subgroup analysis indicated that heterogeneity may be influenced by country and data source, while no significant differences were associated with imaging techniques.

Primary maxillary molars are predominantly three-rooted with three canals, while primary mandibular molars typically had two roots with four canals. Variations in root anatomy and canal configuration should be considered during endodontic treatment of primary teeth. High heterogeneity and methodological inconsistencies limit the current evidence, highlighting the need for future research to address contributing factors to heterogeneity and to develop standardized methods for assessing root and canal morphology in the primary teeth.

PROSPERO registration no. CRD42023414536 on 2023.04.