Background and Aim: This study reviewed the prevalence of C-shaped root canal morphology in different provinces of Iran.
Materials and Methods: This systematic review was conducted according to the PRISMA guidelines. Embase, Medline, PubMed, Scopus, Web of Knowledge, Google Scholar, Cochrane Library, Ovid, SID, CIVILICA, Magiran, IranMedex, and ISC electronic databases were searched for articles published from 2000 to 2021. The searched keywords included “C-shaped root canal system” and “prevalence”, “molar teeth”, “premolar teeth”, and “Iranian population”. Full-text assessment of the articles and critical appraisal were performed using the CONSORT and STROBE checklists. Gender, tooth type (first/second molar, first/second premolar), upper/lower jaw, and type of C-shaped classification were extracted from the eligible articles, pooled, and analyzed using forest plots with proportions and odds ratio with 95% confidence interval (CI). Meta-regression was performed to evaluate possible sources of heterogeneity.   
Results: The prevalence of C-shaped canals was 0.06% (95% CI: 0.04-0.08). The prevalence of C-shaped canals was 0.08% (95% CI: 0.05-0.11) based on cone-beam computed tomography (CBCT) scans. The pooled prevalence of C-shaped root canal system was higher in Mazandaran (Sari and Babol) and East Azarbaijan (Tabriz) (0.10%) than other provinces. There was no significant difference between the pooled prevalence of C-shaped root canal system in males (0.26%) and females (0.36%). The pooled prevalence of C-shaped morphology was 0.03% in first molars and 0.12% in second molars.
Conclusion: The prevalence of C-shaped morphology is high in the Iranian population. Tooth type has a significant effect on the prevalence of C-shaped canals.