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• The prevalence of C-shaped canals in mandibular premolars is low. • Mandibular C-shaped premolars present complex inner morphologies. • Grooves on the mesiolingual surface of the root are associated with C-shaped pattern. To evaluate cone-beam computed tomography images in an Argentine population in order to determine the presence of mandibular premolars with C-shaped canal system and classify them. 697 images were observed, 170 of them fulfilling the selection criteria. Once established the presence of a C-shaped canal system, premolars were classified using Fan's criteria. Data description was made by frequencies and percentages rates, with a 95% confidence interval according to the score method. Comparisons were assessed by means of the Chi-square test with a significance level equal to 5%. Of 269 first premolars, 27 teeth showed C-shaped canal system, i.e. 10%, and of 231 second premolars, 4 presented C-shaped canal system, i.e. 2%. Out of 17 patients presenting first premolars in both sides, 6 showed a bilateral C-shaped canal system pattern and 11 did not present this condition. When the condition was unilateral (n = 15), 7 patients showed C-shaped canal in the tooth 3.4 and 8 patients showed C-shaped canal in the tooth 4.4. The second premolars showed C-shaped canals unilaterally. Along the canal, configuration variations at the three-thirds have been observed for the first and second mandibular premolars. The C-shaped canal system pattern prevalence in mandibular first and second premolars was estimated for the first time in an Argentine population, in vivo. The present report contributes to the epidemiological understanding of the anatomical variable of the inner dental configuration and its extrapolation to the clinical practice. [ABSTRACT FROM AUTHOR]

• Mandibular first premolars with RGs had a high incidence of complex canals. • C-shaped canals were mostly observed in first premolars with a Type V configuration. • RGs started on middle thirds, extended to apical and showed mostly deep depressions. • Most of the C-shaped canals exhibited semilunar-type configuration. To conduct an in vivo evaluation of prevalence of root canal configurations, lengths of C-shaped canals, prevalence and depths of radicular grooves (RGs), in mandibular first and second premolars in a Turkish subpopulation using cone beam computed tomography (CBCT). CBCT images of 327 first and 264 second premolars were included. Canal configurations, locations, lengths, and types of C-shaped canals, and RGs were evaluated on CBCT images. Data were statistically analyzed (P < 0.05). First and second premolars were classified as follows: type I, (83.8%, 97.72%); type V, (12.22%, 0.76%); type III, (3.06%, 0.76%); and other types. RGs were exhibited by 14.68% of first and 2.27% of second premolars (P < 0.05). Incidence of complex canals (types III, V and other types, 89.8%) in first premolars with RGs was significantly higher versus without RGs (P < 0.05). C-shaped configuration was exhibited by 4.58% of first (80% semilunar-type), and 1.13% of second premolars (P < 0.05). All first premolars with C-shaped canals showed RGs and complex canals. Complex canals and RGs frequently co-exist in mandibular premolars. C-shaped canals are not common in mandibular premolars, and mostly located in middle thirds. Type V is the most prevalent complex canal configuration in first premolars, and frequently associated with a C-shaped semilunar-type anatomy. [ABSTRACT FROM AUTHOR]