It is necessary to have in-depth knowledge in mandibular premolars, their wide anatomic variations and canal morphology to apply clinical skills for its proper treatment [6, 13, 18]. The American Endodontic Association (AAE) and the American Academy of Oral and Maxillofacial Radiology (AAOMR) have suggested the use of Cone Beam Computed Tomography in endodontics to identify abnormalities or variations where complex morphology is suspected, based in conventional radiographs .
Conventional intraoral radiographs are routinely used to assess root canal anatomy, but in cases with principal canal fuzziness in any third, the best method for accurate determination of this root canal morphology is CBCT; 3D images provide maximum information to the clinician of the canal shape along the root and cross-sectional details of the tooth [9, 14, 15].
Venezuela is a variety ethnic country, to our knowledge it does not have statistical studies about C-shaped mandibular premolars; the only available information were cases reports with this configuration [6, 13]. For this reason, the present study used a database from patients of a Venezuelan imaging diagnostic center to analyze this anatomical variation and their characteristics.
Based on the CBCT analysis of this database, the most frequent morphology in the mandibular first premolars was a single root, in more than 91% of the cases and 67% a single canal; similar to other studies [3, 4, 10, 11, 18, 19, 32]. Two roots in 8% of the samples, higher than Cleghorn, Rahimi and Yu et al. studies [3, 4, 19], and lower than Bürklein, Zillich, Tian and Huang et al. [2, 10, 11, 32]. 0.52% showed three roots, which matches with other studies [3, 10, 11, 32]. 30.5% samples had two canals, it was in discrepancy with other studies whose appearance rate was around 20% [3, 4, 10, 18, 32]. Only 0.8% showed three canals, in approximate ranges with the Zillich and Yu et al. studies [10, 19]. The C-shaped root canal system was represented 29%, similar with other Chinese population studies: 24%, 27.8% [22, 31] And different with 14% in the USA , 0.55%, 1.14%, and 4.1% in China [18, 19, 26], 0.92%, and 10% in India [17, 25], 1.4%, and 2.4% in the Iranian population [4, 27], as well as 9% in the Finnish population . This discrepancy may be due to differences in races, the number of samples, analysis technique, and application of statistical parameters. The highest C-shape root canal system according to Fan criteria  was C3, similar to Khedmat et al. study . The most frequent canal bifurcation was in the middle third, similar with Liu and Jaju et al. results [9, 31]. Radicular grooves were located in the mesial area nearly to the lingual zone, similar to other findings [1, 9, 20,21,22, 25, 27].
This study reported five cases of mandibular first premolars that could not be classified according to Fan criteria. Three with a single root and two canals; two with three roots and three canals. Canal bifurcation was located in three cases in the middle third, one in cervical third and other in apical third. Radicular grooves were located in the mesial and lingual area in two sample, one case showed buccal and lingual area simultaneously.
Based on the CBCT analysis of this database, the most frequent morphology in the mandibular second premolars was a single root in more than 91% of the cases and 92% a single canal, similar to other studies [10, 11, 19]. Two roots in 1.62% of the samples, higher than Cleghorn study  and lower than Bürklein study . 0.32% showed three roots, which matches with Cleghorn and Bürklein et al. studies [2, 11]. 6.50% samples had two canals, approximate ranges with other studies. [10, 11, 19]. Only 0.64% showed three canals, similar to Bürklein and Zillich studies [2, 10]. The C-shaped root canal system was represented 7%, different with 0.7% in India  0.9–2% in the Iranian population [1, 4], and 0.6% in China . The highest C-shape root canal system according to Fan criteria  was C4a, which could not be correlated with any other study. The most frequent canal bifurcation was in the middle third, similar with Liu and Jaju et al. results [9, 31]. Radicular grooves were located in the mesial area nearly to the lingual zone, similar to other findings [1, 9, 20,21,22, 25, 27].
This study reported four cases of mandibular second premolars that could not be classified according to Fan criteria. Twos cases with a single root and single canal, two with a single root and two canals; Canal bifurcation level was located in one case in the cervical third and three cases in the middle third. Radicular grooves were located in the buccal area in three samples, and the lingual area in another sample.
According to the gender and C-shaped configuration to Fan criteria to the 100% of the C-shaped samples studied, male patients showed 47.72% and Female patients showed 52.27%. Statistical analyses showed that women had a slightly more incidence of C-shape mandibular premolars, similar to Huang and Sert findings [32, 33]. However most other investigations did not pay a special attention to compare the difference between male and female patients studied .
The importance of a proper diagnosis and analysis of cases with anatomical variations implies the application of rigorous criteria in clinical action. In cases of mandibular premolars with C-shaped root canal system configurations, use of magnification and instrumentation with anti-curvature technique is recommended due to the roots concavities, dentinal thinness walls on the lingual zone near to the mesial area and their narrow canals. Excessive dentinal remove could cause band perforations, transportation, or apical perforation. It is necessary the use of copious irrigation with sodium hypochlorite, ultrasonic activation to clean the presence of isthmus and use of EDTA. Obturation with thermoplastic gutta-percha technique is recommended, thus guarantees the success of the therapy or reduces its failure [6, 35].