## 3 Results  
608 CBCT images were included in the study and 859 lower second molars were analyzed; 423 (49.2%) belonging to the third quadrant and 436 (50.8%) to the fourth quadrant. Data were collected from 608 subjects, with 251 (41.2%) subjects having lower second  
Figure 1: [PERSON]’s classification: (**a**) CATEGORY I (C1): continuous “C” shaped canal running from the canal orifice to the apex; (**b**) CATEGORY II (C2): the shape of the canal resembles a semicolon (_j_), which is the result of “C”-shaped canal separated from another distinct canal; (**c**,**d**) CATEGORY III (C3): two or three separate canals; (**e**) CATEGORY IV (C4): one round or oval canal; (**f**) CATEGORY V (C5): the canal lumen is not visible and cannot be observed.  
molars present on both sides; while in 357 subjects, a lower second molar was present unilaterally.  
The analyzed sample of 859 teeth included 282 males and 577 females with an average age of 30 years. Given that in the Croatian population mandibular molars are the most frequently extracted or endodontically treated teeth, which excludes them from this research, the majority of the subjects whose scans could be used for the purpose of this study were scans of subjects between the ages of 18 and 35.  
A \"C\"-shaped canal was present in 78 subjects (9.1%, with a confidence interval of CI 7.2-11.0%). The canal was divided into three thirds: coronal, middle and apical, and each third was classified according to [PERSON]'s classification (Figures 2 and 3). The results of the frequency of different types of \"C\"-shaped canals in all three thirds of root canals are shown in Table 1.  
In the mesial root, two canals were the most frequently present, in six hundred and eighty-nine cases (88.2%, CI 86.0-90.5%), in ninety-one roots, one root canal was found (11.7%, CI 9.4-13.9%), while three canals were found in only one root (0.1%, CI 0.1-0.4%). In  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Root Canal**} & \multicolumn{4}{c}{**Root Canal Type According Melton’s Classification**} \\ \cline{2-6}  & **C1** & **C2** & **C3c** & **C3d** & **C4** \\ \hline Coronal third & 14.1\% & 24.4\% & 35.9\% & 15.4\% & 10.3\% \\ \hline Middle third & 6.4\% & 21.8\% & 44.9\% & 19.2\% & 7.7\% \\ \hline Apical third & 10.3\% & 14.1\% & 33.3\% & 26.9\% & 15.4\% \\ \hline \hline \end{tabular}
\end{table}
Table 1: Frequency of different Melton’s types of “C”-shaped canals in lower second molars in all three cross sections.  
Figure 3: Horizontal cross section of coronal (**a**), middle (**b**) and apical third (**c**) of the same category of “C”-shaped canal in lower second molar (**C4**).  
Figure 2: Horizontal cross section of coronal (**a**), middle (**b**) and apical third (**c**) of “C”-shaped canal in lower second molar showing different categories according to [PERSON]’s classification (C1, C2, C4, respectively).  
the distal root, one root canal was most frequently present, in 758 teeth (97%, CI 95.9-98.2%), and two canals were found in 23 teeth (3.0%, CI 1.8-4.1%). No statistically significant differences were found in the number of mesial root canals in teeth on the left side of mandible when compared to the teeth on the right side (Chi Square test, \(p=0.592\)).  
Regarding the Vertucci classification of the canals in the mesial roots, the most frequently observed types of root canals were: Type IV in 352 cases (45.1%, CI 41.6-48. 6%), Type II in 320 cases (41.0%, CI 37.5-44.4%) and Type I in 94 cases (12.0%, CI 7.8-14.3%) (Table 2).