## 4 Discussion
Before endodontic treatment, clinicians should consider general patient data such as ethnicity or age to increase the chances of successful treatment. Data about root canal morphology and variations obtained from studies in different populations, such as the present study, are necessary because it can help clinicians to plan and modify endodontic treatment accordingly but also to avoid procedural mistakes. Furthermore, it is necessary to be aware of differences in root canal anatomy along its length, from the coronal to the apical part, given that the results of this study indicate a different frequency of a certain categories of \"C\"-shaped canal in different cross sections of the root. Bilateral occurrence of \"C\"-shaped canals was found in 41.2% of patients in the present study, in contrast to significantly lower occurrence in the Korean and Chinese populations [19; 34]. These data can direct the clinician if the anomaly is found to be uni- or bilateral. Data obtained by these types of studies may also help to avoid unnecessary CBCTs, following the principle of \"as low as reasonably achievable\" (ALARA), due to high doses of radiation [43]. Differences in the availability of dental care, preventive and therapeutic procedures within a given population may also influence the results of epidemiological studies. \"C\"-shaped canals and extra roots were found more frequently in the younger population. This can be explained by the fact that the diagnosis and treatment of such teeth is extremely difficult and challenging. The frequency of extracted teeth having a \"C\"-shaped canal or an additional root increases with age, which decreases their frequency in the older population, and this is inversely proportional to the quality of preventive dental care and the preservation of the dentition of a given population. Although some studies used periapical X-rays and orthopantomograms [28; 44; 45], standard radiographs provide only limited information and CBCT is an appropriate three-dimensional technique that can more precisely detect certain morphological variations. Therefore, many recent epidemiological studies on anatomical variations in the endodontic space are carried out using CBCT analysis, and due to ethical reasons, i.e., avoiding unnecessary exposure to relatively high doses of ionizing radiation, the studies usually include those patients for whom CBCT is indicated for various diagnostic or therapeutic reasons. The selection of such participants carries the risk of potential differences in comparison to the general population, and the risk is lower if the number of dental patients included is as high as possible. In total, 608 patients were included in the current study, the same as in the study of the Chinese population [38], which is a relatively high number of subjects in comparison to some other studies [32; 33]. The occurrence of additional roots (radix entomolaris and paramolaris) on lower second molars has not been investigated in the Croatian population so far. Although this study showed that the occurrence of this anomaly in these teeth is low (3.4%), there should be awareness of the possibility of additional roots during endodontic treatment as one of the common reasons for endodontic failure are missed root canals, especially if additional roots and canals are present, which is more common for premolar or molar teeth [46]. One of the reasons for overlooking that supernumerary root is common superimposition with distal root in bucco-lingual direction which makes diagnosis difficult on 2D radiographs. An additional root on the lower molars is more common in the Mongolian race, where it is found in up to 30% of molars [47], and it is considered a normal anatomical variation for this group of ethnicities in contrast to Caucasians where this is rare condition, reported in only 3.4% to 4.2% of patients, and it is considered an anatomical aberration [48]. The root canal system is complex with root canals apically splitting and uniting during its course.