DOI: https://doi.org/10.21203/rs.3.rs-1772983/v1
This study evaluated the prevalence of first and second maxillary and mandibular molars with C-shaped canal separately according to gender, type and side of teeth and in terms of C-shaped classification in an Iranian sub-population
In this study, 3233 CBCT scans were obtained by Planmeca Scanner device by exposure time = 12 seconds, voxel size = 0.2mm, voltage of 80 kV and 15 mA. The images were observed by visualization software and the incidence of C-shaped canal was classified by Fan et al. (2004) methods.
In this study the prevalence of C-shaped molars was equal to 4.86%. The incidence of the first and second C-shaped molars was also 2.81% and 5.47%; the incidence of the mandibular first and second C-shaped molars were 4.49% and 8.38%; and this prevalence in maxilla was also 1.47% and 2.32%. Significant differences existed regarding the incidence of C-shaped canal configurations in the first and second molars in total molars (p < 0.001) and mandibular molars (p < 0.004); however, no significant differences were seen regarding C-shaped canal configurations in the first and second maxillary molars .No significant difference was generally observed in the prevalence of C-shaped canals according to side of teeth and between males and females except in the maxilla. Among mandibular molars, C1 and C2 C-shaped configurations were seen more frequently.
Since the racial factors influence the anatomy of teeth, evaluating the prevalence of C-shaped canals in different populations to identify and raise the level of caution in the treatment of this type of root canals become more and more important.
Since the anatomical variety of teeth faces the process of endodontic treatment with many complications; therefore, comprehensive knowledge of morphology and possible anatomical shapes of the root canal system is a critical causal factor in achieving successful treatment outcome. (1, 2)
One of the most common anomalies among human teeth is the presence of C-shaped root canals. A C-shaped canal appears when fusion either on the buccal or lingual aspect of the tooth between distal and mesial roots occurs. The result of this adhesion is the presence of a canal in form of a band, including distal, mesiobuccal, and sometimes mesiolingual canals. In C-shaped canals pulp chamber has a single ribbon-shaped orifice with a 180 ° arc starts from the mesiolingual surface and ends in the distal region of the pulp chamber.(3, 4)
Cook and Cox (1979) were the first to demonstrate the clinical importance of C-shaped canals. Irregular areas containing residual soft tissue or inflamed and infected zone in C-shaped canals may be out of reach during the cleansing. (5) To that end, Fan et al. revealed that radiographic images, including the identification of cohesive roots, can be a guide to the existence of C-shaped channels, although diagnosis of C-shaped channels based on radiography alone is not always possible. (5, 6)
Likewise, previously published literature reported that use of cone-beam computed tomography (CBCT) to evaluate the anatomy of root canals is valid and accurate method. To put it another way, root morphological images of teeth using CBCT technique are higher resolution compared to conventional radiography. (7, 8)
As the anatomy of the root canals has even been influenced by factors such as ethnic and geographical dispersion, race factor is one of the influential parameters in the prevalence of C-shaped canals among molars. (9, 10)
After extensive review of literature, no study has been conducted on the prevalence of this form of canals in the maxillary and mandibular molars in the population of Hamadan City. For this reason, aim of the current study was to evaluate the prevalence of C-shaped canals according to CBCT images in mentioned population.
In this experimental and laboratory study, 3233 CBCT images of first and second molars of mandible and maxillae were selected and analyzed. All scans were prepared for diagnostic purposes and before implant treatments. Since the present study is an observational study and all images have already been prepared for the purpose of implant treatment and their preparation was not related to the present research, therefore; under the supervision of the Ethics and Research Committee of Hamadan University of Medical Sciences there is no need to obtain patient consent and there was no special problem in terms of observing ethical considerations. in addition; all experimental protocols were approved by Ethics and Research Committee of Hamadan University of Medical Sciences and all methods were carried out in accordance with relevant guidelines and regulations.
An inclusion criterion was the presence of at least one molar in clinical examination and exclusion criteria included previous root canal treatments and teeth with artificial images.
CBCT scans were performed using the New tom 3G device and all images were taken in size 0.2 mm voxel, 80 kV and 15 mA with an exposure time of 12 seconds. Tooth images were examined using visualization software. The cross sections used in the study were 0.6 mm thick and noise reduction and artifact filters were used to observe the teeth. Finally C-shaped molar's root canal systems were classified. (Fig. 3)
Classification in molar teeth is based on 2 different criteria: Root fusion and 3 consecutive cross sections with upper C1 (UC1) or UC2 configuration. According to Fan et al. study; the configuration system for the upper and lower molar teeth is different. (11)
The UC system has 5 axes of configuration for the root canal:
UC1: Large, continuous C-shaped canal system
UC2: Continuous C-channel with 2 main canal lumens connected at the end by a large strait.
UC3: Existence of 2 separate root canals
UC4: Single round or elliptical root canal
UC5: Root canal without canal lumen
Cross-sectional images were observed at 5 levels of the root canal system. These levels were:
2 mm below the orifice (crown), 2 mm above the anatomical head (head), intermediate distance of canal orifice and anatomical head (middle), distance between the crown and the middle part (one third) and the distance between the middle and the top (two thirds).
Figure 1 shows the C-shaped canals classification system for the maxilla.
Figure 2 shows the C-shaped canals classification system for the mandible, according to this, 4 different types of C-shaped canals are C1, C2, C3 and C4, respectively, from left to right.
Data analysis in the present study was performed with SPSS statistical software (Statistical Package for Social Sciences) version 0.23. For this purpose, the frequency of C-shaped canals in the first and second molars of the maxilla and mandible were determined and reported in the CBCT images of patients according to gender, position of the teeth and overally.Comparison of C-shaped canals frequency by gender, the position of the teeth and the type of molar teeth were performed using chi-square test. Kappa test was used to determine the degree of observer agreement in 2 observations of CBCT images to determine the prevalence of C-shaped canals. The type1 error in the present study was equal to 0.05 (α = 0.05).
To assess the internal reliability of CBCT image observations in the peresent study, one observer assessed 10% of the total teeth (323 teeth) twice at 1-month intervals and the kappa agreement coefficient between two observations was 91.1% with a standard error of approximately 0.083 (0.911 ± 0.083). Also, the agreement for all teeth (3233) was estimated at a high and very good level (0.919 ± 0.025).
Out of 3233 molars, 157 teeth (4.86%) had C-shaped canals. Prevalence of C-shaped canals in males equal to 4.49% (52 teeth, prevalence confidence interval is 3.3% -5.68%) and in females equal to 5.06% (105 teeth, prevalence confidence interval equal to 4.12% -6.0%) was reported (p = 0.52).(Table 1)
Prevalence of molar teeth with C-shaped canals on the right was 4.66% (76 teeth, prevalence confidence interval is 3.64% − 5.68%) and on the left was equal to 5.05% (81 teeth, prevalence confidence interval equal to 3.98% -6.12%) (p = 0.66).(Table 2)
Prevalence of first molars with C-shaped canals was equal to 2.81% (38 teeth, prevalence confidence interval equal to 1.93% -3.69% ) and the prevalence of second molars with C-shaped canals was estimated to be 6.3% (119 teeth, prevalence confidence interval equal to 4.44% -6.5%). The prevalence of C-shaped canals in the second molar teeth was significantly higher than the first molars (chi-square test: p < 0.0001).(Table 3)
In details and according to the fallowing tables, in the mandible out of a total of 1580 molars, 43 teeth out of 567 molars belong to males (7.58% with a prevalence interval of 5.4% -9.76%) and 66 out of 1013 teeth belonged to females (6.52% with a confidence interval of prevalence equal to 5.0% -8.04%) were reported with C-shaped canals. There were no significant differences in the prevalence of C-shaped canals in mandibular molars according to gender (chi-square test: p = 0.48).(Table 4)
Out of a total of 1580 mandibular molars, 49 of the 733 teeth are located on the right (6.68% with a prevalence interval of 4.87% -8.49%) and 60 of the 847 teeth on the left side (7.08% with a prevalence confidence interval of 5.35% -8.81%) of patients's mouth had C-shaped root canals (without significant differences: p = 0.83).(Table 5)
Among mandibular molars, 27 first molars out of a total of 602 mandibular first molars(4.49% with a prevalence confidence interval equal to 2.84% -6.14%) and 82 second molars out of 978 mandibular second molars(8.38% prevalence confidence interval equal to 6.64% -10.12%)had C-shaped root canals. The prevalence of C-shaped canals in mandibular first molar teeth was significantly lower than mandibular second molars (chi-square test: p < 0.004).(Table 6)
Among the mandibular first molars, out of 27 teeth with C-shaped root canals, 24 teeth (3.99%, prevalence confidence interval equal to 2.43% -5.55%) had C1 structure, 2 teeth (0.33%, prevalence confidence interval equal to 0.13% -0.79% -) with C2 structure and 1 tooth (0.17%, confidence interval equal to 0.5% − 0.16% -) also had C3 structure.(Table 7)
Likewise, among the mandibular second molars, out of 82 teeth with C-shaped root canals, 54 teeth (5.52%, prevalence confidence interval equal to 4.09% -6.95%) had C1 structure, 24 teeth (2.45%, prevalence confidence interval equal to 1.48% -3.32%) had C2 structure and 4 teeth (0.41%, prevalence confidence interval equal to 0.81% -0.01%) had C3 structure. .(Table 7)
In the maxilla and out of a total of 1653 molars, 9 teeth out of 591 molars belong to males (1.52%, with a prevalence interval of 0.53% -2.51%) and 39 out of 1062 teeth belonged to females (3.67% with a confidence interval of prevalence equal to 2.54% -4.8%) were estimated with C-shaped canals. The prevalence of C-shaped canals in maxillary molars was significantly higher in females than males (chi-square test: p < 0.02).(Table 8)
Out of a total of 1653 maxillary molars, 27 of the 897 teeth located on the right (3.01% with a prevalence interval of 1.89% -4.13%) and 21 of the 756 teeth on the left side of patients's mouth (2.78% with a prevalence confidence interval of 1.61% -3.95%) had C-shaped root canals (without significant differences: p = 0.89).(Table 9)
Among maxillary molars, 11 first molars out of a total of 749 maxillary first molars(1.47% with a prevalence confidence interval equal to 0.61% -2.33%) and 37 second molars out of 904 maxillary second molars(4.10% prevalence confidence interval equal to 1.34% -3.3%)had C-shaped root canals.There was no significant difference in the prevalence of C-shaped canals between the first and second maxillary molars (chi-square test: p = 0.28). (Table 10)
In the maxilla and out of 749 first molars, 11 teeth had C-shaped canals. Of these teeth, 1 tooth (0.13%, prevalence confidence interval equal to 0.13% -0.39% -) with structure A,2 teeth (0.27%, prevalence confidence interval equal to 0.1% -0.64% -) with B1 structure, 6 teeth (0.8%, prevalence confidence interval equal to 0.16% -1.44%) with Structure C,1 tooth (0.13%, prevalence confidence interval equal to 0.13% − 0.39% -) with D structure and 1 tooth (0.13%, prevalence confidence interval equal to 0.13% − 0.39% -) with E2 structure was observed (Table 11).
Also,In the maxilla out of 904 second molars, 37 teeth had C-shaped canals. Of these teeth, 8 teeth (0.88%, prevalence confidence interval equal to 0.27% -1.49%) have structure A, 4 teeth (0.44%, prevalence confidence interval equal to 0.01% -0.87 0%) has structure B1, 7 teeth (0.77%, prevalence confidence interval equal to 1.34% 0.2%) with B2 structure, 5 teeth (0.55%, prevalence confidence interval equal to 0.03% -0.07%) with structure C and 13 teeth (1.44%, prevalence confidence interval equal to 2.22% -0.66%) also had E2 structure (Table 11).
comprehensive knowledge and appropriate visualization of of root canals anatomy is a crucial factor in increasing the success rate of endodontic treatments and treatment prognosis. Numerous studies have reported different variations in the number and shape of root canals in different races, which appear to be due to genetic factors (1, 9, 10).
Most previously published literature in this field have evaluated the prevalence of C-shaped canals only in the first or second molars and in the maxilla or mandible.To that end in the curent study prevalence of first and second maxillary and mandibular molars with C-shaped canal has been evaluated separately according to gender, type and side of teeth and in terms of C-shaped classification in an Iranian sub-population.
The results demonstrated that the overall prevalence of maxillary and mandibular molars with C shape root canals was 4.86%.Moreover, prevalence of first and second molars with C-shaped root canals was overally estimated to be 2.81% and 6.3% .In details, prevalence of C shape root canals in first and second mandibular molars was estimated to be 4.49% and 8.38%, and in the maxilla it was estimated to be 1.47% and 4.1% respectively. In the present study, significant differences in the prevalence of C-shaped canals in the first and second molars in total molar teeth, also in mandibular molars as well as the maxillary molars were observed.
Prevalence of C-shaped anatomies in the first and second maxillary molars in the Turkish population was equal to 1% and 4.9% (12) and in a Portuguese population equal to 1.1% and 3.8% (13). Lilewise in a study on a Chinese population, the prevalence in the second maxillary molars was reported to be 4.9% (14).Findings from the present study are in the range of prevalence reported in mentioned research.
The prevalence of C-shaped anatomies in the mandibular first and second molars of Israelite population is 0.16% and 4.6% (15) respectively, in the second molars of the Korean population is 36.8% (16)(the prevalence of C-shaped canals is more common in Koreans) ,besides this prevalence in Brazilian population equel to 21.32% has been reported (17). Differences between populations in the prevalence of Cshaped root canal systems emphasize the effect of ethnicity on the root canal anatomy of mandibular molars.
In Iranian population and in the studies of Koozekanani et al (18), Hasheminia et al (19) ,Normandipour et al.(20) The prevalence of mandibular second molars is estimated to be 5.0%, 6.25%, and 30%, respectively, which is less than the findings of present study .this discerpency between reported statistics may be as a result of technical differences in the method of canals evaluation.
According to the results of the present study, no significant difference was generally observed in the prevalence of C-shaped canals between males and females.In details, except in the maxilla, where the prevalence in females was about twice that of males and there were statistically significant differences, in mandible no significant difference was observed.
Similary to the results of curent study no obvious differences were reported in the prevalence of C-shaped mandibular molars of an Israelite population according to gender (15). By contrast, in a study by von Zuben et al. prevalence of C-shaped mandibular second molars in females was significantly higher than males(21).
In a systematic and meta-analysis study conducted in 2019, which examined the prevalence of C-shaped morphology using CBCT, no significant difference between the two gender was mentioned in the first and second molars of the mandible(9).Thus,these differences by gender may be related to the racial factor.
Based on the findings of the study, no obvious differences were reported in the prevalence of C-shaped molars on the right and left side in the maxilla and mandible and also in total number of teeth. This study agrees with Shemesh et al (15) and von Zuben et al studies(21), which demonestrate no significant differences in the prevalence of C-shaped structures on either side of the mouth. The position of the tooth in the mouth does not seem to have obvious effects on the prevalence of C-shaped canals in the molar teeth.
Simillar to Vaz de Azevedo (17) and Yang (16) findings;in the present study, C1 and C2 structures were seen more frequently among mandibular molars.However, no obvious difference in the prevalence of different types was detected in the maxilla between the first and second molars. The different structures of C-shaped root canals in the mandibular molars are well defined; however, in maxillary molars, there is no clear classification of the different C-shaped root canal structures. Therefore, a detailed explanation and specific classification of C-shaped root canals structure in maxillary molars is required (1).
The limitation of the present study is the older age groups of patients referred for implant treatment; however, evaluation of C-shaped canals prevalence requires examination on a wide age range from young to old.
This retrospective CBCT study of a Iranian population showed significant differences in the prevalence of C-shaped canals in the first and second maxillary and mandibular molars. On the other side, no significant difference was generally observed in the prevalence of C-shaped canals according to side of teeth and between males and females except in the maxilla. Since the racial factors influence the anatomy of teeth, evaluating the prevalence of C-shaped canals in different populations to identify and raise the level of caution in the treatment of this type of root canals become more and more important.
Ethics approval and consent to participate
Since the present study is a retrospective study and all images have already been prepared for the purpose of implant treatment and their preparation was not related to the present research, therefore; requirement of patient's informed consent was waived by the Research Ethics Committee of Hamadan University of Medical Sciences. In addition, there was no special problem in terms of observing ethical considerations. in addition; all experimental protocols were approved by Ethics and Research Committee of Hamadan University of Medical Sciences and all methods were carried out in accordance with relevant guidelines and regulations.
Consent for publication
Not applicable
Availability of data and materials
All data generated or analysed during this study are included in this published article.
Competing interests
The authors declare that they have no competing interest.
Funding
This study was supported by Hamadan University of Medical Sciences. (Grant Number 9603161664)
Authors' contributions
In the present study, all authors contributed to the design and implementation of the research, to the analysis of the results and to the writing of the manuscript. All authors read and approved the final manuscript.
Acknowledgements
Not applicable
Tables 1 to 11 are available in the Supplementary Files section.