CBCT and Micro-CT analysis of the mandibular first premolars with C-shaped canal system in Chinese population

CBCT and Micro-CT analysis of the mandibular first premolars with C-shaped canal system in Chinese population | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article CBCT and Micro-CT analysis of the mandibular first premolars with C-shaped canal system in Chinese population Yimeng Zhang, Xunben Weng, Yu Fu, Xuekai Qi, Yihuai Pan, Yu Zhao This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2735845/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Purpose The purpose of this study was to determine the prevalence of C-shaped root canal system in mandibular first premolar in Chinese population and to analyze the anatomical characteristics by Cone-beam computed tomography (CBCT) and Micro–computed tomography (Micro-CT) together. Methods CBCT images of 760 patients (1520 mandibular first premolars) were evaluated for the prevalence of C-shaped root canal system and the correlation with gender, age and position. 66 mandibular first premolars with C-shaped root canal system were scanned by Micro-CT and analyzed for morphologic features of the root canal anatomy (radicular groove, C-shaped root canal categories, accessory and connecting canals, apical foramina and accessory foramina). Results C-shaped root canal system was found in 16.9% of mandibular first premolars. The minimum mesial wall thickness was mostly measured at the lingual site (69.7%). Among the cross-sectional C-shaped root canal system classifications, the highest prevalence was C2 type (41.5%). In the 3D C-shaped root canal system classification, the highest prevalence was S type (34.8%). Accessory canals were observed in 48.5% of the samples, mostly in the middle region. The presence of 1-3 variable connecting canals was observed in 42.4% of the samples. The number of apical foramina was predominantly 1 (40.9%). Conclusions The incidence of C-shaped root canal system in mandibular first premolars was 16.9% in the Chinese population. It mostly had anatomical features such as deep root surface grooves, with C2 type and S type being the most prevalent. C-shaped canal morphology mandibular first premolar Micro-CT Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction The anatomy of the root canal system is the foundation of root canal therapy. Inadequate root canal therapy processes, such as cleaning and filling, as well as a lack of knowledge of root canal morphology, can all lead to root canal treatment failure. Mandibular first premolar architecture varies, with a high proportion of C-shaped canal configurations [16, 20] . The C-shaped canal system of mandibular first premolars are typically composed of two main pulp canals that combine to form a C-shaped strip in horizontal cross section. The prevalence of the characteristic C-shaped canals has been reported to be 12.5-67.47 % in Asia and South America, which is higher than other sites [23, 34] . Because of its noninvasion, cone-beam computed tomography (CBCT) has been widely employed to understand the complex root canal anatomy in clinical practice, whereas the usual axial slices of CBCT, 108-300m [1, 5, 6, 19, 20, 24, 25, 34] , are too large to give exact pictures of the apical root canal. Thus, despite the fact that it can only be utilized in vitro, micro-computed tomography (Micro-CT), which can offer accurate 3D re-construct, is regarded as the gold standard in the root canal anatomical research [33] . In order to understand the root canal anatomy in public, it may therefore be appropriate to combine the use of CBCT and Micro-CT. The purpose of this study was to investigate the prevalence of mandibular first premolar with C-shaped canal in Chinese as well as to accurately assess its anatomic characteristics by CBCT and Micro-CT. Materials And Methods Sample selection CBCT images of mandibular first premolars were selected from the date of the examinations performed from January 2020 to December 2022 in the hospital of stomatology Wenzhou Medical University. The selection of the mandibular first premolar followed the criteria: the root fully developed without any caries, fracture, resorption, calcification or endodontic treatment. Vague or blurred CBCT images were excluded. The sample including 1520 mandibular first premolars was finally selected from images satisfied those criteria. All of the images were acquired using Newtom VGi (Cefla, Imola, Italy）set at 110kV, 3mA, 150 × 150 mm field of view, and 250 μm voxel size, and were observed though NNT Viewer (12.1.0.0, Cefla, Imola, Italy). All procedures in this study were approved by the Ethics Committee of School and Stomatology Wenzhou Medical University (WYKQ2021007). The extracted teeth were collected from clinical practice. The reasons of extraction were unrelated to this study. Including criteria were the same as previous. The teeth were examined according to the morphologic criteria [26] and were clearly identified as mandibular first premolars. The teeth were ultrasonic cleaned to remove attached soft tissues and calculus and stored in 10% neutral buffered formalin. Every 7 samples were attached to one specimen holder (6 mm diameter) via a sponge custom-made accessory and scanned by Newtom VGi (Cefla, Imola, Italy）to make sure the samples with the C-shaped canal anatomy. Finally 66 mandibular first premolars were selected to analysis the anatomic characteristics. In this study, the definitions of C-shaped root canals were categorized according to Fan's [8] criteria: continuous C-shaped root canals (C1), interrupted C-shaped root canals resembling a semicolon (C2), and two separated root canals with a round, oval, or flattened morphology (C3). The sample was classified as C-shaped root canal morphology when it contained a root surface groove and showed the aforementioned morphology in at least one cross-section. CBCT image analysis The patient's age and gender were recorded for each image file. The prevalence of C-shaped canal system in different gender and age groups was calculated. The presence or absence of root surface grooves, as well as the direction in which they are distributed in the roots (buccal, lingual, mesial and distal) were recorded. A brief examination of the cross-sectional pictures to locate mandibular first premolar teeth with C-shaped root canals, noting their left and right location. A thorough examination was conducted to differentiate the presence of various types of C-shaped root canals in the coronal, middle, and apical zones of the roots. Micro CT evaluation All the 66 mandibular first premolars were scanned by Micro-CT( SkyScan 1176; Bruker-micro-CT, Kontich, Belgium) at 90 kV , 270 µA, 0.1 mm Cu filter, 17.54 µm pixel size, and 360° rotation with a rotation step of 0.5°. The raw data was reconstructed by NRecon (v 1.6.10.4; Bruker-micro-CT, Kontich, Belgium) and was exported in TIFF format. Micro CT image analysis The teeth in one specimen holder were segmented by DataViewer (v 1.5.6.2; Bruker-micro-CT, Kontich, Belgium). Information as followed that was evaluated and analyzed by CTAn (v 1.20.3.0; Bruker-micro-CT, Kontich, Belgium), and 3D models were created in STL format by the same software. The canals were observed by CTVol (v 2.3.2.0; Bruker-micro-CT, Kontich, Belgium) and the roots by CTVox (v 3.3.0.0; Bruker-micro-CT, Kontich, Belgium). The radicular groove: a) The number, depth and angle [28] of the radicular groove from the cemento-enamel junction (CEJ) to the apex [8] (Fig.1 ) and its location on the mesial, distal, buccal or lingual surface of the root were measured. The measurement levels were selected as the cementoenamel junction (CEJ); 1 mm below the cementoenamel junction (CEJ-1); 2 mm below the cementoenamel junction (CEJ-2); the junction of the coronal third and middle third of the root (CM); 1 mm above the middle of the root (M+1); the middle of the root (M); 1 mm below the middle of the root (M-1); the junction of apical third and middle third of root (AM); 2 mm above the apical (A+2); 1 mm above the apical (A+1); and the apical (A). b) The minimum mesial wall thickness of a cross section that showed C-shaped configuration according to the method of Chai et al [7] (Fig.2) was recorded. The measurement sites were classified as buccal, which included the buccal side of C1 and the buccal canal of C2 and C3; isthmus, which included the constricted region of C1 and the equivalent portions of C2 and C3; and lingual, which included the lingual side of C1 and the lingual canal of C2 and C3. The root canal configurations: The three-dimensional C-shaped root canal system proposed by Fan et al [10] was divided into four categories according to the continuous variation of root canal morphology in the axial direction as follows: Continuous C-shaped canal only (C); Semilunar buccal canal only (S); Combination of continuous C-shape and semilunar buccal canal (CS); C-shaped canal interrupted by non-C-shaped canal (CS+N). The accessory and connecting canals: The number and its location in the root thirds were recorded. The apical foramina: The number and its widest and narrowest diameter according to the method described by Wolf et al [32] (Fig.3）. They concluded that when multiple apical foramina exist, the difference in diameter between apical foramina should not be more than 0.2 mm. Otherwise, the side with the smaller diameter is considered to be the accessory foramen. The accessory foramina: The number and its location in the apex were recorded (Fig.4）. Statistical analyses Each measurement was repeated three times, and the mean was taken. All the recorded data were introduced in SPSS (v 23; SPSS Inc., Chicago, IL, USA). The normal distribution of the data was confirmed by the Shapiro–Wilk test ( p <0.05). The Kruskal-Wallis statistical test was used to analyze the difference among C-shaped canals and cross-section levels and the Mann-Whitney U test was used to analyze the difference between groups. Spearman's multiple linear regression tests for interparameter dependence. Statistical significance was considered at p <0.05. Results CBCT findings In the 1520 mandibular first premolar images, 29.41% (447/1520) had radicular groove and 16.9% (257/1520) had the C-shaped canal. The sample was collected from 760 different patients (343 men and 417 women) with an average age of 32.2 years old. From the 257 C-shaped canal mandibular first premolars, 119 were from males (17.3%) and 138 from females (16.5%). The difference of C-shaped canal system prevalence between sex was considered nonsignificant at p ＞0.05. In different age groups, patients of the youngest (15-20, 25.5%) group showed significant higher prevalence than any other group and the younger (21-40, 16.6%) group also showed significant higher prevalence than the oldest (＞60, 7.6%) group. Regarding the left and right sides, 136 were found on the left side (17.9%) and 121 were found on the right side (15.9%). The difference between the sides was considered nonsignificant at p ＞0.05 (Table 1). The analysis of the different types of C-shape configurations in the three different axial levels showed in Table 2 (Fig 5). The highest prevalence of C-shaped canal system showed in C2 type (51.5%). In the apical third (59.7%), C-shaped canal system was mostly observed( p <0.05). The distribution of C3 type at each axial level differed from C1 type and C2 type ( p <0.05), which was more common in the apical third (79.5%). Micro CT findings The anatomic characteristic of 66 C-shaped canal mandibular first premolars were analyzed by Micro-CT. The mesial surface of the root was the location of the most (61.4%) of all 169 radicular grooves (Table 3). A total of 188 cross sections with C-shaped canal were scattered from CM to A+1 (Table 4), while the highest prevalence showed in M-1 52(27.7%) and the lowest in A+1 3(1.6%). Among the cross sections the difference of the minimum mesial wall thickness was statistically not significant ( p >0.05). The minimum mesial wall thickness frequently showed in lingual site 131(69.7%) and rarely in buccal site 25(13.3%) ( p <0.05). The minimum mesial wall thickness decreased at closing to the apex (Table 5). The median of the groove depth and angle were reached the extreme value in M-1. In those cross sections, C2 showed the highest prevalence 78 (41.5%) agreeing with the CBCT result (Table 6). Among C-shaped canal types, the differences observed between the isthmus zone and the other two groups were significant ( p 0.05). Among the locations, the C-shaped canal type showed statistically significant ( p <0.05). The correlation analysis with the mesial wall thickness and location of the measurement as the dependent variable is presented (Table 7). Cross section level ( p <0.05, r =-0.433), location ( p <0.05, r =0.396), depth ( p <0.05, r =-0.371) and angle ( p <0.05, r =0.438) of the groove were related to the mesial wall thickness. Depth ( p <0.05, r =0.462) and angle ( p <0.05, r =0.460) were related to the location of the measurements. The percentage of S type (Table 8) was the highest 23(34.8%). The three-dimensional morphology of each classification was shown in Fig 6.CS+N type showed the lowest prevalence 5(7.6%), the difference between the types was statistically significant ( p 0.05). Accessory canals were present in 24(46.2%) specimens (Table 9). In the specimens present, accessory canals were majorly located in the middle 23(59.0%) and less often in the coronal 2(5.1%). The number of accessory canals in different locations was no statistically significant ( p >0.05) with a single one. Among C-shaped canal types, S type showed the highest incidence of accessory 18(42.9%) and C type showed the lowest incidence 2(4.8%) (Table 10). Connecting canals were observed in 28(42.4%) specimens. The number of connecting canals differed from 1 to 3 among different roots (Table 11). One connecting canal was more prevalent 26(81.3%) in the specimens. In the apical third, connecting canals were more frequently observed 19(59.4%). S type was more commonly observed 15(46.9%) with connecting canals (Table 12). One physiological foramen was mostly observed in specimens 27(40.9%). The more numerous the physiological foramina there were, the smaller the narrow ( p <0.05, r =-0.591) and the wide ( p 0.05). Accessory foramina were found in 45(68.1%) specimens (Table 14). Two accessory foramina accounted for the highest ratio 26(26.0%) and six for the lowest 6(6.0%). The highest proportion of opening orientation was found in the mesial 46(46.0%). The number of accessory foramina was not correlated with C-shaped canal types ( p >0.05). Discussion It was the region and the race [8, 10, 12, 20, 21, 23, 33] that possibly varied the prevalence and characteristics in mandibular first premolars as reported. In this study, CBCT images were collected from 760 patients in China, of whom 343 were males and 417 were females, and the prevalence of C-shaped root canals was 17.3% and 16.5%, respectively. There was no statistically significant difference between the two. This was consistent with the findings of most previous studies, Martins [21] et al reviewed the prevalence, odds ratio and heterogeneity of C-shaped root canal system in mandibular first premolar by gender, where no significant differences were observed ( p >0.05). In this study, the prevalence of C-shaped root canal system tended to decrease as the age of the patients increased. It is considered that this was mainly due to the fact that the teeth in the 15-20 years old group are young permanent teeth with fully developed roots and have large canals and pulp chambers [11, 31] , which are more easily observed at the same resolution. Whereas, natural physiological aging on the one hand, and on the other hand, long-term environmental stimulation, such as occlusal trauma and periodontal disease, can modify the deposition of dentine [17] and root canal system morphology [15] , together lead to thickening of the root canal wall and thinning of the root canal. These canals are more blurred at the same resolution, and the characteristic C-shaped root canal morphology is more difficult to discern. Amongst 1520 CBCT images, C2 showed the highest prevalence 51.5% and distributed mainly in the middle 49.3% and the apex 47.3%, C3 showed secondly 38.7% and mainly in the apex 79.5%. This suggests that root canal bifurcations are typically located in the lower and middle segments, which are not visible with the naked eye, and that lingual root canals are more curved and possess a distinct presence of dentin cusp collars and a narrower diameter than buccal root canals. Similar results were obtained in a study by Ordinola-Zapata et al [23] , that C1 and C2 being more prevalent in the coronal and middle of the root, and C3 being more common at the apical, with the apical being more prone to complex root canal morphology. In the present study, the buccal and the lingual canal of CS type were combined in only 36.4% (8/22) of the three-dimensional classification of C-shaped canals by Micro-CT. And most of the CS type, the buccal and the lingual canal were still present separate, increasing the anatomical complexity of the mandibular first premolar in the middle and apex. According to Li et al [18] , 69% of the Vertucci V class's mandibular first premolars bifurcated in the middle of the root to form a lingual root canal. In the proximal directions, the lingual root created a modest angle with the buccal root, while an average of 33.54° angle existed in the buccolingual direction, with 77% of the sample considerably twisted. Therefore, root canal misses are prone to occur when probing is performed during root canal treatment. It is recommended that clinicians take CBCT preoperatively to fully grasp the root canal morphology and pre-curved K files intraoperatively under the microscope or with the use of ultrasound to remove part of the root canal cusp collar in order to explore the lingual root canal, which is divided into the middle and lower parts of the root canal. The Micro-CT results of this study revealed that C-shaped root canals were most prevalent from M+1 to AM cross-section of the root canal, which varied with the CBCT results, most likely due to the huge disparity in accuracy between CBCT and Micro-CT. The voxel size of CBCT (250 μm) is larger than the diameter of the middle and apical root canal [4, 29] . According to the Shannon-Nyquist theory, when 1/2 the size of the object was larger than the resolution of CBCT, the image of the object could be observed in CBCT [3] . And Moreno et al [22] reported a narrower diameter of 0.24 ± 0.10 mm at 3 mm from the root apex measured by Micro-CT (voxel size 17 μm), at which time some of the tiny root canals could not be easily distinguished, creating inaccuracies. Previous studies on mandibular second molars have shown that the wall of the C-shaped root canal is thinner on the side near the root surface groove than on the remaining side [7, 9, 14] . In the present study, the cross-section of the C-shaped root canal was measured and the lingual mesial wall was usually the thinnest (69.7%). Gu et al [12] measured the canal wall thickness at various levels in C-shaped root canals of mandibular first premolar teeth and confirmed that the above findings were also applicable in mandibular first premolar teeth, while the lingual measurement site was frequently found to have the minimum mesial wall thickness (67.3%). The irregular morphology of C-shaped root canals is more likely to result in strip perforation during root canal preparation [10, 27] . Huysmans et al [13] used a mock cephalometric model to imitate the root canal cleaning procedure of the mandibular first premolar and discovered that more dentin was removed from the mesial wall of the prepared mandibular first premolar than from the remaining three lateral walls. Nonlinear regression study revealed that the further the distance from the cemento-enamel junction, the greater the depth of the root radicular groove, and the smaller the angle, the thinner the mesial wall thickness. As a result, mechanical preparation of the root canal, particularly the lingual root canal and the apical segment, must be done carefully during treatment to prevent unwanted deviation and perforation, which could lead to root canal treatment failure. In this work, the morphology of C-shaped root canals was classified by Fan's criteria, and the relationship between the classification and the various characteristic morphologies was investigated. The C-shaped root canal cross-sectional classification, did not correlate with each characteristic morphology ( p >0.05), that is, there were no distinguishable dental morphological features between the different C-shaped root canal cross-sectional categories. Three-dimensional classification of C-shaped root canals correlated with the number of accessory canals ( p <0.05, r =0.330) and connecting canals ( p <0.05, r =0.369), that means, the number of accessory canals was ranked in closer to C type, S type, CS type, CS+N type. The more complicated the C-shaped root canal anatomy, the greater the likelihood of accessory canals and connecting canals. For a healthy mandibular first premolar tooth means a richer nerve and blood supply support, which aids in the resistance to pulp infection in its early stages, as well as additional communication pathways to the oral condition. When the infection spreads it becomes an insidious area of infection and places a higher demand on the debridement. Deep grooves on the root surface enhance the periodontal membrane's attachment site, which contributes to maintaining the integrity of the tooth. On the other hand, when periodontitis occurs, it is more likely to develop deep periodontal pockets and infect the pulp through the accessory canals of the root canal. The results of this study showed that the number of mandibular first premolar apical foramina was predominantly 1-2. The number of foramina varies and there is a significant difference of the maximum diameter and the narrowest diameter measured. To thoroughly clean the apical region, the primary file size must be large enough to contact all canal walls [2] , and therefore the primary file diameter should be larger than the maximum diameter. However, for oval root canals, prepping the root canal in a round shape may excessively remove the dentin and weaken the root [30] . Therefore, taking into account the traditional opinion that the primary file should be 2 or 3 sizes larger than the initial file, this study proposed the following suggested primary file numbers for mandibular first premolar teeth with different number of apical foramina: #35 for 1 apical foramen and #30 for 2 and 3 apical foramina. Conclusion The findings of this study suggested that C-shaped root canal system in mandibular first premolar teeth was prevalent in Chinese population. The anatomical structure was complex and variable, mostly distributed in the middle and the apex of the root canal. The mesial wall was thin on the lingual side and should be protected against perforation during preparation. Declarations Conflict of Interest All authors have no conflicts of interest to declare. Funding This study was supported by the National Natural Science Foundation of China (80218095). Ethical approval All procedures performed in studies involving human participants were in accordance with the ethical standards of the Ethics Committee of School and Stomatology Wenzhou Medical University (WYKQ2021007). Informed Consent statements For this type of study, formal consent is not required. Data Availability The CBCT and micro-CT images data used to support the findings of this study are restricted by the local institutional review board at the Wenzhou Medical University in order to protect patients’ privacy. Author Contribution YM Zhang: Project development, Data management, Data analysis, Manuscript writing XB Weng: Data management, Data analysis, Manuscript writing Y Fu: Data collection XK Qi: Data collection YH Pan: Project development, Manuscript editing Y Zhao: Project development, Manuscript editing Authorship changes are no longer possible after the final acceptance of an article! References Alfawaz H, Alqedairi A, Alkhayyal AK, Almobarak AA, Alhusain MF and Martins JNR (2019) Prevalence of C-shaped canal system in mandibular first and second molars in a Saudi population assessed via cone beam computed tomography: a retrospective study. Clin Oral Investig 23:107-112. https://doi.org/ 10.1007/s00784-018-2415-0 Arora S and Tewari S (2009) The morphology of the apical foramen in posterior teeth in a North Indian population. Int Endod J 42:930-9. https://doi.org/ 10.1111/j.1365-2591.2009.01597.x Blackledget JM (2006) Digital Signal Processing. 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Restor Dent Endod 40:161-5. https://doi.org/ 10.5395/rde.2015.40.2.161 Szabo BT, Pataky L, Mikusi R, Fejerdy P and Dobo-Nagy C (2012) Comparative evaluation of cone-beam CT equipment with micro-CT in the visualization of root canal system. Ann Ist Super Sanita 48:49-52. https://doi.org/ 10.4415/ANN_12_01_08 Tan BT and Messer HH (2002) The quality of apical canal preparation using hand and rotary instruments with specific criteria for enlargement based on initial apical file size. J Endod 28:658-64. https://doi.org/ 10.1097/00004770-200209000-00008 Thomas RP, Moule AJ and Bryant R (1993) Root canal morphology of maxillary permanent first molar teeth at various ages. Int Endod J 26:257-67. https://doi.org/ 10.1111/j.1365-2591.1993.tb00570.x Wolf TG, Paque F, Sven Patyna M, Willershausen B and Briseno-Marroquin B (2017) Three-dimensional analysis of the physiological foramen geometry of maxillary and mandibular molars by means of micro-CT. Int J Oral Sci 9:151-157. https://doi.org/ 10.1038/ijos.2017.29 Wu YC, Cathy Tsai YW, Cheng WC, Weng PW, Su CC, Chiang HS, Chung MP, Chung CH, Shieh YS and Huang RY (2018) Relationship of the Incidence of C-shaped Root Canal Configurations of Mandibular First Premolars with Distolingual Roots in Mandibular First Molars in a Taiwanese Population: A Cone-beam Computed Tomographic Study. J Endod 44:1492-1499 e1. https://doi.org/ 10.1016/j.joen.2018.05.016 Yin X, Cheung GS, Zhang C, Masuda YM, Kimura Y and Matsumoto K (2010) Micro-computed tomographic comparison of nickel-titanium rotary versus traditional instruments in C-shaped root canal system. J Endod 36:708-12. https://doi.org/ 10.1016/j.joen.2010.01.003 Tables Tables 1 to 14 are available in the Supplementary Files section. Additional Declarations No competing interests reported. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-2735845","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":186649547,"identity":"e7c4fc14-b02e-42dc-b819-2a161667295f","order_by":0,"name":"Yimeng Zhang","email":"","orcid":"","institution":"Wenzhou Medical University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yimeng","middleName":"","lastName":"Zhang","suffix":""},{"id":186649548,"identity":"e79cc6a5-bbb4-4e10-87e0-67b586bf0e8a","order_by":1,"name":"Xunben Weng","email":"","orcid":"","institution":"Wenzhou Medical University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Xunben","middleName":"","lastName":"Weng","suffix":""},{"id":186649549,"identity":"29499501-c8d0-412d-86c3-4a24a750e7f4","order_by":2,"name":"Yu Fu","email":"","orcid":"","institution":"Wenzhou Medical University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yu","middleName":"","lastName":"Fu","suffix":""},{"id":186649550,"identity":"5b6066c1-ac6c-4248-9ee1-f7b336f9d71c","order_by":3,"name":"Xuekai Qi","email":"","orcid":"","institution":"Wenzhou Medical University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Xuekai","middleName":"","lastName":"Qi","suffix":""},{"id":186649551,"identity":"00ea428d-2c5e-4074-a337-5a9f28376d66","order_by":4,"name":"Yihuai Pan","email":"","orcid":"","institution":"Wenzhou Medical University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yihuai","middleName":"","lastName":"Pan","suffix":""},{"id":186649552,"identity":"d30f7bcf-89d0-4e04-88eb-960cd2894127","order_by":5,"name":"Yu Zhao","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA6ElEQVRIiWNgGAWjYBACAwYGxgMgBmN78wGI0AGCWpghaph7jiWQqIV9Ro4BcVrMJfIPHPi453Bi74ycb1I32xjk+G4kMH4uwKPFckYyw8EZzw4nzux5u006t43BWPJGArP0DHwOu5HMcJjnwOHEje25224DtSRuuJHAxsxDSMsfoJb9B3KegbTUE6eFAailsSOHDaQlwYCQFsuexwYHew6kGzf2HDP/nXNOwnDmmYfN0vi0mLMnPnzw44C1bGN782PjnDIbeb7jyQc/49MCBc0whgQQMzYQ1sDAUEeMolEwCkbBKBipAAAcZlkuoGv+XgAAAABJRU5ErkJggg==","orcid":"","institution":"Wenzhou Medical University","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Yu","middleName":"","lastName":"Zhao","suffix":""}],"badges":[],"createdAt":"2023-03-25 14:44:12","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-2735845/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-2735845/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":34925891,"identity":"7b110b36-3b44-4624-a538-adc57bfc0dca","added_by":"auto","created_at":"2023-03-28 14:21:41","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":261013,"visible":true,"origin":"","legend":"\u003cp\u003eCross-sectional measurement level.\u003c/p\u003e\n\u003cp\u003eCEJ, the cementoenamel junction; CEJ-1, 1 mm below the cementoenamel junction; CEJ-2, 2 mm below the cementoenamel junction; CM, the junction of the coronal third and middle third of the root; M+1, 1 mm above the middle of the root; M, the middle of the root; M-1, 1 mm below the middle of the root; AM, the junction of apical third and middle third of root; A+2, 2 mm above the apical; A+1, 1 mm above the apical; and A, the apical.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-2735845/v1/3440a1a0cdeeabf3137a2dad.png"},{"id":34925892,"identity":"90fecc49-2223-49b9-9489-b792e1c4ab1d","added_by":"auto","created_at":"2023-03-28 14:21:41","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":602298,"visible":true,"origin":"","legend":"\u003cp\u003eC-shaped root canal cross-sectional measurements.\u003c/p\u003e\n\u003cp\u003e(A) Minimum mesial wall thickness measurement site in C1. (B) Minimum mesial wall thickness measurement site in C2, C3. (C) Line ab is the tangent line of the outer edge of the radicular groove; point c is the midpoint of the tangent points (a and b); the distance from point c to the bottom of the groove (point d) is the depth; ∠adb is the groove angle.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-2735845/v1/366579eb66874bb08827d131.png"},{"id":34926903,"identity":"2739c75f-4b29-4049-ad8c-4065e46f7a65","added_by":"auto","created_at":"2023-03-28 14:29:41","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":143953,"visible":true,"origin":"","legend":"\u003cp\u003eApical foramina diameter measurement.\u003c/p\u003e\n\u003cp\u003eLine ab is the narrowest diameter. Line cd is the maximum diameter.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-2735845/v1/bab8d5cc4f3af8046a2149d9.png"},{"id":34925896,"identity":"62e3d6f2-5cfa-4c42-b357-c269e69d4db7","added_by":"auto","created_at":"2023-03-28 14:21:41","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":323055,"visible":true,"origin":"","legend":"\u003cp\u003e3D modeling picture of accessory foramina.\u003c/p\u003e\n\u003cp\u003e(A) (B) accessory foramina. (C) apical foramen.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-2735845/v1/13907a790b61ec8305247a7a.png"},{"id":34927689,"identity":"e0dbc66c-b980-471c-b23d-00acd84500b1","added_by":"auto","created_at":"2023-03-28 14:37:41","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":350850,"visible":true,"origin":"","legend":"\u003cp\u003eC-shaped root canal representative images of CBCT.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-2735845/v1/9ace2a1b43730c7b296a0404.png"},{"id":34925897,"identity":"d5568c9f-46b1-462a-acea-ce6436127818","added_by":"auto","created_at":"2023-03-28 14:21:41","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":822575,"visible":true,"origin":"","legend":"\u003cp\u003eThree-dimensional C-shaped root canal classification proximal and 45° angle views.\u003c/p\u003e\n\u003cp\u003eRed: non-C-shaped canal; Green: continuous C-shaped canal; Yellow: semilunar buccal canal. (A) Continuous C-shaped canal only; (B) Semilunar buccal canal only; (C) Combination of continuous C-shape and semilunar buccal canal; (D) C-shaped canal interrupted by non-C-shaped canal.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-2735845/v1/dd97a2acd87d7adc41be3035.png"},{"id":35924968,"identity":"c168838f-35dc-476d-90d4-cd27ec1920ef","added_by":"auto","created_at":"2023-04-18 09:29:49","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2439058,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2735845/v1/90b44bbc-1c70-4647-93ce-1da48968f0c1.pdf"},{"id":34925893,"identity":"cb0afd81-0c9a-499a-bb8b-4b11d208c3fa","added_by":"auto","created_at":"2023-03-28 14:21:41","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":122007,"visible":true,"origin":"","legend":"","description":"","filename":"Tables.docx","url":"https://assets-eu.researchsquare.com/files/rs-2735845/v1/d34b7d9de979a3816630265d.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"CBCT and Micro-CT analysis of the mandibular first premolars with C-shaped canal system in Chinese population","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe anatomy of the root canal system is the foundation of root canal therapy. Inadequate root canal therapy processes, such as cleaning and filling, as well as a lack of knowledge of root canal morphology, can all lead to root canal treatment failure.\u003c/p\u003e\n\u003cp\u003eMandibular first premolar architecture varies, with a high proportion of C-shaped canal configurations \u003csup\u003e[16, 20]\u003c/sup\u003e. The C-shaped canal system of mandibular first premolars are typically composed of two main pulp canals that combine to form a C-shaped strip in horizontal cross section. The prevalence of the characteristic C-shaped canals has been reported to be 12.5-67.47 % in Asia and South America, which is higher than other sites \u003csup\u003e[23, 34]\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eBecause of its noninvasion, cone-beam computed tomography (CBCT) has been widely employed to understand the complex root canal anatomy in clinical practice, whereas the usual axial slices of CBCT, 108-300m \u003csup\u003e[1, 5, 6, 19, 20, 24, 25, 34]\u003c/sup\u003e, are too large to give exact pictures of the apical root canal. Thus, despite the fact that it can only be utilized in vitro, micro-computed tomography (Micro-CT), which can offer accurate 3D re-construct, is regarded as the gold standard in the root canal anatomical research \u003csup\u003e[33]\u003c/sup\u003e. In order to understand the root canal anatomy in public, it may therefore be appropriate to combine the use of CBCT and Micro-CT.\u003c/p\u003e\n\u003cp\u003eThe purpose of this study was to investigate the prevalence of mandibular first premolar with C-shaped canal in Chinese as well as to accurately assess its anatomic characteristics by CBCT and Micro-CT.\u003c/p\u003e"},{"header":"Materials And Methods","content":"\u003cp\u003e\u003cstrong\u003eSample selection\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCBCT images of mandibular first premolars were selected from the date of the examinations performed from January 2020 to December 2022 in the hospital of stomatology Wenzhou Medical University. The selection of the mandibular first premolar followed the criteria: the root fully developed without any caries, fracture, resorption, calcification or endodontic treatment. Vague or blurred CBCT images were excluded. The sample including 1520 mandibular first premolars was finally selected from images satisfied those criteria. All of the images were acquired using Newtom VGi (Cefla, Imola, Italy）set at 110kV, 3mA, 150 \u0026times; 150 mm field of view, and 250 \u0026mu;m voxel size, and were observed though NNT Viewer (12.1.0.0, Cefla, Imola, Italy). All procedures in this study were approved by the Ethics Committee of School and Stomatology Wenzhou Medical University (WYKQ2021007).\u003c/p\u003e\n\u003cp\u003eThe extracted teeth were collected from clinical practice. The reasons of extraction were unrelated to this study. Including criteria were the same as previous. The teeth were examined according to the morphologic criteria \u003csup\u003e[26]\u003c/sup\u003e and were clearly identified as mandibular first premolars. The teeth were ultrasonic cleaned to remove attached soft tissues and calculus and stored in 10% neutral buffered formalin. Every 7 samples were attached to one specimen holder (6 mm diameter) via a sponge custom-made accessory and scanned by Newtom VGi (Cefla, Imola, Italy）to make sure the samples with the C-shaped canal anatomy. Finally 66 mandibular first premolars were selected to analysis the anatomic characteristics.\u003c/p\u003e\n\u003cp\u003eIn this study, the definitions of C-shaped root canals were categorized according to Fan's \u003csup\u003e[8]\u003c/sup\u003e criteria: continuous C-shaped root canals (C1), interrupted C-shaped root canals resembling a semicolon (C2), and two separated root canals with a round, oval, or flattened morphology (C3). The sample was classified as C-shaped root canal morphology when it contained a root surface groove and showed the aforementioned morphology in at least one cross-section.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCBCT image analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe patient's age and gender were recorded for each image file. The prevalence of C-shaped canal system in different gender and age groups was calculated. The presence or absence of root surface grooves, as well as the direction in which they are distributed in the roots (buccal, lingual, mesial and distal) were recorded. A brief examination of the cross-sectional pictures to locate mandibular first premolar teeth with C-shaped root canals, noting their left and right location. A thorough examination was conducted to differentiate the presence of various types of C-shaped root canals in the coronal, middle, and apical zones of the roots.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMicro CT evaluation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll the 66 mandibular first premolars were scanned by Micro-CT( SkyScan 1176; Bruker-micro-CT, Kontich, Belgium) at 90 kV , 270 \u0026micro;A, 0.1 mm Cu filter, 17.54 \u0026micro;m pixel size, and 360\u0026deg; rotation with a rotation step of 0.5\u0026deg;. The raw data was reconstructed by NRecon (v 1.6.10.4; Bruker-micro-CT, Kontich, Belgium) and was exported in TIFF format.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMicro CT image analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe teeth in one specimen holder were segmented by DataViewer (v 1.5.6.2; Bruker-micro-CT, Kontich, Belgium). Information as followed that was evaluated and analyzed by CTAn (v 1.20.3.0; Bruker-micro-CT, Kontich, Belgium), and 3D models were created in STL format by the same software. The canals were observed by CTVol (v 2.3.2.0; Bruker-micro-CT, Kontich, Belgium) and the roots by CTVox (v 3.3.0.0; Bruker-micro-CT, Kontich, Belgium).\u003c/p\u003e\n\u003col\u003e\n\u003cli\u003e\n\u003cp\u003eThe radicular groove:\u003c/p\u003e\n\u003c/li\u003e\n\u003c/ol\u003e\n\u003cp\u003ea) The number, depth and angle \u003csup\u003e[28]\u003c/sup\u003e of the radicular groove from the cemento-enamel junction (CEJ) to the apex \u003csup\u003e[8]\u003c/sup\u003e (Fig.1 ) and its location on the mesial, distal, buccal or lingual surface of the root were measured.\u003c/p\u003e\n\u003cp\u003eThe measurement levels were selected as the cementoenamel junction (CEJ); 1 mm below the cementoenamel junction (CEJ-1); 2 mm below the cementoenamel junction (CEJ-2); the junction of the coronal third and middle third of the root (CM); 1 mm above the middle of the root (M+1); the middle of the root (M); 1 mm below the middle of the root (M-1); the junction of apical third and middle third of root (AM); 2 mm above the apical (A+2); 1 mm above the apical (A+1); and the apical (A).\u003c/p\u003e\n\u003cp\u003eb) The minimum mesial wall thickness of a cross section that showed C-shaped configuration according to the method of Chai et al \u003csup\u003e[7]\u003c/sup\u003e (Fig.2) was recorded.\u003c/p\u003e\n\u003cp\u003eThe measurement sites were classified as buccal, which included the buccal side of C1 and the buccal canal of C2 and C3; isthmus, which included the constricted region of C1 and the equivalent portions of C2 and C3; and lingual, which included the lingual side of C1 and the lingual canal of C2 and C3.\u003c/p\u003e\n\u003col start=\"2\"\u003e\n\u003cli\u003e\n\u003cp\u003eThe root canal configurations:\u003c/p\u003e\n\u003c/li\u003e\n\u003c/ol\u003e\n\u003cp\u003eThe three-dimensional C-shaped root canal system proposed by Fan et al \u003csup\u003e[10]\u003c/sup\u003e was divided into four categories according to the continuous variation of root canal morphology in the axial direction as follows: Continuous C-shaped canal only (C); Semilunar buccal canal only (S); Combination of continuous C-shape and semilunar buccal canal (CS); C-shaped canal interrupted by non-C-shaped canal (CS+N).\u003c/p\u003e\n\u003col start=\"3\"\u003e\n\u003cli\u003e\n\u003cp\u003eThe accessory and connecting canals: The number and its location in the root thirds were recorded.\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003eThe apical foramina: The number and its widest and narrowest diameter according to the method described by Wolf et al \u003csup\u003e[32]\u003c/sup\u003e (Fig.3）. They concluded that when multiple apical foramina exist, the difference in diameter between apical foramina should not be more than 0.2 mm. Otherwise, the side with the smaller diameter is considered to be the accessory foramen.\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003eThe accessory foramina: The number and its location in the apex were recorded (Fig.4）.\u003c/p\u003e\n\u003c/li\u003e\n\u003c/ol\u003e\n\u003cp\u003e\u003cstrong\u003eStatistical analyses\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEach measurement was repeated three times, and the mean was taken. All the recorded data were introduced in SPSS (v 23; SPSS Inc., Chicago, IL, USA). The normal distribution of the data was confirmed by the Shapiro\u0026ndash;Wilk test (\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05). The Kruskal-Wallis statistical test was used to analyze the difference among C-shaped canals and cross-section levels and the Mann-Whitney U test was used to analyze the difference between groups. Spearman's multiple linear regression tests for interparameter dependence. Statistical significance was considered at \u003cem\u003ep\u003c/em\u003e\u0026lt;0.05.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cstrong\u003eCBCT findings\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIn the 1520 mandibular first premolar images, 29.41% (447/1520) had radicular groove and 16.9% (257/1520) had the C-shaped canal. The sample was collected from 760 different patients (343 men and 417 women) with an average age of 32.2 years old.\u003c/p\u003e\n\u003cp\u003eFrom the 257 C-shaped canal mandibular first premolars, 119 were from males (17.3%) and 138 from females (16.5%). The difference of C-shaped canal system prevalence between sex was considered nonsignificant at \u003cem\u003ep\u003c/em\u003e＞0.05. In different age groups, patients of the youngest (15-20, 25.5%) group showed significant higher prevalence than any other group and the younger (21-40, 16.6%) group also showed significant higher prevalence than the oldest (＞60, 7.6%) group. Regarding the left and right sides, 136 were found on the left side (17.9%) and 121 were found on the right side (15.9%). The difference between the sides was considered nonsignificant at \u003cem\u003ep\u003c/em\u003e＞0.05 (Table 1).\u003c/p\u003e\n\u003cp\u003eThe analysis of the different types of C-shape configurations in the three different axial levels showed in Table 2 (Fig 5). The highest prevalence of C-shaped canal system showed in C2 type (51.5%). In the apical third (59.7%), C-shaped canal system was mostly observed(\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05). The distribution of C3 type at each axial level differed from C1 type and C2 type (\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05), which was more common in the apical third (79.5%).\u003c/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eMicro CT findings\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe anatomic characteristic of 66 C-shaped canal mandibular first premolars were analyzed by Micro-CT. The mesial surface of the root was the location of the most (61.4%) of all 169 radicular grooves (Table 3).\u003c/p\u003e\n\u003cp\u003eA total of 188 cross sections with C-shaped canal were scattered from CM to A+1 (Table 4), while the highest prevalence showed in M-1 52(27.7%) and the lowest in A+1 3(1.6%). Among the cross sections the difference of the minimum mesial wall thickness was statistically not significant (\u003cem\u003ep\u003c/em\u003e\u0026gt;0.05). The minimum mesial wall thickness frequently showed in lingual site 131(69.7%) and rarely in buccal site 25(13.3%) (\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05). The minimum mesial wall thickness decreased at closing to the apex (Table 5). The median of the groove depth and angle were reached the extreme value in M-1.\u003c/p\u003e\n\u003cp\u003eIn those cross sections, C2 showed the highest prevalence 78 (41.5%) agreeing with the CBCT result (Table 6). Among C-shaped canal types, the differences observed between the isthmus zone and the other two groups were significant (\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05) and the difference between the buccal and the lingual was statistically not significant (\u003cem\u003ep\u003c/em\u003e\u0026gt;0.05). Among the locations, the C-shaped canal type showed statistically significant (\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05). The correlation analysis with the mesial wall thickness and location of the measurement as the dependent variable is presented (Table 7). Cross section level (\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05, \u003cem\u003er\u003c/em\u003e=-0.433), location (\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05, \u003cem\u003er\u003c/em\u003e=0.396), depth (\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05, \u003cem\u003er\u003c/em\u003e=-0.371) and angle (\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05, \u003cem\u003er\u003c/em\u003e=0.438) of the groove were related to the mesial wall thickness. Depth (\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05, \u003cem\u003er\u003c/em\u003e=0.462) and angle (\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05, \u003cem\u003er\u003c/em\u003e=0.460) were related to the location of the measurements.\u003c/p\u003e\n\u003cp\u003eThe percentage of S type (Table 8) was the highest 23(34.8%). The three-dimensional morphology of each classification was shown in Fig 6.CS+N type showed the lowest prevalence 5(7.6%), the difference between the types was statistically significant (\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05). In 36.4% (8/22) samples of CS type, semilunar buccal canals merged with the lingual canals. Among those types, the occurrence of groove was similar (\u003cem\u003ep\u003c/em\u003e\u0026gt;0.05).\u003c/p\u003e\n\u003cp\u003eAccessory canals were present in 24(46.2%) specimens (Table 9). In the specimens present, accessory canals were majorly located in the middle 23(59.0%) and less often in the coronal 2(5.1%). The number of accessory canals in different locations was no statistically significant (\u003cem\u003ep\u003c/em\u003e\u0026gt;0.05) with a single one. Among C-shaped canal types, S type showed the highest incidence of accessory 18(42.9%) and C type showed the lowest incidence 2(4.8%) (Table 10).\u003c/p\u003e\n\u003cp\u003eConnecting canals were observed in 28(42.4%) specimens. The number of connecting canals differed from 1 to 3 among different roots (Table 11). One connecting canal was more prevalent 26(81.3%) in the specimens. In the apical third, connecting canals were more frequently observed 19(59.4%). S type was more commonly observed 15(46.9%) with connecting canals (Table 12).\u003c/p\u003e\n\u003cp\u003eOne physiological foramen was mostly observed in specimens 27(40.9%). The more numerous the physiological foramina there were, the smaller the narrow (\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05, \u003cem\u003er\u003c/em\u003e=-0.591) and the wide (\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05, \u003cem\u003er\u003c/em\u003e=-0.534) diameter there was (Table 13). There was no statistically significant difference in number and diameter among the C-shaped canal type (\u003cem\u003ep\u003c/em\u003e\u0026gt;0.05). Accessory foramina were found in 45(68.1%) specimens (Table 14). Two accessory foramina accounted for the highest ratio 26(26.0%) and six for the lowest 6(6.0%). The highest proportion of opening orientation was found in the mesial 46(46.0%). The number of accessory foramina was not correlated with C-shaped canal types (\u003cem\u003ep\u003c/em\u003e\u0026gt;0.05).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIt was the region and the race \u003csup\u003e[8, 10, 12, 20, 21, 23, 33]\u003c/sup\u003e that possibly varied the prevalence and characteristics in mandibular first premolars as reported.\u003c/p\u003e\n\u003cp\u003eIn this study, CBCT images were collected from 760 patients in China, of whom 343 were males and 417 were females, and the prevalence of C-shaped root canals was 17.3% and 16.5%, respectively. There was no statistically significant difference between the two. This was consistent with the findings of most previous studies, Martins \u003csup\u003e[21]\u003c/sup\u003e et al reviewed the prevalence, odds ratio and heterogeneity of C-shaped root canal system in mandibular first premolar by gender, where no significant differences were observed (\u003cem\u003ep\u003c/em\u003e\u0026gt;0.05). In this study, the prevalence of C-shaped root canal system tended to decrease as the age of the patients increased. It is considered that this was mainly due to the fact that the teeth in the 15-20 years old group are young permanent teeth with fully developed roots and have large canals and pulp chambers\u003csup\u003e \u003c/sup\u003e\u003csup\u003e[11, 31]\u003c/sup\u003e, which are more easily observed at the same resolution. Whereas, natural physiological aging on the one hand, and on the other hand, long-term environmental stimulation, such as occlusal trauma and periodontal disease, can modify the deposition of dentine \u003csup\u003e[17]\u003c/sup\u003e and root canal system morphology\u003csup\u003e \u003c/sup\u003e\u003csup\u003e[15]\u003c/sup\u003e, together lead to thickening of the root canal wall and thinning of the root canal. These canals are more blurred at the same resolution, and the characteristic C-shaped root canal morphology is more difficult to discern.\u003c/p\u003e\n\u003cp\u003eAmongst 1520 CBCT images, C2 showed the highest prevalence 51.5% and distributed mainly in the middle 49.3% and the apex 47.3%, C3 showed secondly 38.7% and mainly in the apex 79.5%. This suggests that root canal bifurcations are typically located in the lower and middle segments, which are not visible with the naked eye, and that lingual root canals are more curved and possess a distinct presence of dentin cusp collars and a narrower diameter than buccal root canals. Similar results were obtained in a study by Ordinola-Zapata et al \u003csup\u003e[23]\u003c/sup\u003e, that C1 and C2 being more prevalent in the coronal and middle of the root, and C3 being more common at the apical, with the apical being more prone to complex root canal morphology. In the present study, the buccal and the lingual canal of CS type were combined in only 36.4% (8/22) of the three-dimensional classification of C-shaped canals by Micro-CT. And most of the CS type, the buccal and the lingual canal were still present separate, increasing the anatomical complexity of the mandibular first premolar in the middle and apex. According to Li et al \u003csup\u003e[18]\u003c/sup\u003e, 69% of the Vertucci V class\u0026apos;s mandibular first premolars bifurcated in the middle of the root to form a lingual root canal. In the proximal directions, the lingual root created a modest angle with the buccal root, while an average of 33.54\u0026deg; angle existed in the buccolingual direction, with 77% of the sample considerably twisted. Therefore, root canal misses are prone to occur when probing is performed during root canal treatment. It is recommended that clinicians take CBCT preoperatively to fully grasp the root canal morphology and pre-curved K files intraoperatively under the microscope or with the use of ultrasound to remove part of the root canal cusp collar in order to explore the lingual root canal, which is divided into the middle and lower parts of the root canal.\u003c/p\u003e\n\u003cp\u003eThe Micro-CT results of this study revealed that C-shaped root canals were most prevalent from M+1 to AM cross-section of the root canal, which varied with the CBCT results, most likely due to the huge disparity in accuracy between CBCT and Micro-CT. The voxel size of CBCT (250 \u0026mu;m) is larger than the diameter of the middle and apical root canal \u003csup\u003e[4, 29]\u003c/sup\u003e. According to the Shannon-Nyquist theory, when 1/2 the size of the object was larger than the resolution of CBCT, the image of the object could be observed in CBCT\u003csup\u003e[3]\u003c/sup\u003e. And Moreno et al \u003csup\u003e[22]\u003c/sup\u003e reported a narrower diameter of 0.24 \u0026plusmn; 0.10 mm at 3 mm from the root apex measured by Micro-CT (voxel size 17 \u0026mu;m), at which time some of the tiny root canals could not be easily distinguished, creating inaccuracies.\u003c/p\u003e\n\u003cp\u003ePrevious studies on mandibular second molars have shown that the wall of the C-shaped root canal is thinner on the side near the root surface groove than on the remaining side \u003csup\u003e[7, 9, 14]\u003c/sup\u003e. In the present study, the cross-section of the C-shaped root canal was measured and the lingual mesial wall was usually the thinnest (69.7%). Gu et al \u003csup\u003e[12]\u003c/sup\u003e measured the canal wall thickness at various levels in C-shaped root canals of mandibular first premolar teeth and confirmed that the above findings were also applicable in mandibular first premolar teeth, while the lingual measurement site was frequently found to have the minimum mesial wall thickness (67.3%). The irregular morphology of C-shaped root canals is more likely to result in strip perforation during root canal preparation \u003csup\u003e[10, 27]\u003c/sup\u003e. Huysmans et al \u003csup\u003e[13]\u003c/sup\u003e used a mock cephalometric model to imitate the root canal cleaning procedure of the mandibular first premolar and discovered that more dentin was removed from the mesial wall of the prepared mandibular first premolar than from the remaining three lateral walls. Nonlinear regression study revealed that the further the distance from the cemento-enamel junction, the greater the depth of the root radicular groove, and the smaller the angle, the thinner the mesial wall thickness. As a result, mechanical preparation of the root canal, particularly the lingual root canal and the apical segment, must be done carefully during treatment to prevent unwanted deviation and perforation, which could lead to root canal treatment failure.\u003c/p\u003e\n\u003cp\u003eIn this work, the morphology of C-shaped root canals was classified by Fan\u0026apos;s criteria, and the relationship between the classification and the various characteristic morphologies was investigated. The C-shaped root canal cross-sectional classification, did not correlate with each characteristic morphology (\u003cem\u003ep\u003c/em\u003e\u0026gt;0.05), that is, there were no distinguishable dental morphological features between the different C-shaped root canal cross-sectional categories. Three-dimensional classification of C-shaped root canals correlated with the number of accessory canals (\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05, \u003cem\u003er\u003c/em\u003e=0.330) and connecting canals (\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05, \u003cem\u003er\u003c/em\u003e=0.369), that means, the number of accessory canals was ranked in closer to C type, S type, CS type, CS+N type. The more complicated the C-shaped root canal anatomy, the greater the likelihood of accessory canals and connecting canals. For a healthy mandibular first premolar tooth means a richer nerve and blood supply support, which aids in the resistance to pulp infection in its early stages, as well as additional communication pathways to the oral condition. When the infection spreads it becomes an insidious area of infection and places a higher demand on the debridement. Deep grooves on the root surface enhance the periodontal membrane\u0026apos;s attachment site, which contributes to maintaining the integrity of the tooth. On the other hand, when periodontitis occurs, it is more likely to develop deep periodontal pockets and infect the pulp through the accessory canals of the root canal.\u003c/p\u003e\n\u003cp\u003eThe results of this study showed that the number of mandibular first premolar apical foramina was predominantly 1-2. The number of foramina varies and there is a significant difference of the maximum diameter and the narrowest diameter measured. To thoroughly clean the apical region, the primary file size must be large enough to contact all canal walls \u003csup\u003e[2]\u003c/sup\u003e, and therefore the primary file diameter should be larger than the maximum diameter. However, for oval root canals, prepping the root canal in a round shape may excessively remove the dentin and weaken the root \u003csup\u003e[30]\u003c/sup\u003e. Therefore, taking into account the traditional opinion that the primary file should be 2 or 3 sizes larger than the initial file, this study proposed the following suggested primary file numbers for mandibular first premolar teeth with different number of apical foramina: #35 for 1 apical foramen and #30 for 2 and 3 apical foramina.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe findings of this study suggested that C-shaped root canal system in mandibular first premolar teeth was prevalent in Chinese population. The anatomical structure was complex and variable, mostly distributed in the middle and the apex of the root canal. The mesial wall was thin on the lingual side and should be protected against perforation during preparation.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eConflict of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors have no conflicts of interest to declare.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was supported by the National Natural Science Foundation of China (80218095).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll procedures performed in studies involving human participants were in accordance with the ethical standards of the Ethics Committee of School and Stomatology Wenzhou Medical University (WYKQ2021007).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInformed Consent statements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFor this type of study, formal consent is not required.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe CBCT and micro-CT images data used to support the findings of this study are restricted by the local institutional review board at the Wenzhou Medical University in order to protect patients\u0026rsquo; privacy.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contribution\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eYM Zhang: Project development, Data management, Data analysis, Manuscript writing\u003c/p\u003e\n\u003cp\u003eXB Weng: Data management, Data analysis, Manuscript writing\u003c/p\u003e\n\u003cp\u003eY Fu: Data collection\u003c/p\u003e\n\u003cp\u003eXK Qi: Data collection\u003c/p\u003e\n\u003cp\u003eYH Pan: Project development, Manuscript editing\u003c/p\u003e\n\u003cp\u003eY Zhao: Project development, Manuscript editing\u003c/p\u003e\n\u003cp\u003eAuthorship changes are no longer possible after the final acceptance of an article!\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAlfawaz H, Alqedairi A, Alkhayyal AK, Almobarak AA, Alhusain MF and Martins JNR (2019) Prevalence of C-shaped canal system in mandibular first and second molars in a Saudi population assessed via cone beam computed tomography: a retrospective study. 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J Endod 28:658-64. https://doi.org/ 10.1097/00004770-200209000-00008\u003c/li\u003e\n\u003cli\u003eThomas RP, Moule AJ and Bryant R (1993) Root canal morphology of maxillary permanent first molar teeth at various ages. Int Endod J 26:257-67. https://doi.org/ 10.1111/j.1365-2591.1993.tb00570.x\u003c/li\u003e\n\u003cli\u003eWolf TG, Paque F, Sven Patyna M, Willershausen B and Briseno-Marroquin B (2017) Three-dimensional analysis of the physiological foramen geometry of maxillary and mandibular molars by means of micro-CT. Int J Oral Sci 9:151-157. https://doi.org/ 10.1038/ijos.2017.29\u003c/li\u003e\n\u003cli\u003eWu YC, Cathy Tsai YW, Cheng WC, Weng PW, Su CC, Chiang HS, Chung MP, Chung CH, Shieh YS and Huang RY (2018) Relationship of the Incidence of C-shaped Root Canal Configurations of Mandibular First Premolars with Distolingual Roots in Mandibular First Molars in a Taiwanese Population: A Cone-beam Computed Tomographic Study. J Endod 44:1492-1499 e1. https://doi.org/ 10.1016/j.joen.2018.05.016\u003c/li\u003e\n\u003cli\u003eYin X, Cheung GS, Zhang C, Masuda YM, Kimura Y and Matsumoto K (2010) Micro-computed tomographic comparison of nickel-titanium rotary versus traditional instruments in C-shaped root canal system. J Endod 36:708-12. https://doi.org/ 10.1016/j.joen.2010.01.003\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTables 1 to 14 are available in the Supplementary Files section.\u003c/p\u003e "}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"C-shaped canal, morphology, mandibular first premolar, Micro-CT","lastPublishedDoi":"10.21203/rs.3.rs-2735845/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2735845/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003ePurpose\u003c/strong\u003e The purpose of this study was to determine the prevalence of C-shaped root canal system in mandibular first premolar in Chinese population and to analyze the anatomical characteristics by Cone-beam computed tomography (CBCT) and Micro–computed tomography (Micro-CT) together.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods\u003c/strong\u003e CBCT images of 760 patients (1520 mandibular first premolars) were evaluated for the prevalence of C-shaped root canal system and the correlation with gender, age and position. 66 mandibular first premolars with C-shaped root canal system were scanned by Micro-CT and analyzed for morphologic features of the root canal anatomy (radicular groove, C-shaped root canal categories, accessory and connecting canals, apical foramina and accessory foramina).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults\u003c/strong\u003e C-shaped root canal system was found in 16.9% of mandibular first premolars. The minimum mesial wall thickness was mostly measured at the lingual site (69.7%). Among the cross-sectional C-shaped root canal system classifications, the highest prevalence was C2 type (41.5%). In the 3D C-shaped root canal system classification, the highest prevalence was S type (34.8%). Accessory canals were observed in 48.5% of the samples, mostly in the middle region. The presence of 1-3 variable connecting canals was observed in 42.4% of the samples. The number of apical foramina was predominantly 1 (40.9%).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusions\u003c/strong\u003e The incidence of C-shaped root canal system in mandibular first premolars was 16.9% in the Chinese population. It mostly had anatomical features such as deep root surface grooves, with C2 type and S type being the most prevalent.\u003c/p\u003e","manuscriptTitle":"CBCT and Micro-CT analysis of the mandibular first premolars with C-shaped canal system in Chinese population","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-03-28 14:21:36","doi":"10.21203/rs.3.rs-2735845/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"f997beb0-b9ad-4ac3-872c-ea7d650675bb","owner":[],"postedDate":"March 28th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2023-04-18T09:29:29+00:00","versionOfRecord":[],"versionCreatedAt":"2023-03-28 14:21:36","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-2735845","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2735845","identity":"rs-2735845","version":["v1"]},"buildId":"-HB7Z8yhvgn0wM9Nzuekk","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}