Clinical Research

Analysis of C-shaped Canals by Panoramic Radiographyand Cone-beam Computed Tomography:Root-type Specificity by Longitudinal DistributionAlper Sinanoglu, DDS, PhD,* and Dilek Helvacioglu-Yigit, DDS, PhD†

Abstract

Introduction: The purpose of this study was to docu-ment the characteristics of C-shaped canal systems inpermanent mandibular second molars using a combi-nation of orthopantomogram (OPT) and cross-sectional cone-beam computed tomographic (CBCT)imaging. Methods: Two hundred participants (94men and 106 women, mean age = 35 years) whounderwent both routine CBCT and OPT examinationswere enrolled. One endodontist and 1 oral radiolo-gist examined the images of 339 mandibularsecond molars and described the radiographic featuresof C-shaped canals from OPT images as confirmed byCBCT imaging. Root morphology was classified asnonfused (NFRI–II) or fused (FRI–III) based on OPTimages. Cross-sectional root canal configurations(C1–C5) were identified from CBCT imaging at 3different levels (coronal, middle, and apical). Fre-quency distributions of root morphology and root canalconfigurations were compared at each level, and inter-observer reliability was tested using the Cohen kappatest. Results: Of the 339 teeth, 29 (8.6 %) hadC-shaped root canal systems. Most of the root canalswere NFR type (86%); only 2% had C-shaped rootcanals (all NFRII). In the FR category, 23 teeth withC-shaped canals were equally distributed betweenthe FRI and FRII subtypes. Interobserver agreementwas almost perfect (k = 0.89 and k = 0.91; right andleft second molars, respectively). Per CBCT imaging,the most common configuration was C3 at all levels;no C5 case was detected. Conclusions: OPT usagecan assist in recognizing and diagnosing C-shapedroot canal systems. Radicular fusion or proximity is acharacteristic feature of C-shaped canal systems. How-ever, nonfused root appearances should also beconsidered suspicious. (J Endod 2014;40:917–921)

Key WordsCone-beam computed tomography, C-shaped canal,mandibular second molars, panoramic radiography

From the Departments of *Oral and Maxillofacial Radiology andAddress requests for reprints to Dr Alper Sinanoglu, Departmen

Basiskele, Kocaeli, Turkey. E-mail address: alpersinanoglu@yahoo.c0099-2399/$ - see front matter

Copyright ª 2014 American Association of Endodontists.http://dx.doi.org/10.1016/j.joen.2014.03.014

JOE — Volume 40, Number 7, July 2014

The term C-shaped canal was first introduced by Cooke and Cox (1) in 1979 todescribe the cross-sectional morphology of roots that resembled the letter C. The

characteristic feature of such roots is the connection of the root canals by a fin orweblike structure to form a C shape at the root canal orifice (2). The complexity ofC-shaped canals makes them difficult to clean, shape, and obturate effectively (3, 4).The thin dentinal wall of the buccal or lingual groove may lead to strip perforation,which poses a considerable threat to tooth prognosis (5). To maximize a successfultreatment outcome, it is necessary to have a good understanding of the C-shaped canalanatomy and to perform a careful interpretation of its radiographic features. A highprevalence of C-shaped canals has been reported in mandibular second molars (6).However, they can also be found in other maxillary and mandibular molars (7–10),mandibular premolars (11), and maxillary lateral incisors (12).

Proper diagnosis and recognition of this morphology by radiographic examinationis critical for effective endodontic management. Recent studies have investigatedC-shaped canals using cone-beam computed tomographic (CBCT) imaging andreported that it is a potentially effective tool for the detection of this morphology(13–15). Although CBCT imaging has a role in the identification of root canalsystems, it is not indicated as a standard method for routine demonstration of rootcanal anatomy. The use of CBCT scanning in endodontics has been limited toselected cases in which conventional intraoral radiographs provide information onthe root canal anatomy that is equivocal or inadequate for planning treatment (16).These complex endodontic conditions involve the identification of root canal systemanomalies and the determination of root curvature, an indication related to C-shapedcanals (17).

Radiographic features of C-shaped root canals have been described in variousstudies. C-shaped canals can have different shapes if evaluated longitudinally(18, 19). Haddad et al (20) considered C-shaped canals a third canal that was in be-tween a large distal canal and a narrow mesial canal on a periapical (PA) radiograph.Furthermore, Wang et al (21) showed that teeth with C-shaped root canals had a moreapically positioned furcation with a longitudinal groove separating the root into mesialand distal parts revealed by preoperative, postoperative, and working length PA radio-graphs. It has also been reported that the radiographic evaluation of C-shaped canalswith preoperative PA radiography is challenging if the fin connecting the roots is thinand not visible (22). Although it is more accurate to assess root shape on PA radiog-raphy (23), orthopantomogram (OPT) is often the first diagnostic image of choice forroutine radiologic examination and is widely used for screening at various institutions(24). The recognition of C-shaped canals by means of OPT was suggested to be a goodsurveying modality (25). Nonetheless, preoperative radiographs, whether OPT or PA,have limitations. They are 2-dimensional images with anatomic noise and geometric

†Endodontics, Faculty of Dentistry, Kocaeli University, Kocaeli, Turkey.t of Oral and Maxillofacial Radiology, Faculty of Dentistry, Kocaeli University, Yuvacik Yerleskesi,om

Analysis of C-shaped Canals 917

Clinical Research

distortion (26). In such complex cases, before the decision to performadvanced imaging, these preoperative radiographs should be well inter-preted in order to justify the need to expose a patient to radiation. Theaim of this study was to document the presence of C-shaped canals andtheir different variants in permanent mandibular second molars by us-ing the longitudinal resolution of OPT images along with confirmationby CBCT imaging among members of a Turkish population.

Materials and MethodsThe Ethics Committee of Kocaeli University (KOU KAEK 2013/78)

approved this retrospective study. The participants were referred to theUniversity of Kocaeli, Faculty of Dentistry, Kocaeli, Turkey, betweenMarch 2010 and December 2012 and required both CBCT and OPT ex-aminations as part of their routine examination. The aim of the CBCTscans was for the diagnostic imaging of maxillofacial tumors and cysts,presurgical assessment of impacted teeth, and proposed implant sites.The OPT and CBCT images from these patients were retrieved from thedatabase in the oral and maxillofacial radiology department and wereinvestigated retrospectively.

The inclusion criterion was the presence of at least 1 well-developed mandibular second molar with complete root formation.The exclusion criteria were the existence of root canal fillings, PA le-sion(s), or deep caries. CBCT images were acquired using an i-CATscanner (Xoran Technologies, Ann Arbor, MI, and Imaging Sciences In-ternational, Hatfield, PA) according to the manufacturers’ protocol. AllCBCT images were obtained at a 0.25-mm voxel size and were recon-structed to be a 1-mm-thick slice. To investigate the mandibularsecondmolars, the i-CAT Vision viewer software was used to reconstructthe cross-sectional images. The OPT images were obtained with Vera-viewpocs (Morita, Kyoto, Japan) that was operated at 70 kVp and10 mA.

After evaluation, 339 mandibular second molars in 200 CBCT im-ages fulfilled the previously mentioned inclusion criteria. The studygroup consisted of 94 male and 106 female patients with a mean ageof 35 years. One endodontist and 1 oral radiologist investigated all im-ages independently.

OPT EvaluationThe mandibular second molar root morphology was classified ac-

cording to whether the root shape was considered a fused root (FR) or anonfused root (NFR) as presented in Figure 1. FR and NFR types weredivided into the following subgroups as modified from the classificationof Fan et al (18): NFRI, nonfused typewith 2 divergent or parallel separateroots; NFRII, nonfused type with 2 convergent separate roots with trabec-ular patterns between them; FRI, fused root type with distal and mesialcanals merging at the apical level; FRII, fused root type with separate

Figure 1. Root morphology classification. Nonfused root types (NFRI and NFRII) w(Adapted from Fan B, Cheung GS, Fan M, et al. C-shaped canal system in mandibu

918 Sinanoglu and Helvacioglu-Yigit

distal and mesial canals that appear to continue on their own pathwaytoward the apex; and FRIII, fused root type with separate distal andmesialcanals (1 canal was curved to and superimposed on a radiolucent linethat separated the root into distal and mesial regions, and the other canalappeared to continue on its own path toward the apex). The 2 investiga-tors independently scored the right and left mandibular second molarsaccording to root morphology classification on OPT images, and a finalconsensus was reached for each tooth afterward.

CBCT EvaluationThemandibular secondmolars were evaluated for the presence of a

C-shaped canal. The canal system was defined as C-shaped according tothe following criteria stated by Fan et al (2):

1. Fused roots2. A longitudinal groove on the lingual or buccal surface of the root3. At least 1 cross-section of the canal showed a C1, C2, or C3 config-

uration

Configuration of the C-shaped canal was categorized in cross-sections of the roots at 3 different levels: coronal, middle, and apex.The following 3 levels were selected:

Coronal: C = 2 mm from the orificeMiddle: M = root length/2Apical: A = 2 mm from apex

After segmentation into 1-mm slices, the configuration of the rootcanal at each level of the root was categorized into the following types inaccordance with the classification of Fan et al (2) (Fig. 2):

C1: Continuous C-shaped canalC2: Semicolon shaped because of a discontinuation in the ‘‘C’’outline; however, either angle, a or b, should be no less than 60�C3: 2 (C3a) or 3 (C3b) separate canals, and both angles, a and b,were less than 60�C4: Single round or oval canalC5: No canal lumen

To confirm the canal shapes, C2 and C3, Image ProPlus 4.0 (Me-dia Cybernetics Inc, Silver Spring, MD)was used formeasurement of theangles,a andb (2, 14) (Fig. 3A andB). The frequency of each type of C-shaped canal and the distribution of the canal configurations at eachlevel were analyzed.

Data AnalysisThe roots were analyzed for morphology (NRFI, NRFII, FRI, FRII,

and FRIII) by longitudinal OPT images and the different types ofC-shaped canals (C1–C5) by using cross-sectional CBCT images

ere added to the classification of Fan et al (18). FR refers to the fused root type.lar second molars: part II–radiographic features. J Endod 2004;30:904–8.)

JOE — Volume 40, Number 7, July 2014

Figure 2. Classifications of C-shaped canal configurations. (From Fan B,Cheung GS, Fan M, et al. C-shaped canal system in mandibular second molars:part I–anatomical features. J Endod 2004;30:899–903.)

Clinical Research

(Fig. 4). All data were compiled as absolute counts and percentages.They were analyzed for regional differences in frequency distributionsby the chi-square and Fisher exact tests using SPSS 15.0 software forWindows (SPSS Inc, Chicago, IL). A P < .05 was considered significant.Interobserver reliability was calculated using the Cohen kappa test.

ResultsA total of 200 cases were included in the study group (94 men and

106 women, mean age = 35 years). General root morphology was firstassessed longitudinally by using OPT images. The frequency distributionof the different types of root canals is given in Table 1. Among the 339teeth evaluated, the vast majority of the root canals exhibited NFRmorphology, and a total of 29 teeth (8.6%) exhibited a C-shaped canal.The FR group presented a significantly higher frequency of C-shaped ca-nals than the NRF group (P = .001). The 2 observers reached a highlevel of agreement regarding the classification of the different root typesthat was considered almost perfect (k = 0.89 and k = 0.91; right andleft second molars, respectively). Collectively, these data suggest that C-shaped canals are rarely detected in themost common type of root canal(NFRI) but should be expected in about half of the permanent mandib-ular second molars presenting with FR morphology.

The cross-sectional characteristics of FR and NFR types are shownin Table 2 for the coronal, middle, and apical regions. At all levels of the

Figure 3. Measurements of the angles a and b to differentiate the C2 and C3 canathe other canal cross-section. M, middle point of line AD; a, angle between line AMuration, angle b > 60�; (B) C3 canal configuration, a < 60�, b < 60�. (From Fmolars:part I–anatomical features. J Endod 2004;30:899–903.)

JOE — Volume 40, Number 7, July 2014

roots, the most common canal configuration was C3, whereas the C5configuration was not detected in any of the sections. Chi-square anal-ysis showed that the cross-sectional radiographic images of the middleor apical regions could equally detect all 4 types of C-shaped root ca-nals, whereas examination of the coronal region did not detect anyC4 types. In addition, the ability to identify each type of C-shaped rootcanal depends on the position of the radiographic scan along the lengthof the tooth (Table 2). These data show that cross-sectional analysismust be conducted in all 3 levels of each tooth in order to avoid falsenegatives regarding the existence of a C-shaped root canal.

DiscussionRadiographic identification of the variations of root canal

morphology is a basic requirement for successful endodontic treatment.Preoperative radiographs are important diagnostic tools in the evaluationprocess of various root canal configurations, particularly for complexones, such as C-shaped root canal systems (18, 20, 21, 25). The useof conventional radiography for the detection of this morphology hasbeen investigated in various studies. Cooke and Cox (1) emphasizedthe difficulty of diagnosing C-shaped root canals with preoperative radio-graphs. Difficulty in recognition of C-shaped canals in OPT was also re-ported for hypertaurodont mandibular molars (27). Lambrianidis et al(28) suggested that working length PA radiographs were more helpfulthan that of preoperative ones and that clinical diagnosis can only be es-tablished after access to the chamber. Nonetheless, numerous studies re-ported that the existence and configuration of C-shaped canals could bepredicted from preoperative radiographs according to the appearance ofthe roots (18, 20–22, 25). As a common approach, these studies statedthat a C-shaped canal must be suspected if the preoperative radiographsdisplay radicular fusion or proximity. A classification was developed byFan et al (18) for the radiographic appearance of C-shaped roots accord-ing to the pathways of the mesial and distal canals. They used PA radio-graphs of extracted teeth; therefore, the images did not present anyanatomic noise (ie, presence of surrounding bone), facilitating a detailedassessment of the root morphology. In the present study, radiographicappearances revealed by OPT were investigated, and specific evaluationof root canal morphology was not a precedence. Our findings were inaccordance with Fan et al (18), suggesting the high prevalence of C-shaped canals in fused roots. The FRI type was the most commonlyseen radiographic appearance of roots with C-shaped canals and hada higher prevalence than that of prior studies (18, 21).

Other than the characteristic feature, some additional radiographicproperties were also reported in teeth with C-shaped root canals. Gula-bivala et al (29) reported that C-shaped root canals might be present in

l configurations. (A and B) Ends of one canal cross-section. (C and D) Ends ofand line BM; b, angle between line CM and line DM (2). (A) C2 canal config-an B, Cheung GS, Fan M, et al. C-shaped canal system in mandibular second

Analysis of C-shaped Canals 919

Figure 4. Representative OPT images with corresponding CBCT cross-sections at the coronal (c), middle (m), and apical (a) levels.

TABLE 1. Frequency Distribution of the Different Types of Root Canals andPercentages of C-shaped Canals

Root morphology

NFR(n = 293)

FR(n = 46)

Types NFRI NFRII FRI FRII FRIII

Number of teeth 203 90 20 21 5Number of teeth with aC-shaped canal (%)

0 6 11 10 26 (2%) 23 (50%)

FR, fused root; NFR, nonfused root.

Clinical Research

not only fused roots but also 2 separate roots with a dentin fin that mightbe difficult to recognize in PA radiographs. In a recent study, 76 of the1,146 cases with 2 separate roots were found to be C-shaped root canalson the basis of PA examinations (21). Therefore, in the present study, theclassification by Fan et al (18), in which all 3 types were fused roots, wasmodified, and the NFR types were added (Fig. 1). Interestingly, 6 NFRII-type roots presented as C-shaped canals with CBCT evaluation. Thisfinding can be explained by the difficulty of recognizing root fusionwith OPT, possibly related to the trabecular pattern of the alveolarbone because of the deep grooves of the roots and the thin dentin fin

920 Sinanoglu and Helvacioglu-Yigit JOE — Volume 40, Number 7, July 2014

TABLE 2. Frequency Distribution of the C-shaped Canal Configurations at theCoronal, Middle, and Apical Levels for Each Root Morphology

Root levelRoot morphologyrevealed by OPT

C-shaped canalconfiguration revealed

by CBCT

C1 C2 C3 C4 Total

Coronal NFRI 0 2 4 0 6FRI 1 5 5 0 11FRII 1 3 6 0 10FRIII 1 0 1 0 2

Middle NFRI 0 0 6 0 6FRI 1 1 6 3 11FRII 0 1 8 1 10FRIII 0 0 2 0 2

Apical NFRI 0 0 5 1 6FRI 1 0 4 6 11FRII 0 1 7 2 10FRIII 1 0 1 0 2

FR, fused root; NFR, nonfused root.

Clinical Research

connecting the roots. This finding may not influence clinical manage-ment, but consideration of the NFRII type for C-shaped canal existencemay be another parameter for preoperative radiologic examination.

Jung et al (25) classified teeth that had 2 separate roots merging atthe apex into 2 different groups based on the presence of trabecularbone between the roots. This distinction between radiographic typeswas related to their cross-sectional features. The thickness of thecommunication between the roots and the distance between the 2 rootswere suggested to be responsible for this appearance, rather than thepresence of a trabecular pattern. In their study, 3 of the 90 molarsthat had 2 distinct and divergent roots as identified with OPT exhibitedC-shaped root canal morphology. Although this root type had also beenadded to the classification of the present study, a C-shaped canal systemwas not detected with the NFRI type. This might be related to the smallnumber of cases analyzed in the study. Moreover, we believe this partic-ular type of root morphology should also be investigated in futurestudies with a larger population.

Atypical morphology presents a clinical challenge if it is unknownwhether a C-shaped orifice continues throughout the root because theshape of the canal at the orifice level does not present an accurate depic-tion regarding the morphology of the rest of the canal (3). This findingwas also confirmed in our previous study (14). The current studyfocused on the correlation of the cross-sectional configurations andthe longitudinal root-shape morphology. In the apical region, the FRIroot types revealed mostly a C4 canal configuration, which is in accor-dance with an observation supported by Fan et al (18) confirming thatthe 2 canals merge into 1 canal in the apical region with respect to rootmorphology. In the apical region, NFRII and FRII hadmore of a C3 canalconfiguration, which is in accordance with Fan et al for type FRII (30).The presence of these 2 types may be a warning regarding the possibledifficulties that might be experienced while cleaning, shaping, and ob-turating because of the morphologic features related to C3.

While evaluating OPT images, radicular fusion or proximity is acommon characteristic of C-shaped canal systems. Our findings suggestthat images with nonfused root appearances (NFRII) should also beconsidered suspicious. The use of OPT can assist in the recognitionand diagnosis of C-shaped root canal systems.

AcknowledgmentsThe authors deny any conflicts of interest related to this study.

JOE — Volume 40, Number 7, July 2014

References1. Cooke HG 3rd, Cox FL. C-shaped canal configurations in mandibular molars. J Am

Dent Assoc 1979;99:836–9.2. Fan B, Cheung GS, Fan M, et al. C-shaped canal system in mandibular second mo-

lars: part I–anatomical features. J Endod 2004;30:899–903.3. Melton DC, Krell KV, Fuller MW. Anatomical and histological features of C-shaped

canals in mandibular second molars. J Endod 1991;17:384–8.4. Solomonov M, Paque F, Fan B, et al. The challenge of C-shaped canal systems:

a comparative study of the self-adjusting file and ProTaper. J Endod 2012;38:209–14.5. Chai WL, Thong YL. Cross-sectional morphology and minimum canal wall widths in

C-shaped roots of mandibular molars. J Endod 2004;30:509–12.6. Manning SA. Root canal anatomy of mandibular second molars. Part II. C-shaped

canals. Int Endod J 1990;23:40–5.7. Carlsen O, Alexandersen V, Heitmann T, et al. Root canals in one-rooted maxillary

second molars. Scand J Dent Res 1992;100:249–56.8. De Moor RJ. C-shaped root canal configuration in maxillary first molars. Int Endod J

2002;35:200–8.9. Yilmaz Z, Tuncel B, Serper A, et al. C-shaped root canal in a maxillary first molar: a

case report. Int Endod J 2006;39:162–6.10. Martins JN, Quaresma S, Quaresma MC, et al. C-shaped maxillary permanent first

molar: a case report and literature review. J Endod 2013;39:1649–53.11. Lu TY, Yang SF, Pai SF. Complicated root canal morphology of mandibular first premo-

lar in a Chinese population using the cross section method. J Endod 2006;32:932–6.12. Boveda C, Fajardo M, Millan B. Root canal treatment of an invaginated maxillary

lateral incisor with a C-shaped canal. Quintessence Int 1999;30:707–11.13. Yin XZ, Cheung GSP, Zhang CF, et al. Micro-computed tomographic comparison of

nickel-titanium rotary versus traditional instruments in C-shaped root canal system.J Endod 2010;36:708–12.

14. Helvacioglu-Yigit D, Sinanoglu A. Use of cone-beam computed tomography to eval-uate C-shaped root canal systems in mandibular second molars in a Turkish sub-population: a retrospective study. Int Endod J 2013;46:1032–8.

15. Silva EJNL, Nejaim Y, Silva AV, et al. Evaluation of root canal configuration ofmandibular molars in a Brazilian population by using cone-beam computed tomog-raphy: an in vivo study. J Endod 2013;39:849–52.

16. European Commission. Radiation Protection No. 172: Cone Beam CT for DentalandMaxillofacial Radiology, Evidence Based Guidelines. Luxembourg: Directorate-Gen-eral for Energy Directorate D—Nuclear Energy Unit D4—Radiation Protection; 2012.

17. American Association of Endodontists. Colleagues For excellence: cone beamcomputed tomography in endodontics. Summer 2011. Available at: https://www.aae.org/uploadedfiles/publications_and_research/endodontics_colleagues_for_excellence_newsletter/ecfe%20summer%2011%20final.pdf. Accessed April 22, 2014.

18. Fan B, Cheung GS, Fan M, et al. C-shaped canal system in mandibular second mo-lars: part II–radiographic features. J Endod 2004;30:904–8.

19. Zheng Q, Zhang L, Zhou X, et al. C-shaped root canal system in mandibular secondmolars in a Chinese population evaluated by cone-beam computed tomography. IntEndod J 2011;44:857–62.

20. Haddad GY, Nehme WB, Ounsi HF. Diagnosis, classification, and frequency of C-shaped canals in mandibular second molars in the Lebanese population. J Endod1999;25:268–71.

21. Wang Y, Guo J, Yang HB, et al. Incidence of C-shaped root canal systems in mandib-ular second molars in the native Chinese population by analysis of clinical methods.Int J Oral Sci 2012;4:161–5.

22. Jafarzadeh H, Wu YN. The C-shaped root canal configuration: a review. J Endod2007;33:517–23.

23. Sameshima GT, Asgarifar KO. Assessment of root resorption and root shape: peri-apical vs panoramic films. Angle Orthod 2001;71:185–9.

24. Martinez Beneyto Y, Alcaraz Banos M, Perez Lajarin L, et al. Clinical justification ofdental radiology in adult patients: a review of the literature. Med Oral Patol Oral CirBucal 2007;12:E244–51.

25. Jung HJ, Lee SS, Huh KH, et al. Predicting the configuration of a C-shaped canal sys-tem from panoramic radiographs. Oral Surg Oral Med Oral Pathol Oral Radiol En-dod 2010;109:e37–41.

26. Patel S, Dawood A, Whaites E, et al. New dimensions in endodontic imaging: part 1.Conventional and alternative radiographic systems. Int Endod J 2009;42:447–62.

27. Radwan A, Kim SG. Treatment of a hypertaurodontic maxillary second molar in apatient with 10 taurodonts: a case report. J Endod 2014;40:140–4.

28. Lambrianidis T, Lyroudia K, Pandelidou O, et al. Evaluation of periapical radio-graphs in the recognition of C-shaped mandibular second molars. Int Endod J2001;34:458–62.

29. Gulabivala K, Aung TH, Alavi A, et al. Root and canal morphology of Burmesemandibular molars. Int Endod J 2001;34:359–70.

30. Fan W, Fan B, Gutmann JL, et al. Identification of C-shaped canal in mandibular sec-ond molars. Part I: radiographic and anatomical features revealed by intraradicularcontrast medium. J Endod 2007;33:806–10.

Analysis of C-shaped Canals 921