Asymmetry of C-shaped
The prevalence and asymmetry of C-shaped root canals in second mandibular molars in a European–Russian population. A CBCT study in vivo.
Dmitry Rogazkyn DMD1; Zvi Metzger, DMD2; Michael Solomonov, DMD3
1 Roentgenological Center, Smolensk, Russia
2 Department of Endodontology, School of Dental Medicine, Tel Aviv University, Tel Aviv, Israel
3 Department of Endodontics, Sheba Hospital, Tel Hashomer, Israel
Prevalence of C-shaped canals in a Russian population
Keywords: C-shaped, Anatomic variation, Cone-Beam Computed Tomography, CBCT
Acknowledgement: Dr. Metzger serves as a consultant to ReDent-Nova, manufacturer of the Self-Adjusting File. The other authors deny any conflicts of interest related to this study.
Michael Solomonov, DMD
Department of Endodontics, Sheba Hospital,
Tel Hashomer 52621, Israel
Fax: 972- 37377178, email: email@example.com
Introduction: Familiarity with the shape of the root canal system is essential for the quality of endodontic treatment. C-shaped canals are anatomic variations most often encountered in mandibular second molars, and they pose an operational challenge to the clinician. The incidence of C-shaped canals varies widely in different populations. The aim of this study was to investigate for first time the incidence of C-shaped root canals in a European-Russian population using cone beam computes tomography (CBCT). Methods: A total of 300 CBCT scans of patients with two second mandibular molars were randomly chosen, screened and evaluated. Results: Forty-two patients (14%) had C-shaped canals. Of those patients, twenty-three (54.8%) had bilateral C-shaped canals, and 19 (45.2%) had unilateral C-shaped canals. Conclusion: The prevalence of C-shaped canals in this European–Russian population is higher than that reported in other Caucasian populations, and in such cases, asymmetry between right and left is often encountered.
Familiarity with the shape of the root canal system is essential for high-quality endodontic treatment. The C-shaped root canal system is one of the most commonly observed anatomical variations (Cooke & Cox 1979). The main anatomic feature of C-shaped canals is the presence of a large fin or web connecting the individual canals. The coronal orifice of these canals is usually located apically to the cemento-enamel junction and may appear as a single, ribbon-shaped opening with a 180∞ arc linking all the main canals (Fan et al. 2004a, Gulabivala et al. 2002) or a ribbon-shaped canal that includes the mesio-buccal and distal canals (Yang et al. 1988a); in cross-section (axial section), its outline resembles the letter “C” (Figures 1, 2). These root canal systems tend to have flat, wide-spreading fins, which may have mesh-like connections between them (Solomonov et al. 2012). Accordingly, this root canal system presents the clinician with unique challenges when cleaning, shaping and obturating such root canals (Chai & Thong 2004, Fan et al. 2007).
Selection of the instrumentation system may greatly affect the ability of the clinician to meet the challenge of C-shaped canals. A recent comparative study showed that the Self-Adjusting File (SAF) System was more effective than a Ni-Ti rotary file system in the cleaning and shaping of C-shaped canals (Solomonov et al. 2012). When the SAF system was used, a higher percentage of the canal wall was affected by the procedure compared to rotary files, and the shape of the canal was better preserved (Solomonov et al. 2012). Selection of the obturation method may also be important when filling C-shaped canals. Thus, awareness of the incidence of C-shaped canals has practical clinical importance for the operator.
C-shaped canal anatomy may rarely be found in mandibular first premolars (Baisden et al. 1992), mandibular first molars (Rice & Gilbert 1987), third molars (Sidow et al. 2000,Keinan et al. 2009), maxillary first molars (Newton & McDonald 1984), and maxillary second molars (Yang et al. 1988b). However, this root canal configuration is mostly found in mandibular second molars, and its prevalence differs among races, ranging between 8% in Caucasian populations (Cooke & Cox 1979) to 52% in native Chinese populations (Walker 1988). Consequently, many dentists believe that C–shaped canals are very rare anatomic variations that are found mostly in Asian populations. Unawareness of the prevalence of C-shaped canals on the one hand, and the inability of traditional, planar 2-dimensional periapical radiographs to disclose this anatomical variation (Solomonov et al. 2012, Lambrianidis et al. 2001, Fan et al. 2004b,Fan et al. 2008) (Figure 1A), on the other hand, may lead to a situation in which the operator becomes aware of the anatomy of a given root canal only when encountering an unfamiliar shape of the pulp chamber and its floor (Figure 1B). In other cases, even after opening the pulp chamber, it is not possible to identify the anatomy as C-shaped (Shemesh et al. 2014) because C-shaped canals can have a different configuration along the root (Fan et al. 2004a). The assumption that contralateral teeth should be symmetrical may also lead to mistakes (Plotino et al. 2013). Therefore, it is of clinical interest to check for the prevalence and symmetry of C-shaped canals in different populations and to increase the awareness of practitioners about the incidence of C-shaped canals in the population in which they practice.
The present study was designed to investigate, for the first time, the prevalence of C-shaped canals in mandibular second molars in a European-Russian population using a contemporary noninvasive method, cone-beam computed tomography (CBCT) (Patel 2009).
Material and Methods
During the period from May 2012 to February 2013, a total of 1600 CBCT scans were performed in the Smolensk Roentgenological Center (Smolensk, Russia). Patients were referred for CBCT for reasons unrelated to the present study, such as implant treatment planning, visualization of impacted teeth before surgery or orthodontic treatment. From the above, the radiologist who prepared the report of the CBCT scans selected 300 consecutive cases that fit the following inclusion criteria: (a) Russian patients (b) who had both second mandibular molars in their mouths.
The CBCT images were scanned using a PaX-Reve3D CBCT device (Vatech, Secaucus, South Korea) at 360∞ x-ray head rotation. All CBCT scans were performed using the standard manufacturer’s settings: tube voltage, 85 kV; tube current, 8 mA; and field of view, 80×120 mm with a resolution of 0.08-0.2 voxel size.
C-shaped canal definitions
Teeth presenting C1, C2, or C3 configuration, as defined by Fan’s modification of the original Melton classification, were defined as C-shaped canals in the present study (2, 21). Teeth with canals presenting C4 configuration, namely, those with a single large round canal were not included in the C-shaped category. They were defined as «pyramidal teeth» and evaluated as a separate group. This distinction was made because pyramidal teeth, unlike C-shaped canals, present no special problems for the clinician. C5 configurations, namely, roots with no patent root canal space, were excluded from the present study.
Evaluation of the images
Evaluation of the images was performed using axial plane views. Each CBCT record was independently evaluated by an endodontist with 10 years of experience (MS) and a radiologist (DR) using OnDemand3D software (CyberMed, Irvine, USA). There were no disagreements between the two observers with regard to the definition of any case.
Of the 300 patients included in the present study, 42 (14%) had C-shaped canals and 16 (5.3%) had pyramidal teeth.
Bilateral C-shaped canals were found in 23 (7.6%) of the patients (Figure 2A), while 19 (6.3%) of the patients presented with a unilateral C-shaped canal (Figure 2C). Asymmetry between right and left was found in 45.2% of the patients who had C-shaped canals.
Ten patients (3.3%) had a C-shaped canal on one side and a pyramidal tooth on the other (Figure 2B), while 9 (3%) of the patients had a C-shaped canal on one side and a normal tooth on the other (Figure 2C). Five (1.5%) of the patients had bilateral pyramidal teeth, and 1 (0.3%) patient had a pyramidal tooth on one side and a normal tooth on the other.
When taken together, patients with either C-shaped canals or pyramidal teeth were found in 48 (15.8%) of the patients.
The C-shaped canal is one of the most extreme variations of the shape of the root canal system. Its cause has been attributed to a failure of the Hertwig’s epithelial root sheath to fuse apically to the cemento-enamel junction, thus failing to form two separate, mesial and distal roots. Such a failure to fuse may result in a single root with a deep groove on either the lingual or the buccal side of the developing root (Manning 1990). The ribbon-shaped anatomy of C-shaped canals presents a challenge to the operator when using Ni-Ti rotary files, which may often fail to shape them adequately (Yin et al. 2010) (Figure 2 C). Furthermore, substantial localized decrease of the remaining dentin wall thickness may occur and may even lead to perforation ( Chai & Thong 2004, Melton et al. 1991).
The recently introduced Self-Adjusting File (SAF) system (Metzger et al. 2010) may allow the operator to perform more efficient shaping of C-shaped root canals (Solomonov et al. 2012). Such shaping with the SAF may be defined as minimally invasive, as it removes a uniform layer of dentin from the canal walls without sacrificing too much of the sound dentin (Figure 1 D). Nevertheless, even the SAF system may fail to instrument the entire canal surface due to the intricate, web-like anatomy often found in C-shaped canals (Solomonov et al. 2012).
The best obturation approach for oval canals in general is the warm gutta-percha technique (De-Deus et al. 2012, Wu et al. 2001). A C-shaped canal can be considered an extreme form of a long oval canal, and thermo-plasticized gutta-percha obturation techniques may be successfully applied in such cases (Shemesh et al. 2014). Therefore, familiarity with C-shaped canal anatomy and its prevalence in a given population may be important to the clinician, as it may help him/her to select a suitable treatment approach for endodontic treatment in these challenging teeth.
The present study was conducted in the westernmost town in Russia, Smolensk. Due to its specific geographic location, this region was expected to be less subject to East-Asian ethnic influence. According to a 2010 census of the Russian population, 90.68% of the population of Smolensk were ethnic Russians (http://www.gks.ru/free_doc/new site/perepis2010/croc/perepis_itogi1612-tom4.htm.)
Additionally, in previous centuries, the Tatar-Mongol horde, which could potentially have had an effect on the genetic background of local populations, had not reached the Smolensk area (Карамзин 1803). Therefore, in the present study, the Russian population of Smolensk was considered representative of the European part of Russia (European-Russian population).
The prevalence of mandibular second molars with C-shaped canals in this population was found to be higher than that reported in other Caucasian populations (Cooke & Cox 1979). Clinicians performing root canal treatments in this population must be aware of the increased possibility of encountering this anatomical variation during their usual clinical work.
A clinician may assume that the teeth in a given individual have right-to-left symmetry. Therefore, it is important to note that a recent report found asymmetry between right and left in second mandibular molar anatomy in 20% of the individuals of a Caucasian population (Plotino et al. 2013). The present report indicates that in cases with C-shaped canals in mandibular second molars, asymmetry between the right and left sides was as high as 45%. Awareness of such a high incidence of asymmetry may be clinically important when performing root canal treatment in two mandibular second molars in the same patient.
The prevalence of mandibular second molars with C-shaped canals in a European-Russian population was 14%, which is higher than that reported in other Caucasian populations. In individuals with C-shaped canals, asymmetry between the right and the left may be expected in 45% of cases. Knowledge of this anatomical variation and its prevalence in the population, as well as its high incidence of right-to-left asymmetry, may help the clinician to be aware of this challenge and choose an appropriate treatment approach.