C-shaped Canals: A Diagnostic and Operational Hurdle to Endodontic Success

Early recognition of unusual canal configurations is a key component of successful endodontic therapy – particularly in cleaning, shaping, and obturation. As cited by the Department of Conservative Dentistry and Endodontics at the B.P. Koirala Institute of Health Sciences, a recent case study declared that the main cause of the C-shaped root formation is when Hertwig’s epithelial root sheath fails to fuse to the buccal or lingual root surface. Moreover, the most characteristic feature of these canals is the presence of a fin or web that connects individual root canals together.

Nevertheless, proper identification can still be difficult, especially if a traditional periapical radiograph is used since the two-dimensional image can often become distorted and/or produce anatomical noise. It is also not uncommon to see that these canals look completely normal at the pulp, but underneath their apical anatomy is deceivingly complex. Once identified, C-shaped canals can put a strain on the clinician to efficiently diagnose and provide treatment.

With these canals being such a common challenge in the endodontic field, below is a list of evidence-based facts that can be helpful for current practitioners: 

• C-shaped canals were first documented in endodontic literature by Cooke and Coxin in 1979, and were named after the cross-sectional morphology of the root and canal system.
• Instead of having several discrete orifices, the pulp chamber of the C-shaped canal is a single ribbon-shaped orifice with a 180° arc (or more)—which, in mandibular molars, starts at the mesio lingual line and sweeps around the buccal back to the distal aspect of the pulp chamber.
• C-shaped canals have a distinct ethnic variance and are highly frequent in Asian patients with a prevalence rate of approx. 31.5% (versus 2.7%-9% for Caucasians).
• C-shaped canals are most frequently found in the mandibular second molar, with a prevalence rate of 2.7%—44.5% (according to the International Endodontic Journal); interestingly, a newer study found that 2.4% of C-shaped canals actually occur in the mandibular second premolar, which had never been documented before in endodontic literature.
• Altogether, there are three categories of C-shaped canals—Type I is a continuous C-shaped canal; Type II is a semicolon-shaped canal (with dentin separating one distinct canal from a buccal or lingual C-shaped canal); while Type III involves two or more separate canals.
• Another defining characteristic of C-shaped canals is that they are not geometrically center in the cross section of the root, and that the wall of the mesial canals will often be thinnest. 
• Irregular areas in C-shaped canals can potentially contain soft-tissue remnants and/or infectious debris, which can escape during cleaning or filling. If so, the patient at hand will likely experience severe pain and undergo a substantial amount of bleeding.
• In a study from the Journal of Endodontics, it was determined that the shortest and longest diameter of the apical constriction of mesial canals (in C-shaped molars) were found to be 0.15-0.26 mm.
• C-shaped canals can change configuration or morphology at different levels along the length of the root. The dentin thickness between the external root surface and the internal root canal wall is less than in other teeth, so stripping the walls during shaping or post placement is a typical concern.
For more information on this topic, and/or review the sources used in this article, please check out the following:
•  The C-shaped Root Canal Configuration: A Review (American Association of Endodontics [AAE])
•  C-shaped Root Canal (Dental Research Journal)