Authors: Dr.Padmanabh Jha, Dr. Vineeta Nikhil, Dr. Mukul Verma.
Subharti dental college, N. H. 58, Subhatipuram, Meerut.

Abstract
The complex configuration of C-shaped canals in mandibular second molars make root canal treatment unusually difficult. The present case report highlights their unpredictable canal anatomy and describes the use of newer materials and techniques such as the NiTi rotary file systems and thermoplasticized gutta percha. The effect of such modification on the treatment outcome of such complicated canal systems is discussed.

Introduction
The objective of endodontic therapy is the restoration of a treated tooth to its proper health, form and function in the masticatory apparatus. Knowledge of pulp anatomy is essential for success of endodontic treatment and lack of such knowledge may lead to treatment failure. Knowledge of both the normal and unusual configurations of the pulp and possible variations is critical for success in endodontics.

Mandibular second molars are commonly more variable in shape than other molar teeth¹. Due to the high incidence of root fusion in the mandibular second molars, C – shaped canals are frequent. The existence of single rooted mandibular second molars with a continuous slit connecting two, three or four canals was first described in the dental literature by Cooke and Cox in 1979, although several clinicians had suggested its presence earlier. C-shaped molars are so named because of the cross-sectional morphology of their roots and root canals. The C-shaped configuration refers to a continuous slit between all the canals so that a horizontal section through the roots yields a space in the shape of letter C. Instead of having several discrete orifices, the pulp chamber of molar with a C-shaped root canal system is a ribbon- shaped orifice with an arc of 180 degrees or more². This canal shape results from the fusion of the mesial and distal roots on either the buccal or the lingual root surface³. Although there have been reported cases of C – shaped canals in other teeth such as the maxillary lateral incisor, first molar, second molar, third molar and mandibular first premolar, first molar and third molars, the most numerous reports are of C-shaped mandibular second molars.

There is significant ethinic variation in the incidence of C-shaped molars. Reported prevalences have included 2.7-8% for Americans, 31.5% for Chinese, 19.1% for Lebanese, 10.6% for Saudi Arabia and 32.7% for Korean population. This anatomy is much more common in Asians than Cuacasians³.

The C-shaped canals posses many challenges for the clinician which requires good knowledge, proper identification and various modifications in the root canal procedures for the management of such canal systems.

This paper presents a case report of the management of C-shaped canals with contemporary endodontic techniques.

Case report
A 30 yr old female patient reported to the Dept. Of Conservative Dentistry & Endodontics with the chief complaint of pain in lower left posterior region. The medical history was non contributory. Clinical examination revealed grossly carious mandibular left second molar. The tooth was tender on percussion. Radiographic examination revealed deep caries involving pulp in mandibular left second molar. The roots appeared to be fused. A diagnosis of chronic irreversible pulpitis with apical periodontitis was established. Treatment plan of root canal therapy for mandibular left second molar was made.

On the first appointment, LA was administered, the tooth was isolated with rubber dam. Access cavity was prepared and the pulp was extirpated. During inspection of the pulpal floor, it was seen that there was continuous slit connecting the distal and the mesiobuccal orifice and the mesiolingual orifice was separate. The working length radiograph was taken, which showed that the mesiolingual canal was separate but the distal and the mesiobuccal canal fused in the apical third. The working length was determined by radiographic method as well as using third generation electronic apex locators. Biomechanical preparation was done with protaper files, mesiolingual canal was prepared till F2, mesiobuccal and distal canals were prepared till F3. Sodium hypochlorite was used as an irrigant after each instrument alongwith ultrasonic activation. The canals were dried with paper points and metapex was placed in the canals.

Fig.1: Preoperative radiograph of left mandibular second molar showing fused roots.	Fig. 2: Working length radiograph showing the canals are merging to exit through a single apical foramen.	Fig. 3: Postoperative radiograph showing obturation of the C-shaped canal system.

On the next appointment, the metapex was removed, canals irrigated with sodium hypochlorite and dried with paper points. Resin based sealer was applied with lentino spirals. A F2 GP point was used to obturate the mesiolingual canal. In the distal canal an F3 GP point was placed till the full working length and then Obtura II was used to fill the mesiobuccal canal and the slit connecting the distal and mesiobuccal canal. Post operative radiograph was taken to confirm the flow of gutta percha in the canals. The access cavity was sealed with cavit and the rubber dam removed. Patient was discharged and was recalled for postendodontic restoration.

Discussion
The C-shaped tooth looks like a routine second molar when viewed on the preoperative radiograph^4,5. Initial identification of the presence of C-shaped canal is essential. Morphologically, the only resource at the disposal is the dental radiographs6. Knowing that the mandibular second molar is the most common tooth that exhibits this aberrant morphology¹, the clinician should be alerted to this possibility during radiographic examination. Based on the 3D reconstructed Micro-CT images, the C-shaped canal system could be classified into 3 categories:

Category I: Canals merge into one major canal before exiting at the apical foramen.

Category II: The mesial and distal canals are nearly equal in size and have openings at the apex respectively.

Category III: There are mesial canals and distal canal. The distal canal or mesial canal has a big isthmus or fin area crossing the fused area. The mesial canals and distal canal have openings at the apex respectively.

The C- shaped canals in mandibular second molars could have canal orifices in various shapes. According to Melton’s original classification, the canal orifices of C-shaped canals has 3 appearances:

C1: A continuous C-shaped canal from the pulp chamber to apex.

C2: A semicolon where one canal was separated by dentin from the C-shaped canal.

C3: C-shaped anatomy is described as having a C-shaped orifice with two or more distinct and separate canals.8

C-shaped canals may start at the mesiolingual line angle and sweeps around either to the buccal or the lingual to end at the distal aspect of the pulp chamber. The closed area of the “C” may be either buccal or the lingual⁹. If it is to the buccal, the canal is continuous from the mesiobuccal to the mesiolingual around the lingual to the distolingual to distobuccal. In some cases, mesiolingual canal is separate and distinct, although it may be significantly shorter than the mesiobuccal and distal canals. In these molars the mesiobuccal canal swings backand merges with the distal canal, and these exit onto the root surface through a single foramen.

The access cavity for C-shaped canal system varies considerably and depends on the pulpal morphology of the individual tooth. When the access cavity is prepared, from the occlusal it appears that the orifices of the canals are not individually distinct but there is a C-shaped trough on the floor of the chamber⁷. If one file is placed in the mesial and one in the distal, the radiograph may reveal that both the files are in the same canal or the more mesial file has, perhaps, caused a perforation. Working length positions in teeth with C-shaped canals can be highly variable, as the canals exit in multiple areas at any level in the root. The use of tactile sensation, radiographs and apex locators are all recommended.

Once the chamber have been penetrated, efforts must be made to debride the chamber fully. This is best accomplished through the use of stainless steel K-files, orifice shapers and the shaping and finishing files of Protaper system⁸. Copious irrigation with sodium hypochlorite and the use of ultrasonics are also encouraged to penetrate into the minor irregularities of the canal system.

Obturation of the cleaned, shaped and disinfected C-shaped canal system is best accomplished using a softened gutta percha technique and root canal sealer, such as AH Plus⁶. Vertical compaction of softened gutta percha along with injected gutta percha such as Obtura II or the use of core-carrier technique such as Thermafil is recommended. The use of lateral compaction to obdurate fully cleaned and shaped C-shaped canals is not recommended as no individual canal appears well condensed despite deep penetration of spreaders and high number of auxillary cones.¹⁰

Although these types of cases are not very frequent, the clinician should be aware of their existence and should be able to undertake the appropriate measures to identify, clean, shape, disinfect and fill the canal systems in three dimensions and consequently avoid a potential failure.

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