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Logo of ascroatActa Stomatologica Croatica
Acta Stomatol Croat. 2016 December; 50(4): 354–358.
PMCID: PMC5328646

A C-Shaped Canal in a Maxillary Second Molar: Prexion 3D Cone-Beam Computed Tomography Analysis


Objective: The aim of this study was to present an atypical case of a C-shaped root canal that was present in the vestibular root of a permanent maxillary second molar using PreXion 3-D cone-beam computed tomography (CBCT) as a diagnostic device. Materials and Methods: A 50-year-old female patient was referred for routine examination to a private diagnostic imaging clinic in Recife-Pernambuco. During the physical examination, the presence of an unusual C-shaped anatomy in the vestibular canal with a mesiodistal interconnection that extended from the apical to the cervical third was detected in axial slices acquired with a PreXion 3-D scanner. Results: Although C-shaped root canals are most frequently observed in the mandibular second molar, this case presented a rare finding in the permanent maxillary second molar. Conclusions: PreXion 3-D CBCT has emerged as a new high-resolution imaging test technology, thus assisting with the diagnosis of anatomical variations such as C-shaped root canals. However, such imaging technology is not recommended for routine use.

Key words:
Tooth Root, Dental Pulp Cavity, ConeBeam Computed Tomography, Tooth Abnormalities


A good knowledge of the internal dental anatomy and its variations is an absolute necessity for successful endodontic therapy. In cases where variations are not detected therapeutic failure can be expected to occur. The “C-shaped” configuration is among the various anatomical configurations of the root canal system, and this configuration was originally described by Cooke & Cox in 1979 (1). C-shaped root canals are characterized by a single ribbon-shaped orifice of 180ş (or more). The C-shaped canal system can assume different anatomical variations (2-4).

Such canal systems are a significant ethnic variation and are predominantly observed in Asian people (31.5% to 44.5%), (5) but are also present in Caucasian populations (2.7%) (1).

C-shaped root canals are commonly observed in mandibular permanent second molars (6) at a frequency of 39%, although they also occur in permanent first molars in the maxillary region (7) with an incidence of 0.091%. There are also reports of such occurrences in the permanent second (8) and third molars in the maxillary region (9).

A "C-shaped" root canal configuration of permanent maxillary molars results from the fused distovestibular and palatal roots that reach the apical third and lead to an intercommunication between the root canal that is responsible for the shape (10).

Although routine techniques, such as periapical analysis, are useful for preoperative evaluations of the anatomy of the root canal, these techniques have limited value in determining the complexities of such anatomies; for example, these techniques are limited in the diagnosis of C-shaped root canals based on superposition of two-dimensional images. Cone beam computed tomography (CBCT) has been suggested to be sufficiently precise for morphological studies with diagnostic purposes because CBCT is a tool for investigating roots and canals and their complexities. Cone beam computed tomography results in three-dimensional scans that produce images of multiple sections of roots and canals (11).The Prexion 3D is one of the most advanced new scanners available. It has a higher spatial resolution with voxel sizes of 0.05 to 0.15 mm, the most variable image acquisition time (19-37 sec) and employs lower kilo voltages and mill amperages than other pioneering equipment such as the i-CAT. In addition, CBCT has a small field of view, which allows for adjustments to the radiation dose absorbed by the patient and provides a greater number of image projections by rotation (12). However, as with any ionizing radiation-emitting device, the benefits of CBCT should outweigh the risks (13).

Therefore, the aim of this study was to present an atypical case of a C-shaped root canal that was present in the vestibular root of a permanent maxillary second molar using the PreXion 3-D CBCT as a diagnostic device.

Materials and Methods

During a routine examination of a 50-year-old female patient of mixed ethnicity with Negroid features in a private diagnostic imaging clinic, an unusual anatomic occurrence was observed in the maxillary region. This occurrence was present in the vestibular root of a permanent second molar. It was detected by 3-D cone-beam computerized tomography (CBCT) using a Prexion scanner (Yoshida Dental Mfg. Co. LTD., Tokyo. Japan). The following parameters were considered: field of view (FOV), 80x80 mm, spatial resolution, 0.10-mm voxels, 90 kVp and 4 mA. According to the studies of Fan et al. 2004b, based on axial slices and later confirmed on sagittal and coronal slices, three axial slices perpendicular to the long axis of the tooth were selected: one slice from the cervical third, one slice from the middle third and one slice from the apical third (Figure 1, ,2,2, ,3),3), (3).

Figure 1
Cone-beam computed tomography image of a maxillary second molar with a C-shaped canal. An axial section of the cervical third acquired with the PrexViewer software is shown.
Figure 2
Cone-beam computed tomography image of a maxillary second molar with a C-shaped canal. An axial section of the middle third acquired with the PrexViewer software is shown.
Figure 3
Cone-beam computed tomography image of a maxillary second molar with a C-shaped canal. An axial section of the apical third acquired with the PrexViewer software is shown.

The sections revealed the presence of two root canals: one oval-shaped canal that was present in the palatal root and an additional, larger canal with a shape that resembled the capital letter C. It extended from the entrance of the distovestibular canal to the mesiovestibular canal and from the cervical to the apical thirds and was confirmed on sagittal and coronal slices.

Thus, the presence of a C-shaped root canal was observed in a permanent second molar in the maxillary region. This canal and was radiographically and anatomically classified (2, 3) as Type I and Class I, respectively, and was characterized by a continuous image of a large canal with a curved shape extending to the apical foramen. A longitudinal radiolucent line in its coronal portion or across its entire extension was also present.


This paper describes the occurrence of a rare anatomical variation in the root canal of the vestibular root of a permanent second molar in the maxillary region that involved a C-shaped root canal as assessed with cone-beam computerized tomography image analysis with a 3D Prexion scanner.

A limited number of studies have demonstrated the existence of root canals with this configuration in maxillary second molars (9) because maxillary first and second molars commonly have three roots with three or four root canals (1). Additionally, the mandibular second molar is also the most likely of the permanent teeth to exhibit this morphological variation (1-4, 10), which highlights the importance of this paper for further studies. Typically, this canal configuration is found in teeth in which the roots are fused, which occurs due to a failure in the formation of Hertwig`s epithelial sheath that leads to longitudinal communication between canals (10). In the present case, the fusion occurred between the mesiovestibular and distovestibular roots and extended to the apical third. Similar results were reported in previous studies that have reported fusion in maxillary molars (1, 10).

Cone-beam computed tomography has emerged as a valuable tool for acquiring highly detailed information on morphology and exact topography of the root canal system, although it should be kept in mind that this technique should only be utilized when it is associated with additional benefits that justify the exposure dose (13, 14). We must highlight the importance of the axial slices for defining the canal configuration as C-shaped because, although conventional radiograph is commonly used, it does not provide sufficient information on more complex cases that challenge the inherent two-dimensionality of these systems (8, 11).

The tomographic data obtained for this paper were of particular relevance to a thorough evaluation of the root and, also, to morphologies of the respective canals. In this study, we reported an unusual case of a C-shaped root canal in a Brazilian patient which was diagnosed using a PreXion 3D scanner, which is one of the newest scanners available. For the case described here, we used slices so that each slice had 0.1mm x 0.1mm voxel size and a small FOV of 8 x 8 mm that allowed for a greater number of rotation image projections.

The importance of this study should be emphasized because it is a report of an unusual morphological variation in a Brazilian patient. A C-shaped configuration in an upper second molar with an atypical fusion of the vestibular roots was observed and analyzed with the most modern cone-beam computed tomography device available in this area: the Prexion 3D.

With regard to clinical implications, the findings of this study represent a major step towards harmonization of limited and standardized concepts related to numbers and shapes of root canals because, in certain situations, undetected extra roots or root canals with different morphologies are a major reason for failure of endodontic therapy due to the inability to detect their presence. Further studies are needed to expand the use of this imaging tool, which may facilitate even more accurate diagnoses.


In conclusion, the present study described a rare variation in morphology of vestibular C-shaped roots in a maxillary molar, which has an important didactic value since such cases are rarely described in textbooks.


The authors deny any conflicts of interest related to this study


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Articles from Acta Stomatologica Croatica are provided here courtesy of University of Zagreb: School of Dental Medicine