Author: Prof. Hani F. Ounsi DCD, PhD, FICD

Assistant Professor, Department of Endodontics and Restorative Dentistry, School of Dental Medicine, Lebanese University, Lebanon Visiting Professor, Department of Endodontics and Restorative Dentistry, School of Dental Medicine, University of Siena, Italy

Introduction

Thorough chemomechanical debridement of root canal systems is crucial for optimal outcome of root canal treatments and clinicians should always be aware of possible root canal configurations and possible additional canals. In maxillary molars for instance, locating the second mesiobuccal canal often proves to be a challenge during cleaning and shaping and mapping out the internal anatomy in teeth presenting complex and variable configurations is understandably useful. Conventional periapical radiographs provide limited information as they give a 2D image of a complex 3D anatomy with risks of geometric distortion and superimposition of dental and anatomical structures. The introduction of cone-beam computed tomography (CBCT), which gives a 3D image of the tooth and surrounding dentoalveolar structures provides more information for diagnosis and treatment planning before or during root canal treatment and surgical endodontic procedures.

Case Report

A 49 year-old man was referred for treatment, reporting discomfort in the region of his left upper molars, specifically pointing the upper left second molar. Upon clinical examinations, a large carious lesion was present and the pulp responded positively to cold and electric tests in the maxillary second molar with no tenderness to percussion. No periapical bone resorptions was observed on the panoramic radiograph provided by the patient (fig.1), but a distal carious lesion was noted on the distal aspect of the left upper first molar. After local anesthesia and isolation, the carious lesion was removed using carbide round burs and the pulp chamber was opened using a safe-end bur (FKG, La Chaux de Fonds, Switzerland). The pulp stone was eliminated using an ultrasonic endodontic tip (BUC-1 and 3, Obtura Spartan Endodontics, Algonquin, IL, USA) mounted on an EMS miniPiezon unit at full power (EMS, Nyon, Switzerland) (fig.2).

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The chamber was filled with teflon, and a pre-endodontic build-up was done using a photopolymerizable resin-modified glass-ionomer cement (Fuji II LC, GC Corp, Tokyo, Japan).  Access was done through the restoration using a diamond round bur, the teflon was eliminated and the walls smoothed using the safe-end bur. Mesiobuccal canal and Palatal canals were both rapidly identified and instrumented according to the following sequence: K10 file for pathfinding (FKG) and PreRace 30/.06 (FKG) was used for preshaping. After electronic WL determination (Root ZX2, J Morita Corp, Kyoto, Japan),  iRace rotary files were used in the following sequence: 20/.02; 25/.04 and 30/.04 to working length. Sodium hypochlorite (5.25%) was used for irrigation using a side-vented round-ended 30 gauge needle (Max-i-Probe, Dentsply Sirona Endodontics). Neither the distobuccal nor the MB2 canal could be found despite the use of the operatory microscope (Global G6, Global Surgical Corp, Saint Louis, MO, USA).

At that point, sodium hypochlorite was left in the canals and the access was sealed using IRM (Dentsply DeTrey, Konstanz, Germany). A small field cone-beam computed tomography was performed (Promax 3D, Planmeca, Helsinki, Finland) to attempt to locate the discobuccal canal and the patient was scheduled for a second appointment. Examination of the CBCT revealed an invaginated aspect of the tooth and the presence of both canals (figs.3-5).

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Upon the second visit, access was reestablished as during the first visit and ultrasonic troughing was performed to locate the DB canal according to the triangulation performed on the CBCT using the position of the existing canals (fig. 6,7).

The DB canal was found and cleaning and shaping followed uneventfully as for the previous canals. Upon drying the palatal canal, the entrance of the MB2 was evidenced 1.5 mm beneath the floor of the pulp chamber (fig.8). Pathfinding and cleaning and shaping procedure followed as for the other canals. All canals were gauged and tuned manually and filling was performed using a single gutta percha cone (FKG) and tricalcium silicate cement (TotalFill, FKG) according to the cold hydraulic compaction technique (fig.9). Subsequently, the access cavity was cleaned and the tooth was referred back for restoration.

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Discussion

Cleaning and shaping the root canal system in its entirety is the major challenge of the endodontic treatment, and knowledge of root canal anatomy is paramount when performing endodontic treatments. Although maxillary molars have generally 3 roots, they often present with a second mesiobuccal canal and an inability to detect and treat MB2 canal is a reason for decreased long-term prognosis. The use of CBCT has considerably simplified endodontic diagnosis and treatment planning.

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Adding the third dimension to imaging modalities allows to evaluate a tooth in the sagittal and axial planes (in additional to the traditional coronal view of standard radiographs) and provides additional information that will lead to the identification of missing structures preservation of sound dentin by reducing the blind approach as demonstrated in this case report.

In 2017, the American Association of Endodontists and the American Academy of Oral and MaxilloFacial Radiology issued a joint statement in which recommendation #3 states: “Limited FOV CBCT should be considered the imaging modality of choice for initial treatment of teeth with the potential for extra canals and suspected complex morphology, such as mandibular anterior teeth, and maxillary and mandibular premolars and molars, and dental anomalies” and recommendation #4 states: “If a preoperative CBCT has not been taken, limited FOV CBCT should be considered as the imaging modality of choice for intra-appointment identification and localization of calcified canals” which is what was done in this case. Nevertheless, a major concern with CBCT remains the radiation dose which is why, as was done in the present case, the primary tool for finding hidden root canal anatomy should be the operatory microscope (5,6), with the CBCT being used only if said anatomy cannot be accessed (recommendation 4). Small field of view CBCT increases the definition of the image while reducing the area subjected to radiation and as such should be a preferred imaging modality over full-volume. The MB2 canal can be very challenging to negotiate even for an experienced endodontist and MB2 canals are present in 50.7% in maxillary second molars. The location of the MB2 canal orifice is usually found mesial to an imaginary line between the MB1 and palatal orifices and about 2 to 3 mm palatal to the MB 1 orifice. This imaginary line is more appropriately described as an arc with an apogee toward the mesial, following the contours of the mesial surface of the root. In the present case, the MB2 originated from the buccal wall of the palatal root 1.5 mm below the pulp floor, but presented with a Vertucci type IV configuration and a separate portal of exit.

Conclusion

Knowledge of root canal anatomy is paramount to ensure the success or root canal treatments and additional anatomy should be suspected until proven otherwise. The rationale for combining CBCT with the operatory microscope should be such as to allow for detection of complicated anatomy while minimizing the irradiation dose.