| Abstract|| |
Context: Imaging techniques and endodontics are inseparable from each other as the former have always been the cornerstone for successful endodontic diagnosis and treatment.
Aims: The objective of this study was to detect the presence of extra canals in the mesiobuccal root of the maxillary first molar using cone-beam computed tomography (CBCT).
Materials and Methods: In this study, 75 freshly extracted human maxillary first molars were mounted on arches and exposed to CBCT and digital radiography (control). The incidence of additional canals is then evaluated using CBCT and the teeth identified with additional canals were marked and again exposed to RVG.
Statistical Analysis Used: The results were analyzed by three examiners two endodontists and an oral radiologist to eliminate bias. Inter and intra rater agreement was analyzed using the kappa coefficient.
Results: Statistical analysis revealed the incidence of extra canals to be at 47.1% with the difference between the readings of the 3 examiners being statistically insignificant.
Conclusions: CBCT can be considered an advanced diagnostic tool for primary and secondary endodontic treatments.
Keywords: Cone beam computed tomography, maxillary first molar, mesiobuccal 2 canal
|How to cite this article:|
Karunakar P, Solomon RV, Byragoni C, Sanjana L, Komali G. Demystifying the mesiobuccal root of maxillary first molar using cone-beam computed tomography. Indian J Dent Res 2015;26:63-6
Successful endodontic therapy essentially depends on accurate diagnosis in which thorough knowledge of the internal anatomy of the root plays a vital role. A precise evaluation of the internal anatomy is imperative mainly in teeth presenting complex and variable configurations related to root canals like maxillary molars. It has therefore become an increasingly common phenomenon to observe a second root canal in the mesiobuccal root, increasing the total of root canals to four. 
|How to cite this URL:|
Karunakar P, Solomon RV, Byragoni C, Sanjana L, Komali G. Demystifying the mesiobuccal root of maxillary first molar using cone-beam computed tomography. Indian J Dent Res [serial online] 2015 [cited 2020 Jul 2];26:63-6. Available from: http://www.ijdr.in/text.asp?2015/26/1/63/156810
The occurrence of a fourth canal ranges from 50.4% to 95% ,,,, and a fifth canal 2.25%  and a few authors have also reported cases with six canals. , These anatomical variations can compromise the endodontic therapy when not observed.
The incidence of a second mesiobuccal canal (MB2) significantly affects the success observed between initial root canal treatments and secondary root canal treatments (retreatments).  This entails that the main reason for the technical deficiencies in maxillary first molars leading to a poor long-term prognosis as a result of residual infection is the inability to properly detect, debride or fill an MB2 canal. ,,
The morphology of the maxillary first molar has been extensively studied and reported in the literature. Various methods have been used to identify this additional canal. These include clearing technique combined with dye penetration, , cross-section analysis in vitro, endodontic access with radiography and instruments,  conventional radiography  macroscopic examination, and magnification with operating microscope. But the conventional radiographic images yield limited information due to several reasons such as compression of three-dimensional (3D) anatomy, geometric distortion, anatomic noise, and temporal perspective. 
The potential applications of cone-beam computed tomography (CBCT) including analysis of canal morphology were first reviewed by Tachibana and Matsumoto in 1990.  This noninvasive 3D imaging technique uses a cone-shaped beam of radiation to acquire data in single 360° rotation which reveals the internal architecture of an object. It provides increased accuracy, higher resolution, reduced scan time, and low radiation dose when compared to conventional CT imaging. 
Though CBCT imaging existed for nearly 30 years, it became available as a feasible option for the private dental office only in the recent times.  It has been primarily used in the treatment planning for the placement of implants, , but several potential applications exist from the endodontic standpoint including the assessment of nonendodontic pathosis, internal and external resorption analysis, presurgical planning, pathosis of endodontic origin, and canal morphology. ,,
When compared to the gold standard of physical sectioning of the specimen, CBCT was found to be a reliable method for the detection of MB2 canal.  In a study conducted by Filho et al. to assess the internal morphology of maxillary first molars using three methods (CBCT, ex vivo and clinical) CBCT was found to be effective for the initial identification of such morphology. 
Therefore, in the present study, CBCT has been used as a diagnostic tool to evaluate the incidence of additional canals in maxillary first molars.
| Subjects and Methods|| |
Seventy-five extracted human maxillary first molars, carious or noncarious were collected, cleaned of any adherent soft tissues and bone fragments, stored at 100% relative humidity and randomly inserted into 5 U-shaped wax arches.
Each U-shaped arch made up of modeling wax, mimicking natural arch form consisted of 15 teeth each with the roots Inside the wax and occlusal surface exposed as shown in [Figure 1]. The base of the wax encasing was made flat so that it sits stationary on the flat plastic bite plane of CBCT scanner. All the samples were scanned by a CBCT scanner (KODAK 9000 extraoral imaging system) with tube voltage of 70 kv and tube current of 10 mA and constant slice thickness of 125 μm. The teeth were viewed in axial, coronal, and sagittal sections to Confirm the internal anatomy as shown in [Figure 2] and [Figure 3].
|Figure 2: Cone-beam computed tomography sections of the arch showing MB2 canal|
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|Figure 3: Sagittal section of the mesiobuccal root showing MB and MB2 canals|
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The scanned images were analyzed by three examiners (two endodontists and one oral radiologist). The study was performed as a triple blinded study to reduce further the incidence of bias among the three examiners.
The following features were analyzed by the examiners:
Inter rater agreement was measured between the endodontists and oral radiologist. Intra rater agreement was measured by having the endodontists and radiologist evaluates one-half of the CBCT images evaluated at each of 2 separate sessions. Finally, the teeth identified with extra canals were numbered and again exposed to digital radiography (RVG).
- Number of roots per tooth
- Number of root canals per tooth
- If at all an additional canal exists in a tooth, the root with additional canal.
| Results|| |
All the analysis was done using SPSS version 14 (Developed by IBM corporation SPSS statistics). The level of inter rater agreement between the examiners was done by computing the kappa coefficient. The three examiners were found to be in agreement with each other based on the values of kappa coefficient as shown in [Table 1] and [Table 2].
- Number of roots:
- There was found to be no variation in the number of roots with three separate roots commonly in all the teeth examined.
- Number of root canals per tooth:
- Three root canals were found in about 52.9% of the teeth examined, and about 47.1% of the teeth showed four canals.
- Root with additional canal:
- All the additional canals identified were found to be in the mesiobuccal roots of the teeth.
| Discussion|| |
The occurrence of a second mesiobuccal canal (MB2) has been most widely investigated owing mainly due to its staggering effect on the success of primary and secondary (retreatment) cases of maxillary molars. In a study conducted by Witherspoon et al. to identify the incidence of additional or missed canal systems in molar retreatment cases in a private clinical setup, it was found that missed canals were identified in 64 of the 133 previously treated teeth (48%) out of which 11% involved a maxillary second molar and 44% involved a maxillary first molar. For the maxillary first molars, 93% of all missed canals were identified in the mesiobuccal root.  The MB2 possesses a tactical challenge to the clinician as it is most often inconspicuous in its location and is frequently missed in routine clinical practice; unless steps are adopted to rule out its existence. 
Various studies dealing with the occurrence of MB2 canal have shown that the success rate of detection of MB2 canal is more for in vitro studies rather than in vivo studies as evidenced in [Table 3] above with highest incidence seen in the studies conducted using surgical operating microscope followed by clearing technique. It can also be inferred that majority of the in vitro studies used clearing technique to study the root canal systems which makes use of various acids to make tooth transparent, and dying solution to make the root canal systems visible. 
The definition of a canal as treatable canals used in clinical studies versus the more complex canal configurations that are visible through clearing studies can also lead to different results. 
The present study evaluated the detection of additional canals specifically the MB2 canals in 75 extracted maxillary first molars using CBCT irrespective of age and gender. 47.1% of the total teeth evaluated showed the presence of MB2 canals. Unlike the usually employed techniques to identify complex canal morphology, CBCT provide noninvasive 3D images or simultaneously axial, coronal, and sagittal 2D sections of target that can be applied in endodontic diagnosis morphologic analysis, endodontic epidemiologic investigation, and clinical outcome study. 
A systematic review of the literature performed by Cleghorn et al. in 2006  estimated the anatomy of the permanent maxillary first molar through a meta-analysis of data of about 8399 teeth from 34 laboratory studies and of 2576 teeth from 14 clinical studies. They reported that the incidence of two canals in the mesiobuccal root was 56.8% similar to that reported by corbella et al. 
An issue to be considered is the age of the subject as several studies have shown less occurrence or detection of MB2 canals as the age advances due to progressive calcifications of the canals. In a study conducted by Zheng et al. where CBCT images of maxillary molars in 627 subjects between 10 and 86 years of age were analyzed, more additional canals were detected in patients between 20 and 30 years and <½of the mesiobuccal roots was found to have additional canals in patients older than 40 years.  Hence, the importance of age in the detection of MB2 canals cannot be undermined as the incidence of detection of extra canals differs in various studies due to the age of the population taken into consideration.
| Conclusion|| |
Detection of the extra canal in the maxillary first molar has become an indelible factor in the success of primary and secondary endodontic treatments. Various methods have been conceived to detect these canals with the in vitro methods always showing a higher success rate. The use of advanced techniques like surgical operating microscopes and loupes has to an extent increased the ability to detect the extra canals in in vivo scenarios as well. CBCT is a progressively new technique that can be used in the clinical picture with greater success and eventually aid in providing an uncompromised a superior endodontic treatment.
| Acknowledgment|| |
Secunderabad diagnostic centre, Hyderabad.
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Department of Conservative Dentistry and Endodontics, Panineeya Mahavidyalaya Institute of Dental Sciences and Research Centre, Hyderabad, Telangana
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3]