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Assessment of Mesial Root Morphology and Frequency of MB2 Canals in Maxillary Molars using Cone Beam Computed Tomography/Determinacion de la Morfologia de la Raiz Mesial y la Frecuencia del Canal MB2 en Molares Maxilares usando Tomografia Computadorizada de Haz Conico.


One of the main purposes of endodontic treatment is to clean and disinfect root canal systems in order to reduce the number of microorganisms and extract necrotic tissue, and finally to obturate this system and thus prevent recontamination (Del Fabbro et al, 2007). However, it is agreed that one of the most frequent causes of failure in endodontic therapy is the inability to recognize and adequately treat the entire canal system (Karaman et al, 2011; Verma & Love, 2011; Vertucci, 2005; Zheng et al., 2010). In order to achieve treatment success, perfect knowledge of dental morphology is relevant, particularly of the internal anatomy (Cleghorn et al., 2006).

Root anatomy complexity is undermined in available literature, and its emphasized that the clinician should understand its possible variations (al Shalabi et al., 2000; Prabhakar et al, 2013; Abarca et al., 2014; Jimenez et al, 2015; Vaillard Jimenez et al., 2015). The canal system of the maxillary first and second molar is complex and difficult to study. It is reported that the mesiobuccal (MB) root presents the greatest variation and many studies have stressed the need to be aware of the presence of extra canals in this root (al Shalabi et al.).

The presence of a second canal in the MB root (MB2) is reported to be between 18% and 95% (Bauman et al., 2011). This wide range is due to the designs and methods used in these studies (Peeters, Suardita, & Setijanto, 2011) and could also be associated with ethnic differences, gender and age of the study populations (Cleghorn et al.).

The aim of this study was to determine the morphology of the mesial root canal system of maxillary molars and the frequency of the MB2 canal in the mesial root of first and second molars in the different root thirds and its relation with patient's age and sex.


This study was conducted following approval from the Scientific Ethics Committee of the University of La Frontera, in accordance with the ethical standards set forth in the Declaration of Helsinki. Cone-beam computed tomography (CBCT) scans of the maxilla of1280 Chilean patients, taken as part of the diagnosis or planning of dental treatments, between January 2010 and June 2013 in the Begmax Center in Santiago, Chile, were examined. The CBCT scans that were included presented first or second molars in patients between 8 and 77 years olds. Those who had teeth with endodontic treatment, open apex, signs of apical resorption, apical surgery, or extensive metallic restorations that prevented correct observation were excluded.

CBCT scans were obtained with a Gendex CB500 imaging system that uses 120kVp and 5 mA. The voxel size was 0.2 mm and the thickness of the cut was 0.2 mm. Every scan was taken by dental radiologists following the manufacturer's instructions. Prior to the evaluation of the scans, two observers underwent theoretical training to agree on protocol and observation criteria. Then, 20 teeth scans were evaluated independently by each observer under the same conditions of time of day, light and screen resolution. Ten days later the procedure was repeated under the same conditions. With the collected data the intraobserver and interobserver agreement was calculated using Cohen's Kappa index, and a very good agreement was obtained (kappa= 0.81) (Cerda & Villarroel, 2008).

The scans were analysed using the iCATVision software v in a darkroom on 21" LCD monitors with a resolution of 1280 x 1024 pixels. The root was divided in equal thirds (Fig. 1), and each third was checked for the presence of the MB2 canal. It was considered present when it was found in at least one root third.

Vertucci's classification was used to determine the morphology of the mesial root canal system of the maxillary first and second molars.

Data were processed with the Stata software v.11.0. A descriptive analysis was conducted to establish the distribution of the study variables. Pearson's chi-squared test was used to compare the percentages. Cuzick's test for trend was used for the trend analysis. The level of significance was 5%.


Of the 1280 CBCT scans examined, 508 fulfilled the selection criteria. Fifty nine point three percent of the CBCT scans included were of women and the average age was 33.3 [+ or -] 15.6, ranging from 8 to 77 years olds.

The total number of teeth observed was 1374, of which 802 were maxillary first molars, 406 rights and 396 left. Five hundred seventy two maxillary second molars were included: 283 right and 289 left.

The frequency of the MB2 canal in maxillary first molars (1MS) was 73.44% and in second molars (2MS) 42.48%. Table I shows the frequency of the MB2 canal by root third and side.

The presence of the MB2 canal in all root thirds was 32.5% in the right first molars (1MSR) and 16.6% in the right second molars (2MSR). In the left first molars (1MSL) 34.3% of the canals separated at the apical third and 12.8% of the left second molars (2MSL) had MB2 in all thirds. Figure 2 illustrates the presence of the MB2 canal in maxillary first and second molars.

No statistically significant association was found for the presence of the MB2 canal according to side in maxillary first and second molars (Table II). Nor was any statistically significant association found in the frequency of the MB2 canal according to gender (Table III).

However, when presence of MB2 was associated with age range, a statistically significant association was found. As the age increased, so did the presence of the MB2 canal in the maxillary first and second molars (P<0.001 and P= 0.023, respectively) (Table IV). The morphology of the mesial root canal system of maxillary first and second molars is shown in Table V.


Knowing the frequency of the MB2 canal in maxillary first and second molars and its relation with a patient's gender and age is relevant to the success of endodontic treatment. Many techniques have been used to study the morphology of the root canal system, including staining and bleaching, conventional and digital x-rays, and most recently CBCT (Neelakantan et al., 2010; Betancourt et al, 2015). In this work CBCT was used to determine the frequency of the MB2 canal because it is a non-invasive method with an effectiveness similar to bleaching and staining (Neelakantan et al.). It is currently considered the gold standard for these types of studies. Moreover, CBCT guarantees the ability to evaluate age, gender and side of the tooth (Zheng et al.).

The results in this study revealed a frequency of 74.44% in maxillary first molars and 42.48% in second molars, results very similar to those of Lee et al. (2011), who found a frequency of 70.5% in first molars and 41.6% in second molars, and the results of al Shalabi et al., who obtained 78% and 58% frequency of the MB2 canal in the first and second molars, respectively. This is in contrast to the results obtained by Silva et al. (2014), with frequencies of 42.65% for the maxillary first molar and 34.32% for the second molar, and those obtained by Reis et al. (2013), with 91% and 79.3% for the first and second molar, respectively. These differences in frequency reveal the anatomical variability of the mesial root in maxillary molars, which could be explained by the sample size, the observation technique (Peeters et al., 2011) and the patients' ethnicity (Cleghorn et al.; Zhang et al., 2011).

In this study, as was observed in the work by Reis et al., the frequency in the MB2 canal decreased towards the root apex (Reis et al.).

When the presence of the MB2 canal and the patient's age was assessed, we observed a tendency to increase with age, which is different from what was observed by other authors (Reis et al.; Lee et al.), who found that the presence of the MB2 canal decreased with age. This may be because in our study the sample of patients over 55 years of age represented only 5% of all the teeth included.

It should be mentioned that the visualization of two canals in the MB root is complex in young patients, because in the formation of the MB2 canal, the septum that separates the two canals is of secondary dentin, which means it works itself into position as the person ages. Therefore, in many cases, they are categorised as one "ribbon shaped" canal and not as two canals.

When the relationship between gender and tooth side was assessed, no significant differences were found, which is consistent with what has been published in current literature (Lee et al.; Reis et al.; Zhang et al.).

In relation to morphology it was found that type II and IV of Vertucci's Method were the most prevalent when the MB2 canal was present, just as was reported by Ng et al. (2001) and by Kim et al. (2012).


In this study, it was determined that more than 30% of first molars had MB2 canals present in all root thirds and that more than 13% of the maxillary second molars also exhibited this characteristic. Overall, 70% of maxillary first molars and over 40% of maxillary second molars show MB2 canals, results that are of clinical relevance. This could explain the high rate of treatment failure in these teeth and might encourage the clinician to pay more attention to the localization and treatment of this canal in order to improve the prognosis.

Given the anatomical complexity of the mesiobuccal root and the high frequency of the MB2 canal, the clinician must assume the existence of two canals in this root, and CBCT scanning is a good way to initially identify the MB2 canal in the different root thirds.


Jaime Abarca is a student in the Master of Dentistry Program in the Dentistry Faculty of the Universidad de La Frontera, Temuco, Chile.


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Correspondence to:

Jaime Abarca

Faculty of Dentistry

Universidad San Sebastian

Lago Panguipulli 1390

Pelluco Alto

Puerto Montt--CHILE


Received: 07-06-2015

Accepted: 24-09-2015

J. Abarca *,**; B. Gomez ***; C. Zaror ****,*****; H. Monardes ******, L. Bustos ******* & M. Cantin ****,********

* Master of Dentistry program, Faculty of Dentistry, Universidad de la Frontera, Temuco, Chile.

** Faculty of Dentistry, Universidad San Sebastian, Puerto Montt, Chile.

*** Begmax Radiology Center, Santiago, Chile.

**** Department of Pediatric Dentistry and Orthodontic, Faculty of Dentistry, Universidad de la Frontera, Temuco, Chile.

***** CIEESPO, Faculty of Dentistry, Universidad de la Frontera, Temuco, Chile.

****** Faculty of Dentistry, Universidad San Sebastian, Santiago, Chile.

******* Department of Public Health, Faculty of Medicine, Universidad de la Frontera, Temuco, Chile.

******** Center of Research in Biomedical Science, Universidad Autonoma de Chile, Temuco, Chile.

Caption: Fig. 1. Measurement system used to determine the presence of the second mesiobuccal canal. (a) Coronal cut used to determine in each root third the presence of the MB2 canal. (b) Sagittal cut used to locate the most apical and most coronal point of the root and to divide it in equidistant thirds; it was also used to leave the canal as vertical as possible. (c) Axial cut used to corroborate the type of canal and that this was as vertical as possible.

Caption: Fig. 2. Presence of the MB2 canal in maxillary first and second molar.
Table I. Distribution of MB2 canal according to root third.

Tooth     n     Cervical (%)   Middle (%)   Apical (%)

1MSR     406       71.43         56.90        37.93
1MSL     396       69.44         54.55        37.63
2MSR     283       39.93         32.16        19.43
2MSL     289       36.33         29.76        16.96

1MSR= Right first molar, 1MSL= Left first molar, 2MSR= Right
second molar, 2MSL= Left second molar.

Table II. Prevalence of MB2 canal in first and second molars
according to side.

Maxillary 1st Molar               Maxillary 2nd Molar

Prevalence MB2    n       p     Prevalence MB2    n       p

75.12            406    0.275       43.11        122    0.764
71.72            396                41.87        289
73.44            802                42.48        572

Table III. Presence of MB2 canal according to sex.

           Maxillary 1st Molar             Maxillary 2nd Molar

Sex      Prevalence MB2    n       p     Prevalence MB2    n       p

Female       71.28        477    0.093       38.98        313    0.062
Male         76.62        325                46.72        259
Total        73.44        802                42.48        572

Table IV. Frequency of MB2 by age range.

                 Maxillary 1st                 Maxillary 2nd
                     Molar                         Molar

Age (y)       Prevalence    n        p      Prevalence    n        p
                 MB2                           MB2

8 to 18         55.75      226    0.001 *     28.30       53    0.023 *
19 to 44        79.65      403                42.48      379
[greater        82.08      173                47.86      140
  than or
  equal to]
Total           73.44      802                42.48      572

* P<0.05, statistically significant. Cuzick's test for trend.

Table V. Morphology distribution of the mesial root canal system of
maxillary first and second molars according to Vertucci's Method.

             1MSR           1MSL           2MSR           2MSL
Types    n       %      n       %      n       %      n       %

I       101    24.88   112    28.28   161    56.89   168    58.13
II      147    36.2    133    33.59    64    22.61    68    23.53
III      4     0.99     2     0.51     3     1.06     4     1.38
IV      132    32.51   136    34.34    47    16.61    37    12.8
V        11    2.71     7     1.77     6     2.12     12    4.17
VI       11    2.71     6     1.52     2     0.71     0      0%

1MSR= Right first molar, 1MSL= Left first molar, 2MSR= Right second
molar, 2MSL= Left second molar.
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Author:Abarca, J.; Gomez, B.; Zaror, C.; Monardes, H.; Bustos, L.; Cantin, M.
Publication:International Journal of Morphology
Date:Dec 1, 2015
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