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Year : 2019  |  Volume : 31  |  Issue : 1  |  Page : 98-103

Dimensional correlation between morphology and root canal anatomy in mesiobuccal root of permanent maxillary first molar: An ex vivo study

Department of Conservative Dentistry, Subharti Dental College, Meerut, Uttar Pradesh, India

Date of Web Publication19-Jun-2019

Correspondence Address:
Dr. Shikha Jaiswal
Department of Conservative Dentistry, Subharti Dental College, Meerut, Uttar Pradesh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/endo.endo_76_18

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Aim: The aim of the present study was to establish a correlation between morphology and root canal anatomy of mesiobuccal (MB) root of the permanent maxillary first molar using cone-beam computed tomography (CBCT) and stereomicroscope.
Methodology: Access cavities were prepared on sixty permanent maxillary first molars. Efforts were made to locate MB second (MB2) canals without magnification and with magnification using methylene blue dye and ultrasonic troughing. The number of teeth possessing MB2 canal with both methods was recorded. Thereafter, the MB root was resected and observed under CBCT. The MB root was then sectioned at different levels and observed under stereomicroscope. Both the methods were used to assess the number of canals and root forms which were classified as long oval, oval, and round. The data thus obtained were then subjected to statistical analysis using ANOVA and Z-test.
Results: Clinical techniques such as magnification, dyes, and troughing were found to be more efficient in the detection of MB2 canals as compared to unaided techniques. As observed with CBCT and stereomicroscope, the incidence of MB2 canal was significantly more in coronal as compared to middle and apical, and a statistical correlation between root form and number of canals was observed.
Conclusion: Majority of the MB roots were long oval and oval in axial section and the incidence of finding MB2 in long oval and oval root forms was found to be greater as compared to round root form, although it is not necessary that all long oval or oval roots shall have two or more canals.

Keywords: Cone-beam computed tomography, maxillary first molars, mesiobuccal canal, root form/geometry, stereomicroscope

How to cite this article:
Prasad AC, Gupta S, Nikhil V, Jaiswal S, Raj S, Arora R. Dimensional correlation between morphology and root canal anatomy in mesiobuccal root of permanent maxillary first molar: An ex vivo study. Endodontology 2019;31:98-103

How to cite this URL:
Prasad AC, Gupta S, Nikhil V, Jaiswal S, Raj S, Arora R. Dimensional correlation between morphology and root canal anatomy in mesiobuccal root of permanent maxillary first molar: An ex vivo study. Endodontology [serial online] 2019 [cited 2020 Jan 29];31:98-103. Available from: http://www.endodontologyonweb.org/text.asp?2019/31/1/98/260537

  Introduction Top

Predictable shaping and cleaning depends on the knowledge and application of precise techniques and instruments in locating, exploring, and treating each individual canal to allow complete three-dimensional obturation. Failure to identify, explore, clean, and obturate the root canal system often leads to failure of endodontic therapy and origin or persistence of periapical disease.

Root canal anatomy is highly variable and differs among different populations and individuals. The mesiobuccal (MB) root of maxillary molars frequently has a root canal system containing more than one canal (first described by Hess and Zurcher in 1925) called as MB second (MB2).[1] The incidence of MB2 canal has been reported to be as low as 18.6% in an in vivo study conducted by Hartwell and Bellizzi[2] and as high as 95.2% in an in vitro study conducted by Kulild and Peters.[3] Weine et al.[4] suggested that inability to identify, instrument, and obturate the MB2 canal could lead to endodontic failure in these teeth. Therefore, it is worthwhile for the practitioner to put the time and effort into properly locating and treating MB2 canals in an attempt to increase the prognosis of endodontic therapy in maxillary molars.

Different strategies, armamentarium, and techniques such as angulated radiographs, dental operating microscope, use of surgical length burs, micro-openers, and use of ultrasonic tips have enabled better instrumentation and visibility of access cavities for better exploration of orifices. In addition, dyes such as methylene blue, which is a water-soluble dye, can be irrigated into a dry pulp chamber and subsequently rinsed with water, dried, and visualized to “map” hard-to-find orifices, fins, and grooves, or certain coronal fractures.[5]

Traditional radiography, scanning electron microscopy, and root canal staining or micro-computed tomography (CT) scanning are commonly used in vitro tools in identifying the configuration of canals. Several studies evaluating the occurrence of MB2 canals have been conducted; however, most of them are based on either histologic or conventional X-ray examination which have their own limitations.[6]

The stereoscopic or dissecting microscope is an optical microscope variant designed for low-magnification observation of a sample, typically using light reflected from the surface of an object rather than transmitted through it. It is a tool in investigating complex variation in root canal anatomy by visualization at higher magnification but involves sectioning of teeth.[7]

In contrast to invasive methods, cone-beam CT (CBCT) scanning is an important noninvasive resource in the assessment of root canal systems notably to identify MB2 canals in maxillary molars, as CBCT scans allow in vivo dental investigation in axial, sagittal, and coronal planes simultaneously.[6]

Variation in root and root canal anatomy of permanent maxillary first molar has been vastly studied with respect to populations in different geographical areas, using various techniques. Variations in root canal anatomy occur most often because of genetic and local influences during tooth development.[7] Since root formation and completion is influenced by cells of dental papilla as well as follicle, there might be a correlation between root morphology and root canal variation, although literature is scarce in establishing this correlation.

Several studies to evaluate the incidence and frequency of MB2 canal have been illustrated, but there is a lack of studies in the literature to corroborate or contradict the correlation between root geometry and canal variation. Hence, this study is an effort to generate a correlation, if any, between the dimensions of MB root and variation in its root canal anatomy, utilizing CBCT and stereomicroscope.

  Methodology Top

Sixty freshly extracted (storage time <3 months) permanent maxillary first molars were selected for the study following strict inclusion criteria which comprised of complete root formation and apical closure; intact MB root without caries; crack, resorption, restoration, or fracture; no evidence of endodontic treatment; and no evidence of fusion with distobuccal or palatal root. The selected teeth were cleaned and debrided by ultrasonic scaling and brushes, and then observed for the defects under magnification and illumination. The teeth with defects were discarded and the selected teeth were then stored in chloramine solution till further usage.

Preparation of samples

The samples were sequentially numbered and mounted in a customized apparatus for stabilization. The endodontic access cavity was prepared using Endo Access and Endo-Z burs (DENTSPLY Maillefer, Switzerland) in a high-speed Airotor. The chamber was thoroughly debrided and cleaned by irrigation with 3% sodium hypochlorite (Prime Dental Products Pvt Ltd., Thane, India) and normal saline.

Initially, the access cavities were prepared in a triangular shape. MB1, distobuccal, and palatal canal orifices were located with the help of an endodontic explorer (DG16, API Delhi), and the canals were negotiated with a #8, #10, or #15 K-file (Dentsply Maillefer, Ballaigues, Switzerland). The outline of the access cavity was then modified from a triangular to a rhomboidal shape and the chamber was cleaned and dried, to improve the accessibility and visibility of the extra canal orifice (MB2).

The access cavities were then carefully examined for the presence of MB2 orifice with unaided visual and tactile examination under illumination using direct vision, endoexplorer, and #6, #8, #10 K–files. The samples in which MB2 was detected in this manner were counted and kept separately. The remaining samples were visualized under microscope, using dye and ultrasonic troughing.

Dye penetration (1% methylene blue)

The access cavity was filled with the dye for 2 min and subsequently rinsed with saline, dried, and examined for location of the MB2 orifice indicated by the areas of dye retention using magnification and ultrasonics.

Magnification and ultrasonic troughing

Under magnification of × 8 × 10, ultrasonic troughing was carried out using START-X TIPS #2 and #3 (DENTSPLY Maillefer, Switzerland) from MB1 to palatal canal and 2 mm mesially till a depth of 2 mm to locate MB2 orifices. The samples in which MB2 orifices were located in this manner were counted and stored with other samples with MB2.

Root resection

The MB roots of all the samples were horizontally resected at the orifice level using double-sided diamond-coated disc.

Cone-beam computed tomography examination

The resected roots were mounted on a wax sheet, three samples at a time, and were scanned with the effective radiation dose of 15–273 μSv, field of view at 5 cm × 5.5 cm height with exposure time of 2–5 s, and scan time of 14 s in high-definition mode with the isotropic voxel size of 0.08. The current and voltage used were 3–16 mA and 60–90 kVp, respectively. The distance of source to object was 8–8.5' and distance of object to sensor was 8–8.5'. The axial section of samples was observed under CBCT at the orifice level, midroot level, and 1 mm short of the apex by Sidexis 4.1 (Sirona, Bensheim, Germany) program [Figure 1]. The samples were observed for the following:
Figure 1: (a) Sagittal cone-beam computed tomography image for coronal, middle, and apical reference points, (b) cone-beam computed tomography image (axial) representing canal configuration, (c) cone-beam computed tomography image (axial) for dimensional analysis

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  1. The number of canals and configuration of each root at each level
  2. The root morphology was classified based on the ratio of buccolingual to mesiodistal dimensions at the three levels.

Based on this ratio, the root shapes at each level were classified morphologically as follows:

  1. Round = B − L/MD ≃ 1
  2. Oval = B − L/MD ≃ 2
  3. Long oval = B − L/MD >2

All the readings were carried out by two different observers individually. In case of disagreement, the samples were re-evaluated.

Stereomicroscope evaluation

The resected root samples were then horizontally sectioned at cervical (C), middle (M), and apical (A) parts, using a diamond-coated disc in micromotor. The resected samples were placed and stabilized over a printed cellophane graph paper sheet under stereomicroscope at ×45 magnification for observing the canal configuration and dimension at each level [Figure 2].
Figure 2: Stereomicroscope view of axial root section for canal configuration and dimensional analysis

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The observations so obtained were tabulated and statistically analyzed by using analysis of variance (ANOVA) and Z-test for calculating:

  • Dimensional accuracy between CBCT and stereomicroscope
  • Correlation between root geometry and number of canals at different levels.

  Results Top

Root form

The predominant root form at the coronal and middle third of MB root was long oval, whereas it was oval at apical. The least observed root form at all the levels was round [Table 1]. The observations for the root form with CBCT and under stereomicroscope were comparable at all the levels.
Table 1: Cone-beam computed tomography and stereomicroscope evaluation of root geometry at different levels

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Canal variation

The samples possessing MB2 using dental operating microscope, dye, and troughing were 35, i.e. 58% which were significantly more than that with unaided technique (38%). Magnification and CBCT imaging resulted in significantly improved identification of MB2 (68%). The incidence of MB2 canal at different levels as observed with CBCT and stereomicroscope can be arranged as coronal >middle >apical [Graph 1] and [Table 2], and the difference was statistically significant (P < 0.0001). This observation points toward the confluence of MB2 canal with MB1 in middle and apical areas.
Table 2: Analysis of variance test for the incidence of mesiobuccal at different levels as observed with cone-beam computed tomography and stereomicroscope

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Correlation between root form and canal variation

CBCT and stereomicroscopic observations at different levels revealed a statistical correlation between root form and number of canals [Table 3]. The incidence of MB2 was greater in long oval and oval canals. More number of MB2 canals were detected with stereomicroscope as compared to CBCT although the difference was not significant.
Table 3: “Z” test for statistical correlation between root form and number of mesiobuccal canals

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  Discussion Top

The maxillary molars are one of the most complex teeth by virtue of their multifaceted internal and external anatomy. The MB root is the most complex root which is broad in a buccolingual direction and usually contains two root canals: MB1 and MB2 canals. Various in vitro and in vivo studies have been carried out to comprehensively study and understand the anatomy of MB root of the maxillary first molar. Pineda and Kuttler[8] and Vertucci[9] also developed a system for canal anatomy classification for any tooth that has a broad buccolingual diameter.

Various studies have discussed the role of dental operating microscope (DOM) in locating MB2 orifice with increased success rate.[10],[11],[12],[13] Studies also support the use of methylene blue dye to improve the detection of MB2 canal. Weller et al.[14] emphasized the importance of using dye to recognize root canals and isthmuses. Cantatore et al. have comprehensively discussed the use and rationale of different Start-X™ ultrasonic tips in access cavity refinement.[15]

CBCT was introduced in the field of endodontics in 1990.[16] The application of CBCT provides a noninvasive three-dimensional confirmatory diagnosis as a complement to conventional radiography. CBCT images accurately depict anatomical structures in their true state without significant magnification or distortion. Hence, it can be a significant investigatory tool to determine canal variation and measure the root dimensions at different levels.

Stereomicroscope helps to provides three-dimensional view of the surface to be examined. The instrument uses two separate optical paths with two objectives and eyepieces to provide slightly different viewing angles to the left and right eyes. This arrangement produces a three-dimensional visualization of the sample being examined. Spalding et al.[17] while conducting a study on configuration of canal system in the MB root of maxillary first molars found stereomicroscope to be a very useful tool for observing the complex anatomy of MB root. The placement of graph paper below the samples under observation helped in real-time measurement of the dimension and the canal variations. The captured images also served for the reproducibility of dimensional analysis and canal variations later in the study.

In the present study, the root shapes were classified into three main categories, that is, long oval, oval, and round based on the buccolingual and mesiodistal dimensions of the MB root. Little relevance is found in literature regarding similar classification of root forms. A similar classification has been used by Gani and Visvisian[18] for classifying root canal shapes in the apical region of maxillary first molar.

In this study, MB2 was identified in 38% cases without magnification and 58% with aided magnification, dyes, and troughing, and this difference was found to be significant. Schwarze et al.[19] used operating microscope for identifying MB2 canal in MB root and stated 93.7% incidence in detecting the MB2 canal. Alacam et al.[20] stated that the prevalence of MB2 canal in maxillary first molars increased from 62% to 74% by using ultrasonics and magnification. Nallapati et al.[21] stated that although the DOM is an indispensable aid in visualizing the detailed anatomy of the pulp chamber, usage of dyes is essential to develop the visual acuity to appreciate the subtle differences that aid in location of the root canals. Contrary to this, Sempira and Hartwell[11] and Görduysus et al.[22] did not find an increased detection of MB2 canal using magnification, but it led to increased visual acuity and operator's efficacy. Based on these findings, magnification and ultrasonic troughing during access cavity preparation can be suggested as a gold standard for locating extra canal, especially when Krasner and Rankow's[23] laws of symmetry for locating canals cannot be applied for maxillary first molar.

In the present study, advanced imaging techniques such as CBCT resulted in increased detection (68%) of MB2 canals. This is because of the ability of CBCT to produce multiple slices at a higher resolution in axial view. The orifice which might not be detected clinically during ultrasonic troughing and tactile probing would be visible in an axial section of CBCT. Lee et al.[24] in an in vivo CBCT study found that 71.8% of maxillary first molar had an incidence of MB2 canal in a Korean population. Zhang et al.[25] found 52% prevalence of MB2 canal in maxillary first molar of Chinese population. Bauman et al.[26] presented a study to show the effect of voxel size of CBCT images for identification of MB2 canal and stated that, the smaller the voxel size, the greater is the detection rate of MB2. There are no evidence-based criteria indicating scan parameters that are optimal for viewing small anatomical features, such as MB2 canal. Thus, the difference in the detection of MB2 using CBCT among different research studies can be explained on the basis of sample size, sample population group, and technical specifications of CBCT unit used. It has also been observed that training and experience is also an important factor for detection of MB2 canals while using CBCT.

In the present study, sectioning of the samples and visualization under magnification resulted in improved detection of MB2 at each level as compared to CBCT, although the difference was not significant. These results are in accordance with the study by Blattner et al.[27] who found higher incidence of MB2 with stereomicroscope (68.4%) compared to CBCT (57.9%) and the difference was not significant. Stereomicroscope evaluation in the present study resulted in 75% incidence of MB2 canal at coronal level. Weine et al.[4] conducted a landmark study on the prevalence of MB2 by sectioning technique (without magnification) on maxillary first molars and reported the incidence of MB2 to be only 51.7%. Kulild and Peter reported 54.1% of the prevalence of MB2 in maxillary molar during access preparation which increased by 9.6% after aiding with techniques such as sectioning and use of microscope. Although the result for incidence of MB2 canal for the present study corroborated with other studies, a larger sample size from different populations is needed for better appreciation since root canal anatomy is highly varied and individualized.

While establishing the correlation between the root forms and incidence of MB2, three important findings can be observed from the present study:

  1. The predominant root form (combined) was found to be long oval, suggesting that the MB root is majorly long oval, i.e., flat or ribbon shaped
  2. There was no significant predilection of long oval or oval root forms with MB2 canals, but the incidence of MB2 canal was significantly higher in long oval root forms than oval and in oval root forms than round root.

Considering the above-mentioned findings, it can be stated that the incidence of MB2 canals has a definitive correlation with the root form of MB root of permanent maxillary first molar.

Observer's inexperience, interobserver difference, and technical differences in the methods used for studying root canal anatomy have their own role and these factors should always be considered while conducting and reporting such studies. Anatomy is destiny and in endodontics, the destiny is hidden. As a clinician, we must do whatever we can to understand and explore the anatomy successfully.

  Conclusion Top

Within the limitations of the present study, the following conclusions can be drawn:

  1. The incidence of detection of MB2 canal in maxillary first molar depends on the method or technique used, apart from other factors involved
  2. The advanced techniques used in the present study, i.e., CBCT and stereomicroscope showed significantly accurate results in locating MB2 canals compared to other (clinical) techniques such as magnification, dyes, and troughing and unaided eye
  3. Majority of the MB roots are long oval and oval in axial section and the incidence of finding MB2 in long oval and oval root form was found to be greater as compared to round root form, but it is not necessary that all long oval or oval roots shall have two or more canals.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Hess W, Zurcher E. The Anatomy of the Root Canals of the Teeth of the Permanent Dentition. Part 1. New York: William Wood and Co.; 1925.  Back to cited text no. 1
Hartwell G, Bellizzi R. Clinical investigation of in vivo endodontically treated mandibular and maxillary molars. J Endod 1982;8:555-7.  Back to cited text no. 2
Kulild JC, Peters DD. Prevalence and configuration of canal systems in the mesiobuccal root of maxillary first and second molars. J Endod 1990;169:311-7.  Back to cited text no. 3
Weine FS, Healey HJ, Gerstein H, Evanson L. Canal configuration in the mesiobuccal root of the maxillary first molar and its endodontic significance. Oral Surg Oral Med Oral Pathol 1969;28:419-25.  Back to cited text no. 4
Ruddle CJ. Nonsurgical endodontic retreatment. J Calif Dent Assoc 2004;32:474-84.  Back to cited text no. 5
Sharma DS, Sharma H, Khurana N, Varma A. Cone beam computed tomography study of root and canal morphology of mandibular premolars in Indore population. Natl J Dent Sci Res 2015;3:24-7.  Back to cited text no. 6
Green D. A stereomicroscopic study of the root apices of 400 maxillary and mandibular anterior teeth. Oral Surg Oral Med Oral Pathol 1956;9:1224-32.  Back to cited text no. 7
Pineda F, Kuttler Y. Mesiodistal and buccolingual roentgenographic investigation of 7,275 root canals. Oral Surg Oral Med Oral Pathol 1972;33:101-10.  Back to cited text no. 8
Vertucci FJ. Root canal anatomy of the human permanent teeth. Oral Surg Oral Med Oral Pathol 1984;58:589-99.  Back to cited text no. 9
Stropko JJ. Canal morphology of maxillary molars: Clinical observations of canal configurations. J Endod 1999;25:446-50.  Back to cited text no. 10
Sempira HN, Hartwell GR. Frequency of second mesiobuccal canals in maxillary molars as determined by use of an operating microscope: A clinical study. J Endod 2000;26:673-4.  Back to cited text no. 11
Buhrley LJ, Barrows MJ, BeGole EA, Wenckus CS. Effect of magnification on locating the MB2 canal in maxillary molars. J Endod 2002;28:324-7.  Back to cited text no. 12
Rajput F, Kalhoro FA, Shaikh MI, Khatoon S. Validity of different methods for MB2 canal location in permanent maxillary molars. Pak Oral Dent J 2014;34:548-51.  Back to cited text no. 13
Weller RN, Niemczyk SP, Kim S. Incidence and position of the canal isthmus. Part 1. Mesiobuccal root of the maxillary first molar. J Endod 1995;21:380-3.  Back to cited text no. 14
Cantatore G, Berutti E, Castellucci A. Missed anatomy: Frequency and clinical impact. Endod Topics 2006;15:30-1.  Back to cited text no. 15
Scarfe WC, Farman AG. What is cone-beam CT and how does it work? Dent Clin North Am 2008;52:707-30, v.  Back to cited text no. 16
Spalding M, Rezende KM, Silveira MC, Valera MC, Leite HF. Configuration of canal system in the mesiobuccal root of maxillary first molars. Int J Morphol 2017;35:459-64.  Back to cited text no. 17
Gani O, Visvisian C. Apical canal diameter in the first upper molar at various ages. J Endod 1999;25:689-91.  Back to cited text no. 18
Schwarze T, Baethge C, Stecher T, Geurtsen W. Identification of second canals in the mesiobuccal root of maxillary first and second molars using magnifying loupes or an operating microscope. Aust Endod J 2002;28:57-60.  Back to cited text no. 19
Alaçam T, Tinaz AC, Genç O, Kayaoglu G. Second mesiobuccal canal detection in maxillary first molars using microscopy and ultrasonics. Aust Endod J 2008;34:106-9.  Back to cited text no. 20
NallapatiS, Glassman G. Use of ophthalmic dyes in root canal location. Endodontic Pract 2004;30:391-8.  Back to cited text no. 21
Görduysus MO, Görduysus M, Friedman S. Operating microscope improves negotiation of second mesiobuccal canals in maxillary molars. J Endod 2001;27:683-6.  Back to cited text no. 22
Krasner P, Rankow HJ. Anatomy of the pulp-chamber floor. J Endod 2004;30:5-16.  Back to cited text no. 23
Lee JH, Kim KD, Lee JK, Park W, Jeong JS, Lee Y, et al. Mesiobuccal root canal anatomy of Korean maxillary first and second molars by cone-beam computed tomography. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2011;111:785-91.  Back to cited text no. 24
Zhang R, Yang H, Yu X, Wang H, Hu T, Dummer PM, et al. Use of CBCT to identify the morphology of maxillary permanent molar teeth in a Chinese subpopulation. Int Endod J 2011;44:162-9.  Back to cited text no. 25
Bauman R, Scarfe W, Clark S, Morelli J, Scheetz J, Farman A, et al. Ex vivo detection of mesiobuccal canals in maxillary molars using CBCT at four different isotropic voxel dimensions. Int Endod J 2011;44:752-8.  Back to cited text no. 26
Blattner TC, George N, Lee CC, Kumar V, Yelton CD. Efficacy of cone-beam computed tomography as a modality to accurately identify the presence of second mesiobuccal canals in maxillary first and second molars: A pilot study. J Endod 2010;36:867-70.  Back to cited text no. 27


  [Figure 1], [Figure 2]

  [Table 1], [Table 2], [Table 3]


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