Occurrence of Second Mesio-buccal Canal in Maxillary First Permanent Molar : A CBCT Study

Introduction: Complexity in root canal morphology leads to chances of failure in endodontic treatment due to missed canal. Availability of Cone-beam Computed Tomography (CBCT) has contributed to assess second mesiobuccal canals in maxillary first molars. Objective: To study the presence of second mesiobuccal (MB2) canals, classify morphology of canals according to Vertucci’s classification and to measure the distance between MB1 and MB2 canals. Materials & Method: 72 CBCT scans including 115 permanent maxillary first molars were evaluated by endodontist and oral radiologist separately using Dicom software to study the mesiobuccal root canal morphology. Oral radiologist and endodontist individually evaluated the scans through coronal, axial and oblique views to study canal configurations. Vertucci’s Classification was used to classify the canal configurations. Statistical tests were done to assess the gender variation and arch side difference. Result: Among 115 images evaluated; 30.4% samples had second mesiobuccal canal. The most common canal configuration was Type I (60.9 %) in mesiobuccal root. The mean distance between MB1 and MB2 canals was 2.39 mm in female and 2.56 mm in male. Conclusion: The occurrence of second canal in mesiobuccal root of maxillary permanent molar is considerable in Nepali patients. CBCT can be an effective tool to detect MB2 canal and other complexities of root canal system to achieve clinical success.


INTRODUCTION
Maxillary first molar is one of the longest standing teeth in the dental arch which serves as a key of occlusion 1 and anchorage in most of the orthodontic treatments.
However, they are susceptible to various insults such as dental caries, attrition etc.The tooth is very important in masticatory process and overall balance of the occlusion; hence it is strategically important to maintain the tooth in dental arch as far as possible, which often requires endodontic treatment.
Success of endodontic treatment is attributed to adequate cleaning, disinfecting, shaping, and three dimensionally sealing the root canal system. 2 The process is routinely challenged by the complexity of root canal morphology.Knowledge of root canal morphology is a key factor which aids in successful treatment outcome.

Maxillary molars possess complex morphology which
has highest rate of clinical failures due to missed second

MATERIALS AND METHOD
The retrospective study was conducted by evaluating the CBCT scan records of the Department of Oral Medicine & Radiology, Kantipur Dental College during June 2016 to March 2017.The CBCT were taken for diagnostic or treatment planning purposes.The CBCT scans were taken on patients by using principles of ALARA on Carestream machine CS9300 (USA).The Field of View (FOV) of the machine was 17x13.5 cm.The scans were taken in either 5x5 cm,10x5 cm or 10x10 cm endo, perio or implant mode.The patients were exposed to a Dose Area Product of 315 mGY.cm 2 to 956mGY.cm 2 dose depending on built of the patient.
A total of 72 scans with the presence of 115 permanent first molars on either one side or two sides of the maxillary arch were selected based on the inclusion criteria.The subjects selected were within the age range of 16-60 years.The scans were excluded if the tooth had incomplete root development, fused root, developmental anomaly, endodontically involved or obturated root canal, crown restoration, root resorption or gross loss of coronal tooth structure.Blurred or unclear images were also excluded.
The data were anonymized before evaluation.The images were evaluated by using Dicom CS 3D imaging software version 3.5.18.To standardize the data a voxel size of 180µ was chosen across all scans.An oral radiologist and endodontist individually evaluated the scans through coronal, axial and oblique views to check the morphology of canals (Figure 1), assess the presence of MB2 canal, classify canals based on Vertucci's Classification (Figure 2), and measure the distance between MB1 and MB2 canals if present at the level of pulpal floor.
The data was recorded in excel sheet and was statistically analyzed using SPSS 20 software.Statistical tests were done by using chi square test to check the association between M2 canal and gender and arch side.Independent t-test was used to compare the statistical difference between distance between the canals and gender.Level of significance was set at p<0.05.Kappa test was done to check the inter-observer reliability between the oral radiologist and endodontist.Cronbach alpha test was done to check the inter-observer reliability in measuring the distance between MB1 and MB2 canals.

Type Description Configuration
Type I A single canal from pulp chamber to the canal terminus 1-1 Type II Two separate canals leaving the chamber but merging short of the canal terminus to form a single canal 2-1 Type III A single canal that divides into two and subsequently merges to exit as one 1-2-1 Type IV Two distinct canals from pulp chamber to the canal terminus 2-2 Type V A single canal leaving the chamber and dividing into two separate canals at the canal terminus 1-2 Type VI Two separate canals leaving the pulp chamber, merging in the body of the root, and dividing again into two distinct canals short of the canal terminus 2-1-2 Type VII A single canal that divides, merges and exits into two distinct canals short of the canal terminus 1-2-1-2 Type VIII Three distinct canals from pulp chamber to the canal terminus 3-3  The study revealed that 30.4% of maxillary first molars showed the presence of MB2 canal in mesiobuccal root.
The most common canal configuration was Vertucci's Type I (60.9%), followed by Type II (19.1%),Type IV (7.8%) (Graph 1).There was no finding of Type V and Type VI in any sample.

DISCUSSION
[8] Various studies have reported various occurrences of MB2 canal in maxillary permanent first molar.Hartwell et al reported 40-95%, 2 Weine et al reported 51% prevalence, 9 Buhrley et al reported 93%, 10 Pardo et al 23.81%. 11The present study revealed 30.4% occurrence of MB2 canal which is consistent with the study of Hartmann et al with 29.2%. 12The abridgement of literature on prevalence of MB2 in maxillary molar is enlisted in Table 4. 11 The variation in results in different studies is attributed to difference in age, gender, ethnicity/race, procedures and conditions of conducting research. 13Alacam et al compared direct observation, microscope, combination of microscope and ultrasonic method and dissecting techniques for evaluating MB2.The results were 62%, 67%, 74% and 82% respectively revealing difference in results. 14Pardo et al compared the efficacy of three methods of canal identification; viz CBCT, clinical analysis and operating microscope and revealed CBCT as the best in finding the canals. 11 In the present study, canal configurations were identified according to Vertucci's classification system 15 revealing the most prevalent type as Type I in 60.9%.However, Faramarzi et al found Type II canal configuration as the most common in 71.3%. 16ccording to Rwenyonyi et al; Type I was the most frequent accounting up to 75.1-100%. 17Synopses of various literatures regarding canal configuration is listed in Table 5. 18 MB2 canal orifice in pulpal floor of the mesiobuccal root is commonly situated within the developmental groove on an approximate line between MB1 and the palatal orifice, parallel to mesial marginal ridge. 7The present study found maximum and minimum distance between MB1 and MB2 orifices as 3.80 mm and 1.40 mm respectively, with mean value being 2.39 mm and 2.56 mm in female and male respectively.These values are in accordance with Faramarzi et al with maximum and minimum distance as 4 mm and 1.5 mm respectively. 16Zhang et al ascertained that MB2 canal lies less than 1 mm mesially to MB-P line and 2 mm palatally to MB orifice. 19Furthermore, no statistically significant association was found among gender groups and bilateral sides in occurrence of MB2 canal.These findings are is consistent with the study of Das et al.

Table 3 : Association between M2 canal and side
NS: Not significantShrestha S, Sapkota MR, Saha A, Rajbhandari S, Sapkota P: Occurrence of Second Mesio-buccal Canal in Maxillary First Permanent Molar: A CBCT Study

Table 5 : Canal configuration in mesiobuccal root of maxillary first molar in various studies
palatally in an imaginary line joining MB1 and palatal orifice to access MB2 canal orifice.Conventional radiographs usually do not yield the presence of MB2 canal; thus CBCT is the gold standard diagnostic tool in complex, doubtful and in retreatment of missed canal cases.