Validity of Dental Operating Microscope on Identification of MB2 Canal in Maxillary Molars

Validity of Dental Operating Microscope on Identification of MB2 Canal in Maxillary Molars
Fozia Rajput1, Rafique Ahmed Memon2, Feroze Ali Kalhoro3, Naresh Kumar4

How to CITE:

Rajput F, Memon RA, Kalhoro FA, Kumar N. Validity of Dental Operating Microscope on identification of MB2 Canal in Maxillary Molars. J Pak Dent Assoc 2013;22(1):23-26.


This study aimed to assess the effectiveness of Dental-operating microscope (DOM) for detection of second mesiobuccal canal (MB-2) in extracted maxillary first and second molars compared with unaided vision.


One hundred extracted permanent maxillary first and second molars (50 each) were taken. The location of MB-2 canal was attempted using an endodontic explorer with naked eye. Teeth, in which MB-2 canal was failed to locate, were further explored under DOM. Finally, the mesiobuccal roots of each tooth were sectioned and observed at a magnification of 12X to confirm the actual presence of MB-2 canal. The results were analyzed by screening test.


In maxillary first molars, 21 (42%) MB-2 canals were identified with naked eye, 9 with DOM making a total of 30 (60%), and additional 3 with sectioned roots under DOM bringing the total to 33 (66%). Whereas, in maxillary second molars total 10 (20%) MB-2 canals were identified with naked eye, while nine were identified with DOM bringing the total to 19 (38%), and additional 2 when observing the sectioned roots under DOM bringing the total to 21 (42%).


The results of this study demonstrate that the adjunctive use of DOM may assist the dental clinician in locating the MB-2 canal orifice.


Dental operating microscope, Magnification, Maxillary molars, Second mesiobuccal canal (MB-2).


he ultimate success of endodontic treatment is dependent upon the location of all canals and their proper cleaning, shaping and obturation. An error in the canal detection may lead to failure in endodontic therapy.1 The visualization of the canal orifices with naked eye is severely limited especially when there is additional / extra orifice, due to its relatively small size. As a result, most of the clinicians rely upon their tactile dexterity as well as mental image of the canal system for the canal detection. Moreover, the conventional radiographs are less likely to aid in the detection of the additional canals due to superimposition of one canal over the other canal. However, dental computed tomography has proven to be superior over other diagnostic modalities in the detection of anatomicvariations.2 The enhanced vision systems namely head lamps and dental loupes have been utilized for exploring the additional orifice.
The operating microscope has been used widely in some of the medical specialties since long time. In dental sciences, endodontics has become the first discipline to adopt the use of the dental operating microscope (DOM).3 Most of the scientific and clinical research has been conducted on the mesiobuccal root of maxillary molars compared with other teeth in mouth due to its complex anatomy.4 It is well known that mesiobuccal root possesses second mesiobuccal canal (MB-2.) Therefore, this canal should be located and treated for the good clinical outcome. However, this canal is usually missed during routine endodontic procedures which could compromise the treatment success.1 These canals usually lie mesial to the line drawn between the main mesiobuccal and palatal canals, situated under the mesial marginal ridge. Several recommendations have been made to aid the recognition of the MB-2 canal during root canal treatment of maxillary molars such as modification of access cavity preparation, removal of dentine bridge from the mesial wall and 1-2 mm troughing of the isthmus joining mesiobuccal and palatal canals.5
The prevalence of MB-2 canal has been reported to be as low as 18.6% in an in vivo study5, and as high as 95.2% in an in vitro study.6 A recent study has reported 68.5% prevalence of MB-2 canal in Indonesian population.7 The incidence varies widely, depending on the methods used, whether done with or without dye penetration, various sectioning techniques, record reviews, different social groups, different age groups and with or without magnification etc. To date, only a few studies have reported the use of enhanced vision with DOM for location of MB- 2 canal. This study is aimed to determine whether DOM improves the location of hidden MB-2 canal orifice compared with unaided vision.


One hundred extracted permanent maxillary first and second molars (50 each) were collected from Oral Surgery Department, Civil Hospital, Hyderabad and were placed in 10% neutral formalin until the start of access cavity preparation. Only teeth with well defined external morphology were used. No information was available regarding the reason for their extraction or the age and sex of patient. Standard endodontic access cavities were prepared using a high speed handpiece (NSK, Japan), the chamber was cleaned with 2.5% sodium hypochlorite. After locating the mesiobuccal, distobuccal and palatal canals initially, the location of MB-2 canal was attempted using only endodontic explorer (DG-16) (Dentsply, Philadelphia, USA) with naked eye and canal confirmed with 10# stainless steel K-file (Dentsply, Philadelphia, USA). The MB-2 canal orifice was either located or failed to be located with this procedure. Teeth in which MB-2 were unable to be located were further explored under DOM (YZ20P5,China) with X12 magnification at 200mm focus length using endodontic explorer (DG-16). MB-2 canal orifice was again either located or were failed to be located. Finally, the mesiobuccal roots of each tooth were
Figure: Methodology Flow Chart

sectioned in a horizontal plane 6mm below the cementoenamel junction with a crosscut fissure bur (Dentsply, Philadelphia, US) in high speed headpiece. The sections were explored with sharp endodontic explorer and 10# k file with the adjunctive use of DOM at 12X to determine the actual presence of MB-2 canal. In this study, each tooth served as its own control.


The results were analyzed by screening test. Sensitivity, specificity, positive predictive values and negative predictive values for the presence or absence of MB-2 canal were calculated by taking DOM findings on sectioned tooth as a gold standard.


In the maxillary first molars, 21out of 50 (42%) MB-2 canal orifices were detected with the unaided vision, whereas the number of canal orifices increased up to 30 out of 50 (60%) using DOM. Subsequently, 3 MB-2 canal orifices were located whilst sectioning of teeth, in which MB-2 were missed with the previous naked-eye and DOM examination and the count raised to 33out of 50 (66%) (Table 1).
Table: 1: Frequency of MB-2 canal identification using different methods of assessment

Similarly, 10 out of 50 (20%) MB-2 canal orifices were detected in maxillary second molar with unaided vision while under DOM examination, the number of MB-2 canal orifices was 19 of 50 (38%). After sectioning all teeth, 2 additional MB-2 canal orifices were located in the remaining 31 teeth, thus 21 (42%) MB-2 canals were actually present in maxillary second molar (Table 1).


Most of the clinicians feel difficulty whilst locating the MB-2 canal in maxillary molars. Recently, the operating microscope was introduced to endodontics and has significantly improved magnification and illumination. In the current study, the effectiveness of DOM for detection of MB-2 canal orifices in extracted maxillary molars has been investigated. The findings of this study highlight that DOM significantly increases detection of MB-2 canals.
The results of different studies have shown the occurrence of MB-2 canal in maxillary first molar from 18.6% 8 to 96.1% 9 depending on the methodology used. The literature 1,6,8,10,12 suggests that more MB-2 canals can be found in the laboratory than clinically. Majority of clinical studies reported an incidence of MB-2 canal from 18% to 36%.5,11,13 However, some inherent problems with clinical studies are evident. For instance, variability in the teeth, since some teeth are more difficult to treat than others for various reasons, another problem is the negligence of some clinician to locate a hidden canal. It is possible that in some instances, the most important factor in locating the MB-2 canal is not the magnification but the persistence of the operator.
Experience for using DOM and instruments adapted for its location can also be another factor that influences the detection rate of MB-2 canal. Stropko14 reported that MB-2 canals were located in 93% of first molars and 60% of second molars in a clinical setting when the operator become experienced in DOM use, scheduled sufficient time for treatment, and employed specific instruments for micro endodontics, whilst MB-2 canals were found in 74% of first molars and 51% of second molars under conventional treatment. Sempira and Hartwell15 mentioned that although the microscope did not significantly increase the number of MB-2 canals located, the enhanced visibility significantly increased confidence levels in using rotary burs and ultrasonic tips to remove calcific deposits (dentinal protuberance) covering many of the canal orifices and make its location difficult. Similar observations were obtained in the present study where rotary burs have been used at the chamber floor to remove such dentinal protuberance without a single perforation in the teeth included in the study.
In present study, the MB-2 canal was often located anterior to line from the MB-1 and palatal canals. Similar observation has been reported by Weine et al.1
The orifices of the MB-2 canals are usually smaller, narrower, inclined more mesially and located more apically than MB-1. Sometimes, the MB-2 lies in the same orifice as MB-1.14 It is called the bifurcation. Similar findings noted in 3 maxillary first molar included in this study where the MB-2 shares the orifice with MB-1 and there cross-sections showed two separate canals. It has been noted that if the dentinal protuberance is only attached up to the junction of the mesial wall and the floor and when it is darker in color then there are more chances for the presence of MB-2 canal than when it is extended up to the floor and yellowish in color. These findings were visualized under DOM, otherwise, it would have been very difficult to locate with naked eye.
Like other several studies the results of this study showed more MB-2 canals in maxillary first molar than maxillary second molar, it is due to the reason of high incidence of MB-2 canals in first molar than in second molars.
Baldassari-Cruz et al.16 suggested that frequency of locating the MB-2 canals can be increased with different access cavity shapes and the DOM is very handy to achieve this goal. Enhanced vision to the area in addition to operator’s knowledge about root canal system morphology and accessibility may increase the possibility of locating MB-2 canals and it was confirmed by the high prevalence of the MB-2 canal orifice found in the current study.


The prevalence of MB-2 canal in our sample was 66% and 42% among maxillary first and second molars respectively. The DOM correctly identified MB-2 canals among 31 out of 33 first molars (90.90%) and 19 out of 21 (90.47%) second molars (Table 2).
Table: 2. Validity of different methods of MB-2 canal identification

Presence of MB-2 canal on Sectioning of the tooth was considered as gold standard.


The DOM should be routinely used in the field of endodontics to increase the treatment success rate.


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