|Year : 2016 | Volume
| Issue : 2 | Page : 66-70
Frequency of middle mesial canals in mandibular first molars in North Indian population - An in vivo study
Osama Adeel Khan Sherwani, Ashok Kumar, Rajendra Kumar Tewari, Surendra Kumar Mishra, Syed Mukhtar Un Nisar Andrabi, Sharique Alam
Department of Conservative Dentistry and Endodontics, Dr. Z. A. Dental College, AMU, Aligarh, Uttar Pradesh, India
|Date of Web Publication||18-Apr-2016|
Osama Adeel Khan Sherwani
Department of Conservative Dentistry and Endodontics, Dr. Z. A. Dental College, AMU, Aligarh - 202 002, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
Objectives: The primary aim of the study was to determine the frequency of middle mesial (MM) canals in mandibular first molars in North Indian population. The secondary aim was to analyze whether an association exists between the detection rate of MM canals and age, gender, and number of distal canals. Materials and Methods: All mature mandibular first molars endodontically treated between March 2013 and March 2015 were included in the study. After instrumenting the main canals, the clinician inspected the mesial developmental groove under dental operating microscope (DOM) using ultrasonic tips and endodontic explorer to detect accessory mesial canals. The canal, if found, was negotiated, cleaned, shaped, and recorded. Results were analyzed using Chi-square test. Results: A total of 258 first molars from 243 patients were treated during the specified period, of which 28.3% had negotiable MM canals. The frequency of MM canals was 36.6% in patients 11-30 years old, 22.6% in patients 31-50 years old, and 18.4% in patients >50 years. Statistical analysis revealed a significant relationship of different age groups with the incidence of MM canals (P < 0.05). A significant relationship was also found between the detection rate of two canals in distal root and the presence of MM canals (P < 0.05) with gender having no influence. Conclusion: The presence of MM canals is quite high in North Indian population. Younger patients had a higher incidence of MM canals. Mandibular first molars with two separate distal canals showed a tendency to have MM canals.
Keywords: Dental operating microscope, incidence, mandibular first molars, middle mesial canal
|How to cite this article:|
Sherwani OA, Kumar A, Tewari RK, Mishra SK, Andrabi SM, Alam S. Frequency of middle mesial canals in mandibular first molars in North Indian population - An in vivo study. Saudi Endod J 2016;6:66-70
|How to cite this URL:|
Sherwani OA, Kumar A, Tewari RK, Mishra SK, Andrabi SM, Alam S. Frequency of middle mesial canals in mandibular first molars in North Indian population - An in vivo study. Saudi Endod J [serial online] 2016 [cited 2019 Mar 21];6:66-70. Available from: http://www.saudiendodj.com/text.asp?2016/6/2/66/180618
| Introduction|| |
Post-treatment endodontic disease is often a result of inadequate cleaning and shaping of root canal system.  Teeth with unusual canal morphologies are probably more prone to treatment failures due to insufficient knowledge of canal anatomy and aberrations associated with it. Thorough chemo-mechanical preparation of the entire root canal system is essential for endodontic treatment success. A sterile environment free from microbes and necrotic tissue is required to facilitate healing of the periapical tissues.  However, this is not always possible due to the presence of lateral canals, ramifications, and intercanal communications. 
Mandibular molars are one of the teeth with complex root canal anatomy. Two roots with two canals in mesial root and one to two canals in distal root is a common occurrence.  Nevertheless, the incidence of variation is quite high including seven to eight canals, , separate distolingual and mesiobuccal (MB) roots,  C-shaped canals,  isthmus,  and an additional third canal in the mesial root. 
The middle mesial (MM) canal, an occasional entity, lies in the developmental groove between the MB and mesiolingual (ML) canals.  Since its first reporting by Vertucci and Williams  as well as Barker et al.  in 1974, the MM canal has been extensively studied. Its incidence has been reported to be 0-46%. ,,,, Pomeranz et al.  classified MM canals into three categories - (1) Fin: The file passes freely between the main mesial canal (ML or MB) and the MM canal (transverse anastomosis), (2) confluent: The MM canal merges with the main mesial canals in the apical third, and (3) independent: The MM canal originates as a separate orifice and ends with a separate apical foramen.
Magnification has improved the clinician's ability to locate and negotiate unusual root canal morphology. A study on mandibular molars revealed that dental operating microscope (DOM) enhances the probability of locating and negotiating MM canals.  Gorduysus et al.  stated that additional accessory canals were not found with DOM but their ability to explore and negotiate the canals improved by over 10% when compared with no magnification. Although several studies have recorded the incidence of MM canals but none has been reported from India. ,,,,, Ours is the first in vivo study from North India that was aimed primarily to record the incidence of MM canals in patients who underwent endodontic treatment at a Dental School in North India. The secondary aim was to evaluate the relationship of age, gender, and number of distal canals with the detection rate of MM canals in mandibular first molars.
| Materials and Methods|| |
The study was conducted in Department of Conservative Dentistry and Endodontics, Dr. Z. A. Dental College, AMU, Aligarh over a 2-year period ranging from March 2013 to March 2015. A total of 258 mature mandibular first molars from 243 patients referred to the first author for primary root canal therapy or retreatment were included in the study. The mean age of the patients was 29 years. The study was approved by the ethical committee and written informed consent was taken from the patients prior to initiating root canal procedures.
After local anesthesia and rubber dam isolation, access cavities were prepared and the mesial and distal canals located under magnification using DOM (Seiler IQ, Chicago, IL, USA). Glide path was established with stainless steel K-files #8, #10, #15 (Dentsply Maillefer, Ballaigues, Switzerland) and coronal halves prepared using rotary nickel-titanium (Ni-Ti) instruments (Protaper Universal, Dentsply Maillefer, Ballaigues, Switzerland). In retreatment cases, the previous root canal filling was removed with H files (Dentsply Maillefer, Ballaigues, Switzerland) and Endosolv E (Septodont, Delaware, USA) and the coronal halves subsequently prepared with rotary Ni-Ti instruments. The pulp chamber floor was then carefully examined under ×4 magnification for any additional root canal orifice(s). The developmental groove between the main mesial canals was troughed 1-2 mm by ultrasonic tips (Start X™, Dentsply Maillefer, Ballaigues, Switzerland) away from the furcation in the mesio-apical direction. After troughing, a DG 16 endodontic explorer was carefully moved over the groove. If the explorer detected a catch at any point in the groove, exploration and negotiation of that point was done with #6, #8, and #10 K files. Working length (WL) was established with electronic apex locator (RayPex 5 VDW, Konstanz, Germany) and confirmed with periapical radiographs. Biomechanical preparation of the root canals was performed up to the established WL. Irrigation was done with 6% sodium hypochlorite and 17% ethylenediaminetetraacetic acid (Glyde, Dentsply Maillefer, Ballaigues, Switzerland) between each file size. The canals were then dried with paper points, and the master cone periapical radiographs were taken from mesial angulation. Obturation was done with gutta percha (GP) and AH Plus sealer using cold lateral compaction of GP in apical third followed by vertical compaction of thermoplasticized GP (System B, Sybron Endo, CA, USA). Final radiographs were taken after teeth were permanently restored.
The incidence of MM canals, their course and location with respect to main mesial canals were recorded and categorized using the Pomeranz classification.  The distribution of MM canals with respect to age, gender, and number of distal canals was also noted. The data were analyzed using Chi-square test. Statistical analysis was performed using SPSS (Version 20; IBM Corp., Armonk, NY) and P < 0.05 was considered as statistically significant.
| Results|| |
Of the 258 molars treated, 73 (28.3%) had negotiable MM canals. The incidence of MM canals based on age, gender, and number of distal canals is shown in [Table 1].
|Table 1: Frequency distribution (%) of MM canals in mandibular first molars based on age, gender, and number of distal canals |
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There was a significant decrease in the incidence of MM canals with an increase in age. Patients in the younger age group (11-30 years) had a significantly higher percentage of MM canals (36.6%) compared to those in middle age (30-50 years) and older age groups (>50 years), respectively (P < 0.05). The distribution of MM canals based on gender was found to be non-significant (P > 0.05).
Two distal canals were present in 74% (54/73) of teeth with an MM canal. Among the teeth without MM canals, only 35.1% (65/185) had two distal canals. A significant relationship was found between the occurrence of MM canals and presence of two distal canals (P < 0.05).
Of the 73 located MM canals, 75.3% (55/73) showed confluent anatomy merging with either the MB or ML canals [Figure 1]a, 21.9% (16/73) showed fin anatomy [Figure 1]b and only 2.7% (2/73) showed independent MM canals with separate orifices and apical foramen [Figure 1]c. The orifices of MM canals were located midway between the main mesial canals in 67.1% (49/73) of the cases [Figure 2]a, and closer to or in close proximity to ML canal in 20.5% (15/73) of the cases [Figure 2]b and towards the MB canal in 12.3% (9/73) of the cases [Figure 2]c.
|Figure 1: Mesially angulated radiographs showing three different patterns of middle mesial canals. (a) Radiograph showing middle mesial canal merging with mesiobuccal canal in apical third. (b) Radiograph showing all three canals in close communication with each other. (c) Radiograph showing middle mesial canal with separate apical foramen|
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|Figure 2: Intra-oral clinical images showing middle mesial canals at different locations with respect to mesiobuccal and mesiolingual canals. (a) Tooth 46 with middle mesial canal lying mid-way between mesiobuccal and mesiolingual canals. (b) Tooth 36 with middle mesial canal communicating with mesiobuccal and mesiolingual canals (fin anatomy). (c) Tooth 46 with middle mesial canal communicating with mesiobuccal canal|
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| Discussion|| |
Post-treatment endodontic disease or failure of endodontic treatment can be attributed to the presence of bacterial biofilms in root canal ramifications such as fins, deltas, loops, accessory canals, and istmuses.  An isthmus is a narrow connection between two root canals that contains pulp tissue.  Researchers have employed different techniques to study isthmuses in mesial roots of mandibular molars. One in vitro study found isthmuses in 33% of the specimens at 3-5 mm from the apex.  Fan et al.  using micro-computed tomography reconstruction found isthmuses in 85% of the mesial roots of mandibular molars. de Pablo et al.  in a systematic review reported that isthmuses were present in 54.8% of the mesial roots. Von Arx et al.  using an endoscope reported the highest ever incidence of isthmuses in mesial roots of mandibular molars (88.5%). The isthmuses of mandibular first molars are classified into five types - type I is two separate canals, type II is two separate canals connected by an isthmus, type III is three canals connected by an isthmus, type IV is two elongated canals that join in the center, and type V is a single, very broad, and elongated canal. 
The MM canal or accessory mesial canal lies in the sub-pulpal groove or the isthmus connecting the main mesial canals. Since its first mention in literature in 1974,  the incidence of MM canal has been reported by various authors in both in vivo and in vitro studies. ,,,,, These studies can be further classified into those done with and without magnification. The use of operating microscope has enhanced the detection of accessory canals that is evident by the increased incidence rates reported by studies done under magnification. A recent in vivo study reported the highest ever occurrence of MM canals (46.2%).  In our study, DOM was used that could account for the higher detection rate (28.3%) of MM canals.
Mortman and Ahn  suggested that the third mesial canal is not an accessory or extra canal rather sequelae of instrumenting the isthmus between MB and ML canals. However, these accessory canals when negotiated, cleaned, and shaped can constitute a pathway into the otherwise inaccessible isthmus providing access for removal of bacterial biofilms and necrotic tissue. This might reduce the number of failures of non-surgical root canal therapy in mandibular molars.
Troughing the mesial pulpal groove in a mesio-apical direction away from the furcation is a significant factor in detection and negotiation of MM canals. Troughing the groove up to 2 mm has resulted in increased detection rates and subsequent negotiation of MM canals. A recent in vivo study has demonstrated that 39.6% more MM canals were detected and explored after controlled troughing to within 2mm depth using a 1 mm diameter round bur head as a depth guide.  However, it requires clear visibility, specialized instruments, and care to avoid perforation and its potential complications. 
Age of the patients appeared to be a determining factor influencing the incidence of MM canals. The incidence rate in our study decreased with an increase in age. The results are in agreement with the previous studies reporting the impact of age on MM canals. ,,, Another clinically significant finding was the association between two distal canals and MM canal. In contrast, Nosrat et al.  found no significant association between MM canal and the presence of a separate second distal canal.
Regarding the location of MM canal orifice with respect to the orifices of main mesial canals, we found that in 67% of the cases, the MM canal orifice was located in the middle of the MB and ML canal orifices, 20% had the orifice located closer to the ML canal while remaining 12% had orifices towards MB canals. These findings are inconsistent with those of previous studies which reported that the MM canal was located closer to the ML canal in majority of the cases followed by the MM orifice located in the middle of MB and ML canals while the least number of cases showed the orifice closer to the MB canal. ,
In our study, the most common configuration was confluent anatomy followed by fin anatomy while only two cases showed independent anatomy. These findings are consistent with those of previous studies. Karapinar-Kazandag et al.  in their study reported all MM canals to have confluent anatomy with no incidence of independent or fin anatomy. Nosrat et al.  reported nearly half of their specimens (46.7%) to have confluent anatomy. Recently Azim et al.  in their in vivo study too found that the highest proportion of teeth had confluent anatomy (78.5%).
| Conclusion|| |
The frequency of MM canals reported in this study in mandibular first molars was higher in contrast to many previously reported studies. This could be attributed to careful tactile exploration of the isthmus under DOM. The use of operating microscope in routine endodontic practice has increased the detection and successful exploration of MM canals. Younger patients and molars with two separate distal canals showed a higher incidence of MM canals. After establishing an adequate access cavity, clinicians should always spend time in examining the mesial sub pulpal groove to detect and negotiate any additional canal. This will help in increased successful outcomes of non-surgical root canal therapy. However, long-term clinical studies are warranted to determine the impact of cleaning and shaping of MM canals on success of endodontic treatment in mandibular molars.
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[Figure 1], [Figure 2]