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 Table of Contents  
Year : 2016  |  Volume : 28  |  Issue : 2  |  Page : 92-96

Advanced methods for identification of middle mesial canal in mandibular molars: An in vitro study

Department of Conservative Dentistry and Endodontics, Government Dental College and Hospital, Ahmedabad, Gujarat, India

Date of Web Publication9-Dec-2016

Correspondence Address:
Seema Mehrish Chavda
201, May Rose Tower, Besides Ellis Bridge Post Office, Paldi, Ahmedabad - 380 006, Gujarat
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0970-7212.195425

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Introduction: Failures of root canal treatment are mainly due to missed canals and ignorance about the anatomy of the root canal system. The middle mesial (MM) canal is one such type of canal in mandibular molars which is often missed. The aim of this study was to identify MM canals first with unaided eyes, then after troughing, followed by magnification and to compare it with cone beam computed tomography (CBCT).
Materials and Methods: Fifty extracted mandibular first and second molars were taken. Preoperative CBCT scans were done for these intact teeth, which were not studied at this stage. Access cavities were made and detection and negotiation of the MM canals was done first with unaided eyes, followed by other added aids like troughing and magnification. Then, CBCT scans were evaluated to compare the incidence obtained and to study the configuration of the found canals.
Results: The number of MM canal found with unaided eyes was 29% and 46% in the first and second molars which increased to 41.6% and 50% after troughing the groove between mesiobuccal and mesiolingual canal. It further increased to 45.85% and 53.8% after magnification. CBCT analysis showed same number of canals, but studying the canal configuration, clinically helped in negotiation of five otherwise nonnegotiable canals. Ninety percent of MM canals in the first molars and 100% in the second molars were confluent type, whereas 10% in the first molars were independent type.
Conclusion: Troughing, magnification, and CBCT can help us in better identification and negotiation of otherwise difficult to find MM canals.

Keywords: Cone beam computed tomography; magnification; middle mesial; troughing.

How to cite this article:
Chavda SM, Garg SA. Advanced methods for identification of middle mesial canal in mandibular molars: An in vitro study. Endodontology 2016;28:92-6

How to cite this URL:
Chavda SM, Garg SA. Advanced methods for identification of middle mesial canal in mandibular molars: An in vitro study. Endodontology [serial online] 2016 [cited 2023 Jan 31];28:92-6. Available from: https://www.endodontologyonweb.org/text.asp?2016/28/2/92/195425

  Introduction Top

It is a well-known fact that all the pulp space should be cleaned and obturated with inert material for the successful outcome of the root canal treatment. Complexity of the root canal morphology is one of the greatest challenges that the clinicians face and a thorough knowledge of the pulp space anatomy is thus necessary.[1],[2]

Mandibular molars usually have two roots and three or four root canals. However, several variations such as an additional distolingual or mesiobuccal (MB) root, C-shaped root canal system, and isthmuses connecting the canals may also be present.[3],[4] Moreover, sometimes a third canal may be present in the isthmus between the MB and mesiolingual (ML) canal known as the middle mesial (MM) canal.

Although the internal anatomy of mandibular molars has been studied extensively, there is limited information about MM canals. Its prevalence in different studies is shown in the range of 10–37.5% in the first molars and 18–60% in the second molars.[5],[6],[7],[8] MM canal is a small orifice deep in the isthmus/developmental groove joining the MB and ML canal and this is likely to be missed as it is difficult to see.

Pomeranz et al. have classified the MM canal into three types: Fin, confluent, and independent.[9] Fin type does not have a separate orifice and it is usually small linear extension of MB or ML canal of very small length allowing free movement of the file between the main canal and fin. The confluent type has separate orifice but it merges either with the MB or the ML canal. Independent type has a separate orifice and separate exit at the foramen. The primary aim of this study was to locate MM canals first with unaided eyes, followed by various aids like troughing the groove, magnifying the floor with dental operating microscope, and then comparing it with the incidence obtained by cone beam computed tomography (CBCT) images analysis, whereas the secondary aim was to study their configuration with CBCT.

  Materials and Methods Top

Sound, intact, bi-rooted, freshly extracted human 24 mandibular first and 26 second molars were collected and stored in 10% formalin for the study. Molars with previous endodontic treatment, fused roots, single roots, or with more than two roots were excluded from the study.

The teeth were embedded in 5 cm × 5 cm cylinder of modeling wax [Figure 1]. A preoperative CBCT scan was done for all the teeth but they were not evaluated at this stage. In the first stage, conventional endodontic access cavities [Figure 1] were made. Round carbide bur no. #4 (SS White, NJ, USA) was used to penetrate the roof of the pulp chamber and safe tip tapered bur (Endo Z bur, Dentsply Maillefer, Ballaigues, Switzerland) was used to deroof the pulp chamber. The chamber was flooded with 3% NaOCl (Prevest Den Pro, Brussels, Belgium). Canal orifices were then explored with sharp endodontic explorer (DG 16, Hu-Friedy, Chicago, IL, USA). After finding the MB, ML, and distal canals, attempts were made to locate the MM canal carefully in the mesial subpulpal developmental groove with the explorer. The detected canals were negotiated with size 8/10 K type hand files (Dentsply Maillefer, Ballaigues, Switzerland) and irrigated with 3% NaOCl (Prevest Den Pro, Brussels, Belgium) to optimize visibility. The number of canal orifices found was recorded. Fin type was excluded and not counted as separate canals.
Figure 1: (a) Wax model used for cone beam computed tomography, (b) molars with access cavities, (c) middle mesial canal seen with unaided eyes, (d) troughing

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In the second stage, the teeth in which the canal could not be found with unaided eyes, 2 mm deep troughing [Figure 1] with the help of endoguide bur no. five (SS White, NJ, USA) was done in the isthmus/developmental groove connecting the MB and ML canal to widen it. Then, again it was explored with sharp endodontic explorer (DG 16, Hu-Friedy, Chicago, IL, USA) to locate the canal. If it was detected then size 8/10 K type hand files (Dentsply Maillefer, Ballaigues, Switzerland) was used to negotiate them.

In the third stage, all the teeth were examined under dental operating microscope at 5×, 10× and 20× for further detection and negotiation of the canals.

After obtaining the incidence clinically, in the fourth stage preoperative CBCT scans of all the teeth were independently evaluated [Figure 2] to find the incidence of MM canal. The number of canals found was compared with that obtained at each stage by various techniques. Then the detected canals were traced. The course of the canals was studied to obtain guidance for the clinical negotiation of nonnegotiable canals and to find their configuration [Figure 2].
Figure 2: Cone beam computed tomography images showing the middle mesial canal and its types. (a) Axial view, (b) axial view with the canal tracing, (c and d) coronal view, (e) canal tracing, (f) fin, (g) confluent, (h) independent type, (i) two middle mesial canals

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  Results Top

The number of MM canals detected and negotiated at various stages is shown in [Table 1]. The configuration of the canals is shown in [Table 2]. The length of the fin types varied between 1.17 mm and 2.16 mm (they were excluded), confluent type between 2.7 mm and 8.73 mm and the independent types was 7.1 mm long.
Table 1: Number and proportion of detected and negotiable middle mesial canals in the mandibular molars with different techniques

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Table 2: Anatomy/configuration of the middle mesial canals detected in the mandibular molars

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As seen in the table, though the number of canals found in the second molars (53.8%) is more than the first molars (45.85%), it was not statistically significant (Chi-square [χ2] test, P = 0.5). Further on comparing the different methods used, no statistically significant difference was found for detection (χ2 test, P = 0.5) and negotiation (χ2 test, P = 0.2) of the canals.

It should be noted that two MM canals were noted in one of the first molars and second molars.

  Discussion Top

Most of the time, the number of canals present in any tooth is predetermined by the data given in books. However, additional canals may be present. In this study, various advanced techniques were compared with CBCT for the detection of MM canal in the mandibular molars. Though CBCT scan was done at the initial stage before access cavity preparation, it was not analyzed at that stage to avoid getting biased about the existence of MM canals. All clinical techniques like troughing and magnification were used for the detection of the canals.

MM canals have very small orifices and may be lying deep into the isthmus; hence, troughing to widen and deepen the isthmus and then exploring the developmental groove improves the chances of canal detection. In this study also, after troughing the incidence increased by 12.4% in the first molars and 3.8% in the second molars. Shallow troughing not more than 2 mm deep was done with long shank bur to remove the dentin protuberance covering the developmental groove/isthmus, to explore the canal orifice lying in it. The advantage of using such bur rather than the ultrasonic tip is that it allows the formation of large debris, which can be easily removed by irrigation.

Magnification with loupes or microscope improves the visibility and thus helps in the detection of small hidden canals. In this study, with the use of magnification, additional two second MM canals were detected, one each in the first and second molar. Such presence of two MM canals has been reported in twoin vitro studies [10],[11] and four case reports.[12],[13],[14],[15]

When the CBCT scans were studied, the incidence obtained was same as that obtained by the sum of the various techniques. No additional canals were found. Many studies have [16],[17] found CBCT to be a significant contributing factor in the identification of canals. However, in our study, we uncovered the canal orifice by troughing and then by magnification, thereby detecting all the canals which were present. In our study, CBCT analysis provided clinical guidance for negotiation of the canals which were otherwise not negotiable.

CBCT scan was also analyzed for the canal configuration and lengths. The fin types are likely to be removed during the biomechanical preparation of the main canals, not affecting the outcome of the treatment. Therefore, they were not counted as separate canals and their incidence was excluded from our study as was also done in earlier studies.[6] The confluent types have separate orifices but they merge with the main canal. They usually lead to isthmus/lateral interconnection/transverse anastomosis/intercanal communication connecting the MB and ML canals, commonly found at the level of 3–6 mm coronal to the apical foramina in mesial roots, noted in 17–83% of the first molars [18],[19] facilitating irrigation of otherwise such inaccessible areas. Hence, they have a significant role in cleaning of the pulp space. Independent types have separate orifice and exit, so undoubtedly needs to be treated.

In this study, teeth were mounted in the wax cylinder for the CBCT scan, so there were no interferences like bony tissues and artifacts of metallic restorations which allowed clear images of the canals, but this may not be the case in patients. Hence, the results may be extrapolated cautiously. CBCT is more expensive and has more radiation exposure as compared to intraoral radiographs, but the cost-benefit ratio could favor its use to increase the success rate of the treatment.

In the earlier studies, the incidence of MM canal found has been reported as 0–15%.[1],[9],[11],[20],[21],[22],[23] Troughing, magnification, and CBCT analysis were not used in all these studies, whereas in this study, with these advanced techniques it increased to 45.85% in the first molars and 53.8% in the second molars. This is in agreement with a recent study [9] where also the incidence after troughing under magnification was reported to be 46.2%.

Age also plays an important role in the presence of MM canals and small accessory canals. In one of thein vitro study of isthmus anatomy of mandibular molars [24] higher prevalence (50%) of isthmuses was found in patients aged 20–39 years as compared to 24% in patients older than 60 years. In otherin vivo study [8] also, the incidence of MM in patients aged less than 20 years was 32.1% and in patients aged more than 40 years was 3.8%. With increasing age, calcification occurs and it is very likely for the small MM canals to get obliterated decreasing its incidence. In this study, the age of the patients was not known and the samples collected were of mixed population.

The incidence of MM canals was more in the second molars than the first molars. This is in agreement with a recent study of Azim et al., who also found the incidence to be 60% in second molars and 37.5% in the first molars. However, it was not in agreement with findings of de Carvalho and Zuolo,[25] who found them to be more common in the first molars (17.2%) as compared to the second molars (4.5%).

  Conclusion Top

Thus, within the limitations of the study, it can be concluded that though advanced techniques like troughing and magnification help in finding and negotiating MM canals, three dimensional radiographies like CBCT can be used as a valuable adjunct to the above-mentioned methods. When these canals are treated, the success rate of the endodontic treatment would definitely increase.

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Conflicts of interest

There are no conflicts of interest.

  References Top

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  [Figure 1], [Figure 2]

  [Table 1], [Table 2]

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