Deviations from the norm such as multiple orifices, apical deltas, accessory canals, and other variations are frequent in the roots of the posterior teeth.
Two clinical reports of mandibular molars are presented in which three canals in the mesial roots were treated endodontically. Review of the literature encountered a prevalence ranging from 1% to 15%.
Clinically, the third canal is difficult to find and exhibits a very variable morphology, which may present anastomosis with the other canals.
Keywords: Isthmuses, middle mesial canal, orifice location
|How to cite this article:
Matta MS, Kaur M. Endodontic management of middle mesial canal in mandibular first molar. Ann Trop Med Public Health 2015;8:60-3
|How to cite this URL:
Matta MS, Kaur M. Endodontic management of middle mesial canal in mandibular first molar. Ann Trop Med Public Health [serial online] 2015 [cited 2020 Oct 31];8:60-3. Available from: https://www.atmph.org/text.asp?2015/8/3/60/157631
The mandibular first molar is the earliest permanent posterior tooth to erupt. It is most frequently in need of endodontic treatment. It usually has two roots, but occasionally three, usually with a supernumerary distolingual root.
The probability of a mandibular first molar having a fifth canal is 1-15%. ,,,,,, The purpose of this paper is to present clinical reports of three canals in the mesial root of mandibular molars in the Indian population.
It is important to visualize and to have knowledge of internal anatomic relationships before undertaking endodontic therapy. The main objective of root canal therapy is thorough shaping and cleaning of all pulp spaces and its complete obturation with an inert filling material. The presence of an untreated canal may be a reason for failure.
The root canal system is complex and canals may branch, divide and rejoin. Weine categorized the root canal systems in any root into four basic types. 
Vertucci et al. utilizing cleared teeth which had their pulp cavities stained with hematoxylin dye, found a much more complex canal system and identified eight pulp space configurations. 
Gulabivala et al. examined mandibular molars in a Burmese population and found seven additional canal configurations. 
Middle mesial canal in mandibular first molar presents itself as a rare anatomical variant. According to Mortman,  the third mesial canal is not an extra canal but rather the sequelae of instrumenting the isthmus between the mesiobuccal and mesiolingual canals.
According to Von Arx,  isthmuses in the mesial root of mandibular first molars may be classified into 5 types:
- Type I is two separate canals with no isthmus.
- Type II is two separate canals joined by an isthmus.
- Type III is three canals joined by an isthmus.
- Type IV is two elongated canals that join in the centre.
- Type V is a single, very broad and elongated canal.
The mesial root of the mandibular first molar is most frequently of Type IV or V.
A 35-year-old female patient presented to the Department of Conservative Dentistry and Endodontics in Rayat and Bahra Dental College, Mohali with the chief complaint of pain in the lower back right tooth. She gave history of latex allergy. On clinical examination, a metal crown was present on the right mandibular first molar that was tender on percussion. Radiograph [Figure 1] showed inadequate previous endodontic therapy with secondary caries under the metal crown and periapical lesion associated with mesial root.
|Figure 1: Pre-operative x-ray (Case 1)
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The crown was removed after cutting with transmetal bur (Dentsply, Switzerland). No rubber dam was applied owing to latex allergy. On the access opening and thorough irrigation with 3% sodium hypochlorite (Vishal Dentocare, Ahmedabad, India), a third canal was observed in the mesial root of the permanent mandibular first molar. The canals were prepared with hand files (Dentsply, Switzerland) using the step-back technique upto apical size 25 [Figure 2] and [Figure 3]). Calcium hydroxide powder and saline (Ammdent, Mohali, India) dressing was given for 2 weeks and tooth was temporised with temporary non eugenol filling (TMP-RS, Prime Dental Products, Mumbai, India) After 2 weeks, isolation was achieved with cotton rolls, final irrigation was done with 2% chlorhexidine (Vishal Dentocare, Ahmedabad, India) and canals were dried with sterile paper points (Hygienic Corporation,Coltene Whaledent, Deutschland). obturation was completed with lateral condensation technique [Figure 4].
|Figure 2: Working length x-ray (Case 1)
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|Figure 3: Master-cone x-ray (Case 1)
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|Figure 4: Post-operative x-ray (Case 1)
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A 30-year-old female presented to the private practice in Patiala with the chief complaint of pain in lower back left tooth.
Clinical examination revealed deep carious lesion and the tooth was tender on percussion. A radiograph [Figure 5] showed a small periapical lesion associated with the mesial root.
|Figure 5: Pre-operatve x-ray (Case 2)
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Cotton rolls were used for isolation as patient objected to the use of rubber dam for isolation. On access opening and thorough irrigation with 3% sodium hypochlorite (Vishal Dentocare, Ahmedabad, India), a third canal was observed in the mesial root located between the mesiobuccal and mesiolingual canal.
Further angled working length radiograph ([Figure 6]) pointed out the merger of the mesiobuccal and middle mesial canal. The canals were prepared with hand files (Dentsply, Switzerland) using the step-back technique upto size 25. Calcium hydroxide powder (Ammdent, Mohali, India) and saline dressing was given for 2 weeks and tooth was temporised with temporary non eugenol filling (TMP-RS, Prime Dental Products, Mumbai, India). After 2 weeks, under isolation, final irrigation was done with 2% chlorhexidine (Vishal Dentocare, Ahmedabad, India), and canals were dried with sterile paper points (Hygienic Corporation,Coltene Whaledent, Deutschland). obturation was completed with lateral condensation technique [Figure 7].
|Figure 6: Working length x-ray (Case 2)
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|Figure 7: Post-operative x-ray (Case 2)
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The clinician is confronted daily with a highly complex and variable root canal system. Prior to beginning treatment, the dentist cannot precisely determine the actual number of root canals present. Microcomputed tomography has been an essential tool for the evaluation of the isthmuses in vitro,  but cone beam computed tomography (CBCT) has been essential tool in Identification of independent middle mesial canal in mandibular first molar in vivo.  Microcopmputed tomography and CBCT are still non-feasible and expensive tools in practical dental clinical practice.
There are many aids Aids in locating root canal orifices,  pulp chamber floor and wall anatomy being perfect guide to determine what morphology is actually present.
Variation in the mesial root of mandibular first molars can be identified through very careful observation of angled radiographs. Conventional radiographs taken at a 0° orientation provided less information than 30° radiographs. Contrast medium improved radiographic interpretation of canal anatomy, especially when used with 30° radiographs. 
The following are important steps to identify the canal orifices in the pulp chamber floor: Examination of the pulp chamber floor with a sharp explorer; troughing of grooves with ultrasonic tips; staining the chamber floor with 1% methylene blue dye; performing the sodium hypochlorite “champagne bubble” test; and visualizing canal bleeding points. 
An important aid for locating root canals is the dental-operating microscope (DOM). It brings minute details into clear view. It enhances the dentist’s ability to selectively remove dentine with great precision, thereby minimizing procedural errors. Several studies have shown that it significantly increases the ability to locate and negotiate canals. 
An examination of the floor of the pulp chamber offers clues to the location of orifices and to the type of canal system present. When there is only one canal, it is usually located in the center of the access preparation.
If only one orifice is found that is not in the center of the preparation, it is probable that another is present and one should be searched for on the opposite side. All such orifices, particularly if oval in shape, must be thoroughly explored with apically precurved small K-type files to determine if more than one canal is present. The relationship of the two orifices to each other is also significant. The closer they are to each other, the greater the chance that the two canals join at some point within the body of the root. The direction that a file takes upon introduction into an orifice is also important. If the initial file placed into the distal canal of a mandibular molar, for example, points to the buccal or lingual, one should suspect a second canal. If two canals are present, each will be smaller than a single canal. Whenever a root contains two canals which join, the palatal/lingual canal is generally the one with straight line access to the apex. 
Rotary nickel titanium files must also be used with caution when this type of anatomy is present because instrument separation can occur as the file traverses the sharp curvature into the common part of the canal.
The presented case reports confirm that the third canal in the mesial root of mandibular first molars is a reality and can be encountered in almost 15% of these roots [Table 1].
|Table 1: Prevalence of a third canal in the mesial root of mandibular first molars, according to different authors
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During endodontic treatment of the mandibular first molar, the middle mesial canal orifice must be sought along the line between the two mesial canals. After thorough removal of the pulp chamber roof and cervical stenosis using burs or ultrasonic tips, the opening of the middle mesial canal can easily be negotiated.
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Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]