Root canal anatomy of the permanent mandibular first molar. Clinical implications and recommendations

Root canal anatomy of the permanent mandibular first molar. Clinical implications and recommendations

The world of endodontics has incorporated new technologies, instruments and materials in the past decade. Among them, operating microscopes, digital radiography, cone beam computed tomography (CBCT), 3D nickel titanium files, sonic and ultrasonic instruments and new irrigation delivery systems. However, despite all these improvements, the overall outcome, especially of non-surgical endodontics, has not increased significantly. Why? If we think critically, there are two important factors directly related to prognosis on which our advancements were limited: predictable eradication of microorganisms and access to the full anatomy of the canal system in which they might be harbored.


The mandibular first molar is the more frequently endodontically treated tooth. In a study by Swartz et al, the success rate of endodontically treated teeth was 87.79%, demonstrating the mandibular firs molar a significant lower success rate of 81.48%. It is well accepted that a unique cleaning and shaping technique is not suitable for all cases. Therefore, the endodontist should be able to fully understand the tooth morphology and root canal configurations in order to select the most appropriate treatment modality for a particular case and increasing the healing rate. 


Number of roots

Review of the literature revealed a strong correlation between the presence of a third root in 13% of teeth and the ethnicity of the patients, particularly Asians, Mongolians and Eskimos. This macrostructure was term radix entomolaris with high variation regarding the coronal, mesio-distal plane.  When the position of this third root was buccal, it is called radix paramolaris. Its shape and curvature are highly variable. Several radiographic exposures are required to clearly observe the presence of additional roots. Treating a mandibular first molar without initial off-angle radiographs could lead to third roots go unnoticed (Fig 1). Initially, a file located in the extra root, may give the appearance of a perforation. To prevent mishaps, it is advisable to choose a small and highly flexible instrument when treating the apical portion.


Number of root canals

In a systematic review compiling data on 4,745 mandibular first molars, three canals were present in 61.3%, followed by 4 canals in 35.7% of cases and 5 canals in almost 1% (Fig 2). However, in vivo studies performed by endodontists demonstrated the presence of 4 canals in 45% of the treated cases. Five canals were found in 0.8% of the samples while case reports have demonstrated the possibility of six and even 7 root canals.



1.      The number of roots in the first mandibular molar is directly related to the ethnicity of the population studied.

2.      The instrumentation of the third root requires a different access and the use of small and flexible instruments, considering the curvature at the apical third.

3.      Mesial roots present 2 canals on a regular basis, adopting 2-2 and 2-1 as the most frequent configurations. A third canal might be present in 2.6% of the population.

4.      The most common configuration in the distal root is 1-1 (62.7%), followed by 2-1 (14.5%) and 2-2 (12.4%).

5.      Access modifications are required in order to find extra roots and/or canals.

6.      The presence of isthmuses reaches 55% in the mesial root and 20% in the distal. This anatomical configuration should be taken into consideration during endodontic treatment as well as during periapical surgery.


Nestor Cohenca, DDS, FIADT

Diplomate. American Board of Endodontics


PS. Full references available per request.

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