Journal discussion on the root canal systems of maxillar 1st and 2nd molars

4 min

This article gives basic info about the maxillary first and the second molars pertaining to their anatomy and a small intro into cone-beam CT.

This will be followed by inference from the journal of discussion today – Analysis of root canal system of maxillary first and second molars and their correlations by cone-beam computed tomography by Li ting Tzeng et al.


Maxillary 1st molar:

  • It is the largest maxillary teeth and rhomboidal in shape.
  • It has 4 cusps namely, 2-buccal cusp & 2-palatal cusp. Sometimes it has a 5th cusp at the distal end called the cusp of carebelli.
  • A molar has four lobes: mesiobuccal (MB), distobuccal (DB), mesiolingual (ML) & distolingual (DL).
  • It has an oblique ridge running from the distobuccal cusp to the mesiolingual cusp.
  • It has 4 fossae, 6 developmental grooves & 3 pits.
  • It has three roots of which the mesiobuccal root is broader than the distobuccal root and has prominent depressions in the mesial and the distal surfaces.
  • The mesiobuccal roots contain 2 canals while the ovoid distobuccal root contains 1 canal.
  • The palatal root is ovoid in shape and broader mesiodistally than buccolingually. It has a single canal with buccal curvature in the apical third of the root.

Maxillary 2nd molar:

  • The crown is shorter in height and narrower mesiodistally than 1st molar. They have a not very well developed distal cusp.
  • It has three roots with 3 canals that are less divergent & might be fused together.
  • There is no evidence of the 5th cusp.
  • The buccolingual diameter is greater than the mesiodistal diameter.


Computed tomography (CT) imaging was developed in the year 1972 and reported in 1973 which enabled 3D imaging. Continual research & development In the field of science and radiology paved the way for newer compact versions of CT. Arai & colleagues in 1997 created the 1st prototype device of Cone Beam COMPUTED Tomography for dental use. This was used to evaluate approximately 2000 cases. Newer and modified versions of CBCT are available nowadays.

How CBCT works?

CBCT has an extra-oral image scanner specially designed for head and neck imaging. The apparatus involves a unit comparable in size with a panoramic radiographic machine (OPG). It uses X-rays in the form of a large cone-beam focusing on the region to be examined. They don’t need an array of detectors like a CT scanner. They use a 2D planar detector and it is focused on a preferred object. Multiple rotations like CT are not needed. They can reconstruct the necessary information of the region of interest in just one rotation. Thus allowing the clinician to obtain a 2D image in all planes and 3D images of the desired with a minimal amount of radiation exposure.

CBCT has machines that capture images while sitting/ standing/ lying position of the patient. The clinician can choose the scanner based on his need and comfort. CBCT is classified into a small volume, medium volume and large volume scanner based on the size of the Field of View (FOV). Small volume CBCT can capture a sextant/ quadrant to one jaw with higher resolution as the FOV is small. Medium volume CBCT can capture both the jaws. Large volume CBCT can capture the entire head. The image resolution is not compromised if the smaller voxel size is selected. This is mostly suggested for orthodontic & orthognathic surgery. The change in resolution is due to an X-ray scatter caused by an increased field of view (FOV).


The study used CBCT of maxillary molars for diagnostic or other dental purposes at the dental department of National Taiwan university hospital during the period of January to December 2014. A total of 514 patients (282-female/237-male) belonging to the age group of 18 to 65 years were examined. The number of teeth examined was 1741 (846-maxillary 1st molar & 895- mandibular 2nd molar). The CBCT used was an i-cat scanner and image system. The images were examined by two endodontists; any disagreement in the identification of the root canal was discussed thoroughly and concluded. Weine classification was used to analyze the root canal morphology. Fused roots were explained by the method of Ross.

All the examined cases stated that permanent maxillary 1st molars mostly had 3-roots with 4-canals and maxillary 2nd molars had 3-roots with 3-canals. Gender variations were observed in the number of canals as men mostly had 3-roots with 4-canals in maxillary 1st molar (80.96%) and women had 3-roots with 3-canals (25.27%). All the cases uniformly stated the presence of three roots in maxillary 1st and 2nd molar as 98.8% & 93.07% respectively without any gender variations. Evidence of C-shaped configuration of roots in 1st molars was found only in 2 cases and in 12 cases for maxillary 2nd molars. Similarities exist between the bilateral maxillary 1st molar and maxillary 2nd molar. Individuals with bilateral maxillary molars and additional root canal (277 examined cases) in the mesiobuccal root are 77.80%. Adjacent maxillary 1st molar or second molar having 2 mesiobuccal canals are 40.89% & 19.26% respectively. Patients who had both the bilateral maxillary 1st molar and 2nd molar had 2 mesiobuccal canals in bilateral first molars 78.56% & 38.06 %( n=110) showed 2 mesiobuccal canals in bilateral second molars. The above 110 patients showed 99.0% 2 mesiobuccal canals in bilateral maxillary 1st molars.

Thus the study concludes by stating that 3-root with 4-canals as the most common type of root morphology in maxillary 1st molar and 3-root with 3-canals in maxillary second molar. The rate of occurrence of 2 mesiobuccal canals is 77.8% in maxillary 1st molar and 35.97% in maxillary second molar.


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Dr Arun

Dr. Arun is a practicing dentist with more than 11 years of experience. Loves to blog and in constant search of new knowledge in dentistry and health niche.


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