Versiani et al from the University of Sao Paulo, Brazil, conducted a study to determine the thorough cleaning and shaping procedures, which are necessary for successful endodontic treatment that may be adversely affected by the highly variable root canal anatomy. The presence of additional canals must be recognized to avoid incomplete instrumentation and the persistence of bacterial biofilm and resulting toxins, which can compromise the outcome of treatment. The knowledge of the internal anatomy of each tooth is a prerequisite for successful endodontic therapy.

The mesial root of mandibular molars commonly presents 1 mesiobuccal canal (MBC) and 1 mesiolingual canal (MLC). However, extra canals have been reported in the literature.

This extra canal has been called the
■ intermediate canal
■ mesio-central canal
■ third mesial canal
■ accessory mesial canal
■ middle mesial canal (MMC; Figure 2)

In the literature, this anatomical variation has been found in 0.26% to 46.15% of teeth, depending on the method used. Recently, micro-computed tomographic (micro-CT) imaging has gained increasing importance in the study of hard tissues in endodontics because it offers a reproducible 3-dimensional technique for the assessment of the root canal anatomy.

Currently, endodontic literature has a dearth of morphological descriptions for the anatomy of the MMC in mandibular molars. This study sought to describe the morphological aspects of the MMC in mandibular first molars, which were collected from Brazilian and Turkish populations, using a micro-CT imaging system.

Images of mandibular first molars collected from the Brazilian (n = 136) and Turkish (n = 122) populations were scanned (voxel size: 9.9  um) and mesial roots with MMC (n = 48) evaluated for several morphological aspects. MMC incidence for each population was statistically compared using a X2 test (a = 0.05).

figure a and b

Figure 2. (A) Access preparation of mandibular molar. Three mesial canal orifices are seen: MBC, MLC and MMC. (Image courtesy of Dr. Frederic Barnett.) (B) Micro-CT re-cOnstruction of -mandibular molar. The mesial root has MBC, MLC and MMC canals. (Image courtesy of Dr. Marco Versiani.)

figure a and b

Figure 2. (A) Access preparation of mandibular molar. Three mesial canal orifices are seen: MBC, MLC and MMC. (Image courtesy of Dr. Frederic Barnett.) (B) Micro-CT re-cOnstruction of -mandibular molar. The mesial root has MBC, MLC and MMC canals. (Image courtesy of Dr. Marco Versiani.)

After the reconstruction of the acquired projection images into cross-sectional slices, polygonal surface representations of the internal anatomy of mesial roots presenting MMC were obtained and classified according to the system of Pomeranz et al (J Endod 1981):

Independent: 3 independent canals extend from the pulp chamber to the apex;

Fin: in the coronal third, MMC orifice is connected to the MBC and/ or MLC orifice(s) by a groove, but the mesial canals leave the root in 3 separate foramina;

Confluent: MMC leaves the pulp chamber, separately or not to the other mesial canals, and joins the MBC and/or MLC by transverse anastomosis, intercanal connections or isthmus during its trajectory to the apical foramen.”

Overall, the incidence of MMC was 18.6% (48 of 258 molars) and was higher in the Brazilian (n = 30; 22.1%) than in the Turkish (n = 18; 14.8%) population (p < .05). In both populations, confluent configuration of the MMC was the most frequent anatomy. Most of the specimens with MMC had 3 independent orifices (54.2%) and 3 apical foramina (43.8%). The mean diameter of the MMC orifice was 2x to 3x less than the diameter of the other mesial orifices. In the specimens with canal confluence (54.2%), MMC merged in to the MBC in 16.7%, MLC in 8.3% or both MBC and MLC in 29.2%.

Conclusion

Using micro-CT imaging, the incidence of MMC was 18.6%. A confluent configuration was the most prevalent anatomic variation, while independent and fin configurations, as well as double MMC, were found in only a few specimens. It is apparent that the clinician must be cognizant of this anatomical variation in the endodontic treatment of mandibular molars.

Versiani MA, Ordinola-Zapata R, Keles A, et al. Middle mesial canals in mandibular first molars: a micro-CT study in different populations. Arch Oral Biol 2016;61: 130-137.