Mandibular First Molar with Four Distal Canals Jamileh Ghoddusi, DDS, MSc,* Neda Naghavi, DDS, MSc, † Mina Zarei, DDS, MSc,* and Ehsan Rohani, DDS ‡ Abstract A mandibular first molar with more than four canals is an interesting example of anatomic variations, espe- cially when four of these canals are located in distal roots. This report describes a case of a mandibular first molar with six canals (two mesial and four distal canals in two distal roots). The canals were equipped with a K-file and irrigated with NaOCl (5.25%) and normal saline as the final irrigant. The canals were filled lat- erally with gutta percha and AH26 sealer (De Trey, Dentsply, Switzerland). This case shows a rare anatomic configuration and points out the importance of looking for additional canals. (J Endod 2007;33:1481–1483) Key Words Four root canal, mandibular molar, two distal root T he mandibular first molar is the first posterior tooth that erupts and is the tooth that most often requires root canal treatment (1). This tooth usually has two roots, but, occasionally, it has three, with two or three canals in the mesial root and one, two, or three canals in the distal roots (2–6). Mesial canals are usually MB and ML, but sometimes there is a middle mesial canal in the developmental groove. In the distal root, there is one canal (distal canal) or two canals (DL and DB), but sometimes there is a middle distal canal as a third. Skidmore and Bjorndal (7) in 1971 reported that about 88.8% of distal roots of the mandibular first molars have only one canal.The amounts vary from the maximum percentage of 56.7% that was reported by Wasti et al (8). Many researchers have studied the presence of two canals in the distal roots of mandibular first molars. The results differ from 43.3% (8) to a minimum of 11.2% in Skidmore and Bjorndal’s study (7). The presence of two distal roots is rare but does occur. This additional root that can usually be found distolingually was first mentioned in literature by De Moor et al (9) and was called “radix entomolaris” (RE) (10). An RE was found on the first, second, and third mandibular molars, occurring least frequently on the second molar (10). Some studies reported a bilateral occurrence of the RE from 50% to 67% (11, 12). The presence of these three-rooted mandibular first molars appears to be less than 3% in blacks (13), about 3% to 4.2% in whites (14), less than 5% in Eurasian and Asian populations (15), and approximately 5% to more than 30% in Mongoloid traits (11, 15, 16). Case Report A 30-year-old female patient was referred to the Department of Endodontics of the Mashad Dental Faculty, Iran, with severe spontaneous pain in tooth #19. Pretreatment examinations (thermal and electric pulp tests) revealed irreversible pulpitis in tooth #19 and pulp necrosis in tooth #20. For both of them (first in the molar teeth because of its emergency condition), root canal therapy was recommended. Initial radiographic x-rays showed that the tooth had an additional distolingual root (Fig. 1). From the Departments of *Endodontics and ‡ Operative Dentistry, Mashad University of Medical Sciences, Mashad, Iran; and † Private Practice, Mashad, Iran. Address requests for reprints to Dr Jamileh Ghoddusi, Department of Endodontics, Mashad Dental School, PO Box 984, Mashad, Iran. E-mail address: jghoddusi@gmail.com. 0099-2399/$0 - see front matter Copyright © 2007 by the American Association of Endodontists. doi:10.1016/j.joen.2007.08.018 Figure 1. A diagnostic radiograph; an additional distal root was presented. Case Report/Clinical Techniques JOE — Volume 33, Number 12, December 2007 Mandibular First Molar with Four Distal Canals 1481