Document Type : Original Article(s)


1 Associate Professor, Craniomaxillofacial Research Center and Department of Endodontics, Dental Branch, Islamic Azad University, Tehran, Iran

2 Associate Professor, Department of Endodontics, Dental Branch, Islamic Azad University, Tehran, Iran

3 Private Practice, Tehran, Iran

4 Assistant Professor, Department of Endodontics, Dental Branch, Islamic Azad University Tehran, Iran

5 Associate Professor, Department of Endodontics/Periodontics, School of Dentistry, Loma Linda University, California, USA


BACKGROUND AND AIM: Isthmuses are narrow and strip shaped connections between two canals containing pulpal tissue that may encompass bacteria as well. They are hardly accessible for cleaning; therefore, success and failure of root canal treatments could be affected by their presence. The present study was carried out aiming to evaluate the incidence, location, and type of isthmus in mandibular second molars (MSMs) among individuals of an Iranian population.METHODS: 80 MSMs with inclusion criteria, belonging to individuals of an Iranian population were collected and disinfected. After embedding the samples’ roots in the acrylic resin, teeth were sectioned horizontally at 2, 4, and 6 mm distances from the apices. Then they were viewed and recorded by a stereomicroscope under × 30 magnification. According to Kim classification, two endodontists recorded the number of canals, incidence, and type of the isthmuses. In cases of disagreement, a third endodontist was involved to judge on the right opinion between the two. The acquired data were analysed using chi-square test.RESULTS: The results showed that 96.3% and 3.75% of MSMs had two and three roots, respectively. Type V (described in the following) was the most frequent type of isthmus at mesial and distal roots. C-shaped canals composed 3.7% of the samples and showed isthmus at all the three sections. There was a significant difference in the distribution of isthmuses (P < 0.001).CONCLUSION: According to this study, different types of isthmuses prevail in high rate of mesial and about half of the distal roots of MSMs, which are important for root canal cleaning and shaping.


  1. Rubinstein RA, Kim S. Long-term follow-up of cases considered healed one year after apical microsurgery. J Endod 2002; 28(5): 378-83.
  2. Teixeira FB, Sano CL, Gomes BP, Zaia AA, Ferraz CC, Souza-Filho FJ. A preliminary in vitro study of the incidence and position of the root canal isthmus in maxillary and mandibular first molars. Int Endod J 2003; 36(4): 276-80.
  3. von Arx T. Frequency and type of canal isthmuses in first molars detected by endoscopic inspection during periradicular surgery. Int Endod J 2005; 38(3): 160-8.
  4. Weller RN, Niemczyk SP, Kim S. Incidence and position of the canal isthmus. Part 1. Mesiobuccal root of the maxillary first molar. J Endod 1995; 21(7): 380-3.
  5. Fan B, Pan Y, Gao Y, Fang F, Wu Q, Gutmann JL. Three-dimensional morphologic analysis of isthmuses in the mesial roots of mandibular molars. J Endod 2010; 36(11): 1866-9.
  6. Hsu YY, Kim S. The resected root surface. The issue of canal isthmuses. Dent Clin North Am 1997; 41(3): 529-40.
  7. Mannocci F, Peru M, Sherriff M, Cook R, Pitt Ford TR. The isthmuses of the mesial root of mandibular molars: A micro computed tomographic study. Int Endod J 2005; 38(8): 558-63.
  8. Vertucci FJ. Root canal anatomy of the human permanent teeth. Oral Surg Oral Med Oral Pathol 1984; 58(5): 589-99.
  9. Lima FJ, Montagner F, Jacinto RC, Ambrosano GM, Gomes BP. An in vitro assessment of type, position and incidence of isthmus in human permanent molars. J Appl Oral Sci 2014; 22(4): 274-81.
  10. Mehrvarzfar P, Akhlagi NM, Khodaei F, Shojaee G, Shirazi S. Evaluation of isthmus prevalence, location, and types in mesial roots of mandibular molars in the Iranian Population. Dent Res J (Isfahan) 2014; 11(2): 251-6.
  11. Silva EJ, Nejaim Y, Silva AV, Haiter-Neto F, Cohenca N. Evaluation of root canal configuration of mandibular molars in a Brazilian population by using cone-beam computed tomography: An in vivo study. J Endod 2013; 39(7): 849-52.
  12. de Pablo OV, Estevez R, Peix Sanchez M, Heilborn C, Cohenca N. Root anatomy and canal configuration of the permanent mandibular first molar: A systematic review. J Endod 2010; 36(12): 1919-31.
  13. Pecora JD, Estrela C, Bueno MR, Porto OC, Alencar AH, Sousa-Neto MD, et al. Detection of root canal isthmuses in molars by map-reading dynamic using CBCT images. Braz Dent J 2013; 24(6): 569-74.
  14. Naseri M, Haghighi AK, Kharazifard MJ, Khavid A. Prevalence of C-shaped root canals in Iranian population: A systematic review. J Dent (Tehran) 2013; 10(2): 186-96.