C-Shaped Molars

Dental practitioners who perform root canal treatment are familiar with the fact that anatomical variations within the radicular structures of the human dentition are abundant.  One especially interesting type of variation that can perplex dentists providing root canal treatment is the C-shaped molar.  This anatomical variant occurs most commonly in mandibular second molars and is present in approximately 8% of the population according to one study. (1)  The prevalence is much higher in specific ethnic groups and was reported at 32% in one study of a Korean population. (2)

C-shaped molars display a wide range of anatomical variation but in general they exhibit a conical shaped root with a deep groove on one side that gives the root the appearance of a letter "C" when viewed in cross section.  The pulp system within the root usually contains a thin band of web-like pulp tissue that may or may not contain distinct canals.  The following cartoon, though over-simplified, is helpful in visualizing the configuration of C-shaped molars in three dimensional space.

                                                                                          

While the cartoon above represents the root canal system as a continuous sheet of pulp tissue, the following diagram (showing cross sections of various types of C-shaped roots) presents a more realistic representation of the variation of canal configurations that can be found.

                                                                          

 From Fan B, Cheung G, Fan M, Guttman J: J Endod 30:899, 2004.

The following micro-CT image shows multiple cross sectional views along the length of a C-shaped molar.  Notice the multiple portals of exit (POE) at the root apex.

                                                                                   

                                                                                                                     rootcanalanatomy.blogspot.com

The complexity of the root canal systems in C-shaped molars increases the difficulty of endodontic treatment.  The dental operating microscope, ultrasonic instruments, agitation of irrigation solutions and 2-appointment endodontics (with inter-appointment placement of calcium hydroxide to penetrate areas that escape direct instrumentation) are all helpful adjuncts that can improve the outcomes of endodontic treatment of C-shaped molars.

The following images display cases of C-shaped molars treated at Mountain View Endodontics. In the image below, webbing between the canals can be appreciated in the coronal aspect of the tooth.  

In the second case (below), webbing can be appreciated in coronal, middle and apical 3rds.

Treatment of the final case (below) was complicated by the presence of a large pulp stone.  The stone was loosened with ultrasonic instruments and the adherent pulp tissue was extirpated almost entirely in tact. 

1. Journal of Endodontics, Volume 24, Issue 5, Pages 372-375, May 1998   2. International Endodontic Journal, Volume 37, Issue 2, pgs. 139-144, February 2004.