Root Canal Anatomy in Cross-section
Root canals presenting an oval cross-section are found in 50%-70% of root canals. In addition, canals with a "tear-shaped" cross section are common whenever a single root contains two canals (e.g., mesial roots of lower molars). Nevertheless, these aspects of root-canal anatomy are not seen or recognized in conventional 2D radiographs, as the long axis of their flat cross section is usually directed in parallel to the direction of the x-ray beam. With the increased use of Cone Beam Computerized Tomography (CBCT), these shapes are likely to be more and more often seen and recognized not only by endodontists but also in the clinical environment of general practice.
When rotary NiTi files are used in canals with flat-oval or tear-shaped cross sections, a circular bore is created, while the buccal and/or lingual recesses remain un-instrumented. It takes (a) the awareness that a given canal is flat and (b) expertise in creative use of hand instruments to try to overcome this problem.
Tissue or biofilm remnants along such un-instrumented recesses may lead to failure due both to inadequate disinfection and to the inability to properly obturate the root-canal space.
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