C-shaped root canals are characterized by a continuous, continuous strip or arc-like structure of the root anatomy, resembling the letter C in a horizontal cross-section. This anatomical variation is most common in the lower second molars (particularly in individuals of Asian descent). While standard root canals are independent, round tubes, C-shaped canals are connected by thin dentin bridges and gaps. This makes treatment extremely difficult because conventional rotary files only expand by circular motion, unable to reach the infected pulp tissue within these strip-shaped gaps and flat areas. Cleaning these cases requires intensive and prolonged use of ultrasonic and laser-activated irrigation systems and chemical tissue-dissolving agents, rather than mechanical files; otherwise, tissue will remain inside, and treatment will fail.
