A root canal is the space within the root of a tooth. It is part of a naturally occurring space within a tooth that consists of the pulp chamber (within the coronal part of the tooth), the main canal(s), and more intricate anatomical branches that may connect the root canals to each other or to the surface of the root.

The smaller branches, referred to as accessory canals, are most frequently found near the root end (apex) but may be encountered anywhere along the root length. There may be one or two main canals within each root. Some teeth have more variable internal anatomy than others. This space is filled with a highly vascularized, loose connective tissue, the dental pulp.