Ideal root canal preparation involves following the natural anatomical pathway of the root canal to create a smooth channel. Canal deviation occurs when the preparation deviates from this natural path, leading to various issues. The mildest form of deviation is when one side of the canal wall is excessively cut while the other side is minimally prepared. More severe deviations can result in the formation of steps or elbows at the curved sections of the canal. In extreme cases, the deviation may lead to canal perforation or widening of the apical foramen, causing complications during treatment.

Canal deviation poses several risks. First, excessive removal of dentin from one side of the canal wall while the other side remains untreated can leave bacterial biofilms intact, especially in cases of infected canals. This undermines the purpose of root canal preparation, which is to thoroughly clean the canal. Additionally, if a step or elbow forms due to deviation, it complicates the subsequent canal filling process. If the deviation is severe enough to widen the apical foramen, the treated tooth may experience persistent discomfort, pain, or even an inability to chew properly after the procedure. Thus, canal deviation can result in poor cleaning of the canal at best and post-treatment pain and dysfunction at worst.

In cases of mild canal deviation, the use of appropriate filling techniques can still ensure a tight seal of the canal. However, if a step has formed, the infection below the step may be difficult to remove, affecting the outcome of the treatment. In such situations, re-establishing the canal path to remove the infection below the step is critical for achieving a good treatment result. If the apical foramen has been widened, materials with strong antibacterial properties and excellent sealing capabilities, such as nano-ceramic materials like MTA or iRoot BP, can be used to form an apical barrier and tightly seal the widened foramen, yielding satisfactory clinical outcomes.

To prevent canal deviation, taking precautionary measures during treatment is essential. Before treatment, a comprehensive evaluation of the tooth's root canal anatomy is necessary. This requires the dentist to be skilled in interpreting radiographs, ensuring a pre-treatment radiograph is taken to understand the canal's curvature and size. In cases of curved or narrow canals, smaller stainless steel K-files, such as sizes 6, 8, or 10, should be used for initial navigation. Pre-bending these instruments to match the canal's shape can help prevent deviation. Throughout the preparation process, the use of irrigation fluids is critical to wash away dentin debris and prevent blockages at the canal's apex, which could further exacerbate deviation.