In evaluating the quality of root canal obturation, which scenario is considered more clinically concerning?

An underfilled root canal (short obturation) is more clinically concerning than a slight overfill because it leaves residual canal space that serves as a bacterial reservoir, preventing healing of periapical pathology. Studies and long-term case series have shown that if the apical third of the canal is not sealed adequately, bacteria and their byproducts continue to cause periapical inflammation and treatment failure. A slight overfill, if the canal is properly decontaminated and a good three-dimensional seal exists at the apex, often resolves over time as extruded material is resorbed. The key determinant of endodontic success is the quality of the apical seal — not whether the material is 1–2 mm beyond the apex.