What cavity preparation concept allows direct access to the root canal during endodontic instrumentation?

Straight-line access (also called linear access or direct access) is a fundamental principle of endodontic access cavity preparation. It allows endodontic instruments to be inserted into the canal(s) in a straight line without deflection by the access cavity walls or coronal tooth structure. This minimizes instrument stress and fatigue, reduces the risk of ledging, transportation, and instrument separation, and improves the efficiency of canal shaping and cleaning. Achieving straight-line access typically involves removing the pulp roof, the triangular dentin (dentin triangles), and any obstruction in the coronal third of the canal.