What is the most important geometric principle of endodontic access cavity preparation?

Straight-line access is the most critical principle of endodontic access preparation. It means the access cavity should be designed so that endodontic files can enter the root canal system in a direct, unobstructed path without contacting the walls of the access cavity. This maximizes the efficiency of canal instrumentation, reduces the risk of procedural errors (ledging, perforations, file separation), and facilitates thorough cleaning and shaping. Conservation of tooth structure is also important, but cannot compromise straight-line access.