This study compared the accuracy of traditional endodontic access to conservative access cavities prepared with or without novel nonrestrictive endodontic access guides by operators with different levels of clinical experience without visual aids, using a three‐dimensional volumetric accuracy analysis method. The accuracy of the preparations was analysed using a novel 3D volumetric analysis by calculating the intersection and volume of the actual cavities to the planned model cavities. The experienced operator significantly outperformed the inexperienced operator in the free hand groups, while accuracy of conservative access cavities prepared using the novel guides were comparable and significantly higher than the other groups (p < 0.05). The results demonstrated clinical experience enhanced endodontic preparations accuracy and that nonrestrictive guides achieve accurate conservative access cavities which are independent of the operator skill level. Additionally, the three‐dimensional volumetric analysis is a consistent and objective method to judge the accuracy of guided endodontic techniques.