Background: The aim of the study was to evaluate and compare the effect of different access cavity designs, using CBCT, on root canal transportation and centeralization performed on 2 rooted maxillary premolars. Methods: Twenty maxillary premolars were randomly divided into 2 groups. In group 1, traditional endodontic cavities (TECs) were prepared. In group 2, contracted endodontic cavities (CECs) were prepared. Mechanical preparation was done by Protaper Next files in both groups. CBCT imaging was performed pre and post root canal preparation for calculations of root canal transportation and centering ability. Results: Data were analyzed using Mann-Whitney U test and Kruskal-Wallis test. For transportation, teeth with CECs showed the statistically significantly highest median amount of transportation, while as for centering ability, results showed no significant difference between both groups at 6 mm and 9 mm of the root level. At root level of 3 mm, teeth with CECs showed the statistically significantly lowest median amount of centering ability. Conclusion: Under the conditions of this study, Protaper Next prepared canals with different access cavity designs without significant shaping errors. TEC showed less transportation than CEC, while both TEC and CEC had no effect on the file centering ability at the middle and coronal third of the root.