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INTRODUCTION The aim of this study was to determine and compare the difference in volume of dentin and enamel removed (DER) to prepare three different access cavities and to propose a standardization of the access cavities according to their volume of DER. METHODS One hundred and twenty maxillary and mandibular molars and premolars were assigned to 3 subgroups for each tooth type (n=10): Traditional endodontic cavity (TEC) group; conservative endodontic cavity (CEC) group with partial unroofing and convergent walls and ultra-conservative endodontic cavity (UEC) group, preserving most part of the pulp chamber roof and the occlusal surface. The sliced image data of CBCTs before and after access cavity preparation were exported as DICOM-files and imported into the MeVisLab framework system. After segmentation, volumes of coronal dentin and enamel were measured and the difference in percentage of volume of DER for endodontic access cavities preparation was calculated. The data were subjected to statistical analyses (ANOVA) with a level of significance set at P<.05. RESULTS The percentage of volume of DER was less than 6% for UEC group, up to 15% for CEC group and more than 15% for TEC group with a statistically significant difference among all groups in all the tooth types analyzed (P< .05). CONCLUSIONS The present study showed significantly different percentages of volume of DER among the groups analyzed, being teeth with UEC