Background: The use of cone beam computed tomography could overcome the inherent limitations of intra-oral radiographs that caused by compression of 3D structures in 2D images. Endodontic treatment of maxillary first molars has the highest clinical failure rates due to its complex root anatomy and variation of mesiobuccal roots.
Aim of the study: An in vitro study to detect 2^ndmesiobuccal canal in upper first molar teeth with one machine at different voxel sizes.
Materials and methods: In this study, fifty freshly extracted human first maxillary molars teeth were selected. The teeth were cleaned, disinfected and arranged in horse shoe shaped epoxy resin mold. Then, the molds were exposed using  Morita CBCT operated at 0.125 mm voxel size and 0.250 mm voxel size, then sectioned, stained and finally evaluated with stereomicroscope.
Results: Overall, the smaller voxel sizes showed high accuracy in detection of MB2 than higher voxel sizes but with no significant difference between the two voxel sizes(0.125mm³ and 0.250mm³).Also, Using voxel size 0.125mm³ showed that the percentage of detection of MB2 was 100% in the coronal third, 94.1%in the middle third and 77.8% in the apical third. Using voxel size 0.250 mm³ the percentage was 95.3% in the coronal third, 94.1% in the middle third and 77.8% in the apical third.
Conclusion: CBCT is reliable method for detection of MB2 with different voxel sizes.