الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
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 molar has the highest clinical failure rates due to its complex root anatomy and variation of mesiobuccal roots. CBCT has been suggested to detect second mesiobuccal canals to overcome this problem. Aim : An in vitro study to detect 2ndmesiobuccal canal in upper first molar teeth by different CBCT machines 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 scanned using two machines. First one is PlanmecaPromax 3D CBCT (Promax 3D mid; Planmeca Oy, Helsinki Finland) operated at 0.15mm3 voxel size and 0.2mm3 voxel size. Second machine is Veraviewpoces 3D R100(J. Morita Manufacturing Corporation, Kyoto, Japan) operated at 0.125 mm3 voxel size and 0.250 mm3 voxel size, then sectioned, stained and finally evaluated with stereomicroscope. Result : The study showed that the detection of MB2 was higher in coronal thirds than middle thirds and the middle thirds than the apical thirds. Also, the accuracy of Morita CBCT machine was higher than the Planmeca CBCT machine. The study showed that the lower voxel sizes (0.125 mm3-0.15 mm3) were more accurate than the larger voxels (0.250mm3 -0.2 mm3). There was only significant difference between Morita 0.250 mm3 and Planmeca 0.2 mm3 in the coronal third at p value = 0.04 Conclusions : CBCT is reliable method for detection of MB2 with different machines and different voxel sizes. Focusing on different voxel sizes, they had relatively similar results. We can conclude that Morita machine at 0.250 mm3 voxel size was the best choice in detecting MB2, due to its lower radiation dose, shorter scanning time and high accuracy. Recommendations :Prospective studies are needed to compare between CBCT and serial sectioning in detection of MB2 in maxillary first molar teeth.More clinical studies should be done to compare between smaller and larger voxel sizes to allow the professional radiological society to make new guidelines for using of CBCT in endodontic field especially in detecting MB2 in maxillary first molar teeth. More studies should be performed to investigate the effect of low dose CBCT protocols on other diagnostic tasks and in relation to other exposure parameters.