CBCT provides accurate anatomical details in three dimensions, offering the possibility to view an individual tooth in axial, sagittal, and coronal views. This study performed an investigation of the occurrence of pulp stones by CBCT.

Objectives: To evaluate the action of a metal artefact reduction (MAR) tool when artefactgenerator metal object is at different positions in the field of view (FOV). Methods: A cylindrical utility wax phantom, with a metal alloy sample inside, was made. The phantom was positioned centrally and peripherally in the FOV for image acquisition, with and without the MAR tool activation. The standard deviation values (image noise levels) from areas around the metal sample and the control area were obtained. The numbers were compared by Student's t-test (a 5 0.05).

Aim To evaluate the influence of the metal artefact reduction (MAR) tool in the diagnosis of fractured instruments in root canals of extracted mandibular molars, with or without root canal fillings. Methodology The root canals of 31 mandibular molars were divided into four groups: (i) the control group, without root fillings; (ii) the fracture group, without fillings and with fractured files; (iii) the fill group, with root filling; and (iv) the fill/fracture group, root filled and with fractured files. The following instruments were used as fractured endodontic instruments: stainless steel hand files, NiTi reciprocating files and NiTi rotary files. Each tooth was inserted in a dry mandible to obtain cone‐beam computed tomography (CBCT) images using a CBCT OP300 3D Maxio (Instrumentarium Dental, Tuusula, Finland) and Picasso Trio (Vatech, Hwaseong, Republic of Korea), with and without application of the MAR tool. All images were evaluated by three radiologists for the presence or absence of fractured files on a 5‐point scale. The diagnostic accuracy (area under ROC curve) was calculated. Image noise was measured in regions of trabecular and cortical bone and soft tissue. The comparison between the ROC curve values with the MAR tool enabled or disabled was performed using a t‐test. A t‐test was also employed for comparing image noise when the MAR tool was enabled and disabled. The significance level was set at 5%. Results The use of the MAR tool did not influence the diagnostic accuracy for identifying fractured endodontic instruments in root canals with and without fillings in both CBCT systems (P > 0.05), nor did it influence the image noise (P > 0.05). Conclusions The MAR tool on these two devices did not increase the detection of fractured endodontic instruments and did not reduce image noise using extracted mandibular molars. Therefore, the MAR tool is not recommended for evaluation of fractured endodontic instruments in teeth with and without root fillings in mandibular molars.

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Objectives: To evaluate three methods of geometric image reconstruction for digital subtraction radiography (DSR). Methods: Digital periapical radiographs were acquired of 24 teeth with the X-ray tube at 6 different geometric configurations of vertical (V) and horizontal (H) angles: V0°H0°, V0°H 10°, V10°H0°, V10°H10°, V20°H0°and V20°H10°. All 144 images were registered in pairs (Group V0°H0°1 1 of the 6 groups) 3 times by using the Emago ® (Oral Diagnostic Systems, Amsterdam, Netherlands) with manual selection and Regeemy with manual and automatic selections. After geometric reconstruction on the two software applications under different modes of selection, all images were subtracted and the standard deviation of grey values was obtained as a measure of image noise. All measurements were repeated after 15 days to evaluate the method error. Values of image noise were statistically analyzed by one-way ANOVA for differences between methods and between projection angles, followed by Tukey's test at a level of significance of 5%. Results: Significant differences were found between most of the projection angles for the three reconstruction methods. Image subtraction after manual selection-based reconstruction on Regeemy presented the lowest values of image noise, except on group V0°H0°. The groups V10°H0°and V20°H0°were not significantly different between the manual selection-based reconstruction in Regeemy and automatic selection-based reconstruction in Regeemy methods. Conclusions: The Regeemy software on manual mode revealed better quality of geometric image reconstruction for DSR than the Regeemy on automatic mode and the Emago on manual mode, when the radiographic images were obtained at V and H angles used in the present investigation. Dentomaxillofacial Radiology (2016Radiology ( ) 45, 20160120. doi: 10.1259 Cite this article as: Queiroz PM, Oliveira ML, Tanaka JLO, Soares MG, Haiter-Neto F, Ono E. Assessment of three methods of geometric image reconstruction for digital subtraction radiography. Dentomaxillofac Radiol 2016; 45: 20160120.