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CAD/CAM - international magazine of digital dentistry, Italian Edition, No.1, 2017

research _ computed tomography Figs. 2a-c_Basal plane: (a) positioning of mandibles in PMMA boxes to support the lower edge against the container’s anterior wall; (b) use of the occlusal plane as the axial reference plane; (c) use of the basal plane as the axial reference plane. Fig. 2 in the anterior region by measuring a height of 1 cm (the usual height of the mandibular incisal crowns) and in the posterior region by dividing the retromolar trigone into three parts: upper, middle and lower. Thereafter, a meeting point between the upper third and the middle part was chosen; this point usual- ly measured 1 cm in height (Fig. 1b).20 Once the occlusal planes of the mandi- bles had been established, a Moyco wax piece (Thompson Dental Manufacturing, Mont- gomeryville, Pa., U.S.) was molded to follow the previously established plane. After plac- ing the wax simulation of the occlusal plane (Fig. 1c), this was divided into 18 parts using 2 mm lead strips. These strips were placed 6 mm apart so that they corresponded to the 18 tomographic slices performed for each mandible (Fig. 1d). Lastly, Fox planes were attached to the wax on each of the 39 mandibles (to be used as a guide for delimiting the occlusal plane radiographically) and each assembly was placed into a polymethyl methacrylate (PMMA) box for radiographic study. _Basal plane In order to establish a good axial refer- ence from the basal plane, all of the mandi- bles were positioned in PMMA boxes to sup- port the lower edge (basal plane) against the container’s anterior wall (Fig. 2a). _Dental CT The CT equipment used was a Toshi- ba Multi CT scan Aquilion 16 TSX-101A/6A (Toshiba America Medical Systems, Tustin, Calif., U.S.). Thirty-six sagittal tomographic slices were performed for each mandible, 18 taking the occlusal plane as the axial refer- ence plane (Fig. 2b) and 18 using the basal plane (Fig. 2c). The exposure parameters were set at 57 Kv, 56 s and 1.0–3.2 mA, and a rect- angular collimator was used. The radiograph- ic images were processed using SIMPLANT software (Materialise Dental, Madrid, Spain). All of the measurements were scored in- dependently by two oral surgeons. When measuring the sagittal tomograph- ic slices, the observers were blinded as to which axial reference plane, occlusal (Fig. 3a) Figs. 3a-c_Measurements taken from the mandibles: (a) radiographic measurement of a sagittal tomographic slice using the occlusal plane as the axial reference plane; (b) radiographic measurement of a sagittal tomographic slice using the basal plane as the axial reference plane; (c) bone measurement taken using a digital calibrator. Fig. 3 18 1_2017