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

research _ computed tomography 0.5 mm were produced when the basal plane was used than when the occlusal plane was used (44.44%), with the difference being sta- tistically significant (p = 0.001; Table 3). _Discussion Ever since the first dental implants were introduced by Brånemark et al. in 1969, den- tal practitioners and researchers have sought methods that might improve the accuracy of surgical implant placement.21 CT has been widely used for preop erative assessment of dental implant treatments.22 It provides good images of the thickness of vestibular cortical bone and interalveolar distances, as well as of important anatomical features in jaws.23 When used for imaging the mandible, the main advantage of CT scans over periapical or panoramic radiographs is that they provide a relatively accurate assessment of the alveolar crestal bone height and width and its spatial relationship with the mandibular canal.24 However, although there is a wide range of dental CT equipment marketed as provid- ing accurate bone data at a 1:1 scale, several studies have shown discrepancies between the radiographic measurements taken using CT and clinical measurements taken direct- ly from the bone.14,25 In 1996, Covino et al. used ten rectangular acrylic blocks (prepared with titanium–molybdenum alloy) as markers spaced from 1 to 10 mm, respectively.14 A plastic sphere was prepared with ten sets of titanium markers spaced at variable intervals of 1–10 mm. Each object was scanned three times at slice thicknesses of 3.0 mm and slice thick- nesses of 1.5 mm with 0.5 mm overlap, po- sitioned in the CT scanner in two different positions in relation to the scanning beam (perpendicular and parallel). The authors concluded that when CT was carried out with slices every 3.0 mm, if the procedure was not performed correctly, sig- Fig. 4 Fig. 4_Bar graph comparing discrepancies between radiographic measurements (mm) and measurements taken directly from the mandibles (mm) using both axial reference planes studied. 1_2017 21