Computed tomography for dental implants: the influence of the gantry angle and mandibular positioning on the bone height and width

To investigate the effect of deviation of mandibular positioning, by changing the gantry angle, on the measured height and width of dental implant sites in reformatted cross-sectional computed tomography (CT) scans. CT images of ten human dry mandibles were made in three gantry positions to simulate changes in patient positioning: (1) parallel to the lower base of the mandible (standard); (2) with a gantry inclination of +19 degrees ; and (3) with an inclination of -19 degrees . One examiner measured the bone height and width at selected sites in the images at three different times. Results were compared with a paired test in SAS 8.02. In relation to bone height, when the jaws were inclined to the inferior direction (gantry angle +19 degrees ), there was no statistically significant difference for any region studied. There was a statistically significant difference for the incisor region when the jaws were inclined to the superior direction (gantry angle -19 degrees ). With respect to the width of the bone rim, there was a statistically significant difference only for the region of the molars when the jaw was inclined to the inferior direction and for the region of the canine, when the inclination was to the superior direction. Errors in mandibular positioning of 19 degrees produced image discrepancies with regard to bone height and width which were not excessive. Thus, examinations do not have to be repeated owing to variation of mandibular positioning because the differences were lower than 10% of the value found for the standard position.