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Journal of Oral Science & Rehabilitation Volume 2 | Issue 3/2016 45 A x i a l p l a n e i n c o m p u t e d t o m o g r a p h y Figs. 3a–c Figs. 3a–c Measurements taken from the mandibles: (a) radio- graphic 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. a b c blinded as to which axial reference plane, occlu- sal (Fig. 3a) or basal (Fig. 3b), had been used. Lastly, the observers’ mean scores were calcu- lated. D i r e c t m a n d i b u l a r m e a s u r e m e n t s These measurements were taken using a digital calibrator(AMIGT304B.W-1220,AMIG,Amore- bieta-Etxano, Spain). The interedges (apical- coronaldistance in mm)were measured perpen- dicularly from the base of the mandibular body to the alveolar ridge, along each of the lines correspondingtothetomographicslices(Fig.3c). S t a t i s t i c a l a n a l y s i s The data were analyzed using SPSS statistical software (Version 12.0; SPSS, Chicago, Ill., U.S.). Descriptivestatisticswereobtainedforeachvari- able. The associations between the different qualitativevariableswerestudiedusingPearson’s chi-squared test. Student’s t-test for two inde- pendent samples was applied to quantitative variables,ineachcasedeterminingwhethervari- ances were homogeneous. Statistical signifi- cance was set at p ≤ 0.05. Results In comparing measurements taken from the 18 tomographic slices ofeach mandiblewith meas- urements taken directlyfrom the bone when the occlusal plane was used as the axial reference plane, discrepancies were found in all of the tomographic slices assessed. These discrepan- cies were positive in nine (50%) of the slices, while in the remaining nine (50%), the measure- ments taken from the CT scans were lower than the measurements taken from the bone. In six of the 18 slices analyzed (33.33%), the discrepan- cies observed showed statistically significant differences (p ≤ 0.05; Table 1). When the basal plane was used as the axial reference plane, discrepancies were also found betweenmeasurementstakenfromtomographic slices and clinical measurements of the man- dibles in all 18 slices analyzed. These discrepan- cies were negative in all cases. In 17 of the slices (94.44%), the discrepancies showed statistical- ly significant differences (p ≤ 0.05; Table 2). In this sense, with regard to positioning the patientwhenthe CTscansweretaken, use ofthe occlusal plane as axial reference produced the most accurate measurements (Fig. 4). When the distribution of discrepancies in millimeters found in each of the 18 tomographic sliceswas compared in relationtothe axialrefer- ence plane, a higher percentage (99.44%) of discrepancies greater than 0.5 mm were pro- ducedwhenthe basalplanewas usedthanwhen the occlusal plane was used (44.44%), with the difference being statistically significant (p = 0.001; Table 3). Discussion Ever since the first dental implants were intro- duced by Brånemark et al. in 1969, dental practi- tionersandresearchershavesoughtmethodsthat might improve the accuracy of surgical implant placement.21 CT has been widely used for preop- Volume 2 | Issue 3/201645