الفهرس 
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Abstract
This study was designed to investigate the effect of data acquisition method on the marginal adaptation and 3D internal fit of CAD/CAM crowns fabricated by CEREC 3 (CEREC inLab), using two different convergence angle 8 and 12 degrees, and using two finish line design, chamfer and shoulder.
Four stainless steel metal dies representing a prepared mandibular first premolar were machine crafted. (Figure 6). The first die was prepared with 8°convergence ( total occlusal convergence = 16° )45 and chamfer finish line, the second die was prepared with 8° convergence ( total occlusal convergence = 16° ) and shoulder finish line, the third die was prepared with 12° convergence ( total occlusal convergence = 24° )46 and chamfer finish line, while the fourth and last die was prepared with 12° convergence ( total occlusal convergence = 24° ) and shoulder finish line. (Figure 8,9)
A total number of forty anatomical crowns were constructed and classified into eight equal divisions. Five crowns for each division. Divisions are classified according to the scanning method, degree of convergence and finish line design. All crowns were fabricated by CAD / CAM milling technique (CEREC inLab) (Table 2)
The samples were tested for marginal adaptation using a Stereomicroscope with a fixed magnification of 40X, and then 3D internal fit was tested using cement replica technique. The data obtained were collected, tabulated and subjected to statistical analysis.
group I (master die scanning) recorded lower marginal gap mean value (65.1700 ± 26.87964 µm), than group II (stone die scanning) which recorded marginal gap mean value (83.4370 ± 31.18621). Stone die group showed increased marginal gap. (Table 3, Figure 44)
Within group I ( master die scanning), subgroup B division S (CEREC crowns fabricated with 12 degrees convergence and shoulder finish line) recorded the lowest marginal gap mean value (36.5500 ± 12.15546 µm), and subgroups A division S, (CEREC crowns fabricated with 8 degrees convergence and shoulder finish line) B division C (CEREC crowns fabricated with 12 degrees convergence and chamfer finish line) recorded the intermediate marginal gap mean value (62.2521 ± 19.01697 µm ) and (68.8320 ± 19.46251 µm ) respectively , while subgroup A division C (CEREC crowns fabricated with 8 degrees convergence and chamfer finish line) recorded highest marginal gap mean value (93.0460 ± 21.09077 µm). (Table 4, Figure 45)
Within group II , subgroup B division S (CEREC crowns fabricated with 12 degrees convergence and shoulder finish line) recorded the lowest marginal gap mean value (51.5610 ± 18.31944 µm), and subgroups A division S, (CEREC crowns fabricated with 8 degrees convergence and shoulder finish line) B division C (CEREC crowns fabricated with 12 degrees convergence and chamfer finish line) recorded intermediate marginal gap mean value of (79.3950 ± 20.77420 ) and (83.2270 ± 8.97449 ) respectively , while subgroup A division C (CEREC crowns fabricated with 8 degrees convergence and chamfer finish line) recorded highest marginal gap mean value (119.5650 ± 18.31944 µm). (Table 5, Figure 46).
group I (master die scanning) recorded lower internal gap mean value (23.147± 76.5589 µm), than group II (stone die scanning) which recorded internal gap mean value of (31.017 ± 69.4587 µm). Stone die scanning (group II) showed increased internal gap (Table 9, Figure 50).
Within group I (master die scanning), subgroup A division S (CEREC crowns fabricated with 8 degrees convergence and shoulder finish line) recorded internal gap mean value of (20.333±79.9771 µm), and subgroups A division C, (CERCE crowns fabricated with 8 degrees convergence and chamfer finish line) recorded internal gap mean value of (23.59±47.1050 µm), subgroup B division C (CEREC crowns fabricated with 12 degrees convergence and chamfer finish line) recorded internal gap mean value of (24.333±79.9771 µm), while subgroup B division S (CERCE crowns fabricated with 12 degrees convergence and shoulder finish line) recorded internal gap mean value of (24.333±13.0024 µm).(Table 10, Figure 51)
Within group II ( stone die scanning) subgroup B division S (CEREC crowns fabricated with 12 degrees convergence and shoulder finish line) recorded internal gap mean value of (20.933 µm ± 35.118 µm), subgroups A division S , (CEREC crowns fabricated with 8 degrees convergence and shoulder finish line) recorded internal gap mean value of (32.800±47.00 µm), subgroup B division C (CERCE crowns fabricated with 12 degrees convergence and chamfer finish line) recorded internal gap mean value of (34.200±49.00 µm) while subgroup A division C (CERCE crowns fabricated with 8 degrees convergence and chamfer finish line) recorded internal gap mean value of (36.133 ± 27.1539 µm).(Table 11, Figure 52)