الفهرس 
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Abstract
Aim: The current study aimed to investigate and evaluate the impact of two different milling
protocols on the marginal accuracy and fracture resistance of crowns fabricated from glass-ceramic
(CEREC Tessera) material.
Methodology: A maxillary first molar of a typodont model was prepared according to the
conventional full-contour all-ceramic crown preparation with a heavy chamfer finish line following
the manufacturer’s recommendation. The crowns (n = 18) were divided into two groups (n = 9)
based on their production with milling machines. group A: (Sirona CEREC MC XL 4-axis milling
machine); group B: (CEREC InLab MCX5 5-axis milling machine). The marginal accuracy was
assessed using a stereomicroscope at 30×magnification. The 18 crowns were bonded to their
corresponding epoxy resin dies which were duplicated from the prepared typodont tooth using
rubber base duplicating material to obtain 18 epoxy resin dies. The fracture resistance of both
groups was evaluated using a universal testing machine. One Way ANOVA test was used to
compare the marginal accuracy of different surfaces in both groups, the independent t-test was used
to compare fracture resistance results between both groups. Statistical analysis of the results and
comparison between the two groups were performed using an independent t-test (significance: P ≤
0.05).
Results: Regarding the marginal accuracy results, there was a significant difference between both
groups overall, as group A (140.46 μm ± 16.07) was significantly higher than group B (109.68 μm
± 16.91). The fracture resistance values for the CEREC Tessera crowns in both groups were
(1458.92 N ± 207.92) for the 4-axis milling group and (1783.22 N ±428.05) for the 5-axis milling
group, which revealed insignificant differences between the 4-axis and the 5-axis groups, with P = 0.06.
Conclusions: Within the limitations of this in vitro study, both milling protocols showed fracture
resistance and marginal accuracy within the clinically acceptable range. The number of CAD/CAM
axes showed an influence the marginal accuracy of CEREC Tessera glass-ceramic crowns. The
number of milling axes in both different milling protocols didn’t significantly impact the fracture
resistance of CEREC Tessera glass-ceramic material. The CEREC Tessera is a promising material
as far as aesthetics in concerned and is capable of maintaining high intrinsic strength.
Keywords: Marginal accuracy, Fracture resistance, CAD/CAM system, Glass ceramics, CEREC Tessera.