الفهرس 
AbstractOnly 14 pages are availabe for public view
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Abstract
The primary challenge of restorative dentistry is achieving excellent aesthetic results while preserving tooth structure using minimally invasive preparation techniques. Minimizing tooth preparation promotes the preservation of the tooth structure which plays an important role in stress redistribution, crack resistance, and tooth durability. Three main factors should be considered to achieve an optimal dental restoration; resistance to fracture, marginal adaptation, and aesthetic value. So that ,The aim of this study is to evaluate the external marginal gap and internal fit of ceramic crowns restoration with different minimal invasive margin designs . 45 3D printed PMMA dies with three different finish line configurations (deep chamfer 1mm, chamfer 0.5mm and feather edge 0.1-0.2mm) were scanned for crowns fabrication using a completely digital workflow and three different CAD-CAM ceramic materials (zirconia DMAX (multi-layer zirconia), ZLS Celtra Duo (zirconia reinforced lithium silicate), and Shofu HC (Hybrid ceramic) )(n=15 for each group). Crown restorations were adhesively cemented by resin cement under a static load of 5 kg. All specimens were exposed to a thermal bath with a temperature of 5–55 °C for 2500 cycles and a chewing simulator that repeated 37500 cycles, which are equivalent to three months exposure to thermal and chewing action. Marginal gaps between the cervical margin of the crown and the outer end of the finish line were measured using a digital microscope with a power of 300x. The mean vertical gap for each crown was then calculated before and after cementation and thermomechanical cycles. The samples were spilt bucco-palatal using the Iso Met 4000 to assess internal fit. Two-way ANOVA and Tukey post hoc tests were used to compare the values between the experimental groups. The marginal gap values were statistically highly significant differences between groups. The marginal gap differences were found to be the smallest in multilayer zirconia with a deep chamfer finish line (6.816± 1.06), and the highest in Shofu HC with a feather edge finish line (14.736 ±2.639). The lowest internal fit of this study was reported for multilayer zirconia with a feather edge (64.924± 2.743), and the highest values were recorded for Shofu HC with a deep chamfer finish line (110.476± 3.484).