الفهرس 
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Abstract
This invitro study was carried out to assess the flexural strength, shear bond strength and color of veneering porcelain modified with silica nanoparticles on zirconia core.
Silica nanoparticles were added to the veneering porcelain powder at a rate of 5% by weight using a delicate digital balance.
The incorporation of silica nanoparticles in the modified veneering porcelain was demonstrated using x-ray diffraction and energy dispersive X-ray spectroscopy (EDX).
A total number of 60 samples was constructed and classified into two groups. group 1 (control group) veneered porcelain without any modification (n=30). group 2 (Modified group) veneered porcelain modified with silica nanoparticles (n=30). Each group was classified into 3 subgroups according to type of test performed (n=10).
Subgroup: For flexural strength test.
Subgroup: For shear bond strength test.
Subgroup: For color change test.
Then each subgroup was classified into two classes (n=5).
Class: Samples subjected to thermo cycling
Class: Samples not subjected to thermo cycling.
Universal testing equipment was used to determine flexural strength and shear bond strength. The color change was measured using a spectrophotometer. Mode of failure was detected using digital microscope and scanning electron microscope.
The flexural strength results of the control group and the modified group were (285.06±11.41) MPa and (414.79±29.04) MPa respectively. (P Value < 0.001). There was significant increase in flexural strength in modified samples compared with control samples without thermo cycling. There was also a significant increase in flexural strength of the modified group (431.78±22.73) compared to the control group (280.97±29.85) with thermo cycling.
Shear bond strength values in the modified group (42.1±4.07) were significantly higher than in the control group (28.38±6.81) without thermo cycling. Significant increase in the modified group (34.13±5.6) compared to the control group (26.97±4.03) with thermo cycling. Modified group showed mixed failure type mainly in comparison to the control group which was mainly adhesive failure type.
Color change was within the clinical acceptable range between the control group and the modified group without thermo cycling (∆E=1.87±0.44) and with thermo cycling (∆E=1.71±0.32).
Conclusions:
Within the limits of this investigation, the following conclusions could be drawn:
1-The addition of silica nanoparticles to the veneering porcelain improves its flexural strength significantly.
2-The use of Nano silica improves the veneering porcelain’s shear bond strength to the zirconia substrate.
3-The addition of silica nanoparticles had no effect on the color of the veneering porcelain.
4- The addition of silica nanoparticles to the veneering porcelain improves its flexural strength and shear bond strength significantly after thermo cycling without significant color change.