الفهرس 
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Abstract
Statement of the problem: Recent ceramics provide wide range of indications for restorative dentistry, however one of the most common failures is loss of retention & de-bonding of ceramic restorations, that’s because achieving maximum adhesive bonding strength is a major goal. So Long-term survival of adhesive esthetic restorations remains a challenging matter and depends on the success of a reliable bond among ceramic, the luting agents and the dental substrates, In an attempt to improve bonding of resin cements to ceramics, various surface treatments have been recommended to facilitate chemical and micromechanical retention, yet choosing the right protocol for each particular material is the key for success of different adhesive restorations.
Aim of the study: This research was performed to study the effect of different surface treatments which are: Acid etching & silanation (5 % HF acid etching), Al2O3 sandblasting & silanation, 2W, Er,Cr:YSGG laser etching with repition rate 20 HZ for 20 secs & silanation, to two recent ceramic materials: Lithium silicate ceramic (Obsidian) & Zirconia reinforced lithium disilicate ceramic. (Vita Suprinity).
Materials & methods: Blocks of two CAD CAM esthetic restorative materials (VITA Suprinity and Obidian) were used to prepare slices with the following dimensions:10mm x 10mm x 1.5mm for both Vita Enamic Suprinity material & 10mm x 10mm x 1.5mm for Obsidian ceramic material. Using IsoMet 4000 microsaw with cutting speed 2500 rpm. For easier handling and fixation during the shear test, a number of 21 discs of Obsidian Material & 21 discs of Vita Suprinity material were embedded in an acrylic block, before any surface treatments, to easily differentiate between the two materials two different acrylic colors were used. Then One Ceramic disc of each material was examined under scanning Electron microscope to determine surface features before any further surface treatment done. Obsidian, and Vita Suprinity ceramic slices embedded in acrylic blocks carrying OA & SA initials were etched using HF acid 5%, then washed and air-dried with oil-free air/water syringe. Followed by silane application for both type of ceramics & then air dried. On the second group Sandblasting was performed on Vita Suprinity & Obsidian ceramic slices embedded in acrylic blocks holding OB & SB initials, using 50 microns aluminium oxide powder at an angle of 90, distance ≈10 mm for 20 seconds and 2.8 bar pressure followed by Silane application then air dryness. On the third group the ceramic slices were subjected to laser irradiation followed by silane application. In this group the laser parameters were adjusted so that, the power was 2 W for SL & OL acrylic blocks carrying Vita Suprinity & Obsidian ceramic discs with repetition rate of 20 Hz for 20 seconds at surface of the slices. This was followed by silane application & air dryness. After finishing surface treatments, ceramic slice of each group was examined using Scanning Electron microscope determine the changes that happened after each surface treatment.
The specimens were bonded to Composite resin using RelyX™ Ultimate adhesive resin cement then light cured according to the manufacturers recommendation and the subjected to the universal test machine to test the shear bond strength after the test all the specimens were examined under scanning electron microscope to determine mode of failure that occurred.
Results: For VITA Suprinity, HF acid etching & silanation as Surface treatment had the highest (mean ± SD) value, followed by sandblasting & silanation, while Laser surface etching followed by silanation had the lowest (mean ± SD) values. For Obsidian, sandblasting & silanation had slightly the highest (mean ± SD) value, followed by hydrofluoric acid etching & silanation, but with no significantly difference between both surface treatments, while the laser surface etching followed by silanation had significantly the lowest (mean ± SD) value.
While for mode of failure statistical analysis, there was no significant difference in the distribution of different mode of failures within both ceramic materials (p=0.115). For Obsidian, most of the samples had a mixed mode of failure 24 (40.0%), lower percentage failed cohesively 22 (36.7%) while only 14 (23.3%) of the samples had an adhesive mode of failure. For Vita Suprinity, most of the samples had an adhesive mode of failure 24 (40.0%), lower percentage failed cohesively 20 (33.3%) while only 16 (26.7%) of the samples had a mixed failure mode.