الفهرس 
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Abstract
Summary:
The purpose of the present study was to evaluate the effect of carbon dioxide laser irradiation and Cojet silica coating surface treatments of Nanocrystalline zirconia materials on their surface roughness and shear bond strength to adhesive resin cement.
Forty two nanocrystalline zirconia plates were constructed with standardized dimensions for this study.
Samples were divided into two groups according to type of zirconia material used:
• group I: Ultra translucent zirconia samples (n=21).
• group II: Translucent zirconia samples (n=21).
Each group was further subdivided into three subgroups according to surface treatment received:
• Subgroup (C): Zirconia samples were sandblasted by AL2O3 and used as a control group (n=7).
Ultra translucent zirconia (IC). Translucent zirconia (IIC).
• Subgroup (L): Zirconia samples were treated with CO2 laser irradiation (n=7).
Ultra translucent zirconia (IL). Translucent zirconia (IIL).
• Subgroup (S): Zirconia samples were sandblasted by silica coated alumina particles with Cojet device (n=7).
Ultra translucent zirconia (IS). Translucent zirconia (IIS).
All samples were then subjected to surface roughness evaluation by a scan electron microscope (SEM) to assess the effect of different treatments on their surface morphology.
All samples were bonded to resin composite discs surface treated by 37% phosphoric acid etching gel. All samples after different surface treatmentsd were treated by zirconia primer and then cemented with RelyX ultimate adhesive resin cement. A computer controlled materials testing machine was used to test the effect of different surface treatments of the zirconia plates on the shear bond strength to RelyX ultimate resin cement, compared with the control. Finally, deboneded samples were examined under the scan electron microscope to determine their mode of failure.
Data were collected and statistically analysis was performed in several steps. Initially, descriptive statistics for each group results. Two way ANOVA was done to detect effect of variable (group and subgroups). One way ANOVA followed by pair-wise Tukey’s post-hoc tests were performed to detect significance between subgroups with each group. Student t-test was performed to detect significance between groups with each subgroup. Statistical analysis was performed using Graph-Pad Prism version 4.00 for Windows. P values ≤ 0.05 are considered to be statistically significant in all tests.
The results showed that non-significant (P>0.05) difference between (control and laser irradiated) and (silica coated and laser irradiated) by Pair-wise Tukey’s post-hoc and the difference between all surface treatments was statistically significant as indicated by one way ANOVA in ultra translucent zirconia. The results showed that the difference between all surface treatments was statistically non-significant as indicated by one way ANOVA in Translucent zirconia.
Regardless to surface treatment design, totally it was found that translucent zirconia recorded statistically non-significant higher bond strength mean value than ultra translucent zirconia mean value as indicated by two way ANOVA test.
Regardless to CO2 laser irradiation the results showed that the lowest bond strength mean value in all groups for translucent zirconia and lower bond strength mean value than sandblasting group and higher than silica coated group for ultra translucent zirconia with the difference between other groups of surface treatments was statistically non-significant. Due to the formation of a damaged layer and micro-cracks due to overheating after CO2 laser application to the surface of zirconia ceramic may be responsible for the decrease in SBS compared to the control group. During the heating of the ceramic surface caused by the absorption of the laser radiation, superficial emission of ions, electrons, and atoms takes place.
Regardless to silica coated the results showed that silica coated recorded lower bond strength mean value than sandblasting group and higher than laser irradiated group for translucent zirconia and recorded the lowest bond strength mean value in all groups for ultra translucent zirconia with the difference between other groups of surface treatments was statistically non-significant. Due to the surface roughness resulted from air abrasion, providing a larger surface area for micromechanical retention. Microscopic analysis of the blasted surface reveals a thin and microretentive layer which might have caused increase in the bond strength to resin and the silica coated surface promotes a chemical bonding with silane and consequently resin adhesives.
Regardless to control group the results showed that Al2O3 Air abrasion recorded the highest bond strength mean value for translucent zirconia and ultra translucent zirconia with the difference between other groups of surface treatments was statistically non-significant. Due to the progress of resin cement flow into microretentions due to increased roughness and surface energy, which create micromechanical interlocking between the resin cements and zirconia. Moreover, air abrasion may generate hydroxyl groups on the zirconia surfaces, facilitating the chemical reaction with phosphate monomers.