الفهرس 
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Abstract
This study was conducted to evaluate the effect of contamination on the bond strength of repair composite to ceramic, enamel and dentin. Twenty ceramic discs were prepared using the lost wax technique for heat pressed ceramics according to the manufacturer’s instructions. The discs were 15 mm diameter and 1 mm thickness. The discs were then wet ground using # 600 SiC abrasive paper for 30 seconds to remove the superficial ceramic layer and to standardize the surface roughness. The discs were then divided into 10 groups (n=2), each ceramic block then received 10 resin composite cylinders. The two hundred specimens were divided into ten groups (n=20) according to two levels of the study, Level 1: Surface treatment for repair (hydrofluoric acid and silica coating) and Level 2: Adhesive protocol (no adhesive, silane containing adhesive in etch-and-rinse mode, silane containing adhesive in self-etch mode, silane-free adhesive in etch-and-rinse mode and silane-free adhesive in self-etch mode). The shear bond strength was performed using the Universal Testing machine at a crosshead speed of 1mm/min. The shear bond strength was calculated by dividing the load at fracture (Newton) over the surface area (mm2).
Sixty sound non-carious human molars were collected, each molar was ground flat from the buccal and lingual surfaces then it was sectioned mesiodistally to obtain one hundred and twenty halves. The halves were then divided into 12 groups (n=10). The halves were then wet ground manually using # 600 SiC abrasive paper for 30 seconds to create smear layer. Each half obtained 2 composite cylinders on enamel and 2 composite cylinders on dentin. The two hundred forty specimens for enamel and dentin were divided into twelve groups (n=20) according to two levels of the study, Level 1: Surface treatment for repair (no surface treatment, hydrofluoric acid and silica coating) and Level 2: Adhesive protocol (silane containing adhesive in etch-and-rinse mode, silane containing adhesive in self-etch mode, silane-free adhesive in etch-and-rinse mode and silane-free adhesive in self-etch mode). The shear bond strength was performed using the Universal Testing machine at a crosshead speed of 1mm/min. The shear bond strength was calculated by dividing the load at fracture (Newton) over the surface area (mm2).
Results of shear bond strength showed significant effect of surface treatment and adhesive protocol on ceramic (p=0.0001 and p=0.001 respectively), enamel ((p=0.0001 and p=0.0001 respectively) and dentin (p=0.0001 and p=0.0001 respectively).
Under the limitations of this study, the following conclusions could be suggested:
1. The use of HF acid is crucial to improve the bond strength between Lithium Disilicate Ceramics and resin composite regardless to the type of adhesive used. On the contrary, the use of silane-containing adhesive in SE mode is not recommended with silica coating treatment to improve the bond strength.
2. It is necessary to etch enamel and dentin before the application of universal adhesives to improve the bond strength of resin composite.
3. Surface contamination of enamel and dentin using either HF acid or silica coating negatively affected the bond strength of resin composite to enamel and dentin, especially when E&R mode was used.
4. The use of silane-free adhesive in SE mode is not recommended to bond resin composite to dentin when HF acid contaminates dentin.
5. Both Silane-containing and silane-free adhesives must be applied in E&R mode, especially when silica contaminates dentin surface.
Recommendations:
1. Hydrofluoric acid is better to be used upon lithium disilicate ceramic repair.
2. Universal adhesives must be applied in etch-and-rinse mode, especially when both ceramic and tooth structure are exposed to surface treatment for repair purpose.
As repair procedure could involve both ceramic material and tooth structure, further research studies should be conducted to evaluate the effect of other surface contaminants on the bond strength of resin composite to tooth substrates.