الفهرس 
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Abstract
This in-vitro study was performed to evaluate the effect of different surface treatments on the shear bond strength of repaired aged bulk-fill composites. Sixty cylindrical shaped specimens of X-tra fil composite were prepared. Then they were stored in artificial saliva for 3 months at 37o C to be aged. These specimens were divided randomly into 2 groups according to the different repair material (n=30). • group I: repaired with X-tra fil bulk-fill composite. • group II: repaired with Grandio nanohybrid composite. Each experimental group (n= 30) was divided into three subgroups (n= 10) according to the different surface treatments. • Subgroup A: control group (no physical surface treatment) • Subgroup B: the outer surface of each specimen was treated with a coarse diamond bur. • Subgroup C: the outer surface of each specimen was treated with air abrasion unit (Aquacut Quattro Air Abrasion System) using 50-μm AL2O3 particles for 10 s. Futurabond U universal adhesive was applied on all specimens. Then a polyethylene tube was placed on the surface of the aged composite and filled with the repair material (X-tra fil®, Grandio®) according to the corresponding group. The specimens in each group were thermocycled for 500 cycles from 5°C to 55°C with a dwell time of 30s and 20 s transfer time. These specimens were tested for shear mode using an Instron testing machine. A shear force was applied to each specimen at a crosshead speed of 1mm/min until fracture. All fractured surfaces were examined under a stereomicroscope at magnification 40X to determine the mode of failure. Another 30 specimens were fabricated to assess the surface roughness resulted from each surface treatment. And representative SEM micrographs for each treatment were taken to assess the surface topography with different magnifications (500X and 1000X). The results of this study revealed that: ➢ Shear bond strength test: • Concerning group I: The highest mean shear bond strength value was recorded in group IB (diamond bur abrasion / X-tra fil ®) followed by group IC (AL2O3 air abrasion / X-tra fil®) and the lowest mean bond strength was recorded in group IA (control group / X-tra fil®). There were statistically significant differences between groups IA & IB and IA& IC. • Concerning group II: The highest mean shear bond strength value was recorded in group IIB (diamond bur abrasion / Grandio®), followed by group IIC (AL2O3 air abrasion / Grandio®) and lowest mean bond strength was recorded in group IIA (control group / Grandio®). There was a statistically significant difference was recorded between groups IIA & IIB. And by comparing the two main groups (I&II) to assess the effect of using different repair materials in the repair process, it showed no significant difference between the two groups. It was observed that, most of the specimens in all groups showed mixed and cohesive failures. ➢ Surface roughness analysis: group B (bur abrasion) showed the highest roughness value, followed by group C (air abrasion) then group A (control). There was a highly statistically significant difference between group A&B, group A&C and group B&C. The SEM examination of the specimens showed different roughness pattern and topography. Conclusions: Under the limitations of this study, the results suggest that: 1- Surface roughening of the aged composite is necessary when fresh composite is added. 2- Shear bond strength of X-tra fil bulk-fill composite after repair with either a bur or airborne particle abrasion was comparable and greater than not having any physical surface treatment. 3- No differences between the two types of composites used to repair the aged bulk fill restorations were recorded; thus, the repair material is not a factor affecting the longevity of the restoration.