الفهرس 
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Abstract
This research was designed to investigate the effect of different rotary cutting tools and aggressiveness of self-etch adhesive on microshear bond strength of resin composite bonded to normal dentin.
A total of 40 freshly extracted, sound, non-carious, human permanent molars were used in the study. Each tooth was sectioned mesio-distally into two halves down to the root then each half was cut at level of a cemento-enamel junction to remove root portion, then each half was embedded into a self-curing acrylic resin to give 80 samples. For microshear bond strength testing, a total of 80 samples were assigned into four groups according to the type of rotary cutting tool used for dentin surface preparation. First group was prepared by #245 carbide bur, second group was prepared by coarse-grit diamond stone, third group was prepared by medium-grit diamond stone, forth group was prepared by fine-grit diamond stone. Each group was equally divided into 2 equal subgroups (10 each) according to aggressiveness of self-etch adhesive either intermediate-aggressive single bond universal adhesive or aggressive G-aenial bond adhesive.
The tested adhesives was then applied to the prepared dentin surface and cured according to manufacturers’ instructions. The flowable resin composite material was packed inside the 0.9 mm diameter tygon tube and cured for 20 seconds using visible light curing unit.
Dentin specimens were then loaded to failure using specially constructed chisel attachment fixed to a universal testing machine at across head speed of 0.5 mm/minute. The microshear bond strength values were recorded, tabulated and statistically analyzed.
The results of the current study revealed that tested preparation tools had significant influence on the microshear bond strength when using intermediate aggressive self-etch adhesive. In which specimens prepared with coarse and fine-grit diamond stones had a significant increase in microshear bond strength than specimens prepared with medium-grit diamond stones. While specimens prepared with carbide bur #245 had no significant difference in microshear bond strength values than specimens prepared with different grit size diamond stones. The results also revealed that tested preparation tools had no significant influence on the microshear bond strength when using aggressive self-etch adhesive. The results also revealed that aggressiveness of self-etch adhesives had no significant influence on the microshear bond strength when preparing dentin surface with carbide bur #245 and medium-grit diamond stone. However, intermediate aggressive self-etch adhesive demonstrated significantly high microshear bond strength values as compared with aggressive self-etch adhesive when preparing dentin surface with coarse and fine-grit diamond stones.
Conclusions:
Under the conditions of this investigation, the following conclusions could be drawn:
1. Different preparation tools had an influence on the micro-shear resin dentin bond strength when using intermediate-aggressive self-etch adhesives.
2. Different preparation tools had no significant influence on the micro-shear resin dentin bond strength when using aggressive self-etch adhesives.
3. Increasing aggressiveness of self-etch adhesives didn’t translate into higher micro-shear resin dentin bond strength although stronger acid may resulted in considerable dissolution and more defined etching pattern.
4. Intermediate-aggressive self-etch adhesive had a positive influence on the micro-shear resin dentin bond strength than aggressive self-etch adhesives when preparing dentin surface with coarse-grit and fine-grit diamond stones.
Recommendations:
Intermediate aggressive self-etch adhesive is more recommended for dentin surface adhesion with gentle agitation (scrubbing) with micro-brush to the dentin surface for 20 seconds to increase the acidic monomer concentration and increase the micro-shear resin dentin bond strength.