الفهرس 
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Abstract
This research was designed to investigate the effect of smear layer thickness and chlorhexidine application on shear bond strength of resin composite bonded to normal dentin utilizing a universal adhesive in self-etch mode.
A total of 24 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 48 dentin specimens. Forty dentin specimens were used in shear bond strength testing and eight specimens for scanning electron microscopic examination. Forty dentin specimens were divided into two main groups according to smear layer thickness. Each main group was subdivided into two subgroups according to 2 % Chlorhexidine treatment of dentin surface.
The Single Bond Universal adhesive was then applied to the dentin surface according to manufacturers’ instructions. The resin composite was packed inside the hole of a specially designed split Teflon mould, then the resin composite was cured for 20 seconds using visible light curing unit.
Dentin specimens were then loaded to failure using specially constructed attachment fixed to a universal testing machine at across head speed of 0.5 mm/minute. The shear bond strength values were recorded, tabulated and statistically analyzed. ESEM analysis of dentin surface was performed.
The results of the current study revealed that the application of 2% chlorhexidine as a cavity disinfectant had a significant reduction of the shear bond strength. The results also revealed a highly significant influence of the smear layer thickness tested on the shear bond strength, where thin smear layer demonstrated significantly high bond strength values as compared with thick smear layer.
Under the limitations of this research, the following conclusions were evident:
1- Use of 2% chlorhexidine as a surface treatment negatively impacted the shear bond strength of the tested universal adhesive to dentin.
2- Dentine surface preparation had an influence on the shear bond strength. Thick smear layer had an undesirable effect on the shear bond strength of the tested universal adhesive to dentin.