الفهرس 
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Abstract
Our study aimed to investigate the effect of EGCG different application techniques on the bond strength of dental adhesive to dentin under different aging methodologies. An etch and rinse dental adhesive was used. Also, the dental adhesive degree of conversion was analysed after EGCG application.
According to literature, a Matrix metalloproteinases activity was detected after the etching step of etch and rinse dental adhesives. Matrix metalloproteinases were reported to have a collagen degradation ability which would adversely affect the bond strength to dentin. EGCG is one of the natural flavonoids that are reported to have a favourable effect on the dental adhesive bond strength to dentin. This was suggested to be achieved through collagen cross-linking and matrix metalloproteinases inhibitory effect of EGCG.
EGCG was applied to dentin in a concentration of EGCG 200. It was applied in the form of EGCG/ adhesive complex or an EGCG adhesive pre-conditioner. Micro-shear bond strength testing of the dental adhesive in the two different methodologies was measured in comparison with the control group. Bond strength testing was performed using a universal testing machine ((Lloyd LR 5k, Lloyd Instruments Ltd., Hampshire, UK ). Load was applied with a cross head speed of 1mm/min until debonding occured, and then micro shear stress was automatically measured through Nexogen software. After micro-shear bond strength testing, mode of failure of the debonded specimens was analysed using a light microscope (80X) .
Summary and conclusions
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The ability of EGCG to preserve resin dentin bond durability was challenged by specimen storage in distilled water for 6 months. Also, thermocycling was one of the aging methodologies to evaluate the effect of EGCG on the bond strength of dental adhesive to dentin. Another importance of thermocycling was to test the ability of EGCG to cross-link collagen and increase its denaturation temperature.
Scanning electron microscope imaging (SEM) of the resin dentin interface (3000X) was performed using Quanta 250 FEG (Field Emission Gun) attached with EDX Unit (Energy Dispersive X-ray Analyses). SEM imaging allowed hybrid layer analysis after different EGCG application techniques and different aging methodologies.
Degree of conversion of the dental adhesive was measured after EGCG application in the form of a complex or a pre-adhesive conditioner. Degree of conversion measurements was performed using chemical analysis through FTIR (Fourier Transfer Infra-Red spectroscopy).
Results of the micro-shear bond strength testing showed a significant increase in the bond strength after EGCG application in the two different techniques. The application of EGCG in the form of an adhesive complex showed the significantly highest values. After 6 month water storage and thermocycling , specimen lacking EGCG in the bonding procedure showed a significant deterioration in the bond strength. EGCG when used as an pre-adhesive conditioner, showed a significant decrease in the bond strength after both water storage and thermocycling. Still, EGCG in the adhesive pre-conditioner showed significantly higher bond strength in comparison with the control
Summary and conclusions
138
group. The use of EGCG as an adhesive complex was able to maintain bond strength after water storage. Also, thermcycling showed significantly higher bond strength when EGCG was applied in the form of adhesive complex.
On analysing the failure mode among different subgroups, the predominant fracture mode among all subgroups was a mixed failure of the adhesive and resin composite. After EGCG application no mixed failure of the adhesive and dentin was detected except for specimens being thermocycled.
SEM images were supporting to the bond strength tests results only the EGCG/adhesive complex was able to preserve hybrid layer thickness after aging and thermocycling. The EGCG pre-adhesive conditioner showed a decrease in hybrid layer thickness. For the control group, the hybrid layer was very thin in discrete areas after water storage and no clear hybrid layer was detected after thermocycling.
Results of the degree of conversion measurements showed that EGCG didn’t affect the polymerization kinetics of the dental adhesive when applied according to the suggested methodologies.
Finally, within the limitations of the present study, we can conclude that the incorporation of EGCG in the bonding procedure to dentin had a great influence on the bond strength.