Effect of green tea extract antioxidant on dentin shear bond strength and resin-tag penetration depth after non-vital bleaching

Background: 35% Hydrogen peroxide (H 2 O 2 ) as an active material for internal bleaching produce free radicals that can affect the adhesive system. Application of 10% and 35% green tea (GT) extract as an antioxidant after 2 minutes are expected can remove free radical residues. The aim of this study is to evaluate the effect of 10% and 35% GT extract after 2 minutes of application on dentin shear bond strength and resin tags penetration depth after non-vital bleaching. Methods: : The crown part of 30 extracted healthy human premolars were cut horizontally 2 mm from the cementoenamel junction, then split in mesio-distal direction. The specimens were divided into five groups: normal dentin, post-bleaching dentin, delayed 2 weeks, 10% GT, and 35% GT group. Non-vital walking bleach with 35% H 2 O 2 gel was done to all groups except control group. Soon after, 10% and 35% GT extract gel were applied on dentin for 2 minutes, then the specimens were rinsed off with distilled water for 2 minutes and dried. All specimens were etched and bonded with an etch-and-rinse adhesive system and filled with resin composite. The shear bond strength assessment was done using a Universal Testing Machine with a cross-head speed of 0.5 mm/minute. Confocal laser scanning microscopy with a wavelength of 560 nm and a lens magnification of 40x was used to analyze the resin tag penetration. Data were analyzed by one-way ANOVA. Results: : There was a significant difference in resin tag penetration depth and shear bond strength between 10% and 35% GT group (p < 0.05). The 35% GT group resulted in a significantly longer resin tag penetration than the 10% GT group. Conclusions: : The application of 35% GT extract is more effective than 10% GT extract as an antioxidant for increasing the shear bond strength of composite resin after internal bleaching.