EVALUATION OFMICROTENSILE BOND STRENGTH AND NANOLEAKAGE AFTER DOUBLE LAYER ADHESIVE COATING APPLICATION USING BULK FILL COMPOSITE.

Aim:The present study used toevaluatenanoleakage and microtensile bond strength after double layer adhesive coating application. The tensile bond strength of an adhesive system is mostly influenced by the hybrid layer, followed by resin tags in the dentinal tubule and finally by chemical bonding. However, porosities can be observed at the bottom of hybrid layers. This phenomenon was termed ?nanoleakage? Sano et al,They had seen incomplete penetration of hybrid layers during adhesive bonding techniques.Thenanoleakage effect has been discussed to be one factor negatively affecting the quality of dentinal bonding. Influence of nanoleakage on microtensile bond strength was determined using different visualization techniques. For instance, resin?dentin specimens were prepared and immersed in silver nitrate that penetrated into nanoleakage. Subsequently, specimens were broken at the adhesive interface (commonly using tensile testing), and nanoleakage was visualized indirectly on the exposed surface using scanning electron microscopy (SEM). It has been postulated that, between polymerization shrinkage and microtensile bond strengths (μTBS) a highly significant correlation was found because forces developed during the polymerization of dental restorative composites placed in a restricted setting, cause tension in the material, with possible subsequent distortion of the bond to the tooth. Material and methods: 40 human molars stored in deionized water will used. Teeth will be divided into four equal groups according to application mode (self-etch vs. Etch-and-rinse mode). group A: using filtekTM bulk fill with single bond universal adhesive (self-etching mode), then application of hydrophopic resin coating (Heliobond). group B: using filtekTM bulk fill with single bond universal adhesive (self-etching mode), without application of hydrophobic resin coating. group C: using filtekTM bulk fill with single bond universal adhesive (etch and rinse mode), then application of hydrophobic resin coating. group D: using filtekTM bulk-fill with single bond universal adhesive (etch-and-rinse mode), without application of hydrophobic resin coating. Results: It was found that the filtekTM bulk fill composite with self-etch mode application of adhesive followed by coating application revealed the highest mean ?-TBS value (41.9 MPa) followed by filtekTM bulk fill composite with self-etch mode application of adhesive without coating application (39.7MPa). FiltekTM bulk fill with self-etch mode followed by coating, showed the highest Nanoleakage results (55.4%), while FiltekTM bulk fill with etch-and-rinse mode followed by coating, showed the lowest Nanoleakage results (39.9%).Conclusion: multiple consecutive coating during dentin bonding improved the bond strength for etch-and-rinse adhesive and reduced nanoleakage due to increases in the amount of resin impregnation within the hybrid layer. Nevertheless the better performance of the bulk-fill composites, all clinician should not consider that the bulk-fill composites are perfect substitutes for conventional composites