Fig. 1

a Representative SEM micrograph of the resin-dentin interface formed by the Gluma Comfort Bond + Desensitizer two-step etch-and-rinse adhesive (×2000 magnification). Samples were storage in water for 24 h (CR composite resin, HL hybrid layer, RT resin tag). b Representative SEM micrograph of the resin-dentin interface formed by the Gluma Comfort Bond + Desensitizer two-step etch-and-rinse (×2000 magnification). Samples were storage in water for 1 year (CR composite resin, HL hybrid layer, RT resin tag). c Representative SEM micrograph of the resin-dentin interface formed by the Optibond FL three-step etch-and-rinse adhesive (×2000 magnification). Samples were storage in water for 24 h (AL adhesive layer, HL hybrid layer, RT resin tag). d Representative SEM micrograph of the resin-dentin interface formed by the Optibond FL three-step etch-and-rinse adhesive (×2000 magnification). Samples were storage in water for 1 year (AL adhesive layer, HL hybrid layer, RT resin tag). e Representative SEM micrograph of the resin-dentin interface formed by the One Coat Bond SL two-step etch-and-rinse (×2000 magnification). Samples were storage in water for 24 h (CR composite resin, HL hybrid layer, RT resin tag). f Representative SEM micrograph of the resin-dentin interface formed by the One Coat Bond SL two-step etch-and-rinse (×2000 magnification). Samples were storage in water for 1 year. Arrows show porosities in resin tags (RT) (CR composite resin, HL hybrid layer). g Representative SEM micrograph of the resin-dentin interface formed by the Peak Universal Bond two-step etch-and-rinse (×2000 magnification). Samples were storage in water for 24 h (CR composite resin, HL hybrid layer, RT resin tag). h Representative SEM micrograph of the resin-dentin interface formed by the Peak Universal Bond two-step etch-and-rinse (×2000 magnification). Samples were storage in water for 1 year (CR composite resin, HL hybrid layer, RT resin tag)