Resin dentin bonding can be performed immediately after sodium perborate bleaching without the need for sodium ascorbate pretreatment; however, the two-step self-etching adhesive performed better than the all-in-one system. The all-in-one adhesive, Xeno IV, exhibited significantly lower microshear bond strength when bonded to positions associated with larger-diameter dentinal tubules. SUMMARYThis was an in vitro study to evaluate the effect of sodium ascorbate on the microshear bond strength (MSBS) of resin composite to sodium perborate-bleached dentin. Molar dentin sections were divided into six groups: 1) control, 2) sodium perborate (SP) bleach and immediate bonding, 3) SP and 30 second sodium ascorbate (SA); 4) SP and 1 minute SA; 5) SP and 2 minute SA; and 6) SP and 7 day delay before bonding. They were further divided into two-step self-etching (Clearfil SE Bond) or allin-one self-etching (Xeno IV) adhesive systems. Resin composite microtubes were bonded according to dentin location-center, pulp horn, and peripheral positions-and an MSBS test was carried out. Failure mode was determined using light microscopy and scanning electron microscopy. There were no significant differences between the treatment types/groups. MSBSs were significantly higher for two-step self-etching adhesive compared with all-in-one self-etching adhesive (p=0.028). For the all-inone adhesive, MSBSs at the center and pulp horn positions were significantly lower than the peripheral positions (p,0.001). All-in-one groups had significantly more adhesive failures than two-step adhesive groups (p=0.015). The odds of adhesive failure were higher at the pulp horn position than the peripheral position (p=0.004). Sodium perborate bleaching of dentin had no effect on MSBS or mode of failure for either two-step or all-in-one selfetching adhesives; therefore, the effect of sodium ascorbate was negligible. The two-step