Objective: To evaluate the influence of Expasyl ® gingival retraction paste on the shear bond strength of self-etch and total-etch adhesive systems. Materials and methods:Twenty-four specimens of extracted, caries-free, sound human molars were used in this study. The molars were then cut vertically into halves through the buccal and lingual cusps. Forty-eight specimens were divided into four groups (total-etch, total-etch with Expasyl application, self-etch, self-etch with Expasyl application) and the shear bond strength was tested.Results: Expasyl significantly reduced the shear bond strength of the self-etch and total-etch adhesive systems. The self-etch system showed relatively lower performance compared with the total-etch adhesive system. The shear bond strength values of the total-etch adhesive without Expasyl showed the highest bond strength (21.48 ± 2.89), while the self-etching group adhesive treated with Expasyl showed the lowest shear bond strength value (14.89 ± 1.81). Conclusion:From the observations of this in vitro study, it can be concluded that the use of Expasyl ® gingival retraction system can negatively affect bond strength of adhesives. The total-etch system showed better compatibility to the Expasyl gingival retraction system than the self-etch.