The effect of oral ambient air on shear strength to etched enamel and dentin was determined for OptiBond FL (Kerr Corp., Orange, CA) and Prodigy resin composite (Kerr Corp.). Enamel and dentin specimens of extracted human teeth were treated both in a dry environment and after exposure to oral humidity according to manufacturer's instructions. Shear strengths of this system are 22.6 MPa for etched, dry enamel; 22.2 MPa for etched, wet enamel; and 18.4 MPa for etched, dry or wet dentin. Differences in shear strengths between the wet and dry enamel or the wet and dry dentin were not significant. Multiple Student's t-tests were used for statistical analysis. Fracture modes for all specimens were examined under a stereomicroscope. Within the parameters of this in vitro study, OptiBond FL was not affected by oral humidity.