PurposeThe purpose of this in vitro study was to evaluate the bond strengths of a bonding agent and composite resin system to human enamel and dentin treated with five contaminants (saliva, plasma, zinc oxide–eugenol cement, noneugenol zinc oxide cement, and handpiece lubricant) using air, moisture, and water as controls.Materials and MethodsA commercial bonding agent (Gluma 2000; Bayer AG, Dormagen, Germany) and its composite (Pekafill; Bayer AG) were applied to tooth structure under two conditions (contaminated and re‐etched). Samples were debonded in tension after 24 hours using an inverted, truncated cone bond test.ResultsAmong the controls, the highest bond strengths were obtained to enamel (20 MPa) and dentin (12 MPa) with air drying. Contaminants lowered the bond strength by 20% to 100%. Re‐etching without additional mechanical preparation resulted in bond strengths similar to the air control.ConclusionsBond strength of Gluma 2000/Pekafill to tooth structure is sensitive to common forms of contamination but can be improved by re‐etching after contamination