An investigation was conducted to determine the clinical adhesiveness of some commonly used dental materials. Contact angle measurement data, obtained under clinical conditions, were used to calculate thein vivo-critical surface tensions for enamel, gold, stainless steel, and a resin polymer. The results of this study showed that the adhesive properties of the artificial surfaces studied were considerably modified in the oral environment. Thus, after two hours these solids with diverse original surface chemistries were observed to producein vivo-critical surface tensions common to those recorded for enamel. The observed changes were attributed to be adsorbed biofilm (acquired pellicle), which forms on all solid surfaces in the oral cavity.