Purpose: Provisional restorations exhibit various degrees of microleakage when cemented. Incorporation of quaternized polyethyleneimine nanoparticles (QPEI) into provisional cements may be effective against bacteria in vivo. Materials and Methods: Nine polymethylmethacrylate provisional restorations in human volunteers were evaluated after cementation with and without QPEI nanoparticles. Bacterial load in the provisional cement was assessed after 1 week of cementation. Results: The number of colonyforming units in the cement with QPEI was significantly lower (P .05) than in the control cement. Conclusion: The results of this in vivo study clearly indicate that provisional cement incorporating QPEI nanoparticles significantly reduces viable bacterial counts in the provisional cement in all patients.