Because many factors influence the acid-forming ability of dental plaque in the mouth, a model system was used in which reproducible Stephan curves could be generated after exposure of a gel-stabilized plaque to sucrose. Simulation of the use of a high-bicarbonate dentifrice at a time when plaque pH had fallen to about 4.5 caused a rapid return of the pH toward neutrality, whereas simulation of the use of a low-bicarbonate dentifrice had much less effect.