 The aim of this study was to investigate the buffering effect of a calcium glycerophosphate-fluoride CaGP-F dentifrice on in vivo dental biofilm after a cariogenic challenge and evaluate its probable 12-hour protective effect. Twelve young adults took part in this randomized, double blind, 14-day 4-phase crossover study. Between each phase, the volunteers had a 1-week wash-out period. Coded dentifrices were randomly assigned to the volunteers: A no F and no CaGP; B CaGP-only 0.13; C F-only 1500 ppm ppm parts per million of fluoride which is equivalent to mgkg; D CaGP-F 0.13, 1500 ppm, respectively. The pH measurements were taken from a single-site using a microelectrode, with salt bridge established by a 1M KCl one molar potassium chloride solution with a reference electrode. pH measurements were taken at 0 baseline, 1, 7, 14 and 21 min minutes after a cariogenic challenge 10 wv sucrose solution, wv percent weight per volume. Four sets of measurements were carried out: D0BS before test dentifrice usage; D01min 1-min after test dentifrice usage; and D712h 7 days and D1412h 14 days using the test dentifrice, 12 hours hafter brushing. Stephen curves and mean AUC area under the curve were obtained. 