Intra-oral remineralization of enamel with a MFP/DCPD and MFP/silica dentifrice using surface microhardness

The present study was undertaken to ascertain the effect of dicalcium phosphate dihydrate (DCPD) abrasive in a dentifrice on the remineralizaton of enamel using a surface microhardness technique. The method of assessing enamel remineralization via surface microhardness (SMH) was validated in a randomized, crossover, double-blind, intra-oral remineralization study conducted with 12 healthy adults. Enamel demineralization was achieved in vitro by covering bovine enamel blocks with exogenous oral bacteria, S. Mutans 1600 Ingbritt, containing glucan which was then exposed to sucrose. In the intra-oral treatment phase, subjects were fitted with oral maxillary palatal retainers, each holding four demineralized enamel blocks. Subjects brushed their teeth for 30 seconds with a test dentifrice, swished for an additional 60 seconds, rinsed with water and then retained the blocks intra-orally for 4 hours. Percent mineral recovery for each enamel block was calculated as the ratio of the changes in enamel microhardness due to treatment (remin) and sucrose challenge (demin). Treatments included DCPD-based dentifrices containing 0, 250 and 1000 ppm fluoride (F) from sodium monofluorophosphate (MFP). Using SMH, respective mean percent mineral recoveries of 5.7, 18.7 and 41.4% were obtained. All ADA criteria for model validation were fulfilled. This same model was then used to compare the remineralization effects of a silica placebo, DCPD placebo, 1000 ppm F MFP/silica and 1000 ppm F MFP/DCPD dentifrice. Mean percent mineral recoveries of -0.9, 24.1, 30.2 and 55.7% were obtained, respectively. The MFP/DCPD dentifrice was superior to MFP/silica (<0.01) with use of the MFP/DCPD dentifrice when compared to MFP/silica or the silica placebo. These results indicate that more active calcium and a higher degree of saturation (DS(EN)) with respect to enamel exists for an extended period of time after use of a MFP/DCPD dentifrice. Since an elevation in DS(EN) is considered a major parameter controlling the extent of enamel remineralization, this finding may partly explain the superior remineralization of enamel observed with the MFP/DCPD dentifrice. The significant increases in calcium activity and intra-oral enamel remineralization by the DCPD-based dentifrice are consistent with earlier findings that a DCPD abrasive provides added benefit for enamel remineralization.