In an erosive process, the dissolution pH of the products deposited on enamel by fluoride dentifrices is exceeded. The addition of sodium hexametaphosphate (HMP) has been shown to increase the ability of fluoridated dentifrices in caries processes in vitro. However, it was not determined whether dentifrices containing HMP would have an effect in the erosive process. Thus, the present in vitro study will evaluate the effect of fluoride dentifrice containing sodium hexametaphosphate on initial enamel erosion. Bovine enamel blocks (n=48) will be selected by initial surface hardness (SHi) and subjected to 4 experimental treatments (12 blocks/group): placebo (without F and without HMP), 1100 ppm F (1100), 1100 ppm F associated with 1% HMP (1100HMP) and 1% HMP (HMP). The blocks will be immersed in dentifrice suspension only once. Next, 4 erosive challenges (citric acid, 0.75%, pH 3.5, 1 minute, under agitation) will be performed. Final surface hardness measurements (SHf) will be performed after each challenge, to calculate the percentage of surface hardness change (%SHC). For analysis of the data the dentifrices and the time of exposure to the acid will be considered as factors of variation. The %SHC variable at each time will be submitted to analysis of variance of repeated measurements at two criteria followed by Student-Newman-Keuls test (p<0.05).
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