In vitro microhardness studies on a new anti-erosion desensitizing toothpaste.

OBJECTIVE: To evaluate in vitro the efficacy of a new anti-erosion desensitizing toothpaste to inhibit enamel surface softening by a dietary acid, and promote re-hardening of artificial erosive lesions. METHODOLOGY: The ability of the toothpaste to inhibit formation and promote repair of erosive lesions in human enamel has been investigated. In an enamel surface softening study, sound human enamel was pre-treated with one of four toothpaste slurries for two minutes, before exposure to 1.0% citric acid, pH 3.8, for a total of 30 minutes. The surface microhardness (SMH) of the specimens was determined at baseline and at 10-minute intervals using a Struers Duramin-1 microindentor. In an enamel re-hardening study, the erosive lesions were prepared by exposure of the specimens to 1.0% citric acid, pH 3.8, for 30 minutes. After two minutes treatment with a toothpaste slurry, lesion repair was monitored by SMH after 4, 24, and 48 hours incubation in artificial saliva. This remineralizing phase was modified by the addition of an aliquot of the relevant toothpaste slurry, to mimic in vivo carryover of the formulation. RESULTS: The new test formulation, Elmex Sensitive, and Colgate Sensitive exhibited statistically significant inhibition of citric acid-mediated enamel surface softening versus a fluoride-free placebo at all time points. The test toothpaste gave statistically superior protection against the erosive challenge compared to Elmex Sensitive and Colgate Sensitive after 20- and 30-minute exposures. In the remineralization studies, erosive lesions treated with the test toothpaste exhibited statistically superior re-hardening versus lesions treated with Elmex Sensitive and Colgate Sensitive after 24- and 48-hour incubation in the artificial saliva. Lesions treated with Elmex Sensitive re-hardened to a statistically significant extent versus the fluoride-free placebo toothpaste. A re-hardening study, in which a series of the new toothpaste-base formulations containing increasing concentrations of NaF were evaluated, showed a clear fluoride dose response. CONCLUSION: The present microhardness studies show that treatment with fluoride-containing toothpastes helps protect sound enamel from acid-mediated surface softening, and promotes re-hardening of erosive lesions. The new test toothpaste exhibited statistically superior efficacy to Elmex Sensitive and Colgate Sensitive in both in vitro models.