Surface rehardening of softened enamel by fluoride varnishes

The widespread use of fluoride varnishes as in-office fluoride treatments has raised the question of whether these durable coatings that hold fluoride in the oral cavity for up to 24 hours will provide rapid and detectable surface rehardening benefits of softened enamel. The applications of varnishes are infrequent compared to fluoride dentifrice so immediate benefits are of particular interest. OBJECTIVE: The aim of this research was to determine if softened enamel could indeed be rehardened or repaired by single applications of different fluoride varnishes. Three sequential applications with intermediate specimens analysis were accomplished to determine if the benefit is enhanced with multiple varnish applications. METHODS: 3mm diameter bovine enamel specimens were prepared in the usual manner, then demineralized in a carbopol-lactic acid solution [White, DJ: Caries Res 21 1987 228-42] for a period of 24hrs. Following softening (median VHN = 45), specimens (N=11) were treated with one of 5 varnishes including (a) fluoride-free Vanish®, (b) Vanish®, (c) Modified Vanish® (containing calcium) (d) Prevident® or (e) Enamel Pro® containing ACP and then placed immediately into artificial saliva [ten Cate, et al.: Caries Res 22 1988 20-6] for 24hrs. After 24hrs specimens were removed, cleaned with acetone, and evaluated for surface microhardness. Specimens were re-treated and placed into fresh artificial saliva for another 24hrs. This was repeated again for a total of three 24hr treatments. RESULTS: Mean surface microhardness recoveries (±SEM) after 24hrs were (a)7.74±1.26, (b)10.92±1.84, (c)8.32±2.75, (d)-0.81±1.00 and (e)-5.33±1.23. After three treatments, recovery from baseline was (a)3.88±1.23, (b)10.59±2.17, (c)14.02±1.83, (d)-1.72±1.52 and (e)1.54±3.46 with d = e < a < b £ c (Tukey-Kramer, p>0.05). CONCLUSIONS: The model was sensitive to fluoride's rehardening benefits demonstrated by a clear separation of the fluoride-free Vanish and fluoride-containing Vanish. Two of the varnishes did not exhibit detectable rehardening after three applications. The Modified Vanish exhibited greater rehardening than the unmodified Vanish.