Re- and demineralization characteristics of dentin depending on fluoride application and baseline characteristics in situ.

OBJECTIVES

The aim of this double-blinded, randomized, cross-over in situ study was to evaluate the re- and demineralization characteristics of sound dentin as well as highly and lowly demineralized dentin after the application of different fluoride concentrations.

METHODS

In each of four experimental legs of four weeks 20 participants wore intraoral mandibular appliances containing two (highly demineralized [E]) bovine enamel and four (lowly and highly demineralized [D,D]) bovine dentin specimens (n = 480). Each specimen included one sound (ST) and one demineralized lesion area (DT). The four randomly allocated treatments included the following dentifrices: fluoride-free, zinc-carbonate-nano-hydroxyapatite [nHA], 0 ppm F [negative control,NaF], 1100 ppm F as NaF [standard therapy,NaF] and 5000 ppm F as NaF [positive control,NaF]. Differences in integrated mineral loss (ΔΔZ) and lesion depth (ΔLD) were calculated between values before and after the in situ period using transversal microradiography.

RESULTS

After the in situ period specimens of nHA and NaF showed signs of demineralization, indicated by significantly lower ΔZ&LD values for E and D (only nHA)(p ≤ 0.028), whereas specimens of NaF and NaF showed signs of remineralization, indicated by significantly higher ΔZ values for E (only NaF), D and D (p ≤ 0.012). The correlation between ΔΔZ/ΔΔZ and F was moderate for E(r = 0.497;r = 0.463) and D(r = 0.575;r = 0.598) and strong for D(r = 0.700;r = 0.611)(p < 0.001). No significant differences for ΔΔZ/ΔΔZ were observed between nHA and NaF(p ≥ 0.333;ANCOVA).

CONCLUSION

The present in situ model was capable to reveal a fluoride dose-response on sound, lowly and highly demineralized dentin and also enamel specimens. Furthermore, both fluoride-free dentifrices, one containing nanohydroxyapatite, did not hamper demineralization.

CLINICAL SIGNIFICANCE

The present in situ model was capable to reveal a fluoride dose-response on dentin similar to the anticipated clinical efficacy. Highly demineralized specimens seem to be recommendable for measuring anti-caries effects on dentin in situ. Furthermore both fluoride-free dentifrices, one containing nanohydroxyapatite, did not hamper demineralization. The study was registered in the German Clinical Trials Register (DRKS-ID: DRKS00011653).