Fluoride Dose-Response and Anticaries Effect of Herbal Antibacterial Agents and (Nano-)Hydroxyapatite on Dentin Caries: An In Vitro Study.

Objectives: The aim of the study was to investigate the caries-preventive effect of fluoride-free toothpastes, containing either herbal agents or (nano-)hydroxyapatite.

Methods: Bovine dentin specimens each having a sound [ST], and a demineralized area [DT]) were prepared and randomly allocated to eleven groups (n=187). Treatments during pH-cycling (28 days;6x120min demineralization/day) were brushing 2x/day with: 0ppm F- [NaF0], 500ppm F- [NaF500], 1,100ppm F- [NaF1100], grape seed extract [GSE], (nano-)hydroxyapatite [nHA, HA], melaleuca oil [MO1, MO2, MO-CU] and propolis + myrrh [PM1, PM2] containing dentifrices. Dentifrice slurries were prepared with deionized water (1:3w/w). Differences in integrated mineral loss (∆∆Z) and lesion depth (∆LD) were evaluated before and after pH-cycling using transversal microradiography (TMR).

Results: The correlation between ΔΔZ/ΔLD and F- concentration (NaF0, NaF500, NaF1100) was strong for the DT (rΔΔZ,DT=0.681; p<0.001) and very strong for ST (rΔΔZ,ST=0.861; p<0.001); indicating a fluoride dose-response for both baseline substrate conditions. For ΔΔZDT and ΔLDDT only NaF1100 and GSE revealed significant differences compared with NaF0 (p<0.001, ANOVA). For ΔΔZST and ΔLDST significant differences could be found for NaF1100 and NaF500 compared to all fluoride-free groups (p≤0.002;ANOVA), without significant difference between fluoride-free groups (p=1.000;ANOVA). For DT and ST a hypermineralized surface layer and no surface loss could only be observed when fluoride was present.

Conclusion: A dose-response for fluoride concentrations was observed in this mild demineralization pH-cycling model. Fluoride-free dentifrices containing grape seed extract or melaleuca oil showed certain preventive effect against further progression of root caries lesions. However, surface loss was observed for all fluoride-free dentifrices.