Objective: The effect of enamel caries lesion baseline severity on fluoride dose-response under pH cycling conditions was investigated.
Methods: Human enamel specimens (n=144) were demineralized (0.1M lactic acid, 0.2% Carbopol 907, 3mM CaCl2×2H2O, 6mM KH2PO4, 63mM KCl, 3mM NaN3, pH 5.0) for 8; 16; 24 or 36h. Lesions were allocated to treatment groups (0; 83; 367ppm fluoride as sodium fluoride) based on Vickers surface microhardness (VHN) and pH cycled for 5d. The cycling model comprised 3×1min fluoride treatments sandwiched between 2×60min demineralization challenges with specimens stored in artificial saliva in between. VHN was measured again and changes vs. baseline calculated (ΔVHN). Data were analyzed using two-way ANOVA (p<0.05).
Results: Sound enamel VHN did not vary between or within groups (mean VHNsound = 345). Increased demineralization times led to increased surface softening. Fluoride dose-response was observed in all groups. Lesions initially demineralized for 16 and 8h showed similar overall rehardening and more than 24 and 36h lesions, which were similar. The lesion severity×fluoride concentration interaction was significant (p<0.001) for ΔVHN. Table shows results:
Lesion | Fluoride | VHNlesion (mean±sd) | ΔVHN (mean±sd) | Stats for ΔVHN |
8 | 0 | 176±16 | -27±30 | G |
8 | 83 | 178±15 | 43±17 | BC |
8 | 367 | 180±16 | 85±16 | A |
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16 | 0 | 122±11 | -7±10 | EFG |
16 | 83 | 123±10 | 30±14 | CD |
16 | 367 | 124±11 | 91±13 | A |
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24 | 0 | 93±11 | -13±5 | FG |
24 | 83 | 95±11 | 12±7 | DE |
24 | 367 | 96±10 | 59±11 | B |
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36 | 0 | 72±8 | 3±28 | EF |
36 | 83 | 73±8 | 7±4 | DEF |
36 | 367 | 74±8 | 29±17 | CD |
The 8h lesions showed the greatest fluoride response differential (367 vs. 0 ppm F) which diminished with increasing lesion baseline severity. The extent of rehardening as a result of the 0 ppm F treatment increased with increasing lesion baseline severity, whereas it decreased for the fluoride treatments.
Conclusions: Lesion baseline severity impacts the extent of the fluoride dose-response.