The aim of this study was to compare the ability of quantitative light-induced fluorescence (QLF) and surface microhardness (SMH) to measure the remineralization of enamel subsurface lesions, using a pH-cycling model including treatment with 0-ppm, 550-ppm or 1,100-ppm sodium fluoride (NaF) dentifrices. Methods: Subsurface lesions were created in human enamel specimens (n = 36) and exposed to a remineralization pH-cycling model for 14 days. The pH-cycling model was performed in an automated system where specimens were subjected to a demineralizing solution for 20 min and treatment for 1 min and were then remineralized for 7 h 39 min, 3 times daily. The treatments consisted of 3 NaF, silica-containing dentifrices (0 ppm F; 550 ppm F; 1,100 ppm F). The outcome variables were: change from baseline in surface hardness and percentage change from baseline in fluorescence. An ANCOVA explored differences between different treatment groups (at the p < 0.05 level). Associations between QLF and SMH were evaluated using Spearman's correlation coefficient. Results: The percentage SMH changes were 14.9 ± 2.1%, 56.6 ± 9.6% and 103.9 ± 14.6% for the 0-, 550- and 1,100-ppm F dentifrices, respectively. The percentage fluorescence changes were 15.6 ± 7.1%, 59.8 ± 11.9% and 85 ± 13.2%, respectively. The differences between all pairwise comparisons were statistically significant for both methods (p = 0.001). QLF correlated with SMH (r = 0.67). Conclusions: Both the SMH and QLF methods demonstrated a significant F dose response for toothpaste in this in vitro remineralization model, and both methods were able to distinguish treatments with different F levels.

We evaluated the potential of a pyrophosphate-fluoride solution to affect the remineralizing-demineralizing equilibrium, i.e., caries-inhibiting/-promoting effects on enamel in vivo. Fifteen subjects carried dentin blocks and enamel thin sections with artificial caries lesions in removable partial dentures for periods of two weeks, during which time they rinsed twice daily in a double-blind, randomized cross-over design with solutions containing (a) 90 ppm F, (b) 90 ppm F and 1% pyrophosphate, or (c) no active agents (placebo). A severe cariogenic challenge provided to the lesions by plaque under a stainless steel mesh cover resulted in the placebo-treated lesions losing 70.2% +/- 72.1% mineral. The pyrophosphate rinse with fluoride held the mineral loss to only 28.1 +/- 52.8%, while the fluoride rinse without pyrophosphate held the loss to 24.2 +/- 50.1%. The differences between the fluoride and placebo results were significant (p less than 0.01), but the difference between the two fluoride groups was not. A large amount of fluoride was deposited in the dentin lesions. In the surface layer, the concentration was increased from 1000 ppm F to more than 2300 ppm F by both fluoride treatments. The concentration of fluoride in both groups of fluoride-treated lesions further increased to more than 3500 ppm F in the approximate center of the lesion before declining in deeper layers toward the level found in the placebo-treated group. The findings from both mineral change and fluoride uptake phases of this study show that in the presence of 90 ppm F, 1% pyrophosphate did not promote demineralization of artificial caries lesions.

Eighty thin enamel sections with artificially-formed caries lesions were implanted in the buccal surfaces of molars (in the removable partial dentures of ten subjects) and covered with a steel mesh for plaque accumulation to occur. The mesh was placed in contact with the enamel surface in half the lesions and 0.5 mm above the lesions in the other half, thus facilitating formation of thin and thick plaque samples. Following two-week use of a non-fluoride dentifrice, the lesions were analyzed for mineral change by quantitative microradiography. Significant mineral was lost from lesions in both groups, but the loss was twice as large in the thick-plaque group. These findings are important to in vivo remineralization models, since they show that plaque thickness should be controlled for minimization of variation.

Enamel slabs and thin sections with artificially formed caries lesions were placed in the removable dentures of 15 subjects who brushed them three times daily for 2 weeks with a 1.3% pyrophosphate/1,100 ppm F/1.5% Gantrez dentifrice, a 1,100-ppm F dentifrice without pyrophosphate or Gantrez, or a placebo dentifrice in a double-blind, crossover study. Analysis of the thin sections by quantitative microradiography showed that the pyrophosphate/F dentifrice remineralized the lesions 15.9% (p < 0.05) and the fluoride dentifrice 11.2%, whereas the placebo produced 4.4% demineralization. Fluoride uptake by the enamel slabs was similar for both fluoride dentifrices and significantly greater from the placebo dentifrice (p < 0.05). The findings suggest that the anticaries mechanisms of fluoride include not only the prevention of demineralization, but also the promotion of remineralization.

The purpose of this study was to determine whether an in situ remineralization model was able to show a difference in the effects of two dentifrices of different fluoride concentrations and significantly different clinical efficacies. Three dentifrices were tested in a double-blind, cross-over study design. The products contained 0 ppm F, 250 ppm F, or 1000 ppm F from sodium fluoride and were formulated with a silica base according to the formulations used in a human caries trial (Koch et al., 1990). Nineteen subjects each carried three or four thin sections of enamel in their partial dentures. The thin sections, containing artificial caries lesions, were covered with a steel mesh to provide space for plaque formation and then brushed in situ three times daily with the dentifrices. Following the two-week treatment periods, the specimens were removed from the dentures and analyzed for changes in mineral content. The findings showed that the placebo dentifrice (0 ppm F) resulted in 56.8 +/- 74.3% demineralization, the 250-ppm-F dentifrice produced 12.9 +/- 41.3% demineralization, thereby showing partial caries protection, and the 1000-ppm-F dentifrice produced 17.3 +/- 32.1% remineralization. Linear regression analysis showed that the percent remineralization was significantly related to the fluoride concentration in the dentifrice (p less than 0.001). The 250-ppm-F dentifrice was also significantly less effective than the 100-ppm-F dentifrice (p = 0.04, one-tailed Fisher Protected LSD test). These findings are in accord with the human caries trial and support the use of the present in situ remineralization model for prediction of the anticaries efficacy of fluoride dentifrice products.