J.R. Mellberg

In vivo Remineralization by a Monofluorophosphate Dentifrice as Determined with a Thin-section Sandwich Method

Artificial caries lesions were formed in thin sections of subsurface enamel sandwiched between protective sheets of plastic. Six lesions were placed into the buccal surfaces of lower partial dentures of seven subjects, covered with a stainless steel mesh to provide a plaque cover, and brushed with either a sodium monofluorophosphate or placebo dentifrice for four weeks, by means of a double-blind random cross-over design. Analysis of the lesions by quantitative microradiography revealed that significant remineralization (21%) occurred in the monofluorophosphate group and significant further demineralization (27%) in the placebo group. The difference between the active and placebo treatments was significant (p = 0.02), showing that the monofluorophosphate was effective not only in preventing lesion progression but also in promoting mineral deposition. The simultaneous presence of remineralized lesions and lesions with increased demineralization showed the non-uniformity of conditions within a mouth.

Fluoride Uptake by Artificial Caries Lesions from Fluoride Dentifrices in vivo

Artificial caries lesions were implanted in removable dentures and were brushed for two wk or two mo with several fluoride-containing dentifrices. An analysis of thin layers of enamel removed from the lesions showed that more fluoride was deposited after two mo of brushing, and that fluoride deposition from the sodium monofluorophosphate was similar to deposition from the sodium fluoride dentifrice.

A Study of the Ability of an in situ Remineralization Model to Differentiate between the Effects of Two Fluoride Dentifrices that Produced Significantly Different Clinical Caries Results

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 < 0.001). The 250-ppm-F dentifrice was also significantly less effective than the 1000-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.

Evaluation of Topical Fluoride Preparations

For practical reasons, evaluation of topical fluoride products must depend upon clinical and laboratory assessments. While not always a good predictor of clinical efficacy by itself, fluoride uptake is the most commonly used laboratory test. A consideration of the relationship between possible anticaries mechanisms of fluoride, different product types, and the meaning of various kinds of fluoride uptake data suggests that both the amount of fluoride taken up by early lesions and the amount of ambient fluoride present at a cariogenic site may play key roles in determining the efficacy of a product. While formulations applied annually or semi-annually probably depend on fluoride deposition, those used daily might not. There are no clear data supporting the superiority of one fluoride compound over another, even for infrequently used products, although there are significant differences among them in fluoride uptake by enamel. This suggests that fluoride uptake in vivo at a cariogenic site might actually be different from that suggested by in vitro data, or that larger differences are required for a clinical effect to be observable. Clinical data support the conclusion that a large increase in the fluoride concentration of a product will somewhat increase its Anticaries effectiveness, although the increase will not be linearly related to concentration. There also are no obvious differences in clinical effectiveness caused by the addition of gelling agents to topical solutions. Fluoride varnishes are clinically effective but have not been shown to be superior to topical solutions or gels. The abrasive, humectant, and thickener systems used in most prophylaxis pastes reduce both fluoride uptake and clinical effectiveness, even though, in some cases, the components may be chemically compatible. Precleaning prior to a topical application appears unnecessary, but a delay in rinsing after the application and longer application times appear beneficial. Mouthrinse formulations essentially differ only in fluoride source, concentration, and pH. Higher fluoride concentrations are likely to provide greater benefits, but pH differences probably will not. The stannous ion in SnF2 rinses is unstable, and its effect on anticaries activity is unknown. This review of the composition of topical fluoride products emphasizes the lack of clear evidence for the making of definite scientific judgments regarding relative clinical efficacy. Future efforts should be directed toward the development of test models that utilize the natural oral environment, so that more precise and valid comparison of compositions may be made.

Remineralization in vivo of Artificial Caries Lesions by a Monofluorophosphate Dentifrice

Blocks of human enamel containing artificial caries lesions covered with Dacron mesh were implanted in the dentures of 14 subjects. Each subject, according to random design, was instructed to brush his/her teeth, with their denture in place, three times daily for 2 months using a sodium monofluorophosphate-dicalcium phosphate dihydrate (MFP/DCPD) dentifrice or a placebo dentifrice containing no fluoride, soluble calcium or phosphate. Every subject used both dentifrices in a crossover, double-blind design. Matched pairs of enamel blocks with artificial lesions were used, one of which was treated with a dentifrice and one kept untreated as a control. Statistically significant remineralization as determined by several parameters occurred in the artificial lesions treated with both the MFP/DCPD and the placebo dentifrices (p

Effect of Calcium in Model Plaque on the Anticaries Activity of Fluoride in vitro

The uptake of calcium by a polysaccharide (agarose) gel used as a model for plaque from a two-step treatment (consisting of a calcium rinse followed by a fluoride treatment) and the effect ofthe deposited calcium in model plaque on caries lesion formation in enamel were determined. Calcium uptake was measured by treatment of the model plaques with [45Ca]-CaCl2 solutions with or without NaF. A two-step treatment consisting of calcium followed by fluoride produced a 100% increase in calcium content of model plaque, presumably due to the formation of CaF2, compared with a treatment with artificial saliva followed by calcium alone. The effects of these increased plaque minerals on caries lesion formation were studied by subjecting model-plaque-covered enamel blocks to a cyclic demineralization-remineralization treatment. Artificial-plaque-covered enamel blocks were treated daily with 180 ppm calcium for ten min, then 100 ppm fluoride for ten min, followed by demineralization for 16 h, and finally, remineralization for seven h and 40 min. After five days, the blocks were sectioned, and lesion formation was determined by microradiography-microdensitometry. Artificial plaque treated with a calcium rinse followed by a fluoride rinse reduced lesion size by 90%, compared with a 68% reduction by a fluoride rinse alone. When the experiment was repeated with a simulated pre-brush calcium rinse (180 ppm calcium) followed by a fluoride dentifrice suspension (110 ppm fluoride), lesion size was reduced by 46%, compared with a 32% reduction by the fluoride dentifrice suspension alone.

Remineralization by a Monofluorophosphate Dentifrice in vitro of Root Dentin Softened by Artificial Caries

Artificial caries-softened dentin lesions in root surfaces were treated with 50% slurries of a monofluorophosphate (MFP®) dentifrice or a placebo dentifrice twice daily for ten days. Between dentifrice treatments, the lesions were kept in a remineralizing solution. Both treatments resulted in statistically significant remineralization, with the MFP dentifrice being significantly better than the placebo. Deposition of new mineral from the MFP dentifrice occurred about equally at or within the surface zone and at the deepest part of the lesion. Mineral deposition from the placebo appeared to be more uniformly distributed within the lesion.

Acceleration of Remineralization in vitro by Sodium Monofluorophosphate and Sodium Fluoride

Sixteen groups of artificial caries lesions were treated with from 75-900 ppm F from MFP, NaF, combinations of the two, or water for five min twice daily for ten days. Between treatments, the lesions were placed in a remineralizing solution at 37°C. Quantitative microradiography of the treated lesions vs. matched untreated lesions showed significant remineralization of the surface layer and lesion body of all groups, including the water-treated control group. Fluoride treatments improved remineralization. Increasing the concentration of NaF had only a small effect on remineralization, but MFP was more effective at higher concentrations. Evaluation of MFP/NaF mixtures showed that greatest remineralization was obtained from a 75/225 ppm F ratio of NaF/ MFP. This combination of F- and PO3F= was more effective than a fluoride concentration of 300 ppm F from either agent alone.

Analysis of Dental Hard Tissue by Computerized Microdensitometry

One method of quantitating mineral content in thin sections of dental hard tissue is microdensitometry of contact radiographs. This method is often applied to analysis of artificial caries lesions. Because there is great inter- and intra-tooth variability, a single microdensitometric scan will not accurately reflect the content or distribution of mineral within an individual lesion, or within a group of lesions. To increase the number of replicates that can be handled routinely, a computer-driven microdensitometer has been used with a step series of aluminum and enamel to quantitate mineral content values at approximately 1-μm intervals. Accurate assessment of an individual lesion was made possible by averaging multiple scans of the lesion on each of several thin sections prepared from the lesion. Mean mineral profiles of treatment groups were then made from the profiles of the individual lesion. These data reduction techniques allowed for a large number of replicates to be used in the measurement of remineralization. The computerized microdensitometric system described here was developed to allow for an objective, quantitative analysis of the mineral content of dental hard tissue.

The Effect of Plaque Thickness on Progression of Artificial Caries Lesion Formation in situ

Eighty thin enamel sections with artificially-fonned 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.