Remineralisation of Carious Lesions and Fluoride Uptake by Enamel Exposed to Various Fluoride Dentifrices In Vitro

Purpose: To evaluate the relative performance of fluoride (F) dentifrices to promote remineralisation and enamel F acquisition using an in vitro pH-cycling model. Enamel surface morphology was investigated. Materials and Methods: Thirty-six white spot lesions and 36 sound enamel sections from extracted premolars and molars were randomly assigned to 8 experimental groups and a placebo group. Eight commercially available brands of Fdentifrices were used: A. 0.8% monofluorophospate (MFP)-silica; B. 0.8% MFP-calcium carbonate and calcium phosphate; C. 0.8% MFP-calcium carbonate and calcium phosphate; D. 0.76% MFP-aluminium hydroxide; E. 0.24% sodium fluoride (NaF)-silica and sodium pyrophosphate; F. 0.24% NaF-silica and sodium pyrophosphate; G. 0.76% MFP and 0.10% NaF-dicalcium phosphate and sodium pyrophosphate (1450 ppm F); H. 0.76% MFP and 0.33% NaF-silica (2500 ppm F). The placebo (I) contained non-fluoridated silica. The cycling regimen comprised the following: three 2-min and one 4-min daily treatments with dentifrice slurries, rinsed with water and stored in fresh whole saliva at 37°C until the next experimental day, when specimens were activated in acid buffer solutions prior to each dentifrice treatment. This pH cycling continued for 21 consecutive days. Lesion depths and size were measured using a polarising microscope and enamel F uptake was determined using the acid-etch biopsy technique. The morphology of enamel surfaces was examined using scanning electron microscopy. The data were statistically analysed using Student's t-test, analysis of variance (ANOVA) and Pearson's correlation coefficient (r). Results: All tested fluoride dentifrices significantly enhanced remineralisation by reducing the lesion depths from 6.4 to 17.1 µm and lesion sizes by 10% to 34% relative to the pre-cycling measurements. Overall, the degree of remineralisation was as follows: NaF-silica-pyrophosphate dentifrices (1000 ppm F) averaged 41%; NaF/MFP-silica (1500/1000 ppm F) 38%; MFP/NaF-dicalcium phosphate (1000/450 ppm F) 30%; MFP dentifrices (1000 ppm F) ranged from 15 to 23%. Enamel F uptake by NaF and NaF/MFP was significantly greater than MFP dentifrices (P 0.05 to P 0.001), with the area under the depth curve being 2.4 and 2.2 times greater, respectively. At all enamel depths, fluoride dentifrices significantly increased F concentrations relative to the control (P 0.001). A strong correlation was found between ionic F levels in dentifrices and their efficacy. Dentifrices produced different enamel surface morphologies. Conclusions: The present study demonstrates that commercially available dentifrices vary in their degree of effectiveness and mode of action depending on formulations. Keywords: carious lesion, dentifrices, enamel, fluoride, fluoride uptake, pH cycling, remineralisation