Importance of bioavailable calcium in fluoride dentifrices for enamel remineralization
Introduction
Dental caries is initiated via the demineralization of tooth hard tissue by organic acids from the fermentation of dietary carbohydrates by dental plaque bacteria [1]. The use of fluoride-containing dentifrices is an important strategy in the control of dental caries [2]. A major anticariogenic mechanism of the fluoride ion is to drive remineralization of caries-affected tooth hard tissue in the presence of bioavailable calcium (Ca2+) and phosphate (PO43−) ions to form fluorhydroxyapatite [3]. However to remineralize with fluorhydroxyapatite [Ca10(PO4)6(OH)2-2xF2x] a molar excess of bioavailable Ca2+ and PO43− ions to the F ion are required [4].
During the caries process PO43− is removed from equilibrium with tooth mineral as HPO42- and H2PO4- and the Ca2+ removed as calcium complexes (e.g. calcium lactate, CaHPO4°, CaH2PO4+) [5,6]. Bioavailable Ca2+ and PO43− ions can be provided by saliva but even in otherwise healthy people, lifestyle, diet and other factors can affect salivary calcium bioavailability. Since the mid 1990s there has been an increase in the consumption of soft drinks which contain not only fermentable carbohydrate (sugars) but many also contain calcium-complexing food acids (e.g. citric and phosphoric acids) which can act to further reduce the bioavailability of salivary Ca2+ [7,8]. The increase in global consumption of these drinks is associated with an increase in the global prevalence of dental caries and erosion [[9], [10], [11]]. The requirement for a molar excess of Ca2+ and PO43− ions to F− ion to remineralize with fluorhydroxyapatite helps to explain why remineralization of enamel and dentine lesions in situ has been reported to be limited by the bioavailability of calcium and phosphate ions [4,[12], [13], [14]].
This limitation of the bioavailability of calcium and phosphate ions on the application of topical fluorides has resulted in innovation in fluoride-containing dentifrices that also contain calcium phosphate technologies. A range of calcium phosphate technologies has been developed to enhance the ability of fluoride to promote remineralization. These technologies can be divided into the following types: (1) crystalline, such as functionalized tricalcium phosphate (TCP) [15] and calcium carbonate/dicalcium phosphate with arginine (Pro Argin) [16]; (2) bioglasses, such as calcium sodium phosphosilicates (CSP, NovaMin) [17]; (3) unstabilized salts such as the amorphous calcium phosphate technology (ACP) [18]; and (4) phosphopeptide-stabilized complexes such as casein phosphopeptide-amorphous calcium phosphate nanocomplexes (CPP-ACP) [13].
However, a concern on adding calcium to dentifrice formulations is the unwanted reactions between calcium, fluoride and phosphate to form poorly soluble phases in the paste on storage and/or delivery thereby reducing the bioavailability of, not only the fluoride ion, but also the calcium ion [19]. Hence it is imperative to compare these new calcium and fluoride dentifrices with fluoride alone dentifrices for fluoride, calcium and phosphate ion bioavailability as well as for their ability to remineralize enamel subsurface lesions in situ.
The aim of this study was to determine the bioavailability of fluoride, calcium and phosphate ions and the efficacy in remineralization of enamel subsurface lesions in situ of five commercially available fluoride dentifrices with added calcium phosphate technologies in comparison with conventional fluoride-alone dentifrice formulations. The null hypothesis was no significant difference in remineralization efficacy between the dentifrice formulations with the same level of fluoride.
Section snippets
Dentifrices
The dentifrices purchased for the study included (1) Maximum Cavity Protection containing CaCO3/Arg/CaHPO4 and 1450 ppm F as Na2MFP (Colgate); (2) Sensodyne Protect and Repair containing calcium sodium phosphosilicate (CSP, NovaMin) and 1450 ppm F as Na2MFP (GSK); (3) Enamelon containing ACP and 1150 ppm F as SnF2 (Premier Dental); (4) ClinPro 5000 containing TCP and 5000 ppm F as NaF (3 M ESPE); (5) MI One containing CPP-ACP and 1100 ppm F as NaF (GC America); (6) 5000 ppm F as NaF control
Dentifrice calcium, phosphate and fluoride levels
The total (acid soluble) and bioavailable (water soluble) calcium, inorganic phosphate and fluoride levels of the seven dentifrices are shown in Table 1. The Colgate (CaCO3/Arg) dentifrice contained the greatest amount of total (acid soluble) calcium due to the very high level of total calcium (calcium carbonate/dicalcium phosphate) added to the formulation. However, the dentifrice with the greatest amount of bioavailable calcium was GC America’s MI One Paste containing CPP-ACP. The order of
Discussion
The results of this study have shown that added calcium and inorganic phosphate in various forms to F dentifrices significantly enhanced enamel subsurface lesion remineralization over a F alone dentifrice in situ and that the enhanced remineralization was significantly correlated with the bioavailable calcium level in the F dentifrice. The null hypothesis that there was no significant difference in the remineralization efficacy of the different dentifrice formulations with the same level of
Conclusion
Calcium remineralization technologies added to fluoride dentifrices significantly enhanced their ability to remineralize enamel subsurface lesions in situ over fluoride alone. Bioavailable (water soluble) calcium delivered from the dentifrices significantly correlated with their ability to enhance fluoride remineralization. Stabilized calcium phosphate produced the highest levels of bioavailable calcium and inorganic phosphate and together with fluoride produced the highest level of
Acknowledgement
This study was supported by the Australian Government Department of Industry, Innovation and Science grant 20080108.
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