Elsevier

Journal of Dentistry

Volume 78, November 2018, Pages 59-64
Journal of Dentistry

Importance of bioavailable calcium in fluoride dentifrices for enamel remineralization

https://doi.org/10.1016/j.jdent.2018.08.005Get rights and content

Abstract

Objectives

To compare remineralization of enamel subsurface lesions by fluoride dentifrices with added calcium in a double-blind, randomized, cross-over, in situ study.

Methods

Human enamel with subsurface lesions were prepared and inserted into intra-oral appliances worn by volunteers. A slurry (1 g toothpaste/4 ml H2O) was rinsed for 60 s, 4 times per day for 14 days. Seven toothpastes were tested: (i) 1450 ppm F (NaF), (ii) 5000 ppm F (NaF), (iii) 1450 ppm F (MFP) with calcium sodium phosphosilicate (CSP), (iv) 1450 ppm F (MFP) with CaCO3/Arg, (v) 1150 ppm F (SnF2) with amorphous calcium phosphate (ACP), (vi) 1100 ppm F (NaF) with casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) and (vii) 5000 ppm F (NaF) with functionalized tri-calcium phosphate (TCP). Total (acid soluble) and bioavailable (water soluble) calcium, inorganic phosphate and fluoride levels of the dentifrices were measured using ion chromatography (F/MFP) and spectrophotometry (Ca and inorganic phosphate). Enamel lesion mineral content was measured using transverse microradiography. Data were statistically analysed using a linear mixed model.

Results

All calcium and fluoride containing toothpastes released > 90% of bioavailable fluoride and were superior to the respective fluoride alone toothpastes in remineralization of enamel subsurface lesions. The level of remineralization followed the order: CPP-ACP/1l00 ppm F > ACP/1150 ppm F = TCP/5000 ppm F > 5000 ppm F = CaCO3/Arg/1450 ppm F = CSP/1450 ppm F > 1450 ppm F. Bioavailable calcium levels significantly correlated with enhanced remineralization of enamel subsurface lesions.

Conclusions

Bioavailable calcium in fluoride dentifrices enhanced remineralization of enamel subsurface lesions.

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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