Ca2+ release and buffering effects of synthetic hydroxyapatite following bacterial acid challenge

Abstract

Background: Synthetic particulate hydroxyapatite (HAP; Ca 5 (PO 4 ) 3 (OH)) is used as ingredient in oral care products but its effects on cariogenic biofilms are not clear yet. The primary mode of action of HAP may be acting as a calcium phosphate reservoir when deposited in oral biofilms and release Ca 2+ and (hydrogen) phosphate ions upon bacterial acid challenge. The aim of this in vitro study was to test this hypothesis by investigating release of Ca 2+ ions and potential buffering effects from HAP upon bacterial acid challenge in planktonic cultures and biofilms of Streptococcus mutans. Methods: Planktonic cultures of S. mutans were grown in BHI broth with 1% sucrose or with additional 5% HAP or 5% silica for up to 48 h. Separately, biofilms of S. mutans were grown in BHI for 72 h in total. After 24 h of this biofilm culture, either BHI alone or BHI with additional 0.5% HAP or 0.5% silica was added. After 48 h, BHI with 1% sucrose was added to allow bacterial acid formation. Ca 2+ release was determined colorimetrically and pH measurements were performed using a pH electrode. For statistical analysis, non-parametrical procedures were applied (n ≥ 10; Mann-Whitney U test; α = 0.05).Results: Relevant release of Ca 2+ was only evident in planktonic cultures or biofilms with HAP but not in both other groups (p ≤ 0.001). In suspended biofilms with HAP, median pH was 4.77 after 72 h and about 0.5 pH units higher as compared to both other groups (4.28 or 4.32, respectively; p ≤ 0.001).Conclusions: Under the tested conditions, synthetic HAP releases Ca 2+ ions upon bacterial acid challenge and may also show some buffering capacity but further studies are needed to investigate whether the concentrations tested here can also be reached clinically in dental biofilms.

Comparison of hydroxyapatite and fluoride oral care gels for remineralization of initial caries: a pH-cycling study

“… 39 Particulate HAP when adsorbed on tooth surface induce remineralization of initial caries lesions by directly filling micropores in demineralized tooth tissue, 40 , 41 where it acts as a crystal nucleus, and promotes crystal deposition and growth by continuously attracting large amounts of calcium and phosphate ions from the surrounding remineralization solution. 41 , 42 A recent study demonstrated that the HAP oral care gel tested in the present study released calcium and phosphorus on application on tooth surfaces, 26 , 43 thus further highlighting the potential of this gel formulation to influence remineralization and demineralization process on tooth surface. The effectiveness of fluoride in remineralizing early caries lesions in the present study once again contributed to the wealth of evidence supporting fluoride as having the most consistent benefit in preventing caries and remineralizing initial caries lesions.…”

In Vitro Whitening Effect of a Hydroxyapatite-Based Oral Care Gel

“…It can be easily applied by using the finger after tooth brushing and also showed both remineralization effects 26 and erosion protective properties. 17,28 Bommer et al reported that a self-assembling peptide matrix can act as an adhesive for HAP particles improving the whitening effect of HAP alone. 6 A similar effect could be observed in HAP group of our study.…”

“…19 This can be helpful to buffer cariogenic biofilms, and with increased calcium-levels leading to a shift from tooth demineralization to remineralization. 11,17 The aim of this in vitro study was to test the whitening effect of a newly developed gel formulation based on microcrystalline HAP. To exclude any abrasive influence by toothpaste abrasives harder than natural enamel, 20 and more importantly by the toothbrush that is used in daily oral care, this HAP-gel formulation does not contain commonly used abrasives (e.g.…”

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“…It can be easily applied by using the finger after tooth brushing and also showed both remineralization effects 26 and erosion protective properties. 17,28 Bommer et al reported that a selfassembling peptide matrix can act as an adhesive for HAP particles improving the whitening effect of HAP alone. 6 A similar effect could be observed in HAP group of our study.…”

“…5 One of these agents belong to the group of calcium phosphates like particulate hydroxyapatite (HAP; Ca 5 [PO 4 ] 3 [OH]). 1,[5][6][7][8][9] In particular, biomimetic HAP is inspired by structure and composition of natural enamel crystallites 10 and shows a broad range of applications in preventive oral health care, [11][12][13][14][15][16][17] such as antibiofilm properties. 18 A recently published Eur J Dent:2020;14:335-341…”