Synthetic particulate hydroxyapatite (HAP; Ca5(PO4)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 Ca2+ and (hydrogen) phosphate ions upon bacterial acid challenge. The aim of this in vitro study was to test this hypothesis by investigating release of Ca2+ ions and potential buffering effects from HAP upon bacterial acid challenge in planktonic cultures and biofilms of Streptococcus mutans. 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. Ca2+ 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). Relevant release of Ca2+ 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). Under the tested conditions, synthetic HAP releases Ca2+ 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.

中文翻译：

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细菌酸攻击后，合成羟基磷灰石的Ca2 +释放和缓冲作用。

合成颗粒羟基磷灰石（HAP; Ca5（PO4）3（OH））被用作口腔护理产品的成分，但其​​对致龋生物膜的影响尚不清楚。当沉积在口腔生物膜中时，HAP的主要作用方式可能是充当磷酸钙储存库，并在细菌酸激发后释放Ca2 +和（氢）磷酸根离子。这项体外研究的目的是通过调查Ca2 +离子的释放以及HAP在变形链球菌的浮游培养和生物膜中细菌酸攻击后对HAP的潜在缓冲作用来检验这一假设。变形链球菌的浮游细胞培养物在含1％蔗糖或额外5％HAP或5％二氧化硅的BHI肉汤中生长长达48小时。另外，变形链球菌的生物膜在BHI中总共生长72小时。生物膜培养24小时后，单独使用BHI或将BHI加0。加入5％的HAP或0.5％的二氧化硅。48小时后，加入含1％蔗糖的BHI，以形成细菌酸。比色法测定Ca2 +的释放，并使用pH电极进行pH测量。为了进行统计分析，应用了非参数程序（n≥10； Mann-Whitney U检验；α= 0.05）。Ca 2+的相关释放仅在具有HAP的浮游培养物或生物膜中明显，而在其他两组中均不明显（p≤0.001）。在具有HAP的悬浮生物膜中，72小时后的中位pH为4.77，与其他两组相比分别高出约0.5个pH单位（分别为4.28或4.32； p≤0.001）。在测试条件下