Development and Characterisation of Fluoride-Charged Hydrotalcites as Anti-Caries Agents

Objectives: The prevention of early-stage carious lesions requires a sustained therapeutic low-level release of fluoride in the oral cavity. Hydrotalcites, also known as Layered double hydroxides (LDH) have the potential to achieve this by continuously absorbing and releasing fluoride. The aim of this study was to prepare and explore the effects of charging LDH with two different fluoride solutions (sodium fluoride-NaF and monofluorophosphate-MFP) and its potential as an effective fluoride-releasing agent for caries prevention.
Methods: 2:1 ZnAl and MgAl-LDH were synthesised using a co-precipitation method. The LDH materials were then subjected to an ion exchange procedure with NaF and MFP solutions to obtain fluoride-LDH (F-LDH) products.The amount of fluoride uptake from charging solutions and the release of fluoride and other ions in deionised water (DW) over 24h were measured using a Fluoride Ion Selective Electrode (ISE) and Inductively-Coupled-Plasma-Optical-Emission-Spectrometry (ICP-OES), respectively. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR) techniques were employed to characterise the LDH powder.
Results: FTIR and XRD characterisation of F-LDH demonstrated the most stable form of LDH structure. ¹⁹F-NMR revealed various fluorine environments in F-LDH samples. LDHs were able to uptake and release an efficacious dose of fluoride in DW. MgAl-LDH demonstrated the greatest fluoride uptake (53.4 ppm) and release (8.4 ppm) compared to ZnAl-LDH (absorbed 31.8 ppm and released 2.8 ppm) when charged with NaF. Mean fluoride released between ZnAl and MgAl-LDHs were significantly different (ANOVA, p<0.001). The results of ICP-OSE analysis indicated that MPF-charged LDHs showed less amount of species release (Zn, Mg, Al) compared to NaF-charged ones.
Conclusions: LDHs can be charged with diverse fluoride solutions, resulting in the subsequent release of fluoride ions and other species. These findings have implications for developing efficient anti-caries agents. Conducting clinical research that simulates the oral environment to thoroughly study the cariostatic effects is essential.