A Novel Fluoride Dental Composite Coating Containing Ca²⁺ LDH

Objectives: To develop calcium (Ca²⁺) layered double hydroxide (LDH)–polycarboxylic acid (polymer) composite coatings painted on hydroxyapatite (HA) discs and to study their hardness, chemical composition and fluoride (F^-) release. LDH-polymer composite coatings/varnishes may provide a therapeutic level of F^- in the oral environment to prevent early-stage caries.
Methods: Ca-LDH was synthesised incorporating polycarboxylic acid in situ, characterised using powder X-ray diffraction (pXRD), Fourier-transform infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX). The resulting powders absorbed F^- in 1500ppm sodium fluoride (NaF) and F^- release was measured in de-ionised water (DW)(1g/L), using ion selective electrodes (ISE NICO2000). Readings were taken every 10sec for 13h (n=3). 0.1mL of calcium-LDH-polymer in NaF (solution) was pipetted on to each HA disc surface (n=5), allowed to dry and rinsed in DW, to remove excess LDH-polymer. Control discs (non-coated), and polymer coatings with no LDH were also tested. All discs went through 3-cycles of remineralisation (pH7 artificial saliva, 3h) and demineralisation (pH4 0.1M acetic acid, 3h), with the last remineralisation stage conducted for 15h. The coated surfaces were analysed using SEM/EDX. Vickers hardness (Micromet-4, VHN) was measured at all cycle stages.
Results: Ca-LDH-polycarboxylic acid polymer powders were successfully synthesised and after charging, they released increased amounts of F^- (16.5-9.9±3.8ppm) compared to LDH-control (9.5±2.2; P>0.05). Ca-LDH- polymer coatings on HA discs were confirmed using pXRD, FTIR and SEM/EDX. These coatings increased VHN values in comparison to the non-coated and polymer alone discs (Ca-LDH-polymer: ~200±7.8 compared to HA-polymer alone: ~167±3.8 and HA-No treatment: 156±4.8VHN), indicating prevention of demineralisation.

Conclusions: Ca-LDH-polycarboxylic acid composite coatings were successfully attached to HA discs. They released F^- and the hardness of the discs in demineralisation solution was maintained. Therefore, these coatings may have the potential to prevent early stage caries via a controlled release of F^-.