The Use of Nanoparticles as a Strategy for the Remineralisation of Dentine Affected by Caries or Acid Erosion

There is a clinical need to remineralise dentine beneath the surface, relatively deep within the collagen matrix. Nanoparticles have the potential to infiltrate between the collagen fibres, and previous studies have demonstrated that silica and hydroxyapatite nanoparticles may enhance remineralisation. Dentine remineralisation research uses in vitro models based on fully or partially demineralised dentine prepared by exposure to non-specific acids, and to date this approach has been based on the assumption that these acids affect dentine in a similar manner. Moreover, for methodological reasons, the demineralised dentine requires fixation, but it is unknown if this additional step affects the soundness of the model. The aim of this study was therefore to undertake a detailed and systematic study of dentine remineralisation by silica nanoparticles in the presence of low molecular weight organic acids, with additional experiments directed at understanding the effect of chemical fixation on the validity of the model. Each demineralising agent that was investigated had a unique effect on the dentine composition and structure and it was concluded that acids reported to date have substantial limitations when used to simulate the effects of caries or erosion acids. A novel infiltration method was developed which suggested that silica nanoparticles infiltrated through collagen networks and adhered to collagen fibres, creating a nanoparticle-collagen complex or scaffold. The use of chemical fixatives and different demineralising agents did not appear to inhibit the adherence of nanoparticles. Furthermore, by monitoring the zeta potential of the nanoparticles under various conditions, it was discovered that the negatively charged silica nanoparticles had a high affinity for calcium ions that were present in a remineralising solution. This appeared to form part of the mechanism responsible for dentine remineralisation by infiltrated silica nanoparticles. This interpretation was further supported by studies using energy dispersive spectroscopy in the electron microscope. This research has added considerably to current knowledge of remineralisation of dentine using inorganic nanoparticles, with signs of remineralisation detected beneath the tissue surface and paving the way towards a therapeutic intervention.