Homeostasis of Dental Hard Tissues

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Dental erosion can be defined as the irreversible loss of tooth structure due to chemical dissolution by acids not of bacterial origin. The most common causes of erosion are acidic foods and drinks. Dental erosion has been described as an increasingly relevant problem. Fluoride from many delivery vehicles, but especially fluoride-containing toothpastes, has led to marked reductions in teeth lost through dental caries. However, fluoride has a limited effect on enamel erosion. Coupled with increased longevity, this means that not only are people living longer but that their teeth will be increasingly exposed to dietary acids over the life-course. Intuitively one might think that newly-erupted teeth would be at their strongest. However, this is not the case and during Post-Eruptive Maturation (PEM) they become harder and less porous via chemical interactions with the oral fluids. Species with the ability to reduce enamel solubility, such as fluoride and metal ions, are also incorporated into the tooth surface. It has been proposed that this process is driven by the formation of plaque around the gum margin (as a result of difficulty brushing new, partially erupted teeth) contributing to a constantly shifting dynamic of demineralisation and remineralisation states within the oral environment. Although the physical changes in the tooth are relatively well understood, very little is known about the chemical interactions between saliva and the tooth that effect these changes, i.e. we know what happens, but not how. Further, while the protective effect conferred against dental caries by PEM is widely reported, information relating to the effect of PEM on erosion is essentially absent from the literature. The aim of the project has been to develop greater understanding of the effects of the physico-chemical interactions at the tooth-saliva interface during PEM on subsequent susceptibility to erosion. This has been achieved using a novel in vitro PEM pH-cycling model that mimics fluctuations in the de- and remineralisation states within in the oral environment over the course of a regular day. Following pH-cycling, samples are exposed to an erosive challenge in order to assess the efficacy of different test conditions used within the model, using techniques such as; quantitative light-induced fluorescence (QLF-D), transverse micro-radiography (TMR) and non-contact surface profilometry (NCSP). Initial findings demonstrated that samples exposed the pH-cycling model were more resistant to acid erosion compared to control groups. Building on these findings, studies evaluating the efficacy of different anti-erosive treatments within the context of this model have been/ are being conducted. So far, metal ion treatments (i.e. Stannous Fluoride and Zinc) have affected significant reductions in demineralisation from erosive challenges when exposed to the pH-cycling model. Moving forward, studies evaluating the effect of promising anti-erosive agents (i.e. Titanium Tetrafluoride and Strontium) will also be conducted. In addition to these studies, analysis of the chemical composition of enamel from exposure to this model will be assessed using scanning electron microscopy (SEM) in conjunction with techniques such as energy-dispersive x-ray spectroscopy (EDX) or wavelength dispersive spectroscopy (WDS), which will provide much needed insight into chemical interactions occurring in the oral cavity which contribute to PEM.