Effect of Fluoride on Enamel Dissolution Utilising Localised Electrochemical Approaches

Objective: The dissolution of enamel is a key process in acid erosion. Studies described herein focused on understanding the effect of fluoride on the erosion process, kinetics and morphology. An electrochemical method was developed to create a localised proton challenge to enamel surfaces. A key advantage of this approach is that the challenge can be effected on a range of timescales in a quantitative and reproductive fashion. High-resolution techniques, such as white light interferometry (WLI) and atomic force microscopy (AFM) are used to image enamel topography and provide information on reactivity.

Method: A localised electrochemical method is used whereby an ultramicroelectrode (UME) is used to generate protons in the vicinity of the enamel to create highly localised, controlled and measurable acid challenges. The time and flux of protons produced by the UME are quantifiable and have been varied on both treated and untreated enamel. Ex situ optical microscopy, AFM and WLI techniques have revealed how treated (1000 ppm fluoride (as NaF) for two minutes) and untreated samples react. Measurements were made on enamel obtained from the buccal sides of bovine incisors, polished using 4000 grit pads.

Results: In this study, the pre-treatment methods are detailed and the localised electrochemical technique is shown to successfully etch enamel samples. The dependence of the etching rate of acid flux has been elucidated and a model has been developed for the kinetics. The nature of the etching process has been obtained with AFM and WLI. A key result is that the dissolution susceptibility of individual enamel sites is influenced significantly by pre-treatment with fluoride.

Conclusion: A localised electrochemical method has been developed to effect the dissolution of enamel in vitro. The high resolution techniques of AFM and WLI have proven useful in imaging and characterising the etched surfaces.