Assessing the macro and microscale surface changes following citric acid mediated attack on polished and natural human enamel in vitro

Student thesis: Doctoral ThesisDoctor of Philosophy


This thesis investigated the effect of short- and long-term citric acid mediated erosion on polished and natural human enamel and determined which characterisation methods were suitable to create and measure artificial dental erosion lesions on polished and natural human enamel. 
Firstly, an in vitro study characterising early erosion in polished and natural human enamel was conducted. Changes to the enamel surface after citric acid erosion were measured with 3D-step height change (μm), surface roughness (Sa, μm), surface microhardness (KHN), surface reflectivity with optical coherence tomography (OCT) and surface morphology using tandem scanning confocal microscopy (TSM). In polished enamel, mean (SD) 3D-step height change (μm) was measurable after 60s (0.24+0.1), after 10s mean (SD) surface roughness (μm) was 0.270(0.013) and mean(SD) Knoop microhardness decreased to 316(1.82). Only surface roughness change was detectable in natural enamel after 120s (0.830(0.125)). 
Secondly, further work determined how to create/detect/characterise early and late dental erosion in natural human enamel only. This was conducted in 4 separate but interconnected investigations. The first determined the minimum detection threshold of non-contacting laser profilometry (NCLP) in measuring changes in surface form (0.279μm) and roughness (0.072μm) in natural enamel, the second, calculated the effect of thermal variation on NCLP sensor displacement according to different scanning periods and NCLP conditions (open vs closed). The third determined the optimum scanning parameters for assessing/scanning surface form change in natural human enamel (3.5x3.5mm grid, 351x351 points, with step over distance 10 μm). The fourth then validated a new in vitro dental erosion lesion model using natural human enamel; in this model, the erosion lesion could be defined using changes in step height (ISO and non-ISO methods), surface roughness, surface reflectivity (OCT), and surface morphology (TSM). 
Thirdly, this new natural enamel dental erosion model was further tested according to different factors that are seen clinically which would affect the erosion process; this consisted of 3 further studies. The effect of three factors were all separately tested for their effect (if any) on dental erosion lesion formation using this new model: sodium fluoride toothpaste pre-treatment (factor 1) reduced mean (SD) step height formation (0.38(0.20)), acquired enamel pellicle (factor 2) did not produce any significant protective benefit against mean (SD) step height formation (1.22(0.75)), and an experimental calcium silicate/sodium phosphate/sodium monofluorophosphate toothpaste (factor 3) also reduced mean (SD) step height formation (0.51(0.22)). 
Overall, the effects of early and late citric acid erosion could be measured on both polished and natural human enamel. Most importantly, however, enamel loss could be measured and quantified on the natural enamel surface as step height formation using both ISO and non-ISO methods. This new in vitro model using natural human enamel is a closer representation of the clinical scenario (versus using polished enamel). The methods developed have potential applications beyond those demonstrated in this Thesis.
Date of Award1 Dec 2019
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorDavid Bartlett (Supervisor) & Rebecca Moazzez (Supervisor)

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