Abstract
Natural human enamel (NHE) is a complex freeform surface which has presented significant difficulties in measuring surface form change using non-contacting laser profilometry (NCLP). Measuring surface form change on NHE is a metrology proxy for measuring dental tooth structure loss, and characterising this using non-ISO parameters (volume, surface area, and normalised lesion depth) has been seldom studied due surface complexity and undetermined measurement errors. This study determines NCLP measurement errors (instrument repeatability and method reproducibility) for non-ISO parameters, characterises change in surface form on NHE following a dietary pH-cycling model. NHE (n = 1) was scanned consecutively twenty-times using NCLP with/without sample replacement producing consecutive surface profile data. Residual data was created after subtracting consecutive filtered profile data (80 μm, Gaussian filter), and mean (SD) volume, surface area, and normalised lesion depth was determined within a 1.5 mm circular region of interest (ROI). Volume error (expressed as height variation across ROI surface area) was 0.022 μm (instrument repeatability) and 0.149 μm (method reproducibility), whilst surface area error (expressed as percentage change of the surface area deviation across the entire surface area) was 0.034% (repeatability error) and 0.081% (reproducibility error). Sixty-four natural enamel surfaces taped with polyvinyl-chloride tape leaving 1.5 mm exposed ROI underwent dietary erosion cycling (three 5-min cycles, 0.3% citric acid w/v, pH 3.2) generating artificial erosion lesions. Samples were scanned with NCLP before/after each erosion cycle, scans filtered for microtexture, and after-erosion scans were subtracted from before-erosion scans. NCLP results show mean (SD) volume, surface area, normalised depth, and 3D step-height of the eroded area increased significantly after each erosion cycle, with no significant difference in calcium and phosphate release after each cycle. We demonstrate a robust and valid dental model with analysis workflow to measure surface form change in NHE using NCLP, improving understanding of measuring surface form change in complex freeform surfaces.
Highlights
Surface profilometry remains the gold-standard for measuring surface form changes to measurement/operating limits of the profilometer [1,2,3,4]
A representative example of the erosion lesion visualisation and analysis is shown by Figure 2 and Figure 3
Multiple comparisons revealed statistically significant (p
Summary
Surface profilometry remains the gold-standard for measuring surface form changes to measurement/operating limits of the profilometer [1,2,3,4]. The outer surface of natural human enamel comprises a complex freeform surface consisting of irregular peaks and troughs which have been previously shown to be difficult to measure accurately. Previous research using natural human enamel has minimised the problems associated with measuring this complex freeform surface by utilising profile subtraction of before and after scans to produce a residual data set, from which data analysis are conducted [4]. This is a type of form removal, which minimises the impact of the irregular peaks and troughs by subtracting one data set from another, leaves a residual data set containing points of difference [4]. The quantification of enamel loss using three-dimensional (3D) step height formation has been used on natural human enamel by using the profile subtraction method and analysing the residual data set [4]
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