This thesis investigated the role of 3D surface roughness measurement for the quantification of erosive tooth wear. The aim of this thesis was to develop a method for quantifying 3D surface roughness changes occurring in natural unpolished enamel and polished enamel during erosion.
Firstly, an in vitro erosion model was developed for quantifying mechanical and optical surface changes of natural unpolished enamel during dietary erosion through a series of pilot studies. Following this a series of validation studies were conducted to identify measurement error (measurement noise, accuracy, precision and software errors) when quantifying surface texture of complex biological structures using optical profilometry. The measurement protocol was validated for measuring 3D roughness over different locations across natural unpolished enamel and polished enamel samples by comparing the results of imaging five central areas (each 0.004 mm²) over the apex of the curvature of the sample, in comparison to measuring 20 peripheral areas (each 0.004 mm²) in order to reliably measure surface roughness. The optimised surface texture measurement protocol was then used to quantify surface roughness changes of natural and polished enamel from in vitro three cycle erosion regimes (15, 30 and 45 minutes) using a commercially available orange juice drink. Finally, an in situ investigation into the effects of the 15, 30 and 45 minutes of erosion times was conducted with acid immersion occurring both ex vivo and in vivo.
The initial work suggested significant reduction in Sa roughness of natural unpolished enamel following 45 minutes of erosion in orange juice from median (IQR) 0.62 (0.27) μm to 0.38 (0.06) μm (P<0.01). Subsequent validation studies revealed no significant differences between the median (IQR) Sa roughness of the central 1.45 (2.58) μm and peripheral areas 1.32 (4.86) μm before erosion for natural unpolished enamel, and whilst the median (IQR) roughness significantly decreased to 0.38 (0.35) μm and 0.34 (0.49) μm respectively (p<0.0001) there were no significant differences between measuring the centre or peripheral areas. For polished enamel, there were no significant differences across the sample with 0.04 (0.17) μm for central and 0.05 (0.15) μm for the peripheral areas before erosion. Whilst Sa roughness significantly increased after erosion to 0.27 (0.08) μm (p<0.0001) there were no significant differences between measuring the central or peripheral areas. When investigating three erosion times in vitro there were only significant changes in natural unpolished enamel after 45 minutes of erosion: median (IQR) Sa roughness decreased from 0.50 (0.29) μm to 0.42 (0.14) μm (P<0.05). Whereas, median (IQR) Sa of polished enamel significantly increased for all three erosion times from 0.08 (0.10) μm to 0.26 (0.02) μm (p<0.001) (15 minutes), 0.15 (0.11) μm to 0.25 (0.07) μm (p<0.001) (30 minutes) and 0.10 (0.08) μm to 0.27 (0.04) μm (p<0.001) (45 minutes). Finally, the in situ study demonstrated no significant changes in Sa roughness of natural unpolished enamel regardless of either erosion time or whether exposure was ex vivo or in vivo. However, mean (SD) Sa roughness of polished enamel significantly increased for all three erosion times from 0.04 (0.01) μm to 0.09 (0.03) μm (p<0.05) (15 minutes ex vivo), 0.04 (0.01) μm to 0.12 (0.04) μm (p<0.05) (30 minutes ex vivo), 0.04 (0.01) μm to 0.13 (0.04) μm (p<0.05) (45 minutes ex vivo), 0.04 (0.02) μm to 0.08 (0.04 μm) (p<0.05) (15 minutes in vivo), 0.04 (0.01) μm to 0.10 (0.04) μm (p<0.05) (30 minutes in vivo) and 0.04 (0.01) μm to 0.07 (0.03) μm (p<0.05) (45 minutes in vivo).
By optimising the measurement protocol in the early part of the thesis 3D (Sa) enamel surface texture was quantified over different locations of the natural unpolished enamel. This confirmed that the roughness of the central area of unpolished enamel samples was representative of the overall sample which allowed reliable measurements from this area in future studies. This central area of the samples represented the apex of curvature and thus provided the least data drop out from the optical scanners and was also in the region of more homogenous natural prism morphology. The in vitro investigation of the different erosion times identified that not only was natural unpolished enamel more resistant to erosion than polished samples but moreover natural enamel behaved differently to polished enamel by becoming smoother following erosion rather than rougher. The protocol developed for the in situ study successfully provided further confirmation of the resistance of unpolished natural enamel when the natural inhibitory effects of the oral environment were combined. This demonstrated the positive effects of natural resistance to erosive tooth wear.
Therefore, this thesis has developed a method for quantifying 3D surface roughness changes occurring in natural unpolished enamel and polished enamel during erosion, which revealed significant complexity in the surface texture response of natural unpolished enamel to a dietary erosive challenge.
The role of 3D surface texture measurement of natural human enamel for assessment of erosive tooth wear
Mullan, F. (Author). 2018
Student thesis: Doctoral Thesis › Doctor of Philosophy