Measurement of surface roughness changes of unpolished and polished enamel following erosion

Abstract

ObjectivesTo determine if Sa roughness data from measuring one central location of unpolished and polished enamel were representative of the overall surfaces before and after erosion.MethodsTwenty human enamel sections (4x4 mm) were embedded in bis-acryl composite and randomised to either a native or polishing enamel preparation protocol. Enamel samples were subjected to an acid challenge (15 minutes 100 mL orange juice, pH 3.2, titratable acidity 41.3mmol OH/L, 62.5 rpm agitation, repeated for three cycles). Median (IQR) surface roughness [Sa] was measured at baseline and after erosion from both a centralised cluster and four peripheral clusters. Within each cluster, five smaller areas (0.04 mm2) provided the Sa roughness data.ResultsFor both unpolished and polished enamel samples there were no significant differences between measuring one central cluster or four peripheral clusters, before and after erosion. For unpolished enamel the single central cluster had a median (IQR) Sa roughness of 1.45 (2.58) μm and the four peripheral clusters had a median (IQR) of 1.32 (4.86) μm before erosion; after erosion there were statistically significant reductions to 0.38 (0.35) μm and 0.34 (0.49) μm respectively (p<0.0001). Polished enamel had a median (IQR) Sa roughness 0.04 (0.17) μm for the single central cluster and 0.05 (0.15) μm for the four peripheral clusters which statistically significantly increased after erosion to 0.27 (0.08) μm for both (p<0.0001).ConclusionMeasuring one central cluster of unpolished and polished enamel was representative of the overall enamel surface roughness, before and after erosion.

Precision of 655 nm Confocal Laser Profilometry for 3D surface texture characterisation of natural human enamel undergoing dietary acid mediated erosive wear

“…Baseline values for natural enamel indicate a complex textured surface, which is supported by visual evidence from the confocal images, thereby the effect of roughness change value is partly determined by the baseline values and the variation within the sample micro-structure. Natural enamel became significantly smoother after erosion whilst polished enamel became rougher, following recent trends [15,24,27,33]. These differences in behaviour between the two surfaces cannot be attributed to the differences in measurement capabilities and remain true representations.…”

“…This study identified that the optical measurement system could reliably identify Sa roughness changes as small as 5 nm for polished enamel and 23 nm for natural enamel. Whilst there were differences in the precision of measurement across the five measurement areas, these differences were minimal of 4 nm for polished and 16 nm for natural enamel therefore suggesting that the level of precision is within the limits of detection required for reliable measurement of 3D surface texture changes of enamel undergoing erosion [18,20,27].…”

“…However, difficulties have been identified specific to optical devices, whereby measurement drop out occurs over curvatures with push the angular tolerance of the device [25]. Previously, we conducted a study comparing the Sa roughness over different locations of natural and polished enamel samples, identifying that measurements from the centre of a natural enamel sample could be considered representative of the overall sample [27]. This area could also be described as 'zenith' or apex of the curvature which is attributed to area 3 of measurement in this study.…”

“…To simulate dietary wear an erosion model was designed to investigate surface roughness changes following in vitro exposure to dietary acid, based upon previously published protocols [14,27].…”

“…The profilometer had a spot size of 2 µm and vertical resolution of 100 nm, with a 4 µm lateral scanning interval. An image analysis workflow was designed to apply a 25 µm robust Gaussian filter and extract 3D (Sa) roughness values (µm) centred around the centre of the polished enamel surface and the zenith (maximum bulbosity) of the natural enamel sample surface as shown in Figure 1, following previously published protocols [27].…”