Measurement of surface roughness changes of unpolished and polished enamel following erosion
Measurement of surface roughness changes of unpolished and polished enamel following erosion
Francesca Mullan 1 2
Rupert S. Austin 1 2
Charles R. Parkinson 0 2
Adam Hasan 1 2
David W. Bartlett 1 2
0 GSK Consumer Healthcare , Weybridge , United Kingdom
1 King's College London Dental Institute, Guy's, King's and St.Thomas' Hospitals , London , United Kingdom
2 Editor: Sarbin Ranjitkar, University of Adelaide , AUSTRALIA
Data Availability Statement: All relevant data are
within the paper and its Supporting Information
Funding: This study was funded by GSK Consumer
Healthcare, Weybridge, UK, http://www.gsk.com/
funding source had involvement in the writing of
the report and the decision to submit the article for
publication. The funder provided support in the
form of salaries for author [CP] and PhD funding
for author [FM], but did not have any additional
To 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.
Twenty 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
For 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).
Measuring one central cluster of unpolished and polished enamel was representative of the
overall enamel surface roughness, before and after erosion.
role in the study design, data collection and
analysis, decision to publish, or preparation of the
manuscript. The specific roles of these authors are
articulated in the `author contributions' section.
Currently there are no in vivo diagnostic tests that can measure the activity of dental erosion,
despite early detection and diagnosis being important to prevention [1±3]. A possible
predictor of early erosion might be changes to enamel surface roughness, and therefore there is a
need to validate if non-invasive high quality measurements have the potential to be applied in
There are inherent challenges in carrying out high-resolution characterisation of intra-oral
dental hard tissue surface features. Enamel is a highly mineralised tissue, made up from 96%
hydroxyapatite crystallites, 3% water and 1% organic proteins [
]. Enamel composition varies
in its location, with the enamel at the gingival margin being the thinnest [
] and whilst most
enamel prisms run longitudinally from the enamel-dentinal junction (DEJ) emerging
perpendicular to the occlusal plane, they can also cross each other to form decussation patterns,
commonly seen over cusps [
]. A study by Cuy et al [
], which combined nanoindentation and
chemical characterisation of the mineral content of polished enamel using an electron
microprobe found that the chemical composition [with respect to calcium and phosphorous] of
enamel decreased towards the DEJ, and also identified a correlation with the surface becoming
softer. Whilst in the uneroded tooth the outer surface enamel is aprismatic with intact enamel
Unpolished enamel has a curved, richly textured surface, which presents challenges for
digital mapping. Therefore, most erosion studies have utilised polished and flattened enamel
surfaces for accurate digital mapping, however this has limited applicability for clinical studies
[7±9]. A previous study suggested that the surface of unpolished enamel was more variable
than polished enamel. Ganss et al [
] used a contact profilometer to measure profile tissue
loss of unpolished and polished enamel following erosion. They observed that unpolished
enamel was less susceptible to erosive changes than polished enamel and suggested the
topographical characteristics varied over the surface. Therefore, it would be beneficial to ascertain
if a sample area is representative of the whole unpolished enamel surface.
A surface is constituted of form (profile), waviness and roughness. Form is the overall
shape of a surface and is commonly quantified as vertical loss or step height. Waviness is the
medium wavelength band within a surface, whereas 3D areal surface roughness measurements
give an indication of the nature of a surface and are deviations within the form [
]. There are
different ways to quantify surface roughness, with amplitude parameters being one such
method. Amplitude parameters quantify the height deviations of a measured surface, 2D
parameters are calculated from a single profile [
] but may not be truly representative of
complex surfaces such as teeth. In comparison 3D parameters are calculated from the overall
surface measured and provide a robust and more balanced description of the surface. This
permits stable results to be obtained. For highly accurate analysis of 3D surface roughness the
scan area can be as small as 0.129 by 0.129 μm . The 3D areal measurements have been
reported to quantify the micro-structural surface of enamel and change during erosion in vitro
[3,8,14±17]. There are 7 defined 3D height parameters, of which Sa was the parameter used in
this study which equates to the arithmetical mean of the height deviations in the surface
measured and reflects the deviation in height at each point from the arithmetic mean of the
A series of in vitro studies have attempted to model early clinical erosion [18,19]. They ini
tially measured 2D roughness change of polished enamel along with other techniques such as
calcium analysis and reflectometry. In their earlier study, Rakhmatullina et al [
that following erosion, polished enamel samples exhibited an increase in diffuse reflection and
decrease in spectral reflection, concurrent with a loss in enamel surface microhardness and
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surface calcium, and suggested a relationship between the increase in diffuse reflection and
increase in surface roughness with the progression of erosion. In a follow-up study, using
native and polished enamel Rakhmatullina et al [
] reported that the increase in diffuse
reflections was related to surface roughness. Other studies have used surface texture
measurements to investigate the changes that occur from erosive tooth wear. Hara et al [
surface texture measurements to differentiate between different wear aetiologies using polished
enamel, unpolished enamel and dentine samples. More recently Ranjitkar et al [
] used a
combination surface texture measurement and anisotropy to identify structural differences
between wear caused by erosion with wear caused by erosion and attrition. They suggested
that erosive wear resulted in a more complex structure whilst wear from attrition had a less
complex structure but increase in anisotropy. Atomic Force Microscopy AFM] can also be
used to characterise the surface of enamel [
]. Kashkosh et al [
] used AFM to characterise
surface roughness changes of bovine enamel samples after 10 minutes of erosion followed by
remineralising. They identified that the surfaces became significantly rougher after erosion.
However, the surfaces then became significantly smoother again after remineralization. This
increased smoothness was interpreted as success of the remineralising product. These are
promising steps towards developing a method to quantify pathological wear at an early stage.
The aim of this study was to determine if Sa roughness of unpolished and polished enamel varies over the surface of enamel. The null hypotheses were that surface roughness would not be uniformly distributed over the surface of unpolished and polished enamel and unaffected by erosion.
Ten extracted human maxillary and mandibular third molars without visible signs of caries or
tooth wear were collected under ethics' approval (REC: 12/LO/1836) from London
Bloomsbury Research Ethics Committee. Written consent was obtained from the participants
donating teeth that were planned for extraction for clinical reasons. The extracted teeth were stored
in sodium hypochlorite for a minimum of three days. The roots were removed and the crowns
sectioned using a circular diamond saw (XL 12205, Benetec Ltd., London, UK) to produce 20
(4 x 4 mm) buccal enamel samples. These buccal enamel sections were randomly allocated to
produce ten unpolished (curved) and ten flat (polished) enamel samples. Both groups were
embedded in bisacryl composite (Protemp4 3M ESPE, Germany) using custom made mould
trays. The surfaces of the unpolished samples were left untouched by the composite and were
cleaned using a soft toothbrush and non-fluoridated toothpaste (Kingfisher, Norwich, UK).
The smear layer was removed with ethanol. Those polished, were placed in a water-cooled
rotating polishing machine following previously published protocols to produce ten optically
flat samples [
All samples were imaged using a non-contact profilometer (NCP), Laser Confocal
Displacement Meter (NCP, LT-9010M, Keyence Corporation, Japan) and motion controlled stage
(Xyris 2000, Taicaan, UK), before and after erosion. Surface roughness was calculated using
surface metrology software (Mountains Map, DigitalSurf, France). The NCP had a laser light
source with a spot size of 2 μm and vertical resolution of 10 nm and was kept in a
temperaturecontrolled room (22.0ÊC) within a specially designed unit to minimise external vibrations.
Previous investigations suggest a repeatability of 1 nm measuring Sa roughness of polished enamel
and 7 nm measuring unpolished enamel, based upon 30 continuous measurements. The laser
was emitted onto the enamel surface and the reflected light was used to construct images of the
surface. The baseline measurement error of the NCP, was measured by pre-scanning an optical
flat producing a background noise of 12 nm [
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Fig 1. Representative diagrammatic images of an unpolished and polished enamel sample with the 5
scan areas for the central cluster and 20 scan areas for the peripheral cluster mapped out separately.
A representative baseline scan image for the central cluster and peripheral cluster are also shown for each
Surface roughness (Sa) was measured at baseline and after erosion in both a single central
cluster (0.5 mm wide) and four equally sized peripheral clusters, each cluster approximately
1.5 mm apart and selected to represent the entire surface. Within each cluster, five smaller
areas (each 200 X 200 μm) provided the Sa roughness data. The five areas within each cluster
were methodically selected as shown in Fig 1. The NCP used in this study had a live video
screen of the surface with a horizontal indicator line to identify the optimum focus and
position the scanner. The scans from the NCP were automatically analysed using a custom
designed macro program based on previously published protocols from our research group to
extract Sa roughness using a Gaussian cut-off filter of 25 μm [
The unpolished and the polished enamel samples underwent a 3-cycle erosion at room tem
perature. For each cycle, unpolished or polished samples were fully immersed in 100 mL
commercial orange juice (Sainsbury's basic orange juice drink, pH 3.2, titratable acidity 41.3mmol
OH/L) for 15 minutes under constant agitation at 62 rpm using an orbital shaker (Stuart Scien
tific, Mini Orbital Shaker S05, Bibby), with a total immersion time of 45 minutes. After one
cycle, the samples were removed, rinsed with distilled water and then reinserted into the
erosion cycling repeated until three cycles were completed, following which the samples were
rinsed with distilled water and left to air dry for 24 hours.
One unpolished and one polished enamel sample were randomly selected for imaging with
Scanning Electron Microscopy [SEM] using a Phenum ProX desktop SEM (Phenom-World
BV, The Netherlands) after erosion. Five representative areas on the surface were selected simi
larly to the method used for the surface roughness measurements to provide a single image of
the central cluster and one each of the peripheral clusters. The scan area used for the roughness
measurements was 200 X 200 μm, therefore to image an area of similar size the magnification
at 1100 X was selected providing a total area of 246 X 246 μm.
One representative peripheral SEM scan and one representative central SEM scan were selected for each. Two representative SEM images of uneroded polished and unpolished enamel samples, that were prepared in the same manner as those for this study and imaged using the same SEM and settings, were selected to aide as a comparison in Fig 2.
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Fig 2. Representative SEM images before erosion. (A) Central polished enamel sample (B) Central
unpolished enamel (both 1100 X magnification).
To determine the sample size, a calculation was carried out using G Power3.1.92
(Heinrich-Heine-University, Dusseldorf) using mean and standard deviations based on results,
from previous studies we had conducted, (mean (SD) of 0.67 (0.13) μm for unpolished enamel
and 0.12 (0.02) μm for polished enamel). SPSS version 22 (IBM, United States) was used for
the statistical analysis. The data were non-normally distributed. Friedman tests were used with
paired Wilcoxon tests to compare the results for the singe central cluster versus the four
peripheral clusters and comparing the results before erosion versus after erosion. A Bonferroni
correction for multiple comparisons was carried out and significant difference was set at
p<0.008. The raw and summarized data used for the statistics are in S1, S2 and S3 Files. The
statistical report is in S4 File.
Median (IQR) was used to express the data, as the results were not normally distributed. The
single central cluster for unpolished enamel 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,
which reduced to 0.38 (0.35) μm and 0.34 (0.49) μm respectively after erosion (p<0.0001). For
the polished enamel the Sa roughness values were 0.04 (0.17) μm measuring from the single
central cluster and 0.05 (0.15) μm from the four peripheral clusters before erosion, increasing
to 0.27 (0.08) μm and 0.27 (0.08) μm, respectively, after erosion (p<0.0001). Sa roughness
values from the single central cluster before and after erosion for unpolished and polished enamel
are expressed as a box plot in Fig 3. The unpolished samples had a relatively rougher surface
before erosion with a large interquartile range, but after erosion the surface roughness and
interquartile range were reduced. The polished samples had a very smooth surface and low
interquartile range before erosion and whilst they became rougher after erosion, they were still
smoother than the unpolished samples. The Median IQR of polished enamel after erosion was
similar to that of unpolished enamel after erosion, despite unpolished enamel becoming
smoother and polished enamel becoming rougher. For both unpolished and polished enamel
there were no significant differences measuring the central cluster or the four peripheral
clusters before or after erosion (p>0.008).
Fig 4 shows representative SEM images of the central and peripheral areas (0.06 mm2) of
unpolished and polished enamel samples after erosion. These images revealed the presence of
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Fig 3. Boxplot of median (IQR) Sa roughness results of unpolished and polished enamel before and
after erosion measuring 5 areas in a central cluster. 1 = unpolished enamel before erosion, 2 = unpolished
enamel after erosion, 3 = polished enamel before erosion and 4 = polished enamel after erosion.
some similar textural features regardless of whether the images were taken from central or
peripheral location for both polished and unpolished enamel following erosion. The images of
polished eroded enamel clearly demonstrate the characteristic honeycomb appearance, where
the core of the enamel prisms has been dissolved by acid, and the adjacent interpismatic areas
appear more pronounced creating a typical appearance of type 1 enamel dissolution (Fig 4A &
4B) . The images of the unpolished enamel showed a less homogenous appearance, with variations of the number of exposed prisms and varying striations of perikymata within an imaged area but with similar characteristics observed between the central cluster and peripheral clusters (Fig 4C & 4D).
This current study identified surface changes of unpolished enamel and polished enamel
occurred after 45 minutes of erosion and that Sa roughness measurements from the centre of
unpolished enamel samples and polished enamel samples were representative of the overall
samples. There were no significant differences between median (IQR) Sa roughness
measurements from five scan areas located in the central cluster compared to 20 scan areas in four
peripheral clusters (five scan areas in each cluster) for unpolished enamel and polished enamel.
The SEM images for both unpolished and polished enamel also showed similar features
whether located in the central or peripheral cluster of the samples. Therefore, it is reasonable
to propose that measuring a single, but, central cluster of enamel samples is sufficient to
achieve representative data for the whole enamel surface and so the null hypothesis can be
rejected. This study has also demonstrated that whilst polished enamel becomes significantly
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Fig 4. Representative SEM images after erosion. (A) Central polished enamel sample (B) Peripheral
polished enamel (C) Central unpolished enamel and (D) peripheral unpolished enamel (all 1100 X
rougher, unpolished enamel becomes significantly smoother following exposure to dietary
The extracted molars used in this study may have had previous fluoride exposure as fluoride
incorporation can occur either during tooth formation or after tooth eruption and the
polishing protocol would have removed any fluoride benefits for these samples. However after 45
minutes of cyclical erosive challenges, any benefits the unpolished enamel samples may have
had from any fluoride exposure would have been overridden [
The shape of a specimen influences the output when using optical tomography as flat
surfaces reflect most of the light perpendicularly, whereas curved surfaces distort the light beam
]. This curvature is visible in the SEM images of unpolished enamel where the periphery of
the images is slightly out of focus. It was not possible to image the full area of an unpolished
enamel sample, as the different heights over the curved surface required different focus levels;
therefore, multiple smaller areas (5 X 0.04 mm2) were scanned. For unpolished enamel
samples, the best area of focus was the apex of the curvature, which equates to the central cluster
area. These relatively small surface areas for each scan area (200 X 200 μm) were chosen to
minimize drop out over the curvature of the unpolished enamel samples as did using the video
screen indicator to locate optimum level of focus at each region of the samples central and
peripheral, based upon previous pilot work. By comparing the Sa roughness from the central
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cluster to peripheral areas close by, an estimate of the overall surface features of the enamel
sample was possible.
Surfaces which have higher and lower step height deviations have higher Sa roughness
values and therefore classed as rougher [
]. Previous erosion studies have shown that polished
enamel becomes rougher after erosion which is the same pattern seen in this study however,
interestingly our unpolished enamel samples became significantly smoother [
]. It could be
suggested that this is due to polished enamel having less textural features at baseline than
unpolished enamel, as was seen in the SEM images. The finding that the unpolished enamel
samples became smoother after erosion may be more representative of the clinical pattern of
erosion and supports previous work [3,31±33]. Comparing the representative SEM images in
Figs 2 and 4 of uneroded unpolished enamel and the eroded unpolished enamel from this
study there is visible evidence of a breakdown in structure. However, in this study the SEM
images show the form of the surface and not the roughness. Other authors have used
specialised software and stereo SEM to transform the imaged surfaces into topographical maps from
which roughness parameters were calculated . Our combined roughness and SEM results
suggest that there has been structural breakdown at a profile level and the roughness changes
we have identified are occurring within these areas of tissue loss. A recent study by Hara et al
] investigated the use of surface texture parameters to differentiate between different wear
patterns using polished and unpolished enamel and dentine samples. The authors were unable
to differentiate between sound and worn lesions by measuring Sa roughness of unpolished
enamel. However, there were differences compared to the methods used in our study. They
immersed samples in acid four times a day for 2 minutes without agitation. As well as a
reduced immersion time compared to our study, agitation can also have an effect on erosive
wear. Agitation increases fluid dynamics which facilitates more tissue loss [
]. Hara et al [
also immersed their samples in a remineralising solution which was not carried out in our
study. Furthermore, the filtering used in the analysis for Sa roughness in the study by Hara
et al [
] was not specified and may have influenced the outcome. Filtering is a way of
extracting roughness, waviness and form error, from a measurement and the filter cut-off is the limit
wavelength between waviness and roughness. Choosing the correct filter cut-off can affect the
overall measurement outcome, for some materials the cut offs are defined by ISO standards
but for biological materials such as human enamel a value that best separates the waviness and
the roughness by using the spectral representation of the profile must be found [14,35±37].
The Gaussian filter used in this current study was 25 μm set at 5 times the feature detail of the
diameter of an enamel prism.
In a study investigating surface texture parameters for polished surfaces, Austin et al  rec
ommended that the lateral resolution of optical scanning equipment should be less than
2.5 μm, as above this level the prismatic features of enamel are lost. However, this present
study has revealed that for unpolished enamel surfaces, the nature of the textural changes are
so different that instruments with a lateral resolution below this are able to reliably characterise
enamel surfaces following an erosive wear process.
The current state of the art high-resolution means measuring equipment cannot be used
intra orally, however there are replica techniques that can be used for in vivo studies. The use
of replica techniques or impressions for longitudinal studies measuring volume loss has been
established in erosion studies [
]. Replica techniques have also been established for
qualitative assessment in enamel erosion studies using SEM . Goodall et al [
noncontact scanning of replicas to measure surface roughness of rough and smooth surfaces using
silicon impression material and acrylic replicas. The method developed in this study to
measure surface roughness of unpolished enamel has the potential for future in vivo studies with
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Measuring one central cluster of unpolished and polished enamel samples to determine Sa
roughness is sufficient for subsequent studies. Polished enamel becomes significantly rougher
after erosion and unpolished enamel becomes significantly smoother after erosion. These
observations suggest that surface roughness derived from optical profilometry at a relatively
low lateral resolution, utilizing replica methodologies, may be a relevant in vivo measure of
S1 File. Summarised and raw data for unpolished and polished enamel.
S2 File. Expanded raw data for polished enamel.
S3 File. Expanded raw data for unpolished enamel.
S4 File. Statistical report.
This study was funded by GSK Consumer Healthcare
Conceptualization: Francesca Mullan, Rupert S. Austin, David W. Bartlett.
Data curation: Francesca Mullan.
Formal analysis: Francesca Mullan, Adam Hasan.
Investigation: Francesca Mullan.
Methodology: Francesca Mullan, Rupert S. Austin, David W. Bartlett.
Supervision: Rupert S. Austin, Charles R. Parkinson, David W. Bartlett.
Writing ± original draft: Francesca Mullan, Rupert S. Austin, Charles R. Parkinson, Adam
Hasan, David W. Bartlett.
Writing ± review & editing: Francesca Mullan.
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1. Huysmans MC , Chew HP , Ellwood RP. Clinical studies of dental erosion and erosive wear . Caries research . 2011; 45[Suppl. 1]:60±8.
2. Rodriguez JM , Austin RS , Bartlett DW . A method to evaluate profilometric tooth wear measurements . Dental Materials . 2012 Mar 31 ; 28 : 245 ± 51 . https://doi.org/10.1016/j.dental. 2011 . 10 .002 PMID: 22094292
3. Austin RS , Giusca CL , Macaulay G , Moazzez R , Bartlett DW . Confocal laser scanning microscopy and area-scale analysis used to quantify enamel surface textural changes from citric acid demineralization and salivary remineralization in vitro . Dental Materials . 2016 Feb 29 ; 32 : 278 ± 84 . https://doi.org/10. 1016/j.dental. 2015 . 11 .016 PMID: 26748980
4. Cuy JL , Mann AB , Livi KJ , Teaford MF , Weihs TP . Nanoindentation mapping of the mechanical properties of human molar tooth enamel . Archives of Oral Biology . 2002 Apr 30 ; 47 : 281 ± 91 . PMID: 11922871
5. Gracia LH , Rees GD , Brown A , Fowler CE. An in vitro evaluation of a novel high fluoride daily mouthrinse using a combination of microindentation, 3D profilometry and DSIMS . Journal of dentistry . 2010 Nov 1 ; 38 : S12 ± 20 . https://doi.org/10.1016/S0300- 5712 ( 11 ) 70004 - 5 PMID: 21256400
6. Bajaj D , Arola D. Role of prism decussation on fatigue crack growth and fracture of human enamel . Acta biomaterialia . 2009 Oct 31 ; 5 : 3045 ± 56 . https://doi.org/10.1016/j.actbio. 2009 . 04 .013 PMID: 19433137
7. Carvalho TS , Lussi A . Combined effect of a fluoride-, stannous-and chitosan-containing toothpaste and stannous-containing rinse on the prevention of initial enamel erosion±abrasion . Journal of dentistry . 2014 Apr 30 ; 42 :450±9. https://doi.org/10.1016/j.jdent. 2014 . 01 .004 PMID: 24440712
8. Sar Sancakli H , Austin RS , Al-Saqabi F , Moazzez R , Bartlett D. The influence of varnish and high fluoride on erosion and abrasion in a laboratory investigation . Australian dental journal. 2015 Mar 1 ; 60 : 38 ± 42 . https://doi.org/10.1111/adj.12271 PMID: 25721276
9. Hara AT , Barlow AP , Eckert GJ , Zero DT . Novel in-situ longitudinal model for the study of dentifrices on dental erosion±abrasion . European journal of oral sciences. 2014 Apr 1 ; 122 :161±7. https://doi.org/ 10.1111/eos.12108 PMID: 24372921
10. Ganss C , Klimek J , Schwarz N. A comparative profilometric in vitro study of the susceptibility of polished and natural human enamel and dentine surfaces to erosive demineralization . Archives of oral biology . 2000 Oct 31 ; 45 : 897 ± 902 . PMID: 10973563
11. Field J , Waterhouse P , German M. Quantifying and qualifying surface changes on dental hard tissues in vitro . Journal of dentistry . 2010 Mar 31 ; 38 : 182 ± 90 . https://doi.org/10.1016/j.jdent. 2010 . 01 .002 PMID: 20079800
12. ISO . The ISO 4287:1997 Written Standard [Internet] . 1997 [cited 2015 Oct 27 ]. Available from: http:// www.imagemet.com/WebHelp6/Default.htm#RoughnessAnalysis/RoughnessISO4287.htm
13. Specifications GP . Surface Texture: Profile MethodÐTerms, Definitions and Surface Texture Parameters . International Organisation for Standardisation, Geneva . 1997 .
14. DigitalSurf. MountainsMap Reference Manual . 2013 . Avaialble from: http://www.digitalsurf.com/en/ usermanual.html
15. Rodriguez JM , Austin RS , Bartlett DW . In vivo measurements of tooth wear over 12 months . Caries research. 2012 ; 46 :9± 15 . https://doi.org/10.1159/000334786 PMID: 22156738
16. Mann C , Ranjitkar S , Lekkas D , Hall C , Kaidonis JA , Townsend GC , et al. Three-dimensional profilometric assessment of early enamel erosion simulating gastric regurgitation . Journal of dentistry . 2014 Nov 30 ; 42 : 1411 ± 21 . https://doi.org/10.1016/j.jdent. 2014 . 06 .011 PMID: 24995810
17. Austin RS , Mullen F , Bartlett DW . Surface texture measurement for dental wear applications . Surface Topography: Metrology and Properties . 2015 Apr 2 ; 3 : 023002 .
18. Rakhmatullina E , Bossen A , HoÈschele C , Wang X , Beyeler B , Meier C , et al. Application of the specular and diffuse reflection analysis for in vitro diagnostics of dental erosion: correlation with enamel softening, roughness, and calcium release . J Biomed Opt. International Society for Optics and Photonics; 2011 Oct 1 ; 16 :107002. https://doi.org/10.1117/1.3631791 PMID: 22029364
19. Rakhmatullina E , Bossen A , Bachofner KK , Meier C , Lussi A. Optical pen-size reflectometer for monitoring of early dental erosion in native and polished enamels . J Biomed Opt. International Society for Optics and Photonics; 2013 Nov 1 ; 18 :117009. https://doi.org/10.1117/1.JBO. 18 .11.117009 PMID: 24247749
20. Hara AT , Livengood SV , Lippert F , Eckert GJ , Ungar PS . Dental surface texture characterization based on erosive tooth wear processes . Journal of dental research . 2016 May; 95 : 537 ± 42 . https://doi.org/ 10.1177/0022034516629941 PMID: 26848070
21. Ranjitkar S , Turan A , Mann C , Gully GA , Marsman M , Edwards S , et al. Surface-Sensitive Microwear Texture Analysis of Attrition and Erosion . Journal of dental research . 2017 Mar; 96:300±7 . https://doi. org/10.1177/0022034516680585 PMID: 27927887
22. Zavala-Alonso V , MartÂõnez-Castanon GA , Patiño-MarÂõn N , Terrones H , Anusavice K , Loyola-RodrÂõguez JP . Characterization of healthy and fluorotic enamel by atomic force microscopy . Microscopy and Microanalysis . 2010 Oct; 16 :531±6. https://doi.org/10.1017/S1431927610093748 PMID: 20813079
23. Kashkosh LT , Genaid TM , Etman WM . Effect of remineralization on metrology of surface feature of induced acid eroded tooth enamel . Egyptian dental Journal Jan ; 62 : 514 .
24. Mistry M , Zhu S , Moazzez R , Donaldson N , Bartlett DW . Effect of model variables on in vitro erosion . Caries research . 2015 Aug 20 ; 49 : 508 ± 14 . https://doi.org/10.1159/000438725 PMID: 26288189
25. Giusca CL , Leach RK , Helary F , Gutauskas T , Nimishakavi L . Calibration of the scales of areal surface topography-measuring instruments: part 1. Measurement noise and residual flatness . Meas Sci Technol. IOP Publishing; 2012 Mar 1 ; 23 : 35008 .
26. Mullan F , Paraskar S , Bartlett DW , Olley RC . Effects of tooth-brushing force with a desensitising dentifrice on dentine tubule patency and surface roughness . Journal of dentistry . 2017 May 31 ; 60 : 50 ±5. https://doi.org/10.1016/j.jdent. 2017 . 02 .015 PMID: 28249744
27. Mullan F , Bartlett D , Austin RS . Measurement uncertainty associated with chromatic confocal profilometry for 3D surface texture characterization of natural human enamel . Dental Materials . 2017 Jun 30 ; 33 :e273± 81 . https://doi.org/10.1016/j.dental. 2017 . 04 .004 PMID: 28473225
28. Silverstone LM , Saxton CA , Dogon IL , Fejerskov O. Variation in the pattern of acid etching of human dental enamel examined by scanning electron microscopy . Caries research . 1975 ; 9 : 373 ± 87 . PMID: 1055640
29. Austin RS , Stenhagen KS , Hove LH , Dunne S , Moazzez R , Bartlett DW , et al. A qualitative and quantitative investigation into the effect of fluoride formulations on enamel erosion and erosion±abrasion in vitro . Journal of dentistry . 2011 Oct 31 ; 39 : 648 ± 55 . https://doi.org/10.1016/j.jdent. 2011 . 07 .006 PMID: 21820483
30. Hewlett ER , Orro ME , Clark GT . Accuracy testing of three-dimensional digitizing systems . Dental Materials . 1992 Jan 1 ; 8 : 49 ± 53 . PMID: 1521684
31. Creeth JE , Kelly SA , Martinez-Mier EA , Hara AT , Bosma ML , Butler A , et al. Dose±response effect of fluoride dentifrice on remineralisation and further demineralisation of erosive lesions: A randomised in situ clinical study . Journal of dentistry . 2015 Jul 31 ; 43 : 823 ± 31 . https://doi.org/10.1016/j.jdent. 2015 . 03 .008 PMID: 25837532
32. Arnold WH , Haddad B , Schaper K , Hagemann K , Lippold C , Danesh G. Enamel surface alterations after repeated conditioning with HCl . Head & face medicine. 2015 Sep 25 ; 11 : 32 .
33. Bartlett DW . The role of erosion in tooth wear: aetiology, prevention and management . International dental journal. 2005 Aug 1 ; 55 [S4]: 277 ± 84 .
34. Limandri S , GalvaÂn Josa V , Valentinuzzi MC , Chena ME , Castellano G. 3D scanning electron microscopy applied to surface characterization of fluorosed dental enamel . Micron . 2016 ; 84 : 54 ± 60 . https:// doi.org/10.1016/j.micron. 2016 . 02 .001 PMID: 26930005
35. Leach R . Characterisation of Areal Surface Texture . Characterisation of Areal Surface Texture . 2013 .
36. Leach R. Fundamental Principles of Engineering Nanometrology . Elsevier Science; 2014 . 384 p.
37. Leach R , Brown L , Jiang X , Blunt R , Conroy M , Mauger D . Guide to the measurement of smooth surface topography using coherence scanning interferometry . Measurement good practice guide . 2008 Apr; 108 : 17 .
38. Tantbirojn D , Pintado MR , Versluis A , Dunn C , Delong R . Quantitative analysis of tooth surface loss associated with gastroesophageal reflux disease: a longitudinal clinical study . The Journal of the American Dental Association . 2012 Mar 31 ; 143 : 278 ± 85 . PMID: 22383209
39. Seong J , Virani A , Parkinson C , Claydon N , Hellin N , Newcombe RG , et al. Clinical enamel surface changes following an intra-oral acidic challenge . Journal of dentistry . 2015 Aug 31 ; 43 : 1013 ± 20 . https://doi.org/10.1016/j.jdent. 2015 . 04 .002 PMID: 25868879
40. Goodall RH , Darras LP , Purnell MA . Accuracy and precision of silicon based impression media for quantitative areal texture analysis . Sci Rep . Nature Publishing Group; 2015 Jan 20 ; 5: 10800 . https://doi. org/10.1038/srep10800 PMID: 25991505