Mean Step Height Research Articles

Pilot clinical study to evaluate the efficacy of a professionally delivered high fluoride varnish on erosive tooth wear in an in-situ model

ObjectivesThe aim for this pilot study was to investigate the effect of a sodium fluoride varnish on step height measured by a profilometer from human enamel worn by healthy volunteers with a novel in situ/ex vivo erosion design. MethodHealthy volunteers aged 18–70 years wore a palatal splint containing 8 human enamel samples and underwent two 3-day treatment periods for 6 h a day with a varnish containing sodium fluoride at 22,600 ppm and the control with the same ingredients but without fluoride. Each splint contained 4 polished and 4 unpolished samples. The interventions were applied to the surface of the enamel samples in randomised order, removed after 6 h, then immersed ex-vivo in 1 %, pH 2.7 citric acid for 2 min, repeated 4 times a day, over 2 days. Measurements of enamel were assessed blindly by microhardness on day 2 and by non-contact laser profilometry on day 3 for the two treatments. Results24 volunteers, 2 males and 22 females aged 27–54 years, were screened and recruited. The delta microhardness, from polished samples removed at the end of day 2, for the control and fluoride treatment was 95.7 (22.9) kgf/mm2 and 123.7 (28.9) kgf/mm2, respectively (p < .005). The mean (SD) step height for the control polished enamel surfaces was 3.67 (2.07) µm and for the fluoride varnish was 1.79 (1.01) µm (p < .0005). The control unpolished enamel surfaces had a mean 2.09 (1.53) µm and the fluoride varnish was 2.11 (1.53) µm but no statistical difference was detected. ConclusionsThe results from this pilot study, utilizing an in-situ model where enamel was exposed to acid over the course of 2 days, demonstrated that a high fluoride varnish containing sodium fluoride at 22,600 ppm prevented erosive wear compared to a control on the polished enamel surfaces. Clinical significanceIntra-oral study demonstrated that a high fluoride varnish containing sodium fluoride at 22,600 ppm reduced erosive tooth wear.

The effect of location/site on polished human enamel after mechanical and chemical wear

ObjectiveTo compare profilometry and microhardness of polished occlusal and buccal human enamel following a mechanical and chemical wear regime. MethodsEnamel from polished human molars were sectioned into buccal and occlusal surfaces and randomly allocated into two groups (n = 10) and then exposed to 0.3 % citric acid at pH 2.7 for 10, 20, 40 and 60 mins each followed by abrasion with non-fluoridated toothpaste for 240 strokes in a reciprocating brushing machine. A white light profilometer with a spot size of 12 um measured mean step-height following each cycle. Microhardness indentations were conducted following the final cycled 60 mins erosion/abrasion using 0.01, 0.02, 0.1, 0.5 and 2.5 kgf indentation load. Statistical disparity were evaluated using a two-way ANOVA and post-hoc Sidak's multiple comparisons tests at α = 0.05. ResultsAfter erosion/abrasion, the mean (SD) step-heights on occlusal and buccal surfaces were not significantly different until 60 mins, when occlusal surfaces exhibited greater step-heights, 32.9 µm (2.8) and 31.1 µm (1.8) and p = 0.02, respectively. Buccal and occlusal microhardness was statistically lower following erosion/abrasion at loads of 0.01 kgf (p = 0.0005) and 0.02 kgf (p = 0.0006) but no significant differences were observed in the microhardness between the surfaces at any loads. ConclusionThe occlusal and buccal surfaces were not statistically different for microhardness or step height suggesting the susceptibility to wear is not related to the anatomy and structure of the tooth and is more likely related to other factors such as the environment. Clinical SignificanceThe study emphasizes that a notable difference in wear between occlusal and buccal enamel surfaces emerges only after prolonged exposure to simultaneous chemical and mechanical stress. This finding necessitates a preventive dental approach that accounts for both the duration of exposure and environmental factors.

The early wear susceptibility of cementum, enamel and dentine in vitro

ObjectivesTo assess the differential early wear susceptibility of cementum, enamel and dentine at a micron level. MethodsWhole human molar buccal surfaces incorporating natural enamel and cementum (n = 20) confirmed by imaging (digital microscopy: Keyence, VHX-7000 Milton Keynes, UK), were mounted, scanned (profilometry: XYRIS 4000, Taicaan, Southampton, UK), and allocated to receive erosion (citric acid, pH 2.7, 30 min (n = 10)) or erosion/abrasion challenges (3 cycles of (citric acid, pH 2.7, 10 min, 60 300 g linear abrasion strokes), n=10). Samples were polished and the experiment repeated on polished enamel, and polished coronal and radicular dentine within the same tooth. Profilometric wear data were obtained using superimposition: GeoMagic (3Dsystems, Darmstadt, Germany) and subtraction: MountainsMap (DigitalSurf, Besancon, France). Data were normal. A general linear model was used to assess differences between groups and substrates. ResultsThe mean step height (SD) for natural enamel was 8.82 μm (2.53) for erosion and 11.48 μm (2.95) for erosion/abrasion. For natural cementum, the mean step height was 6.00 μm (2.29) for erosion and 4.67 μm (1.58) for erosion/abrasion. Dentine step heights ranged from 7.20 μm (1.53) for erosion and 9.79 μm (1.01) for erosion/abrasion with no statistical differences in dentine wear. Natural cementum surfaces had the lowest wear (p<0.001). Dentine had significantly less wear than natural enamel (p<0.02). ConclusionsCementum surfaces demonstrated the most wear resistance, followed by dentine under erosion dominant conditions in this in vitro study. Further in-vivo investigations are needed to confirm the intraoral stability of cementum. Clinical SignificanceCementum may be the least susceptible of dental substrates to wear and dentine does not wear at a faster rate than enamel under erosive conditions. This adds to our knowledge on the development of non-carious cervical lesions and questions whether wear rates will accelerate once dentine is exposed.

Proteins from whole mouth saliva mediate greater protection against severe erosive tooth wear than proteins from parotid saliva using an in vitro model

Objectivesto investigate how the composition of the acquired enamel pellicle (AEP) affected a laboratory model of erosive tooth wear (ETW) on human enamel by comparing whole mouth saliva (WMS) to parotid saliva (PS). Methods60 enamel specimens were prepared from extracted human teeth and were randomly assigned to 4 experimental groups: WMS (n = 20), PS (n = 20), artificial saliva (AS, n = 10) and deionised water (DW, n = 10). Following incubation, a subset of WMS (n = 5) and PS (n = 5) groups were used to collect the AEP before the erosive challenge. The rest of the blocks, had their AEP collected after five cycles of acid, wash and saliva and were then assessed for mean step height changes using a non-contacting profilometer (n = 10 each). AEP samples were collected from the enamel specimens by rubbing with filter papers soaked in sodium dodecyl sulfate. Total protein in AEP was quantified using BCA assay, individual protein components of AEP were separated and analysed using SDS-PAGE and western blot for [mucin 5b, albumin, carbonic anhydrase VI (CA VI), statherin]. Specific antibody binding was quantified using purified protein standards of known concentration. Samples of AEP were also analysed by LC/MS/MS sequencing. ResultsWMS group had significantly (p < 0.0001) less acid-induced erosion (step height [4.16 (0.9) μm]) than PS group [6.41 (0.3) μm]. The amount of total protein, mucin 5b and albumin were more dominant in WMS pellicles than PS (p < 0.0001) whereas CA VI and statherin were dominant in PS pellicles (p < 0.0001). ConclusionThe composition of the acquired enamel pellicle influences the degree of protection from acid attack, possibly by altering the mechanism of protection. The in-vitro model used in this study was severe enough to cause tissue loss as opposed to just softening of the surface structure. AEP from WMS was more protective than that of PS, and its likely mechanisms of protection seem to be as a physical barrier rather than stabilising the crystal structure. SignificanceThe protective salivary proteins against in-vitro erosion models differ from in-vivo studies. Therfore, it can be recommended that in-vitro laboratory models of ETW need to be assessed carefully to represent the clinical environment more closely.

The presence of acquired enamel pellicle changes acid-induced erosion from dissolution to a softening process

Erosive wear undermines the structural properties of enamel resulting in irreversible enamel loss. A thin protein layer formed from natural saliva on tooth surfaces, acquired enamel pellicle (AEP), protects against erosive wear. The exact components in saliva responsible for such protection are not yet known. We prepared three solutions containing different components: proteins and ions [natural saliva (NS)], minerals with no proteins [artificial saliva (AS)] and neither proteins nor ions [deionised water (DW)]. To assess the protection of the three solutions against citric acid enamel erosion, enamel specimens were immersed in the corresponding solution for 24 h. All specimens were then exposed to five erosion cycles, each consisted of a further 30 min immersion in the same solution followed by 10-min erosion. Mean step height using a non-contacting profilometer, mean surface microhardness (SMH) using Knoop microhardness tester (final SMH), and roughness and 2D profiles using atomic force microscopy were measured after five cycles. The final SMH values were compared to the starting values (after 24 hr). NS group had significantly less tissue loss but greater SMH change (P < 0.0001) than AS and DW groups. Specimens in NS were softer and rougher (P < 0.001) but less eroded than specimens in AS and DW.

A novel approach to study in situ enamel erosion and abrasion lesions

ObjectivesThis study investigated previous hypotheses that the tongue can abrade acid softened/eroded enamel surfaces. MethodsTwelve upper removable appliances each retaining 2 anterior and 2 posterior human enamel specimens were constructed. Each specimen was exposed to acid on both surfaces, but only one surface was allowed contact with the tongue. Therefore, 96 surfaces were assessed. Appliances were worn from 9.30 to 17.00 Monday to Friday for 22days. Acid eroded lesions were created by immersing the specimens for 5min in 50ml orange juice three times daily. Enamel loss was measured using Quantitative light- induced fluorescence (QLF) and Non- contact profilometry (NCLP) and the differences (D) between tongue (Dt) and palate facing (DP) surfaces determined. Results%ΔFD(t-p) from the two anterior specimens were greater than from those placed posteriorly with mean values of 15.9% (±9.1) and 14.4% (±8.4), 5.6% (±8.7) and 4.5% (±6.6) respectively. Similarly, NCLP data showed anterior specimens had greater differences for mean step height (MSH) between tongue- facing and the palate- facing (control) surfaces than posterior specimens. MSHD(t-p) values were 59.4μm (±30.3) for anterior tongue facing surfaces and 55.5μm (±29.4) for posterior palate facing surfaces. For the posterior specimens MSH was 48.1μm (±26.1) and 51.7μm (±30.4) respectively (p<0.05). ConclusionThe greater enamel surface loss of the anterior specimens demonstrates that abrasion by the tongue on acid softened/eroded enamel in situ is likely.

Effect of Model Variables on in vitro Erosion

The aim of this study was to investigate the effects of tooth type (molar/premolar), tooth surface (buccal/lingual), smear layer or no smear layer, storage of specimens in deionised water, mode and speed of agitation, and rinsing method between cycles on mean step height loss and Knoop microhardness (KHN) change. Polished human enamel specimens embedded in acrylic resin were prepared from sound permanent molar and premolar tooth surfaces. A 0.3% (pH 3.2) solution of citric acid was used to erode the specimens, in a cycling procedure, consisting of 10 min immersion followed by rinsing in deionised water for 30 s with a spray bottle, for 5 cycles. The specimens were analysed with a non-contact white light profilometer and KHN. Molar teeth (148.99 ± 24.49 KHN) and buccal surfaces (155.62 ± 30.35 KHN) produced significantly less microhardness change compared to premolar (186.40 ± 20.74 KHN) and lingual surfaces (179.76 ± 23.21 KHN; p < 0001). The effect of storage and rinsing showed little difference in mean step height loss (<1 µm) and microhardness change. With no smear layer a significantly lower mean step height loss and microhardness change (p < 0.001) was observed. Agitation was performed with Orbital, Gyro and See-Saw rockers at 30, 40, 60, and 70 rpm. The mean step height loss was largest for See-Saw at 70 rpm (11.73 ± 0.91 μm) and lowest for Orbital at 30 rpm (2.76 ± 1.12 μm). A statistical difference was found between all types of agitation and speeds (p < 0.001). In conclusion, this study has shown that the variables investigated here have a significant impact on the measurable outcome, highlighting the importance of accurate and detailed method sections.

May caries-preventive fluoride regimes have an effect on dental erosive wear? An in situ study

Objective. High and low concentration NaF regimes have shown caries protective properties, but the preventive effect against erosive/abrasive wear is unclear. Aim. To measure the inhibiting effect on enamel wear of low and highly concentrated sodium fluoride (NaF) toothpastes and a stannous (SnF2) fluoride gel in a single-blind, randomized in situ study, using a White Light Interferometer. Materials and methods. Sixteen human molars were each divided into four specimens, mounted on acrylic mouth appliances and worn by eight volunteers for 9 days. Experimental procedures were performed in the laboratory. The enamel specimens were brushed every day with fluoride-free toothpaste. Treatments; group 1: no fluoride treatment (control), group 2: SnF2 gel 2500 ppm F (5 min) every third day, group 3: NaF toothpaste 5000 ppm F 5 min every third day and 2 min the other days, group 4: NaF toothpaste 1450 ppm F (2 min) every day. In order to mimic gastric reflux/vomiting, the specimens were etched with 0.01 M HCl for 2 min twice a day. Results. The mean step height (µm) for the control specimens was −32.9 (SD = 6.8). The mean values for the other groups were −22.2 (SD = 8.4) (group 2), −30.8 (SD = 7.8) (group 3) and −31.4 (SD = 7.7) (group 4). Compared with the control, the SnF2 treated specimens showed significantly lower wear. The NaF toothpastes gave no significant protective effect. Conclusions. Application of SnF2 gel every third day gave protection against erosive–abrasive challenges. Daily application of both low concentration and high concentration NaF toothpaste provided no protection.

Comparison of the Possible Protective Effect of the Salivary Pellicle of Individuals with and without Erosion

The acquired pellicle adheres to tooth surfaces and has been suggested to provide differing degrees of protection against acidic erosion. This study investigated whether pellicle formed on enamel blocks in patients suffering dietary dental erosion modified the effect of an in vitro simulated dietary challenge, in comparison with pellicle formed on enamel blocks in healthy subjects and to no-pellicle enamel samples. Sixty subjects recruited from dental erosion clinics were compared to healthy age-matched controls. Subjects wore a custom-made maxillary splint holding human enamel blocks for 1 h during which the acquired enamel pellicle was formed. Enamel blocks were removed from the splints and a simulated dietary erosive challenge of 10 min was performed. In addition the challenge was performed on 30 enamel samples without pellicle. Profilometry showed no statistical difference between samples from the erosion subjects with a mean step height of 1.74 µm (SD 0.88) and median roughness (Sa) of 0.39 µm (interquartile range, IQR 0.3-0.56) and the controls with 1.34 µm (SD 0.66) and 0.33 µm (IQR 0.27-0.38), respectively. The control samples without pellicle had Sa of 0.44 µm (IQR 0.36-0.69) and these differences were statistically significant compared to those from the healthy subjects (p = 0.002). Mean (SD) microhardness reduction with a 100-gram load for the erosion group was 113.5 (10) KHN, for healthy subjects was 93 (15.4) KHN and for the enamel samples without pellicle 139.6 (21.8) KHN and all groups were statistically different. The microhardness and roughness data suggested the pellicle influenced erosion under these study conditions.

Turbulent flow over a rough backward-facing step

This work characterizes the impacts of the realistic roughness due to deposition of foreign materials on the turbulent flows at surface transition from elevated rough-wall to smooth-wall. High resolution PIV measurements were performed in the streamwise-wall-normal (x–y) planes at two different spanwise positions in both smooth and rough backward-facing step flows. The experiment conditions were set at a Reynolds number of 3450 based on the free stream velocity U∞ and the mean step height h, expansion ratio of 1.01, and the ratio of incoming boundary layer thickness to the step height, δ/h, of 8. The mean flow structures are observed to be modified by the roughness and they illustrate three-dimensional features in rough backward-facing step flows. The mean reattachment length Xr is significantly reduced by the roughness at one PIV measurement position while is slightly increased by the different roughness topography at the other measurement position. The mean velocity profiles at the reattachment point indicate that the studied roughness weakens the perturbation of the step to the incoming turbulent flow. Comparisons of Reynolds normal and shear stresses, productions of normal stresses, quadrant analysis of the instantaneous shear-stress contributing events, and mean spanwise vorticity reveal that the turbulence in the separated shear layer is reduced by the studied roughness. The results also indicate an earlier separation of the turbulent boundary layer over the current rough step, probably due to the adverse pressure gradient produced by the roughness topography even before the step.

On the impacts of coarse-scale models of realistic roughness on a forward-facing step turbulent flow

The present work explores the impacts of the coarse-scale models of realistic roughness on the turbulent boundary layers over forward-facing steps. The surface topographies of different scale resolutions were obtained from a novel multi-resolution analysis using discrete wavelet transform. PIV measurements are performed in the streamwise–wall-normal (x–y) planes at two different spanwise positions in turbulent boundary layers at Reh=3450 and δ/h=8, where h is the mean step height and δ is the incoming boundary layer thickness. It was observed that large-scale but low-amplitude roughness scales had small effects on the forward-facing step turbulent flow. For the higher-resolution model of the roughness, the turbulence characteristics within 2h downstream of the steps are observed to be distinct from those over the original realistic rough step at a measurement position where the roughness profile possesses a positive slope immediately after the step’s front. On the other hand, much smaller differences exist in the flow characteristics at the other measurement position whose roughness profile possesses a negative slope following the step’s front.

Non-universal equilibrium crystal shape results from sticky steps

The anisotropic surface free energy, Andreev surface free energy and equilibrium crystal shape (ECS) z = z(x,y) are calculated numerically using a transfer matrix approach with the density matrix renormalization group (DMRG) method. The adopted surface model is a restricted solid-on-solid (RSOS) model with ‘sticky’ steps, i.e. steps with a point-contact-type attraction between them (p-RSOS model). By analyzing the results, we obtain a first-order shape transition on the ECS profile around the (111) facet; and on the curved surface near the (001) facet edge, we obtain shape exponents having values different from those of the universal Gruber–Mullins–Pokrovsky–Talapov (GMPT) class. In order to elucidate the origin of the non-universal shape exponents, we calculate the slope dependence of the mean step height of ‘step droplets’ (bound states of steps) ⟨n(p)⟩ using the Monte Carlo method, where p = (∂z/∂x,∂z/∂y) and ⟨⋅⟩ represents the thermal average. Using the result of the |p| dependence of ⟨n(p)⟩, we derive a |p|-expanded expression for the non-universal surface free energy feff(p), which contains quadratic terms with respect to |p|. The first-order shape transition and the non-universal shape exponents obtained by the DMRG calculations are reproduced thermodynamically from the non-universal surface free energy feff(p).

Spatial organization in the step‐pool structure of a steep mountain stream (Vogelbach, Switzerland)

Spatial organization in the step‐pool structure of a 1.58 km long section of the Vogelbach, a steep mountain stream (average channel bed slope 0.17 m/m) in the Alpthal basin, Switzerland, is analyzed to evaluate the extent of randomness in the occurrence of steps and to isolate the potential hydraulic and topographic controls on step placement. Statistics of the observed step sequence are compared with those of random sequences generated by permutation from the observed step height distribution. Hydraulic and topographic controls on step placement are analyzed from step length and steepness distributions and relations between mean step properties and step height and channel gradient for both observed and random sequences. Results show that (1) observed step length distributions are statistically significantly different from randomly generated sequences, (2) step steepness is significantly different in observed data because of a positive correlation between mean step length and height and it remains fairly constant for all step sizes, (3) spatial organization in steps does not extend far beyond the nearest step, and (4) the influence of channel gradient on step properties is insignificant and highly variable, indicating that hydraulic rather than topographic controls are dominant for step placement in this stream. Although the Vogelbach is a steep stream on the boundary between a cascading and step‐pool morphology where we would expect randomness to dominate, spatial organization was nevertheless detected in many important aspects of the step‐pool geometry.

Hole transport in SiGe channels on step-bunched vicinal Si surfaces

Hole transport in narrow modulation doped Si 1− x Ge x channels grown on vicinal Si(1 1 3) by molecular beam epitaxy is studied. Owing to the strong step-bunching properties of the Si(1 1 3) surface, the Si 1− x Ge x channels exhibit regular terraces with a width of typical 250 nm and a mean step height of 4 nm , corresponding to 25 monolayers, when appropriate growth conditions are used. Considerable amount of Si 1− x Ge x material accumulates at the step edges resulting in regular wire-like channel thickness variations. At low temperatures, we find a pronounced resistivity anisotropy for transport perpendicular and parallel to the step edges. The resistivity is maximum for the current flow perpendicular to the step edges. This can be explained by a lateral modulation of the hole confinement potential caused by the channel thickness variation near the step edges. Lowering the doping concentration, i.e. decreasing the effective carrier density in the channel, enhances the resistivity anisotropy up to ρ ⊥/ ρ ||≈16. We attribute this to an increasing resistivity of depleted SiGe layer regions in between the wire-like structures, when the Fermi energy gets comparable to the lateral potential barriers.

Characteristics of log and clast bed-steps in step-pool streams of northwestern Montana, USA

The role of log and clast steps was studied in 53 step-pool reaches in 32 streams in northwestern Montana. In each reach, 20 consecutive steps were sampled. Drainage areas ranged from 0.5 to 11.5 km 2. Mean step spacing was found to be proportional to channel gradient, width of the bankfull channel, and drainage area; mean step height was proportional to the width of the channel. No significant difference exists between clast and log steps with regard to step spacing and step height. This suggested either that (1) woody debris is mobile in even the smallest channels in the study area, or (2) channel flows arrange clast steps around immobile woody debris. Calculations of theoretical entrainment and transport of sediment suggest that the coarse clasts forming steps are capable of being entrained at bankfull discharge in most channels. The presence of immobile log steps (composed of living roots) in the upstream reaches, an increase in the percentage of log steps with gradient, and a decrease in this percentage with the width of the bankfull channel and drainage area, imply that woody debris is mobile primarily in the downstream reaches. Calculations of flow resistance suggest that most steps serve to maximize flow resistance. These results support the second hypothesis, that the height and spacing of clast steps are adjusted around immobile log steps to maintain consistent step characteristics.

Crossover scaling of growing surfaces with threshold

We investigate a crossover behaviour of the conservative and non-conservative growing models in which the surface relaxation is restricted by the given value of threshold, H. The time dependence of the mean step height, which scales as , is found to be responsible for the observed crossover behaviour of the surface width. A modified scaling ansatz is also proposed to describe the crossover behaviour in the growing models of this kind.

Structural studies of (511) and (711) GaAs surface

High-index GaAs (511) and (711) surfaces, prepared by sputtering and annealing chemically polished substrates, are studied with low energy electron diffraction, Auger electron spectroscopy, and electron energy loss spectroscopy. The inequivalent A and B surfaces of each orientation are investigated. The four surfaces exhibit an ordered array of steps. The terraces and steps correspond to (100) and (111) planes, respectively. Calculations of the splitting of the LEED spots and of in-phase, out-of-phase diffraction from the terraces are performed to determine the mean terrace width and step height. The appearance of the Ga surface exciton peak in the energy loss spectrum is linked to the local bonding of the top Ga atoms and is used to distinguish the A surface from the B surface.

Unit Cell Step Structure on Vapour Grown CdCr2Se4 Single Crystals

In order to study the mechanism of the crystal growth of CdCr2Se4 by the chemical vapour deposition, the surface micro-structure was examined with an interference contrast microscope. On the well-developed {111} face of the spinel we can find often regularly arranged monomolecular step structure which is intimately related with the crystal growth process. The mean step height was found to be 6.5±0.5 Å which is equal to one third of the unit cell dimension in <111> direction. All the steps are generated either from a single spiral dislocation or from one point at the edge of the crystal. The steps are arranged with a regular separation of several micrometers. The bunching of the steps would have been prevented by the Schwoebel effect.