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Impact of surface micromorphology and demineralization severity on enamel loss measurements by cross-polarization optical coherence tomography
摘要： Objectives: Optical Coherence tomography (OCT) is a promising clinical imaging technology for quantitative and objective assessment of dental erosion. We aimed to determine the influence of enamel surface roughness and demineralization severity (by erosive challenge) on dental surface loss measurements by cross-polarization OCT (CP-OCT). Materials and methods: Human enamel specimens were prepared with three surface roughness levels (very rough, rough and polished; n = 10 each). They were evaluated using CP-OCT and optical profilometry (gold standard) at baseline, and after 1, 2, 4, 6, 8, 16 and 24 h of erosion demineralization. The effects of roughness and demineralization on enamel loss were analyzed using ANOVA (alpha = 0.05). Intraclass correlation coefficients (ICCs) and Bland-Altman plots were used to evaluate inter-method agreement and intra-examiner repeatability. Results: CP-OCT surface loss measurements did not significantly differ with the changes in enamel surface roughness (p = 0.27). Among demineralization severities, CP-OCT surface loss measurements at 1, 2, 4 and 8 h did not differ among each other, but they showed significantly lower enamel loss than 16 and 24 h; 6 and 16 h were significantly lower than 24 h (p < 0.05). Overall, CP-OCT and optical profilometry measurements did not differ (p = 0.73); however, ICC was relatively low (ICC = 0.34). Enamel loss estimation by CP-OCT presented an error of approximately ± 150 μm compared to profilometry. Intra-examiner repeatability with CP-OCT was excellent (ICC = 0.98). Conclusions: Enamel roughness did not affect CP-OCT measurements. The estimated error of CP-OCT measurements limited the appropriate assessment of enamel erosion surface loss, in the magnitude simulated in this study. Clinical relevance: Enamel thickness measurement by CP-OCT presents potential as an objective method for monitoring dental erosion lesions; however, its use may be limited for the assessment of the initial stages of enamel surface loss by erosion.
关键词： Tooth wear,Optical coherence tomography,Surface roughness,Enamel,Dental erosion,Demineralization
更新于2025-09-23 15:23:52
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The stability and degradation of PECVD fluoropolymer nanofilms
摘要： Fluoropolymer films are frequently used in microfabrication and for producing hydrophobic and low-k dielectric layers in various applications. As the reliability of functional coatings is becoming a more pressing issue in industry, it is necessary to determine the physical stability and degradation properties of this important class of films. To this end, a study has been undertaken to ascertain the aging characteristics of fluoropolymer films under various environmental conditions that such a film may experience during its use. In particular, fluorocarbon films formed by plasma-enhanced chemical vapour deposition (PECVD) using octafluorocyclobutane, or c-C4F8, as a precursor gas have been exposed to abrasive wear, elevated temperatures, ultraviolet radiation, as well as oxygen plasma and SF6 plasma, the latter being commonly used in conjunction with these films in ion etching processes. The results show that sub-micron thick fluoropolymer films exhibit a significant amount of elastic recovery during nanoscratch tests, minimising the impact of wear. The films exhibit stability when exposed to 365 nm UV light in air, but not 254 nm light in air, which generated significant decreases in thickness. Exposure to temperatures up to 175 °C did not generate loss of material, whereas temperatures higher than 175 °C did. Etching rates upon exposure to oxygen and SF6 plasmas were also measured.
关键词： Octafluorocyclobutane,Plasma deposition,Atomic force microscopy,Wear,Ellipsometry
更新于2025-09-23 15:23:52
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Microstructure and tribological properties of laser cladded self-lubricating nickel-base composite coatings containing nano-Cu and h-BN solid lubricants
摘要： In the present work, nickel-base composite powder (Ni60), nickel-base composite powder with the addition of h-BN solid lubricants (h-BN/Ni60) and nickel-base composite powder with the addition of nano-Cu encapsulated h-BN solid lubricants (nano-Cu/h-BN/Ni60) were used as raw materials to synthesize three different coatings on Q235 steels by laser cladding. Microstructures of these coatings were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. Tribological properties of these coatings were investigated at the temperatures from 25 °C to 600 °C. High temperature micro-hardness measurement was performed by Vickers micro-hardness tester. The results showed that the h-BN particles survived after laser cladding and displayed a homogeneous distribution in the nickel-base composite matrix. The encapsulation of h-BN by nano-Cu resulted in an increase of h-BN content in the coating. Although the addition of nano-Cu and h-BN led to a decrease on hardness, the nano-Cu/h-BN/Ni60 coating had the lowest friction coefficient and wear rate among the three coatings in a wide range of temperature from 25 °C to 500 °C. The mechanism of wear reduction by addition of nano-Cu encapsulated h-BN solid-lubricants was also discussed in this research.
关键词： Laser cladding,Self-lubricant coating,Steel substrate,Wear,Wide temperature range,Nickel-base composite
更新于2025-09-23 15:23:52
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Interaction between Debris Particles and Polishing Powder Wear Particles in Polishing Optoelectronic Components
摘要： The analysis of interaction between debris particles and polishing powder wear particles has demonstrated that the scattering of particles occurs through angles of 136.8° to 173.2°, and the effective differential scattering cross-section is 0.4 to 1.8 Tb. The trajectories of particles are rings located near the workpiece surface within a zone whose thickness approximates the mean grain radius of the polishing powder.
关键词： scattering cross-section,polishing powder wear particles,scattering angle,debris particles
更新于2025-09-23 15:23:52
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Effects of Nd:YAG laser surface treatment on tribological properties of cold sprayed Ti-6Al-4V coatings tested against 100Cr6 steel under dry condition
摘要： The surfaces of cold sprayed Ti-6Al-4V (Ti64) coatings were laser irradiated with different laser powers of 50-200 W to study the effects of Nd:YAG laser surface treatment on their tribological properties. The hardness of the laser treated Ti64 coatings became higher with higher laser power due to the more rapid cooling caused by a larger temperature difference between the coating surface and room temperature. The wear of the laser treated Ti64 coatings tested against 100Cr6 steel balls under dry condition at room temperature decreased with increased laser power as a result of their increased surface wear resistance associated with their increased surface hardness. It could be concluded that the laser surface treatment of the cold sprayed Ti64 coatings improved their surface wear resistance compared to that of the untreated Ti64 coatings.
关键词： Ti-6Al-4V,laser power,hardness,wear,laser surface melting,Cold spray
更新于2025-09-23 15:23:52
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Investigation on tool wear process of milling wave-transmitting Si <sub/>3</sub> N <sub/>4</sub> ceramics
摘要： Due to the low fracture toughness of wave-transmitting Si3N4 ceramics, the special material removal mechanism causes the tool wear to be different. The paper presents the tool wear forms and mechanism under different milling depth. The effect of tool wear on cutting force and machined surface morphology is discussed. Tests have been performed under typical conditions of cutting depth of 0.3 mm (in plastic-domain processing) and 0.4 mm (in brittle-domain processing). The results show that the abrasive wear caused by the chips is the main mechanism of the cutting edge wear and the flank wear, the increase of the side edge rear angle with tool wear is the main cause of the chipping phenomenon. The cutting depth is a significant influence parameter to the wear characteristics, and two types have been distinguished. As the material removal volume ascending, the cutting edge wear and the flank face wear has a stable period, and the root-mean-square deviation of processing surface increases to 1.6 μm, while that increase with the material removal volume continuously, and the processing surface decreases to 1.4 μm. It has been proved that the cutting force tends to increase first and then decrease as the material removal volume is about 4320 mm3.
关键词： ceramics,milling,morphology,plastic-domain,chipps,wear,Tool,brittle-domain,surface
更新于2025-09-23 15:23:52
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Assessment of tooth wear based on autofluorescence properties measured using the QLF technology in vitro
摘要： Background: The difference in autofluorescence between enamel and dentine layer has prompted recommendations to use the quantitative light-induced fluorescence (QLF) method for quantifying tooth wear (TW). This study investigated the potential of QLF for distinguishing the severity of occlusal TW based on differences in the autofluorescence intensity. Methods: In total, 106 extracted permanent molars and premolars having suspected wear without pulp exposure were used. The severity of wear was determined by visually examining all teeth using the tooth wear index (TWI) of Smith and Knight. QLF images were captured and converted into 8-bit grayscale images. The difference in the fluorescence intensity (ΔG) was calculated by comparing mean grayscale levels between sound and worn areas. Finally, histological examination was conducted by stereomicroscope to confirm the presence of dentine exposure. Results: 100 teeth were included in the final analysis without six teeth having enamel cracks around worn area. The ΔG values increased with the severity of TW as quantified using conventional TWI codes, and differed significantly between the sound and enamel- and dentine-wear teeth (P<0.001). The histology indicated that enamel remained on 57 teeth, while 43 teeth had dentine-exposed wear and showed significant differences in ΔG compared with enamel-remained teeth. Conclusions: The fluorescence intensity differed significantly depending on the presence of dentine exposure. ΔG could be used to distinguish between sound and enamel- and dentine-wear teeth with a significant correlation. These findings indicate that QLF could be useful for determining the severity of TW of occlusal surfaces noninvasively.
关键词： tooth wear index (TWI),fluorescence intensity,tooth wear,quantitative light-induced fluorescence (QLF),occlusal wear
更新于2025-09-23 15:22:29
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Evaluation of tooth wear by estimating enamel thickness with quantitative light-induced fluorescence technology
摘要： Background: Various techniques have been suggested to quantitatively assess tooth wear; most have limited clinical application. The first aim of this in vitro study was to estimate the residual enamel thickness of teeth with various degrees of occlusal wear using quantitative light-induced fluorescence (QLF). The second aim was to identify relationships between the fluorescence parameters of QLF and the conventional tooth wear index (TWI) system. Methods: Sixty-nine extracted permanent premolars and molars with initial stages of tooth wear (TWI score 1a-2: enamel wear to dentin exposure) were used. Two blinded and trained examiners participated in evaluation procedures. Occlusal QLF-digital (QLF-D) images were acquired for selecting area of interest (AOI) and calculating fluorescence for occlusal tooth wear (ΔFwear) of the AOI by the first examiner. Each specimen was cross-sectioned in the buccal-lingual direction. Enamel thickness from images obtained by stereomicroscopy and TWI of each sample was determined by the second examiner. Spearman correlation was used to determine the relationship of ΔFwear with enamel thickness and TWI. ΔFwear values were compared between histological scores with the Mann-Whitney U test. Results: Seventy-six AOIs were analyzed. As enamel thickness decreased, ΔFwear values significantly increased and strongly correlated with enamel thickness (Spearman rho = -0.825, P < 0.01). There were significant differences in ΔFwear values among TWI scores (P < 0.01); ΔFwear strongly correlated with TWI (Spearman rho = 0.753, P < 0.01). Conclusions: ΔFwear values, which denote fluorescence difference by using QLF, showed a strong correlation with residual enamel thickness and tooth wear severity.
关键词： QLF,quantitative light-induced fluorescence,auto-fluorescence,tooth wear,occlusal wear
更新于2025-09-23 15:22:29
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A comparative study of the growth dynamics and tribological properties of nanocrystalline diamond films deposited on the (110) single crystal diamond and Si(100) substrates
摘要： Nanocrystalline diamond (NCD) films were grown on the High Pressure High Temperature (HPHT) (110) single crystal (SC) diamond substrates by Microwave Plasma Enhanced Chemical Vapor Deposition (MPCVD) in methane/hydrogen/nitrogen plasma. The thickness of the films was varied between 2.2 and 22.5 μm. The cauliflower-like surface morphology was observed by means of Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The scaling behavior of NCD films growth was investigated. The relatively high value of the roughness exponent αs = 1.5–1.6 was found indicating anomalous scaling. Therefore, shadowing and diffusional instabilities can affect the film growth. The tribological properties of the NCD films deposited on the SC(110) diamond were compared with the NCD films prepared on the Si(100) substrates. Both types of specimens were tested under similar Hertzian contact pressure. The lower wear volume losses were observed on the NCD/SC(110) specimens. Therefore, the influence of substrate and substrate/film interface properties on the tribological behavior of the NCD films grown on Si(100) can be expected to cause NCD films deflection.
关键词： Wear,Single crystal,Tribology,NCD
更新于2025-09-23 15:22:29
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Effect of Nb addition on microstructure and properties of laser cladding NiCrBSi coatings
摘要： NiCrBSi coatings with different Nb additions have been prepared by laser cladding. The microstructure, phase composition, hardness, and wear resistance of the coatings were studied by scanning electron microscopy (SEM), electron probe microanalyser (EPMA), X-ray diffraction (XRD), microhardness tester and M-200 wear tester. The results show that the phases in the NiCrBSi coating without Nb addition include γ-Ni, Cr23C6, Cr7C3, Ni3B, Ni3Si2 and CrB. The NbC phase appears in coatings after the addition of Nb element. When the addition of Nb is 2 wt-%, the NbC particles with a size of about 1.2 μm were found in the coating, and the amount of NbC is about 1.8 vol.-%. With the increase of Nb addition, the size and amount of NbC in the coatings also increased. When the addition of Nb is 6 wt-%, the size of NbC is about 2.3–6.1 μm and the morphology of NbC changed from particle to quadrangular and petaloid shaped. In addition, when the addition of Nb is 2 wt-%, the hardness and wear resistance of the coating are the best, and the wear resistance of the coating is 104% higher than that without Nb addition.
关键词： Nb addition,wear resistance,microstructure,hardness,Laser cladding,NiCrBSi coatings
更新于2025-09-23 15:21:21