Changes in surface characteristics of dental resin composites after polishing

The objectives of this study were (1) to determine in vitro changes in surface roughness and color of dental resin composites after application of three finishing and polishing systems; (2) to evaluate the difference in color stability after immersion in a dye solution after polishing; and (3) to evaluate the effects of surface condition, especially roughness, on measured color depending on the color measuring geometries of specular component excluded (SCE) and specular component included (SCI). Color and surface roughness (R_a) of resin composites of four brands of A2 shade and one brand of Yellow Enamel shade were measured after polymerization, after polishing with Enhance (Dentsply), Sof-Lex (3M ESPE), or Super-Snap (Shofu) composite finishing and polishing systems. Color was also measured after immersion in 2% methylene blue solution. Color was measured according to the CIELAB color scale. Color changes (E*_ab) after polishing/staining and by the measuring geometry were calculated by the equation; E*_ab = [(L*)² + (a*)² + (b*)²]^1/2. Ra value was measured with a surface roughness tester. E*_ab and L* values after polishing and after staining varied among polishing systems when measured with SCE geometry. Composites polished with Super-Snap and Sof-Lex systems showed higher E*_ab and L* values than those polished with Enhance polishing system with SCE geometry. E*_ab and L* values between specimens with different surface conditions measured with SCE geometry were significantly higher than those with SCI (p < 0.01). Changes in R_a value after polishing was insignificant in most cases.     

The influence of substratum topography on bacterial adhesion to polymethyl methacrylate

The effect of substratum roughness on the adhesion of Pseudomonas aeruginosa and Staphylococcus epidermidis was investigated using PMMA. A small increase in Ra values (0.04–1.24 m) resulted in a significant increase (P<0.05) in bacterial attachment. Subsequent increases in surface roughness (Ra=1.86–7.89 m) resulted in a decrease in adhesion, although adhesion was still higher than to the smooth surface. When the PMMA surfaces were coated with protein (bovine serum albumin), no difference (P<0.05) could be determined in the amount of protein adsorbed, irrespective of surface topography. However, the influence of the underlying topography on adhesion was still evident. Substratum topography is an important parameter affecting bacterial adhesion to surfaces.     

琉璃瓦颜色测量方法研究

选择常用的两类分光光度计,以色差为评价指标,探索分光光度计在不同测量参数下,对琉璃瓦颜色测量的规律。研究结果表明:在SCI和SCE两种测量模式下,固定测量孔径重复测量结果稳定性好,但不同测量孔径对测量结果具有显著影响;在CIE推荐测量条件下不同测量孔径时,SCI与45°/0°的色差稳定性优于SCE与45°/0°的色差,但SCI与45°/0°的色差显著大于SCE与45°/0°的色差,且SCE在10 mm测量孔径下与45°/0°的色差最接近;琉璃瓦曲率越大,不同测量模式结果的稳定性越差,采用较大孔径(10 mm)测量结果差异最为明显;与SCI和45°/0°相比,SCE对于琉璃瓦表面形态的变化更加敏感。总体而言,积分球式分光光度计的SCE测量模式更适合于琉璃瓦颜色的测量,测量时应选择较大尺寸的测量孔径。     

Evaluation of subsurface damage in CAD/CAM machined dental ceramics

Commercial ceramics for dental computer aided design/computer aided manufacture (CAD/CAM) restorations suffer from surface chipping defects and microcracking. The influence of CAD/CAM machining of dental materials on the mechanical strength and extension of the damage zone was studied. Two different commercial dental ceramics, a feldspathic porcelain and a glass–ceramic, were CAD/CAM machined according to dental practice. The extension of the damage zone was analysed by a stepwise erosion of the surface, and the biaxial flexural strength was measured. To simulate the adhesive fixing of ceramic inlays, the specimens were sealed using a light-curing monomer. The different machining behaviour is dominated by the microstructure of the investigated materials. Owing to the high amount of glassy phase, the feldspathic porcelain shows extensive microcracking and chipping defects. The extent of the damage zone can be determined as 40–60 m. Sealing of the surface did not affect the flexural strength of the machined samples. The dominating response to machining of the glass–ceramic is crushing and crumbling with a major contribution of plastic deformation on a microscopic scale. The extent of the damage zone is less than 20 m. These cracks can be bridged by sealing of the surface, resulting in a substantial increase in strength. © 1998 Chapman & Hall     

Finite element analysis of stress distribution in porcelain discs

Achievement of a controlled stress distribution in feldspathic porcelain is essential for successful dental restorations. In this study, a program for visco-elastic finite element analysis (FEM) of the stress distribution produced during processing of porcelain was developed. This method was applied to simulate the stress change in porcelain discs that were subjected to convective cooling. The heat transfer coefficient was assumed to be 2.1 J mm-2 min-1 °C-1 at the surface of the discs. These discs were 2 mm in thickness and had radii varying between 4.8 and 38 mm.As the discs cooled from their sintering temperature, stresses initially developed at about 600°C. Residual tensile stress of 8.3 MPa was produced at the centre of the top surface of a 16-mm diameter disc compared with a compressive stress of –7.6 MPa for a 50-mm diameter disc.     

X-ray diffraction characterization of dental gold alloy-ceramic interfaces

X-ray diffraction (XRD) was employed to study dental alloy-ceramic interfaces. A Au-Pd-In alloy, which requires oxidation before porcelain firing, and a Au-Pt-Pd-In alloy, which does not require oxidation before porcelain firing, were selected in this study. Alloy specimens were centrifugally cast. Specimen surfaces were metallographically polished through 0.05 m Al_2,O_3} slurries. A thin layer (<50 m) of a dental opaque porcelain was fired on the alloy surfaces with and without initial oxidation. XRD was conducted at room temperature on four types of alloy specimens: polished, oxidized, porcelain fired after alloy oxidation, and porcelain fired without initial alloy oxidation. XRD was also performed on fired opaque porcelain without an alloy substrate. The detection of prominent gold solid solution peaks from alloy-ceramic specimens indicated that the incident X-ray beam reached the alloy-ceramic interface. In₂O₃ and -Ga₂O₃ were identified on the oxidized Au-Pd-In alloy, while In₂O₃ and SnO₂ were detected on the oxidized Au-Pt-Pd-In alloy. Preferred orientation was observed for all the oxides formed on the alloys. Minimum lattice parameter changes (<1%) for the gold solid solutions were observed for both alloys before and after oxidation and porcelain firing. Leucite (KAlSi₂O₆), TiO₂, ZrO₂ and SnO₂ were detected on the fired opaque porcelain. For both alloys, no additional oxides were identified at the metal-ceramic interfaces beyond those present in the oxidized alloys and the opaque porcelain. Similar results were obtained from alloy-ceramic interfaces where there was no prior alloy oxidation. The results indicate the critical role of alloy surface oxides in metal-ceramic bonding and support the chemical bonding mechanism for porcelain adherence. © 2001 Kluwer Academic Publishers     

Characterization of microblasted and reactive ion etched surfaces on the commercially pure metals niobium, tantalum and titanium

In surface-roughened metallic implant materials, the topography, chemistry and energy of the surfaces play an important role for the cell and tissue attachment. The highly reactive commercially pure metals niobium, tantalum and titanium were analysed after microblasting (with Al2O3 powder and consecutive shot-peening with ZrSiO2), and after additional reactive ion etching (RIE, with CF4). Scanning electron microscopy in combination with energy-dispersive X-ray analysis and surface roughness measurements showed, for all microblasted surfaces, a heterogeneous roughening (Ra about 0.7 m), and a contamination with blasting particles. RIE resulted in a further roughening (Ra about 1.1 m), and a total cleaning from contaminations, except for traces of aluminium. Determination of surface energy by dynamic contact angle measurements showed an increase in surface energy after microblasting, which further increased after RIE, most pronounced for commercially pure niobium. In conjunction with superior electrochemical properties, this makes niobium and tantalum promising candidates for implant purposes, at least equal to the generally used titanium.     

Determination of Thermal Transmittance of Insulated Double Low-E Glazing Panel Using Portable <Emphasis Type="BoldItalic">Uglass</Emphasis> Measuring Technique

Windows are regarded as the primary object of energy efficiency in buildings because window is one of the major energy loss areas in building construction. Existing methods were not field measurements and were not enough to get the correct thermal transmittance. We used portable \(U_{g}\) measuring device on field and measured the thermal transmittance with low-E coated and uncoated double glazing panels in existing houses, apartments and buildings. In addition, we prepared four test benches and compared the insulation performance according to the construction conditions. In results, the insulation performance of double glazing panel with low-E coating is up to about 41 % higher than uncoated panel due to low-E coating inside and the glazing panel filled with about 90 % of argon gas decrease about 0.15 \(\hbox {W} \cdot \hbox {m}^{-2} \cdot \hbox {K}^{-1}\) than glazing panel filled with air gas. The measured results were compared with the theoretically calculated results according to DIN EN 673 to confirm the reliability of the analytical results. In this study, portable NETZSCH Uglass is used to increase the accuracy of calculation of thermal transmittance with various double and triple glazing panels. The paper analyzes the insulation performance of the double glazing panels in accordance with the construction conditions.     

Numerical simulation of the casting process of titanium tooth crowns and bridges

The objectives of this paper were to simulate the casting process of titanium tooth crowns and bridges; to predict and control porosity defect. A casting simulation software, MAGMASOFT, was used. The geometry of the crowns with fine details of the occlusal surface were digitized by means of laser measuring technique, then converted and read in the simulation software. Both mold filling and solidification were simulated, the shrinkage porosity was predicted by a feeding criterion, and the gas pore sensitivity was studied based on the mold filling and solidification simulations. Two types of dental prostheses (a single-crown casting and a three-unit-bridge) with various sprue designs were numerically poured, and only one optimal design for each prosthesis was recommended for real casting trial. With the numerically optimized design, real titanium dental prostheses (five replicas for each) were made on a centrifugal casting machine. All the castings endured radiographic examination, and no porosity was detected in the cast prostheses. It indicates that the numerical simulation is an efficient tool for dental casting design and porosity control. © 2001 Kluwer Academic Publishers     

The influence of surface roughness and pre-oxidation state on the wettability of aluminium nitride by commercial brazes

The effects of roughness (Ra = 0.17–0.20 m) and of pre-oxidation of the AlN ceramic surface on its wettability and contact interaction with commercial brazing alloys CB4 and CB5 of Ag-Cu-Ti composition have been studied. Wettability has been determined by the sessile drop method at three holding temperatures (810, 900 and 950°C). Particularities of the interface interaction have been identified by microprobe analysis for pre-oxidized samples. Experimental data are compared with data for samples polished to Ra = 0.02–0.03 m not subjected to pre-oxidation. The results show that, for the systems under study, surface roughness does not influence the contact angle value significantly. Pre-oxidation of the AlN in air at 1250°C, however, tends to reduce wettability as a result of the replacement of braze-aluminium nitride interaction by braze-surface aluminium oxide interaction.     

Adherent bacteria cells in five dental materials: sonication effect

Adherent bacterial cells on the surfaces of two dental porcelain ceramics, three composite resins and human enamel were examined using four types of bacteria strains. Their adherent cells were counted on saliva-coated and uncoated material surfaces after sonication, and contact angle and potential were measured for each adherent cell tested. A correlation between contact angle and bacterial cells on an uncoated surface was found to be higher in two Streptococcus sanguis cells than in S. mutans Ingbritt and S. sobrinus OMZ 176, whereas there appeared to be a higher correlation between S. mutans Ingbritt or S. sobrinus OMZ 176 and potential on the uncoated surface. On the saliva-coated surface, a significantly high correlation was found between the adherent cells, with the exception of S. sanguis ATCC 10 557, and the potential. Contact angle and potential values were small when the surfaces of the materials were coated with saliva, as compared with those on the uncoated surface. The sonication condition (120 s) of adherent cells on the surface of the material significantly depended on the types of bacteria cells, showing that S. mutans Ingbritt (>50–60%) had a greater removal percentage than the others (<50%). © 1998 Chapman & Hall     

The effect of indium on porcelain bonding between porcelain and Au−Pd−In alloy

The effect of small In additions on oxide structure and porcelain adherence to Au–Pd alloys was studied. In was oxidized internally as In₂O₃. No uniform external oxide layer could be seen. Small In addition (1 at %) did not have any detectable effect on porcelain adherence (12 MPa), whereas higher In concentration (5 at %) caused significant increase in bond strength (26 MPa). This increase was probably a result of higher In₂O₃ concentration at the surface.     

Cathodic-Polarization Effects on the Long/Short Corrosion-Fatigue Crack Growth Rate of an Offshore Steel

We study the cyclic crack growth rate of an offshore steel. Compact specimens with long cracks and cylindrical specimens with short surface cracks were tested in air (at frequencies of 5–10 Hz) and in a 3.5% aqueous solution of NaCl (0.2 Hz). In the presence of cathodic polarization (–950 mV/SCE), the growth rate of long cracks is higher than under the conditions of free corrosion. The plateau appearing in this case in the da/dN–K diagrams indicates the presence of hydrogen embrittlement. For K > 10 MPa, the growth rates of short and long cracks coincide.     

Analytic solution for separating spectra into illumination and surface reflectance components

The measured light spectrum is the result of an illuminant interacting with a surface. The illuminant spectral power distribution multiplies the surface spectral reflectance function to form a color signal--the light spectrum that gives rise to our perception. Disambiguation of the two factors, illuminant and surface, is difficult without prior knowledge. Previously [IEEE Trans. Pattern Anal. Mach. Intell.12, 966 (1990); J. Opt. Soc. Am. A21, 1825 (2004)], one approach to this problem applied a finite-dimensional basis function model to recover the separate illuminant and surface reflectance components that make up the color signal, using principal component bases for lights and for reflectances. We introduce the idea of making use of finite-dimensional models of logarithms of spectra for this problem. Recognizing that multiplications turn into additions in such a formulation, we can replace the original iterative method with a direct, analytic algorithm with no iteration, resulting in a speedup of several orders of magnitude. Moreover, in the new, logarithm-based approach, it is straightforward to further design new basis functions, for both illuminant and reflectance simultaneously, such that the initial basis function coefficients derived from the input color signal are optimally mapped onto separate coefficients that produce spectra that more closely approximate the illuminant and the surface reflectance for any given dimensionality. This is accomplished by using an extra bias correction step that maps the analytically determined basis function coefficients onto the optimal coefficient set, separately for lights and surfaces, for the training set. The analytic equation plus the bias correction is then used for unknown input color signals.     

AFM,SEM and XPS characterization of PAN-based carbon fibres etched in oxygen plasmas

Atomic force microscopy (AFM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) have been used to investigate changes in topography and surface chemical functionality on PAN-based carbon fibres exposed to low-temperature, lowpower, oxygen plasmas. Unsized, type II, Cellion 6000 carbon fibres were treated in oxygen plasmas for 2–60 min at a power of 25 W. Increasing treatment time caused an increase in oxidation from surface alcohol(ether) to carbonyl and carboxyl species, but the total amount of oxidized carbon near the surface remained constant. SEM confirmed that treatments longer than 15 min resulted in pitting on the fibre surface, but even treatments of 60 min did not significantly reduce the overall fibre diameter. AFM showed surface morphology changes after oxygen plasma treatments for 2 and 15 min. 1 m×1 m AFM scans of untreated fibres showed processing grooves with a distribution of depths. Enlarged images along these grooves revealed that their walls were smooth. Oxygen plasma treatments of 2 min roughened fibre surfaces and created holes of the order of 50 nm evenly distributed with a spacing of 150 nm along the bottoms of the grooves. Treatment for 15 min smoothed the overall topography and resulted in smaller holes, of the order of 5–10 nm, with a spacing of < 50 nm. Calculated RMS roughnesses from the AFM data showed an initial increase in roughness with treatment, followed by a decrease to final values lower than those for untreated fibres.     

Effects of nano-scaled particles on endothelial cell function in vitro: Studies on viability, proliferation and inflammation

Recent studies give support for a connection between the presence of inorganic particles (of m and nm size) in different organs and tissues and the development of inflammatory foci, called granulomas. As the potential source of particles (e.g. porcelain dental bridges) and the location of particle detection were topographically far apart, a distribution via the blood stream appears highly probable. Thus, endothelial cells, which line the inner surface of blood vessels, would come into direct contact with these particles, making particle–endothelial interactions potentially pathogenically relevant. The objective of this study was to evaluate the effects that five different nano-scaled particles (PVC, TiO₂, SiO₂, Co, Ni) have on endothelial cell function and viability. Therefore, human endothelial cells were exposed to different amounts of the above-mentioned particles. Although most particle types are shown to be internalised (except Ni-particles), only Co-particles possessed cytotoxic effects. Furthermore, an impairment of the proliferative activity and a pro-inflammatory stimulation of endothelial cells were induced by exposure to Co- and, to a lesser extent, by SiO₂-particles. If a pro-inflammatory stimulation of endothelial cells occurs in vivo, a chronic inflammation could be a possible consequence.     

金银卡纸的镜面反射对颜色复制的影响

目的针对金银卡纸表面因具有强烈的镜面反射作用且印刷适性较差的缺点,研究金银卡纸镜面反射对印刷品颜色的质量控制。方法试验分析金银卡纸印刷镜面反射作用对印品明度值的影响,用曲线拟合的方法找出包含和不包含镜面反射作用测出的明度值之间的关系。结果经过检验分析,SCE条件下的测量数据相对于SCI明度偏小,这是因为SCE测量模式中,镜面反射光被排除在外面,只测量了漫射光。从青色的线性拟合图来看,所得线性拟合图大致为一条斜率为45°的直线。结论包含和不包含镜面反射明度值这2组数据之间存在数学关系,在实际应用中,可以考虑使用明度差这种线性关系来作为金银卡纸颜色控制和评价的依据。     

Tensile force testing of optimized coin-shaped titanium implant attachment kinetics in the rabbit tibiae

In the present study, the bone response of titanium implants at early bone healing stages, was evaluated using a tensile test. Test surface of coin-shaped cp. titanium implants were standardized by grit blasting with TiO₂, grain size 180–220 m. The surface topography of the implant specimens was examined by SEM, and by a confocal laser scanner for evaluation of S _a, S _t and S _dr. The implants were placed onto the leveled site on the tibia of 12 New Zealand White rabbits, 4 implants in each animal. The rabbits were divided into three groups with different observation times i.e. 2, 4 and 6 weeks. The retention of 12 implants were tested by measuring the pull-out force needed to detach the implant from the bone. There was a significant increase in implant retention from 2 to 4 and to 6 weeks healing time (p<0.05). Four implants from each time point were randomly chosen for histological evaluation. The histological appearance of the implant–bone interface at the different healing times showed noticeable differences in the degree of bone healing and maturation, suggesting that, in rabbits, 6 weeks healing time is a suitable observation point for tensile testing of surface optimized osseointegrating implants.     

Estimating illuminant color based on luminance balance of surfaces

To accomplish color constancy the illuminant color needs to be discounted from the light reflected from surfaces. Some strategies for discounting the illuminant color use statistics of luminance and chromaticity distribution in natural scenes. In this study we showed whether color constancy exploits the potential cue that was provided by the luminance balance of differently colored surfaces. In our experiments we used six colors: bright and dim red, green, and blue, as surrounding stimulus colors. In most cases, bright colors were set to be optimal colors. They were arranged among 60 hexagonal elements in close-packed structure. The center element served as the test stimulus. The observer adjusted the chromaticity of the test stimulus to obtain a perceptually achromatic surface. We used simulated black body radiations of 3000 (or 4000), 6500, and 20000 K as test illuminants. The results showed that the luminance balance of surfaces with no chromaticity shift had clear effects on the observer's achromatic setting, which was consistent with our hypothesis on estimating the scene illuminant based on optimal colors.     

Fluorapatite-mullite glass sputter coated Ti6Al4V for biomedical applications

A number of bioactive ceramics have been researched since the development of Bioglass in the 1970s. Fluorapatite mullite has been developed from the dental glass-ceramics used for more general hard tissue replacement. Being brittle in nature, glass-ceramics are currently used mainly as coatings. This paper shows that fluorapatite glass LG112 can be used as a sputtered glass coating on roughened surfaces of Ti6Al4V for possible future use for medical implants. An AFM was used to measure the roughness of the surface before and after coating to determine the change in the topography due to the coating process as this greatly affects cell attachment. The sputter coating partially filled in the artificially roughened surface, changing the prepared topography. Osteoblasts have been successfully grown on the surface of these coatings, showing biocompatibility with bone tissue and therefore potential use in hard tissue repair.