Porcelain laminate veneers have been a common treatment strategy in dental clinics. It is a conservative method for treatment of esthetic and functional problems in anterior region of oral cavity. Wide range of dental...Porcelain laminate veneers have been a common treatment strategy in dental clinics. It is a conservative method for treatment of esthetic and functional problems in anterior region of oral cavity. Wide range of dental ceramics is now available on market for fabrication of laminate veneers. Clinician should have enough knowledge regarding the composition and properties of these materials in order to be able to choose the appropriate one according to clinical situations.展开更多
A system of finished Componeer composite veneers is a unique and having no analogy in the world elaboration of the Swisscompany Coltene/Whaledent, an outcome of almost halfa century experience of the company working i...A system of finished Componeer composite veneers is a unique and having no analogy in the world elaboration of the Swisscompany Coltene/Whaledent, an outcome of almost halfa century experience of the company working in a field of composite materials.It combines the best features of direct and indirect restoration methods. The system is fulfilled of nanocomposite Synergy D6 that hashigh mechanical strength, convenience for workable consistency, color stability and a system of halftone shades, which facilitates colormatching. All this allows achieving excellent aesthetic results in minimal time. Application of an original standard scale givespossibility effectively assess optical properties of dental hard tissues and develop an implementation strategy of restoration before workstarted. Formation of Componeer form, polymerization and polishing at factory allow a practitioner fully utilize effect of＂fluorescence＂ inherent to the material. All this allows us to position the Componeer system as a serious alternative to non-directmethods of restoration with the possibility of both high aesthetic and cosmetic reconstruction reliability.展开更多
The discoloration of Scot pine （Pinus sylvestris var. Mongolica） veneers caused by resin-eliminated treatment and the reversion of the color were studied. The result showed that the color of the veneers changed from...The discoloration of Scot pine （Pinus sylvestris var. Mongolica） veneers caused by resin-eliminated treatment and the reversion of the color were studied. The result showed that the color of the veneers changed from buff to yellowish brown after the treatment of resin elimination and the discoloration of heartwood was more severe than that of sapwood; the degree of discoloration was significantly positively correlated with the medicament strength, temperature and resin-eliminated duration. The variance analysis showed the effects of those three factors on the discoloration were significant. With hydrogen peroxide （H2O2） as color reversion medicament and inorganic compound as medium of the reaction, the reversion of the color of heartwood was more inaccessible than that of sapwood; the degree of the color’s reversion was positively correlated with the H2O2 strength, temperature and treating time; the H2O2 concentration has significant effects on the discoloration. In order to reduce discoloration of Scot pine veneers, medicament of resin-eliminated used have to be at some low concentration, and the optimal concentration of H2O2 is 0.35% during the process of color’s reversion.展开更多
The impregnation of nanoparticles magnetified into wood had been developed by different methods,like surface chemical coprecipitation and vacuum-pressure coprecipitation of magnetic nanoparticles(NPs).However,there is...The impregnation of nanoparticles magnetified into wood had been developed by different methods,like surface chemical coprecipitation and vacuum-pressure coprecipitation of magnetic nanoparticles(NPs).However,there is a lack of information on the best method to coprecipitation NPs.Then,the present study has the objective to measure the effects of the impregnation process of wood veneers through two in situ processes(immersion and vacuum-pressure)using a solution of FeCl_(3)·6H_(2)O,FeCl_(2)·4H_(2)O and ammonia in three tropical species(Pinus oocarpa,Vochysia ferruginea and Vochysia guatemalensis).It was measured the degree of synthesis of iron NPs using weight and density gains,Fe^(3+) absorption,emission scanning electron microscope(SEM),Fournier transform infrared spectroscopy(FT-IR)and for magnetic properties were measured using vibrating sample magnetometry(VSM).After 5-layer veneer panels were fabricated,we evaluated their physical and mechanical properties.Wood samples impregnated by vacuum-pressure methods showed the higher amount of Fe_(3)O_(4)NPs formation,which was observed in the SEM,X-ray diffraction(XDR),FT-IR and VSM.Vacuum-pressure on treatment presented higher ferrite signals and better magnetic properties.Vochysia ferruginea presented the greatest magnetization properties.The magnetization treated causes probably a degradation of the cell wall,which weakens its mechanical properties,especially internal bonding.展开更多
Three types of material as platen in contact drying process were tested in Composition Board Laboratory of Northeast Forestry University in 1998. Poplar veneers were dried under’0.3 MPa at 160℃ or 180℃. Through com...Three types of material as platen in contact drying process were tested in Composition Board Laboratory of Northeast Forestry University in 1998. Poplar veneers were dried under’0.3 MPa at 160℃ or 180℃. Through comparison a non-metal flexible material was chosen as screen for designing contact dryer and replacing curved metal plate. The new type contact dryer solved the problem of long auxiliary time by loading wet veneers into press and unloading dried veneers out of press at the same time. This increased productivity. Veneer’s moisture content(MC) varied with drying time in index law. The process of contact drying with non-metal flexible screen was analyzed by stages of preheating, high-speed drying, retarded drying and extremely slow drying.展开更多
The level of aesthetic requirement in clinical practice has increased over the past decade, and this has made it necessary for dentist to explore this field in order to satisfy the existing demand in this field. Techn...The level of aesthetic requirement in clinical practice has increased over the past decade, and this has made it necessary for dentist to explore this field in order to satisfy the existing demand in this field. Technology can provide a solution to many of the routine hassles in dental practice. While optimal systems are far from fully realized, technology undeniably has made enormous progress. This review aims to provide an update on some of the recent advances in the field of aesthetic dentistry. MEDLINE (1990 to Jan 2014), PubMed (using medical subject headings), and Google Scholar searched using the following terms “Dental Composites”, “Ceramic Crowns”, “Aesthetic Posts”, “Ceramic Veneers”, and “Computer-Aided Design/Computer Aided Manufacturing (CAD/CAM)”. This was supplemented by hand-searching in peer-reviewed journals and cross-referenced with the articles accessed. Dentist and dental technician alike must be aware of the current technologies in their fields and be able to use it to their and their patient’s advantage. The learning objective of this article is to review the advantages and disadvantages of recent esthetic materials and technology to aid in the proper utilization of the available treatment options with discretion.展开更多
Tooth surface loss is a common condition with nearly three-quarter of the population in Trinidad & Tobago exhibiting signs and about one-fifth of those persons have moderate or severe wear. These patients become d...Tooth surface loss is a common condition with nearly three-quarter of the population in Trinidad & Tobago exhibiting signs and about one-fifth of those persons have moderate or severe wear. These patients become difficult to treat due mainly to loss of clinical crown height and also loss of occlusal vertical dimension. This case depicts the use of a conservative approach to treating a patient with moderate tooth surface loss, as assessed via the tooth wear index, with aetiology of acid erosion. The poor appearance of the dentition was the patient’s chief presenting complaint. With the use of 3M Filtek? Z 250 Universal Restorative Composite (St Paul, MN, USA), temporary posterior build-ups were placed to increase the patient’s Occlusal Vertical Dimension (OVD) and were subsequently replaced with metal onlays. Anterior composite veneers were placed to achieve an aesthetically pleasing result at the increased OVD. The combined use of composite and metal onlays allowed for an economical and more conservative treatment modality for dental erosion rather than full coverage posterior and anterior crowns.展开更多
In this paper, the effects of different processes on the DMFA content of synthetic leather were studied. The changes of DMFA content of different products and processes were compared. The effects of different chemical...In this paper, the effects of different processes on the DMFA content of synthetic leather were studied. The changes of DMFA content of different products and processes were compared. The effects of different chemicals and processes on the DMFA content of synthetic leather were investigated. Through experiments, the best solution at this stage is found to solve the problem of high content of DMFA in finished products. The results show that: 1. There are two critical control points with high DMFA content: 1 is direct coating (veneer) process (the most obvious increment), and the increment of this process is not easy to be processed in the later stage, and 2 is Besbe. The effect of reducing DMFA content is remarkable after optimizing the process. 2. The content of DMFA increased by direct coating process is larger than that of veneer process. The materials used in this process have the greatest influence on DMFA, and the oven temperature has certain influence on this process, but it can't achieve the expected effect of our company on ultra-low DMFA products without changing the materials. The best solution is to change the materials. 3. After changing the materials, the DMFA of direct coating process tends to be 0. Tracking the effect of the scheme, it is found that there is a large DMFA increment during treatment, but the increment can be treated in the later stage, and the scheme has a comprehensive influence on the DMFA content of a product, not limited to the local part. Up to now, the best scheme to reduce DMFA is to select ultra-low DMFA bass on bass, use 2030 DMFA-free material for direct coating process, properly bake, emboss and bake the finished product. (The quality inspection department needs to conduct follow-up sample tracking test).展开更多
Electrical and electromagnetic shielding wood metal composite was prepared by using electroless nickel plating. The effects of solution amount, plating time and plating temperature on surface resistivity and electroma...Electrical and electromagnetic shielding wood metal composite was prepared by using electroless nickel plating. The effects of solution amount, plating time and plating temperature on surface resistivity and electromagnetic shielding effectiveness were investigated. And P content, microstructure and surface feature of layers obtained at different temperatures were analyzed by energy dispersion spectrometer （EDS）, X-ray diffraction （XRI）） and scanning electron microscopy （SEM）. The results showed that layers with higher electro-conductivity and electromagnetic shielding effectiveness were obtained under the optimum conditions that plating solution was 500 mL, plating time was 30 min and plating temperature was 62℃. The results showed by EDS analysis; that P content increased gradually in a small extent with plating temperature increased. It was showed by XRD and SEM analysis that layers plated at different temperatures were all microcrystalline structure and uniform and successive, which had noticeable metal luster. Those indicated that plating temperature had little influence on microstructure and surface feature under pH value invariable.展开更多
A newly drying technology, intermittent-contact drying of veneer with flexible screen belt (ICD-fbs), was invented and used in poplar veneer drying. Productive test was carried out for validating the practical use of ...A newly drying technology, intermittent-contact drying of veneer with flexible screen belt (ICD-fbs), was invented and used in poplar veneer drying. Productive test was carried out for validating the practical use of this drying method. The test result shows that to dispose flexible screen belts on the two sides of hot board could help steam discharge remarkably. The veneer dried using ICD-fsb method had smooth and level surface, less deformation and warping, even moisture content, and high utilization rate. The time for opening hot board to discharge steam,which, early or late, is a key to obtain good drying result, was determined at the time when the core's temperature of veneer reaches 100℃ (vaporization). Using ICD-fsb method, the shrinking rates in tangent of veneer were from 1.90% to 2.26% for veneer of 0.4 mm in thickness,2.49% to 4.50% for veneer of 1 mm in thickness and 1.34% to 3.30% for veneer of 1.7 mm in thickness, which are much lower than the results obtained by other drying methods. The method of ICD-fsb offers a reliable technological guarantee for solving the deformation problem of veneer drying, especially the deformation of wood from quick-growing plantation.展开更多
Wood is a kind of porous natural material with very poor electro-conductivity, and it has almost no function of electromagnetic shielding. The method of electroless nickel plating was used to produce wooden material w...Wood is a kind of porous natural material with very poor electro-conductivity, and it has almost no function of electromagnetic shielding. The method of electroless nickel plating was used to produce wooden material with electrical and effective electromagnetic shielding properties. Ni-P alloy layer was obtained on wood surface. The surface feature of plated wood veneer was observed by SEM and the surface composition and microstructure of the layer under different conditions were investigated by EDS and XRD respectively. Meanwhile, the relevant surface resistivity and electromagnetic shielding effectiveness were measured. Correlations of the phosphorous content in the layer to the structure of Ni-P alloy, electro-conductivity and electromagnetic shielding of plated veneers were discussed. SEM photos showed that the surface of electroless nickel plated veneers were covered with Ni-P alloy layer entirely, which made wood veneers more like metal. At the same time, the results showed that with the decreasing of the phosphorous content in the layer, the microstructure of Ni-P alloy layer transformed to be microcrystalline and electro-conductivity and electromagnetic shielding effectiveness were improved. When the phosphorous content was less than 2.37wt pct in the layer, the microstructure of Ni-P alloy layer was microcrystalline structure and its sur- face resistivity and electromagnetic shielding effectiveness were nearly 0.5Ω/□ and 55-60dB respectively.展开更多
In an effort to find suitable wood from natural forest to meet the demand for veneer products, the yield and tensile strength of veneers produced from Brachystegia nigerica were investigated. Two trees of B. nigerica ...In an effort to find suitable wood from natural forest to meet the demand for veneer products, the yield and tensile strength of veneers produced from Brachystegia nigerica were investigated. Two trees of B. nigerica were separately selected from 10 different natural forest zones while two logs were obtained from each tree. The logs were debarked and steamed in a vat prior to rotary peeling and slicing for veneer production. The optimum steam temperature was determined by considering different temperatures： 50℃, 60℃, 70℃, 80℃ and 90℃ for 24 h. Thereafter, optimum steam time was determined at the optimum temperature by considering durations of 24, 48, 72 and 96 h. The average taper of 0.75 mm per 1.0 m length was recorded for B. nigerica, indicating that the logs were reasonably cylindrical; thereby its logs are good for the production of veneer. The yield ranged from 44% to 61% with an average of 52% of the log input. The tensile strength of the veneer was tested perpendicular to grain and both peeled and sliced veneers had the highest tensile strength between 70℃ and 90℃, suggesting that softening of wood polymers, especially lignin, is between 70℃ and 90℃. The optimum temperature and time for veneer production are 70℃ and 48 h, respectively. Commercial production of veneer from B. nigerica is feasible based on the yield and mechanical properties of the obtained veneer, thereby encouraging the expansion of the scope of its utilization.展开更多
Equilibrium isotope fractionation of thallium(Tl) includes the traditional mass-dependent isotope fractionation effect and the nuclear volume effect(NVE). The NVE dominates the overall isotope fractionation, especiall...Equilibrium isotope fractionation of thallium(Tl) includes the traditional mass-dependent isotope fractionation effect and the nuclear volume effect(NVE). The NVE dominates the overall isotope fractionation, especially at high temperatures. Heavy Tl isotopes tend to be enriched in oxidized Tl^3+-bearing species. Our NVE fractionation results of oxidizing Tl^+ to Tl^3+ can explain the positive enrichments observed in ferromanganese sediments. Experimental results indicate that there could be0.2–0.3 e-unit fractionation between sulfides and silicates at 1650 ℃. It is consistent with our calculation results,which are in the range of 0.17–0.38 e-unit. Importantly,Tl’s concentration in the bulk silicate Earth(BSE) can be used to constrain the amount of materials delivered to Earth during the late veneer accretion stage. Because the Tl concentration in BSE is very low and its Tl isotope composition is similar with that of chondrites, suggesting either no Tl isotope fractionation occurred during numerous evaporation events, or the Tl in current BSE was totally delivered by late veneer. If it is the latter, the Tl-contentbased estimation could challenge the magnitude of late veneer which had been constrained by the amount of highly siderophile elements in BSE. Our results show that the lateaccreted mass is at least five-times larger than the previously suggested magnitude, i.e., 0.5 wt% of current Earth’s mass. The slightly lighter 205 Tl composition of BSE relative to chondrites is probable a sign of occurrence of Tlbearing sulfides, which probably were removed from the mantle in the last accretion stage of the Earth.展开更多
Tungsten isotope is a powerful tracer for the Earth’s accreting materials because of the distinct W isotope compositions of the non-carbonaceous meteorites and carbonaceous meteorites.To better understand the evoluti...Tungsten isotope is a powerful tracer for the Earth’s accreting materials because of the distinct W isotope compositions of the non-carbonaceous meteorites and carbonaceous meteorites.To better understand the evolution of the early Earth,here we calculated the expectedμ^(183)W of the bulk silicate Earth for different assumed compositions of the proto-Earth’s mantle,the Moon-forming giant impactor,and the late veneer using a Monte Carlo approach.The result shows that the proto-Earth likely has a non-carbonaceous composition,while the carbonaceous chondrite-like materials were delivered to the Earth at the late stages of accretion.The predicted difference inμ^(183)W values between the bulk silicate Earth and the non-carbonaceous meteorites of the scenarios assuming a pure carbonaceous composition for the giant impactor is slightly bigger than that of the scenarios assuming either a pure non-carbonaceous or a mixed carbonaceous-non-carbonaceous composition for the giant impactor(~5 ppm versus~2 ppm).The ancient mantle reservoir that partially lacks the late veneer with carbonaceous composition should have a negativeμ^(183)W value(from-3 to 0).Uncertainties introduced by the cosmogenic effects and mass-independent fractionation should be concerned during the high precision measurement ofμ183W for meteorites and ancient terrestrial samples in further work.展开更多
Late veneer is an important paradigm in early Earth and planetary studies.It refers to the late addition of extraterrestrial materials to the Earth’s mantle after the core formation,which leads to the overabundances ...Late veneer is an important paradigm in early Earth and planetary studies.It refers to the late addition of extraterrestrial materials to the Earth’s mantle after the core formation,which leads to the overabundances of highly siderophile elements in the primitive upper mantle.In this review,the origin,evolution,and expansion of the late veneer hypothesis are summarized,including some unresolved problems.I hope this review would be helpful for the new entrants to this field.展开更多
To overcome warping in thin bamboo bundle veneer laminated composites(TBLC),their hydrothermal deformation characteristics were systematically investigated in this study.It was found that TBLCs accelerated the release...To overcome warping in thin bamboo bundle veneer laminated composites(TBLC),their hydrothermal deformation characteristics were systematically investigated in this study.It was found that TBLCs accelerated the release of internal stress in the thickness direction in a hydrothermal environment,which increased their warpage.TBLCs showed increased warpage in the width and diagonal directions upon increasing the temperature.The warpage of Type E increased by 155.88%and 66.67%in the width and diagonal directions,respectively,when the temperature increased from 25C to 100C.The symmetrical TBLC with cross-lay-up and odd layers displayed better hydrothermal stability.We revealed that the deformation of the TBLCs could be regulated under the synergistic effect of water and temperature.These results provide a scientific basis for improving the uniformity of bamboo bundle composite materials and for developing thin bamboo bundle fiber composite materials with designable structures and controllable performance.展开更多
The aim of this study was to evaluate the effect of controlled intraoral grinding and polishing on the roughness of full-contour zirconia compared to classical veneered zirconia. Thirty bar-shaped zirconia specimens w...The aim of this study was to evaluate the effect of controlled intraoral grinding and polishing on the roughness of full-contour zirconia compared to classical veneered zirconia. Thirty bar-shaped zirconia specimens were fabricated and divided into two groups（n515）. Fifteen specimens（group 1） were glazed and 15 specimens（group 2） were veneered with feldspathic ceramic and then glazed. Prior to grinding,maximum roughness depth（Rmax） values were measured using a profilometer, 5 times per specimen. Simulated clinical grinding and polishing were performed on the specimens under water coolant for 15 s and 2 N pressure. For grinding, NTI diamonds burs with grain sizes of 20 mm, 10 mm, and 7.5 mm were used sequentially. The ground surfaces were polished using NTI kits with coarse, medium and fine polishers. After each step, Rmaxvalues were determined. Differences between groups were examined using one-way analysis of variance（ANOVA）. The roughness of group 1 was significantly lower than that of group 2. The roughness increased significantly after coarse grinding in both groups. The results after glazing were similar to those obtained after fine grinding for non-veneered zirconia. However, fine-ground veneered zirconia had significantly higher roughness than venerred, glazed zirconia. No significant difference was found between fine-polished and glazed zirconia, but after the fine polishing of veneered zirconia, the roughness was significantly higher than after glazing.It can be concluded that for full-contour zirconia, fewer defects and lower roughness values resulted after grinding and polishing compared to veneered zirconia. After polishing zirconia, lower roughness values were achieved compared to glazing; more interesting was that the grinding of glazed zirconia using the NTI three-step system could deliver smooth surfaces comparable to untreated glazed zirconia surfaces.展开更多
Objective : To evaluate the color change of the two-layer porcelain laminate veneer after adding veneering porcelain of different thickness to the 0. 2 mm thick aluminum oxide. Methods : Ten aluminum oxide disks were ...Objective : To evaluate the color change of the two-layer porcelain laminate veneer after adding veneering porcelain of different thickness to the 0. 2 mm thick aluminum oxide. Methods : Ten aluminum oxide disks were randomized into 2 groups. Each of five disks was veneered with Vita Lumin Shade 54 porcelain of thickness 0/0.4 mm and 0. 6 mm respectively. The L'a'b* color notations of the substrate covered with nan-veneered disks and 2 thickness porcelain veneered disks were measured separately and the color differences (AE) were calculated. Results ?Statistically significant differences in color coordinates of dark substrates were recorded after the substrate was covered by an aluminum oxide disk and also after the addition of veneering porcelain to the aluminum oxide disks in group 1 (P=0. 000 2) and group 2(P=0. 007 5) and between 2 groups (P=0. 000 1). Conclusion -The ability of masking underlying discoloration was increased and shifted to gray when the thickness of veneering porcelain increased.展开更多
文摘Porcelain laminate veneers have been a common treatment strategy in dental clinics. It is a conservative method for treatment of esthetic and functional problems in anterior region of oral cavity. Wide range of dental ceramics is now available on market for fabrication of laminate veneers. Clinician should have enough knowledge regarding the composition and properties of these materials in order to be able to choose the appropriate one according to clinical situations.
文摘A system of finished Componeer composite veneers is a unique and having no analogy in the world elaboration of the Swisscompany Coltene/Whaledent, an outcome of almost halfa century experience of the company working in a field of composite materials.It combines the best features of direct and indirect restoration methods. The system is fulfilled of nanocomposite Synergy D6 that hashigh mechanical strength, convenience for workable consistency, color stability and a system of halftone shades, which facilitates colormatching. All this allows achieving excellent aesthetic results in minimal time. Application of an original standard scale givespossibility effectively assess optical properties of dental hard tissues and develop an implementation strategy of restoration before workstarted. Formation of Componeer form, polymerization and polishing at factory allow a practitioner fully utilize effect of＂fluorescence＂ inherent to the material. All this allows us to position the Componeer system as a serious alternative to non-directmethods of restoration with the possibility of both high aesthetic and cosmetic reconstruction reliability.
基金Sponsored by the Science Fund of Harbin City(Grant No.2005AA6CN080) and Science Found of Heilongjiang Province(Grant No.GB06B303 -3).
文摘The discoloration of Scot pine （Pinus sylvestris var. Mongolica） veneers caused by resin-eliminated treatment and the reversion of the color were studied. The result showed that the color of the veneers changed from buff to yellowish brown after the treatment of resin elimination and the discoloration of heartwood was more severe than that of sapwood; the degree of discoloration was significantly positively correlated with the medicament strength, temperature and resin-eliminated duration. The variance analysis showed the effects of those three factors on the discoloration were significant. With hydrogen peroxide （H2O2） as color reversion medicament and inorganic compound as medium of the reaction, the reversion of the color of heartwood was more inaccessible than that of sapwood; the degree of the color’s reversion was positively correlated with the H2O2 strength, temperature and treating time; the H2O2 concentration has significant effects on the discoloration. In order to reduce discoloration of Scot pine veneers, medicament of resin-eliminated used have to be at some low concentration, and the optimal concentration of H2O2 is 0.35% during the process of color’s reversion.
文摘The impregnation of nanoparticles magnetified into wood had been developed by different methods,like surface chemical coprecipitation and vacuum-pressure coprecipitation of magnetic nanoparticles(NPs).However,there is a lack of information on the best method to coprecipitation NPs.Then,the present study has the objective to measure the effects of the impregnation process of wood veneers through two in situ processes(immersion and vacuum-pressure)using a solution of FeCl_(3)·6H_(2)O,FeCl_(2)·4H_(2)O and ammonia in three tropical species(Pinus oocarpa,Vochysia ferruginea and Vochysia guatemalensis).It was measured the degree of synthesis of iron NPs using weight and density gains,Fe^(3+) absorption,emission scanning electron microscope(SEM),Fournier transform infrared spectroscopy(FT-IR)and for magnetic properties were measured using vibrating sample magnetometry(VSM).After 5-layer veneer panels were fabricated,we evaluated their physical and mechanical properties.Wood samples impregnated by vacuum-pressure methods showed the higher amount of Fe_(3)O_(4)NPs formation,which was observed in the SEM,X-ray diffraction(XDR),FT-IR and VSM.Vacuum-pressure on treatment presented higher ferrite signals and better magnetic properties.Vochysia ferruginea presented the greatest magnetization properties.The magnetization treated causes probably a degradation of the cell wall,which weakens its mechanical properties,especially internal bonding.
文摘Three types of material as platen in contact drying process were tested in Composition Board Laboratory of Northeast Forestry University in 1998. Poplar veneers were dried under’0.3 MPa at 160℃ or 180℃. Through comparison a non-metal flexible material was chosen as screen for designing contact dryer and replacing curved metal plate. The new type contact dryer solved the problem of long auxiliary time by loading wet veneers into press and unloading dried veneers out of press at the same time. This increased productivity. Veneer’s moisture content(MC) varied with drying time in index law. The process of contact drying with non-metal flexible screen was analyzed by stages of preheating, high-speed drying, retarded drying and extremely slow drying.
文摘The level of aesthetic requirement in clinical practice has increased over the past decade, and this has made it necessary for dentist to explore this field in order to satisfy the existing demand in this field. Technology can provide a solution to many of the routine hassles in dental practice. While optimal systems are far from fully realized, technology undeniably has made enormous progress. This review aims to provide an update on some of the recent advances in the field of aesthetic dentistry. MEDLINE (1990 to Jan 2014), PubMed (using medical subject headings), and Google Scholar searched using the following terms “Dental Composites”, “Ceramic Crowns”, “Aesthetic Posts”, “Ceramic Veneers”, and “Computer-Aided Design/Computer Aided Manufacturing (CAD/CAM)”. This was supplemented by hand-searching in peer-reviewed journals and cross-referenced with the articles accessed. Dentist and dental technician alike must be aware of the current technologies in their fields and be able to use it to their and their patient’s advantage. The learning objective of this article is to review the advantages and disadvantages of recent esthetic materials and technology to aid in the proper utilization of the available treatment options with discretion.
文摘Tooth surface loss is a common condition with nearly three-quarter of the population in Trinidad & Tobago exhibiting signs and about one-fifth of those persons have moderate or severe wear. These patients become difficult to treat due mainly to loss of clinical crown height and also loss of occlusal vertical dimension. This case depicts the use of a conservative approach to treating a patient with moderate tooth surface loss, as assessed via the tooth wear index, with aetiology of acid erosion. The poor appearance of the dentition was the patient’s chief presenting complaint. With the use of 3M Filtek? Z 250 Universal Restorative Composite (St Paul, MN, USA), temporary posterior build-ups were placed to increase the patient’s Occlusal Vertical Dimension (OVD) and were subsequently replaced with metal onlays. Anterior composite veneers were placed to achieve an aesthetically pleasing result at the increased OVD. The combined use of composite and metal onlays allowed for an economical and more conservative treatment modality for dental erosion rather than full coverage posterior and anterior crowns.
文摘In this paper, the effects of different processes on the DMFA content of synthetic leather were studied. The changes of DMFA content of different products and processes were compared. The effects of different chemicals and processes on the DMFA content of synthetic leather were investigated. Through experiments, the best solution at this stage is found to solve the problem of high content of DMFA in finished products. The results show that: 1. There are two critical control points with high DMFA content: 1 is direct coating (veneer) process (the most obvious increment), and the increment of this process is not easy to be processed in the later stage, and 2 is Besbe. The effect of reducing DMFA content is remarkable after optimizing the process. 2. The content of DMFA increased by direct coating process is larger than that of veneer process. The materials used in this process have the greatest influence on DMFA, and the oven temperature has certain influence on this process, but it can't achieve the expected effect of our company on ultra-low DMFA products without changing the materials. The best solution is to change the materials. 3. After changing the materials, the DMFA of direct coating process tends to be 0. Tracking the effect of the scheme, it is found that there is a large DMFA increment during treatment, but the increment can be treated in the later stage, and the scheme has a comprehensive influence on the DMFA content of a product, not limited to the local part. Up to now, the best scheme to reduce DMFA is to select ultra-low DMFA bass on bass, use 2030 DMFA-free material for direct coating process, properly bake, emboss and bake the finished product. (The quality inspection department needs to conduct follow-up sample tracking test).
基金The research was supported by the National Natural Science Foundation of China （30571454）. Natural Science Foundation of Heilongjiang Province （C0210） and Harbin City Youth Science Faud （2004AFQXJ027）.
文摘Electrical and electromagnetic shielding wood metal composite was prepared by using electroless nickel plating. The effects of solution amount, plating time and plating temperature on surface resistivity and electromagnetic shielding effectiveness were investigated. And P content, microstructure and surface feature of layers obtained at different temperatures were analyzed by energy dispersion spectrometer （EDS）, X-ray diffraction （XRI）） and scanning electron microscopy （SEM）. The results showed that layers with higher electro-conductivity and electromagnetic shielding effectiveness were obtained under the optimum conditions that plating solution was 500 mL, plating time was 30 min and plating temperature was 62℃. The results showed by EDS analysis; that P content increased gradually in a small extent with plating temperature increased. It was showed by XRD and SEM analysis that layers plated at different temperatures were all microcrystalline structure and uniform and successive, which had noticeable metal luster. Those indicated that plating temperature had little influence on microstructure and surface feature under pH value invariable.
基金This work is supported by "Xing Huo" Program of the Ministry of Agriculture, P. R. China.
文摘A newly drying technology, intermittent-contact drying of veneer with flexible screen belt (ICD-fbs), was invented and used in poplar veneer drying. Productive test was carried out for validating the practical use of this drying method. The test result shows that to dispose flexible screen belts on the two sides of hot board could help steam discharge remarkably. The veneer dried using ICD-fsb method had smooth and level surface, less deformation and warping, even moisture content, and high utilization rate. The time for opening hot board to discharge steam,which, early or late, is a key to obtain good drying result, was determined at the time when the core's temperature of veneer reaches 100℃ (vaporization). Using ICD-fsb method, the shrinking rates in tangent of veneer were from 1.90% to 2.26% for veneer of 0.4 mm in thickness,2.49% to 4.50% for veneer of 1 mm in thickness and 1.34% to 3.30% for veneer of 1.7 mm in thickness, which are much lower than the results obtained by other drying methods. The method of ICD-fsb offers a reliable technological guarantee for solving the deformation problem of veneer drying, especially the deformation of wood from quick-growing plantation.
基金The research was supported by the National Hi-Tech R ＆ D Program （863） of China （2002AA24515）. Natural Science Foundation of Heilonjiang Province （C0210） and Harbin City Youth Science Fund （2004AFQXJ027）.
文摘Wood is a kind of porous natural material with very poor electro-conductivity, and it has almost no function of electromagnetic shielding. The method of electroless nickel plating was used to produce wooden material with electrical and effective electromagnetic shielding properties. Ni-P alloy layer was obtained on wood surface. The surface feature of plated wood veneer was observed by SEM and the surface composition and microstructure of the layer under different conditions were investigated by EDS and XRD respectively. Meanwhile, the relevant surface resistivity and electromagnetic shielding effectiveness were measured. Correlations of the phosphorous content in the layer to the structure of Ni-P alloy, electro-conductivity and electromagnetic shielding of plated veneers were discussed. SEM photos showed that the surface of electroless nickel plated veneers were covered with Ni-P alloy layer entirely, which made wood veneers more like metal. At the same time, the results showed that with the decreasing of the phosphorous content in the layer, the microstructure of Ni-P alloy layer transformed to be microcrystalline and electro-conductivity and electromagnetic shielding effectiveness were improved. When the phosphorous content was less than 2.37wt pct in the layer, the microstructure of Ni-P alloy layer was microcrystalline structure and its sur- face resistivity and electromagnetic shielding effectiveness were nearly 0.5Ω/□ and 55-60dB respectively.
文摘In an effort to find suitable wood from natural forest to meet the demand for veneer products, the yield and tensile strength of veneers produced from Brachystegia nigerica were investigated. Two trees of B. nigerica were separately selected from 10 different natural forest zones while two logs were obtained from each tree. The logs were debarked and steamed in a vat prior to rotary peeling and slicing for veneer production. The optimum steam temperature was determined by considering different temperatures： 50℃, 60℃, 70℃, 80℃ and 90℃ for 24 h. Thereafter, optimum steam time was determined at the optimum temperature by considering durations of 24, 48, 72 and 96 h. The average taper of 0.75 mm per 1.0 m length was recorded for B. nigerica, indicating that the logs were reasonably cylindrical; thereby its logs are good for the production of veneer. The yield ranged from 44% to 61% with an average of 52% of the log input. The tensile strength of the veneer was tested perpendicular to grain and both peeled and sliced veneers had the highest tensile strength between 70℃ and 90℃, suggesting that softening of wood polymers, especially lignin, is between 70℃ and 90℃. The optimum temperature and time for veneer production are 70℃ and 48 h, respectively. Commercial production of veneer from B. nigerica is feasible based on the yield and mechanical properties of the obtained veneer, thereby encouraging the expansion of the scope of its utilization.
基金the funding supports from the strategic priority research program (B) of CAS (XDB18010100)Chinese NSF projects (Nos. 41530210, 41490635)
文摘Equilibrium isotope fractionation of thallium(Tl) includes the traditional mass-dependent isotope fractionation effect and the nuclear volume effect(NVE). The NVE dominates the overall isotope fractionation, especially at high temperatures. Heavy Tl isotopes tend to be enriched in oxidized Tl^3+-bearing species. Our NVE fractionation results of oxidizing Tl^+ to Tl^3+ can explain the positive enrichments observed in ferromanganese sediments. Experimental results indicate that there could be0.2–0.3 e-unit fractionation between sulfides and silicates at 1650 ℃. It is consistent with our calculation results,which are in the range of 0.17–0.38 e-unit. Importantly,Tl’s concentration in the bulk silicate Earth(BSE) can be used to constrain the amount of materials delivered to Earth during the late veneer accretion stage. Because the Tl concentration in BSE is very low and its Tl isotope composition is similar with that of chondrites, suggesting either no Tl isotope fractionation occurred during numerous evaporation events, or the Tl in current BSE was totally delivered by late veneer. If it is the latter, the Tl-contentbased estimation could challenge the magnitude of late veneer which had been constrained by the amount of highly siderophile elements in BSE. Our results show that the lateaccreted mass is at least five-times larger than the previously suggested magnitude, i.e., 0.5 wt% of current Earth’s mass. The slightly lighter 205 Tl composition of BSE relative to chondrites is probable a sign of occurrence of Tlbearing sulfides, which probably were removed from the mantle in the last accretion stage of the Earth.
基金financially supported by the National Natural Science Foundation of China(42103011 and 42288201)National Key R&D Program of China(2016YFC0600109)。
文摘Tungsten isotope is a powerful tracer for the Earth’s accreting materials because of the distinct W isotope compositions of the non-carbonaceous meteorites and carbonaceous meteorites.To better understand the evolution of the early Earth,here we calculated the expectedμ^(183)W of the bulk silicate Earth for different assumed compositions of the proto-Earth’s mantle,the Moon-forming giant impactor,and the late veneer using a Monte Carlo approach.The result shows that the proto-Earth likely has a non-carbonaceous composition,while the carbonaceous chondrite-like materials were delivered to the Earth at the late stages of accretion.The predicted difference inμ^(183)W values between the bulk silicate Earth and the non-carbonaceous meteorites of the scenarios assuming a pure carbonaceous composition for the giant impactor is slightly bigger than that of the scenarios assuming either a pure non-carbonaceous or a mixed carbonaceous-non-carbonaceous composition for the giant impactor(~5 ppm versus~2 ppm).The ancient mantle reservoir that partially lacks the late veneer with carbonaceous composition should have a negativeμ^(183)W value(from-3 to 0).Uncertainties introduced by the cosmogenic effects and mass-independent fractionation should be concerned during the high precision measurement ofμ183W for meteorites and ancient terrestrial samples in further work.
基金supported by NSFC 41703019Strategic Priority ResearchProgram(B)(XDB41000000)CDUT 10912-KYQD2020-08294。
文摘Late veneer is an important paradigm in early Earth and planetary studies.It refers to the late addition of extraterrestrial materials to the Earth’s mantle after the core formation,which leads to the overabundances of highly siderophile elements in the primitive upper mantle.In this review,the origin,evolution,and expansion of the late veneer hypothesis are summarized,including some unresolved problems.I hope this review would be helpful for the new entrants to this field.
基金supported by the Youth Top-notch Talent Program of Science and Technology Innovation for Forestry and Grassland(2019132606).
文摘To overcome warping in thin bamboo bundle veneer laminated composites(TBLC),their hydrothermal deformation characteristics were systematically investigated in this study.It was found that TBLCs accelerated the release of internal stress in the thickness direction in a hydrothermal environment,which increased their warpage.TBLCs showed increased warpage in the width and diagonal directions upon increasing the temperature.The warpage of Type E increased by 155.88%and 66.67%in the width and diagonal directions,respectively,when the temperature increased from 25C to 100C.The symmetrical TBLC with cross-lay-up and odd layers displayed better hydrothermal stability.We revealed that the deformation of the TBLCs could be regulated under the synergistic effect of water and temperature.These results provide a scientific basis for improving the uniformity of bamboo bundle composite materials and for developing thin bamboo bundle fiber composite materials with designable structures and controllable performance.
基金Forschungsgemeinschaft Dental e.V. for supporting this study (project no. 3/2012)
文摘The aim of this study was to evaluate the effect of controlled intraoral grinding and polishing on the roughness of full-contour zirconia compared to classical veneered zirconia. Thirty bar-shaped zirconia specimens were fabricated and divided into two groups（n515）. Fifteen specimens（group 1） were glazed and 15 specimens（group 2） were veneered with feldspathic ceramic and then glazed. Prior to grinding,maximum roughness depth（Rmax） values were measured using a profilometer, 5 times per specimen. Simulated clinical grinding and polishing were performed on the specimens under water coolant for 15 s and 2 N pressure. For grinding, NTI diamonds burs with grain sizes of 20 mm, 10 mm, and 7.5 mm were used sequentially. The ground surfaces were polished using NTI kits with coarse, medium and fine polishers. After each step, Rmaxvalues were determined. Differences between groups were examined using one-way analysis of variance（ANOVA）. The roughness of group 1 was significantly lower than that of group 2. The roughness increased significantly after coarse grinding in both groups. The results after glazing were similar to those obtained after fine grinding for non-veneered zirconia. However, fine-ground veneered zirconia had significantly higher roughness than venerred, glazed zirconia. No significant difference was found between fine-polished and glazed zirconia, but after the fine polishing of veneered zirconia, the roughness was significantly higher than after glazing.It can be concluded that for full-contour zirconia, fewer defects and lower roughness values resulted after grinding and polishing compared to veneered zirconia. After polishing zirconia, lower roughness values were achieved compared to glazing; more interesting was that the grinding of glazed zirconia using the NTI three-step system could deliver smooth surfaces comparable to untreated glazed zirconia surfaces.
文摘Objective : To evaluate the color change of the two-layer porcelain laminate veneer after adding veneering porcelain of different thickness to the 0. 2 mm thick aluminum oxide. Methods : Ten aluminum oxide disks were randomized into 2 groups. Each of five disks was veneered with Vita Lumin Shade 54 porcelain of thickness 0/0.4 mm and 0. 6 mm respectively. The L'a'b* color notations of the substrate covered with nan-veneered disks and 2 thickness porcelain veneered disks were measured separately and the color differences (AE) were calculated. Results ?Statistically significant differences in color coordinates of dark substrates were recorded after the substrate was covered by an aluminum oxide disk and also after the addition of veneering porcelain to the aluminum oxide disks in group 1 (P=0. 000 2) and group 2(P=0. 007 5) and between 2 groups (P=0. 000 1). Conclusion -The ability of masking underlying discoloration was increased and shifted to gray when the thickness of veneering porcelain increased.
