Objectives： Polymerization shrinkage of dental composites remains a major concern in restorative dentistry because it can lead to micro-cracking of the tooth and debonding at the tooth-restoration interface. The aim ...Objectives： Polymerization shrinkage of dental composites remains a major concern in restorative dentistry because it can lead to micro-cracking of the tooth and debonding at the tooth-restoration interface. The aim of this study was to measure the full-field polymerization shrinkage of dental composites using the optical digital image correlation （DIC） method and to evaluate how the measurement is influenced by the factors in experiment setup and image analysis. Methods： Four commercial dental composites, Premise Dentine, Z 100, Z250 and Tetric EvoCeram, were tested. Composite was first placed into a slot mould to form a bar specimen with rectangular-section of 4 mmx2 mm, followed by the surface painting to create irregular speckles. Curing was then applied at one end of the specimen while the other part were covered against curing light for simulating the clinical curing condition of composite in dental cavity. The painted surface was recorded by a charge-coupled device （CCD） camera before and after curing. Subsequently, the volumetric shrinkage of the specimen was calculated with specialist DIC software based on image cross correlation. In addition, a few factors that may influence the measuring accuracy, including the subset window size, speckle size, illumination light and specimen length, were also evaluated. Results： The volumetric shrinkage of the specimen generally decreases with increasing distance from the irradiated surface with a conspicuous exception being the composite Premise Dentine as its maximum shrinkage occurred at a subsurface distance of about 1 mm instead of the irradiated surface. Z100 had the greatest maximum shrinkage strain, followed by Z250, Tetric EvoCeram and then Premise Dentine. Larger subset window size made the shrinkage strain contour smoother. But the cost was that some details in the heterogeneity of the material were lost. Very small subset window size resulted in a lot of noise in the data, making it difficult to discern the general pattern in the strain distribution. Speckle size did not seem to have obvious effect on the volumetric shrinkage strain along specimen length; however, larger speckles resulted in higher level of noise or heterogeneity in the shrinkage distribution. Compared with bright illumination, dimmer lighting produced larger standard deviations in the measured shrinkage~ indicating a higher level of noise. The longer the specimen, the greater was the rate of reduction with distance from the irradiated surface, especially for the longitudinal strain. Significance： The image correlation method is capable of producing full-field polymerization shrinkage of dental composites. The accuracy of the measurements relies on selection of optimal parameters in experimental setup and DIC analysis.展开更多
Fabrication of silicon carbide(SiC)ceramics by digital light processing(DLP)technology is difficult owing to high refractive index and high ultraviolet(UV)absorptivity of SiC powders.The surface of the SiC powders can...Fabrication of silicon carbide(SiC)ceramics by digital light processing(DLP)technology is difficult owing to high refractive index and high ultraviolet(UV)absorptivity of SiC powders.The surface of the SiC powders can be coated with silicon oxide(SiO_(2))with low refractive index and low UV absorptivity via high-temperature oxidation,reducing the loss of UV energy in the DLP process and realizing the DLP preparation of the SiC ceramics.However,it is necessary to explore a high-temperature modification process to obtain a better modification effect of the SiC powders.Therefore,the high-temperature modification behavior of the SiC powders is thoroughly investigated in this paper.The results show that nano-scale oxide film is formed on the surface of the SiC powders by short-time high-temperature oxidation,effectively reducing the UV absorptivity and the surface refractive index(nʹ)of the SiC powders.When the oxidation temperature is 1300℃,compared with that of unoxidized SiC powders,the UV absorptivity of oxidized SiC powders decreases from 0.5065 to 0.4654,and a curing depth of SiC slurry increases from 22±4 to 59±4μm.Finally,SiC green bodies are successfully prepared by the DLP with the the oxidized powders,and flexural strength of SiC sintered parts reaches 47.9±2.3 MPa after 3 h of atmospheric sintering at 2000℃without any sintering aid.展开更多
Ultraviolet(UV)-based vat photopolymerization(VP)of silicon carbide(SiC)ceramics has been challenging because of the strong UV absorbance and high refractive index of SiC.However,strategies such as particle modificati...Ultraviolet(UV)-based vat photopolymerization(VP)of silicon carbide(SiC)ceramics has been challenging because of the strong UV absorbance and high refractive index of SiC.However,strategies such as particle modification or the use of coarser particles have led to low sample densities and/or impurities that diminish the final properties of printed SiC ceramics.Herein,a novel VP method driven by near-infrared(NIR)light to enable direct three-dimensional(3D)printing of SiC ceramics using unmodified fine SiC particles was demonstrated.A type II photopolymerization resin system was first identified and optimized to allow 50–60 wt%SiC particles to be loaded and printed with NIR light.The use of NIR light offered penetration depths of up to 4 times and cure depths of up to 2 times greater than those of UV-based photocuring for a slurry containing 50 wt%SiC particles,along with much better printing fidelities,where the deviation from the designed dimensions was only±6.8%(vs.165.5%for UV light).The NIR-based printed SiC ceramics possessed excellent mechanical properties,with flexural strengths reaching(290±20)MPa at a relative density of 86.29%,which was significantly greater than that of many other VP-printed SiC ceramics(approximately 100–220 MPa)at similar densities.These properties were achieved without any additional particle modification or post infiltration steps,allowing the VP of SiC to be as practical as the VP of common oxide ceramics such as alumina and zirconia.展开更多
文摘Objectives： Polymerization shrinkage of dental composites remains a major concern in restorative dentistry because it can lead to micro-cracking of the tooth and debonding at the tooth-restoration interface. The aim of this study was to measure the full-field polymerization shrinkage of dental composites using the optical digital image correlation （DIC） method and to evaluate how the measurement is influenced by the factors in experiment setup and image analysis. Methods： Four commercial dental composites, Premise Dentine, Z 100, Z250 and Tetric EvoCeram, were tested. Composite was first placed into a slot mould to form a bar specimen with rectangular-section of 4 mmx2 mm, followed by the surface painting to create irregular speckles. Curing was then applied at one end of the specimen while the other part were covered against curing light for simulating the clinical curing condition of composite in dental cavity. The painted surface was recorded by a charge-coupled device （CCD） camera before and after curing. Subsequently, the volumetric shrinkage of the specimen was calculated with specialist DIC software based on image cross correlation. In addition, a few factors that may influence the measuring accuracy, including the subset window size, speckle size, illumination light and specimen length, were also evaluated. Results： The volumetric shrinkage of the specimen generally decreases with increasing distance from the irradiated surface with a conspicuous exception being the composite Premise Dentine as its maximum shrinkage occurred at a subsurface distance of about 1 mm instead of the irradiated surface. Z100 had the greatest maximum shrinkage strain, followed by Z250, Tetric EvoCeram and then Premise Dentine. Larger subset window size made the shrinkage strain contour smoother. But the cost was that some details in the heterogeneity of the material were lost. Very small subset window size resulted in a lot of noise in the data, making it difficult to discern the general pattern in the strain distribution. Speckle size did not seem to have obvious effect on the volumetric shrinkage strain along specimen length; however, larger speckles resulted in higher level of noise or heterogeneity in the shrinkage distribution. Compared with bright illumination, dimmer lighting produced larger standard deviations in the measured shrinkage~ indicating a higher level of noise. The longer the specimen, the greater was the rate of reduction with distance from the irradiated surface, especially for the longitudinal strain. Significance： The image correlation method is capable of producing full-field polymerization shrinkage of dental composites. The accuracy of the measurements relies on selection of optimal parameters in experimental setup and DIC analysis.
基金supported by grants from the Key Project Fund for Science and Technology Development of Guangdong Province (2020B090924003)the National Natural Science Foundation of China (51975230)Major Special Projects of Technological Innovation in Hubei Province (2019AAA002).
文摘Fabrication of silicon carbide(SiC)ceramics by digital light processing(DLP)technology is difficult owing to high refractive index and high ultraviolet(UV)absorptivity of SiC powders.The surface of the SiC powders can be coated with silicon oxide(SiO_(2))with low refractive index and low UV absorptivity via high-temperature oxidation,reducing the loss of UV energy in the DLP process and realizing the DLP preparation of the SiC ceramics.However,it is necessary to explore a high-temperature modification process to obtain a better modification effect of the SiC powders.Therefore,the high-temperature modification behavior of the SiC powders is thoroughly investigated in this paper.The results show that nano-scale oxide film is formed on the surface of the SiC powders by short-time high-temperature oxidation,effectively reducing the UV absorptivity and the surface refractive index(nʹ)of the SiC powders.When the oxidation temperature is 1300℃,compared with that of unoxidized SiC powders,the UV absorptivity of oxidized SiC powders decreases from 0.5065 to 0.4654,and a curing depth of SiC slurry increases from 22±4 to 59±4μm.Finally,SiC green bodies are successfully prepared by the DLP with the the oxidized powders,and flexural strength of SiC sintered parts reaches 47.9±2.3 MPa after 3 h of atmospheric sintering at 2000℃without any sintering aid.
基金the financial support from Temasek Laboratories@Nanyang Technological University(Nos.TLSP23-01 and TLSP22-05).
文摘Ultraviolet(UV)-based vat photopolymerization(VP)of silicon carbide(SiC)ceramics has been challenging because of the strong UV absorbance and high refractive index of SiC.However,strategies such as particle modification or the use of coarser particles have led to low sample densities and/or impurities that diminish the final properties of printed SiC ceramics.Herein,a novel VP method driven by near-infrared(NIR)light to enable direct three-dimensional(3D)printing of SiC ceramics using unmodified fine SiC particles was demonstrated.A type II photopolymerization resin system was first identified and optimized to allow 50–60 wt%SiC particles to be loaded and printed with NIR light.The use of NIR light offered penetration depths of up to 4 times and cure depths of up to 2 times greater than those of UV-based photocuring for a slurry containing 50 wt%SiC particles,along with much better printing fidelities,where the deviation from the designed dimensions was only±6.8%(vs.165.5%for UV light).The NIR-based printed SiC ceramics possessed excellent mechanical properties,with flexural strengths reaching(290±20)MPa at a relative density of 86.29%,which was significantly greater than that of many other VP-printed SiC ceramics(approximately 100–220 MPa)at similar densities.These properties were achieved without any additional particle modification or post infiltration steps,allowing the VP of SiC to be as practical as the VP of common oxide ceramics such as alumina and zirconia.
