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Hitoshi Sumiya - One of the best experts on this subject based on the ideXlab platform.
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real indentation hardness of nano polycrystalline cbn synthesized by direct conversion sintering under hpht
Diamond and Related Materials, 2014Co-Authors: Hitoshi Sumiya, Yuh Ishida, Keiko Arimoto, Katsuko HaranoAbstract:Abstract The hardness characteristic of nano-polycrystalline cBN synthesized by direct conversion sintering was thoroughly investigated using Vickers and Knoop indenters. It was found that nano-polycrystals consisting of smaller cBN grains increase the elastic recovery of indentations during unloading of the indenters and the diagonal of Vickers indentations and the minor diagonal of Knoop indentations significantly decrease in length. Thus, if a Vickers indenter is used, the apparent hardness value increases, making it impossible to perform an accurate evaluation, e.g. incorrect Vickers hardness values in excess of 80 GPa were obtained from nano-polycrystalline cBN with a grain size of 50 nm or less. On the other hand, it was verified that a Knoop indenter ensures an accurate hardness evaluation even if the constituent grains are fine because its major diagonal length which is used for measurement is less susceptible to elastic recovery. In an accurate evaluation of the hardness of different types of nano-polycrystalline cBN using a Knoop indenter, the hardness of each type of cBN was around 45 GPa, and there was no clear Hall–Petch relationship between hardness and grain size without a slight bell-like correlation. These results suggest that reported hardness values higher than 80 GPa of similar nano-polycrystalline cBN evaluated using a Vickers indenter are incorrect values caused by elastic recovery occurring at the indentation.
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Elasticity and hardness of nano-polycrystalline boron nitrides: The apparent Hall-Petch effect
Applied Physics Letters, 2014Co-Authors: Akira Nagakubo, Hitoshi Sumiya, Hirotsugu Ogi, Masahiko HiraoAbstract:Nano-polycrystalline boron nitride (BN) is expected to replace diamond as a superhard and superstiff material. Although its hardening was reported, its elasticity remains unclear and the as-measured hardness could be significantly different from the true value due to the elastic recovery. In this study, we measured the longitudinal-wave elastic constant of nano-polycrystalline BNs using picosecond ultrasound spectroscopy and confirmed the elastic softening for small-grain BNs. We also measured Vickers and Knoop hardness for the same specimens and clarified the relationship between hardness and stiffness. The Vickers hardness significantly increased as the grain size decreased, while the Knoop hardness remained nearly unchanged. We attribute the apparent increase in Vickers hardness to the elastic recovery and propose a model to support this insight.
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Hardness and deformation microstructures of nano-polycrystalline diamonds synthesized from various carbons under high pressure and high temperature
Journal of Materials Research, 2007Co-Authors: Hitoshi Sumiya, Tetsuo IrifuneAbstract:Mechanical properties of high-purity nano-polycrystalline diamonds synthesized by direct conversion from graphite and various non-graphitic carbons under static high pressures and high temperatures were investigated by microindentation testing with a Knoop indenter and observation of microstructures around the indentations. Results of indentation hardness tests using a superhard synthetic diamond Knoop indenter showed that the polycrystalline diamond synthesized from graphite at ⩾15 GPa and 2300–2500 °C (consisting of fine grains 10–30 nm in size and layered crystals) has very high Knoop hardness (Hk ⩾ 110 GPa), whereas the hardness of polycrystalline diamonds synthesized from non-graphitic carbons at ⩾15 GPa and below 2000 °C (consisting only of single-nano grains 5–10 nm in size) are significantly lower (Hk = 70 to 90 GPa). Microstructure observations beneath the indentations of these nano-polycrystalline diamonds suggest that the existence of a lamellar structure and the bonding strength of the grain boundary play important roles in controlling the hardness of the polycrystalline diamond.
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thermally activated deformation under Knoop indentations in super hard directions of high quality synthetic type iia diamond crystals
Diamond and Related Materials, 2006Co-Authors: Hitoshi SumiyaAbstract:Abstract The deformation resistance at room temperature against a Knoop indentation in (001) (the direction on the (001) plane) of high-quality synthetic type-IIa diamond is known to be extremely high. The behavior of deformation in the hard direction activated thermally by heating was investigated, using super-hard Knoop indenters prepared from high-quality diamond crystals by taking the tip orientation to (001) . Indentation tests in (001) with a load of 4.9 N revealed that the formation of normal Knoop impressions arises suddenly at a threshold temperature of 200–240 °C, whereas no impressions are observed up to 200 °C. The hardness values derived from the impressions in (001) formed above the threshold temperatures are as low as 50–60% those in (001) at the same temperatures. The anisotropy in the Knoop hardness at such high temperatures is consistent with the nature of anisotropy predicted by an effective resolved shear stress model for a {111} slip deformation.
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deformation microstructure of high quality synthetic diamond crystal subjected to Knoop indentation
Applied Physics Letters, 2006Co-Authors: Hitoshi Sumiya, K Yamaguchi, Shigenobu OgataAbstract:The deformation microstructures of high-quality synthetic type IIa diamond crystal around a Knoop indentation formed at room temperature were investigated. The atomic force microscopy observation showed that there are smooth deformation areas without cracks or fractures around the indentation. In addition, many dislocation lines which lie on {111} planes and have Burgers vectors in ⟨110⟩ directions were observed beneath the Knoop indentation in transmission electron microscopy investigations. These results reveal that plastic deformation in diamond is possible beneath Knoop indentations even at room temperature, and that the deformation is mainly ascribed to {111}⟨110⟩ slip systems.
Mario Alexandre Coelho Sinhoreti - One of the best experts on this subject based on the ideXlab platform.
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effect of ceramic interposition and post activation times on Knoop hardness of different shades of resin cement
Brazilian Dental Journal, 2018Co-Authors: Marina Barreto Pereira Moreno, Simonides Consani, Mario Alexandre Coelho Sinhoreti, Ana Rosa Costa, Frederick A Rueggeberg, Gláucia Maria Bovi Ambrosano, Lourenco Correr SobrinhoAbstract:: The aim of this study was to evaluate Knoop hardness of different shades of a resin cement light-cured directly or through ceramic discs, measured 15 min or 24 h after light exposure, and at different depths. Specimens of a commercial resin cement (Variolink Veneer) in seven shades, were fabricated in an elastomeric mold, covered with a mylar strip, a 0.7 mm thick ceramic disc (IPS e.max Press) was placed and the cement was light-activated for 20 s using a blue LED (Radii-Cal). The cured resin cement specimens were transversely wet-flattened to their middle portion and microhardness (Knoop) values were recorded at 15 min after light exposure and after deionized water storage at 37 oC for 24 h. Five indentations were made in the cross-sectional area at 100 and 700 μm depths from the top surface. Ten specimens were made for each test conditions. Data were submitted to ANOVA split-plot design (shade, post-cure time, mode of activation and depth), followed by Tukey post hoc test (α=0.05). Significant differences for shade (p 0.05) were found, except for shade x post-cure time (p<0.0045) and mode of activation x post-cure time (p<0.0003). Resin cement shade has a significant effect on Knoop hardness. Indirect activation through a ceramic material reduced significantly Knoop hardness. Hardness Knoop significantly increased after 24 h in all cements shades compared to values obtained after 15 min. Resin cement depth significantly reduced Knoop hardness.
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Influence of photoactivation method and mold for restoration on the Knoop hardness of resin composite restorations
Lasers in Medical Science, 2013Co-Authors: William Cunha Brandt, Eduardo Jose Carvalho Souza-junior, Laís Regiane Da Silva-concílio, Ana Christina Claro Neves, Mario Alexandre Coelho SinhoretiAbstract:The aim of this study was to evaluate in vitro the Knoop hardness in the top and bottom of composite photo activated by different methods when different mold materials were used. Z250 (3M ESPE) and XL2500 halogen unit (3M ESPE) were used. For hardness test, conical restorations were made in extracted bovine incisors (tooth mold) and also metal mold (approximately 2 mm top diameter × 1.5 mm bottom diameter × 2 mm in height). Different photoactivation methods were tested: high-intensity continuous (HIC), low-intensity continuous (LIC), soft-start, or pulse-delay (PD), with constant radiant exposure. Knoop readings were performed on top and bottom restoration surfaces. Data were submitted to two-way ANOVA and Tukey’s test ( p = 0.05). On the top, regardless of the mold used, no significant difference in the Knoop hardness (Knoop hardness number, in kilograms–force per square millimeter) was observed between the photoactivation methods. On the bottom surface, the photoactivation method HIC shows higher means of hardness than LIC when tooth and metal were used. Significant differences of hardness on the top and in the bottom were detected between tooth and metal. The photoactivation method LIC and the material mold can interfere in the hardness values of composite restorations.
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comparative evaluation of Knoop hardness and depth of cure of ormocer based resin composites
Brazilian dental science, 2010Co-Authors: Roberta Caroline Bruschi Alonso, Leonardo Goncalves Cunha, Paulo Henrique Dos Santos, Gisele Maria Correr, Mario Alexandre Coelho SinhoretiAbstract:The purpose of this study was to evaluate the Knoop hardness and the depth of cure of Ormocer based composites and to compare them with traditional Bis-GMA or derivatives based composites. Four composite were selected: Two Ormocer based (Definite and Admira), a hybrid (Z250) and a microfilled (A110). Cylindrical specimens with 3mm in diameter for 5mm in height were prepared in a metallic mould and photoactived according the manufacturer’s instructions with the curing light unit XL2500 (3M/ESPE). After, they were stored for 24 hours at 37o C. Knoop hardness measures were obtained with Micro hardness tester HMV (Shimadzu-Japan), with a load of 50g for 15s. Five specimens were made for each resin composite and three Knoop hardness measurements were obtained on surface, 1mm, 2mm, 3mm and 4mm depths. The results were submitted to ANOVA and Tukey’s test at 5% level. According to the results, at all depths, Z250 was harder than the others composites. The composites Definite, Admira and A110 had no statistical differences in KHN until the depth of 2mm, after A110 showed decrease in hardness values. Generally, for all tested materials the deeper layers showed lower Knoop hardness values than those of the surface. Compared with hardness surface, statistically significant reductions in KHN occurred at depths of 2mm for Z250 and A110 and 3mm for Definite and Admira. It could be concluded that ORMOCER based materials showed intermediated hardness values and satisfactory depth of cure, when compared to the conventional composites.
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comparison of silorane and methacrylate based composite resins on the curing light transmission
Brazilian Dental Journal, 2010Co-Authors: Ricardo Danil Guiraldo, Simonides Consani, Mario Alexandre Coelho Sinhoreti, Rafael Leonardo Xediek Consani, Sandrine Bittencourt Berger, Wilson Batista Mendes, Lourenco CorrersobrinhoAbstract:The aim of this study was to investigate the influence of different composite resins - Filtek P90 (silorane-based composite) and Heliomolar (methacrylate-based composite) - on light transmission and decrease in Knoop hardness between the bottom and top of cured specimens. The irradiance of a light-curing unit (LCU) was measured with a power meter (Ophir Optronics; 900 mw/cm2) and spectral distributions were obtained using a spectrometer (USB 2000). Twenty standardized cylindrical specimens (2 mm thick x 7 mm diameter) of each composite resin were obtained by curing using the LCU for 40 s. Light energy transmission through the composite was calculated (n=10). The Knoop hardness number for each surface was recorded as the mean of 3 indentations. The difference in Knoop hardness between the top and bottom (DKH) of the same specimen was calculated (n=10). The irradiance of light that passed through Filtek P90 (272 mW/cm2) was not significantly greater than that the passed through Heliomolar (271 mW/cm2). The DKH of Filtek P90 (25%) was significantly higher than that of Heliomolar (12%). There was a greater degree of subsurface polymerization of the methacrylate-based composite compared to the silorane-based composite.
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effect of light curing units post cured time and shade of resin cement on Knoop hardness
Brazilian Dental Journal, 2009Co-Authors: Rogerio Vieira Reges, Mario Alexandre Coelho Sinhoreti, Ana Rosa Costa, Regina Maria Puppinrontani, Evandro Piva, Lourenco CorrersobrinhoAbstract:The aim of this study was to evaluate the Knoop hardness after 15 min and 24 h of different shades of a dual-cured resin-based cement after indirect photoactivation (ceramic restoration) with 2 light-curing units (LCUs). The resin cement Variolink II (Ivoclar Vivadent) shade XL, A2, A3 and opaque were mixed with the catalyst paste and inserted into a black Teflon mold (5 mm diameter x 1 mm high). A transparent strip was placed over the mold and a ceramic disc (Duceram Plus, shade A3) was positioned over the resin cement. Light-activation was performed through the ceramic for 40 s using quartz-tungsten-halogen (QTH) (XL 2500; 3M ESPE) or light-emitting diode (LED) (Ultrablue Is, DMC) LCUs with power density of 615 and 610 mW/cm2, respectively. The Koop hardness was measured using a microhardness tester HMV 2 (Shimadzu) after 15 min or 24 h. Four indentations were made in each specimen. Data were subjected to ANOVA and Tukey's test (a=0.05). The QTH LCU provided significantly higher (p<0.05) KHN values than the LED LCU. When the post-cure times were compared for the same shade, QTH and LED at 24 h provided significantly higher (p<0.05) KHN values than at 15 min. It may be concluded that the Knoop hardness was generally dependent on the LCU and post-cure time. The opaque shade of the resin cement showed lower Knoop hardness than the other shades for both LCUs and post-cure times.
Tetsuo Irifune - One of the best experts on this subject based on the ideXlab platform.
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Hardness and deformation microstructures of nano-polycrystalline diamonds synthesized from various carbons under high pressure and high temperature
Journal of Materials Research, 2007Co-Authors: Hitoshi Sumiya, Tetsuo IrifuneAbstract:Mechanical properties of high-purity nano-polycrystalline diamonds synthesized by direct conversion from graphite and various non-graphitic carbons under static high pressures and high temperatures were investigated by microindentation testing with a Knoop indenter and observation of microstructures around the indentations. Results of indentation hardness tests using a superhard synthetic diamond Knoop indenter showed that the polycrystalline diamond synthesized from graphite at ⩾15 GPa and 2300–2500 °C (consisting of fine grains 10–30 nm in size and layered crystals) has very high Knoop hardness (Hk ⩾ 110 GPa), whereas the hardness of polycrystalline diamonds synthesized from non-graphitic carbons at ⩾15 GPa and below 2000 °C (consisting only of single-nano grains 5–10 nm in size) are significantly lower (Hk = 70 to 90 GPa). Microstructure observations beneath the indentations of these nano-polycrystalline diamonds suggest that the existence of a lamellar structure and the bonding strength of the grain boundary play important roles in controlling the hardness of the polycrystalline diamond.
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indentation hardness of nano polycrystalline diamond prepared from graphite by direct conversion
Diamond and Related Materials, 2004Co-Authors: Hitoshi Sumiya, Tetsuo IrifuneAbstract:Abstract Indentation hardness of nano-polycrystalline diamonds (consisting of fine particles of 10–30 nm size) prepared directly from graphite under high pressure and high temperature conditions were investigated. It was found that a measurable indentation with no cracking can only be formed using the Knoop indenter in a limited loading condition of 2–6 N, and a reliable and accurate measurement is obtained at a load around 4.9 N. The Knoop hardness measurement at the applied load of 4.9 N revealed that some of the nano-polycrystalline diamonds obtained at P ≧15 GPa and T ≧2300 °C have extremely high hardness (120–145 GPa), which is equivalent to that in the (001)〈100〉 of the synthetic high-purity (type IIa) diamond crystal (116–130 GPa).
Shuichi Satoh - One of the best experts on this subject based on the ideXlab platform.
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Mechanical properties of synthetic type IIa diamond crystal
Diamond and Related Materials, 1997Co-Authors: Hitoshi Sumiya, Naohiro Toda, Shuichi SatohAbstract:Abstract The mechanical behavior of synthetic type IIa diamond has been investigated by the Knoop hardness measurement and observation of the cleavage surfaces. It was clarified that the Knoop hardness in (100)〈100〉 of synthetic diamonds increases with decreasing of the nitrogen impurities concentration, and that the synthetic type IIa diamond, having few nitrogen impurities, has the highest hardness of synthetic diamonds. In addition, it was found that the Knoop hardness in (100)〈110〉 of synthetic type IIa diamond is extremely high, and the anisotropy in the hardness of the diamond is different from those of natural diamond and synthetic type Ib diamond. The cleavage surfaces of the synthetic type IIa diamonds were very smooth and showed remarkably regular cleavage patterns. These results indicate that there are very few impurities and crystal defects in the synthetic type IIa diamond, and also suggest that the diamond has high resistance to plastic flow.
Americo Bortolazzo Correr - One of the best experts on this subject based on the ideXlab platform.
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Influence of the cavity size, photoactivation method and restorative system on marginal adaptation, Knoop hardness and bond strength to root dentin
2017Co-Authors: Americo Bortolazzo CorrerAbstract:Resumo: O objetivo deste estudo foi verificar a influência do volume de compósito, técnica de fotoativação e sistema restaurador sobre a adaptação marginal, dureza Knoop e resistência de união de compósitos à dentina humana radicular. Este estudo foi dividido em 2 Capítulos. O Capítulo I verificou o efeito do volume de compósito (mantendo-se o mesmo fator C) e sistema restaurador sobre a adaptação marginal, dureza Knoop e resistência de união "push-out" a dentina radicular. Foram utilizados 90 pré-molares hígidos divididos em 9 grupos (n=10), de acordo com o volume de compósito (pequena, média e grande) e sistema restaurador (Filtek Z350, Filtek Z350 Flow e Filtek LS). Os compósitos foram fotoativados por LED Ultralume 5 (Ultradent) por 20 s para Filtek Z350, Filtek Z350 Flow e 40 s para Filtek LS. A adaptação marginal foi avaliada após 24h utilizando o método do corante superficial, medindo-se a porcentagem corada em relação ao perímetro da cavidade (Caries Detector). Após a análise da adaptação marginal, as amostras foram submetidas ao ensaio de resistência de união "push-out" e de dureza Knoopna superfície do compósito. Os dados foram submetidos à análise de variância dois fatores e teste de Tukey (p=0,05). O volume de compósito não influenciou a adaptação marginal dos compósitos. Filtek LS apresentou os melhores resultados de adaptação marginal e resistência de união. Os menores valores de resistência foram apresentados pelo Filtek Z350. O volume de compósito influenciou nos valores de resistência de união e de dureza Knoop, dependendo do compósito utilizado. Os maiores valores de dureza foram apresentados pelos volumes de compósito médios. A maior dureza foi do compósito Filtek Z350, seguido por Filtek LS e Filtek Z350 flow. No Capítulo II o objetivo foi verificar a influência da modulação da intensidade da luz durante a fotoativação e volume de compósito sobre a dureza Knoop e resistência de união do compósito Filtek Z350 à dentina radicular. Foram utilizados 90 pré-molares hígidos divididos em 9 grupos (n=10), segundo o volume de compósito (pequena, média e grande) e método de fototivação (luz contínua, "pulse delay" e "soft-start"). O compósito foi fotoativado por LED Ultralume 5 (Ultradent) pelos métodos citados anteriormente. Após 24h foi realizado o ensaio de resistência de união "push-out" e de dureza Knoop na superfície do compósito. Os dados foram submetidos à análise de variância dois fatores e teste de Tukey (p=0,05). Os resultados de resistência de união mostraram que os métodos de modulação da intensidade da luz foram superiores ao contínuo, sem diferença entre eles. Cavidade média foi significativamente superior que cavidade pequena e grande para o método contínuo. O ensaio de dureza Knoop mostrou que o melhor comportamento foi apresentado pelo método pulse delay e para cavidades médias. O volume de compósito influenciou os valores de resistência de união, dureza Knoop e adaptação marginal a dentina radicular. Os maiores valores de resistência de união e adaptação marginal foram apresentados pelo compósito Filtek LS e os maiores valores de dureza pelo compósito Filtek Z350. Os métodos de modulação da intensidade de luz mostraram os melhores resultados de resistência de união, sem detrimento dos valores de dureza Knoop.Abstract: The polymerization shrinkage is one of the major drawbacks of the resin composites. The polymerization stress depends on the viscosity of the composite, rate of reaction, geometric configuration of the cavity and irradiance used during photoactivation. However, the volume of composite and low shrink monomers has been investigated. The aim of this study was to evaluate the influence of the cavity size, photoactivation technique and composite composition on marginal adaptation, Knoop hardness and push-out bond strength of composites to root dentin. This study was divided into 2 Chapters. In the Chapter 1 was to evaluate the effect of the cavity size (with similar C-factor) and restorative system on marginal adaptation, Knoop hardness and push-out bond strength to root dentin. Ninety premolars were divided into 9 groups, according to cavity size (small, middle and large) and resin composite (Filtek Z350, Filtek Z350 Flow e Filtek P90). The resin composites Filtek Z350, Filtek Z350 Flow were photoactivated with LED Ultralume5 (Ultradent) for 20 s and Filtek P90 for 40 s. The marginal adaptation was analyzed after 24 h using Caries Detector. After that, the specimens were submitted to push-out Bond strength. The Knoop hardness examination was performed at the top surface. The data were submitted to ANOVA two-way and post hoc Tukey-s test at 95% significance level. The cavity size had no influence on marginal adaptation of the resin composites. Filtek P90 presented the best marginal adaptation, significantly better than other composites for large cavity. Filtek P90 showed the highest bond strength, significantly higher than other composites. Filtek Z350 showed the lowest bond strength results. Middle cavity presented Bond strength significantly higher than large cavity with the composite Filtek Z350. The highest Knoop hardness was showed by Filtek Z350, followed by Filtek P90 and Filtek Z350 flow. The aim of the Chapter 2 was to evaluate the influence of modulated photoacivation methods and cavity size on Knoop hardness and push-out bond strength of the composite Filtek Z350 to root dentin. Ninety premolars were divided into 9 groups, according to cavity size (small, middle and large) and photoactivation method (continuous light, pulse delay and soft-start). The composite was inserted and photoactivated with LED Ultralume 5 (Ultradent) by the methods aforementioned. The specimens were submitted to push-out Bond strength and Knoop hardness test. The data were submitted to ANOVA two-way and post hoc Tukey-s test at 95% significance level. Pulse delay showed the highest Bond strength results, significantly higher continuous light for small and large cavities. Middle cavity showed Bond strength significantly higher than small and large cavities for continuous light. Continuous light presented Knoop hardness significantly higher than soft-start for small cavity. For middle cavity, pulse delay showed Knoop hardness significantly higher than continuous light and soft-start. Pulse delay and soft-start showed Knoop hardness significantly higher than continuous light. The cavity size had influence on marginal adaptation, Knoop hardness and bond strength to root dentin. Filtek LS showed the highest bond strength and marginal adaptation results and Filtek Z350 presented the highest Knoop hardness results. The light intensity modulation methods showed the best bond strength results without decrease the Knoop hardness values
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Avaliação da dureza Knoop de compositos restauradores odontologicos fotoativados por diferentes metodos
2017Co-Authors: Americo Bortolazzo CorrerAbstract:Resumo: Os compósitos odontológicos fotoativados são os materiais odontológicos restauradores estéticos mais utilizados atualmente. Dentre suas vantagens estão o controle do tempo de presa e a estética, além de ser desnecessário a confecção de preparo cavitário retentivo. Durante o processo de polimerização, o compósito sofre contração e, dependendo da velocidade da reação, essa contração pode gerar grande tensão na interface dente-restauração, promovendo o aparecimento de fendas e conseqüente falha da restauração. Além disso, para que o compósito apresente propriedades mecânicas adequadas, é necessário que ele atinja alto grau de conversão. O grau de conversão depende da quantidade de energia que é fornecida ao compósito, embora o efeito da densidade energética nas propriedades mecânicas dos compósitos ainda não seja bem evidenciado. Visando o melhor entendimento dos métodos de fotoativação sobre as propriedades finais dos compósitos restauradores odontológicos, este estudo foi dividido em dois trabalhos: O primeiro avaliou o efeito do aumento da densidade energética pelo maior tempo de exposição, mantendo-se a mesma intensidade de luz, sobre a dureza Knoop dos compósitos Z250 e Esthet-X, fotoativados por luz de lâmpada halógena (QTH) - XL2500, luz emitida por diodo (LED) ? Ultrablue Is ou arco de plasma de Xenônio (PAC) ? Apollo 95E. Os resultados mostraram que o aumento da densidade energética produziu maiores valores de dureza Knoop quando utilizado LED ou PAC. Para QTH não houve diferença significativa. Em relação às fontes de luz, o PAC apresentou menores valores de dureza Knoop quando comparado ao LED e QTH, que não diferiram entre si. Menores valores de dureza Knoop foram encontrados em maiores profundidades dos compósitos. O segundo trabalho verificou a influência da relação intensidade de luz versus tempo de exposição, utilizando a mesma densidade energética, sobre a dureza Knoop dos compósitos Z250 e Esthet-X, fotoativados por QTH, LED e PAC. Os resultados mostraram que independente do compósito e da fonte de luz, os grupos fotoativados por intensidade de luz e tempo de exposição intermediários apresentaram as maiores médias de dureza Knoop em camadas profundas. A relação dureza da base/dureza da superfície mostrou que o compósito Z250 apresentou adequada polimerização até 3 mm quando foi fotoativado por QTH e LED, e até 2 mm para PAC. O compósito Esthet-X apresentou adequada polimerização até 3 mm quando foi fotoativado por luz halógena e até 2 mm para LED e PACAbstract: Nowadays, the photoactivated composites are the most used esthetic restorative dental materials in dentistry. The advantages of these materials are the control of setting time and esthetic characteristics. Besides that, it?s unnecessary to prepare retentive cavity. Composites shrink during the polymerization reaction and a tension can be induced on restoration/tooth interface. Depending on composite/tooth interface bond strength, gaps can be formed in the restoration margins, leading to the failure of restorative procedure. Besides that, a high degree of conversion is necessary for composites to obtain adequate mechanical properties. The degree of conversion depends on energy density supplied to composites. The effects of energy density in mechanical properties of composites have not been satisfactory proved. In an attempt to improve the knowledge of the photo-activation methods upon the final properties of the restorative composite resins, this research was divided in two works. The first study evaluated the effect of increase on exposure time on Knoop hardness of composites Z250 and Esthet-X, photoactivated using XL2500 halogen light (QTH), Ultrablue Is Light emitting diode (LED) and Apollo 95E plasma arc curing (PAC). The results showed that higher Knoop hardness were produced by the increase on exposure time when LED and PAC were used. For QTH, the increase on exposure time did not produced significant effect. Regarding to light sources, PAC presented lower Knoop hardness than QTH and LED, which did not present significant difference from each other. Knoop hardness at deep layers was lower than superficial layers. The second study verified the influence of irradiance versus exposure time, using the same energy density, on Knoop hardness of Z250 and Esthet-X composites photoactivated using QTH, LED or PAC. The results showed that with intermediate light intensity and exposure times, the highest Knoop hardness were obtained, compared to others photoactivation methods. Composite Z250 presented adequate polymerization (bottom/surface relation above 0.8) up to 2 mm deep using PAC and up to 3 mm using QTH and LED. Esthet-X composite presented adequate polymerization up to 2 mm deep, using LED and PAC and up to 3 mm using QT
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Influence of the cavity size, photoactivation method and restorative system on marginal adaptation, Knoop hardness and bond strength to root dentin
Universidade Estadual de Campinas . Faculdade de Odontologia de Piracicaba, 2009Co-Authors: Americo Bortolazzo CorrerAbstract:O objetivo deste estudo foi verificar a influência do volume de compósito, técnica de fotoativação e sistema restaurador sobre a adaptação marginal, dureza Knoop e resistência de união de compósitos à dentina humana radicular. Este estudo foi dividido em 2 Capítulos. O Capítulo I verificou o efeito do volume de compósito (mantendo-se o mesmo fator C) e sistema restaurador sobre a adaptação marginal, dureza Knoop e resistência de união "push-out" a dentina radicular. Foram utilizados 90 pré-molares hígidos divididos em 9 grupos (n=10), de acordo com o volume de compósito (pequena, média e grande) e sistema restaurador (Filtek Z350, Filtek Z350 Flow e Filtek LS). Os compósitos foram fotoativados por LED Ultralume 5 (Ultradent) por 20 s para Filtek Z350, Filtek Z350 Flow e 40 s para Filtek LS. A adaptação marginal foi avaliada após 24h utilizando o método do corante superficial, medindo-se a porcentagem corada em relação ao perímetro da cavidade (Caries Detector). Após a análise da adaptação marginal, as amostras foram submetidas ao ensaio de resistência de união "push-out" e de dureza Knoop na superfície do compósito. Os dados foram submetidos à análise de variância dois fatores e teste de Tukey (p=0,05). O volume de compósito não influenciou a adaptação marginal dos compósitos. Filtek LS apresentou os melhores resultados de adaptação marginal e resistência de união. Os menores valores de resistência foram apresentados pelo Filtek Z350. O volume de compósito influenciou nos valores de resistência de união e de dureza Knoop, dependendo do compósito utilizado. Os maiores valores de dureza foram apresentados pelos volumes de compósito médios. A maior dureza foi do compósito Filtek Z350, seguido por Filtek LS e Filtek Z350 flow. No Capítulo II o objetivo foi verificar a influência da modulação da intensidade da luz durante a fotoativação e volume de compósito sobre a dureza Knoop e resistência de união do compósito Filtek Z350 à dentina radicular. Foram utilizados 90 pré-molares hígidos divididos em 9 grupos (n=10), segundo o volume de compósito (pequena, média e grande) e método de fototivação (luz contínua, "pulse delay" e "soft-start"). O compósito foi fotoativado por LED Ultralume 5 (Ultradent) pelos métodos citados anteriormente. Após 24h foi realizado o ensaio de resistência de união "push-out" e de dureza Knoop na superfície do compósito. Os dados foram submetidos à análise de variância dois fatores e teste de Tukey (p=0,05). Os resultados de resistência de união mostraram que os métodos de modulação da intensidade da luz foram superiores ao contínuo, sem diferença entre eles. Cavidade média foi significativamente superior que cavidade pequena e grande para o método contínuo. O ensaio de dureza Knoop mostrou que o melhor comportamento foi apresentado pelo método pulse delay e para cavidades médias. O volume de compósito influenciou os valores de resistência de união, dureza Knoop e adaptação marginal a dentina radicular. Os maiores valores de resistência de união e adaptação marginal foram apresentados pelo compósito Filtek LS e os maiores valores de dureza pelo compósito Filtek Z350. Os métodos de modulação da intensidade de luz mostraram os melhores resultados de resistência de união, sem detrimento dos valores de dureza Knoop.The polymerization shrinkage is one of the major drawbacks of the resin composites. The polymerization stress depends on the viscosity of the composite, rate of reaction, geometric configuration of the cavity and irradiance used during photoactivation. However, the volume of composite and low shrink monomers has been investigated. The aim of this study was to evaluate the influence of the cavity size, photoactivation technique and composite composition on marginal adaptation, Knoop hardness and push-out bond strength of composites to root dentin. This study was divided into 2 Chapters. In the Chapter 1 was to evaluate the effect of the cavity size (with similar C-factor) and restorative system on marginal adaptation, Knoop hardness and push-out bond strength to root dentin. Ninety premolars were divided into 9 groups, according to cavity size (small, middle and large) and resin composite (Filtek Z350, Filtek Z350 Flow e Filtek P90). The resin composites Filtek Z350, Filtek Z350 Flow were photoactivated with LED Ultralume 5 (Ultradent) for 20 s and Filtek P90 for 40 s. The marginal adaptation was analyzed after 24 h using Caries Detector. After that, the specimens were submitted to push-out Bond strength. The Knoop hardness examination was performed at the top surface. The data were submitted to ANOVA two-way and post hoc Tukey-s test at 95% significance level. The cavity size had no influence on marginal adaptation of the resin composites. Filtek P90 presented the best marginal adaptation, significantly better than other composites for large cavity. Filtek P90 showed the highest bond strength, significantly higher than other composites. Filtek Z350 showed the lowest bond strength results. Middle cavity presented Bond strength significantly higher than large cavity with the composite Filtek Z350. The highest Knoop hardness was showed by Filtek Z350, followed by Filtek P90 and Filtek Z350 flow. The aim of the Chapter 2 was to evaluate the influence of modulated photoacivation methods and cavity size on Knoop hardness and push-out bond strength of the composite Filtek Z350 to root dentin. Ninety premolars were divided into 9 groups, according to cavity size (small, middle and large) and photoactivation method (continuous light, pulse delay and soft-start). The composite was inserted and photoactivated with LED Ultralume 5 (Ultradent) by the methods aforementioned. The specimens were submitted to push-out Bond strength and Knoop hardness test. The data were submitted to ANOVA two-way and post hoc Tukey-s test at 95% significance level. Pulse delay showed the highest Bond strength results, significantly higher continuous light for small and large cavities. Middle cavity showed Bond strength significantly higher than small and large cavities for continuous light. Continuous light presented Knoop hardness significantly higher than soft-start for small cavity. For middle cavity, pulse delay showed Knoop hardness significantly higher than continuous light and soft-start. Pulse delay and soft-start showed Knoop hardness significantly higher than continuous light. The cavity size had influence on marginal adaptation, Knoop hardness and bond strength to root dentin. Filtek LS showed the highest bond strength and marginal adaptation results and Filtek Z350 presented the highest Knoop hardness results. The light intensity modulation methods showed the best bond strength results without decrease the Knoop hardness values
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effect of the increase of energy density on Knoop hardness of dental composites light cured by conventional qth led and xenon plasma arc
Brazilian Dental Journal, 2005Co-Authors: Americo Bortolazzo Correr, Lourenco Correr Sobrinho, Mario Alexandre Coelho Sinhoreti, Rubens Nisie Tango, Luis Felipe J Schneider, Simonides ConsaniAbstract:The aim of this study was to evaluate the effect of the increase of energy density on Knoop hardness of Z250 and Esthet-X composite resins. Cylindrical cavities (3 mm in diameter X 3 mm in depth) were prepared on the buccal surface of 144 bovine incisors. The composite resins were bulk-inserted and polymerized using different light-curing units and times: conventional QTH (quartz-tungsten-halogen; 700 mW/cm(2); 20 s, 30 s and 40 s); LED (light-emitting diode; 440 mW/cm(2); 20 s, 30 s and 40 s); PAC (xenon plasma arc; 1700 mW/cm(2); 3 s, 4.5 s and 6 s). The specimens were stored at 37 degrees C for 24 h prior to sectioning for Knoop hardness assessment. Three measurements were obtained for each depth: top surface, 1 mm and 2 mm. Data were analyzed statistically by ANOVA and Tukey's test (p 0.05) were found for QTH. Knoop hardness values decreased with the increase of depth. The increase of energy density produced composites with higher Knoop hardness means using LED and PAC.
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Avaliação da dureza Knoop de compositos restauradores odontologicos fotoativados por diferentes metodos
Universidade Estadual de Campinas . Faculdade de Odontologia de Piracicaba, 2005Co-Authors: Americo Bortolazzo CorrerAbstract:Os compósitos odontológicos fotoativados são os materiais odontológicos restauradores estéticos mais utilizados atualmente. Dentre suas vantagens estão o controle do tempo de presa e a estética, além de ser desnecessário a confecção de preparo cavitário retentivo. Durante o processo de polimerização, o compósito sofre contração e, dependendo da velocidade da reação, essa contração pode gerar grande tensão na interface dente-restauração, promovendo o aparecimento de fendas e conseqüente falha da restauração. Além disso, para que o compósito apresente propriedades mecânicas adequadas, é necessário que ele atinja alto grau de conversão. O grau de conversão depende da quantidade de energia que é fornecida ao compósito, embora o efeito da densidade energética nas propriedades mecânicas dos compósitos ainda não seja bem evidenciado. Visando o melhor entendimento dos métodos de fotoativação sobre as propriedades finais dos compósitos restauradores odontológicos, este estudo foi dividido em dois trabalhos: O primeiro avaliou o efeito do aumento da densidade energética pelo maior tempo de exposição, mantendo-se a mesma intensidade de luz, sobre a dureza Knoop dos compósitos Z250 e Esthet-X, fotoativados por luz de lâmpada halógena (QTH) - XL2500, luz emitida por diodo (LED) ? Ultrablue Is ou arco de plasma de Xenônio (PAC) ? Apollo 95E. Os resultados mostraram que o aumento da densidade energética produziu maiores valores de dureza Knoop quando utilizado LED ou PAC. Para QTH não houve diferença significativa. Em relação às fontes de luz, o PAC apresentou menores valores de dureza Knoop quando comparado ao LED e QTH, que não diferiram entre si. Menores valores de dureza Knoop foram encontrados em maiores profundidades dos compósitos. O segundo trabalho verificou a influência da relação intensidade de luz versus tempo de exposição, utilizando a mesma densidade energética, sobre a dureza Knoop dos compósitos Z250 e Esthet-X, fotoativados por QTH, LED e PAC. Os resultados mostraram que independente do compósito e da fonte de luz, os grupos fotoativados por intensidade de luz e tempo de exposição intermediários apresentaram as maiores médias de dureza Knoop em camadas profundas. A relação dureza da base/dureza da superfície mostrou que o compósito Z250 apresentou adequada polimerização até 3 mm quando foi fotoativado por QTH e LED, e até 2 mm para PAC. O compósito Esthet-X apresentou adequada polimerização até 3 mm quando foi fotoativado por luz halógena e até 2 mm para LED e PACNowadays, the photoactivated composites are the most used esthetic restorative dental materials in dentistry. The advantages of these materials are the control of setting time and esthetic characteristics. Besides that, it?s unnecessary to prepare retentive cavity. Composites shrink during the polymerization reaction and a tension can be induced on restoration/tooth interface. Depending on composite/tooth interface bond strength, gaps can be formed in the restoration margins, leading to the failure of restorative procedure. Besides that, a high degree of conversion is necessary for composites to obtain adequate mechanical properties. The degree of conversion depends on energy density supplied to composites. The effects of energy density in mechanical properties of composites have not been satisfactory proved. In an attempt to improve the knowledge of the photo-activation methods upon the final properties of the restorative composite resins, this research was divided in two works. The first study evaluated the effect of increase on exposure time on Knoop hardness of composites Z250 and Esthet-X, photoactivated using XL2500 halogen light (QTH), Ultrablue Is Light emitting diode (LED) and Apollo 95E plasma arc curing (PAC). The results showed that higher Knoop hardness were produced by the increase on exposure time when LED and PAC were used. For QTH, the increase on exposure time did not produced significant effect. Regarding to light sources, PAC presented lower Knoop hardness than QTH and LED, which did not present significant difference from each other. Knoop hardness at deep layers was lower than superficial layers. The second study verified the influence of irradiance versus exposure time, using the same energy density, on Knoop hardness of Z250 and Esthet-X composites photoactivated using QTH, LED or PAC. The results showed that with intermediate light intensity and exposure times, the highest Knoop hardness were obtained, compared to others photoactivation methods. Composite Z250 presented adequate polymerization (bottom/surface relation above 0.8) up to 2 mm deep using PAC and up to 3 mm using QTH and LED. Esthet-X composite presented adequate polymerization up to 2 mm deep, using LED and PAC and up to 3 mm using QT
