Página 1 dos resultados de 1042 itens digitais encontrados em 0.010 segundos

Influence of hardness of the harder body on wear regime transition in a sliding pair of steels

VIAFARA, C. C.; SINATORA, A.
Fonte: ELSEVIER SCIENCE SA Publicador: ELSEVIER SCIENCE SA
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
37.918027%
In the unlubricated sliding wear of steels the mild-severe and severe-mild wear transitions have long been investigated. The effect of system inputs such as normal load, sliding speed, environment humidity and temperature, material properties, among others, on those transitions have also been studied. Although transitions seem to be caused by microstructural changes, surfaces oxidation and work-hardening, some questions remain regarding the way each aspect is involved. Since the early studies in sliding wear, it has usually been assumed that only the material properties of the softer body influence the wear behavior of contacting surfaces. For example, the Archard equation involves only the hardness of the softer body, without considering the hardness of the harder body. This work aims to discuss the importance of the harder body hardness in determining the wear regime operation. For this, pin-on-disk wear tests were carried out, in which the disk material was always harder than the pin material. Variations of the friction force and vertical displacement of the pin were registered during the tests. A material characterization before and after tests was conducted using stereoscopy and scanning electron microscopy (SEM) methods, in addition to mass loss...

Micro-hardness evaluation of a micro-hybrid composite resin light cured with halogen light, light-emitting diode and argon ion laser

RODE, Katia M.; FREITAS, Patricia M. de; LLORET, Patricia R.; POWELL, Lynn G.; TURBINO, Miriam L.
Fonte: SPRINGER LONDON LTD Publicador: SPRINGER LONDON LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
47.715713%
This in vitro study aimed to determine whether the micro-hardness of a composite resin is modified by the light units or by the thickness of the increment. Composite resin disks were divided into 15 groups (n = 5), according to the factors under study: composite resin thickness (0 mm, 1 mm, 2 mm , 3 mm and 4 mm) and light units. The light activation was performed with halogen light (HL) (40 s, 500 mW/cm(2)), argon ion laser (AL) (30 s, 600 mW/cm(2)) or light-emitting diode (LED) (30 s, 400 mW/cm(2)). Vickers micro-hardness tests were performed after 1 week and were carried out on the top surface (0 mm-control) and at different depths of the samples. Analysis of variance (ANOVA) and Tukey tests (P a parts per thousand currency signaEuro parts per thousand 0.05) revealed no statistically significant difference among the light units for the groups of 0 mm and 1 mm thickness. At 2 mm depth, the AL was not statistically different from the HL, but the latter showed higher micro-hardness values than the LED. In groups with 3 mm and 4 mm thickness, the HL also showed higher micro-hardness values than the groups activated by the AL and the LED. Only the HL presented satisfactory polymerization with 3 mm of thickness. With a 4 mm increment no light unit was able to promote satisfactory polymerization.; Sao Paulo Research Foundation/FAPESP[99/08433-4]; Sao Paulo Research Foundation/FAPESP[99/11408-1]

Relation between magnetic Barkhausen noise and hardness for jominy quench tests in SAE 4140 and 6150 steels

Franco, Freddy A; González, M F R; campos, M F de; Padovese, Linilson
Fonte: New York Publicador: New York
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
47.572017%
he nondestructive Magnetic Barkhausen Noise (MBN) technique was applied for the evaluation of SAE 4140 and SAE 6150 steels after a Jominy end-quench test. Microstructures were also characterized by SEM (Scanning Electron Microscope) and hardness tests. MBN measurements were performed on the same sample regions at three excitation frequencies. Different parameters of the measured signals (signal peak position and height, and Root mean square) were calculated. A relationship between mechanical hardness and MBN parameters was found for both materials, with the best correlation coefficient being found in low excitation frequency range.; The authors would like to thank the State of São Paulo Research Foundation, FAPESP (Process 05/57146-0). M.F. de Campos and L.R. Padovese thank CNPq. We thank Dr. Martin Sab- lik for the critical reading of the manuscript

Análise da qualidade da polimerização e da degradação de cimentos resinosos utilizados na cimentação de pinos de fibra de vidro por meio de testes de microdureza; Microhardness analysis of the polymerization quality and degradation of resin cements used for fiber posts cementation

Pedreira, Ana Paula Ribeiro do Vale
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 16/04/2007 PT
Relevância na Pesquisa
47.885537%
Os cimentos resinosos têm sido largamente utilizados em odontologia restauradora com a finalidade de reter o pino intra-radicular e dissipar tensões entre este e a raiz. Entretanto, o grau de conversão alcançado pelos mesmos influencia suas propriedades mecânicas, biocompatibilidade e degradação pela água e pelos ácidos bucais. Testes de microdureza podem ser aplicados para estimar o grau de conversão de compósitos, uma vez que apresentam boa correlação com a espectroscopia infravermelha. Este trabalho objetivou analisar a microdureza de quatro cimentos resinosos de polimerização dual utilizados na cimentação de pinos de fibra de vidro, nos períodos inicial, após 24 horas de imersão em etanol a 75% e após 3 meses de armazenamento em água, e testar a hipótese de que não há diferença entre a microdureza dos terços cervical, médio e apical na linha de cimento. Quarenta incisivos bovinos tratados endodonticamente foram distribuídos em quatro grupos para a cimentação de pinos Fibrekor® (Jeneric/Pentron) de 1mm de diâmetro, sendo: Grupo 1 - Panavia F 2.0 (Kuraray Medical Inc.), Grupo 2 - Variolink (Ivoclar), Grupo 3 - Rely X Unicem (3M ESPE) e Grupo 4 - Duolink (Bisco). Após a cimentação, as raízes foram divididas em 2 subgrupos...

Avaliação do comportamento mecânico e tribológico de ligas Ni-Cr-Al-C.; Evaluation of the mechanical and tribological behavior of Ni-Cr-Al-C alloys.

Silva, Wanderson Santana da
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 23/11/2006 PT
Relevância na Pesquisa
37.851067%
Este trabalho traz contribuições à linha de pesquisa 'Nova Família de Ligas Baseada no Sistema Ni-Al-Cr-C Resistentes ao Desgaste em Elevadas Temperaturas', estudando o comportamento mecânico, tribológico e a estabilidade superficial destas ligas. Esta família de ligas fundidas, denominada NICRALC - busca conjugar algumas características das superligas à base de níquel e dos ferros fundidos brancos, aliando ao comportamento mecânico anômalo do Ni3Al - aumento da resistência mecânica com a temperatura, até valores da ordem de 800°C - a uma dispersão de carbonetos de cromo de alta dureza. Desta forma, busca-se desenvolver uma alternativa às ligas ferrosas nas temperaturas acima das quais estas ligas perdem significativamente sua resistência mecânica (notadamente 600 °C), assim como uma alternativa mais econômica às ligas a base de cobalto resistentes ao desgaste, em virtude das altas cotações e instabilidades no preço deste elemento. Neste trabalho foram avaliadas as propriedades mecânicas em elevadas temperaturas (compressão e dureza), tenacidade à fratura na temperatura ambiente, comportamento tribológico (cavitação, abrasão, deslizamento e erosão) e a resistência à oxidação ao ar e à carburação em atmosfera redutora...

Estudo in vitro da influência da dureza e módulo de elasticidade de sistemas adesivos na resistência de união à dentina humana; In vitro study of influence of hardness and elasticity module of adhesive sistems in bond strenght to human dentin

Bengtson, Camilla Regina Galvão
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 01/02/2011 PT
Relevância na Pesquisa
47.655454%
O objetivo deste trabalho foi avaliar a dureza e o módulo de elasticidade da região de adesão quando utilizados diferentes sistemas adesivos e uma resina composta imediatamente após o procedimento adesivo e após 6 meses de armazenamento, correlacionando esses valores com a resistência adesiva à dentina humana. Para isso foram medidos a dureza e o módulo de elasticidade da resina composta junto à área de união, da camada de adesivo, da camada híbrida, e da dentina adjacente utilizando testes de nanoendentação. Foram utilizados 40 molares humanos hígidos (n=10). Os dentes foram preparados de modo a obterem-se superfícies planas em dentina, sobre as quais os sistemas adesivos foram aplicados seguindo as instruções dos fabricantes. Foram utilizados quatro sistemas adesivos de diferentes formas de aplicação (Adper Scotchbond Multiuso, Adper Single Bond 2, Adper SE Plus e Clearfil SE Bond). Sobre essas superfícies foram inseridos incrementos de resina composta perfazendo 5 mm de altura. Após 24h de armazenamento em água destilada à 37ºC. Os dentes restaurados foram seccionados para obterem-se corpos-de-prova com área aderida de 1mm2. Dos corpos de prova viáveis, 2 palitos centrais de cada dente foram selecionados para análise da nanodureza e do módulo de elasticidade da interface adesiva. Os demais tiveram a resistência de união testada através do teste de microtração...

Dureza da camada de adesivo e da camada híbrida e a sua relação com a resistência de união à dentina; Hardness of the adhesive layer and the hybrid layer and its relationship to bond strength to dentin

Nunes, Paula Mendes Acatauassú
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 02/09/2013 PT
Relevância na Pesquisa
47.849146%
Este estudo avaliou in vitro a dureza da camada de adesivo e da camada híbrida de uma interface entre resina composta e dentina humana por meio de ensaios de nanodureza (DUH). Foi avaliada a resistência de união por meio de testes de microcisalhamento (MC) com o objetivo de observar a relação desta resistência com a propriedade da dureza. Os fatores de variação compreendem quatro sistemas adesivos (Adper Scotchbond Multiuso, Adper Single Bond 2, Clearfil SE Bond e Single Bond Universal) e duas profundidades dentinárias (dentina rasa e dentina profunda). As unidades experimentais foram compostas por 144 fragmentos dentais obtidos da face vestibular de molares humanos, os quais foram distribuídos em 16 grupos, 8 grupos com n=6 para os ensaios de DUH e 8 grupos com n=12 para os ensaios de MC de forma que os quatro sistemas adesivos foram aplicados sobre fragmentos de dentina rasa e de dentina profunda. Após a confecção das restaurações em resina composta e 24h de armazenamento em estufa a 37°C, os ensaios de DUH foram realizados no ultramicrodurômetro DUH-211S (Shimadzu) com carga de 1mN/mseg. Os testes de MC foram realizados na máquina de ensaios universais Instron 5942(Instron Co) com velocidade de 1mm/min seguido da análise do padrão de fratura em microscópio digital. A análise estatística foi realizada por ANOVA (p<0...

A preliminary study of hardness and modulus of elasticity in sheep mandibles submitted to distraction osteogenesis and low-level laser therapy

Freddo, Angelo Luiz; Hubler, Roberto; Beck, Carlos Afonso de Castro; Heitz, Claiton; Oliveira, Marilia Gerhardt de
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
ENG
Relevância na Pesquisa
47.655454%
Objectives: To investigate the quality of newly formed bone in sheep mandibles submitted to distraction osteogenesis and low-level laser therapy (LLLT), based on hardness and modulus of elasticity values. The ideal moment for laser application (during the latency/activation period vs. during the bone consolidation period) was also evaluated. Computed tomography imaging was used to assess relapse as a result of early device removal. Study design: Extraoral distraction devices were placed in five sheep so as to achieve 1.5 cm of lengthened bone in 60 days. Distraction devices were removed 50, 40, and 33 days after surgery. Four animals were treated with LLLT, at different times, and one was used as control (no LLLT). Results: When applied during the bone consolidation period, LLLT caused an increase in hardness and modulus of elasticity values. On the other hand, animals irradiated with LLLT during the latency/activation period presented a delay in bone healing. A period of consolidation of 13 days (early device removal) was associated with relapse. Conclusions: Nanoindentation tests were able to detect slight abnormalities in bone metabolism and proved to be important tools for the assessment of bone quality following distraction osteogenesis. LLLT provided increased benefits when applied during the bone consolidation period...

Hardness of heat-polymerized acrylic resins after disinfection and long-term water immersion

Neppelenbroek, K. H.; Pavarina, A. C.; Vergani, Carlos Eduardo; Giampaolo, E. T.
Fonte: Mosby, Inc Publicador: Mosby, Inc
Tipo: Artigo de Revista Científica Formato: 171-176
ENG
Relevância na Pesquisa
37.849146%
Statement of the problem. In selecting a disinfectant for dental prostheses, compatibility between the disinfectant and the type of denture base material must be considered to avoid adverse effects on the hardness of the acrylic resin.Purpose. This study investigated the hardness of 2 denture base resins after disinfection and long-term water immersion.Material and methods. Thirty-two disk-shaped specimens (13 mm in diameter and 8 mm thick) were fabricated from each resin (Lucitone 550 and QC-20), polished, stored in water at 37degreesC for 48 hours, and submitted to hardness tests (Vickers hardness number [VHN]) before disinfection. Disinfection methods included scrubbing with 4% chlorhexidine gluconate for 1 minute, immersion for 10 minutes in I of the tested disinfectant Solutions (n=8) (3.78% sodium perborate, 4% chlorhexidine gluconate, or 1% sodium hypochorite), and immersion in water for 3 minutes. The disinfection procedures were repeated 4 times, and 12 hardness measurements were made on each specimen. Control specimens (not disinfected) were stored in water for 56 minutes. Hardness tests (VHN) were also performed after 15, 30, 60, 90, and 120 days of storage in water. Statistical analyses of data were conducted with a repeated measures 3-way analysis of variance (ANOVA) and Tukey post-hoc test (alpha=.05).Results. Mean values +/- SD for Lucitone 550 (16.52 +/- 0.94 VHN) and QC-20 (9.61 +/- 0.62 VHN) demonstrated a significant (P<.05) decrease in hardness after disinfection...

Hardness evaluation of prosthetic silicones containing opacifiers following chemical disinfection and accelerated aging

Goiato, Marcelo Coelho; Haddad, Marcela Filié; dos Santos, Daniela Micheline; Pesqueira, Aldiéris Alves; Moreno, Amália
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 303-308
ENG
Relevância na Pesquisa
47.59442%
We evaluated the effects of disinfection and aging on the hardness of silicones containing opacifiers and intended for use in facial prosthetics. A total of 90 samples were produced using a cylindrical metal mold 3 mm in height and 30 mm in diameter. The samples were fabricated from Silastic MDX 4-4210 silicone in three groups: GI contained no opacifier, GII contained barium sulfate (Ba), and GIII contained titanium dioxide (Ti). The samples were disinfected using effervescent tablets (Ef), neutral soap (Ns), or 4% chlorhexidine (Cl) 3 times a week for 60 days. After this period the samples underwent 1,008 hours of accelerated aging. The hardness was measured using a durometer immediately following the disinfection period and after 252, 504, and 1,008 hours of aging. The data were statistically analyzed using 3-way ANOVA and the Tukey test (p < .05). The GIII group exhibited the greatest variation in hardness regardless of elapsed time. All groups displayed greater hardness after 1,008 hours of accelerated aging independent of disinfectant type. All of the hardness values were within the clinically acceptable range.

Portable Hardness tester for timber classification

Ballarin, Adriano Wagner; Almeida, Pedro; Palma, Hernando Lara; Colenci, Roberto
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 756-762
ENG
Relevância na Pesquisa
38.095503%
Hardness is a property largely used in material specifications, mechanical and metallurgical research and quality control of several materials. Specifically for timber, Janka hardness is a simple, quick and easy test, with good correlations with the compression parallel to grain strength, a strong reference in structural classification for this material. More recently, international studies have reported the use of Brinell hardness for timber assessment which resumes the advantages previously mentioned for Janka hardness and make it easier to be performed in the field, especially because of the lower magnitude of the involved loads. A first generation of an equipment for field evaluation of hardness in wood - Portable Hardness tester for wood - based on Brinell hardness has already been developed by the Research Group on Forest Products from FCA/UNESP, Brazil, with very good correlations between the evaluated hardness and several other mechanical properties of the material when performing tests with different species of native and reforested wood (traditionally used as ties - sleepers - in railways). This paper presents results obtained in the experimental program with the first generation of this equipment and preliminary tests with its second generation...

Influência de soluções fluoretadas na estabilidade de cor, rugosidade e dureza superficial de resinas compostas em função do tempo

Oliveira, Ana Luísa Botta Martins de
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Tese de Doutorado Formato: 123 f. : il. color.
POR
Relevância na Pesquisa
37.88237%
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Pós-graduação em Ciências Odontológicas - FOAR; O objetivo deste estudo foi avaliar a influência de soluções fluoretadas sobre a estabilidade de cor, a rugosidade e a dureza superficiais de diferentes resinas compostas, em curto e em longo prazo. Para isso, foram realizadas pesquisas científicas, apresentadas em três capítulos. Setenta e cinco espécimes de 10 mm de diâmetro e 2 mm de espessura foram confeccionados e polidos com discos de óxido de alumínio (Super-Snap®, Shofu Dental Corp. Kyoto, Japão) em ordem decrescente de granulação. Os grupos experimentais foram divididos de acordo com o tipo de resina composta (nanoparticulada - Filtek Z350 XT, microhíbrida - Filtek Z250 e microparticulada - Durafill VS) e diferentes meios de imersão (saliva artificial, solução de fluoreto de sódio a 0,05%- manipulado, Fluordent Reach, Oral B, Fluorgard). Os espécimes permaneceram imersos em saliva artificial por 24 horas e foram submetidos à análise da cor, rugosidade e dureza iniciais. A partir disso, foram imersos nas diferentes soluções por 1 minuto ao dia durante 60 dias. Nos intervalos entre as imersões foram mantidos em saliva artificial a 370C  1 0C. Após esse período...

Influence of heat treatment and mechanical cycling on hardness and fracture analysis of Ti35Nb5Zr casting alloy

Ribeiro, Ana Lúcia Roselino; Bizinoto, Glícea Maria Silva; Lima, Marcela Fernandes de; Vaz, Luis Geraldo
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 53-57
POR
Relevância na Pesquisa
57.918027%
Fundação de Ampara à Pesquisa do Estado de São Paulo (FAPESP); Titanium alloys are used in Dentistry due to their excellent mechanical, physical and chemical properties. However, it is necessary to find a biocompatible alloy to substitute the Ti-6Al-4V alloy. The presented suggestion was to study mechanical properties of a new titanium alloy without toxic elements. The Ti-35Nb-5Zr (%wt) alloy was produced by arc melting method. The tests were Vickers hardness, tensile strength and mechanical cycling, according to technical standards for titanium biomaterials. Hardness tests were performed in three different stages: before and after heat treatment at 1000°C for 1h, and after mechanical cycling test. The fracture analysis was evaluated by scanning electron microscopy. The mean values of Vickers hardness were 230.3±27.06HV before and 462.6±59.44HV after heat treatment (P<0.0001). The mean hardness values were different among the samples after mechanical cycling test. The comparison of hardness mean values after heat treatment and after dynamic test shows a decrease of the results. The maximum tensile strength mean value, obtained from tensile test, was 3,440N. It was observed, microscopically, the presence of dimples after mechanical cycling test. It was concluded that the hardness values were different at each step and the predominant fracture was the ductile type.

Long-term surface hardness and monomer conversion of a nonofilled and a microhybrid composite resin

Ferreira Jassé, Fernanda; Borges, Carlos Henrique Braga; Tonetto, Mateus Rodrigues; Rastelli, Alessandra Nara de Souza; Bagnato, Vanderlei Salvador; Campos, Edson Alves; Santos, Reidson Stanley Soares; Bandeca, Matheus Coêlho; Saad, José Roberto Cury
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 876-882
ENG
Relevância na Pesquisa
47.5301%
Objective: This study aims to evaluate the degree of conversion (DC) and hydrolytic degradation through the Vickers hardness test (HV) of a nanofilled (Filtek™ Z-250, 3M) and a microhybrid (Filtek™Supreme-XT, 3M) composite resin. Materials and methods: Eight disk-shaped specimens (4 mm diameter × 2 mm thick, ISO 4049) of each material were prepared for each test. Composites were inserted into single increment in a metallic matrix and light-cured for 40 seconds. VH readings were performed for each specimen at predetermined intervals: immediately after polymerization (control), 1, 2, 3, 7, 14, 21, 30 and 180 days. After curing, initial hardness measurements were performed and the specimens were immersed in artificial saliva at 37°C. For DC (%), specimens were ground, pressed with KBr and analyzed by FT-IR spectrophotometer. Results: Student t-test showed that there was no difference between the resins for DC (p = 0.252). ANOVA analysis revealed that Z-250 VH means were all greater than S-XT, for both top and bottom surfaces, whatever the storage-period in artificial saliva (p < 0.001). After 180 days of storage, the hardness obtained for S-XT was similar with that at the baseline, for both top and bottom surfaces. While for Z-250 hardness was not significantly different from baseline only for top surface...

A preliminary study of hardness and modulus of elasticity in sheep mandibles submitted to distraction osteogenesis and low-level laser therapy

Freddo, Angelo Luiz; Hübler, Roberto; Castro-Beck, Carlos Afonso de; Heitz, Cláiton; Oliveira, Marília Gerhardt de
Fonte: Medicina Oral S.L. Publicador: Medicina Oral S.L.
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
47.655454%
Objectives: To investigate the quality of newly formed bone in sheep mandibles submitted to distraction osteogenesis and low-level laser therapy (LLLT), based on hardness and modulus of elasticity values. The ideal moment for laser application (during the latency/activation period vs. during the bone consolidation period) was also evaluated. Computed tomography imaging was used to assess relapse as a result of early device removal. Study design: Extraoral distraction devices were placed in five sheep so as to achieve 1.5 cm of lengthened bone in 60 days. Distraction devices were removed 50, 40, and 33 days after surgery. Four animals were treated with LLLT, at different times, and one was used as control (no LLLT). Results: When applied during the bone consolidation period, LLLT caused an increase in hardness and modulus of elasticity values. On the other hand, animals irradiated with LLLT during the latency/activation period presented a delay in bone healing. A period of consolidation of 13 days (early device removal) was associated with relapse. Conclusions: Nanoindentation tests were able to detect slight abnormalities in bone metabolism and proved to be important tools for the assessment of bone quality following distraction osteogenesis. LLLT provided increased benefits when applied during the bone consolidation period...

Influence of the distance of the curing light source and composite shade on hardness of two composites

Thomé,Thaís; Steagall Jr.,Washington; Tachibana,Arlene; Braga,Sheila Regina Maia; Turbino,Miriam Lacalle
Fonte: Faculdade De Odontologia De Bauru - USP Publicador: Faculdade De Odontologia De Bauru - USP
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2007 EN
Relevância na Pesquisa
47.61797%
This study evaluated the influence of curing tip distance, shade and filler particle size on Vickers microhardness (VHN) of composite resins. Two composites were tested: Filtek Z250 microhybrid (3M ESPE; shades A1 and A3.5) and Filtek Supreme nanofilled (3M ESPE; shades A1B and A3.5B). For each resin, 42 specimens (5 mm in diameter and 2 mm height) were prepared being 21 for each shade. The specimens were exposed using a 20-second exposure to a quartz-tungsten-halogen light source with an irradiance of approximately 560 mW/cm², at the following distances: 0 mm (surface contact), 6 mm and 12 mm from composite surface. Effectiveness of cure of different resins, shades and curing distances was determined by measuring the top and bottom hardness (VHN) of specimens using a digital microhardness tester (load: 50 g; dwell time: 45 seconds) 24 hours following curing. The hardness ratio was calculated by dividing VHN of the bottom surface by VHN of top surface. Three-way ANOVA and Tukey's post-hoc test (p<0.05) revealed statistically significant differences for all analyzed factors. As for top hardness, as microhardness ratio (bottom/top), the factors shade, distance and composite filler particle size exerted influence on resin curing. Lighter shade composites (A1 and A1B) showed higher hardness values. At 6 and 12 mm curing tip distances...

Effect of a multi-layer infection control barrier on the micro-hardness of a composite resin

Hwang,In-Nam; Hong,Sung-Ok; Lee,Bin-Na; Hwang,Yun-Chan; Oh,Won-Mann; Chang,Hoon-Sang
Fonte: Faculdade De Odontologia De Bauru - USP Publicador: Faculdade De Odontologia De Bauru - USP
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2012 EN
Relevância na Pesquisa
47.65436%
OBJECTIVE: The aim of this study was to evaluate the effect of multiple layers of an infection control barrier on the micro-hardness of a composite resin. MATERIAL AND METHODS: One, two, four, and eight layers of an infection control barrier were used to cover the light guides of a high-power light emitting diode (LeD) light curing unit (LCU) and a low-power halogen LCU. The composite specimens were photopolymerized with the LCUs and the barriers, and the micro-hardness of the upper and lower surfaces was measured (n=10). The hardness ratio was calculated by dividing the bottom surface hardness of the experimental groups by the irradiated surface hardness of the control groups. The data was analyzed by two-way ANOVA and Tukey's HSD test. RESULTS: The micro-hardness of the composite specimens photopolymerized with the LED LCU decreased significantly in the four- and eight-layer groups of the upper surface and in the two-, four-, and eight-layer groups of the lower surface. The hardness ratio of the composite specimens was <80% in the eight-layer group. The micro-hardness of the composite specimens photopolymerized with the halogen LCU decreased significantly in the eight-layer group of the upper surface and in the two-, four-, and eight-layer groups of the lower surface. However...

Silicon Photo-Multiplier radiation hardness tests with a beam controlled neutron source

Angelone, M.; Pillon, M.; Faccini, R.; Pinci, D.; Baldini, W.; Calabrese, R.; Cibinetto, G.; Ramusino, A. Cotta; Malaguti, R.; Pozzati, M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
47.2487%
We report radiation hardness tests performed at the Frascati Neutron Generator on silicon Photo-Multipliers, semiconductor photon detectors built from a square matrix of avalanche photo-diodes on a silicon substrate. Several samples from different manufacturers have been irradiated integrating up to 7x10^10 1-MeV-equivalent neutrons per cm^2. Detector performances have been recorded during the neutron irradiation and a gradual deterioration of their properties was found to happen already after an integrated fluence of the order of 10^8 1-MeV-equivalent neutrons per cm^2.; Comment: 7 pages, 6 figures, Submitted to Nucl. Inst. Meth. A

Effect of a multi-layer infection control barrier on the micro-hardness of a composite resin

Hwang, In-Nam; Hong, Sung-Ok; Lee, Bin-Na; Hwang, Yun-Chan; Oh, Won-Mann; Chang, Hoon-Sang
Fonte: Universidade de São Paulo. Faculdade de Odontologia de Bauru Publicador: Universidade de São Paulo. Faculdade de Odontologia de Bauru
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; Formato: application/pdf
Publicado em 01/10/2012 ENG
Relevância na Pesquisa
47.59442%
OBJECTIVE: The aim of this study was to evaluate the effect of multiple layers of an infection control barrier on the micro-hardness of a composite resin. MATERIAL AND METHODS: One, two, four, and eight layers of an infection control barrier were used to cover the light guides of a high-power light emitting diode (LeD) light curing unit (LCU) and a low-power halogen LCU. The composite specimens were photopolymerized with the LCUs and the barriers, and the micro-hardness of the upper and lower surfaces was measured (n=10). The hardness ratio was calculated by dividing the bottom surface hardness of the experimental groups by the irradiated surface hardness of the control groups. The data was analyzed by two-way ANOVA and Tukey's HSD test. RESULTS: The micro-hardness of the composite specimens photopolymerized with the LED LCU decreased significantly in the four- and eight-layer groups of the upper surface and in the two-, four-, and eight-layer groups of the lower surface. The hardness ratio of the composite specimens was

Influence of the distance of the curing light source and composite shade on hardness of two composites

Thomé, Thaís; Steagall Jr., Washington; Tachibana, Arlene; Braga, Sheila Regina Maia; Turbino, Miriam Lacalle
Fonte: Universidade de São Paulo. Faculdade de Odontologia de Bauru Publicador: Universidade de São Paulo. Faculdade de Odontologia de Bauru
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; Formato: application/pdf
Publicado em 01/12/2007 ENG
Relevância na Pesquisa
47.34084%
This study evaluated the influence of curing tip distance, shade and filler particle size on Vickers microhardness (VHN) of composite resins. Two composites were tested: Filtek Z250 microhybrid (3M ESPE; shades A1 and A3.5) and Filtek Supreme nanofilled (3M ESPE; shades A1B and A3.5B). For each resin, 42 specimens (5 mm in diameter and 2 mm height) were prepared being 21 for each shade. The specimens were exposed using a 20-second exposure to a quartz-tungsten-halogen light source with an irradiance of approximately 560 mW/cm², at the following distances: 0 mm (surface contact), 6 mm and 12 mm from composite surface. Effectiveness of cure of different resins, shades and curing distances was determined by measuring the top and bottom hardness (VHN) of specimens using a digital microhardness tester (load: 50 g; dwell time: 45 seconds) 24 hours following curing. The hardness ratio was calculated by dividing VHN of the bottom surface by VHN of top surface. Three-way ANOVA and Tukey's post-hoc test (p