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Effects of Various Thicknesses on Load to Fracture of Posterior CAD/CAM Lithium Disilicate Glass Ceramic Crowns Subjected to Cyclic FatigueAl-Angari, Nadia January 2015 (has links)
Indiana University-Purdue University Indianapolis (IUPUI) / Background: New glass ceramics and Computer-Aided Design/Computer Assisted Manufacture (CAD/CAM) have become common aspects of modern dentistry. The use of posterior ceramic crowns with a high level of esthetics, fabricated using the CAD/CAM technology is a current treatment modality. Several materials have been used to fabricate these crowns, including lithium disilicate glass-ceramics, which have not been fully investigated in the literature.
Objective: to investigate the load to fracture of lithium disilicate glass ceramic posterior crowns fabricated by CAD/CAM technology with different material thicknesses adhesively cemented on epoxy resin.
Methods: Four groups of different ceramic thicknesses (0.5 mm, 1 mm, 1.5 mm, and 2 mm) were fabricated by milling CAD/CAM lithium disilicate IPS emax CAD blocks. A total of 68 posterior crowns were surface treated and luted with a resin adhesive cement on an epoxy resin model. Samples were fatigued then loaded to fracture using a universal testing machine to test the fracture strength. Statistical comparisons between various crown thicknesses were performed using one-way ANOVA followed by Fisher's Protected Least Significant Differences.
Results: There was a significant difference in the load-to-fracture (N) value for all comparisons of the four thickness groups (p < 0.0001), except 2 mm vs. 1.5 mm (p = 0.325). The mean load-to-fracture (N) was significantly higher for 2 mm than for 1 mm or 0.5 mm. Additionally, the mean load-to-fracture was significantly higher for 1.5 mm than for 1 mm or 0.5 mm. Furthermore, the mean load-to-fracture was significantly higher for 1 mm than for 0.5 mm.
Conclusion: Within the limitation of this study, it is advisable for clinical applications to consider a crown thickness of 1.5 mm or greater of milled lithium disilicate for posterior single teeth.
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Radiation Backscatter of ZirconiaLeghuel, Hatim A. January 2013 (has links)
No description available.
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Fracture strength of three-unit fixed partial denture in lithium disilicate, press versus milled, in-vitro studyIsmail Ahmad, Hogir, Khazal, Noor January 2019 (has links)
Syfte: Syftet med denna studie är att jämföra fraktur styrkan och frakturmönster hos tre-leds broar utförda i litiumdisilikat när broarna tillverkas genom pressteknik jämfört med frästa tre-leds broar genom CAD/CAM system.Hypotes: Pressteknik är bättre lämpad med avseende till fraktur resistens då fräsning av litiumdisilikat block kan resultera i defekter och spänning i materialet, detta gör materialet mer benäget till chipping/mikroabrasioner på ytan som skulle kunna propagera och på så sätt påverka fraktur resistensen. P-värde sattes till p ≤0.05.Material och metod: 40 3-leds broar tillverkades med pressteknik jämfört med fräst teknik med CAD/CAM system i grupper. Dessa delades in i undergrupper baserat på anatomin. Broarna genomgick en artificiell åldringsprocess som utgjordes av termocykling och förbelastning. Efter den artificiella åldringsprocessen utsattes broarna för belastning fram till fraktur. Den statistiska datan samlades in och analyserades. Även fraktur mönstret analyserades. Resultat: Där fanns ingen signifikant skillnad gällande fraktur styrkan mellan de full anatomiska grupperna. Där fanns inte heller någon signifikant skillnad gällande fraktur styrkan mellan underkonstruktion grupperna. Hypotesen falsifieras därför.Slutsats: Där fanns ingen signifikant skillnad gällande hur mycket belastning det krävs för att frakturera broarna som tillverkats genom pressteknik jämfört med broarna tillverkade med hjälp av CAD/CAM teknik. Där finns ett tydligt mönster gällande fraktur mönstret men en slutsats kan inte dras med tanke på antalet broar som använts. / Aim: The aim of this study was to compare fracture load and fracture mode of three-unit fixed partial dentures, made in lithium disilicate when the FDPs are made with pressing technique versus milled with a CAD/CAM system.Hypothesis: Pressing technique is better suited with regards to fracture load since milling of lithium disilicate blocks can result in defects and tension build up in the material, leaving the material more prone to chipping/micro-abrasions on the surface that could propagate and thus affecting the fracture load. P-value set to p ≤0.05.Material and methods: 40 FDPs where manufactured with pressing technique versus milled with a CAD/CAM system in each group. Furthermore, each group where subdivided depending on the anatomy. The FDPs thereafter underwent an artificial ageing process consisting of thermocycling and preloading. After the artificial aging process the FDPs were subjected to load to fracture, where the statistical data was collected and analyzed. Also, the fracture mode was observed and analyzed.Results: There was no significant difference regarding the fracture strength between the full anatomy groups. There was also no significant difference regarding the fracture strength between the core-design groups. The hypothesis was therefore rejected.Conclusion: There is no significant difference with regards to how much load is required to fracture FDPs made through pressing technique compared to FDPs made through the use of CAD/CAM technique. There is a clear pattern regarding the fracture patterns, however a conclusion can’t be drawn considering the sample size.
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Caracterização da vitrocerâmica de Li2Si2O5 em função do tratamento térmico e da análise da usinagem /Simba, Bruno Galvão January 2019 (has links)
Orientador: Marcos Valério Ribeiro / Resumo: O dissilicato de lítio, Li2Si2O5, é um material vitrocerâmico muito utilizado na fabricação de próteses dentárias, possui grande destaque por ser biocompatível e devido suas propriedades estéticas, químicas e mecânicas, permite a confecção de próteses a partir da usinagem CAD/CAM (COMPUTER-AIDED DESIGN / COMPUTER-AIDED MANUFACTURING), com elevada precisão dimensional e a possibilidade de restauração imediata em pacientes. Os materiais comerciais são disponibilizados com estrutura Li2SiO3 (metassilicato de lítio) cujas características são: alta usinabilidade e baixa tenacidade à fratura. Após a usinagem das próteses, o material sofre tratamento térmico visando à conversão do Li2SiO3 em Li2Si2O5 (dissilicato de litio), fase de melhor tenacidade e excelente apelo estético. A compreensão desta transformação de fase, seus efeitos na usinabilidade e nas propriedades mecânicas é de interesse tecnológico e científico, pois o material será utilizado como prótese dentária após este processamento. Este trabalho visou à avaliação do Li2Si2O5 em relação as propriedades químicas, físicas e mecânicas quando submetido a diferentes tratamentos térmicos. Foram empregados métodos de caracterização por difração de raios X (DRX), microscopia eletrônica de varredura (MEV), massa específica aparente, além da determinação da dureza, tenacidade à fratura, constantes elásticas e resistência à flexão biaxial sob diferentes condições de tratamento térmico. Também foram analisados a distribuição de partí... (Resumo completo, clicar acesso eletrônico abaixo) / Doutor
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CARACTERIZAÇÃO MECÂNICA E TRANSIÇÃO FRÁGIL-DÚCTIL EM MATERIAIS VITROCERÂMICOSMathias, Ivan 01 April 2015 (has links)
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Previous issue date: 2015-04-01 / Fundação Araucária de Apoio ao Desenvolvimento Científico e Tecnológico do Paraná / In this work two vitreous systems are studied, the lithium disilicate (LS2) and sodiumcalcium-silica with stoichiometry 2Na2O.CaO.3SiO2 (2N1C3S) and the glassceramics
formed from these by heat treatment. Several properties were determined for the two systems as a function of crystallized volume fraction, from glass to fully
crystallization (100%), highlighting the fracture toughness and the brittle-ductile transition, with the last two determined only for the LS2 glass-ceramic. Hardness and
elastic modulus were obtained for the two glass-ceramics and their values increase with the crystallized volume fraction in the glass ceramic, with the exception of
hardness of 2N1C3S, which has its maximum for the crystallized volume fraction of 9%. Thermal expansion coefficients were determined and are larger in the LS2 glassy phase and in the 2N1C3S crystalline phase, thereby generating mean residual stresses obtained by Selsing model of -76 MPa for the LS2 (compression in the crystal) and 232 MPa for the 2N1C3S (traction in the crystal). The indentation fracture toughness was also determined for the two systems using the Anstis' and Niihara's models. The results show an increase of indentation fracture toughness
with the crystalline volume fraction for LS2 glass-ceramic and also a dependence with indentation load. As for the 2N1C3S glass-ceramic, indentation fracture toughness
are reduced at intermediate crystalline fractions, which is attributed to residual stresses arising from the difference between the thermal expansion mismatch between the glass and the crystalline phases. LS2 glass-ceramic flexural strength increases with the crystalline fraction, from 103 ± 3 MPa for the glass to 260 ± 20 MPa for the fully crystallized sample. Without the removal of the crystallization surface layer, this value rises to 290 ± 20 MPa. The increase in flexural strength in the first 20% of the crystallized fraction is more pronounced. As the size of the precipitates was kept constant, this increase can be related only to the increase in the crystallized fraction. The residual stress in the matrix, the critical radius of
spontaneous cracking of the crystals and the crack mean free path between the precipitates were considered in the analysis of the increase in flexural strength. The existence of pores in the samples was a factor that limited its resistance. The fracture toughness (KDTIC) a function of the crystallized fraction was determined for LS2 glassceramics using the double torsion technique. It was found that KDTIC increases with the crystallized fraction, from 0.75 MPa.m1/2 for the glass to about 3.50 ± 0.05
MPa.m1/2 for the fully crystallized sample, a significant increase of approximately five times. Several factors were analyzed as possible causes of the increase in KDTIC. The
experimental data are better adjusted with a recently proposed model with one adjustable parameter that relates the ratio of the crystal and glass areas to the
crystallized volume fraction. The brittle-ductile transition (BDT) of LS2 glass and glass-ceramic samples (39% crystallized volume fraction) were determined for three
different strain rates. BDT temperatures were determined for each strain rate.Activation energies of BDT for the glass and glass-ceramic were obtained, which were 5.2 ± 0.2 eV and 7 ± 2 eV. It was found that BDT activation energy in glass resembles the activation energy of the LS2 viscous flow, thus concluding the BDT in LS2 is governed by viscous flow of the glass matrix. Finally, the fact of the activation energy of the glass ceramic be larger than the glass was attributed to the fact that the viscosity of the vitreous matrix is "hindered" by the presence of crystalline
precipitates. A viscosity model of a rigid spheres composite was used as an analogy to explain this observation. / No presente trabalho são estudados dois sistemas vítreos, o dissilicato de lítio (LS2) e o soda-cal-sílica de estequiometria 2Na2O.CaO.3SiO2 (2N1C3S), bem como os
vitrocerâmicos formados a partir destes através de tratamentos térmicos. Diversas propriedades foram determinadas para os dois sistemas em função da fração
cristalizada, desde vidro até os 100%, com destaque para a tenacidade à fratura e a transição frágil-dúctil, sendo estas últimas determinadas somente para o LS2. Dureza
e módulo de elasticidade foram obtidos para os dois sistemas e seus valores aumentam com a fração volumétrica cristalizada no vitrocerâmico, com exceção da
dureza no 2N1C3S, que tem seu máximo para a fração cristalizada de 9%. Os coeficientes de expansão térmica foram determinados e são maiores na fase vítrea
do LS2 e na fase cristalina do 2N1C3S, gerando assim tensões residuais médias obtidas pelo modelo de Selsing de -76 MPa para o LS2 (compressiva no cristal) e
232 MPa para o 2N1C3S (trativa no cristal). A tenacidade à fratura por indentação (KC) foi determinada também para os dois sistemas, sendo utilizados os modelos de
Anstis e Niihara. Os resultados mostram um aumento com a fração cristalina para o LS2 e também uma dependência com a carga utilizada no teste. Já para o 2N1C3S,
os valores de KC sofrem uma redução em frações cristalinas intermediárias, comportamento atribuído às tensões residuais oriundas da diferença entre os
coeficientes de expansão térmica e anisotropias elásticas do material. Os ensaios de resistência à flexão mostraram que para o LS2 a resistência aumenta com a fração
cristalina, passando de 103 ± 3 MPa para o vidro para 260 ± 20 MPa para a amostra totalmente cristalizada. Se não removermos a camada de cristalização superficial,
este valor sobe para 290 ± 20 MPa. O aumento da resistência à flexão nos primeiros 20% da fração cristalizada é mais pronunciado. Como o tamanho dos precipitados foi mantido constante, esse aumento pode ser relacionado apenas ao aumento na fração cristalizada. A tensão residual na matriz, o raio crítico dos cristais para
trincamento espontâneo e o livre caminho médio da trinca entre os precipitados foram considerados na análise do aumento da resistência à flexão. A existência de
poros nas amostras foi um fator que limitou a sua resistência. Caso amostras sem poros fossem feitas, um aumento em torno de 20 a 30% da resistência seria obtido. A tenacidade à fratura (KDTIC) foi determinada para o LS2 pela técnica de torção dupla em função da fração cristalizada. Foi verificado que KDTIC aumenta com a fração cristalizada, passando de 0,75 MPa.m1/2 para o vidro para cerca de 3,50 ±0,05 MPa.m1/2 para a amostra totalmente cristalizada, um aumento significativo de
aproximadamente cinco vezes. Diversos fatores foram apontados como possíveis causas do aumento da tenacidade e foi verificado que os fatores considerados de
forma isolada não são suficientes para descrever completamente o aumento na tenacidade. Os dados experimentais são melhor ajustados com um modelo de um parâmetro de ajuste recentemente proposto que relaciona a razão entre as áreas dos cristais e do vidro na superfície de fratura com a fração cristalizada. A transição
frágil-dúctil (TFD) de amostras vítreas e vitrocerâmica (39% fração cristalizada) de LS2 foram determinadas para três taxas de deformação. Foram determinadas as
temperaturas de TFD para cada uma das taxas e foi verificada uma dependência com a taxa de deformação. Foram calculadas as energias de ativação para a TFD
no vidro e vitrocerâmico, sendo elas de 5,2 ± 0,2 eV e 7 ± 2 eV. Verificou-se que a energia de ativação da TFD no vidro se assemelha a energia de ativação do
escoamento viscoso do LS2, concluindo assim que a TFD no LS2 é governada pelo escoamento viscoso da matriz vítrea. Por fim, o fato da energia de ativação do
vitrocerâmico ser maior que do vidro foi atribuída ao fato de que a viscosidade da matriz vítrea seria "dificultada" pela presença dos precipitados cristalinos. Um modelo de viscosidade de um compósito com esferas rígidas foi utilizado como analogia para explicar essa observação.
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Análise das propriedades estruturais, morfológicas e mecânicas de duas marcas comerciais diferentes de dissilicato de lítio para o sistema CAD/CAMTavares, Lucas do Nascimento 14 February 2017 (has links)
O objetivo deste presente estudo foi comparar duas marcas comerciais diferentes de Dissilicato de Lítio para o sistema CAD / CAM (IPS e.max CAD e Rosetta SM CAD / CAM), avaliando suas propriedades estruturais, morfológicas e mecânicas. Para avaliar as propriedades estruturais foram necessárias duas amostras de cada grupo, para serem analisadas por meio do DRX (difração de raios X). As propriedades morfológicas foram analisadas utilizando o MEV (Microscopia eletrônica de Varredura) antes e depois do tratamento térmico, e o teste de porosidade, realizado através de uma tomografia computadorizada em 3D (micro-CT). Para avaliar as propriedades mecânicas foi realizado o teste flexural de três pontos e o teste de microcisalhamento, e para isto foram selecionados dez espécimes de cada grupo para cada teste. Os valores médios de porosidade e da resistência flexural de três pontos foram analisados pelo teste t e a resistência de união obtida através do microcisalhamento foi analisada pelo teste Anova Two-way. Todos os testes usaram um nível de significância de α = 0,05.
Os resultados obtidos pela análise estrutural realizada pelo DRX apresentaram picos no difractograma correspondentes ao Metassilicato de Lítio e o Dissilicato de Lítio, com intensidades semelhantes para ambos os grupos testados. Após realizar a microscopia eletrônica de varredura, não foi encontrado diferenças na morfologia dos cristais, em ambas as cerâmicas testadas, antes e depois do tratamento térmico. O teste de porosidade não mostrou diferença estatisticamente significativa entre o valor total de poros encontrados. Ambos os resultados dos testes mecânicos não apresentaram diferenças estatísticas significativas entre os grupos avaliados.
Baseado nos resultados encontrados, não houve diferença entre as duas marcas comerciais testadas, em relação as suas propriedades estruturais, morfológicas e mecânicas. / The aim of the present study was to compare two different brands of lithium disilicate CAD/CAM blocks (IPS e.max CAD and Rosetta SM CAD/CAM), evaluated by structural, morphological and mechanical properties.
Two specimens of each group were analyzed using x-ray diffraction (XRD) to evaluate the structures of the ceramic material. Morphologic properties were analyzed using the Scanning Electron Microscopy (SEM) before and after the heat treatment; and porosity test was performed using a 3D micro-computed tomography analyses (micro-CT). Ten specimens of each group were submitted to three-point flexure strength and microshear bond strength tests, to analyze the mechanical properties of both brands. Mean values of porosity test and three-axial flexural strength were analyzed by t Test, and the microshear bond strength was analyzed by Anova two-way. All tests used a significance level of α=0.05.
The structure results performed by XDR, presented high peak positions corresponding to the standard lithium metasilicate and lithium disilicate, with similar intensities for both tested groups. The morphologic results demonstrated similar patterns of crystalline structure, before and after the heat treatment and the porosity test showed no difference between the number and size of the pores found. Both mechanical tests results did not present statistically significant differences between the samples.
Based on the results, there was no difference in relation to their structural, morphological and mechanical properties, between the two commercial brands tested. / Dissertação (Mestrado)
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Microstructural evolution and physical behavior of a lithium disilicate glass-ceramicLien, Wen January 2014 (has links)
Indiana University-Purdue University Indianapolis (IUPUI) / Background: Elucidating the lithium disilicate system like the popular IPS e.max® CAD (LS2), made specifically for Computer-Aided Design and Computer-Aided Manufacturing (CAD-CAM), as a function of temperature unravels new ways to enhance material properties and performance. Objective: To study the effect of various thermal processing on the crystallization kinetics, crystallite microstructure, and strength of LS2. Methods: The control group of the LS2 samples was heated using the standard manufacturer heating-schedule. Two experimental groups were tested: (1) an extended temperature range (750-840 °C vs. 820-840 °C) at the segment of 30 °C/min heating rate, and (2) a protracted holding time (14 min vs. 7 min) at the isothermal temperature of 840 °C. Five other groups of different heating schedules with lower-targeted temperatures were evaluated to investigate the microstructural changes. For each group, the crystalline phases and morphologies were measured by X-ray diffraction (XRD) and scanning electron microscope (SEM) respectively. Differential scanning calorimeter (DSC) was used to determine the activation energy of LS2 under non-isothermal conditions. A MTS universal testing machine was used to measure 3-point flexural strength and fracture toughness, and elastic modulus and hardness were measured by the MTS Nanoindenter® XP. A one-way ANOVA/Tukey was performed per property (alpha = 0.05). Results: DSC, XRD, and SEM revealed three distinct microstructures during LS2 crystallization. Significant differences were found between the control group, the two aforementioned experimental groups, and the five lower-targeted-temperature groups per property (p<0.05). The activation energy for lithium disilicate growth was 667.45 (± 28.97) KJ/mole. Conclusions: Groups with the extended temperature range (750-840 °C) and protracted holding time (820-840 °C H14) produced significantly higher elastic-modulus and hardness properties than the control group but showed similar significant flexural-strength and fracture-toughness properties with the control group. In general, explosive growth of lithium disilicates occurred only when maximum formation of lithium metasilicates had ended.
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Study of Luminescent Silicon-Rich Silicon Nitride and Cerium and Terbium Doped Silicon Oxide Thin FilmsWilson, Patrick R. 10 1900 (has links)
<p>Silicon nanostructures formed in silicon-rich silicon nitride (SRSN) and cerium and terbium doped silicon oxide thin films grown using different types of plasma-enhanced chemical vapour deposition have been studied through photoluminescence (PL) and synchrotron-based X-ray absorption spectroscopies to determine the effects of deposition and processing parameters on the luminescent and structural properties of these materials. The SRSN films exhibited bright PL attributed to quantum confinement effects in the silicon nanoclusters (Si-ncs) as well as radiative defects in the silicon nitride host matrix. The peak emission energy could be tuned from the near-infrared across the entire visible spectrum by controlling the film composition and the post-deposition annealing temperature and time to change the size of the Si-ncs. Preliminary experiments on cerium doped SRSN samples indicated that although the cerium ions coordinate in the optically active trivalent oxidation state, they were not effectively sensitized by Si-ncs in the films tested, most likely due to the nanoclusters having bandgap energies that were unsuitable for this purpose. In cerium and terbium co-doped silicon oxide films, cerium disilicate (Ce<sub>2</sub>Si<sub>2</sub>O<sub>7</sub>) nanocrystallites were formed by annealing at temperatures of 900°C and higher. The A-Ce<sub>2</sub>Si<sub>2</sub>O<sub>7</sub>, G-Ce<sub>2</sub>Si<sub>2</sub>O<sub>7</sub>, and Ce<sub>6</sub>[Si<sub>4</sub>O<sub>13</sub>][SiO<sub>4</sub>]<sub>2</sub> phases of cerium disilicate were observed to form under different deposition and annealing conditions. All three phases exhibited extremely bright violet-blue PL and were found to efficiently sensitize green emission from co-dopant Tb<sup>3+</sup> ions in the films. The Tb<sup>3+</sup> luminescence predominantly corresponded to the <sup>5</sup>D<sub>4</sub>→<sup>7</sup>F<sub>3–6</sub> emission lines, although weak <sup>5</sup>D<sub>3</sub>→<sup>7</sup>F<sub>2–6</sub> emission lines were also observed in films containing relatively high concentrations of terbium indicating that the sensitization of Tb<sup>3+</sup> ions occurred through the <sup>5</sup>D<sub>3</sub>, <sup>5</sup>L<sub>10</sub>, or <sup>5</sup>D<sub>2</sub> energy levels.</p> / Doctor of Philosophy (PhD)
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