SammanfattningSyfteSyftet med föreliggande pilotstudie är att undersöka abrasion på materialen polerad zirkonia (5YSZ) och glansbränd litiumdisilikat och abrasion på antagonist med eller utan termocykling. Emalj utgör referens. De inkluderade materialen är avsedda för CAD/CAM- framställning av monolitiska konstruktioner.Material och metodFrån en zirkoniadisk (5YSZ, Katana zirconia UTML) och tre litiumdisilikatblock (IPS e.max CAD LT) togs totalt sexton provkroppar fram. Åtta extraherade molarer användes som referensgrupp (n=8) och steatitkulor användes som antagonist. Provkropparna för zirkonia och litiumdisilikat utformades rektangulära med måtten 16x14x3,5 mm efter sintring respektive kristallisering. Provkropparnas testytor genomgick olika ytbehandlingar. Zirkoniaprovkropparna polerades till högglans (ZP), litiumdisilikat glansbrändes med glaze (LG) och de extraherade molarerna planslipades och emaljen polerades (EM). Hälften av materialgrupperna tuggsimulerades i 120 000 cyklar med termocykling i temperaturerna 15°C±2°C respektive 55°C±2°C (ZPT, LGT, EMT). Den andra hälften tuggsimulerades i 120 000 cyklar utan termocykling (ZPU, LGU, EMU). Resultaten analyserades med One-way ANOVA, Tukey’s test med en signifikansnivå på α=0,05 i statistikprogrammet SPSS.ResultatHögst materialförlust påvisades i EMT-gruppen och lägst i ZPU-gruppen. Ingen signifikant skillnad kunde påvisas mellan materialgrupperna. Hos antagonistgrupperna påvisade EMT- gruppen högst materialförlust och LGT-gruppen lägst materialförlust. Hos antagonistgrupperna hade EMT-gruppen en signifikant högre materialförlust i jämförelse med övriga antagonistgrupper förutom LGU- och ZPU-gruppen.SlutsatsPolerad ultratranslucent zirkonia, glansbränd litiumdisilikat, och emalj abraderas likvärdigt av antagonister med eller utan termocykling. Polerad ultratranslucent zirkonia och glansbränd litiumdisilikat abraderar mindre mot antagonister än emalj med termocykling. / AbstractPurposeThe purpose of this pilot study is to investigate the abrasion of polished zirconia (5YSZ) and glazed lithium disilicate on antagonist and antagonists’ abrasion on the materials with or without thermocycling, with enamel as reference. The materials are intended for CAD/CAM production of monolithic restorations.Material and methodFrom zirconia (5YSZ, Katana zirconia UTML) and lithium disilicate (IPS e.max CAD LT) sixteen specimens were made. Eight extracted molars were used as reference group (n=8) and steatite balls used as antagonists. The specimens were designed with the dimensions 16x14x3.5 mm. The zirconia specimens were polished to high gloss (ZP), the lithium disilicate glazed (LG) and the enamel ground flat and polished (EM). Half of the groups underwent chewing simulation in 120,000 cycles with thermocycling (15°C ±2°C/55°C ±2°C) (ZPT, LGT, EMT) and the other half without thermocycling (ZPU, LGU, EMU). The results were analyzed with One-way ANOVA, Tukey's test with a significance level of α= 0.05 in the statistical program SPSS.ResultsThe highest material loss was in EMT and the lowest in ZPU. No significant differences could be shown between the material groups. In the antagonist groups, EMT showed the highest material loss and LGT the lowest. In the antagonist groups, EMT had a significant higher loss in comparison with all the other antagonist groups except LGU and ZPU.ConclusionPolished ultratranslucent zirconia, glazed lithium disilicate and enamel are equally abraded by antagonists with or without thermocycling. Polished ultratranslucent zirconia and glazed lithium disilicate abrade less against antagonists than enamel with thermocycling.

No description available.

The lithium disilicate (LS2) glass system provides the basis for a large number of useful glass-ceramic products. Microwave processing of materials such as glass-ceramics offers unique benefits over conventional processing techniques. Variable frequency microwave (VFM) processing is an advanced processing technique developed to overcome the hot spot and the arcing problems in microwave processing. In general, two main questions are addressed in this dissertation: 1. How does microwave energy couple with a ceramic material to create heat? and, 2. Is there a "microwave effect" and if so what are the possible explanations for the existence of that effect? The results of the present study show that VFM processing was successfully used to crystallize LS2 glass at a frequency other than 2.45 GHz and without the aid of other forms of energy (hybrid heating). Crystallization of LS2 glass using VFM heating occurred in a significantly shorter time and at a lower temperature as compared to conventional heating. Furthermore, the crystallization mechanism of LS2 glass in VFM heating was not exactly the same as in conventional heating. Although LS2 crystal phase (Orthorhombic Ccc2) was developed in the VFM crystallized samples as well as in the conventionally crystallized samples as x-ray diffraction (XRD) confirmed, the structural units of SiO4 tetrahedra (Q species) in the VFM crystallized samples were slightly different than the ones in conventionally crystallized samples as the Raman spectroscopy revealed. Moreover, the observed reduction in the crystallization time and apparent temperature in addition to the different crystallization mechanism observed in the VFM process both provided experimental evidence to support the presence of the microwave effect in the LS2 crystallization process. Also, the molecular orbital model was successfully used to predict the microwave absorption in LS2 glass and glass-ceramic. This model was consistent with experiments and indicated that microwave-material interactions were highly dependent on the structure of the material. Finally, a correlation between the Fourier transform infrared reflectance spectroscopy (FTIRRS) peak intensities and the volume fraction of crystals in partially crystallized LS2 glass samples was established. / Ph. D.

The goal of this research was to create a microstructure graded glass-ceramic and investigate the resulting properties as a function of crystallization processing. The desired glass-ceramic was a lithium disilicate material that has a crystallization gradient across the sample, leading to functionally graded properties as a result of the microstructure gradient. Samples were prepared by melting and pouring glass at 1400°C, annealing at 400°C for 48 hours, and nucleating at 480°C for 2 hours. To ensure that crystallization would not occur homogeneously throughout the sample, a temperature gradient was imposed during crystallization. Samples were crystallized on a self-constructed resistance wire furnace that was open to air. Several crystallization processing parameters were tested, including high temperature for a short time and low temperature for a long time. Samples were ground and polished to 0.25 microns before characterization methods were performed. Scanning electron microscopy (SEM) showed the microstructure transition across the sample cross section, with crystals present on the crystalline side and only nuclei present on the glassy side. Raman spectroscopy showed a transformation of the characteristic spectra across the sample cross section, with defined, high-intensity peaks on the crystalline side and broad, low-intensity peaks on the glassy side. Microhardness showed a slight transition in hardness values across the sample cross section, however the variability was too great to draw any conclusions. The characterization methods showed that the desired material was created and the resulting properties were a function of the crystallization processing parameters. / Master of Science

Submitted by DAYANA CAMPANELLI DE MORAIS null (dayanacampanelli@gmail.com) on 2017-12-22T03:50:36Z No. of bitstreams: 1 para impressão final.pdf: 3931660 bytes, checksum: d52b37974d258d1d9c1647f7cca67f54 (MD5) / Approved for entry into archive by Silvana Alvarez null (silvana@ict.unesp.br) on 2018-01-04T18:53:29Z (GMT) No. of bitstreams: 1 morais_dc_me_sjc.pdf: 3931660 bytes, checksum: d52b37974d258d1d9c1647f7cca67f54 (MD5) / Made available in DSpace on 2018-01-04T18:53:29Z (GMT). No. of bitstreams: 1 morais_dc_me_sjc.pdf: 3931660 bytes, checksum: d52b37974d258d1d9c1647f7cca67f54 (MD5) Previous issue date: 2017-11-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O presente estudo teve como objetivo desenvolver vitrocerâmicas de dissilicato de lítio com gradiente funcional de densidade, inspirado no gradiente natural que existe entre o esmalte e a dentina. Primeiramente o vidro de composição: 33,33% mol de Li2O e 66,67% mol de SiO2 foi obtido pelo método fusão/resfriamento. Em seguida foram preparadas amostras com estruturas homogêneas do vidro a base de dissilicato de lítio para determinação dos melhores parâmetros de sinterização. Três diferentes tratamentos térmicos, determinados com base no resultado da análise diferencial de calorimetria foram utilizados: 850 °C/3h; 900 °C/3h e 950 °C/3h. A caracterização desses materiais foi realizada através da difração de raios X, microscopia eletrônica de varredura, método de Arquimedes e ensaio de flexão biaxial (n=10). O tratamento térmico de 950 oC obteve os melhores resultados, sendo o escolhido para a realização das próximas etapas do estudo. Com a finalidade de otimizar a estética, foi adicionada cerâmica feldspática (VITAVM®9) ao vidro SiO2-Li2O na proporção de 10%, 15% e 20% (n=30). Foi observado que a adição de 10% de VM9 não alterou a resistência do material, e quanto maior a quantidade de VM9, maior foi a translucidez e menor foram o módulo elástico e a densidade. Com isso, foram preparadas vitrocerâmicas bioinspiradas com gradiente funcional de densidade nas seguintes sequências de camadas: uma com 10% de VM9, outra com 15% e a última com 20%. Não houve diferença na resistência à flexão biaxial do grupo com gradiente, quando a camada mais densa estava voltada para o lado de tração, com o grupo com 15% de VM9 com estrutura homogênea. A translucidez do grupo com gradiente foi equivalente ao grupo homogêneo mais translúcido, com 20% de VM9. Concluiu-se que foi possível sintetizar uma vitrocerâmica de dissilicato de lítio funcionalmente graduada, onde uma boa resistência mecânica e uma boa translucidez foram unidas.

Syfte Syftet med föreliggande studie var att undersöka böjhållfastheten hos IPS e.max CAD före och efter termocykling med 10 000 respektive 15 000 cykler. Material och metod Trettio provkroppar framställdes från fem stycken IPS e.max CAD LT-block. Provkropparna var indelade i två testgrupper (GT10 och GT15), och en kontrollgrupp (GK), á 10 provkroppar i varje. Provkropparna utformades enligt måtten L 17,9 ± 0,03 mm x B 2,5 ± 0,03 mm x H 2,5 ± 0,03 mm. Samtliga provkroppar kristalliserades och grupp GK förvarades i rumstemperatur, resterande två grupper, GT10 och GT15 termocyklades i 10 000 respektive 15 000 cykler.Därefter utfördes ett trepunkts böjhållfasthetstest. Resultaten analyserades med One-way ANOVA, Tukey’s test med signifikansnivån α= 0,05 i statistikprogrammet SPSS. Resultat Resultaten visade att det inte fanns någon signifikant skillnad mellan grupp GK och GT10 (p>0,05) respektive mellan grupp GT10 och GT15 (p>0,05). Grupp GT15 hade högst medelvärde (516 MPa) och grupp GK hade lägst medelvärde (450 MPa). Signifikant skillnad fanns mellan grupp GK och GT15 (p<0,05). Grupp GT15 hade en signifikant högre böjhållfasthet (~470-637 MPa) jämfört med grupp GK (~406-494 MPa). Slutsats Inom föreliggande studies begränsningar kan följande slutsatser dras: Termocykling med 10 000 cykler påverkar inte böjhållfastheten, däremot ger ökat antal cykler (15 000) högre böjhållfasthet. / Purpose  The purpose of the present study was to investigate the flexural strength of IPS e.max CAD beforeand after thermal cycling with 10,000 and 15,000 cycles, respectively.  Material and method  Thirty specimens were prepared from five IPS e.max CAD LT blocks, divided into two test groups (GT10 and GT15), and one control group (group GK) (n=10). The specimens were designed with the dimensions L 17.9 ± 0,03 mm x W 2.5 ± 0,03 mm x H 2.5 ± 0,03 mm. All specimens were crystallized and group GK was kept in room temperature, the remaining two groups, GT10 and GT15 were thermocycled with 10,000 and 15,000 cycles respectively. A three-point flexural strength test was performed. The results were analyzed with One-way ANOVA, Tukey's test with a significance level α = 0.05 in the statistical program SPSS.  Results  The results showed that there was no significant difference between groups GK and GT10 (p> 0.05), and between groups GT10 and GT15 (p> 0.05). It was also observed that group GT15 had the highest average (516 MPa) and group GK had the lowest average (450 MPa). There was a significant difference between groups GK and GT15 (p <0.05). Group GT15 had a significantly higher flexural strength (~ 470-637 MPa) compared to group GK (~406-494 MPa).  Conclusion  Within the limitations of the present study, the following conclusions can be drawn:Thermal cycling comprising 10,000 cycles do not affect the flexural strength, however, increasing the number of cycles (15,000) will give higher flexural strength.

Objetivos: (1) determinar a carga de fratura e o modo de falha de laminados cerâmicos ultrafinos processados via CAD-CAM em função da microestrutura do material (vitrocerâmica à base de dissilicato de lítio ou porcelana à base de leucita); (2) desenvolver metodologia de ciclagem mecânica para determinar o tempo de vida e o modo de falha de laminados cerâmicos ultrafinos processados via CADCAM. Materiais e métodos: dezesseis dentes humanos, incisivos centrais superiores, foram utilizados para confecção dos espécimes. Os dentes sofreram mínimo preparo, em esmalte, para adequada adaptação dos laminados cerâmicos ultrafinos. Os laminados de dissilicato de lítio e de porcelana foram confeccionados via CAD-CAM e cimentados com cimento resinoso sobre os dentes. Quatro espécimes de cada grupo foram levados à máquina de ensaios universal para determinação da carga de fratura dos laminados. Para o desenvolvimento de metodologia para determinação do tempo de vida dos laminados, uma série de testes piloto foi realizada, utilizando-se diferentes parâmetros como: tipo de antagonista (dentes naturais ou roletes metálicos), carga aplicada (20, 30 ou 40 N) e esquema de ciclo mastigatório (incisão ou deslizamento). Os padrões de falha dos laminados foram analisados em um estereomicroscópio, e os resultados obtidos no ensaio de carga de fratura foram analisados por ANOVA e teste de Tukey. Resultados: o valor médio obtido de carga de fratura para o dissilicato de lítio foi de 431,8 ± 217,9 N, enquanto que para a porcelana foi de 454,4 ± 72,1 N. Não houve diferença estatística entre os valores de carga de fratura encontrados, porém, o desvio padrão e o coeficiente de variação da vitrocerâmica foram muito superiores em relação aos da porcelana. Houve diferença no modo de falha dos materiais testados, sendo que a porcelana apresentou um maior número de falha por lascamento e o dissilicato de lítio apresentou maior quantidade de falha da estrutura dental. Na ciclagem mecânica, para cada condição testada, uma resposta diferente foi obtida. No tipo de ciclo incisão, os antagonistas (dente natural) fraturaram quando as cargas de 30 N e 40 N foram aplicadas. No tipo de ciclo deslizamento, o antagonista (dente natural) sofreu desgaste da borda incisal com carga de 30 N. Para o antagonista rolete metálico, quando a carga de 30 N foi aplicada ocorreu fratura do laminado, e quando aplicada a carga de 20 N, houve desgaste excessivo do rolete metálico. Conclusão: (1) o material utilizado não afetou a carga de fratura dos laminados cerâmicos ultrafinos quando o teste estático foi utilizado. Entretanto, o modo de falha foi significativamente diferente, sendo que a porcelana sofreu mais lascamentos do que o dissilicato de lítio; o qual, por sua vez, apresentou a maioria das falhas relacionadas à estrutura dental. (2) Não foi possível determinar uma combinação de parâmetros de ciclagem mecânica que permitisse a determinação dos parâmetros de fadiga para laminados cerâmicos ultrafinos, já que o número máximo de ciclos alcançados foi de 536.818 ciclos. Dessa forma, estudos futuros precisam ser realizados para que uma metodologia apropriada permita determinar parâmetros de fadiga clinicamente relevantes para laminados cerâmicos ultrafinos em dentes anteriores. / Objectives: (1) to determine the fracture load and the failure mode of the ultra-thin ceramic laminates processed via CAD-CAM according to the microstructure of the material (lithium disilicate-based glass-ceramic or leucite-based porcelain); (2) to develop a fatigue methodology capable of determining the lifetime of ultra-thin ceramic laminates processed via CAD-CAM. Materials and methods: sixteen human maxillary central incisors were used to produce the specimens. The teeth required minimal preparation on the enamel for proper adaptation of the ultra-thin ceramic laminates. Ceramic laminates made of lithium disilicate and feldspathic porcelain with thicknesses between 0.3 mm to 0.5 mm were produced via CAD-CAM and cemented with resin cement. Four specimens of each group were taken to a universal testing machine to determine the fracture load of the laminates. For the development of a fatigue methodology, a series of pilot tests was performed using different parameters such as: type of antagonist (natural teeth or metal roller), applied load (20, 30 or 40 N), and type of masticatory cycle (incision or sliding). Failure modes were analysed using a stereomicroscope. Fracture load data were analysed by ANOVA and Tukey\'s test. Results: the mean fracture load obtained for the glass-ceramic was 431.8 ± 217.9 N, while that obtained for the porcelain was 454.4 ± 72.1 N. There was no statistical difference between the mean fracture load values; however, the standard deviation and the coefficient of the variation of the glass-ceramic were both higher than those obtained for the porcelain. There was also a difference in the failure modes for the two materials tested. The porcelain showed a higher number of factures due to chipping and the lithium disilicate showed a higher number of tooth structure failure. The fatigue experiment showed different results depending on the condition analysed. In the incision cycle, the antagonists (natural tooth) fractured when loads of 30 N and 40 N were applied. In the slide type of cycle, the antagonist (natural tooth) suffered wear on the incisal edge after applying 30 N of load. For the metal roller antagonist, when a 30 N load was applied, the ceramic laminate fractured, and when a 20 N load was applied, an excessive wear of the metal roller occurred. Conclusion: (1) The material used did not affect the fracture load of ultra-thin ceramic laminates when the static test was used. However, the failure mode was significantly different, as porcelain suffered more chipping than the lithium disilicate; which, in turn, showed most fails related to the tooth structure. (2) It was not possible to determine the combination of the mechanical cycling parameters that would allow the determination of fatigue parameters for ultra-thin ceramic laminates, since the maximum number of cycles reached was 536,818 cycles. In this way, future studies need to be carried out so that a clinically relevant methodology can be developed to determine the fatigue parameters of ultra-thin ceramic laminates in the anterior teeth.

Objective: The primary objective of this study was to evaluate the roughness of CAD/CAM blocks of lithium disilicate glass-ceramic (IPS e.max CAD, Ivoclar Vivadent®, Schaan, Liechtenstein), before and after surface treatment with hydrofluoridric acid 10% and after silane coating by Atomic Force Microscopy and Optical Microscopy. The average size of silane as well as its fit to the valleys after acid etching was also studied. Methods: Ten specimens of CAD/CAM blocks of lithium disilicate glass-ceramic were analyzed by Atomic Force Microscopy. Before surface treatment with hydrofluoridric acid 10%, the specimens were also analyzed by Atomic Force Microscopy. All specimens were also analyzed by Optical Microscopy after the application of a layer of silane. Free software Gwyddion version 2.51 was used on data processing. The 3D surface measurements were: root mean square roughness, average roughness, maximum peak height, maximum pit depth, maximum height, Skewness and Kurtosis of surface and profile roughnesses. Images provided by Optical Microscopy were used to calculate the size of the silane particle, also using the free software Gwyddion version 2.5.1. Non-parametric tests were done by the free software R version 3.5.1. Results: Surface roughness and profile roughness were numerically different, but both increased after acid etching. All the skewness measurements concentrated around zero, indicating a more symmetrical behavior after acid conditioning. Silane cross-sectional area measured from 0,0374m² to 0,424351m² and its radius ranged from 0,115m to 0,3675m and could fit in on about 77,5% of the conditioned surface valleys. Significance: Roughness surface and silane layer are important factors to the bond strength between ceramic and resin cements, ensuring the success of restorative treatment. / Objetivo: O principal objetivo deste estudo in vitro foi analisar a rugosidade de superfície de blocos de CAD/CAM de cerâmica de dissilicato de lítio, antes e depois do condicionamento com ácido fluorídrico a 10% durante 20 segundos e após a aplicação de uma camada de silano, usando a Microscopia de Força Atômica e Microscopia Óptica. A média do tamanho do silano e como eles se ajustam nos vales da superfície condicionada também foram estudados. Metodologia: 10 amostras confeccionadas por blocos para CAD/CAM de cerâmica de dissilicato de lítio foram analisadas por um microscópio de força atômica. Depois do tratamento de superfície com ácido fluorídrico a 10% durante 20 segundos, os espécimes foram novamente analisados por Microscopia de Força Atômica. Todas as amostras foram analisadas em microscópio óptico depois da aplicação de uma camada de silano. O software Gwyddion (versão 2.5.1) foi usado para o processamento de dados. As medidas obtidas para as imagens 3D das superfícies foram: raiz quadrada média da rugosidade, rugosidade média, altura do pico mais alto, profundidade do vale mais baixo, máxima altura, assimetria e curtose, tanto para a análise de superfície quanto para a análise do perfil. As imagens obtidas pela Microscopia Óptica foram usadas para calcular o tamanho da partícula de silano, também usando o software Gwyddion (versão 2.5.1.). Testes não-paramétricos foram calculados pelo software R (versão 3.5.1). Resultados: As rugosidades da superfície e do perfil foram numericamente diferentes, mas ambas aumentaram após o condicionamento ácido. A assimetria concentrou-se próxima a zero, indicando um comportamento mais simétrico após o condicionamento. A área da secção transversal do silano mede entre 0,0374m² a 0,424351m² e o seu raio mediu entre 0,115m a 0,3675m. Esse tamanho de partícula pode ser acomodado em 77,5% dos vales presentes nas superfícies condicionadas. Significância: A rugosidade e a camada de silano são fatores importantes para o aumento da união entre a cerâmica e o cimento resinoso, assegurando o sucesso do tratamento restaurador.

Objetivos: (1) determinar a carga de fratura e o modo de falha de laminados cerâmicos ultrafinos processados via CAD-CAM em função da microestrutura do material (vitrocerâmica à base de dissilicato de lítio ou porcelana à base de leucita); (2) desenvolver metodologia de ciclagem mecânica para determinar o tempo de vida e o modo de falha de laminados cerâmicos ultrafinos processados via CADCAM. Materiais e métodos: dezesseis dentes humanos, incisivos centrais superiores, foram utilizados para confecção dos espécimes. Os dentes sofreram mínimo preparo, em esmalte, para adequada adaptação dos laminados cerâmicos ultrafinos. Os laminados de dissilicato de lítio e de porcelana foram confeccionados via CAD-CAM e cimentados com cimento resinoso sobre os dentes. Quatro espécimes de cada grupo foram levados à máquina de ensaios universal para determinação da carga de fratura dos laminados. Para o desenvolvimento de metodologia para determinação do tempo de vida dos laminados, uma série de testes piloto foi realizada, utilizando-se diferentes parâmetros como: tipo de antagonista (dentes naturais ou roletes metálicos), carga aplicada (20, 30 ou 40 N) e esquema de ciclo mastigatório (incisão ou deslizamento). Os padrões de falha dos laminados foram analisados em um estereomicroscópio, e os resultados obtidos no ensaio de carga de fratura foram analisados por ANOVA e teste de Tukey. Resultados: o valor médio obtido de carga de fratura para o dissilicato de lítio foi de 431,8 ± 217,9 N, enquanto que para a porcelana foi de 454,4 ± 72,1 N. Não houve diferença estatística entre os valores de carga de fratura encontrados, porém, o desvio padrão e o coeficiente de variação da vitrocerâmica foram muito superiores em relação aos da porcelana. Houve diferença no modo de falha dos materiais testados, sendo que a porcelana apresentou um maior número de falha por lascamento e o dissilicato de lítio apresentou maior quantidade de falha da estrutura dental. Na ciclagem mecânica, para cada condição testada, uma resposta diferente foi obtida. No tipo de ciclo incisão, os antagonistas (dente natural) fraturaram quando as cargas de 30 N e 40 N foram aplicadas. No tipo de ciclo deslizamento, o antagonista (dente natural) sofreu desgaste da borda incisal com carga de 30 N. Para o antagonista rolete metálico, quando a carga de 30 N foi aplicada ocorreu fratura do laminado, e quando aplicada a carga de 20 N, houve desgaste excessivo do rolete metálico. Conclusão: (1) o material utilizado não afetou a carga de fratura dos laminados cerâmicos ultrafinos quando o teste estático foi utilizado. Entretanto, o modo de falha foi significativamente diferente, sendo que a porcelana sofreu mais lascamentos do que o dissilicato de lítio; o qual, por sua vez, apresentou a maioria das falhas relacionadas à estrutura dental. (2) Não foi possível determinar uma combinação de parâmetros de ciclagem mecânica que permitisse a determinação dos parâmetros de fadiga para laminados cerâmicos ultrafinos, já que o número máximo de ciclos alcançados foi de 536.818 ciclos. Dessa forma, estudos futuros precisam ser realizados para que uma metodologia apropriada permita determinar parâmetros de fadiga clinicamente relevantes para laminados cerâmicos ultrafinos em dentes anteriores. / Objectives: (1) to determine the fracture load and the failure mode of the ultra-thin ceramic laminates processed via CAD-CAM according to the microstructure of the material (lithium disilicate-based glass-ceramic or leucite-based porcelain); (2) to develop a fatigue methodology capable of determining the lifetime of ultra-thin ceramic laminates processed via CAD-CAM. Materials and methods: sixteen human maxillary central incisors were used to produce the specimens. The teeth required minimal preparation on the enamel for proper adaptation of the ultra-thin ceramic laminates. Ceramic laminates made of lithium disilicate and feldspathic porcelain with thicknesses between 0.3 mm to 0.5 mm were produced via CAD-CAM and cemented with resin cement. Four specimens of each group were taken to a universal testing machine to determine the fracture load of the laminates. For the development of a fatigue methodology, a series of pilot tests was performed using different parameters such as: type of antagonist (natural teeth or metal roller), applied load (20, 30 or 40 N), and type of masticatory cycle (incision or sliding). Failure modes were analysed using a stereomicroscope. Fracture load data were analysed by ANOVA and Tukey\'s test. Results: the mean fracture load obtained for the glass-ceramic was 431.8 ± 217.9 N, while that obtained for the porcelain was 454.4 ± 72.1 N. There was no statistical difference between the mean fracture load values; however, the standard deviation and the coefficient of the variation of the glass-ceramic were both higher than those obtained for the porcelain. There was also a difference in the failure modes for the two materials tested. The porcelain showed a higher number of factures due to chipping and the lithium disilicate showed a higher number of tooth structure failure. The fatigue experiment showed different results depending on the condition analysed. In the incision cycle, the antagonists (natural tooth) fractured when loads of 30 N and 40 N were applied. In the slide type of cycle, the antagonist (natural tooth) suffered wear on the incisal edge after applying 30 N of load. For the metal roller antagonist, when a 30 N load was applied, the ceramic laminate fractured, and when a 20 N load was applied, an excessive wear of the metal roller occurred. Conclusion: (1) The material used did not affect the fracture load of ultra-thin ceramic laminates when the static test was used. However, the failure mode was significantly different, as porcelain suffered more chipping than the lithium disilicate; which, in turn, showed most fails related to the tooth structure. (2) It was not possible to determine the combination of the mechanical cycling parameters that would allow the determination of fatigue parameters for ultra-thin ceramic laminates, since the maximum number of cycles reached was 536,818 cycles. In this way, future studies need to be carried out so that a clinically relevant methodology can be developed to determine the fatigue parameters of ultra-thin ceramic laminates in the anterior teeth.

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.