Com a crescente valorização da estética, o uso das cerâmicas a base de dissilicato de Lítio tem se destacado devido as suas propriedades estéticas e mecânicas. Contudo, este sistema exige um processo de cristalização complexo que limita o seu uso aos fornos mais sofisticados e de alto custo. Este trabalho teve como objetivo avaliar o efeito de dois processos de cristalização na microdureza, resistência à flexão e morfologia do dissilicato de Lítio IPS e.max CAD. De 10 blocos do IPS e.max CAD obteve-se 60 corpos de prova que foram divididos entre o ensaio de microdureza Knoop (n=30) e resistência à flexão (n=30). Cada ensaio teve os corpos de provas separados em 3 grupos conforme processo de cristalização: G1- processo de cristalização preconizado pelo fabricante; G2- processo de cristalização simplificado; G3- sem cristalização. Análise morfológica foi realizada, qualitativamente, por confocal a laser em 1 amostra recolhida, aleatoriamente, de cada grupo do teste de resistência à flexão. Os dados obtidos na microdureza foram tabulados e analisados estatisticamente pelo teste de Friedman, enquanto que os dados da resistência a flexão foram analisados por Análise de Variância e teste de Tukey-Kramer, ambas as análise com significância de p≤ 0,05. Os resultados mostraram que a média da microdureza Knoop dos corpos de prova do grupo G3 (862,13 KHN) foi semelhante ao do grupo G2 (818,9 KNP) e estes foram significantemente maiores que o grupo G1 (645,13 KHN). A resistência à flexão dos corpos mostrou um valor maior para o grupo G1 (302,95 MPa), mas estatisticamente semelhante ao grupo G2 (277,7 MPa), os quais foram significantemente maiores que o grupo G3 (155,2 MPa). Morfologicamente o G3 apresentou uma superfície mais irregular seguido pelo G1, com uma superfície mais regular para o G2. Todos os dois processos de cristalização promoveram um aumento da resistência à flexão, no entanto o processo de cristalização simplificado promoveu uma maior microdureza e superfície mais regular. / Due to the crescent appreciation for esthetic, the use of lithium disilicate glass ceramic has excelled because of their esthetic and mechanical properties. However, this system requires a complex process of crystallization which restricts his use to sophisticated and expensive ovens. This study aimed to evaluate the effect of two crystallization processes in hardness, flexural strength and morphology of the IPS e.max CAD lithium disilicate. Ten blocks of IPS e.max CAD generated 60 specimens that were divided between the Knoop micro hardness test (n = 30) and flexural strength (n = 30). Each trial had the bodies of evidence separated into 3 groups according to the crystallization process: G1-crystallization process recommended by the manufacturer; G2-simplified process of crystallization; G3 without crystallization. It was performed a morphological analysis, qualitatively, by confocal laser scanning microscopy on one sample taken randomly from each group for the flexural strength test. The data obtained by the micro hardness test were statistically analyzed Friedman tests, while the flexural strength data were analyzed by analysis of variance and Tukey-Kramer test, both analysis with significance set at p≤ 0.05. The results showed that the average micro hardness of the specimens in group G3 (862.13 KHN) was similar to G2 (818.9 KNP) and these were significantly higher than the G1 group (645.13 KHN). The flexural strength of the specimens showed a higher value for G1 (302.95 MPa), but statistically similar to G2 (277.7 MPa), which were significantly higher than the G3 group (155.2 MPa). Morphologically G3 exhibited a more irregular surface followed by G1, with a surface more regular for G2. Both of crystallization processes promoted a gain in flexural strength. However, the simplified crystallization process promoted a greater hardness and more regular surface.

Orientador: Ana Cláudia Pavarina / Banca: Eunice Teresinha Giampaolo / Banca: Ricardo Faria Ribeiro / Resumo: O uso do microondas tem sido indicado como um método efetivo na desinfecção de resinas acrílicas. Entretanto, há pouca informação sobre o efeito da irradiação do microondas nas propriedades mecânicas desses materiais. Considerando esses aspectos, o objetivo deste estudo foi avaliar o efeito da irradiação por microondas sobre as propriedades mecânicas de resistência à flexão e dureza de resinas acrílicas. Os corpos-de-prova para a realização dos testes mecânicos foram confeccionados com os seguintes materiais: Kooliner (K), Tokuso Rebase Fast (TR), Ufi Gel Hard C (UGH) e New Truliner (NT), todas resinas indicadas para reembasamento imediato, e Lucitone 550 (L), que é uma resina para base de prótese. Para cada material foram confeccionados 48 corpos-de-prova que foram divididos igualmente em seis grupos. As resinas autopolimerizáveis (K, TR, UGH e NT) foram submetidas à irradiação logo após a confecção, enquanto que os corpos-de-prova da resina termopolimerizável (L) permaneciam 50 l 2 horas em água a 37ºC l 1ºC antes da irradiação. Para o procedimento de irradiação, cada corpo-de-prova foi individualmente imerso em 200 mL de água destilada e submetido a dois ciclos de irradiação pelas microondas, para simular o envio da prótese ao laboratório e o retorno dela ao consultório odontológico. Cada corpo-de-prova foi irradiado a uma potência constante de 650 W, variando-se o tempo de exposição: 1 minuto (T1), 2 minutos (T2), 3 minutos (T3), 4 minutos (T4) ou 5 minutos (T5). O grupo controle (T0) foi submetido aos testes mecânicos sem ser irradiado pelas microondas. Os ensaios de resistência à flexão para todos os corpos-de-prova foram realizados em máquina MTS-810 Material Test System sob velocidade de 5 mm/minuto, utilizando o teste em três pontos a uma distância de 50 mm entre os apoios. Em seguida, um dos fragmentos do ...(Resumo completo, clicar acesso eletônico abaixo) / Abstract: Microwave irradiation was previous suggested as an effective method for the disinfection of acrylic resins. However, little information is available concerning the effect of microwave irradiation on the mechanical properties of acrylic resins. The purpose of this study was to evaluate the effect of two cycles of a microwave disinfection procedure on the flexural strength and Vickers hardness of acrylic resins. Four autopolymerized resins (Kooliner- K, Tokuso Rebase Fast- TR, Ufi Gel Hard- UGH and New Truliner- NT) and one heat-cured resin (Lucitone 550- L) were used for preparing specimens. For each material, 48 specimens were made and equally divided into six groups. The relined specimens were submitted to disinfection procedures after polymerization and the denture base polymer specimens were stored in water for 50 l 2 hours at 37ºC l 1ºC prior to disinfection. The specimens were individually immersed in 200 mL of destilated water and microwaved twice, simulating when dentures come from the patient and before being returned to the patient. Each cycle of microwave disinfection was performed at 650 W for one of the following irradiation times: 1 minute (T1), 2 minutes (T2), 3 minutes (T3), 4 minutes (T4) or 5 minutes (T5). Control group (T0) specimens were subjected to mechanical tests without being disinfected. The flexural strength values of the materials were determined using a testing machine MTS-810 at a crosshead speed of 5 mm/minute using a three-point bending fixture with a span of 50 mm. Thereafter, one fragment of specimen was submitted to Vickers microhardness test. The values were determined by using a 25 gf load, after 30 seconds contact. Twelve hardness measurements were taken on each specimen and the average was then calculated. The flexural and hardness values were submitted to ANOVA and ...(Complete abstract, click electronic access below) / Mestre

Avaliou-se a influência de dois sistemas de acabamento e polimento na resistência à flexão de uma cerâmica feldspática EX-3 (Noritake). Para isto, confeccionou-se blocos cerâmicos com medidas em conformidade com a ISO 6872/1995. Em seguida obteve-se o glaze natural. A padronização da rugosidade superficial foi conferida com auxílio de um rugosímetro, e os blocos foram então divididos em cinco grupos. O Grupo I (controle) foi testado com glaze. Para os testes realizados nos demais grupos, os blocos receberam um tratamento de asperização por meio de uma ponta diamantada 4137 (KG Sorensen). Em seguida foram polidos com diferentes protocolos. No grupo II, o sistema de polimento dura white (Shofu). No grupo III, o sistema de polimento dura white (shofu) associado a uma pasta diamantada aplicada com disco de feltro. No grupo IV o sistema de polimento Exa Cerapol (Edenta) e no grupo V, este mesmo sistema mais pasta diamantada aplicada com disco de feltro. Após os procedimentos de acabamento e polimento, foi avaliada a rugosidade conseguida (Ra), para se avaliar a eficácia dos métodos testados. A análise estatística por ANOVA (p ≤ 0,05) mostrou não haver diferença estatisticamente significante entre os grupos (G2=3,820,58; G3=3,550,61; G4=4,050,40; G5=3,950.47) . Feito isto, os corpos-de-prova foram submetidos a um ensaio mecânico de resistência à flexão em três pontos, e também neste caso, os resultados depois de tratados estatisticamente não demonstraram diferenças estatísticas entre os grupos glazeados e os grupos que receberam tratamento (G1=132,126,9 MPa; G2=123,317,4 MPa; G3=114,519,3 MPa; G4=104,211,9 MPa e G5=104,719,1 MPa) . Após a realização destas avaliações, tornou-se possível concluir que o uso dos sistemas de acabamento e polimento testados neste trabalho permite obter superfícies com rugosidade similar a obtida com o glaze natural e não interferem na resistência à flexão da cerâmica utilizada. / The objective of this study was to evaluate the influence of two systems of finishing and polishing in the flexural resistance of feldspatic ceramic EX-3 (Noritake). Ceramic blocks with measures in compliance with ISO 6872/1995 were confectioned following the manufacturers instructions. After the confection of the blocks and attainment of natural glaze, the standardization in terms of superficial rugosity was evaluated by means of a rugosimeter, and the blocks were then divided into five groups. One of the groups was tested in this condition (natural glaze) being Group I (control). For the tests carried through the other groups, the blocks were burnished by means of a 4137 (KG Sorensen) diamond bur. After that, they were polished with different protocols which characterized the other groups. In group II, the Dura white (Shofu) polishing system was evaluated. In group III, the same system was used, but now followed by a diamond paste in a felt wheel, In group IV, the polishing system Exa Cerapol (Edenta) was used and in the group V, this system was followed by a diamond paste in a felt wheel. After these procedures, the obtained rugosities were evaluated (Ra), in order to evaluate the effectiveness of the tested methods. The statistical analysis of ANOVA (p ≤ 0,05) showed that there were not statistical significant differences between the groups (G2=3.820.58; G3=3.550.61; G4=4.050.40; G5=3.950.47). After that, the specimen were submitted to a three points flexural strength test in a universal testing machine, and also in this case that, the statistically treated results didnt demonstrate statistical differences between the groups (G1=132.126.9 MPa; G2=123.317.4 MPa; G3=114.519.3 MPa; G4=104.211.9 MPa e G5=104.719.1 MPa). It was possible to conclude that the use of the tested systems allows to get polished surfaces similar to the natural glazed ones. and that they dont decrease the flexural resistance of the used ceramics.

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Reinforcement corrosion is the most common deterioration problem observed in reinforced concrete (RC) structures located at coastal or cold regions. The corrosion process can impact the performance of these structures by inducing damage on the bonding action between concrete and steel, either by the splitting of the concrete cover due to the volumetric expansion of corrosion products or the lubricant effect at the steel/concrete interface as the corrosion by-products accumulate. The current research aims at investigating corrosion-induced deterioration of bond between steel and concrete through finite element (FE) analysis of the flexural behaviour of corroded RC components. By treating the concrete cover as a thick-wall cylinder subjected to internal pressure, the analytical evaluation of impaired bond capacity is studied first and verified against published bonding tests. Then, the formulation of a numerical model is performed using ABAQUS, wherein a link element to simulate the bond behaviour is formulated and implemented through the ABAQUS user-subroutine (UEL) feature according to the validated analytical model. By introducing corrosion-induced damages, i.e., smaller cross-sectional area of reinforcement, splitting of concrete and bond deterioration, in the FE analyses, the results of the numerical model show good agreement with experimental observations. Upon validation of the analytical and FE models, a parametric investigation is conducted, wherein the effects of concrete strength, dimension of reinforcing bars, properties of oxide products, different corrosion damage mechanisms and the corrosion location along the longitudinal reinforcement on the flexural behaviour of RC beams are studied. The results show that the analytical evaluation for bond degradation is impacted by the selection of the post-cracking material model and the thickness of cover that determine the ‘holding capacity’ after cracking initiation. Also, the density of rust by-products affects the results of the analytical model at high corrosion levels. From the FE model results, it was observed that each damage mechanism due to corrosion contribute to different levels of flexural degradation, although the flexural strength degradation is mainly due to the loss of bonding action. The parametric study also demonstrates that flexural members which have reinforcement corrosion initiated near the supports suffer greater deterioration in flexural capacity than those with damages at mid span. Finally, based on these observations, suggestions for the application of both analytical and numerical models are made.

This diploma thesis deals with research and preparation of bulk materials based on the Mg–Al–Ti system. The theoretical part summarizes the basic knowledge about magnesium alloys, focusing mainly on Mg–Al and Mg–Ti systems. Furthermore, basic information on powder metallurgy methods was included here, from the production of powder materials, through their compaction, to heat treatment and spark plasma sintering (SPS). The theoretical part ends with literature review on the current research of the Mg–Al–Ti system. In the experimental part, bulk materials based on the Mg–Al–Ti system was prepared using traditional methods of powder metallurgy, as well as using the SPS method. The microstructure of the material, elemental and phase composition was examined in this thesis. Subsequently, Vickers hardness and flexural strength were measured, and fractographic observation of the fracture surface was performed. It was found that the aluminum was completely dissolved during the heat treatment, but the titanium particles remained almost intact in the material and worked as a particulate reinforcement. Materials prepared by methods of conventional powder metallurgy showed increased porosity compared to materials prepared by the SPS, resulting in lower hardness and flexural strength. The hardness increased with increasing the amount of aluminum and titanium and with the amount of magnesium phase . Fractographic observation of the fracture surface suggests that a diffuse connection between the reinforcement and the matrix may have occurred after the sintering process.

OBJECTIVES: To evaluate the effects of different machining modes on the flexural strength CAD-CAM restorative materials. MATERIALS AND METHODS: Four different CAD-CAM materials were used: VITA MARKII, VITA Enamic (VITA Zahnfabrik), Empress CAD, and e.max CAD (Ivoclar Vivadent). Rectangular bars for each material (except e.max CAD) were made by three procedures: saw cut, normal mill and fast mill. Each subgroup had a sample size of 5. Saw cut bars were cut by a BUHLER diamond blade saw. Milled bars were made using SIRONA CEREC MCXL milling unit. The 3-point flexural strength test was performed using a universal testing machine. Surface roughness was measured using a profilomer. Student t-test and Tukey-Kramer statistical analysis were performed to check significant differences. RESULTS: e.max CAD saw cut group was significantly stronger than the milled group. There was no difference in the strength of the Empress CAD groups. Enamic saw cut group was significantly stronger than the normal milled but not the fast milled one. There was no significant difference between the Enamic milled groups. Vita MKII saw cut was significantly stronger than both milled groups. There was no difference in the strength between the milled MKII groups. The surface roughness of the saw cut groups in all materials were significantly less than their milled counterparts in both longitudinal and transverse measurements. CONCLUSION: Machining had a significant effect on the surface roughness of materials. Damage from machining can cause the material to have lower flexural strength.

Yttria stabilized zirconia (YSZ) is a polymorph with possible phase transformation toughening occurring during impact. The fractography and mechanical properties of laminated alumina and YSZ were studied in this thesis. Five sample types were studied in this thesis: (5:5) Al2O3/YSZ (a sequence of 5 alumina tapes stacked on 5 YSZ tapes), (5:5) Al2O3/YSZ (1 wt.% Pure ZrO2), (7:3) Al2O3/YSZ, Al2O3, and YSZ. Scanning electron microscopy (SEM) and X-ray microscopy (XRM) were used to study morphology and crack propagation with three-point tests performed to study the flexural strength. X-ray diffraction (XRD) spectra of all samples pre and post three-point tests were examined to determine if a change in monoclinic zirconia occurred. The combination of SEM and XRM data found microcracks in the YSZ layers of Al2O3/YSZ laminates with none present on YSZ laminates, leading to the conclusion tensile stress was performed on YSZ during sintering with Al2O3. Fracture patterns show a curving of cracks in Al2O3 layers and abrupt, jagged breaks in YSZ layers with crack forking at major YSZ microcrack regions. YSZ laminates were found to have the highest average flexural strength, but a very high standard deviation and low sample count and Al2O3 laminates having the second highest flexural strength. The (7:3) Al2O3/YSZ laminates had a significant increase in flexural strength compared to both types of (5:5) Al2O3/YSZ laminates. Significant change in monoclinic presence was not found except for the (5:5) Al2O3/YSZ (1 wt.% Pure ZrO2) laminates.

PURPOSE: To analyze surface roughness, the edge chipping of different CAD/CAM bur milled dental materials (bar and crown design of 1.0mm and 1.5mm thickness), correlate the effect of machining damage on the material strength, compare the flexural strength of bur milled versus sectioned CAD/CAM blocks and evaluate the tool wear after milling. MATERIALS AND METHODS: Five dental CAD/CAM materials were used: Lithium disilicate glass-ceramic (IPS e.max CAD), Leucite-reinforced glass-ceramic (IPS Empress CAD), Feldspathic porcelain (Vitablocs Mark II), Feldspar ceramic-polymer infiltrated (Enamic), and composite resin (Lava Ultimate). Ten rectangular bars with dimensions of 4 mm × 2 mm × 14 mm were milled using a new set of burs for each material. Then, ten crowns of each material with thicknesses of 1.0 mm and 1.5 mm were milled after scanning a standard aluminum die with corresponding marginal thickness. The bars surface roughness was measured. Then, three specimens were selected for the edge chipping analysis using (SEM). Thereafter, 3-point bend test was used to test the flexural strength of bur milled and saw cut bars with the same dimensions. For the crowns, load to failure test was used. One-way ANOVA and Tukey HSD post hoc tests to determine the difference between the groups using JMP13.0 with α=0.05. RESULTS AND CONCLUSIONS: The surface roughness and edge chipping was significantly affected by the material composition. Comparison of the flexural strength of bur milled to sectioned bars, IPS e.max CAD and IPS Empress CAD show statistically significant less flexural strength (p<0.001). A strong correlation was found between the decrease in flexural strength and the chipping length on the central tensile side of the bur milled materials (R2=0.62, p=0.01). Crown thickness significantly affects the edge chipping as 1.5 mm crown thickness has more edge chipping than 1.0 mm crowns. However, no correlation is found between the load to failure test for the crown design and the edge chipping for 1.5mm and 1.0 mm thickness crowns. Tool wear is significantly affected by the material type. / 2021-07-31

This study’s objective was to evaluate repetitive firing cycles’ effects on the translucency, light’s absorption coefficient, and flexural strength of zirconia-reinforced lithium silicate ceramics. Two zirconia-reinforced lithium silicate ceramics and one lithium disilicate glass-ceramic were tested. Blocks of all materials were sectioned into tiles with different thicknesses and subjected to up to five firing cycles using the firing schedule indicated in the manufacturer’s user instructions. Light transmission ratio (T) and absorption coefficients were determined using a spectrophotometer. Further, bars were sectioned from blocks of all materials and tested for three-point-bend flexural strength using a Universal Testing Machine (Instron), and flexural strength was calculated from load at failure. Factorial ANOVA and Tukey’s HSD tests were conducted to analyze light transmission and flexural strength, while regression was used to analyze the absorption coefficient. Weibull parameters and fractographic analysis also were investigated. The results showed that repetitive firing cycles reduced e.max® and Vita Suprinity’s® translucency, but not that of Celtra® Duo, which showed no significant difference. All materials of greater thickness exhibited less translucency, and e.max® CAD had the highest mean light transmission; however, it was not significantly different than Celtra® Duo. Repetitive firing cycles showed more absorption coefficient of light with Vita Suprinity® and e.max®, except for Celtra® Duo, which showed no difference. Vita Suprinity® showed the highest absorption coefficient; however, it was not significantly different than e.max® CAD. Repetitive firing cycles had no significant effect on flexural strength. High and low flexural strength samples for all materials showed similar characteristics with respect to crack propagation patterns, and fracture origins. In conclusion, repetitive firing cycles decreased both e.max® and Vita Suprinity’s® translucency significantly. Repetitive firing cycles increased e.max® and Vita Suprinity’s® absorption coefficient significantly, particularly at shorter wavelengths. Repetitive firing cycles did not increase flexural strength statistically significantly. Vita Suprinity® showed an inherent and more homogeneous flaw-distribution in the first two firing cycles compared to the distribution of flaws in the other two materials.