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

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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.

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.

OBJECTIVES: This in vitro study aims to compare and evaluate the mechanical properties of different 3D-printed resin materials. Determine the impact of 3D printer type on the mechanical properties. Investigate the filler percentage by weight for each resin material. MATERIALS AND METHODS: Eight resin materials were tested for flexural strength, flexural modulus, microhardness, fracture toughness, and wear resistance. Resin materials: Rodin Sculpture (RS), BEGO VarseoSmile Crown Plus (BVS), Desktop Health Flexcera Smile Ultra Plus (DHF), SprintRay Crown (SRC), SprintRay Ceramic Crown (SCC), Saremco Crowntec (SC), Myerson Trusana (MT), PacDent Ceramic Nanohybrid (PAC). 3D printer Asiga Max and Ackuretta SOL were used to print 12 specimens from each material to compare three-point flexural strength in bar-shape, biaxial flexural strength in disc-shape, fracture toughness in single edge V-notched beam, wear resistance in pin-shape. Three discs shape specimens from each material were used to compare the Vickers microhardness. The filler percentage by weight of each material is determined by Ash burning and Solvent extraction. The microstructure of a polished disc from each material was examined under a scanning electron microscope (SEM), and the elemental composition was investigated by Energy Dispersive Spectrometry (EDS). Results were analyzed using ANOVA, regression of least square means (α = 0.05), Tukey HSD test, Pearson correlation coefficient, and Student’s t-test. RESULTS: The flexural strength test results, utilizing the three-point method, reveal significant differences among the materials tested. The highest average was recorded in SCC at 160 MPa, while the lowest was found in SRC at 84.4 MPa. The flexural modulus also exhibited significant differences, with the highest average observed in SCC, BVS, RS, SRC, DHF, SC, and MT, measuring 7.8, 6.2, 6.0, 5.8, 4.9, 4.5, and 3.0 GPa, respectively. The resin materials with the highest biaxial flexural strength were DHF 217 MPa and MT 200 MPa, with no significant distinction between them and different from the remaining materials. SCC demonstrated a notably higher average value in Vickers microhardness 44 HVN, while DHF exhibited a significantly lower value of 15.58. The Fracture toughness test presented no significant differences between DHF, MT, and SCC, with values of 2.28, 2.27, and 2.11 MPa.m0.5, respectively, exceeding the remaining materials. In the wear test, DHF and MT had a significantly higher weight loss rate of 29.25 and 27.18 mg/million cycle, respectively. In contrast, MT's height loss rate of 2.02 mm/million cycle was the only significantly higher difference from other materials. The data indicates that the printer type does not significantly affect biaxial flexural strength. At the same time, Asiga exhibited significantly higher values in three-point flexural strength, flexural modulus and hardness tests. In contrast, the SOL printer demonstrated higher values in fracture toughness than Asiga. The ash and solvent extraction methods revealed that SCC had the highest filler percentage by weight, while MT had the lowest. SEM imaging showed the existence of filler particles in all materials, with PAC containing the largest particles and MT containing the smallest. DHF was the only resin material that contained exclusively spherical shape filler particles. EDS analysis disclosed the elemental composition of each material with a higher percentage in Silica, Oxygen, Barium, Titanium, and Ytterbium. CONCLUSION: The results demonstrate significant differences in the tested materials' flexural strength, flexural modulus, biaxial flexural strength, Vickers microhardness, fracture toughness, and wear rates. Even though there are significant differences in some of the mechanical properties of the printer type, it is small and might not have an effect clinically. A strong correlation exists between filler percentage with flexural modulus r = 0.83, biaxial flexural strength r = 0.60, microhardness r = 0.73, and wear resistance r= 0.82. There is a low correlation between filler percentage with fracture toughness r= 0.41, with no correlation with flexural strength in the three-point test. Filler particle percentage highly affects the mechanical properties of 3D printed resin materials. These findings could be valuable in selecting appropriate materials for specific applications.

The use of fiber reinforced plastics (FRP) in repairing and strengthening bridges has been researched in recent years. In particular, attaching unidirectional FRP to the tension face of reinforced concrete beams has provided an increase in stiffness and load capacity of the structure. However, due to the brittle nature of the unidirectional FRP, the ductility of the beam decreases. One possible solution to this problem is the use of cross-ply or off-axis FRP laminates. This thesis focuses on the investigation of the flexural behavior of reinforced concrete beams strengthened with one of two different FRP orientations (0°/90° and ±45°). More particularly, the change in strength and ductility of the beams as the number of FRP layers are altered is investigated. Seven under-reinforced concrete beams were constructed and tested to failure. With the exception of the control beam, each specimen was applied with two, three, or four layers of either 0°/90° and ±45° FRP orientations. To predict the flexural behavior of the specimens, a theoretical model was derived using basic concepts, past research, and the tested properties of the concrete, steel reinforcement, and FRP. Also, two methods were used to analyze the ductility of the tested beams. Along with the test details of each specimen; the moment, deflection, CFRP strain, crack patterns, and mode of failure are discussed. The results included an increase in load capacity with respect for the number of CFRP layers applied for both orientations. Also, the ductility of the beams were reduced by adding CFRP orientations. / Master of Science

Silicon nitride (Si₃N₄) has the potential for use in various high-performance applications. However, surface defects such as voids/pits are commonly present on as processed Si₃N₄. When subjected to external forces, fracture originates at such flaws. To reduce or eliminate surface flaws, machining operations are required which constitute a major proportion of production costs. In order to offer an inexpensive alternative to machining and also to enhance the room temperature flexural strength of as fired Si₃N₄, low expansion glaze coatings of lithium aluminosilicate (LAS) and magnesium aluminosilicate (MAS) compositions were developed. Homogeneous and crack-free glaze coatings were successfully formed on as processed Si₃N₄. This ensured formation of compressive surface stresses on the as fired Si₃N₄ which, in turn, led to the reduction of the effects of surface flaws. When compared to the uncoated as fired Si₃N₄, both the glaze coatings helped achieve greater flexural strength. Analyses of the two glazes indicated better strength for the MAS coating compared to the LAS. Wear tests revealed that the MAS glaze exhibited higher wear resistance than the LAS glaze. These differences were attributed to the ability of the magnesium aluminosilicate glaze to achieve greater surface smoothness and better adherence to the substrate than the lithium aluminosilicate. / Master of Science

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