Numerical analysis of the mechanical behavior of ceramic dental implants based on Ce-TZP/Al2O3 composite.

This study aimed to identify the potential use of the ceramic composite ZrO2(CeO2)-Al2O3 as a dental implant due to its intrinsic geometry and different masticatory loads based on finite element simulations. Ceramic samples were sintered at 1500 °C-2h, and characterized: The mechanical properties of the ceramic composite (hardness, fracture toughness, flexural strength, Young's Modulus, and Poisson ratio) were determined, in addition to the relative density and its structural characteristics. Commercial dental implant designs (incisal and third-molar) on CAD models were used in this study as an initial implant geometry applied in a typical simulated mandible anatomy. Finite element models were generated for implant geometries using CAD and CAE techniques. Loading cases were considered based on different intensities (100-500 N) and orientation angles to the implant axis (0° and 45°) to reproduce human masticatory conditions. For comparison purposes, the numerical predictions were compared with finite element simulations of gold-standard titanium implants. Ce-TZP/Al2O3 sintered ceramics showed flexural strength of 952.6 ± 88 MPa, hardness and fracture toughness of 1427 ± 46 HV and 11.3 ± 0.4 MPa m1/2, respectively, beside Young's modulus of 228.3 ± 65 GPa and Poisson ratio of 0.28. For both Ce-TZP/Al2O3 dental implant geometries, the implant prototypes showed adequate mechanical behavior regardless of the masticatory load value or the orientation angle applied in the simulations: All finite element predictions are lower than the values established by Mohr Coulomb's failure criterion, allowing the feasibility, preliminarily, of the proposed ceramics for dental implant applications without fracture risk.

Experimental analysis and numerical simulations of the mechanical properties of a (Ce,Y)-TZP/Al2O3/H6A ceramic composite containing coupled toughening mechanisms.

OBJECTIVES: This study investigates the simulation of the mechanical behavior of a bioceramic composite based on (Ce,Y)-TZP reinforced with equiaxed Al2O3 and platelet-shaped hexaaluminate (H6A) grains using Finit Element Method (FEM). METHODS: A commercial (Ce, Y)-TZP/Al2O3 ceramic powder was compacted into disc-shaped specimens that were sintered at 1500 °C for 2 h. The sintered samples were further subjected to hydrothermal degradation in an autoclave at 134 °C, 0.2 MPa, for 10 h and characterized according to their phase composition, microstructure, and relative density. Their flexural strength values were determined by the piston-on-three-ball test, and Weibull statistics was used to evaluate the results. Their hardness, fracture toughness and elastic parameters were also measured. Numerical simulations of the biaxial strength test were performed using the ABAQUS finite element code. RESULTS: The sintered ceramic composite material presented relative density >99%, high resistance to hydrothermal degradation, average hardness of 1435 ± 35 HV, fracture toughness KIC of 9.7 ± 0.5 MPa m1/2, and average biaxial flexural strength of 952.6 ± 88 MPa. The numerical predictions of the biaxial flexural strength showed a consistently lower average biaxial flexural strength value of 880.9 MPa, ∼10% lower than the average experimental results. CONCLUSIONS: The differences observed are attributed to the complex coupled toughness mechanisms of this material, not included in the finite element simulations.

Optimizing the microstructure of a new machinable bioactive glass-ceramic.

OBJECTIVES: This study aimed to optimize the crystallization process and the microstructure of a new bioactive glass-ceramic (GC) previously developed by our research group to obtain machinable glass-ceramics. METHODS: Differential scanning calorimetry (DSC) analyses were conducted to explore the characteristic temperatures and construct a semi-quantitative nucleation curve. The GC specimens were characterized by X-ray diffraction (XRD) and Rietveld refinement. Their brittleness index (B) and machinability were characterized and compared with IPS e.max-CAD®. Their Young's modulus, fracture toughness, and hardness were assessed. RESULTS: We found that the maximum crystal nucleation rate temperature of this GC is ~470 °C. Treatments were designed based on the 1st DSC peak onset (570 °C), 1st peak offset (650 °C), and 2nd peak offset (705 °C) crystallization temperatures of lithium metasilicate (LS, LiSi2O3) and lithium disilicate (LS2, Li2Si2O5). Rietveld refinement indicated an increase in LS2 and a reduction in LS and amorphous phase for increased temperatures and longer treatment times. Their B values indicate good machinability compared with that of the control group based on statistical analyses. As expected, lower levels of LS2 increase the machinability regardless of the rotation speed adopted, leading to a greater depth of cut and reduced Edge Chipping Damage Depth (ECDD). CONCLUSION: This bioactive GC with optimized microstructure presents high machinability. For treatment temperatures above 570 °C, the number of elongated LS2 crystals increases and decreases the amorphous phase content, which reduce the machinability of the GC, and should therefore be avoided. The best results were obtained using heat treatment at 570 °C, which produces LS crystals embedded in a glassy matrix (67%) with small contents of secondary phases.

Preparation of TiC/Ti3SiC2 Composite by Sintering Mechanical Alloyed Ti-Si-C Powder Mixtures.

The present work aims to evaluate the crystalline phases and microstructure of a TiC-Ti3SiC2 ceramic composite, obtained by mechanical alloying of Ti, C and Si powders and subsequent sintering. A mechanical alloying technique in a planetary ball mill for 1, 10, 50, 100 and 200 h using Ti, Si and C powders with molar ratios of 3:1:2 as feedstock in argon (Ar) gas was employed to prepare nano-sized Ti-Si-C powders. TiC crystallite size and lattice strain were evaluated by X-ray diffraction analysis (XRD) and the morphological characteristics and particle size distribution were examined using scanning electron microscope (SEM). After milling, a reduction of the average particle size and crystallinity is observed. Furthermore, after 10 h of milling time, TiC starts to crystallize. The powder mixture obtained after 200 h of milling was compacted and sintered at 1200 °C under controlled atmosphere, for 15 min, 2 h or 4 h with a heating rate of 5 °C/min. Almost full densification of samples sintered for 2 h and 4 h has been achieved, with relative densities close to 98.8±0.2% and TiC and Ti3SiC2 as crystalline phases with an average crystallite size of TiC near 0.7 µm. Rietveld refinement indicates that the majority TiC-cubic phase (>85 vol%) presents a unit cell volume of 8.03 nm³ after sintering at 1200 °C. Despite the maintenance of the volume of the hexagonal unit cell of Ti3SiC2, (15.05 nm³), the increase of the isothermal sintering time resulted in an increase of the lattice parameter "a", from 0.315 nm to 0.320 nm, and a reduction of the lattice parameter "c" from 1.750 nm to 1.705 nm. The control of the changes in the residual stresses within the TiC matrix and the Ti3SiC2 precipitates, which is associated with the deformation in the lattice parameters, must be controlled to achieve high fracture toughness in the composite.

Modeling of the Influence of Chemical Composition, Sintering Temperature, Density, and Thickness in the Light Transmittance of Four Zirconia Dental Prostheses.

Research has increasingly been conducted to improve the toughness and aesthetics of zirconium oxide (zirconia) used in prosthetic dentistry. However, the balance between better mechanical properties and greater translucency, to ensure aesthetic requirements, is still a challenge in the development of a novel zirconia for dentistry applications. This study evaluated the transmittance of visible light for four types of pre-sintered zirconia blocks used in dentistry (3Y-SBE, Zpex, Zpex-4, and Zpex-Smile). The objective is to analyze the simultaneous influence of sintering temperature, in the range of 1450-1560 °C, as well as the chemical composition (%Y2O3), density, and thickness (1.0, 1.3, 1.6, and 2.0 mm) in the zirconia's transmittance. To evaluate the interactive influence of these variables, a statistical learning model based on gradient boosting is applied. The results showed that the effect of the sintering temperature has an optimal (maximum transmittance) point. Increasing the temperature beyond this point reduces the transmittance of the material for all types of zirconia. Moreover, the optimal transmittance point is affected by the chemical composition of each type of zirconia. In addition, the results showed that the transmittance of all types of zirconia had an inverse relationship with the density, zirconia Zpex-Smile being the most sensitive to this parameter. Furthermore, the transmittance of 3Y-SBE, Zpex, and Zpex-4 decreases approximately linearly with the specimen thickness, whereas zirconia Zpex-Smile has a sublinear decrease, which is expected due to the optical isotropy of the cubic phase.

Mechanical properties of lithium metasilicate after short-term thermal treatments.

OBJECTIVES: The properties of lithium-silicate dental glass-ceramics are very sensitive to heat treatments which are conducted after CAD/CAM (Computer Aided Design/Computer Aided Machining) processing. In particular, temperature variations inside the furnace chamber which may occur between different models of furnaces may result in altered mechanical properties of these materials. In this work, the effect of thermal treatment parameters on the transformation of lithium metasilicate (Li2SiO3) into lithium disilicate (Li2Si2O5) and on the resulting mechanical properties has been investigated. METHODS: Lithium metasilicate samples. containing 59 vol% of amorphous phase, were thermal treated under vacuum at 820 °C for up to 9 min or at 840 °C for 7min (as control group). The samples were characterized by X-ray diffraction analysis using the Rietveld refinement and scanning electron microscopy. Hardness and fracture toughness (n = 30 indentations/group) were evaluated by the Vickers indentation technique. The elastic properties were measured by the Impulse Excitation Technique and the flexural strength (n = 15/group) was measured using the piston-on-three-ball (P-3B) testing assembly. Complementary Weibull statistic were conducted as statistical analysis. RESULTS: The results indicate a progressive reduction of the Li2SiO3 phase with increasing isothermal holding time at 820 °C until the conversion into Li2Si2O5, is completed for treatments longer than 7 min. A complete transformation of Li2SiO3 into Li2Si2O5 has also been observed for the control group of samples treated at 840 °C for 7min. Samples of the control group exhibited hardness, fracture toughness, Young's modulus and Poisson ratio 5.76 ±â€¯0.17 GPa, 1.60 ±â€¯0.03 MPa m1/2, 100.3 GPa e 0.21, respectively. The reduction of the thermal treatment temperature to 820 °C reduced the fracture toughness and the Young's modulus between 5-10%. Furthermore, the fracture strength was significantly reduced by approximately 71%, because of the lower amount of elongated Li2Si2O5 grains and higher amount of residual amorphous phase. CONCLUSION: In general, the glass-ceramic material containing residual amorphous phase associated with various crystalline phases, presented a reduction of its mechanical properties in relation to the lithium disilicate glass-ceramic. The reasons for these differences in the mechanical behavior are discussed by analyzing the influences of different phenomena such as thermal expansion anisotropy, residual stresses, amorphous phase content and microstructure on the properties.

Strength of 3Y-TZP and feldspathic porcelain subjected to different cooling methods

AIM: To investigate the effect of the cooling rate on flexural strength of monolayer and bilayer porcelain/zirconia (Y-TZP) bars. METHODS: Forty-five specimens were made for each design group: (PM) monolithic specimens of veneer porcelain Vita VM9 (Vita, Germany); (ZM) monolithic specimens of zirconia (ZiHP; ProtMat, Brazil); (PB) bilayer specimens zirconia/porcelain with porcelain on lower surface; and (ZB) bilayer specimens porcelain/zirconia with zirconia on lower surface. Each group was cooled by three different methods after porcelain sintering: slow specimens were cooled inside the turned-off furnace; normal specimens were removed from the furnace and cooled in air at room temperature; and fast specimens were removed from the furnace at 910°C and cooled by compressed air for 10 s. Specimens were polished and flexural strength was measured in water at 37 °C (n=15). Maximum load at fracture was recorded, and equations for simple (monolayer) and composite (bilayer) structures were used to calculate the flexural strength. RESULTS were analyzed using one-way ANOVA (p<0.05) and Tukey test separately for each design. RESULTS: The results of one-way ANOVA were statistically significant only for the PB group. The post-hoc Tukey test showed the highest flexural strength for fast cooling and the lowest for slow cooling; the normal cooling was statistically similar to both. CONCLUSIONS: Cooling methods affected only the flexural strength of bilayer specimens with porcelain on low surface (under tension) when the slow cooling method was used...

Avaliação das propriedades de uma zircônia estabilizada com ítria (ZrO 2 -Y 2 O 3 ) de uso odontológico / Evaluation of an yttria-stabilized zirconia ceramic (ZrO 2 -Y 2 O 3 ) used as dental material

Este trabalho tem por objetivo o estudo das propriedades de uma cerâmica comercial de zircônia estabilizada com ¡tria, tendo como base comparativa as exigências da norma ISO 6872. Blocos pré-sinterizados de zircônia estabilizada com 3% em mol de ítria (ZrO 2 -3%mol Y 2 O 3 ) foram sinterizados a 1530§C-2h com taxa de aquecimento de 8§C/min. As fases cristalinas da zircônia foram identificadas por difração de Raios-X (DRX) e an lise microestrutural foi realizada utilizando Microscopia Eletrônica de Varredura (MEV). Os materiais foram avaliados mecanicamente por sua dureza e tenacidade … fratura, utilizando a técnica de indentação Vickers, e por sua resistência a fratura por flexão em quatro pontos. Ensaio de dilatometria, testes biológicos de citotoxicidade e avaliação da solubilidade química foram realizados visando demonstrar a biocompatibilidade e estabilidade química do material com vistas a sua aplicação como prótese sobre implante. Os resultados dos testes mecânicos indicaram que a cerâmica estudada apresenta dureza superior a 1200HV, tenacidade … fratura da ordem de 8 MPam1/2 e resistência … flexão superior a 900 MPa. Essas avaliações mecânicas aliadas …s caracterizações químicas e biológicas realizadas no produto indicam que o mesmo pode ser classificado dentro das exigências da norma ISO 6872, podendo ser utilizado em casos extremos de confecção de próteses multielementares. A zircônia estudada neste trabalho não apresenta potencial tóxico, comprovado pelos testes de citotoxicidade

This study aimed at studying the properties of a commercial ceramic of zirconia stabilized with yttria, with the requirements of the norm ISO 6872 as comparative basis. Pre-sintered zirconia blocks (ZrO2-3%mol.Y2O3) were sintered at 1530øC-2h with a heating rate of 8øC/min. The crystalline phases of zirconia were identified by X-Ray Diffraction (XRD) and microstructural analysis was performed using Scanning Electron Microscopy (SEM). The materials were evaluated for their hardness and fracture toughness, using the Vickers Indentation Technique, and its strength by four point bending testing. Tests of dilatometry, biological and cytotoxicity tests and evaluations of chemical solubility were conducted to demonstrate the biocompatibility and chemical stability of the material focusing their application as implant-supported prosthesis. The results of the mechanical tests indicate that the studied ceramic presents hardness greater than 1200HV, fracture toughness on the order of 8MPam1/2 and flexural strength exceeding 900MPa. These assessments allied to mechanical chemical and biological characterizations performed on the product indicate that it can be classified within the requirements of ISO 6872 and can be used in extreme cases of prosthesis design multi-element. The zirconia studied in this work has no toxic potential, as confirmed by cytotoxicity tests

Comparação das propriedades mecânicas e biocompatibilidade de blocos de zircônia nacionais e importados para uso em próteses implantosuportadas / Mechanical and physics properties of brazilian and imported zirconia blanks for dental prosthesis

O objetivo do presente trabalho foi comparar as propriedades mecânicas, físicas e a biocompatibilidade de blocos comerciais de zircônia (ZrO2) usados na confecção de próteses dentárias implantosuportadas por sistema de usinagem CAD/CAM. Fez-se a comparação de blocos comerciais de zircônia pré-sinterizados produzidos pela empresa nacional ProtMat® com os da empresa VITA®. As amostras comerciais foram sinterizadas a 1530°C, conforme procedimentos recomendados pelos fabricantes, e submetidas à caracterização das fases, ensaios mecânicos e de biocompatibilidade. Os resultados difração de raios-X mostraram que os blocos como recebidos apresentam somente a fase tetragonal a após os ensaios mecânicos foram identificadas as fases tetragonal e monoclínica. A transformação de fase foi responsável pelas excelentes propriedades mecânicas. Os blocos nacionais e importados apresentam propriedades mecânicas e físicas semelhantes, sem diferença estatística significativa quanto à dureza, tenacidade à fratura e resistência à fratura, as quais foram 1300HV, 9Mpam ½ e 910 MPa, respectivamente. Os testes de avaliação biológica primária avaliando a citotoxicidade indicaram que os materiais apresentam total crescimento celular com ausência de morte celular. Os protótipos de próteses usinados na forma de casquetes que foram sinterizados e que receberam os recobrimentos apresentaram boa qualidade

The objective of this study was to compare the mechanical, physical and biocompatibility properties of blanks of zirconia (ZrO2) used in the manufacture of dental prostheses produced by CAD/CAM machining system. It was analyzed commercially zircônia blaks presintered and stabilized with yttria (Y2O3) produced by Brazilian company (ProtMat) and imported from Germany (VITA). The commercially samples were sintered to 1530° as procedures recommended by the manufacturers, and submitted to mechanical and biocompatibility testing. The results of X-ray diffraction showed that the blocks have only the tetragonal phase and after the mechanical tests were identified a tetragonal and monoclinic phases. The transformation phase was responsible for the excellent mechanical properties. Brazilian and imported blocks exhibit similar physical and mechanical properties, with no statistically significant differences on the hardness, toughness and resistance to fracture, which were 1300 HV, 9 MPam ½ and 910 MPa, respectively. The biological evaluation of primary cytotoxicity indicated that the materials have cell growth with total absence of cell death

Incidência e localização das mordidas cruzadas em pacientes portadores de fissura de lábio e/ou palato / Incidence and location of crossbites in cleft lip and/or palate patients

O presente estudo teve por objetivo verificar a incidência e localização da mordida cruzada em uma população de pacientes portadores de fissura de lábio e/ou palato, bem como correlacionar a presença da mesma de acordo com os tipos de fissura, quais sejam pré, trans e pós-forame incisivo. Fizeram parte da amostra 68 pacientes, não sindrômicos, previamente ao início da terapia ortodôntica, sendo 32 do sexo masculino e 36 do sexo feminino. Os indivíduos foram enquadrados de acordo com cinco possibilidades, a saber: ausência de mordida cruzada, presença de mordida cruzada anterior,mordida cruzada posterior bilateral, mordida cruzada anterior + posterior unilateral e mordida cruzada total. Diante dos resultados, pode-se constatar uma marcante incidência de mordida cruzada, acometendo 75 por cento da amostra. Ao analisar a incidência das cinco possibilidades estudadas, observou-se que a mordida cruzada posterior apresentou-se como a situação clínica mais comum na amostra estudada. O grupo de fissura trans-forame incisivo foi o que apresentou mais acometido pela mordida cruzada, com maior incidência de mordida cruzada anterior seguida por mordida cruzada posterior, mordida cruzada anterior + posterior e mordida cruzada total, em relação aos demais grupos. O grupo pós-forame incisivo foi o menos acometido pela mordida cruzada