Effect of fiber addition on slow crack growth of a dental porcelain.

AIMS: To evaluate the effect of the processing method (conventional sintering, S, and heat-pressing, HP) and addition of potassium titanate fibers, PTF, on the microstructure, mechanical properties (flexural strength, σf, and Weibull parameters, m and σ5%), slow crack growth parameters n (stress corrosion susceptibility coefficient), and optical properties (translucency parameter, TP, and opalescence index, OI) of a feldsphatic dental porcelain. METHODS: Disks (n = 240, Ø12 × 1 mm) of porcelain (Vintage-Halo, Shofu) were produced using S and HP methods with and without addition of 10 wt% (conventional sintering) or 5 wt% (heat-pressing) of PTF. For the S method, porcelain was sintered in a conventional furnace. In the HP technique, refractory molds were produced by lost wax technique. The porcelain slurry was dry-pressed (3t/30s) to form a cylinder with 12 mm (diameter) and 20mm (height), which was heat-pressed for 5 min/3.5 bar into the mold. Specimens were tested for biaxial flexural strength in artificial saliva at 37°C. Weibull analysis was used to determine m and σ5%. Slow crack growth (SCG) parameters were determined by the dynamic fatigue test, and specimens were tested in biaxial flexure at five stress rates: 10(-2), 10(-1), 10(0), 10(1) and 10(2)MPa/s (n=10), immersed in artificial saliva at 37°C. Parameter n was calculated and statistically analyzed according to ASTM F394-78. Optical properties were determined in a spectrophotometer in the diffuse reflectance mode. RESULTS: The highest n value was obtained by the combination of heat-pressing with fiber addition (37.1) and this value was significantly higher than those obtained by both sintered groups (26.2 for control group and 27.7 for sintered with fiber). Although heat-pressing alone also resulted in higher n values compared to the sintered groups, there were no significant differences among them. Fiber addition had no effect on mechanical strength, but it resulted in decreased TP values and increased OI values for both processing methods. Heat-pressing alone was able to reduce the porosity level of the porcelain. CONCLUSIONS: Addition of PTF combined with heat-pressing can reduce strength degradation of a dental porcelain compared to sintered materials with or without fibers. Heat-pressing (HP) alone should be considered as a good alternative for clinical cases where high translucency is required.

Abutments de cerâmica de Y-TZP e compósito Al2O3-ZrO2 / Mechanical performance of Y-TZP/Al2O3 ceramic abutments

Abutment, também denominado pilar de fixação, é um material metálico ou cerâmico, instalado acima de um implante que provê suporte para próteses dentais. O sucesso significativo destas aumentou a demanda por melhores resultados estéticos e consequentemente resulta em pesquisas para o desenvolvimento de novos componentes, materiais e conceitos de tratamento. Atualmente, os implantes mais utilizados são aqueles a base de titânio e os abutments, que também eram fabricados com materiais metálicos, estão sendo substituídos por materiais cerâmicos como alumina e zircônia estabilizada com ítria. O presente estudo propôs-se avaliar as propriedades mecânicas de pilares cerâmicos estéticos a base de compósitos alumina-zircônia (Al2O3-ZrO2) e zircônia estabilizada (ZrO2 Y-TZP), através de ensaios mecânicos, a fim de verificar sua viabilidade de produção e comercialização para utilização em procedimentos odontológicos em reabilitação oral. Para tanto, obteve-se pilares cerâmicos a base de compósitos de ZrO2 e Al2O3-ZrO2 e submeteu-os a ensaios mecânicos de fadiga cíclica úmida e carregamento por compressão tangencial. Os resultados foram avaliados por meio de avaliações macroscópicas dos corpos de prova, sobrevida de ciclos e valores de resistência à fratura. Dentro das condições experimentais, os resultados obtidos demonstraram que há possibilidade de se obter pilares de ZrO2 e Al2O3-ZrO2, usinados industrialmente, com elevada resistência mecânica e durabilidade clínica quando corretamente instalados baseado em um planejamento minucioso. Apesar da realização dos ensaios em associação, cuja finalidade foi de se aproximar das condições in vivo, os ensaios laboratoriais apresentam limitações, como os vários tipos de forças intraorais.

An abutment is a metallic or ceramic material installed onto the implant providing support for fixed dental prosthesis. The significant success these dental restorations increased patient demand for better esthetic results, which resulted in research to develop new components, materials and treatment concepts. Currently, the most widely used implants are those based on titanium; the abutments, which were also made of metallic materials, are being replaced by ceramic materials such as alumina and yttrium-stabilized zirconia (ZrO2 Y-TZP). The purpose of this study is to evaluate the mechanical properties of ceramic abutments on the aesthetic composite alumina-zirconia (Al2O3-ZrO2) and stabilized zirconia (ZrO2 Y-TZP) by mechanical tests to verify its feasibility and production marketing for use in dental procedures. The abutments ceramic composites of ZrO2 and Al2O3-ZrO2 were submitted to mechanical tests of wet cyclic fatigue and loading by tangential compression. The results were evaluated by macroscopic evaluations of the specimens, survival after cycling and values of fracture resistance. Within the experimental conditions, the results showed that is possible to produce industrially abutments of ZrO2 and Al2O3-ZrO2 with high mechanical strength and clinic success when properly installed, based on careful planning. Although tests were applied to approach in vivo conditions, there are limitations such as several intra-oral forces.

Effect of ion exchange on strength and slow crack growth of a dental porcelain.

OBJECTIVES: To determine the effect of ion exchange on slow crack growth (SCG) parameters (n, stress corrosion susceptibility coefficient, and sigma(f0), scaling parameter) and Weibull parameters (m, Weibull modulus, and sigma(0), characteristic strength) of a dental porcelain. METHODS: 160 porcelain discs were fabricated according to manufacturer's instructions, polished through 1 microm and divided into two groups: GC (control) and GI (submitted to an ion exchange procedure using a KNO3 paste at 470 degrees C for 15 min). SCG parameters were determined by biaxial flexural strength test in artificial saliva at 37 degrees C using five constant stress rates (n=10). 20 specimens of each group were tested at 1 MPa/s to determine Weibull parameters. The SPT diagram was constructed using the least-squares fit of the strength data versus probability of failure. RESULTS: Mean values of m and sigma(0) (95% confidence interval), n and sigma(f0) (standard deviation) were, respectively: 13.8 (10.1-18.8) and 60.4 (58.5-62.2), 24.1 (2.5) and 58.1 (0.01) for GC and 7.4 (5.3-10.0) and 136.8 (129.1-144.7), 36.7 (7.3) and 127.9 (0.01) for GI. Fracture stresses (MPa) calculated using the SPT diagram for lifetimes of 1 day, 1 year and 10 years (at a 5% failure probability) were, respectively, 31.8, 24.9 and 22.7 for GC and 71.2, 60.6 and 56.9 for GI. SIGNIFICANCE: For the porcelain tested, the ion exchange process improved strength and resistance to SCG, however, the material's reliability decreased. The predicted fracture stress at 5% failure probability for a lifetime of 10 years was also higher for the ion treated group.