ABSTRACT
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...
Subject(s)
Materials Science , Dental Porcelain , Zirconium/adverse effectsABSTRACT
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