Effect of glazing application side and mechanical cycling on the biaxial flexural strength and Weibull characteristics of a Y-TZP ceramic

Abstract Glaze application on monolithic zirconia (Y-TZP) can be a practical approach to improve the mechanical properties of this material. Objective Our study evaluated the effect of glazing side and mechanical cycling on the biaxial flexure strength (BFS) of a Y-TZP. Methodology Eighty sintered Y-TZP discs (Ø:12 mm; thickness: 1.2 mm - ISO 6872) were produced and randomly assigned into eight groups (n=10), according to the factors "glazing side" (control - no glazing; GT - glaze on tensile side; GC - glaze on compression side; GTC - glaze on both sides) and "mechanical aging" (non-aged and aged, A - mechanical cycling: 1.2×106, 84 N, 3 Hz, under water at 37°C). Specimens were subjected to BFS test (1 mm/min; 1,000 Kgf load cell) and fractured surfaces were analyzed by stereomicroscopy and SEM. Hsueh's rigorous solutions were used to estimate the stress at failure of glazed specimens. Two-way ANOVA, Tukey's test (5%), and Weibull analysis were performed. Results The "glazing side", "mechanical aging" and the interaction of the factors were significant (p<0.05). Groups GC (1157.9±146.9 MPa), GT (1156.1±195.3 MPa), GTC (986.0±187.4 MPa) and GTC-A (1131.9±128.9 MPa) presented higher BFS than control groups (Tukey, 5%). Hsueh's rigorous solutions showed that the maximum tensile stress was presented in the bottom of zirconia layer, at the zirconia/glaze interface. Weibull characteristic strength (σo) of the GC was higher than all groups (p<0.05), except to GT, GTC-A and GTC, which were similar among them. The fractography showed initiation of failures from zirconia the tensile side regardless of the side of glaze application and fatigue. Conclusion Glazing zirconia applied on both tensile and compression sides improves the flexural strength of Y-TZP, regardless the mechanical aging.

Avaliação mecânica e microbiológica de resinas acrílicas reforçadas com partículas de sílica revestidas com prata / Mechanical and microbiological evaluation of acrylic resins reinforced with sílica-silver particles

O objetivo desta pesquisa foi sintetizar e caracterizar partículas de sílica recobertas com nanopartículas de prata, e avaliar a influência destas quando incorporadas à resina acrílica termicamente ativada e reembasador rígido, em suas características mecânicas e microbiológicas. Uma solução de sílica foi sintetizada pelo método de hidrólise controlada do tetraetilorto silicato (TEOS) em meio alcoólico. Foi adicionada a essa uma solução de nitrato de prata, em duas molaridades (10 mmols e 30 mmols) formando partículas do tipo núcleocasca. Após centrifugação e secagem, cada pó obtido foi adicionado em duas concentrações: 0.5% e 2%, às resinas analisadas. Foram confeccionadas barras retangulares (n=9) de 30 x 10x 3mm para realização do teste de resistência a flexão de três pontos, rugosidade e ângulo de contato; e 120 amostras em forma de disco (2 mmx10 mm) para análise microbiológica. Como grupo controleteve-se amostras sem nanopartículas. As nanopartículas foram analisadas emmicroscopia eletrônica de varredura com microanalisador por energia dispersiva de raios-X integrado (EDS), Difratômetro de Raios-X e microscopia eletrônica de transmissão. Uma suspensão de Candida albicans foi utilizada para análise de aderência fúngica, halo de inibição e concentração inibitória mínima. As fotomicrografias mostraram que as nanopartículas de 10 mmols apresentam uma distribuição mais homogênea e menor agregação das nanopartículas de prata nasuperfície da sílica do que as de 30 mmols. Os resultados indicaram que a resistência a flexão foi afetada negativamente, em ambos materiais, com a adição de 2% de partículas, independente da molaridade. A adição das partículas não alterou a molhabilidade da superfície dos materiais, nem a rugosidade, exceto do grupo de reembasador com partículas de 10mmols, em ambas concentrações. As partículas não apresentaram ação antifúngica para os materiais testados em nenhuma concentração, ...

This research aimed to synthesize, characterize, and evaluate the influence of the addition of silica-silver core/shell particles in mechanical and antifungal characteristics of thermally active acrylic resins or hard reliner . Silica solution was produced by controlled hydrolysis method of tetraethylortho silicate (TEOS) in an alcoholic. It was added a silver nitratesolution in two molarities, 10 and 30 milimols, forming core-shell particles.After centrifugation and drying, each obtained powder was added in two concentrations 0.5% and 2% in the resins analyzed. Rectangular samples(n=9) with 30 x10 x3 mm were made to three point bend test), roughness and contact angle, and 120 samples in disc (2 mmx10 mm) for microbiological analysis Samples without particles were used as control. The nanoparticles were analyzed by scanning electron microscopy with dispersive energy microanalyzer integrated X-rays (EDS), X-ray diffractometer and transmission electron microscopy. Candida albicans suspension was used to adhesion test, inhibition zone and minimum inhibitory concentration.Photomicrograph showed that nanoparticles with 10 milimols show a distribution more uniform and less aggregation of silver nanoparticles on the silica surface than 30 millimols. The Three point bend test results showed that the flexural strength was negatively affected in both materials, with the addition of 2% particles, in both molarity. The addition of the nanoparticles did not change the surface wettability or roughness of the materials, except for except the reliner group with 10mmols, in both concentrations. The nanoparticles showed no antifungal action for the materials tested at any concentration, neither was zone innibition. However, the solution presented minimal inhibitory concentration to 2.000 ppm. We conclude that low concentrations nanoparticles do not affect the mechanical characteristics and surface of the acrylic resin or reliner, however they do not ...