Effect of polishing procedures and hydrothermal aging on wear characteristics and phase transformation of zirconium dioxide

Abstract

Statement of problem. Yttria-stabilized zirconia used for the fabrication of crowns and fixed\ud \ud prostheses may require intraoral adjustments after placement and cementation. Grinding and\ud \ud polishing methods may result in changes in the surface characteristics of zirconia.\ud \ud Purpose. The purpose of this in vitro study was to assess the effect of polishing procedures on\ud \ud surface roughness, topographical and phase changes of zirconia, and wear of the opposing dentition.\ud \ud Material and methods. Presintered and precut yttria-stabilized zirconia specimens (10×10×1 mm)\ud \ud were divided into 4 groups (control, Intensiv, Shofu, 3M ESPE) depending on the polishing method\ud \ud used to prepare the specimens. All tests were carried out in triplicate. The specimens were polished\ud \ud depending on the polishing regimen, while the control was left untreated. The specimens were\ud \ud thermocycled for 3000 cycles, with a temperature range of 5C to 55C. The surface roughness,\ud \ud elemental, and phase changes caused by polishing before and after thermocycling were assessed\ud \ud with surface profilometry, energy-dispersive spectroscopy, and X-ray diffraction analysis. The wear on\ud \ud antagonist steatite balls was also measured after mastication simulation. Statistical analysis was\ud \ud performed using 1-way ANOVA and the Tukey post hoc test to perform multiple comparison tests (a=.05).\ud \ud Results. The polishing procedures increased surface roughness (Ra) of yttria-stabilized zirconia from\ud \ud 0.52 for the control specimen to 0.73 for Intensiv, 0.70 for Shofu, and 0.70 for 3M ESPE (P<.05), which\ud \ud was reduced by thermocycling to 0.44 (control), 0.58 (Intensiv), and 0.58 (Shofu) (P<.001), while\ud \ud roughness remained unchanged for 3M ESPE specimens (0.75; P=.452). The deposition of aluminum\ud \ud when using Shofu abrasives and nickel in Intensiv was demonstrated. Phase changes were observed\ud \ud on the zirconia surface with formation of the monoclinic phase in all polishing methods. Specimen\ud \ud aging enhanced the surface phase changes and also induced compressive stresses in zirconia\ud \ud polished with Intensiv. The different polishing protocols did not affect the wear to the antagonist (P>.05).\ud \ud Conclusions. Polishing zirconia increased surface roughness and led to surface phase changes, but\ud \ud wear to the antagonist was not affected.peer-reviewe

Effects of polishing vs. glazing on dental ceramic wear: A comparative in vitro study

“…used full-contour zirconia crowns for a period of six months [42]; the present study showed similar results when using flat samples for a one-year simulation. In this study, the tested ceramic restorations showed material wear loss that was comparable between the glazed and polished finishes.…”

“…Wear has little influence on roughness and no influence on phase transformation [41]; however, glazing and/or polishing ceramic can influence the initial stage of the wear process [15]. Some studies have used polishing procedures applied to zirconia to increase the surface roughness, resulting in phase changes on the zirconia surface [38,42]; conversely, other studies have reported that the polishing surface of zirconia resulted in less wear to the antagonist [43][44][45][46]. Verena et al reported that polished or glazed MZ can provide an alternative to veneered dental restoration [47].…”

Comparative Evaluation of Cellular Response to Three Types of Zolid Surface Full Contour: Glazing, Polishing, and CO2 Laser

“…In a standardized temperature glaze method, the underneath ceramic becomes more shrunk when cooled, and compression stress is created at the surface of the glued porcelain. This surface compression stress increases the porcelain strength by preventing the cracks from extending to the porcelain depth, and, by creating a smooth surface in the ceramic, prevents the accumulation of plaque in the ceramic surface (Bartolo et al, 2017).…”

Resistência à tração entre componentes de pilar híbrido Conexão® submetido a teste de fadiga termomecânica

“…A zircônia pura é um cristal polimórfico que pode ser encontrado em três diferentes formas alotrópicas, dependendo da temperatura: monoclínica (em temperaturas até 1170 ºC), tetragonal (de 1170 até 2370 ºC) e cúbica (2370 ºC até o ponto de fusão) (BARTOLO, D et al, 2017). A adição de estabilizadores como óxidos de ítria e cerium previnem a transformação de fase e mantêm os cristais de zircônia na sua forma mais estável tetragonal em temperatura ambiente (DENRY, I.; KELLY, J. R., Esse fenômeno acontece inicialmente nos grãos mais superficiais, onde água vai se incorporando entre os grãos de zircônia devido ao preenchimento das vacâncias de oxigênio e depois continua para o interior da estrutura do material (CHEVALIER, J.; GREMILLARD, L.;DEVILLE, S., 2007).…”

“…A explicação do ocorrido pode estar na possível ocorrência de transformação de fase de tetragonal para monoclínica nos componentes de zircônia dos pilares de G2. Sabe-se que a zircônia pode estar sujeita a essa transformação de fase quando exposta à estresses mecânicos e mudanças de temperatura (HARADA, K. et al, 2016), podendo ser exacerbada na presença de umidade (DENRY, I.; KELLY, J. R, 2008), sendo o fenômeno denominado como degradação em baixa temperatura.Essa transformação de fase ocasiona um aumento de volume nos grãos da zircônia na ordem de 3 a 5%(BARTOLO, D. et al, 2017). Sendo assim, podemos propor que, nas amostras que compõem G2, por terem sido expostas ao dobro de ciclos termomecânicos, o fenômeno da transformação de fase possa ter sido mais expressivo, de modo a compensar a perda de adaptação que houve entre os componentes de titânio e zircônia devido ao desgaste do hexágono do titânio, por meio de um aumento de volume do componente de zircônia.…”