Efeito do envelhecimento mecânico e degradação hidrotérmica sobre a microestrutura, propriedades ópticas e mecânicas da zircônia monolítica indicada para próteses sem cobertura de porcelana
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Data
2017-03-13
Autores
Mariscal Muñoz, Eduardo [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
A zircônia monolítica (com maior translucidez) dispensa a cobertura de porcelana, mas existem dúvidas quanto a seu comportamento frente degradação a baixa temperatura (LTD) devido à exposição direta em meio úmido e estresse mecânico. Este estudo avaliou os efeitos do envelhecimento artificial sobre a microestrutura, a resistência à flexão, as propriedades ópticas, a resistência à fadiga e ao desgaste de duas zircônias monolíticas: sendo uma para dentes posteriores (Prettau Zirkonzahn – ZrP), e a outra para anteriores (Prettau Anterior Zirkonzahn – ZrA) e uma zircônia para infraestrutura (Zirkon Transluzent – Zirkhonzan- ZrI). Espécimes com 12 mm de diâmetro e 1,2 mm de espessura foram submetidos aos seguintes envelhecimentos artificiais: ciclagem mecânica (M); envelhecimento hidrotérmico (H); associação entre ciclagem mecânica e envelhecimento hidrotérmico (M+H); e sem tratamento (controle). A microestrutura, morfologia superficial e tamanho de grãos foi avaliada por microscopia eletrônica de varredura (MEV); a rugosidade (Sa) por microscopia confocal a laser e a composição das fases cristalinas por difração de raios-X (DRX). As propriedades ópticas de refletância média, opacidade (%), parâmetro de translucidez e a soma de dispersão de luz (%) foram calculadas desde medições de luz refletida nos comprimentos de onda de 400 – 740 nm. A caracterização mecânica foi composta por ensaios de resistência à flexão biaxial e limite de fadiga, e resistência ao desgaste por compressão com deslizamento comparando ZrP, ZrA e porcelana de cobertura (VM9, VITA). As zircônias apresentaram diferentes tamanhos de grãos (ZrI<ZrP<ZrA) e alterações superficiais. A rugosidade não foi alterada pelos tratamentos. Em ZrI, a fase tetragonal diminuiu após os tratamentos H e M+H e aumentaram as fases cúbica e monoclínica. Na ZrP, os tratamentos H e M+H diminuíram a fase tetragonal do material, já a monoclínica e cubica aumentaram. Na ZrA a fase monoclínica não ocorreu após qualquer tratamento. As propriedades ópticas foram parcialmente afetadas pelos envelhecimentos. A refletância media foi reduzida após o tratamento M+H nos três materiais, o tratamento M diminuiu a refletância apenas de ZrA. A opacidade aumentou em ZrP e ZrA somente após os tratamentos M e M+H. A translucidez diminuiu em ZrP e ZrA após os tratamentos M e M+H. A soma de absorção e dispersão diminuiu para ZrP após a M+H e ZrA após M e M+H. A resistência a flexão biaxial foi maior para ZrI e ZrP, enquanto ZrA foi afetada após os tratamentos M e M+H. A resistência a fadiga aumentou em ZrI após o tratamento H, enquanto em ZrP aumentou após tratamentos H e M. ZrA não foi susceptível a nenhum dos tratamentos. Os materiais mostraram dessemelhante resistência ao desgaste (porcelana>ZrA>ZrP). Em conclusão, o conjunto dos testes revelam que ZrA não foi susceptível ao tratamento H que simula LTD, mas foi menos resistente que ZrI e ZrP recomendando cautela na sua indicação.
Porcelain veneer covering is not necessary for monolithic high translucency zirconia, and given its direct exposition to humidity and mechanic stress, there exists some concerning about its behavior against to low temperature degradation (LTD). This study evaluated the effects of artificially induced aging on microstructure, flexure resistance, optical properties and fatigue and wear resistance, of two monolithic zirconias, one for anterior teeth restorations (Prettau Anterior Zirkonzahn – ZrA), one for posterior teeth (Prettau Zirkonzahn – ZrP) and another for core fabrication (Zirkon Transluzent – Zirkhonzan- ZrI). Specimens with 12 mm of diameter and 1.2 mm of thickness were submitted to one of the following artificial aging methods; mechanical cycling (M), hydrothermal (H), mechanical cycling and hydrothermal combination (M+H) and no treatment (controle). Superficial morphology, microstructure and grain size were assessed by SEM analysis, changes in roughness (Sa) were measured by laser confocal microscopy and crystalline phase content was quantified by X-ray diffraction (XRD). Optical properties of mean reflectance, opacity (%), translucency parameter and scattering/absorption sum (%) were obtained since reflected light measurement from 400 - 700 nm wavelength. Mechanical characterization was made by biaxial flexure assay and staircase approach fatigue test. Wear resistance was assessed in ZrP, ZrA through a compression/sliding assay comparing to veneering porcelain (VITA VM9). Zirconias showed different grain size (ZrI<ZrP<ZrA) and surface alterations. Aging treatments did not promote alterations in roughness. ZrI tetragonal phase decreased after H and M+H treatments and cubic and monoclinic phases augmented. H and M+H treatments diminished ZrP tetragonal phase and cubic and monoclinic phases increased. In ZrA, monoclinic phase did not appear in any condition. Optical properties were partially affected by aging. Mean reflectance decreased after M+H treatment for the three materials, and M treatment decreased only ZrA reflectance. Opacity in ZrP and ZrA augmented only after M and M+H treatments. Translucency decreased in ZrP and ZrA after M and M+H treatments. Scattering absorption sum diminished for ZrP after M+H and in ZrA when M and M+H were applied. Biaxial flexure resistance was higher in ZrI and ZrP, while in ZrA, this property was affected only by M and M+H. Fatigue resistance augmented in ZrI after H treatment and ZrP after H and M treatments. ZrA fatigue resistance was not susceptible to any treatment. Materials showed different wear resistance capacity (porcelain>ZrA>ZrP). In conclusion, our tests revealed that ZrA was not susceptible to LTD, however were less resistant than ZrI and ZrP suggesting precaution in its indication.
Porcelain veneer covering is not necessary for monolithic high translucency zirconia, and given its direct exposition to humidity and mechanic stress, there exists some concerning about its behavior against to low temperature degradation (LTD). This study evaluated the effects of artificially induced aging on microstructure, flexure resistance, optical properties and fatigue and wear resistance, of two monolithic zirconias, one for anterior teeth restorations (Prettau Anterior Zirkonzahn – ZrA), one for posterior teeth (Prettau Zirkonzahn – ZrP) and another for core fabrication (Zirkon Transluzent – Zirkhonzan- ZrI). Specimens with 12 mm of diameter and 1.2 mm of thickness were submitted to one of the following artificial aging methods; mechanical cycling (M), hydrothermal (H), mechanical cycling and hydrothermal combination (M+H) and no treatment (controle). Superficial morphology, microstructure and grain size were assessed by SEM analysis, changes in roughness (Sa) were measured by laser confocal microscopy and crystalline phase content was quantified by X-ray diffraction (XRD). Optical properties of mean reflectance, opacity (%), translucency parameter and scattering/absorption sum (%) were obtained since reflected light measurement from 400 - 700 nm wavelength. Mechanical characterization was made by biaxial flexure assay and staircase approach fatigue test. Wear resistance was assessed in ZrP, ZrA through a compression/sliding assay comparing to veneering porcelain (VITA VM9). Zirconias showed different grain size (ZrI<ZrP<ZrA) and surface alterations. Aging treatments did not promote alterations in roughness. ZrI tetragonal phase decreased after H and M+H treatments and cubic and monoclinic phases augmented. H and M+H treatments diminished ZrP tetragonal phase and cubic and monoclinic phases increased. In ZrA, monoclinic phase did not appear in any condition. Optical properties were partially affected by aging. Mean reflectance decreased after M+H treatment for the three materials, and M treatment decreased only ZrA reflectance. Opacity in ZrP and ZrA augmented only after M and M+H treatments. Translucency decreased in ZrP and ZrA after M and M+H treatments. Scattering absorption sum diminished for ZrP after M+H and in ZrA when M and M+H were applied. Biaxial flexure resistance was higher in ZrI and ZrP, while in ZrA, this property was affected only by M and M+H. Fatigue resistance augmented in ZrI after H treatment and ZrP after H and M treatments. ZrA fatigue resistance was not susceptible to any treatment. Materials showed different wear resistance capacity (porcelain>ZrA>ZrP). In conclusion, our tests revealed that ZrA was not susceptible to LTD, however were less resistant than ZrI and ZrP suggesting precaution in its indication.
Descrição
Palavras-chave
Zircônio, Envelhecimento, Resistência de materiais, Difração de raios X, Fenômenos ópticos, Desgaste de restauração dentária