The effect of surface treatment and thermocycling on the shear bond strength of orthodontic brackets to the Y-TZP zirconia ceramics: A systematic review

ABSTRACT Introduction: Various surface pre-treatment methods have been adapted to optimize the bonding between the zirconia ceramics and the orthodontic brackets. Objective: This review is aimed at systematically analyzing the relevant data available in the literature, to find out the most effective and durable bonding protocol. Methods: Database search was conducted in PubMed, Scopus, and ScienceDirect, during September 2020. The review was conducted according to the PRISMA guidelines. Results: Based on the inclusion criteria, 19 articles were selected for qualitative analysis. Meta-analysis could not be performed due to the heterogeneity of the methodology among the studies. Most of the studies scored medium risk of bias. Compared to the untreated surface, surface pretreatments like sandblasting and lasers were advantageous. Primers and universal adhesive were mostly used as an adjunct to the mechanical pretreatment of the zirconia surface. In most studies, thermocycling seemed to lower the shear bond strength (SBS) of the orthodontic brackets. Conclusion: Based on this qualitative review, surface pretreatments with lasers and sandblasting can be suggested to optimize the bracket bond strength. To clarify this finding, meta-analysis is anticipated. Hence, high heterogeneity of the included studies demands standardization of the methodology.

RESUMO Introdução: Diferentes métodos de pré-tratamento da superfície foram adaptados para otimizar a colagem entre os braquetes ortodônticos e as cerâmicas de zircônia. Objetivo: A presente revisão teve como objetivo analisar, de forma sistemática, os dados relevantes na literatura, para buscar o protocolo de colagem mais efetivo e duradouro. Métodos: As buscas foram feitas em setembro de 2020, nas seguintes bases de dados: PubMed, Scopus e ScienceDirect. A revisão foi feita de acordo com as diretrizes do PRISMA. Resultados: Com base nos critérios de inclusão, 19 artigos foram selecionados para análise qualitativa. A metanálise não pôde ser feita, devido à heterogeneidade na metodologia dos estudos incluídos. A maior parte dos estudos apresentou risco de viés moderado. Comparadas às superfícies não tratadas, as superfícies com pré-tratamento usando jateamento ou laser apresentaram vantagem. Primers e adesivos universais foram mais usados como adjuntos ao pré-tratamento mecânico da superfície de zircônia. Na maioria dos estudos, a termociclagem parece ter reduzido a resistência ao cisalhamento dos braquetes ortodônticos. Conclusões: Com base nessa revisão qualitativa, os pré-tratamentos de superfície com laser e jateamento podem ser sugeridos para otimizar a resistência ao cisalhamento dos braquetes. Para esclarecer esse achado, uma metanálise é necessária. Para isso, faz-se necessária a padronização da metodologia, para lidar com a alta heterogeneidade dos estudos incluídos.

Early Short-Term Postoperative Mechanical Failures of Current Ceramic-on-Ceramic Bearing Total Hip Arthroplasties.

Although ceramic-on-ceramic (CoC) bearings have been shown to produce the smallest amount of wear volume in vitro as well as in vivo studies when used for total hip arthroplasties (THA), concerns about the failure of these bearing surfaces persist due to early failures observed after short postoperative time. In this study, an exhaustive analysis of the early failure occurred on the new generation of ceramic bearings, consisting of a composite alumina matrix-based material reinforced with yttria-stabilized tetragonal zirconia (Y-TZP) particles, chromium dioxide, and strontium crystals, was performed. For this study, 118 CoC bearings from 117 patients were revised. This article describes a group of mechanical failure CoC-bearing BIOLOX THA hip prosthesis patients without trauma history. The retrieved samples were observed under scanning electron microscopy (SEM), composition was analyzed with energy dispersive X-ray spectroscopy (EDX), and damaged surfaces were analyzed by grazing-incidence X-ray diffraction (GI-XRD) and white light interferometry. In the short term, CoC articulations provided similar mechanical behavior and functional outcome to those in XLPE cases. However, 5% more early mechanical failures cases were observed for the ceramic components. Although the fracture rate of third generation CoC couples is low, the present study shows the need to further improve the third generation of CoC-bearing couples for THA. Despite the improved wear compared to other materials, stress concentrators are sources of initial crack propagation, such as those found in the bore-trunnion areas. Moreover, in view of the evidence observed in this study, the chipping observed was due to the presence of monoclinic phase of the Y-TZP instead of tetragonal, which presents better mechanical properties. The results showed that total safety after receiving a THA is still a goal to be pursued.

Effect of PVA-PEG Binders on Surface Roughness of Y-TZP Zirconia

@#Introduction: Y-TZP Zirconia is a ceramic used for dental implants because it has good biocompatibility and aesthetic properties, and it is affordable. Y-TZP formed from powder using uniaxial pressing with some added binder. The binders used are PVA, PEG and a combination of both. This combination reduce hardness and improve plasticity properties. Significantly increasing of the binder concentration and the surface roughness of the implant increases the porosity of the material as a place for the osseointegration process. Thus, the purpose of this study was to examine the different effect of PVA-PEG binders on the surface roughness of Y-TZP zirconia. Methods: Twelve samples were divided into three treatment groups: 100% PVA, 100% PEG and 4% PVA-PEG added to Y-TZP powder at a ratio of 95:5 (wt.%). The mixture was pressed using a uniaxial pressing machine, sintered and measured: the data was then analyzed using one-way ANOVA and Post Hoc LSD. Results: The result of the ANOVA showed that there were significant differences in the surface roughness of the Y-TZP with three different binders (P<0.05). The average surface roughness of the three binders are as follows: PVA 100% (0.8025±0.23472), PEG 100% (1.2325±0.23866), 4% of PVA-PEG (1.3450±0.27695). The LSD showed that there was significant differences between PVA 100% and PEG 100% (P<0.05), PVA 100% and 4% PVA-PEG (P<0.05). There was no significant difference between PEG 100% and 4% PVA-PEG (P>0.05). Conclusion: 4% PVA-PEG binders combination has effects on the surface roughness of Y-TZP zirconia

Influência de diferentes técnicas de acabamento e polimento na resistência à flexão de zirconia ultratranslucida após envelhecimento in situ / Influence of different finishing and polishing techniques on the flexural strength of ultratranslucent zirconia after in situ aging

Objetivo: Investigar o efeito de técnicas de acabamento/polimento, da espessura e do envelhecimento in situ na resistência à flexão, topografia superficial e adesão celular de uma zircônia ultratranslúcida. Metodologia: Duzentas e quarenta barras de zircônia (UT: Prettau Anterior/Ultratranslúcida, Zirkonzahn, Gais, Itália) foram cortadas, lixadas e sinterizadas, sendo metade (120) nas dimensões finais de 8 x 2 x 1mm e as demais nas dimensões de 8 x 2 x 0,5mm. As barras foram divididas em 16 grupos (n=15) de acordo com três fatores: "envelhecimento in situ" (E: com e sem), "espessura"(1: 1 mm ou 05: 0,5mm) e "Acabamento e Polimento" (C: Controle; B:borrachas DhPro, Paraná Brasil; P: Asperização com pontas diamantadas KG Sorensen 4135; PB: Asperização com pontas diamantadas + Pontas de borrachas ). Para os grupos experimentais submetidos ao envelhecimento in situ, foram selecionados 15 pacientes (comitê de ética - 3.133.187), as amostras foram incluídas nas próteses totais provisórias dos pacientes, que utilizaram as próteses com as barras durante 60 dias. As barras foram submetidas ao ensaio de mini flexão de três pontos (1mm/min, 100 kgf). Duas amostras de cada grupo foram preparadas para as análises topográficas em Microscopia Eletrônica de Varredura (MEV), Difração de raios X (DRX), Microscopia de Força Atômica (AFM) e rugosidade superficial. Para o ensaio de adesão celular, seis blocos de zircônia ultra translúcida (2,5 x 2,5 mm), de cada grupo, foram contaminadas com C. albicans (ATCC 90028) para contagem da unidade formadora de colônia (UFC/mL). Os dados do ensaio de mini flexão (MPa) foram analisados por meio de ANOVA (3 fatores) e Tukey (5%); e os dados do ensaio de adesão celular pelo teste Kruskal Wallis (5%). Resultados: ANOVA (3 fatores) revelou que apenas o fator "Acabamento e Polimento" foi estatisticamente significativo para a resistência à mini flexão (p=0,0001). O desgaste apenas com broca diamantada produziu valores de resistência à mini flexão (variando de 257,1 a 292,9MPa) estatisticamente inferiores em relação aos grupos polidos apenas com discos de borracha (variando de 449,8 a 513,5 MPa), para todas as condições experimentais. No que diz respeito à adesão celular, o teste de Kruskal wallis não revelou diferenças significativas entre os grupos experimentais (p=0,053), apesar da rugosidade ter sido estatisticamente significante por meio do ANOVA (p = 0,001) e diferente entre todos os grupos. Conclusão: O ajuste de peças monolíticas de zircônia ultratranslúcida deve ser realizado idealmente com discos de borracha de poliuretano impregnadas com diamantes. Para a adesão celular, os protocolos de acabamento e polimento não interferem na adesão fúngica, apenas na rugosidade superficial, sendo as amostras polidas com borrachas as de maior lisura (AU).

Introduction: The aim of this study was to investigate the influence of different protocols of finishing and polishing, thickness, and aging in situ on flexural strength and cell adhesion of ultratranslucent zirconia. Methodology: 240 zirconia bars (UT: Prettau Anterior/Ultratranslucent, zirkonzahn, Gais, Italy) were cut, polished and sintered, presenting final dimensions of 1,0 x 2 x 8mm, and 0,5 x 2 x 8mm. The bars were divided among 16 groups (n=15) in accordance to three factors "in situ aging"­ 2 levels (With and Withouth "E"), "thickness" ­ 2 levels (1- 1 mm or 05- 0,5mm) and "Finishing and Polishing" ­ 4 levels (CControl, B- Rubber polishing; P- grinding with burs; PB- grinding with burs + polishing). To the experimental groups submitted to in situ aging, 15 patients were selected (ethics commitee - 3.133.187), the samples were included on the temporary prothesis, and the patients used the prothesis with the bars during 60 days. The bars were submitted to mini flexure three points test (1mm/min, load cell 100 kgf). Two samples of each group were prepared to the topographical analysis on Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), and surface roughness. For the cell adhesion assay, six blocks of ultratranslucent zirconia (2.5 x 2.5 mm), of each group were contaminated with the C. albicans (ATCC 90028) for counting the colony forming units (CFU / mL). Results: The mechanical test results were analyzed using ANOVA (3 factors) and Tukey (5%); and the cell adhesion assay data by the Kruskal Wallis test (5%. Results: ANOVA (3 factors) revealed that only the "Finishing and Polishing" factor was statistically significant for mini-flexure strength (p = 0.0001). The finishing and polishing with rubber polishers produced mini-flexure resistance values (varying from 257,1 to 292,9 Mpa) statistically lower in relation to the groups polished only with rubber discs (varying from 449,8 to 513,5 Mpa) to all experimental conditions. Concerning to cell adhesion, Kruskal wallis test did not reveal any significant differences between the experimental groups (p=0,053), despite of the fact that, the surface roughness presented itself statistically significant through ANOVA (p = 0,001) and difference between all groups. Conclusion: The adjustment of ultratranslucent zirconia monolithic should preferably be performed with rubber polishers impregnated with polyurethan. Concerning to cell adhesion, the protocols of finishing and polishing do not interfer at fungal adhesion, only on surface roughness, when the samples are polished with the smoothest rubbers (AU).

Efeito de diferentes regimes de acabamento e polimento na resistência à flexão e topografia superficial de zircônias monolíticas / Effect of different finishing and polishing regimes on flexural strength and surface topography of monolithic zirconia

Introdução: As restaurações em zircônia monolítica podem exigir ajustes em sua estrutura antes da cimentação. Diversos métodos de acabamento e polimento são sugeridos na literatura, entretanto estes podem promover mudanças estruturais e na superfície da zircônia, o que pode afetar a resistência mecânica do material em longo prazo. Objetivo: Investigar in vitro o efeito de diferentes regimes de acabamento e polimento e da degradação em baixas temperaturas na resistência à flexão e topografia superficial em dois tipos de zircônia monolíticas. Metodologia: 300 barras de zircônia (Z: ice zirkon transluzent/Convencional e UT: Prettau Anterior/Ultratranslúcida, zirkonzahn, Gais, Itália) foram confeccionadas nas dimensões 2,1- 1,3x 2,5x10mm, lixadas e sinterizadas, apresentando dimensões finais de 1,7-1 x 2 x 8mm, divididas em 20 grupos (n=15) de acordo com três fatores: "Zircônia"-2 níveis (Z: Convencional; UT: Ultratranslúcida), "Acabamento e Polimento"- 5 níveis (C- Controle; BBorrachas; P- Asperização com pontas; PB- Asperização com pontas + Borrachas; PGAsperização com pontas + glaze) e "Degradação"- 2 níveis (COMD: autoclave à 127°C, 1,7 bar /24h; sem degradação). Foi realizado o ensaio de resistência à miniflexão (3 pontos), com v:1mm/min e células de carga 500N e 5000N. Duas amostras de cada grupo foram preparadas para microscopia eletrônica de varredura (MEV)/ Espectrometria por Energia Dispersiva de Raios-X (EDS) e microscopia de força atômica (MFA). A rugosidade média de cada grupo foi avaliada qualitativamente. Os dados foram analisados por ANOVA (3 fatores) e Tukey (5%). Resultados: Os fatores "Zircônia" (p=0,0000), "Acabamento e Polimento" (p=0,0000) e "Degradação" (p=0,01) e foram estatisticamente significantes, sendo as maiores médias encontradas nos grupos ZPBD (1670.2 ± 252.73)A , ZBD (1663.5 ± 216.80)A e ZB (1654.7 ± 367.79A ) e as menores na zircônia UT, destacando-se o grupo UTPG (372.1±56.295)G . No MEV pode-se observar que a camada de glaze não recobriu toda superfície da zircônia e as borrachas promoveram uma superfície mais uniforme. O EDS revelou maior quantidade de óxido de ítrio nas zircônias UT, já na MFA maior valor de Ra foi encontrado nos grupos asperizados, sendo UT>Z. Conclusão: O protocolo mais indicado para acabamento e polimento das restaurações em zircônia são o uso de borrachas diamantadas. A asperização seguida pelo glaze reduziu a resistência da zircônia e o uso das borrachas forneceram uma superfície mais uniforme em relação aos demais métodos (AU).

Background: The restorations in monolithic zirconia may require adjustments in their structure prior to cementation. Several methods of finishing and polishing are suggested in the literature, however they can promote structural and surface changes of the zirconia, which can affect the mechanical strength of the material in the long term. Aim: To investigate in vitro the effect of different finishing and polishing regimes and low temperature degradation on flexural strength and surface topography in two types of monolithic zirconia. Method: 300 zirconia bars (Z: ice zirkon transluzent / Conventional and UT: Prettau Anterior / Ultratransluzent, zirkonzahn, Gais, Italy) were made in sizes 2.1-1.3x 2.5x10mm, sanded and sintered, (Z: Conventional; UT: Ultratransluzent), "Finishing and Polishing" - 5 levels (C- Control, B- diamond polishers, Pgrinding with burs, PB- grinding with burs + diamond polishers, PG- grinding with burs + glaze) and "Degradation" - 2 levels (WithD: autoclave at 127 ° C, 1,7 bar / 24h, without degradation). The miniflexion resistance test (3 points) was performed, with v: 1mm / min and 500N and 5000N load cells. Two samples from each group were prepared for Scanning Electron Microscopy (SEM) / X-ray Dispersive Energy Spectrometry (EDS) and Atomic Force Microscopy (AFM). The mean roughness of each group was evaluated qualitatively. Data were analyzed by ANOVA (3 factors) and Tukey (5%). Results: The "Zirconia" (p = 0.0000), "Finishing and Polishing" (p = 0.0000) and "Degradation" factors (p = 0.01) were statistically significant, ZBD (1670.2 ± 252.73)A , ZBD (1663.5 ± 216.80)A and ZB (1654.7 ± 367.79A ) and the lowest in the UT zirconia, standing out the UTPG group (372.1 ± 56.295)G . In the SEM it can be observed that the glaze layer did not cover the whole surface of the zirconia and the diamond polishers promoted a more uniform surface. The EDS showed higher amount of yttrium oxide in the UT zirconia and the AFM showed the higher Ra value was found in the roughened groups, with UT> Z. Conclusion: The most suitable protocol for finishing and polishing restorations in zirconia is the use of diamond polishers. The grinding followed by glaze reduced zirconia resistance and the use of the diamond polishers provided a more uniform surface compared to the other methods (AU).

Making yttria-stabilized tetragonal zirconia translucent.

OBJECTIVE: The aim of this study was to provide a design guideline for developing tetragonal yttria-stabilized zirconia with improved translucency. METHODS: The translucency, the in-line transmission in particular, of 3mol.% yttria-stabilized tetragonal zirconia (3Y-TZP) has been examined using the Rayleigh scattering model. The theory predicts that the in-line transmission of 3Y-TZP can be related to its thickness with grain size and birefringence the governing parameters. To achieve a threshold value of translucency, the critical grain size of 3Y-TZP was predicted for various thicknesses (0.3-2.0mm). The threshold value was defined by a measured average in-line transmission value of a suite of dental porcelains with a common thickness of 1mm. Our theoretical predictions were calibrated with one of the very few experimental data available in the literature. RESULTS: For a dense, high-purity zirconia, its in-line transmission increased with decreasing grain size and thickness. To achieve a translucency similar to that of dental porcelains, a nanocyrstalline 3Y-TZP structure was necessitated, due primarily to its large birefringence and high refractive index. Such a grain size dependence became more pronounced as the 3Y-TZP thickness increased. For example, at a thickness of 1.3mm, the mean grain size of a translucent 3Y-TZP should be 82nm. At 1.5mm and 2mm thicknesses, the mean grain size needed to be 77nm and 70nm, respectively. SIGNIFICANCE: A promising future for zirconia restorations, with combined translucency and mechanical properties, can be realized by reducing its grain size.

The influence of grain size on low-temperature degradation of dental zirconia.

UNLABELLED: The purpose of this study was to evaluate the influence of grain size and air abrasion on low-temperature degradation (LTD) of yttria stabilized tetragonal zirconia polycrystalline (Y-TZP). Disc-shaped specimens were sintered at 1350, 1450, and 1600°C. Air abrasion was performed with different abrasive particles. The specimens were stored for 2 h at 134°C under 2.3 bar water vapor pressure. All specimens were characterized by X-ray powder diffraction analysis (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and field emission scanning electron microscopy (FESEM). Y-TZP sintered at a temperature of 1350°C did not undergo the t-m phase transformation during accelerated aging. The diffusion-controlled t-m phase transformation initiated with the specimens sintered at 1450°C. This transformation was remarkable for the specimens sintered at 1600°C. X-ray photoelectron spectroscopy (XPS) measurements did not confirm the generation of Zr-OH and Y-OH bonds. No increase of yttrium concentration on the grain boundaries of Y-TZP was detected, which could be responsible for the destabilization of dental zirconia ceramics. A slight increase of diffusion-controlled t-m phase transformations was observed for all abraded specimens sintered at 1350 and 1450°C. The size of abrasive particles did not play a crucial role on LTD of Y-TZP. The retardation of diffusion-controlled t-m phase transformation was evident for all abraded specimens sintered at 1600°C by comparison to non-abraded specimens. CONCLUSION: The LTD of Y-TZP can be suppressed when the sintering temperature is set between 1350 and 1450°C.

Efeitos de diferentes tratamentos de superfície na resistência de união de um cimento resinoso à zircônia

As cerâmicas à base de zircônia (Y-TZP) apresentam propriedades mecânicas superiores às das demais cerâmicas odontológicas. Entretanto, o aumento do conteúdo cristalino modificou suas características de adesão a cimentos resinosos, tornando necessário o desenvolvimento de métodos mais efetivos de união a estes materiais. Este trabalho in vitro pretende, portanto, avaliar a influência de diferentes tratamentos de superfície e de diferentes agentes de união na resistência ao cisalhamento entre uma zircônia estabilizada por ítrio e um agente cimentante autoadesivo (RelyX U100®/3M ESPE). Para tal, cilindros de PROCERA® Allzircon receberam como tratamento de superfície jateamento com óxido de alumínio (Al2O3 - 50 µm) ou jateamento com o sistema Rocatec. Sobre a superfície tratada dos cilindros foram aplicados, de acordo com os diferentes grupos experimentais, o sistema adesivo Clearfil SE Bond® (Kuraray Co.), e os primers Metal Zirconia Primer (Ivoclar Vivadent) e Alloy Primer (Kuraray Co.) e, finalmente, o cimento resinoso adotado. Cada espécime foi, então, submetido ao teste de cisalhamento (0,05 mm/min), por meio da ação de uma alça de fio ortodôntico passando o mais próximo possível da interface adesiva. A análise de variância a um critérios (ANOVA) e o teste de Tukey (p < 0,05) mostraram que a realização do tratamento de superfície aumentou os valores de resistência de união entre a cerâmica e o cimento resinoso.

O jateamento com o sistema Rocatec (15,33 MPa) apresentou valores significantemente maiores que o jateamento com Al2O3 (11,93 MPa). A aplicação dos agentes de união resultou em uma maior resistência adesiva, sendo que o sistema adesivo Clearfill SE Bond (17,07 MPa) teve um comportamento estatisticamente superior aos demais materiais. Entre os primers, o Metal Zircônia Primer (11,26 MPa) apresentou maior valor de resistência de união que o Alloy Primer (10,01 MPa). Portanto, a associação de um tratamento superficial com um agente de união é valida, já que promoveu os maiores valores de resistência adesiva.

Yttrium-stabilized tetragonal zircon polycrystal (Y-TZP) ceramics show better mechanical properties than other dental ceramics. However, the high crystalline content modified their adhesiveness to resin cements, making it extremely necessary to develop a more effective adhesive strategy between them. This in vitro study intends to evaluate the influence of different surface treatments and different bond agents on the shear bond strength between a Y-TZP and self-adhesive resin cement. PROCERA® Allzircon cylinders (3.5 mm in diameter) received a surface airborne abrasion treatment with 50 µm aluminum-oxide (Al2O3) particles or with the Rocatec system. According to the experimental groups, the adhesive system Clearfil SE Bond® (Kuraray Co.), and the primers Metal Zirconia Primer (Ivoclar Vivadent) and Alloy Primer (Kuraray Co.) were applied on the treated surface of the cylinders, before the application of the adopted resin cement (RelyX U100®/3M ESPE). Each specimen was submitted to the shear bond strength test (0.5 mm/min), by the action of an orthodontic stainless steel ligature wire (0.5 mm in diameter) loop, wrapped around the resin cement, as close as possible to the adhesive interface. One way- ANOVA and Tukey´s post hoc tests (p < 0.05) revealed that surface treatment increased bond strength between the ceramic and the resin cement. Silica coating with the Rocatec system (15.33 MPa) showed significantly higher values than airborne abrasion with Al2O3 (11.93 MPa). Application of all bond agents improved shear bond strength: adhesive system Clearfil SE Bond (17.07 MPa) showed better performance than the other evaluated materials, and Metal Zirconia Primer (11.26 MPa) showed higher bond strength values than Alloy Primer (10.01 MPa). Therefore, the association of a surface treatment with a bond agent is suitable, once it resulted in higher values of adhesive strength.