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.

A new approach for Y-TZP surface treatment: evaluations of roughness and bond strength to resin cemen

Abstract Objective This study aims to evaluate the effect of sonochemical treatment on the surface of yttria-stabilized tetragonal zirconia (Y-TZP) before and after the final sintering. Material and Methods Twenty-eight Y-TZP discs were divided into four groups (n=7), according to surface treatment: PRE: pre-sintering sonication with 30% nominal power for 15 min; POS: post-sintering sonication with 30% nominal power for 15 min; JAT: air abrasion with 50-μm alumina particles; and CON: control group with no treatment. The POS and JAT groups were sintered before sonication and the PRE group after sonication. Surface roughness was analyzed using confocal microscopy, after which resin cement cylinders were placed on the surface of the Y-TZP discs and subjected to mechanical microshear bond strength test until fracture. Surface roughness and microshear bond strength values underwent ANOVA and the Tukey tests. Results The surface roughness values for the PRE group (299.91 nm) and the POS group (291.23 nm) were not significantly different (p≥0.05), statistically, and the surface roughness value of the JAT group (925.21 nm) was higher than those of PRE and POS (p=0.007) groups. The mechanical microshear bond strength test showed that there was no statistically significant difference between the groups (p=0.08). Conclusions Therefore, the results showed that sonochemical treatment modifies the Y-TZP surface and is similar to the well-established sandblasting surface treatment regarding the strength of the bond with the resin cement.

Y-TZP surface treatments and their effects on the bond strength to resin cement

Aim: This study evaluated the effect of surface treatments of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics on their bond strength to a resin cement. Methods: Seventy zirconia blocks (6 × 6 × 2 mm3, IPS e.max ZirCAD) were assigned into 7 groups (n=10) ­ as-sintered (AS), no treatment; tribochemical silica coating + silanization (TBS; Cojet-sand; ProSil); airabrasion with 45 µm alumina particles + universal primer (AAP; Monobond®Plus); fusion sputtering (FS); SiO2 nanofilm + silanization (SN; ProSil); FS+SN+ silanization (FSSN; ProSil); FS+SN+Universal Primer (FSSNP; Monobond®Plus). Afterwards, a resin cement (RelyX™ ARC) was applied inside cylinders (Ø = 0.96 mm × 1 mm height) placed on the zirconia surfaces. Microshear bond strength tests (µSBS) were carried out (1 mm/min). Failure and phase transformation analysis were performed. Bond strength data (MPa) were subjected to Kruskal-Wallis/Mann Whitney tests. Results: TBS (27 ± 1.2) and AAP (24.7 ± 0.8) showed higher bond strengths than the other groups, followed by FSSNP (15.5 ± 4.2) and FSSN (13.3 ± 3.6). FS (3.4 ± 0.44) and SN (9.5 ± 2.7) showed the lowest values (p < 0.001). Most of the specimens exhibited an adhesive failure. Conclusion: Air-abrasion by silica-coated alumina particles followed by silanization or by alumina particles followed by universal primer resulted in the highest resin bond strength to zirconia. Fusion sputtering and silica nanofilm deposition induced low strengths. However, when these methods are applied in combination and with a primer (FSSN and FSSNP), higher bond strengths may be achieved. Low bond strengths are obtained when no zirconia treatment is performed

Polishing of ground y-tzp ceramic is mandatory for improving the mechanical behavior

Abstract It evaluated the effect of aging by Low Temperature Degradation (LTD), executed after post- processing surface treatments (polishing, heat treatment and glazing), on the surface characteristics (micromorphology and roughness) and on the structural stability (phase transformation and mechanical behavior-flexural strength and structural reliability) of a ground yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramic. Discs of Y-TZP (VITA In-Ceram YZ) were manufactured (ISO:6872-2015; 15 mm in diameter and 1.2 ± 0.2 mm in thickness) and randomly assigned into 10 groups according two factors: "aging" in 2 levels (with or without) and "surface treatment" in 5 levels (Ctrl: as-sintered; Gr: grinding with coarse diamond bur; Gr + HT: grinding plus heat treatment; Gr + Pol: grinding plus polishing; Gr + Gl: grinding plus glazing). Roughness (n=30), biaxial flexural test (n=30), phase transformation (n=2), and surface topography (n=2) analyses were performed. Aging led to an intense increase in monoclinic (m) phase content for all the tested conditions, being the as-sintered samples (Ctrl= 65.6%) more susceptible to the t-m phase transformation. Despite of increasing the m-phase content, aging was not detrimental for characteristic strength (except to the grinding condition). There was no significant reduction in the Weibull modulus after surface treatments. Additionally, heat treatment and glazing after grinding led to a decrease in characteristic strength, while polishing presented the highest characteristic strength values. Thus, polishing is mandatory after grinding the Y-TZP ceramic, while performing glazing or heat-treatment alone after grinding lead to the worst mechanical performance.

Resumo Este estudo avaliou o efeito do envelhecimento através da degradação a baixas temperaturas (low temperaturare degradation - LTD) após a realização de tratamentos de superfície pós- sinterização (polimento, tratamento térmico e glaze) nas características superficiais (micromorfologia e rugosidade), e na estabilidade estrutural (transformação de fase e comportamento mecânico - resistência flexural e confiabilidade estrutural) de uma cerâmica de zircônia tetragonal policristalina estabilizada por ítria (Y-TZP) desgastada. Discos de cerâmica Y-TZP (VITA In-Ceram YZ) foram confeccionados (ISO:6872-2015; 15mm de diâmetro e 1,2 ± 0,2mm de espessura) e randomicamente divididos em 10 grupos de acordo com dois fatores: "envelhecimento" (com e sem) e "tratamento de superfície" (Ctrl - sem tratamento; Gr - desgaste com ponta diamantada grossa; Gr + HT - desgaste mais tratamento térmico; Gr + Pol - desgaste mais polimento; Gr + Gl - desgaste mais glazeamento). Foram realizadas as análises de rugosidade (n=30), flexão biaxial (n=30), transformação de fase (n=2) e topografia de superfície (n=2). O envelhecimento levou a um aumento intenso no conteúdo de fase monoclínica (m) em todas as condições testadas, sendo observada uma maior susceptibilidade de transformação de fase t-m nas amostras do grupo controle (Ctrl= 65.6%). Apesar de provocar elevada transformação de fase, o envelhecimento não apresentou efeitos negativos nos desfechos avaliados. Não houve redução significativa do módulo de Weibull após os tratamentos. Além disso, o tratamento térmico e o glaze após desgaste levaram a uma redução da resistência característica, enquanto que o grupo polimento apresentou o mais alto valor de resistência característica. O glaze e o tratamento térmico geraram o pior desempenho mecânico, portanto a realização do polimento após desgaste de uma cerâmica Y-TZP é obrigatória.

Can the application of multi-mode adhesive be a substitute to silicatized/silanized y-tzp ceramics?

Abstract This study evaluated the effectiveness of a multi-mode adhesive (SBU-Scotch Bond Universal/3M) as a substitute for silica coating and silane application on the bonding of zirconia ceramics to resin cement. One-hundred and twenty sintered zirconia ceramic blocks (5 x 5 x 5 mm) were obtained, finished by grounding with silicon carbide paper (#600, #800, #1000 and #1200) and randomly divided into 12 groups (n=10) in accordance with the factors "surface treatment" (ScSi - silicatization + silanization; ScSBU - silicatization + SBU; SBU - SBU without photoactivation and SBUp - SBU photoactivated) and "ceramic" (Lava / 3M ESPE, Ceramill Zirconia / Amann Girrbach and Zirkonzahn / Zirkonzahn). Dual resin cement cylinders (RelyX Ultimate/3M ESPE) were subsequently produced in the center of each block using a silicon matrix (Ø=2 mm, h=5 mm) and photoactivated for 40 s (1200 mW/cm2). The samples were stored for 30 days in distilled water (37ºC) and submitted to shear bond strength test (1 mm/min, 100 KgF). Data (MPa) were analyzed under ANOVA (2 levels) and Tukey test (5%). Complementary analyzes were also performed. ANOVA revealed that only the factor "surface treatment" was significant (p=0.0001). The ScSi treatment (14.28A) promoted statistically higher bond strength values than the other ScSBU (9.03B), SBU (8.47B) and SBUp (7.82B), which were similar to each other (Tukey). Failure analysis revealed that 100% of the failures were mixed. The silica coating followed by the silanization promoted higher bond strength values of resin cement and ceramic, regardless of the zirconia ceramic or SBU.

Resumo Este estudo avaliou a efetividade de um adesivo "multi-mode" (Single Bond Universal/3M) como um substituto para a silicatização e aplicação do silano na resistência de união das cerâmicas de zircônia e um cimento resinoso. Para isso, 120 blocos cerâmicos sinterizados de zircônia nas dimensões de (5 x 5 x 5 mm) foram obtidos, lixados com lixas de granulação decrescente (#600, #800, #1000 e #1200) e divididos aleatoriamente em 12 grupos (n = 10), de acordo com os fatores "tratamento de superfície" (ScSi - silicatização + silanização; ScSBU - silicatização + Single Bond; SBU - SBU sem fotoativação e SBUp - SBU com fotoativação) e "cerâmica" (Lava/3M ESPE, Ceramill Zircônia/ Amann Girrbach e Zirkonzahn/Zirkonzahn). Posteriormente, cilindros de cimento resinoso dual (RelyX Ultimate/3M ESPE) foram confeccionados no centro de cada bloco com auxílio de uma matriz de silicone (Ø=2 mm; h=5 mm) e fotopolimerizados por 40 s (1200 mW/ cm²). Em seguida, as amostras foram armazenadas durante trinta dias em água destilada (37 °C) e submetidas ao ensaio de resistência de união ao cisalhamento (1 mm/min, 100 kgF). Os dados (MPa) foram analisados sob ANOVA (2 fatores) e teste de Tukey (5%). Análises complementares também foram realizadas. ANOVA revelou que apenas o fator "tratamento de superfície" foi significativo (p=0,0001). O tratamento ScSi (14.28A) promoveu valores de adesão estatisticamente superiores aos demais ScSBU (9.03B), SBU (8.47B) e SBUp (7.82B), os quais foram semelhantes entre si (Tukey). A Análise de falhas revelou que 100% da falhas que ocorreram foram mistas. A silicatização seguida da silanização promoveu a melhor resistência de união entre cimento resinoso e a cerâmica, independentemente do tipo da cerâmica ou do SBU.

Effect of Grinding and Multi-Stimuli Aging on the Fatigue Strength of a Y-TZP Ceramic

Abstract This study aimed to investigate the effect of grinding and multi-stimuli aging on the fatigue strength, surface topography and the phase transformation of Y-TZP ceramic. Discs were manufactured according to ISO-6872:2008 for biaxial flexure testing (diameter: 15 mm; thickness: 1.2 mm) and randomly assigned considering two factors "grinding" and "aging": C- control (as-sintered); CA- control + aging; G- ground; GA- ground + aging. Grinding was carried out with coarse diamond burs under water-cooling. Aging protocols consisted of: autoclave (134°C, 2 bars pressure, 20 hours), followed by storage for 365 days (samples were kept untouched at room temperature), and by mechanical cycling (106 cycles by 20 Hz under a load of 50% from the biaxial flexure monotonic tests). Flexural fatigue strengths (20,000 cycles; 6 Hz) were determined under sinusoidal cyclic loading using staircase approach. Additionally, surface topography analysis by FE-SEM and phase transformation analysis by X-ray Diffractometry were performed. Dixon and Mood methodology was used to analyze the fatigue strength data. Grinding promotes alterations of topographical pattern, while aging apparently did not alter it. Grinding triggered t-m phase transformation without impacting the fatigue strength of the Y-TZP ceramic; and aging promoted an intense t-m transformation that resulted in a toughening mechanism leading to higher fatigue strength for as-sintered condition, and a tendency of increase for ground condition (C < CA; G = GA). It concludes that grinding and aging procedures did not affect deleteriously the fatigue strength of the evaluated Y-TZP ceramic, although, it promotes surface topography alterations, except to aging, and t-m phase transformation.

Resumo Este estudo objetivou investigar o efeito do desgaste e envelhecimento (estímulos combinados) na resistência à fadiga, topografia superficial e transformação de fase de uma cerâmica Y-TZP. Discos para teste de flexão biaxial foram confeccionados segundo as normas da ISO-6872:2008 (15 mm Ø; 1,2 mm espessura) e randomicamente distribuídos de acordo com os fatores "desgaste" e "envelhecimento": C- controle (sinterizado); CA- controle envelhecido; G- desgaste; GA- desgaste envelhecido. O desgaste foi feito com pontas diamantadas de granulação grossa sob irrigação com água. Os protocolos de envelhecimento consistiram em: autoclave (134°C, 2 bar de pressão, 20 horas), 365 dias armazenados em temperatura ambiente, e ciclagem mecânica (106 ciclos a 20 Hz em um intervalo de carga de até 50% da carga monotônica observada em testes estáticos). A resistência à fadiga foi determinada para 20.000 ciclos à 6 Hz sob carregamento sinusoidal através do método de escada. Adicionalmente, análises de topografia superficial em microscopia eletrônica de varredura e de transformação de fase por difração de raios-X foram executadas. A metodologia de Dixon e Mood foi usada para analisar os dados de resistência à fadiga. Foi observado que o desgaste promove uma alteração de padrão topográfico superficial; enquanto o envelhecimento aparentemente não demonstra influência. Em relação à transformação de fase e resistência à fadiga, o desgaste desencadeou um aumento de fase m sem impactar na resistência à fadiga da cerâmica Y-TZP; já o envelhecimento promoveu uma intensa transformação de fase, resultando no mecanismo de tenacificação, que gerou um aumento na resistência à fadiga para a condição sinterizada e uma tendência a aumento na condição desgaste (C < CA; G = GA). Os dados elucidam que o desgaste e o envelhecimento não impactaram negativamente na resistência à fadiga da cerâmica Y-TZP, apesar de promoverem alterações de topografia superficial e intensa transformação de fase de t-m respectivamente.

Effect of grinding and aging on subcritical crack growth of a Y-TZP ceramic

Abstract This study aimed to investigate slow crack growth (SCG) behavior of a zirconia ceramic after grinding and simulated aging with low-temperature degradation (LTD). Complementary analysis of hardness, surface topography, crystalline phase transformation, and roughness were also measured. Disc-shaped specimens (15 mm Ø × 1.2 mm thick, n = 42) of a full-contour Y-TZP ceramic (Zirlux FC, Amherst) were manufactured according to ISO:6872-2008, and then divided into: Ctrl - as-sintered condition; Ctrl LTD - as-sintered after aging in autoclave (134°C, 2 bar, 20 h); G - ground with coarse diamond bur (grit size 181 μm); G LTD - ground and aged. The SCG parameters were measured by a dynamic biaxial flexural test, which determines the tensile stress versus stress rate under four different rates: 100, 10, 1 and 0.1 MPa/s. LTD led to m-phase content increase, as well as grinding (m-phase content: Ctrl - 0%; G - 12.3%; G LTD - 59.9%; Ctrl LTD - 81%). Surface topography and roughness analyses showed that grinding created an irregular surface (increased roughness) and aging did not promote any relevant surface change. There was no statistical difference on surface hardness among different conditions. The control group presented the lowest strength values in all tested rates. Regarding SCG, ground conditions were less susceptible to SCG, delaying its occurrence. Aging (LTD) caused an increase in SCG susceptibility for the as-sintered condition (i.e. G < G LTD < Ctrl < Ctrl LTD).

Can low-fusing glass application affect the marginal misfit and bond strength of Y-TZP crowns?

Abstract To evaluate the effect of different surface treatments on the marginal misfit and retentive strength between Y-TZP crowns and an epoxy resin. Forty (40) epoxy resin (G10) abutments (height: 5mm, conicity: 60, finish line: large chamfer) with equal dimensions were milled and included in polyurethane to simulate the periodontal ligament. Next, 40 Y-TZP crowns (thickness: 1mm) were milled (Cerec in Lab) and randomly divided into four groups (n=10) according to the surface treatment: GS(glaze spray), GP(glaze powder/liquid), P(zirconia primer) and RS(tribochemical silica coating). The conditioned surfaces were cemented with dual self-adhesive cement, light cured and submitted to thermomechanical cycling (2x106, 100N, 4Hz, 5°/55°C). Marginal misfit was analyzed by a stereomicroscope and SEM. Retentive strength test was performed (1mm/min) until crown debonding. Glaze layer thickness was also performed to GS and GP groups. Marginal misfit data were analyzed by Kruskal Wallis and Dunn tests; one-way ANOVA and Tukey (5%) analyzed the tensile strength data. The marginal misfit of the GS (48.6±19.9μm) and GP (65.4±42.5μm) were statistically lower than the RS (96±62.9μm) and P (156±113.3μm) (p=0.001). The retentive strength of the GP (470.5±104.1N) and GS (416.8±170.2N) were similar to the P (342.1±109.7N), but statistically higher than those of the RS (208.9±110N). The GS and GP glaze layer was 11.64μm and 9.73μm respectively. Thus, glaze application promoted lower marginal discrepancy and higher retentive strength values than conventional techniques.

Pre-sintered Y-TZP sandblasting: effect on surface roughness, phase transformation, and Y-TZP/veneer bond strength

Abstract Sandblasting is a common method to try to improve the Y-TZP/veneer bond strength of dental prostheses, however, it may put stress on zirconia surfaces and could accelerate the t→m phase transformation. Y-TZP sandblasting before sintering could be an alternative to improve surface roughness and bonding strength of veneering ceramic. Objectives. The aim of this study was to analyze the effect of Y-TZP pre-sintering sandblasting on surface roughness, phase transformation, and the Y-TZP/veneer shear bond strength. Material and Methods. The Y-TZP specimen surface underwent sandblasting with aluminum oxide (50 μm) pre-sintering (Z-PRE) and post-sintering (Z-POS). Z-CTR was not subjected to surface treatment. After ceramic veneer application, the specimens were subjected to shear bond testing. Surface roughness was analyzed by confocal microscopy. Y-TZP monoclinic and tetragonal phases were evaluated by micro-Raman spectroscopy. Shear bond strength and surface roughness data were analyzed by One-way ANOVA and Tukey tests (α=0.05). Differences in the wave numbers and the broadening bands of the Raman spectra were compared among groups. Results. Z-POS (9.73±5.36 MPa) and Z-PRE (7.94±2.52 MPa) showed the highest bond strength, significantly higher than that of Z-CTR (5.54±2.14 MPa). The Ra of Z-PRE (1.59±0.23 µm) was much greater and significantly different from that of Z-CTR (0.29±0.05 µm) and Z-POS (0.77±0.13 µm). All groups showed bands typical of the tetragonal (T) and monoclinic (M) phases. Y-TZP sandblasting before sintering resulted in rougher surfaces but did not increase the shear bond strength compared to post-sintering and increased surface defects. Conclusions. Surface treatment with Al3O2, regardless of the moment and application, improves the results of Y-TZP/veneer bonding and is not a specific cause of t→m transformation.

Dental ceramics: a review of new materials and processing methods

Abstract The evolution of computerized systems for the production of dental restorations associated to the development of novel microstructures for ceramic materials has caused an important change in the clinical workflow for dentists and technicians, as well as in the treatment options offered to patients. New microstructures have also been developed by the industry in order to offer ceramic and composite materials with optimized properties, i.e., good mechanical properties, appropriate wear behavior and acceptable aesthetic characteristics. The objective of this literature review is to discuss the main advantages and disadvantages of the new ceramic systems and processing methods. The manuscript is divided in five parts: I) monolithic zirconia restorations; II) multilayered dental prostheses; III) new glass-ceramics; IV) polymer infiltrated ceramics; and V) novel processing technologies. Dental ceramics and processing technologies have evolved significantly in the past ten years, with most of the evolution being related to new microstructures and CAD-CAM methods. In addition, a trend towards the use of monolithic restorations has changed the way clinicians produce all-ceramic dental prostheses, since the more aesthetic multilayered restorations unfortunately are more prone to chipping or delamination. Composite materials processed via CAD-CAM have become an interesting option, as they have intermediate properties between ceramics and polymers and are more easily milled and polished.

A study of the modification of Y-TZP and resin cement with titanium dioxide nanotubes / Estudo da modificação de Y-TZP e cimento resinoso com nanotubos de dióxido de titânio

Titanium dioxide nanotubes (TiO2) have been applied to enhance the mechanical properties of dental materials. Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) has been increasingly used in dentistry. Aside from its optimal clinical results, Y-TZP is prone to failures related to insufficient thickness of the fixed prostheses connector and debonding due to its difficult adhesion. The purpose of this study is to evaluate the effect of the addition of different concentrations of TiO2 to YTZP in its mechanical properties and microstructure, and also to evaluate the influence of these nanotubes on the bond strength when added to the ceramic or to the resin cement. To evaluate that, the described purposes were divided in two different papers. Paper 1 describes the tests of biaxial flexural strength, fractography qualitative analysis in scanning electron microscopy (SEM), microstructure evaluation in field emission-SEM and X-ray diffraction. Groups evaluated were commercial YTZP (Ivoclar Vivadent) (ZC) and an experimental Y-TZP with different blends of nanotubes [0 (Z0), 1 (Z1), 2 (Z2), and 5% (Z5), in volume]. In paper 2 shear bond strength test is described. It was carried out with the following groups: commercial YTZP (Ivoclar Vivadent) (ZC) and an experimental Y-TZP with different blends of nanotubes [0 (Z0), 1 (Z1), 2 (Z2), and 5% (Z5), in volume] bonded to the resin cement Panavia F2.0; and commercial Y-TZP bonded to resin cement RelyX U200 added with different blends of nanotubes in two curing methods dual-cured [0 (DC), 0.3 (D03), 0.6 (D06) and 0.9% (D09) of nanotubes in weigth] or self-cured [0 (SC), 0.3 (S03), 0.6 (S06) and 0.9% (S09) of nanotubes in weigth]. Values of flexural strength and shear bond strength were subjected to ANOVA and Tukey (=0.05). Flexural strength values were also subjected to Weibull statistics. Grain sizes values were subjected to Kruskal-Wallis and Dunn tests (=0.05). The flexural strength results were: ZC 896.73±122.70; Z0 577.67±62.26; Z1 477.32±75.65; Z2 492.25±63.19; Z5 437.18±53.55. The Weibull modulus results found were: ZC 7.9; Z0 11.2, Z1 8.7; Z2 8.1; Z5 9.3. Results showed that experimental Y-TZP presented lower flexural strength values than commercial one, but the first presented better Weibull modulus (m). Experimental Y-TZP also presented good microstructure, comparable to commercial Y-TZP, with very similar grain sizes. Nanotubes addition to Y-TZP led to lower flexural strength, although higher m than commercial ceramic. Pores containing Ti were observed in Y-TZP as the nanotubes concentration raised. Shear bond strength results found were, from higher to lower values: Z5 6.46±3.36; DC 6.17±0.87; D03 5.74±1.70; S03 5.73±1.71; Z1 5.16±2.62; D06 4.82±1.06; D09 4.75±1.43; SC 4.73±1.43; S09 4.61±0.85; S06 4.51±1.87; ZC 3.70±1.82; Z0 -3.33±2.05; Z2 2.94±1.38. Shear bond strength was also influenced by nanotubes addition, either in the ceramic or in the cement, although not linearly. Y-TZP added of 5% of TiO2 nanotubes presented the highest bond strength, although with no significant difference from most groups. Group Z1 was probably the group that presented the best combination of flexural strength, m, microstructure and bond strength. More studies of other properties could be carried out with this group.(AU)

Nanotubos de dióxido de titânio (TiO2) tem sido utilizados para melhorar as propriedades mecânicas de materiais odontológicos. Zircônica tetragonal policristalina estabilizada por ítria (Y-TZP) tem sido amplamente utilizada na Odontologia. Apesar de seus excelentes resultados clínicos, a Y-TZP é suscetível a falhas relacionadas à espessura insuficiente do conector da prótese fixa e a soltura da restauração devido à adesão deficiente. O objetivo desse trabalho é avaliar o efeito da adição de diferentes concentrações de nanotubos de TiO2 à Y-TZP nas suas propriedades mecânicas e microestrutura, além de avaliar a influência na resistência de união da adição desses nanotubos na cerâmica ou no cimento resinoso. Para isso, os objetivos descritos foram divididos em dois artigos diferentes. O artigo 1 descreve os testes de resistência flexural biaxial, análise fractográfica qualitativa em microscopia eletrônica de varredura (MEV), avaliação de microestrutura em MEV de emissão de campo e difração de raios-X. Os grupos avaliados foram: Y-TZP comercial (Ivoclar Vivadent) (ZC) e Y-TZP experimental com diferentes concentrações de nanotubos [0 (Z0), 1 (Z1), 2 (Z2), e 5% (Z5), em volume]. No artigo 2 está descrito o teste de resistência ao cisalhamento que foi realizado com os seguintes grupos: Y-TZP comercial (ZC) e Y-TZP experimental com diferentes concentrações de nanotubos [0 (Z0), 1 (Z1), 2 (Z2), e 5% (Z5), em volume] aderidas ao cimento Panavia F2.0; e Y-TZP comercial aderida ao cimento resinoso RelyX U200 com adição de diferentes concentrações de nanotubos em dois métodos de polimerização: dual [0 (DC), 0,3 (D03), 0,6 (D06) e 0,9% (D09) de nanotubos em peso] ou auto [0 (SC), 0,3 (S03), 0,6 (S06) e 0,9% (S09) de nanotubos em peso]. Os valores de resistência flexural e resistência ao cisalhamento foram submetidos aos testes de ANOVA e Tukey (=0,05). A resistência flexural também passou por análise de Weibull. Os valores de tamanho de grãos foram submetidos a testes de Kruskal-Wallis e Dunn (=0,05). Os resultados de resistência flexural encontrados foram: ZC 896,73±122,70; Z0 577,67±62,26; Z1 477,32±75,65; Z2 492,25±63,19; Z5 437,18±53,55. Os resultados de módulo de Weibull encontrados foram: ZC - 7,9; Z0 - 11,2; Z1 - 8,7; Z2 - 8,1; Z5 - 9,3. Os resultados mostraram que a Y-TZP experimental apresentou menores valores de resistência flexural do que a cerâmica comercial, mas a primeira apresentou maior módulo de Weibull (m). A Y-TZP experimental apresentou boa microestrutura, comparável à Y-TZP comercial, com tamanhos de grão muito semelhantes. A adição de nanotubos à Y-TZP levou a menor resistência flexural, porém maior m que a cerâmica comercial. Poros contendo Ti foram observados na Y-TZP conforme a concentração de nanotubos aumentou. Os resultados de resistência ao cisalhamento foram, do maior para o menor: Z5 - 6,46±3,36; DC - 6,17±0,87; D03 - 5,74±1,70; S03 - 5,73±1,71; Z1 - 5,16±2,62; D06 - 4,82±1,06; D09 - 4,75±1,43; SC - 4,73±1,43; S09 - 4,61±0,85; S06 - 4,51±1,87; ZC - 3,70±1,82; Z0 - 3,33±2,05; Z2 - 2,94±1,38. A resistência ao cisalhamento também foi influenciada pela adição de nanotubos, tanto na cerâmica quanto no cimento, porém não linearmente. A Y-TZP adicionada de 5% de nanotubos de TiO2 apresentou maior resistência de união, porém sem diferença estatística da maioria dos grupos. O grupo Z1 foi provavelmente o grupo que apresentou a melhor combinação de resistência flexural, m, microestrutura e resistência de união. Mais estudos de outras propriedades podem ser realizados com o mesmo.(AU)

Effect of ceramic thickness, grinding, and aging on the mechanical behavior of a polycrystalline zirconia

Abstract Monolithic restorations of Y-TZP have been recommended as a restorative alternative on prosthetic dentistry as it allows a substantial reduction of ceramic thickness, which means a greater preservation of tooth structure. However, the influence of grinding and aging when using a thinner layer of the material is unclear. This investigation aimed to evaluate and compare the effects of ceramic thickness (0.5 mm and 1.0 mm), grinding and aging (low-temperature degradation) on the mechanical behavior and surface characteristics of a full-contour Y-TZP ceramic. Y-TZP disc-shaped specimens (15 mm diameter) were manufactured with both thicknesses and randomly assigned into 4 groups considering the factors 'grinding with diamond bur' and 'aging in autoclave'. Surface topography (roughness, 3D profilometry and SEM), phase transformation, flexural strength and structural reliability (Weibull) analyses were executed. Grinding affected the surface topography, while aging did not promote any effect. An increase in m-phase content was observed after grinding and aging, although different susceptibilities were observed. Regardless of zirconia's thickness, no deleterious effect of grinding or aging on the mechanical properties was observed. Thus, in our testing assembly, reducing the thickness of the Y-TZP ceramic did not alter its response to grinding and low temperature degradation and did not impair its mechanical performance.

Mechanical behavior of yttria-stabilized tetragonal zirconia polycrystal: Effects of different aging regimens

Abstract This study aimed to characterize and compare the effect of different aging regimens on surface characteristic (topography and roughness), structural stability (phase transformation) and mechanical performance (Weibull analysis) of a Y-TZP ceramic. Discs (15 × 1.2 mm; VITA In-Ceram YZ) were prepared according to ISO 6872-2015 for biaxial flexural strength testing and randomly assigned into five groups (n = 30): as-sintered, no aging treatment (CTRL); 20 h in autoclave at 134°C, 2 bar pressure (AUT); intermittent mechanical loading at 20 Hz/106 load pulses (MechLoad); AUT followed by MechLoad (AUT+MechLoad); and storage in distilled water at 37°C, for 1 year (STO). The following analyses were performed: roughness (n = 30), surface topography (n = 2), phase transformation (n = 2) and biaxial flexure strength (n = 30). Phase transformation (increase of m-phase content) was shown to be a spontaneous, unavoidable and time-dependent process, occurring even under ambient conditions (dry storage after 1 year = 6.0% increase), and is considerably accelerated in the presence of moisture (STO = 17.6%; AUT= 63.1%; and AUT+MechLoad = 59.9%). For roughness parameters, only Ra was affected by aging, and the highest values were observed for AUT+MechLoad (0.25 ± 0.07 µm). For Weibull analysis, structural reliability (Weibull moduli) and characteristic strength were not impaired after aging, and some aging conditions led to increased values (highest weibull moduli in AUT, and highest characteristic strength in STO). Phase transformation proves to be a time-dependent spontaneous mechanism that is accelerated in the presence of different stimuli. However, none of the aging regimens had a negative effect on the characteristic strength and structural reliability of Y-TZP ceramic.

Effect of Grinding and Resintering on the Fatigue Limit and Surface Characterization of a Y-TZP Ceramic

Abstract This study evaluated the effect of grinding protocols and resintering on flexural fatigue limit and surface characterization of LavaTM Y-TZP. Bar-shaped specimens (20×4.0×1.2 mm, n=40; 20×4.0×1.5 mm, n=80) were obtained. Half of the thinner specimens (1.2 mm) constituted the as-sintered group (AS), while the thicker ones (1.5 mm) were ground with diamond burs under irrigation (WG) or not (G). The other half of thinner and half of ground specimens were resintered (1000 ºC, 30 min), forming the groups ASR, WGR and GR. Fatigue limit (500,000 cycles, 10 Hz) was evaluated by staircase method in a 4-point flexural fixture. Data were analyzed by 2-way ANOVA and Tukey's test (α=0.05). Surface topography (n=3) and fracture area (n=3) were evaluated by SEM. X-ray diffraction data (n=1) was analyzed by Rietveld refinement. ANOVA revealed significant differences (p<0.001) for the grinding protocol, resintering and their interaction. Grinding increased the fatigue limit of non-resintered groups. There was no significant difference among the resintered groups. Resintering significantly increased the fatigue limit of the AS group only. Both protocols created evident grooves on zirconia surface. The failures initiated at the tensile side of all specimens. The percentages (wt%) of monoclinic phase were AS (8.6), ASR (1.2), G (1.8), GR (0.0), WG (8.2), WGR (0.0) before, and AS (7.4), ASR (6.5), G (3.2), GR (0.2), WG (4.6), WGR (1.1) after cyclic loading. Grinding increased the fatigue limit of non-resintered Y-TZP and formed evident grooves on its surface. Resintering provided significant increase in the fatigue limit of as-sintered specimens. In general, grinding and resintering decreased or zeroed the monoclinic phase.

Resumo Este estudo avaliou o efeito de protocolos de desgaste e ressinterização no limite de fadiga flexural e na caracterização da superfície da zircônia LavaTM. Corpos-de-prova em forma de barra (20×4,0×1,2 mm, n=40; 20×4,0×1,5 mm, n=80) foram obtidos. Metade das barras com menor altura (1,2 mm) constituiu o grupo controle (AS), enquanto as de maior altura (1,5 mm) foram desgastadas com fresas diamantadas com (WG) ou sem (G) irrigação. A outra metade dos corpos-de-prova de menor altura e metade dos desgastados foram ressinterizadas (1000 °C, 30 min), obtendo-se os grupos ASR, WGR e GR. O limite de fadiga (500.000 ciclos, 10 Hz) foi avaliado pelo método de escada em dispositivo de flexão em 4 pontos. Os dados foram analisados pelos testes ANOVA a dois fatores e Tukey (α=0,05). A topografia de superfície (n=3) e área de fratura (n=3) foram avaliadas por MEV. Os dados de difração de raios-X (n=1) foram analisados pelo refinamento de Rietveld. ANOVA revelou diferenças significantes (p<0,001) para desgaste, ressinterização e interação entre os fatores. O desgaste aumentou o limite de fadiga para os grupos não ressinterizados. Não houve diferença significante entre os grupos ressinterizados. A ressinterização aumentou o limite de fadiga somente para o grupo AS. Ambos os protocolos criaram riscos evidentes na superfície da zircônia. As falhas iniciaram sempre no lado de tração. A porcentagem de fase monoclínica foi: AS (8.6), ASR (1.2), G (1.8), GR (0.0), WG (8.2), WGR (0.0) antes e AS (7.4), ASR (6.5), G (3.2), GR (0.2), WG (4.6), WGR (1.1) após a ciclagem. O desgaste aumentou o limite de fadiga da zircônia não ressinterizada e formou ranhuras evidentes na sua superfície. A ressinterização promoveu aumento significativo no limite de fadiga somente para o grupo controle. Em geral, o desgaste e a ressinterização diminuíram ou anularam o conteúdo de fase monoclínica.

Effect of grinding and heat treatment on the mechanical behavior of zirconia ceramic

Abstract The present study investigated the effect of grinding on roughness, flexural strength, and reliability of a zirconia ceramic before and after heat treatment. Seven groups were tested (n = 15): a control group (labeled CG, untreated), and six groups of samples ground with diamond discs, simulating diamond burs, with grits of 200 µm (G80); 160 µm (G120), and 25 µm (G600), either untreated or heat-treated at 1200°C for 2 h (labeled A). Yttria tetragonal zirconia polycrystal discs were manufactured, ground, and submitted to roughness and crystalline phase analyses before the biaxial flexural strength test. There was no correlation between roughness (Ra and Rz) and flexural strength. The reliability of the materials was not affected by grinding or heat treatment, but the characteristic strength was higher after abrasion with diamond discs, irrespective of grit size. The X-ray diffraction data showed that grinding leads to a higher monoclinic (m) phase content, whereas heat treatment produces reverse transformation, leading to a fraction of m-phase in ground samples similar to that observed in the control group. However, after heat treatment, only the G80A samples presented strength similar to that of the control group, while the other groups showed higher strength values. When zirconia pieces must be adjusted for clinical use, a smoother surface can be obtained by employing finer-grit diamond burs. Moreover, when the amount of monoclinic phase is related to the degradation of zirconia, the laboratory heat treatment of ground pieces is indicated for the reverse transformation of zirconia crystals.

Surface agents' influence on the flexural strength of bilaminated ceramics

The objective of this study was to evaluate the influence of different surface agents on the flexural strength of a ceramic system. Eighty bar-shaped specimens of zirconia were divided into four groups according to the agent to be used: group Control - to be cleaned with alcohol; group VM9 - application of a fluid layer of porcelain; group Effect Bonder - application of a bonding agent; and group Coloring Liquid - application of coloring liquid. All specimens received the porcelain application by the layering technique and were then subjected to thermocycling. The four-point bending test was performed to calculate the strength values (σ, MPa) and the failure modes were classified. ANOVA did not detect significant differences among the groups. The Weibull modulus were 5 (Control, VM9 and Effect Bonder) and 6 (Coloring Liquid). The cracking of the porcelain ceramic toward the interface was the predominant failure mode. It was concluded that the surface agents tested had no effect on the flexural strength of the bilaminated ceramic specimens.

Study on nano-structured hydroxyapatite/zirconia stabilized yttria on healing of articular cartilage defect in rabbit

PURPOSE: Articular Cartilage has limited potential for self-repair and tissue engineering approaches attempt to repair articular cartilage by scaffolds. We hypothesized that the combined hydroxyapatite and zirconia stabilized yttria would enhance the quality of cartilage healing. METHODS: In ten New Zealand white rabbits bilateral full-thickness osteochondral defect, 4 mm in diameter and 3 mm depth, was created on the articular cartilage of the patellar groove of the distal femur. In group I the scaffold was implanted into the right stifle and the same defect was created in the left stifle without any transplant (group II). Specimens were harvested at 12 weeks after implantation, examined histologically for morphologic features, and stained immunohistochemically for type-II collagen. RESULTS: In group I the defect was filled with a white translucent cartilage tissue In contrast, the defects in the group II remained almost empty. In the group I, the defects were mostly filled with hyaline-like cartilage evidenced but defects in group II were filled with fibrous tissue with surface irregularities. Positive immunohistochemical staining of type-II collagen was observed in group I and it was absent in the control group. CONCLUSION: The hydroxyapatite/yttria stabilized zirconia scaffold would be an effective scaffold for cartilage tissue engineering.

Implantes de zircônia reforçada com ítria (Y-TZP): avaliação histomorfométrica / Y-TZP dental implants: histomorfometry analysis

O objetivo do trabalho foi avaliar in vivo a osseointegração de implantes produzidos em zircônia reforçada com ítria (Y-TZP) e compará-los com o implante de titânio usinado e com o de superfície jateada com brushita. Para tanto, nas tíbias de 20 coelhos machos (n=10) e fêmeas (n=10) foram implantadas em uma das tíbias o implante Y-TZP (GE-1, n=10 implantes) e na outra tíbia o titânio usinado (GC, n=5 implantes) ou jateado com brushita (GE-2, n=5 implantes). Os animais receberam marcadores ósseos fluorescentes, tetraciclina (14 e 21 dias), alizarina (28 e 35 dias) e calceína (42 e 49 dias) após a cirurgia de implantação. Ao final de 56 dias, a região dos implantes foi coletada e processada histologicamente para obtenção de cortes teciduais não desmineralizados. Nas imagens obtidas no microscópio confocal foi avaliado o percentual de área para cada marcador. Nos cortes corados pelo azul de toluidina foi avaliado morfologicamente a qualidade do tecido ósseo formado e a existência de interposição de tecido conjuntivo entre osso e implante, e morfometricamente determinado o percentual de contato osso-implante (BIC) e o percentual de tecido ósseo próximo à superfície do implante (BA). Os resultados mostraram que, não houve diferenças estatisticamente significantes entre machos e fêmeas quanto aos parâmetros avaliados. Com relação aos grupos, GE-1 e GC apresentaram cortical óssea remanescente íntegra e formação de um tecido ósseo maduro/lamelar na superfície dos implantes. No GE-2 ocorreu intensa reabsorção da cortical óssea pre-existente próxima ao implante e extensa formação óssea mais imatura em relação aos observados no GE-1 e GC. Essa intensa reabsorção e extensa formação óssea fez com que o percentual de área dos marcadores fluorescentes fosse em média 0,73 vezes maior no GE-2 em relação aos grupos GE-1 e GC. Com relação ao BIC não houve diferença entre os grupos, sendo em média de 47,8%, porém, o BA no grupo GC (66,2%) foi 0,33 vezes...

The aim of this work was evaluate in vivo the osseointegration of implants produced with yttria stabilized zirconia (Y-TZP) and compare it with machined titanium implant and sandblasted surface with brushita titanium. Therefore, on the tibia of 20 rabbits males (n=10) and female (n=10) were implanted in one of the tibias the implant Y-TZP (GE-1, n=10 implants) and on the other tibia the machined titanium (GC, n=5 implants) or sandblasted surface with brushita titanium (GE-2, n=5 implants). The animals received fluorescent bone markers, tetracycline (14th and 21th days), alizarin (28th and 35th days) and calcein (42th and 49th days). At the end of 56 days, the implants regions were collected and histomorphometrically processed to obtain tissue sections not demineralized. On images obtained from confocal microscopy was evaluated the percentage of area for each bone markers. On slides stained with toluidine blue was measured morphologically the quality of formed bone tissue and the existence of interposition of connective tissue between bone and implant, and was morphometrically determined the percentage of bone-implant contact (BIC) and the percentage of bone tissue next to the implant surface (BA). The results showed that there were no statistically significant differences between male and female regarding to evaluated parameters. Concerning to the groups, GE-1 and GC exhibited wholesome remaining cortical bone and formation of mature/lamellar bone tissue on implants surface. In GE-2 ocurred intense reabsorption of preexisting cortical bone next to the implant and extensive bone formation more immature than GE-1 and GC. This intense reabsorption and extensive bone formation made the GE-2 area percentage for fluorescent markers 0.73 times higher on average when compared to GE-1 and GC. About the BIC, there were no differences between the groups, with an average of 47.8%, however, the BA on GC group (66.2%) was 0.33 higher compared to GE-1...

Reabilitação estética com a utilização de um sistema cerâmico do tipo Y-TZP: relato de caso clínico / Aesthetic rehabilitation using Y-TZP ceramic system: a case report

Materiais restauradores cerâmicos tornaram-se uma excelente alternativa em pr´teses parciais fixas (PPF), tanto em região anterior como posterior, devido aos avanços de propriedades mecânicas e estéticas. Este relato de caso clínico descreve o emprego de uma prótese parcial fixa de três unidades para a substituição de um primeiro pré-molar superior. O sistema cerâmico utilizado consiste em um processamento CAD-CAM de uma cerâmica a base zircônia estabilizada por ítrio (Y-TZP) e sua cerâmica de recobrimento. O protocolo clínico e as vantagens desta opção de tratamento são discutidos.

Influence of grinding procedures on the flexural strength of zirconia ceramics

The surface of zirconia may be damaged during grinding, influencing the mechanical properties of the material. The purpose of this study was to compare the flexural strength of zirconia after different grinding procedures. Twenty bar-type zirconia specimens (21 x 5 x 2 mm) were divided into 4 groups and ground using a high-speed handpiece or a low-speed straight handpiece until the bars were reduced 1 mm using two different grinding times: continuous grinding and short-time grinding (n=5). Control specimens (n=5) were analyzed without grinding. The flexural strengths of the bars were determined by using 3-point bending test in a universal testing machine at a crosshead speed of 0.5 mm/min. The fracture load (N) was recorded, and the data were analyzed statistically by the Kruskal Wallis test at a significance level of 0.05. In the test groups, high-speed handpiece grinding for a short time had produced the highest mean flexural strength (878.5 ± 194.8 MPa), while micromotor continuous grinding produced the lowest mean flexural strength (733.8 ± 94.2 MPa). The control group was the strongest group (928.4 ± 186.5 MPa). However, there was no statistically significant differences among the groups (p>0.05). Within the limitations of the study, there was no difference in flexural strength of zirconia specimens ground with different procedures.

A superfície da zircônia pode ser danificada durante o desgaste, influenciando as propriedades mecânicas do material. O objetivo deste estudo foi comparar a resistência à flexão da zircônia após diferentes procedimentos de desgaste. Vinte amostras de zircônia em formato de barra (21x5x2mm) foram divididos em 4 grupos e desgastados usando uma peça de mão de alta velocidade e um micromotor até as barras terem sido reduzidas 1 mm usando dois tempos diferentes de desgaste: desgaste contínuo e desgaste de curta duração (n=5). Amostras de controle (sem desgaste; n=5) foram analisadas. A resistência à flexão das barras foi determinada utilizando o ensaio de flexäo em três pontos numa máquina universal de ensaios a uma velocidade cruzeta de 0,5 mm/min. A carga de fratura (N) foi registrada, e os dados foram analisados estatisticamente com o teste Kruskal-Wallis com o nível de significância de 0,05. Não houve diferenças estatisticamente significantes entre os grupos (p>0,05). Nos grupos teste, o desgaste de curta duração usando peça de mão de alta velocidade foi o mais alto (878,5 ± 194,8 MPa), e o desgaste contínuo com o micromotor apresentou o valor mais baixo (733,8 ± 94,2 MPa). O grupo controle foi o mais forte (928,4 ± 186,5 MPa). Dentro das limitações do estudo, não houve diferença na resistência à flexão das amostras da zircônia desgastadas com procedimentos diferentes.