Evaluating mechanical and surface properties of zirconia-containing composites: 3D printing, subtractive, and layering techniques.

This study assessed the monotonic and fatigue flexural strength (FS), elastic modulus (E), and surface characteristics of a 3D printed zirconia-containing resin composite compared to subtractive and conventional layering methods. Specimens, including discs (n = 15; Ø = 15 mm × 1.2 mm) and bars (n = 15; 14 × 4 × 1.2 mm), were prepared and categorized into three groups: 3D printing (3D printing - PriZma 3D Bio Crown, Makertech), Subtractive (Lava Ultimate blocks, 3M), and Layering (Filtek Z350 XT, 3M). Monotonic tests were performed on the discs using a piston-on-three-balls setup, while fatigue tests employed similar parameters with a frequency of 10 Hz, initial stress at 20 MPa, and stress increments every 5000 cycles. The E was determined through three-point-bending test using bars. Surface roughness, fractographic, and topographic analyses were conducted. Statistical analyses included One-way ANOVA for monotonic FS and roughness, Kruskal-Wallis for E, and Kaplan-Meier with post-hoc Mantel-Cox and Weibull analysis for fatigue strength. Results revealed higher monotonic strength in the Subtractive group compared to 3D printing (p = 0.02) and Layering (p = 0.04), while 3D Printing and Layering exhibited similarities (p = 0.88). Fatigue data indicated significant differences across all groups (3D Printing < Layering < Subtractive; p = 0.00 and p = 0.04, respectively). Mechanical reliability was comparable across groups. 3D printing and Subtractive demonstrated similar E, both surpassing Layering. Moreover, 3D printing exhibited higher surface roughness than Subtractive and Layering (p < 0.05). Fractographic analysis indicated that fractures initiated at surface defects located in the area subjected to tensile stress concentration. A porous surface was observed in the 3D Printing group and a more compact surface in Subtractive and Layering methods. This study distinguishes the unique properties of 3D printed resin when compared to conventional layering and subtractive methods for resin-based materials. 3D printed shows comparable monotonic strength to layering but lags behind in fatigue strength, with subtractive resin demonstrating superior performance. Both 3D printed and subtractive exhibit similar elastic moduli, surpassing layering. However, 3D printed resin displays higher surface roughness compared to subtractive and layering methods. The study suggests a need for improvement in the mechanical performance of 3D printed material.

A brief review on fatigue test of ceramic and some related matters in Dentistry.

The characteristics of dental ceramics have been extensively studied over the years to provide highly qualified materials for use in prosthetic restorations. The ability to adhere to dental substrates, outstanding aesthetics (translucency, color, and substrate masking ability) and improved mechanical properties provide these materials with optical features and high strength to withstand masticatory stimuli. Different classifications are adopted, and it is generally considered that glass-ceramics have better optical characteristics due to the high glass content, and polycrystalline ceramics have superior strength favored by their densified and organized crystals, hampering crack growth. This knowledge was largely built-up during years of scientific research through different testing methodologies, but mainly employing static loads. It is important to not only take into account the intensity of loads that these materials will be exposed to, but also the effect of the intermittence of cyclic load application leading to mechanical fatigue and the influence of factors related to the crack origin and their propagation under this condition. Furthermore, the bonding surface of ceramic restorations requires surface treatments that improve the bond strength to luting agents; however, these treatments require caution because of their potential to produce defects and affect the structural behavior. Moreover, ceramic restorations often require internal adjustments for proper seating or external adjustments for fitting the occlusal contact with the antagonist. In this sense, finishing/polishing protocols may alter the defect population, as luting agents may also interact by filling in the superficial defects on the restoration intaglio surface. Thus, the balance among all these factors will define the performance of a restorative setup, as well as the posterior exposure to the humid environment and the masticatory stimuli (cyclical loading), which may favor developing slow and subcritical growth of cracks in ceramic materials and the degradation of the bond interface. Therefore, it is essential that the concepts which explain the fatigue mechanism are understood, as well as the crack propagation and failure patterns of restorative ceramic materials.

Translucency and masking ability of a translucent zirconia with different thicknesses over dark backgrounds / Translucidez e capacidade de mascaramento de uma zircônia translúcida com diferentes espessuras sobre substratos escuros

ABSTRACT Objectives: To evaluate the translucency, contrast ratio and masking ability of a translucent zirconia with different thicknesses. Methods: Disc shaped specimens (n= 3) with 10 mm (Ø) x 1.5 mm, 1 mm and 0.7 mm (thickness) were manufactured simulating all-ceramic simplified restorations. Substrate discs (n= 2; Ø: 10 mm; thickness: 2 mm) were simulated with composite resin shades: A2 (positive control) and C4; and metal alloys: silver (Ni-Cr) and golden (Cu-Al). Optical properties of the 9 translucent zirconia specimens placed on the 3 different substrates were analyzed by a spectrophotometer. The color variation (ΔE00) between each ceramic structure over the positive control substrate (A2) and over the dark backgrounds (C4, silvery, golden) were obtained as to their ceramic masking ability and subjected to non-parametric Kruskal Wallis test (5%). The translucency parameter (TP00) and contrast ratio (CR) of the different thicknesses of the ceramic discs were also collected and analyzed by one-way ANOVA and the Tukey test (5%). Results: The translucent zirconia showed greater opacity in the thickness of 1.5 mm, although it was not statistically different between 0.7 and 1.0 mm. All dark backgrounds significantly affected the final color of the simplified restoration in all evaluated thicknesses. However, the increase in ceramic thickness showed a decrease in ΔE00 values for all substrates. Conclusion: The translucent zirconia was not able to mask the dark substrates, independent of the evaluated thickness.

RESUMO Objetivos: Avaliar a translucidez, razão de contraste e capacidade de mascaramento de uma zircônia translúcida com diferentes espessuras. Métodos: Espécimes em forma de disco (n= 3) com 10 mm (Ø) x 1,5 mm, 1 mm e 0,7 mm (espessura) foram confeccionados simulando restaurações simplificadas em cerâmica pura. Discos de substrato (n= 2; Ø: 10 mm; espessura: 2 mm) foram simulados com as cores de resina composta: A2 (controle positivo) e C4; e ligas metálicas: prata (Ni-Cr) e ouro (Cu-Al). As propriedades ópticas dos 9 espécimes de zircônia translúcida posicionados nos 3 substratos diferentes foram analisadas por um espectrofotômetro. A variação de cor (ΔE00) entre cada espécime cerâmico sobre o substrato controle positivo (A2) e sobre os fundos escuros (C4, prateado, dourado) foi calculada quanto à capacidade de mascaramento da cerâmica e submetida ao teste não paramétrico de Kruskal Wallis (5%). O parâmetro de translucidez (TP00) e a razão de contraste (CR) das diferentes espessuras dos discos cerâmicos também foram coletados e analisados por ANOVA de uma via e teste de Tukey (5%). Resultados: A zircônia translúcida apresentou maior opacidade na espessura de 1,5 mm, embora não tenha sido estatisticamente diferente entre 0,7 e 1,0 mm. Todos os fundos escuros afetaram significativamente a cor final da restauração simplificada em todas as espessuras avaliadas. No entanto, o aumento da espessura da cerâmica mostrou uma diminuição nos valores de ΔE00 para todos os substratos. Conclusão: A zircônia translúcida não foi capaz de mascarar os substratos escuros, independente da espessura avaliada.

Cyclic fatigue vs static loading for shear bond strength test of lithium disilicate and dentin substrates: A comparison of resin cement viscosities.

OBJECTIVE: To explore the effect of resin cement viscosities on the shear bond strength under static and fatigue load of lithium disilicate and dentin substrates. METHODS: Bonded tri-layer samples (lithium disilicate ceramic cylinder, resin cement, and substrate - ceramic or dentin) was performed considering 2 factors (n = 15): "resin cement viscosity" (high, HV; or low, LV) and "loading mode" (static, s-SBS; or fatigue shear bond strength, f-SBS). The specimens were subjected to s-SBS (1 mm/min, 1 kN load cell) and f-SBS (cyclic fatigue, initial load: 10 N; step-size: 5 N; 10,000 cycles/step; underwater). Failure mode, topography, and finite element analysis (FEA) were performed. RESULTS: The resin cement viscosity did not influence the s-SBS and f-SBS of lithium disilicate substrate; however, it affected the bond strength to dentin, with HV presenting the worst fatigue behavior (f-SBS = 6.89 MPa). Cyclic loading in shear testing induced a notorious detrimental effect with a relevant decrease (16-56 %) in bond strength and survival rates, except for dentin substrate and LV. Most failures were adhesive. A distinct pattern comparing the disilicate and dentin was identified and FEA demonstrated that there was a stress concentration on the top of the cement layer. SIGNIFICANCE: Cyclic fatigue loading in shear testing has detrimental effects on the adhesive behavior and survival probabilities of bonded lithium disilicate sets, regardless of resin cement viscosity. In contrast, resin cement viscosity affects the bond strength and the survival rates of dentin substrate submitted to cyclic loading mode, in which a low viscosity results in better performance.

Mechanical characterization of a multi-layered zirconia: Flexural strength, hardness, and fracture toughness of the different layers.

This study compared the flexural strength under monotonic (static - sσ) and cyclic load application (fatigue - fσ), hardness (H) and fracture toughness (KIC) of different layers of a multi-layered zirconia (IPS e.max ZirCAD MT Multi, Ivoclar). Each layer was sectioned, classified into three groups according to yttria content (4-YSZ, 4/5-YSZ and 5-YSZ), and shaped on samples for flexural strength and fracture toughness tests (bars: 1.0 × 1.0 × 11 mm); and Vickers hardness test (plates: 1.5 × 4.0 × 5.0 mm). Flexural strength under monotonic load application (sσ; n = 10) was obtained through two different devices (three-point-bending and ball-in-hole device) and fatigue flexural strength (fσ; n = 15; initial load: 10 N; step-size: 5 N; 10,000 cycles/step) was assessed using a ball-in-hole device under cyclic load application. Vickers hardness test (n = 5), fracture toughness test (n = 10), and additional analyzes (Finite Element Analysis - FEA, Energy-dispersive X-ray spectroscopy - EDS and Scanning Electron Microscopy - SEM) were also performed. No differences were found between the different devices in the monotonic flexural strength test, and FEA showed similar tensile stress distribution for the two devices. 4-YSZ showed higher values of flexural strength under monotonic and cyclic load application modes (sσ = 1114.73 MPa; fσ = 798.84 MPa), and fracture toughness (KIC = 3.90 MPa√m). 4/5-YSZ had an intermediate sσ; however, fσ was similar to 5-YSZ (404.00-429.36 MPa) and KIC similar to 4-YSZ (KIC = 3.66 MPa√m). No statistical differences were found for hardness and Weibull modulus for fatigue flexural strength data. The amount of yttria in the layer compositions increased from 4-YSZ to 5-YSZ, and larger zirconia crystals were observed in the topographic images of 5-YSZ. Failures in the flexural strength and toughness tests started from the face subjected to tensile stress. Different layers of the multi-layered zirconia blank presented distinct mechanical properties. 4-YSZ (cervical layer) presented the highest flexural strength under monotonic and cyclic loads (fatigue), and higher fracture toughness even similar to the transition layer (4/5-YSZ). Hardness was similar between the layers. The ball-in-hole device performed similarly to the three-point bending device and can be used as an alternative to the traditional method.

In-lab simulation of CAD/CAM grinding and intaglio surface treatments of 4YSZ monolithic restorations: Effect on its load-bearing capacity under fatigue.

OBJECTIVES: To evaluate the effect of in-lab simulation of CAD/CAM grinding and intaglio surface treatments on the surface characteristics (topography and roughness) and fatigue behavior of adhesively luted 4YSZ simplified restorations. METHODS: Ceramic discs (Ø = 10 mm, thickness = 1 mm) were randomly allocated into 6 groups considering: "In-lab simulation of CAD/CAM grinding" (ground or polished) and "intaglio surface treatments": Ctrl (without surface treatment), AlOx (aluminum oxide air abrasion) or GLZ (glaze spray application). The surface roughness of all samples was measured, the treated discs received a ceramic primer, were luted with resin cement onto a dentin analogue material (woven glass-reinforced epoxy resin) and tested under a cyclic fatigue test (step-stress approach, n = 15; 1.4 Hz, 10,000 cycles/step, step-size of 100N starting at 200N until failure). A complementary analysis was performed to corroborate the findings in the fatigue test that the glaze fill defects increase the mechanical properties of the ceramic. To do so, bars (n= 10; 1.0 × 1.0 × 12 mm; considering the groups: N-ID: non-indented; ID: indented; ID-GLZ: indented plus glaze spray application) were indented in a vickers hardness tester to produce a crack pattern, treated with glaze or not, and then submitted to flexural strength tests (FS). Fractographic and topographic analysis were performed. RESULTS: In-lab simulation of CAD/CAM grinding decreased the fatigue failure load of the 4YSZ ceramic when comparing polished and ground groups, regardless of surface treatment. GLZ induced better fatigue performance compared to the air abrasion, regardless of the grinding condition (ground or polished surface). The results of the flexural strength test corroborated the findings in the fatigue test, as the ID-GLZ group presented superior FS than the ID group, however both had inferior FS than N-ID. There is an inverse association between roughness and fatigue failure load, as the higher the surface roughness, the lower the fatigue failure load. Failures in the fatigue and flexural strength tests started from the face subjected to tensile stresses. CONCLUSION: In-lab simulation of CAD/CAM grinding had a detrimental effect on the fatigue behavior of 4YSZ and glaze spray induced better 4YSZ performance compared to the air abrasion. The intaglio surface treatments differently influenced the 4YSZ fatigue performance, however, only glaze spray can reverse the damage caused by the grinding.

Masking ability of implant abutment substrates by using different ceramic restorative systems.

STATEMENT OF PROBLEM: Information regarding the masking ability of ceramic crowns over different implant abutment materials is scarce. PURPOSE: The purpose of this in vitro study was to evaluate the masking ability of different monolithic or bilayer ceramic materials with different thicknesses over substrates indicated for implant restorations by using opaque and translucent evaluation pastes. MATERIAL AND METHODS: Disk-shaped specimens, shade A1 (VITA Classic; Ø10×1.5 to 2.5 mm), of different ceramics (a bilayer system [yttria-stabilized zirconia infrastructure+porcelain veneer: Zir+Pc] and monolithic systems [lithium disilicate under low, medium, or high translucency: LtLD, MtLD, or HtLD, respectively, and a high-translucent yttria-stabilized zirconia: HtZir]) were made (n=4). The color difference (ΔE00) was assessed by using the CIEDE2000 formula and considering the different ceramic systems over 5 implant abutment materials (A1 shade Zir [Zir A1]; white Zir [White Zir]; A1 low-translucency lithium disilicate [LD]; polyetheretherketone [PEEK]; and titanium [Ti]) when using 2 different evaluation pastes (translucent or opaque). The control comparison was the restorative material positioned over the Zir A1 substrate with a translucent evaluation paste. Statistical analysis was made by using a 2-way ANOVA and Tukey post hoc tests (α=.05) for ΔE00 data considering the restorative material and luting agent factors as their association. Additionally, ΔE00 data were qualitatively analyzed considering the acceptability and perceptibility thresholds. The translucency parameter (TP00) of each restorative material was evaluated, and data were submitted to 1-way ANOVA and Tukey post hoc tests (α=.05). RESULTS: The most predictable masking ability was seen with Zir+Pc regardless of the evaluation paste used. Nevertheless, under 1.5-mm thickness, Zir+Pc did not adequately mask Ti (ΔE00>1.77). Most monolithic ceramics did not mask discolored substrates (PEEK or Ti, ΔE00>1.77). The exception was HtZir, which presented acceptable masking ability over PEEK at 2.5-mm thickness with both evaluation pastes (ΔE00<1.77). Regardless of the restorative material thickness, Zir+Pc showed the lowest (P<.05) TP00 values (TP00=3.45 at 1.5-mm thickness; TP00=2.00 at 2.5-mm thickness), and HtLD presented the highest (P<.05, TP00=23.50 at 1.5-mm thickness; TP00=13.36 at 2.5-mm thickness). HtZir showed similar TP00 to MtLD at 1.5-mm thickness and similar TP00 to Zir+Pc when used at 2.5-mm thickness (P>.05). CONCLUSIONS: Monolithic ceramics should be used with caution over discolored implant abutments. Bilayer systems (Zir+Pc) were the most predictable approach to adequately masking discolored substrates such as PEEK or Ti. An increased restoration thickness provided higher masking ability for all restorative materials tested.

Surface Treatments and Adhesives Used to Increase the Bond Strength Between Polyetheretherketone and Resin-based Dental Materials: A Scoping Review.

PURPOSE: To identify and discuss the available surface treatments and adhesives for polyetheretherketone (PEEK) to increase its bond strength to resin-based materials used in dentistry. MATERIALS AND METHODS: The reporting of this scoping review was based on PRISMA. The study protocol was made available at: https://osf.io/4nur9/. Studies which evaluated PEEK surface treatments and its bond strength to resin-based materials were selected. The search was performed in PubMed, Scopus, Web of Sciences and Cochrane databases. The screening was undertaken by 3 independent researchers using the Rayyan program. A descriptive analysis was performed considering study characteristics and main findings (title, data of publication, authors, PEEK characteristics, surface treatments, control group, bonded set, luting agent, specimen geometry, storage, thermocycling, pre-test failures, test geometry, failure analysis, main findings, and compliance with normative guidelines). RESULTS: The initial search yielded 1965 articles, of which 32 were included for descriptive analysis. The review showed that the use of surface treatments and adhesives are important to promote bond strength to PEEK. Up until now, various surface treatments have been explored for bond improvement to PEEK. Sulfuric acid etching is commonly reported as promoting the highest bond strength, followed by alumina-particle air abrasion. Regarding adhesives, the use of a specific adhesive containing MMA, PETIA (pentaerythritol triacrylate), and dimethacrylates yields the best adhesive performance. CONCLUSION: Sulfuric acid etching and alumina particle air abrasion followed by application of bonding agents containing MMA, PETIA and dimethacrylates are the most effective choices to increase resin-based materials' adhesion to PEEK.

Grinding and polishing of the inner surface of monolithic simplified restorations made of zirconia polycrystals and lithium disilicate glass-ceramic: Effects on the load-bearing capacity under fatigue of the bonded restorations.

This study evaluated the effect of grinding and polishing the inner surface of monolithic discs made of zirconia polycrystals (ZR) and lithium disilicate glass-ceramic (LD) on the load-bearing capacity under fatigue of the restorations bonded onto a dentin analogue material (epoxy resin). ZR and LD ceramic discs (10 mm in diameter, 1 mm in thickness) were produced and randomly allocated into 10 groups considering the internal adjustment approach: Ctrl - No adjustment; F - Grinding with fine diamond bur (46 µm); F + Pol - Grinding with fine diamond bur followed by polishing with 2 tips (finisher and polisher); FF - Grinding with extrafine diamond bur (30 µm); FF + Pol - Grinding with extrafine diamond bur followed by polishing. In addition, discs (10 mm in diameter, 2.5 mm in thickness) of fiber reinforced epoxy resin were produced. Afterwards, the intaglio surface of the ZR discs were air-abraded with 45 µm alumina particles for 10 s, the LD and resin epoxy discs were etched with hydrofluoric acid (5%/20 s and 10%/60 s, respectively), and the treated discs were primed as recommended. Each ceramic disc was luted onto the epoxy resin disc with resin cement. Then, the samples were tested under a step-stress fatigue test (20 Hz, 10,000 cycles/step, step-size of 100 N starting at 200 N, and proceeding until failure detection). Fractographic, topographic and surface roughness analysis were also performed. The adjustments (grinding with or without polishing) (ZR: 733-880 N; LD: 1040-1106 N) triggered a detrimental effect on the fatigue behavior in both ceramics compared with the absence of treatment (control group; ZR: 973 N; LD: 1406 N). The polishing step had no effect on fatigue findings. Thus, grinding the inner surface of the tested ceramics should be avoided wherever possible to prevent introducing damage and its detrimental effects on the fatigue behavior.

Influence of surface treatment of resin composite substrate on the load-bearing capacity under fatigue of lithium disilicate monolithic simplified restorations.

This study evaluated the influence of surface treatments of resin composite substrate on the fatigue behavior of adhesively cemented lithium disilicate glass-ceramic simplified restorations. CAD/CAM lithium disilicate ceramic blocks were shaped into discs (N = 60, Ø = 10 mm; thickness = 1.0 mm). Resin composite discs (N = 60, Ø = 10 mm, thickness = 2 mm) were allocated into four groups considering the "surface treatment" factor: Ctrl - no surface treatment; Bur - grinding with coarse diamond bur (#3101G, KG Sorensen); PA - etching with 37% phosphoric acid (15 s); AA - air abrasion with alumina particles (45 µm, 10 mm distance, 2.8 bars, 10 s). The surface topography, the roughness, the fractal dimension (estimated by the box-counting method) and the contact angle analyses were performed after the surface treatments. The lithium disilicate discs were etched (5% hydrofluoric acid, 20 s), silanized and adhesively cemented (Multilink N, Ivoclar Vivadent) on the resin composite discs. The samples (bonded restoration set) were subjected to a step-stress fatigue test at 20 Hz, 10,000 cycles/step with a step-size of 100 N applied on the ceramic surface, having ceramic up and resin composite down. Fractographic analysis was performed. The fatigue data (Fatigue Failure Load - FFL; and Cycles for Failure - CFF) were analyzed by Kaplan Meier with Mantel-Cox log-rank post-hoc tests (α = 0.05). No statistical difference for fatigue performance could be found among the groups (FFL means: 820-867 N; CFF means: 53,195-61,090 cycles). The bur group showed higher surface roughness and contact angle values. The PA group has the highest average fractal dimension. Therefore, the resin composite surface treatment induces topographical changes, however, it has no effect on the fatigue behavior of lithium disilicate restorations.

Load-bearing capacity under fatigue and FEA analysis of simplified ceramic restorations supported by Peek or zirconia polycrystals as foundation substrate for implant purposes.

The fatigue behavior and FEA analysis of different ceramic materials cemented over distinct substrates for implant-supported crowns were evaluated in this study. Discs of 10 mm in diameter of both restorative and substrate materials were made and randomly allocated into pairs (n = 15) considering the two study factors: 'restorative ceramic material' (1 mm thickness) - polymer-infiltrated ceramic network (PICN), lithium disilicate (LD), zirconia-reinforced lithium silicate (ZLS), or translucent zirconia (TZ); and 'foundation substrate' (2 mm thickness) - polyetheretherketone (Peek) or yttrium-stabilized zirconia (YZ). Adhesive cementation was made with a dual cure resin cement. Fatigue testing was run using the step-stress methodology: initial load of 200 N for 5000 cycles, followed by steps of 10,000 cycles starting at 400 N up to 2800 N or until failure, step size of 200 N, frequency of 20 Hz. Data were analyzed by the Kaplan Meier and log-rank post-hoc tests. Fractography analysis (stereomicroscope and SEM) and FEA were also performed. Both factors under study and their interaction statistically influenced the fatigue failure load (FFL), cycles for failure (CFF) and survival rates (p < 0.001). The restorative materials bonded to YZ had higher FFL and CFF than when adhering to Peek, while restorative materials with more crystalline content (TZ and ZLS) showed higher FFL and CFF than LD and PICN. The fractography analysis showed that all materials bonded to YZ resulted in failures starting at the occlusal surface (Hertzian cone cracks), while materials bonded to Peek had radial cracks from the ceramic-cement intaglio surface. FEA analysis showed that tensile stress concentration decreased in the intaglio surface when testing the restorative material over a stiffer (YZ) foundation substrate. In addition, the higher the restorative material's crystalline content, the more the stress is concentrated within the material (TZ > ZLS ≥ LD > PICN) when bonded to the same foundation substrate. Thus, it concluded that a stiffer foundation substrate (YZ) enhances the load-bearing capacity under fatigue of the restorative set; that restorative materials with higher crystalline content results in higher fatigue performance of the set, regardless of the foundation used; and that the foundation material influences the failure pattern of the restorative set.

Surface treatments and its effects on the fatigue behavior of a 5% mol yttria partially stabilized zirconia material.

This study evaluated the effect of distinct surface treatments on the fatigue behavior (biaxial flexural fatigue testing) and surface characteristics (topography and roughness) of a 5% mol yttria partially stabilized zirconia ceramic (5Y-PSZ). Disc-shaped specimens of 5Y-PSZ (IPS e.max ZirCAD MT Multi) were manufactured (ISO 6872-2015) and allocated into six groups (n = 15) considering the following surface treatments: Ctrl - no-treatment; GLZ - low-fusing porcelain glaze application; SNF - 5 nm SiO2 nanofilm; AlOx - aluminum oxide particle air-abrasion; SiC - silica-coated aluminum oxide particles (silica-coating); and 7%Si - 7% silica-coated aluminum oxide particles (silica-coating). The biaxial flexural fatigue tests were performed by the step-stress method (20Hz for 10,000 cycles) with a step increment of 50N starting at 100N and proceeding until failure detection. The samples were tested with the treated surface facing down (tensile stress side). Topography, fractography, roughness, and phase content assessments of treated specimens were performed. GLZ group presented the highest fatigue behavior, while AlOx presented the lowest performance, and was only similar to SiC and 7%Si. Ctrl and SNF presented intermediary fatigue behavior, and were also similar to SiC and 7%Si. GLZ promoted a rougher surface, Ctrl and SNF had the lowest roughness, while the air-abrasion groups presented intermediary roughness. No m-phase content was detected (only t and c phases were detected). In conclusion, the application of a thin-layer of low-fusing porcelain glaze, the deposition of silica nanofilms and the air-abrasion with silica-coated alumina particles had no detrimental effect on the fatigue behavior of the 5Y-PSZ, while the air-abrasion with alumina particles damaged the fatigue outcomes.

Fatigue resistance of simplified CAD-CAM restorations: Foundation material and ceramic thickness effects on the fatigue behavior of partially- and fully-stabilized zirconia.

OBJECTIVE: To evaluate the fatigue failure load, number of cycles until failure and survival probability of partially (PSZ) and fully-stabilized (FSZ) polycrystalline zirconia disc shaped specimens with different thicknesses adhesively cemented onto foundations with distinct elastic moduli. METHODS: Disc-shaped specimens (n = 15, Ø = 10 mm; thickness = 1.0 and 0.7 mm) of CAD/CAM PSZ and FSZ blocks were adhesively cemented onto discs with different foundations (Ø = 10 mm; thickness = 2.0 mm) made from epoxy resin, composite resin or Ni-Cr metallic alloy. The cemented assemblies were subjected to fatigue testing using a step-stress approach (600-2800 N; step-size of 100 N; 10,000 cycles per step; 20 Hz) and the data was submitted to specific statistical tests (α = 0.05). Fractography and finite element (FEA) analyzes were also performed. RESULTS: PSZ and FSZ presented higher fatigue failure load, number of cycles until failure and survival probabilities when cemented onto metallic alloy. All PSZ specimens survived the fatigue test when cemented onto Ni-Cr alloy (100% probability of survival at 2800 N; 230,000 cycles). Regardless of the foundation type, PSZ had better fatigue behavior than FSZ. For thickness, thinner PSZ restorations underperformed when bonded to softer foundations, while FSZ groups and groups bonded to metallic foundations had no statistical difference. SIGNIFICANCE: The foundation material strongly influences the fatigue performance of PSZ and FSZ restorations, which presented mechanical behavior improvements when bonded to a metallic foundation. PSZ restorations showed better fatigue behavior than FSZ, while the ceramic thickness only influenced PSZ restorations bonded to softer foundations.

Fatigue performance of adhesively luted glass or polycrystalline CAD-CAM monolithic crowns.

STATEMENT OF PROBLEM: Data comparing the fatigue performance of adhesively luted glass or polycrystalline ceramic systems for computer-aided design and computer-aided manufacturing (CAD-CAM) are scarce. PURPOSE: The purpose of this in vitro study was to evaluate and compare the fatigue performance of monolithic crowns manufactured from glass or polycrystalline CAD-CAM ceramic systems adhesively luted to a dentin analog. MATERIALS AND METHODS: Fifty-four pairs of standardized preparations of dentin analog (NEMA Grade G10) and simplified ceramic crowns of 1.5-mm thickness were obtained with 3 ceramic materials: lithium disilicate (LD) glass-ceramic (IPS e.max CAD); zirconia-reinforced lithium silicate (ZLS) glass-ceramic (Vita Suprinity); and translucent yttrium fully stabilized polycrystalline zirconia (Trans YZ) (Prettau Anterior). The simplified crowns (n=15) were adhesively cemented onto the preparations and subjected to step-stress fatigue test (initial load of 400 N, 20 Hz, 10 000 cycles, followed by 100-N increment steps until failure). Collected data (fatigue failure load [FFL] and cycles for failure [CFF]) were submitted to survival analysis with the Kaplan-Meier and Mantel-Cox post hoc tests (α=.05) and to Weibull analysis (Weibull modulus and its respective 95% confidence interval). Failed crowns were submitted to fractography analysis. The surface characteristics of the internal surface (roughness, fractal dimension) of additional crowns were accessed, and the occlusal cement thickness obtained in each luted system was measured. RESULTS: Trans YZ crowns presented the highest values of FFL, CFF, and survival rates, followed by ZLS and LD (mean FFL: 1740 N>1187 N>987 N; mean CFF: 149 000>92 613>73 667). Weibull modulus and cement thickness were similar for all tested materials. LD presented the roughest internal surface, followed by ZLS (mean Ra: 226 nm>169 nm>93 nm). The LD and ZLS internal surfaces also showed higher fractal dimension, pointing to a more complex surface topography (mean fractal dimension: 2.242=2.238>2.147). CONCLUSIONS: CAD-CAM monolithic crowns of Trans YZ show the best fatigue performance. In addition, ZLS crowns also showed better performance than LD crowns.

Fatigue performance of fully-stabilized zirconia polycrystals monolithic restorations: The effects of surface treatments at the bonding surface.

This study evaluated the distinct conditioning effect of the intaglio surface of bonded fully-stabilized zirconia (FSZ) simplified restorations on the mechanical fatigue behavior of the set prior to and after aging. Ceramic disc shaped specimens (Ø= 10 mm and 1 mm thick) were randomly allocated into 14 groups considering: "surface treatments" (Ctrl: no-treatment; PM: universal primer; GLZ: low-fusing porcelain glaze; SNF: 5 nm SiO2 nanofilm deposition; AlOx: air-abrasion with aluminum oxide; SiC: air-abrasion with silica-coated aluminum oxide; 7%Si: air-abrasion with 7% silica-coated aluminum oxide); and "aging" (baseline: 24 h at 37 °C in water; or aged: 90 days at 37 °C in water + 12,000 thermal cycles). The discs were treated, luted with resin cement onto the dentin analog, subjected to aging or not, and then tested under a step-stress fatigue test at 20 Hz, 10,000 cycles/step, step-size of 100N starting at 200N, and proceeding until failure detection. Fractographic, topographic, surface roughness, contact angle, and atomic force microscopy analyzes were performed. The surface treatments at baseline led to statistically similar fatigue failure loads (953N-1313N), except for GLZ (1313N), which was significantly higher than 7%Si (953 N). Meanwhile, Ctrl had 40% pre-test failures (debonding) after aging, and therefore the worst fatigue performance (notable decrease in fatigue results), while all the other groups presented superior and statistically similar fatigue behavior (973-1271N). In fact, when considering baseline Vs aging conditions, stable fatigue results could only be noted when using surface treatments. In conclusion, internal surface treatments of FSZ ceramic restorations are mandatory for fatigue behavior stability after aging the restorative set, while non-treatment induced unstable results.

Stable Resin Bonding to Y-TZP Ceramic with Air Abrasion by Alumina Particles Containing 7% Silica.

PURPOSE: To evaluate the influence of new air-abrasion powders with different silica concentrations (silica-coated aluminum oxide) and aging on the bond strength between composite cement and Y-TZP ceramic. MATERIALS AND METHODS: Ceramic slices (7 x 6.3 x 2 mm3) were randomly allocated into 8 groups (n = 20) considering different surface treatments (SiC: silica-coated aluminum oxide particles; AlOx: aluminum oxide particles; 7% Si and 20% Si: experimental powders consisting of 7% and 20% silica-coated of AlOx respectively) and aging (baseline: 24 h at 37°C in water; aged: 90 days at 37°C in water + 12,000 thermal cycles). A blinded researcher performed the air-abrasion procedure for 10 s (identical parameters for all groups). Composite resin cylinders (Ø = 3 mm) were cemented onto the silanized ceramic surfaces, light cured, and subjected to shear bond-strength testing (wire loop Ø = 0.5 mm). The topography of the powders and air-abraded surfaces was analyzed using SEM and atomic force microscopy (AFM). The elemental composition of the powders and air-abraded surfaces was analyzed with energy dispersive spectroscopy (EDS), and surface wetting of the air-abraded surfaces was also determined by contact-angle measurements. RESULTS: Under baseline conditions, all groups presented similar bond strengths, but only SiC and 7% Si yielded unaltered bond strength after aging. SiC and 7% Si presented lower contact angles. All groups presented similar surface topographies. The silica content was also similar among groups, except for AlOx. CONCLUSION: 7% Si and SiC presented similar bond strength and better bonding performance after aging than AlOx and 20% Si. A higher silica concentration was not able to promote stable adhesion of composite cement after aging.

Air-abrasion using new silica-alumina powders containing different silica concentrations: Effect on the microstructural characteristics and fatigue behavior of a Y-TZP ceramic.

This study assessed the fatigue performance (biaxial flexure fatigue strength), surface characteristics (topography and roughness) and structural stability (t-m phase transformation) of a Y-TZP ceramic subjected to air-abrasion using new powders (7% and 20% silica-coated aluminum oxide particles) in comparison to commercially available powders. Disc-shaped specimens were manufactured (ISO 6872-2015) and randomly allocated into four groups considering the air-abrasion materials: SiC: commercially available silica-coated aluminum oxide; AlOx: commercially available aluminum oxide; 7%Si and 20%Si: experimentally produced materials consisting of 7% and 20% silica-coated AlOx, respectively. Air-abrasion was executed by a blinded researcher (1 cm distance from the tip to the specimen surface, under 2.8 bar pressure for 10 s). The fatigue tests (n = 15) were performed by the staircase method under a piston-on-three-balls assembly. Topography and roughness assessments (n = 30) of abraded samples and fractography of failed discs were performed. The highest fatigue strength (MPa) was observed for 7%Si (887.20 ±â€¯50.54) and SiC (878.16 ±â€¯29.81), while the lowest fatigue strength for 20%Si (773.89 ±â€¯46.44) and AlOx (796.70 ±â€¯46.48). Topography analysis depicted similar surface morphology for all conditions. However, roughness (µm) was only statistically different between 7%Si (Ra = 0.30 ±â€¯0.09; Rz = 2.31 ±â€¯0.63) and SiC (Ra = 0.26 ±â€¯0.04; Rz = 1.99 ±â€¯0.34). Monoclinic phase grains appeared on Y-TZP surface in a similar content (≈11-12%) for the protocols. Fractography showed all failures starting on air-abraded surface/sub-surface defects from the tensile side. In terms of roughness, phase transformation and fatigue, the new 7% silica-coated aluminum oxide presented similar behavior to the commercially available powder. Increasing silica-coating concentration to 20% did not lead to a gentle air-abrasion protocol.