320 research outputs found
Effect of grinding and aging on subcritical crack growth of a Y-TZP ceramic
No full textAbstract 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)
Impact of machining on the flexural fatigue strength of glass and polycrystalline CAD/CAM ceramics
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Previous issue date: 2017Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Objectives. To assess the effect of machining on the flexural fatigue strength and on the surface roughness of different computer-aided design, computer-aided manufacturing (CAD/CAM) ceramics by comparing machined and polished after machining specimens. Methods. Disc-shaped specimens of yttria-stabilized polycrystalline tetragonal zirconia (Y-TZP), leucite-, and lithium disilicate-based glass ceramics were prepared by CAD/CAM machining, and divided into two groups: machining (M) and machining followed by polishing (MP). The surface roughness was measured and the flexural fatigue strength was evaluated by the step-test method (n = 20). The initial load and the load increment for each ceramic material were based on a monotonic test (n = 5). A maximum of 10,000 cycles was applied in each load step, at 1.4 Hz. Weibull probability statistics was used for the analysis of the flexural fatigue strength, and Mann-Whitney test (alpha = 5%) to compare roughness between the M and MP conditions. Results. Machining resulted in lower values of characteristic flexural fatigue strength than machining followed by polishing. The greatest reduction in flexural fatigue strength from MP to M was observed for Y-TZP (40%; M = 536.48 MPa; MP = 894.50 MPa), followed by lithium disilicate (33%; M = 187.71 MPa; MP = 278.93 MPa) and leucite (29%; M = 72.61 MPa; MP = 102.55 MPa). Significantly higher values of roughness (Ra) were observed for M compared to MP (leucite: M = 1.59 mu m and MP = 0.08 mu m; lithium disilicate: M = 1.84 mu m and MP = 0.13 mu m; Y-TZP: M = 1.79 mu m and MP = 0.18 mu m). Significance. Machining negatively affected the flexural fatigue strength of CAD/CAM ceramics, indicating that machining of partially or fully sintered ceramics is deleterious to fatigue strength. (C) 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.[Fraga, Sara] Univ Fed Santa Maria, Postgrad Program Dent Sci, Santa Maria, RS, Brazil[Amaral, Marina] Universidade de Taubaté (Unitau), Postgrad Program Dent[Bottino, Marco Antonio] Sao Paulo State Univ, Dept Dent Mat & Prosthodont, Sao Jose Dos Campos, SP, Brazil[Valandro, Luiz Felipe; May, Liliana Gressler] Univ Fed Santa Maria, Dept Restorat Dent, Santa Maria, RS, Brazil[Kleverlaan, Cornelis Johannes] Univ Amsterdam, Acad Ctr Dent Amsterdam ACTA, Dept Dent Mat, Amsterdam, Netherlands[Kleverlaan, Cornelis Johannes] Vrije Univ Amsterdam, Amsterdam, Netherland
Resin microtensile bond strength to feldspathic ceramic: Hydrofluoric acid etching vs tribochemical silica coating
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Previous issue date: 2007This study aimed to compare the microtensile bond strength of resin cement to alumina-reinforced feldspathic ceramic submitted to acid etching or chairside tribochernical silica coating. Ten blocks of Vitadur-alpha were randomly divided into 2 groups according to conditioning method: (1) etching with 9.6% hydrofluoric acid or (2) chairside tribochemical silica coating. Each ceramic block was luted to the corresponding resin composite block with the resin cement (Panavia F). Next, bar specimens were produced for microtensile testing. No significant difference was observed between the 2 experimental groups (Student t test, P > .05). Both surface treatments showed similar microtensile bond strength values.Univ Fed Santa Maria, Sch Dent, Dept Restorat Dent, Div Prosthodont, BR-97015372 Santa Maria, RS, Brazil; Sao Paulo State Univ, Sao Jose Campos Dent Sch, Sao Paulo, Brazil; Universidade de Taubaté (Unitau), Sch Dent, MS Grad Program; Sao Paulo State Univ, Sao Jose Campos Dent Sch, Dept Dent Mat & Prosthodont, Sao Jose Dos Campos, Brazi
Fatigue limit of monolithic Y-TZP three-unit-fixed dental prostheses: Effect of grinding at the gingival zone of the connector
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Previous issue date: 2017Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)United States National Institutes of Health, National Institute of Dental and Craniofacial Research [2R01 DE017925]Objectives: To determine the fatigue failure loads of three-unit monolithic zirconia fixed dental prosthesis (FDPs) before and after grinding of the gingival areas of connectors with diamond burs. Material and methods: FDPs were milled from pre-sintered blocks of zirconia simulating the absence of the first mandibular molar. Half of the specimens were subjected to grinding, simulating clinical adjustment, and all of them were subjected to glazing procedure. Additional specimens were manufactured for roughness analysis. FDPs were adhesively cemented onto glass-fiber reinforced epoxy resin abutments. Fatigue failure loads and standard deviations were obtained using a staircase fatigue method (n=20, 100,000 loading cycles/5Hz). The initial test load was 70% of the mean load-to-fracture (n=3) and load increments were 5% of the initial test load for both the control and ground specimens. Data were compared by Student's T-test (a <= 0.05). Results: Both the control and ground groups exhibited similar values of load-to-fracture and fatigue failure loads. Neither the surface treatments nor ageing affected the surface roughness of the specimens. Conclusions: The damage induced by grinding with fine-grit diamond bur in the gingival area of the connectors did not decrease the fatigue failure load of the three-unit monolithic zirconia FDP.[Amaral, Marina] Universidade de Taubaté (Unitau), Dept Dent, Dent Prosthesis[Villefort, Regina F.; Melo, Renata Marques; Bottino, Marco Antonio] Sao Paulo State Univ, Sch Dent, Post Grad Program Restorat Dent, Prosthet Dent Unit, Sao Jose Dos Campos, SP, Brazil[Pereira, Gabriel K. R.; Valandro, Luiz Felipe] Univ Fed Santa Maria, Sch Dent, Post Grad Program Dent Sci, Prosthet Dent Unit, Santa Maria, RS, Brazil[Zhang, Yu] NYU, Coll Dent, Dept Biomat & Biomimet, 433 First Ave, New York, NY US
Newer vs. older CAD/CAM burs: Influence of bur experience on the fatigue behavior of adhesively cemented simplified lithium-disilicate glass-ceramic restorations
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Previous issue date: 2019This study evaluated the effect of the CAD/CAM burs experience (newer vs older as consequence of the milling sequence) on fatigue failure load (FFL), number of cycles for failure (CFF), and survival rates of lithium disilicate glass-ceramic simplified restorations adhesively cemented to a dentin analogue substrate. Three sets of CAD/CAM burs were used to mill disc-shaped ceramic specimens (1 bur set - 18 milled discs with 10 mm diameter and 1.5 mm thickness), considering the bur experience as a result of the milling sequence to compose the study groups: G1-6 - discs obtained from the 1st to 6th milling of each bur set; G7-12 - specimens from the 7th to 12th milling; G13-18 - discs from the 13th to 18th. Discs of dentin analogue (G10, 10 mm diameter and 2.0 mm thickness) were made to serve as substrate (base material) and randomly assigned into pairs with the respective ceramic discs. Then, the ceramic discs were adhesively cemented onto the dentin analogue substrate, composing a three-layer specimen that mimics a monolithic restoration of a posterior tooth. Specimens were tested under stepwise fatigue approach: frequency = 20 Hz, 5000 cycles at maximum load of 400 N to accommodate the testing assembly, followed by incremental steps of 200 N with initial load ranging from 10 to 1000 N, to a maximum of 20,000 cycles/each step, until the occurrence of failure (radial crack). FFL and CFF were recorded at the end of the testing and subjected to statistical analysis. Supplementary roughness analysis of the milled surface was performed (n = 18) using a contact profilometer. Residual stress after milling and acid etching were accessed via X-ray Diffractometry analysis. FFL and CFF were not affected by increase on bur experience (no statistical differences among groups), despite that, it affected both Ra and Rz parameters (G1-6 had the smoothest surface). The residual stress concentration was negligible (milling did not induce residual stress concentration). It is concluded that the fatigue behavior of adhesively cemented lithium-disilicate glass-ceramic restorations was not influenced by CAD/CAM bur experience (newer vs older as consequence of the milling sequence), and so the residual stress concentration induced by milling was negligible.[de Andrade, Guilherme Schmitt; Diniz, Vandeberg; Datte, Carlos Eduardo; Bottino, Marco Antonio; de Melo, Renata Marques] Sao Paulo State Univ Unesp, Inst Sci & Technol, Dept Dent Mat & Prosthodont, Sao Jose Dos Campos, Brazil[Venturini, Andressa Bonin; Valandro, Luiz Felipe] Fed Univ Santa Maria UFSM, Fac Odontol, Prosthodont Unit, Oral Sci, Floriano Peixoto 1184, BR-97015372 Santa Maria, RS, Brazil[Rocha Pereira, Gabriel Kalil] Merid Fac IMED, Sch Dent, Passo Fundo, RS, Brazil[Amaral, Marina] Universidade de Taubaté (Unitau) , Dept Dent Prosthet Dent[Bastos Campos, Tiago Moreira] Aeronaut Technol Inst ITA, Dept Phys, Sao Jose Dos Campos, Brazi
Evaluation of marginal leakage after mechanical fatigue cycling of composite inlays luted with different cements
No full textThis in vitro study evaluated the marginal microleakage of composite inlays luted with 3 different cement systems. The null hypothesis was that the luting materials would not influence dye penetration, showing the same degree of microleakage. Thirty-six sound molars were selected, mesio-occlusodistal cavities were prepared, and the teeth were randomly divided into 3 groups (n = 12). Composite resin inlay restorations were made and cemented using a dual-curing resin cement (Calibra), a light-curing flowable composite (Charisma Flow), or a self-adhesive resin cement (RelyX Unicem). The restored teeth were subjected to fatigue cycles and immersed in 0.5% basic fuchsin dye for 24 hours. Two orthogonal cuts were made to enable evaluation of dye penetration at the cervical and occlusal margins. The sections were evaluated with a 4-point scale ranging from 0 (no penetration) to 3 (penetration up to the cavity floor [occlusal margins] or axial wall [cervical margins]). The Calibra and Charisma Flow groups showed greater microleakage, notably at the cervical margins, whereas RelyX Unicem specimens showed the least dye penetration. Significant differences were found between the Calibra and Charisma Flow groups and between the Charisma Flow and RelyX Unicem groups (P < 0.05). No statistically significant differences were detected between the Calibra and RelyX Unicem groups. The microleakage associated with the flowable composite was significantly greater than that associated with both resin cements, results that discourage its use for luting of Class II composite inlays
Fatigue strength of several dental ceramics indicated for CAD-CAM monolithic restorations
No full textAbstract This in vitro study evaluated the fatigue strength of different ceramic materials indicated for monolithic restorations. Disc-shaped specimens were made according to ISO 6872 from five different ceramic materials: feldspathic ceramic (FC), polymer-infiltrated ceramic network (PIC), lithium disilicate glass-ceramic (LD), zirconia-reinforced lithium silicate glass-ceramic (ZLS), and high translucent tetragonal zirconia polycrystals doped by yttrium (YZ-HT). After obtaining the mean of each material (n = 5) from monotonic load-to-failure tests, specimens (n = 20) were subjected to fatigue tests (staircase method) using a biaxial flexural setup (piston-on-three-balls), to determine the fatigue strength. The parameters used for fatigue tests were: 100,000 cycles at 10 Hz, initial load of ~ 60% of mean load-to-failure, and step size of 5% of the initial load (specific for each ceramic material). Kruskal-Wallis and Bonferroni’s test (α = 0.05) were used to analyze the fatigue strength data. Fatigue strength (MPa) of the materials was statistically different among each other as follows: YZ-HT (370.2 ± 38.7) > LD (175.2 ± 7.5) > ZLS (152.1 ± 7.5) > PIC (81.8 ± 3.9) > FC (50.8 ± 1.9). Thus, it can be concluded that, in terms of fatigue, high translucent polycrystalline zirconia is the best choice for monolithic restorations as it bears the highest load before cracking/fracturing
External Marginal Gap Variation and Residual Fracture Resistance of Composite and Lithium-Silicate CAD/CAM Overlays after Cyclic Fatigue over Endodontically-Treated Molars
No full textThe purpose of this in vitro study was to evaluate the external marginal gap variation with a 3D quantitative method and the residual fracture resistance after cyclic fatigue in endodontically treated molars restored with overlays of different materials, with and without fiber posts-supported buildups. Forty-eight human maxillary molars were selected, endodontically treated, prepared with standardized MOD cavities and randomly allocated into 6 study groups considering the “core strategy” (build-up with composite resin; build-up with composite resin supported by a fiber post); and the “restorative material” of the indirect adhesive overlay (GrandioBlocks, Voco; Cerasmart, GC; CeltraDuo, Dentsply). All procedures were executed according with manufacturers guidelines. Micro-CT analysis prior and after cyclic fatigue were executed, followed by scanning electron microscope analysis and fracture resistance test. The Two-Way ANOVA analysis showed that interfacial gap progression was significantly influenced by the “core strategy” (p < 0.01) but not of “restorative material” (p = 0.59). Concerning fracture resistance, “restorative material” was statistically significant (p < 0.01), while “core strategy” (p = 0.63) and the interaction (p = 0.84) were not. In conclusion, the fiber post presence within the build-up promoted a lower interfacial gap opening after fatigue, evaluated through micro-CT scans. In terms of fracture resistance, teeth restored with Cerasmart and Celtra Duo were statistically similar, but superior to GrandioBlocks
Effect of the frequency of mechanical pulses for fatigue aging testing on push-out bond strength between glass fiber posts and root dentin
No full textThe aim of this study was to evaluate the influence of the frequency of mechanical pulses during mechanical fatigue aging on bond strength between glass fiber posts and root dentin. Fiber posts were adhesively cemented in 30 bovine roots and the core was built up with composite. All specimens were subjected to mechanical cycling (45 degrees angle; 37 degrees C; 50N; 2x10(6) pulses) at different frequencies: 2, 4, and 8Hz. After the fatigue, each specimen was submitted to push out test. The bond strength was calculated for data analysis (one-way ANOVA, p=0.05). The frequency did not affect the push-out (p=0.7). The main failure mode was between dentin and cement in all groups. The mechanical pulses were not influenced by the bond strength between root dentin and fiber posts. Thus, it is possible to decrease the time-consuming in vitro tests involving posts without damaging the reliability of the test
Efeito da ciclagem mecânica sobre a resistência de união de pinos intra-radiculares de fibra cimentados com resina à dentina
No full textEste estudo avaliou o efeito da ciclagem mecânica sobre a resistência de união de pinos intra-radiculares de fibra cimentados com resina à dentina. As hipóteses desse trabalho são que a resistência adesiva não varia após o teste de fadiga e também não varia em função do tipo de pino de fibra. A parte coronária de 60 dentes humanos unirradiculares foi seccionada, obtendo-se espécimes (sp) de 16mm, que foram submetidos à instrumentação endodôntica e então 30 sp foram preparados (12mm) para receber um pino de fibra de quartzo (D.T. Light-Post) [DT] e 30 foram preparados para um pino de fibra de vidro (FRC Postec Plus) [FRC]. Os pinos foram cimentados (All-Bond + cimento resinoso Duolink) e a parte radicular dos sp foi embutida em resina epóxica até 3mm da porção cervical. Foram constituídos 6 grupos (n=10), considerando o tipo de pino de fibra e o regime de ciclagem mecânica (carga: 50 N; 45° em relação ao longo eixo do sp; freqüência: 8Hz): G1- DT + sem ciclagem; G2- DT + 20.000 ciclos; G3- DT + 2.000.000 ciclos; G4- FRC + sem ciclagem; G5- FRC + 20.000 ciclos; G6- FRC + 2.000.000 ciclos. Os sp foram então seccionados perpendicularmente ao longo eixo do sp,obtendo-se fatias de aproximadamente 2mm (4 secções / sp) que foram submetidas ao ensaio de push-out em máquina de ensaio universal (1mm.min-1). A média de resistência adesiva das repetições de cada espécime foi obtida e os dados (n=10) foram submetidos à análise estatística (a=0,05). A ANOVA mostrou que: (a) as resistências adesivas do pino DT (7,12 l 2,20 MPa) e do pino FRC (6,87 l 2,12 MPa) foram estatisticamente semelhantes entre si (P=0,665); (b) os valores obtidos para a condição sem ciclagem (6,96 l 2,44 MPa), 20.000 (6,99 l 2,08 MPa) e 2.000.000 (7,02 l 2,00 MPa) foram similares estatisticamente (P=0,996); (c) os 6 grupos foram estatisticamente semelhantes entre si (P=1,000)...This study evaluated the effect of the mechanical cycling on the bond strength of fiber posts resin bonded to root dentin. The tooth crown of the 60 single-rooted human teeth was cut, leaving a 16-mm long root specimens (sp) that were endondontically treated and the space prepared in 12mm. Thirty sp received a quartz fiber post (D.T. Light-Post) and 30 sp received a glass fiber post (FRC Postec Plus). The posts were resin luted in the post space and each sp was embedded with epoxy resin (resin 285, Schaller, Florence, Italy) in a PVC cylinder (height: 25 mm, diameter: 10 mm). Sp were divided into 6 groups, considering the fiber post type and number of the mechanical cycles (load: 50 N; angle of 45°; frequency: 8Hz): G1- DT + without cycling; G2- DT + 20,000 cycles; G3- DT + 2,000,000 cycles; G4- FRC + without cycling; G5- FRC + 20,000 cycles; G6- FRC + 2,000,000 cycles. The sp were cut perpendicular to their long axis, to form 2-mm-thick disk-samples (4 sections / sp), which were submitted to the push-out test (1mm.min-1). The mean bond strength values were calculated for each tooth (n=10) and data were statistical analyzed (a=.05). ANOVA revealed that: (a) the bond strengths of DT (7,12 l 2,20 MPa) and of FRC (6,87 l 2,12 MPa) were statistically similar (P=0,665); (b) the mean values for the without cycling groups (6,96 l 2,44 MPa), 20,000 cycles groups (6,99 l 2,08 MPa) and 2,000,000 cycles groups (7,02 l 2,00 MPa) were not statistically different (P=0,996); (c) the 6 groups were not statistically different (P=1,000). It was concluded that the mechanical cycling did not affect the bond strength of two fiber posts resin bonded to dentin.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES
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