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M V Swain - One of the best experts on this subject based on the ideXlab platform.
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microstructure phase content and thermal stability of a cast co cr dental alloy after Porcelain sintering cycles using electron backscatter diffraction
Journal of Materials Research, 2015Co-Authors: Kai Chun Li, David J Prior, Neil J Waddell, M V SwainAbstract:Phase maps of Co–Cr alloys bonded to dental Porcelain cycled through an incremental number of Porcelain firings at two separate thicknesses (0.5 and 1 mm) were analyzed. Bulk hexagonal close-packed (hcp) phase vol% of the alloy was found to increase with the number of Porcelain firings for both 0.5 and 1 mm specimens. At the metal-Porcelain interface, a uniform fine-grained hcp phase was observed. The depth and grain size of this hcp layer increased with the number of Porcelain firings with the thicker specimens undergoing more substantial growth and transformation. Simple heat transfer modeling of the specimens during heat treatment cycles indicated that the thicker specimen had more time at high temperature to affect the face-centered cubic to hcp phase transformation. Therefore, the amount of Porcelain firings and the thickness of the alloy should be considered and kept to a minimal when manufacturing metal-Porcelain restoration.
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adhesion determination of dental Porcelain to zirconia using the schwickerath test strength vs fracture energy approach
Acta Biomaterialia, 2014Co-Authors: P Kosyfaki, M V SwainAbstract:Two approaches to measure the fracture energy to delaminate four different Porcelains from zirconia substrates are compared using Schwickerath adhesion strength test specimens. In all instances it was possible to stably extend the crack along or adjacent to the Porcelain-zirconia interface. The fracture energy expended to delaminate the Porcelain was found by determining the work of fracture upon loading to 12 N and then unloading. Additional tests were undertaken on specimens notched along the interface, which enabled the compliance of the cracked Schwickerath specimens to be calibrated. The strain energy and deflection of the Schwickerath specimen as a function of crack length were derived. On this basis a simple expression was determined for the strain energy release rate or interfacial fracture toughness from the minima in the force-displacement curves. Consequently two measures of the adhesion energy were determined, the work of fracture and the strain energy release rate. It was found that the ranking for the four Porcelains bonded to zirconia differed depending upon the approach. The work of fracture was substantially different from the strain energy release rate for three of the Porcelain-zirconia systems and appears to be directly related to the residual stresses present in the bonded structures. The relative merits of the strain energy release rate, work of fracture vs. the stress to initiate cracking in the case of the Schwickerath adhesion test, are discussed. The advantage of this test is that it enables three estimates of the adhesion for Porcelain veneers bonded to zirconia.
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cracking of Porcelain surfaces arising from abrasive grinding with a dental air turbine
Journal of Prosthodontics, 2011Co-Authors: Chee W Chang, Neil J Waddell, M V Swain, Karl LyonsAbstract:Purpose: The purpose of this in vitro study was to evaluate Porcelain cracking induced by abrasive grinding with a conventional dental air turbine and abrasive diamond burs. Materials and Methods: Four commercially available Porcelains were examined—Wieland ALLUX, Wieland ZIROX, IPS e.max Ceram, and IPS Empress Esthetic Veneering Porcelain. Sixty discs of each Porcelain type were fabricated according to manufacturer instructions, followed by an auto-glaze cycle. Abrasive grinding using fine, extra-fine, and ultra-fine diamond burs was carried out, using a conventional dental air turbine. The grinding parameters were standardized with regard to the magnitude of the force applied, rotational speed of the diamond bur, and flow rate of the water coolant. A testing apparatus was used to control the magnitude of force applied during the grinding procedure. The ground surfaces were then examined under scanning electron microscope. Results: Cracking was seen for all Porcelain types when ground with the fine bur. Cracking was not seen for specimens ground with the extra-fine or the ultra-fine bur. Conclusion: Wet abrasive grinding with a conventional dental air turbine and fine grit diamond burs has the potential to cause cracking in the four Porcelain types tested. Similar abrasive grinding with smaller grit size particles does not cause similar observable cracking.
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effect of chromium interlayer on the shear bond strength between Porcelain and pure titanium
Dental Materials, 2010Co-Authors: Shaymaa E Elsaka, Ibrahim M Hamouda, Yehia A Elewady, Ossama B Abouelatta, M V SwainAbstract:Abstract Objective This study evaluated the effect of a chromium interlayer deposited by electroplating on the shear bond strength between titanium and Porcelain. Methods Seventy specimens of machined commercially pure titanium (CP Ti) plates grade II (10 mm × 10 mm × 1 mm) were prepared. The specimens were divided into three groups according to the concentration of electroplating solution, Gr I (control without electroplating, n = 10), Gr II (5%, w/v, of chromium nitrate solution, n = 30) and Gr III (10%, w/v, of chromium nitrate solution, n = 30). Groups II and III were further divided into three subgroups (n = 10) according to the electroplating time (0.5, 1 and 2 h). Two titanium-Porcelains (Vita Titankeramik and Triceram) were applied to each subgroup (n = 5). The titanium–Porcelain interfaces were loaded under shear in a universal testing machine (crosshead speed: 0.5 mm/min) until failure occurred. Failure types were examined with stereomicroscope and the titanium–Porcelain interface examined by SEM. Data were analyzed using ANOVA and Tukey's test. Results Bond strength values were significantly affected by the type of electroplating treatment (P 0.05). The CP Ti/Vita Titankeramik (0.5 h, 10%, w/v) and the CP Ti/Triceram (0.5 h 5%, w/v) groups showed the highest bond strength (MPa) (26.72 ± 5.78 and 25.48 ± 4.14) respectively among the groups. Stereomicroscope and SEM images showed that chromium interlayer enhanced the bond strength between Porcelain and titanium. Significance Bond strength between Porcelain and CP Ti can be improved by the use of chromium interlayer prior to Porcelain firing.
Dean Morton - One of the best experts on this subject based on the ideXlab platform.
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the effect of core material veneering Porcelain and fabrication technique on the biaxial flexural strength and weibull analysis of selected dental ceramics
Journal of Prosthodontics, 2012Co-Authors: Carlo Ercoli, Changyong Feng, Dean MortonAbstract:Purpose: The objective of this study was to compare the effect of veneering Porcelain (monolithic or bilayer specimens) and core fabrication technique (heat-pressed or CAD/CAM) on the biaxial flexural strength and Weibull modulus of leucite-reinforced and lithium-disilicate glass ceramics. In addition, the effect of veneering technique (heat-pressed or powder/liquid layering) for zirconia ceramics on the biaxial flexural strength and Weibull modulus was studied. Materials and Methods: Five ceramic core materials (IPS Empress Esthetic, IPS Empress CAD, IPS e.max Press, IPS e.max CAD, IPS e.max ZirCAD) and three corresponding veneering Porcelains (IPS Empress Esthetic Veneer, IPS e.max Ceram, IPS e.max ZirPress) were selected for this study. Each core material group contained three subgroups based on the core material thickness and the presence of corresponding veneering Porcelain as follows: 1.5 mm core material only (subgroup 1.5C), 0.8 mm core material only (subgroup 0.8C), and 1.5 mm core/veneer group: 0.8 mm core with 0.7 mm corresponding veneering Porcelain with a powder/liquid layering technique (subgroup 0.8C-0.7VL). The ZirCAD group had one additional 1.5 mm core/veneer subgroup with 0.7 mm heat-pressed veneering Porcelain (subgroup 0.8C-0.7VP). The biaxial flexural strengths were compared for each subgroup (n = 10) according to ISO standard 6872:2008 with ANOVA and Tukey's post hoc multiple comparison test (p≤ 0.05). The reliability of strength was analyzed with the Weibull distribution. Results: For all core materials, the 1.5 mm core/veneer subgroups (0.8C-0.7VL, 0.8C-0.7VP) had significantly lower mean biaxial flexural strengths (p < 0.0001) than the other two subgroups (subgroups 1.5C and 0.8C). For the ZirCAD group, the 0.8C-0.7VL subgroup had significantly lower flexural strength (p= 0.004) than subgroup 0.8C-0.7VP. Nonetheless, both veneered ZirCAD groups showed greater flexural strength than the monolithic Empress and e.max groups, regardless of core thickness and fabrication techniques. Comparing fabrication techniques, Empress Esthetic/CAD, e.max Press/CAD had similar biaxial flexural strength (p= 0.28 for Empress pair; p= 0.87 for e.max pair); however, e.max CAD/Press groups had significantly higher flexural strength (p < 0.0001) than Empress Esthetic/CAD groups. Monolithic core specimens presented with higher Weibull modulus with all selected core materials. For the ZirCAD group, although the bilayer 0.8C-0.7VL subgroup exhibited significantly lower flexural strength, it had highest Weibull modulus than the 0.8C-0.7VP subgroup. Conclusions: The present study suggests that veneering Porcelain onto a ceramic core material diminishes the flexural strength and the reliability of the bilayer specimens. Leucite-reinforced glass-ceramic cores have lower flexural strength than lithium-disilicate ones, while fabrication techniques (heat-pressed or CAD/CAM) and specimen thicknesses do not affect the flexural strength of all glass ceramics. Compared with the heat-pressed veneering technique, the powder/liquid veneering technique exhibited lower flexural strength but increased reliability with a higher Weibull modulus for zirconia bilayer specimens. Zirconia-veneered ceramics exhibited greater flexural strength than monolithic leucite-reinforced and lithium-disilicate ceramics regardless of zirconia veneering techniques (heat-pressed or powder/liquid technique).
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the effect of core material veneering Porcelain and fabrication technique on the biaxial flexural strength and weibull analysis of selected dental ceramics
Journal of Prosthodontics, 2012Co-Authors: Carlo Ercoli, Changyong Feng, Dean MortonAbstract:Purpose: The objective of this study was to compare the effect of veneering Porcelain (monolithic or bilayer specimens) and core fabrication technique (heat-pressed or CAD/CAM) on the biaxial flexural strength and Weibull modulus of leucite-reinforced and lithium-disilicate glass ceramics. In addition, the effect of veneering technique (heat-pressed or powder/liquid layering) for zirconia ceramics on the biaxial flexural strength and Weibull modulus was studied. Materials and Methods: Five ceramic core materials (IPS Empress Esthetic, IPS Empress CAD, IPS e.max Press, IPS e.max CAD, IPS e.max ZirCAD) and three corresponding veneering Porcelains (IPS Empress Esthetic Veneer, IPS e.max Ceram, IPS e.max ZirPress) were selected for this study. Each core material group contained three subgroups based on the core material thickness and the presence of corresponding veneering Porcelain as follows: 1.5 mm core material only (subgroup 1.5C), 0.8 mm core material only (subgroup 0.8C), and 1.5 mm core/veneer group: 0.8 mm core with 0.7 mm corresponding veneering Porcelain with a powder/liquid layering technique (subgroup 0.8C-0.7VL). The ZirCAD group had one additional 1.5 mm core/veneer subgroup with 0.7 mm heat-pressed veneering Porcelain (subgroup 0.8C-0.7VP). The biaxial flexural strengths were compared for each subgroup (n = 10) according to ISO standard 6872:2008 with ANOVA and Tukey's post hoc multiple comparison test (p≤ 0.05). The reliability of strength was analyzed with the Weibull distribution. Results: For all core materials, the 1.5 mm core/veneer subgroups (0.8C-0.7VL, 0.8C-0.7VP) had significantly lower mean biaxial flexural strengths (p < 0.0001) than the other two subgroups (subgroups 1.5C and 0.8C). For the ZirCAD group, the 0.8C-0.7VL subgroup had significantly lower flexural strength (p= 0.004) than subgroup 0.8C-0.7VP. Nonetheless, both veneered ZirCAD groups showed greater flexural strength than the monolithic Empress and e.max groups, regardless of core thickness and fabrication techniques. Comparing fabrication techniques, Empress Esthetic/CAD, e.max Press/CAD had similar biaxial flexural strength (p= 0.28 for Empress pair; p= 0.87 for e.max pair); however, e.max CAD/Press groups had significantly higher flexural strength (p < 0.0001) than Empress Esthetic/CAD groups. Monolithic core specimens presented with higher Weibull modulus with all selected core materials. For the ZirCAD group, although the bilayer 0.8C-0.7VL subgroup exhibited significantly lower flexural strength, it had highest Weibull modulus than the 0.8C-0.7VP subgroup. Conclusions: The present study suggests that veneering Porcelain onto a ceramic core material diminishes the flexural strength and the reliability of the bilayer specimens. Leucite-reinforced glass-ceramic cores have lower flexural strength than lithium-disilicate ones, while fabrication techniques (heat-pressed or CAD/CAM) and specimen thicknesses do not affect the flexural strength of all glass ceramics. Compared with the heat-pressed veneering technique, the powder/liquid veneering technique exhibited lower flexural strength but increased reliability with a higher Weibull modulus for zirconia bilayer specimens. Zirconia-veneered ceramics exhibited greater flexural strength than monolithic leucite-reinforced and lithium-disilicate ceramics regardless of zirconia veneering techniques (heat-pressed or powder/liquid technique).
Robert R Seghi - One of the best experts on this subject based on the ideXlab platform.
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effect of different high palladium metal ceramic alloys on the color of opaque and dentin Porcelain
Journal of Prosthetic Dentistry, 2004Co-Authors: Minos Stavridakis, Med Dent, Efstratios Papazoglou, William M. Johnston, Robert R Seghi, William A BrantleyAbstract:Abstract Statement of problem The color of dental Porcelain depends on the type of metal substrate. Little research has been done to document the effects of different types of high-palladium alloys on the color of dental Porcelain. Purpose The purpose of this in vitro study was to evaluate the effects of different high-palladium alloys on the resulting color of dentin Porcelain, as well as on that of opaque Porcelain after simulated dentin and glazing firing cycles. Material and methods Three Pd-Cu-Ga alloys, Spartan Plus (S), Liberty (B), and Freedom Plus (F), and 5 Pd-Ga alloys, Legacy (L), IS 85 (I), Protocol (P), Legacy XT (X), and Jelenko No.1 (N), were examined. A Pd-Ag alloy, Super Star (T), was included for comparison to the high-palladium alloys, and the Au-Pd alloy, Olympia (O), served as the control. Six cast discs (16 × 1 mm) were prepared from each of the alloys. Shade B1 opaque Porcelain (Vita-Omega) was applied at a final thickness of 0.1 mm. After 2 opaque Porcelain firing cycles, the surfaces were airborne-particle abraded, and the specimens were divided into 2 groups. In the first group, 0.9 mm of B1 dentin Porcelain was applied. The other group of specimens with only opaque Porcelain underwent the same dentin Porcelain and glazing firing cycles. Color differences (ΔE) were determined with a colorimeter between the control and each experimental group, after the second opaque Porcelain, second dentin Porcelain, and glazing firing cycles. One-way analysis of variance and Dunnett's multiple range test were performed on the ΔE data (α=.05). Results After the application of dentin Porcelain, the 3 Pd-Cu-Ga alloys showed significantly different ( P P P Conclusions The Pd-Cu-Ga alloys with only opaque Porcelain, after the simulated dentin Porcelain and glazing firing cycles, exhibited clinically unacceptable color differences. The application of dentin Porcelain to the Pd-Cu-Ga alloys resulted in clinically acceptable color differences. The application of dentin Porcelain to the Pd-Ag alloy, after the glazing firing cycle, resulted in clinically acceptable color differences (approximately 2.8 to 3.7 ΔE CIELAB units). The Pd-Ag alloy specimens with only opaque Porcelain did not exhibit significant color differences from the control group, whereas significant color differences from the control group after the dentin Porcelain and glazing firing cycles were still clinically acceptable.
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effect of different high palladium metal ceramic alloys on the color of opaque and dentin Porcelain
Journal of Prosthetic Dentistry, 2004Co-Authors: Minos Stavridakis, Med Dent, Efstratios Papazoglou, William M. Johnston, Robert R Seghi, William A BrantleyAbstract:Abstract Statement of problem The color of dental Porcelain depends on the type of metal substrate. Little research has been done to document the effects of different types of high-palladium alloys on the color of dental Porcelain. Purpose The purpose of this in vitro study was to evaluate the effects of different high-palladium alloys on the resulting color of dentin Porcelain, as well as on that of opaque Porcelain after simulated dentin and glazing firing cycles. Material and methods Three Pd-Cu-Ga alloys, Spartan Plus (S), Liberty (B), and Freedom Plus (F), and 5 Pd-Ga alloys, Legacy (L), IS 85 (I), Protocol (P), Legacy XT (X), and Jelenko No.1 (N), were examined. A Pd-Ag alloy, Super Star (T), was included for comparison to the high-palladium alloys, and the Au-Pd alloy, Olympia (O), served as the control. Six cast discs (16 × 1 mm) were prepared from each of the alloys. Shade B1 opaque Porcelain (Vita-Omega) was applied at a final thickness of 0.1 mm. After 2 opaque Porcelain firing cycles, the surfaces were airborne-particle abraded, and the specimens were divided into 2 groups. In the first group, 0.9 mm of B1 dentin Porcelain was applied. The other group of specimens with only opaque Porcelain underwent the same dentin Porcelain and glazing firing cycles. Color differences (ΔE) were determined with a colorimeter between the control and each experimental group, after the second opaque Porcelain, second dentin Porcelain, and glazing firing cycles. One-way analysis of variance and Dunnett's multiple range test were performed on the ΔE data (α=.05). Results After the application of dentin Porcelain, the 3 Pd-Cu-Ga alloys showed significantly different ( P P P Conclusions The Pd-Cu-Ga alloys with only opaque Porcelain, after the simulated dentin Porcelain and glazing firing cycles, exhibited clinically unacceptable color differences. The application of dentin Porcelain to the Pd-Cu-Ga alloys resulted in clinically acceptable color differences. The application of dentin Porcelain to the Pd-Ag alloy, after the glazing firing cycle, resulted in clinically acceptable color differences (approximately 2.8 to 3.7 ΔE CIELAB units). The Pd-Ag alloy specimens with only opaque Porcelain did not exhibit significant color differences from the control group, whereas significant color differences from the control group after the dentin Porcelain and glazing firing cycles were still clinically acceptable.
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relative wear of enamel opposing low fusing dental Porcelain
Journal of Prosthodontics, 2003Co-Authors: Nancy L Clelland, Vaishali Agarwala, Lisa A Knobloch, Robert R SeghiAbstract:PURPOSE: This study evaluated the wear of human enamel opposing 5 low-fusing dental Porcelains and a traditional feldspathic control. In a second experiment, the repeatability of the test method and the effect of ceramic overfiring on enamel wear were also evaluated. MATERIALS AND METHODS: Five low-fusing dental Porcelains--Finesse (FI), Rhapsody (RP), IPS d.Sign (DS), Omega 900 (OM), and Duceram LFC (LFC)--and 1 traditional feldspathic Porcelain--VMK 68 (VMK)--were formed into disks (n = 10) and used as substrate for the wear test. Enamel was harvested from extracted human molars and machined into cusps with a 5-mm spherical radius (n = 60). The Oregon Health Sciences University oral wear simulator was used to simulate chewing and the size of the resulting enamel wear facets (in mm(2)) were evaluated after a specified number of chewing cycles. A portion of the experiment was duplicated to assess the repeatability of the data and determine the effects of overfiring on enamel wear. Data were subjected to analysis of variance and post hoc tests to determine significant differences. After wear testing, scanning electron micrographs were made using representative ceramic samples from each group. RESULTS: The results indicate that none of the low-fusing ceramics resulted in significantly less wear than the VMK control. In fact, 3 of the low-fusing Porcelains (OM, RP, LFC) resulted in significantly greater enamel wear than VMK. Enamel wear was not significantly affected (p = 0.29) by the increased ceramic firing temperature. Wear data were repeatable, with no significant difference (p = 0.56) between the enamel wear from 2 separate experiments. The results from both experiments indicated that ceramic material significantly affected enamel wear (p <0.001). There was significantly less enamel wear opposite DS than LFC. CONCLUSIONS: This work suggests that variations in ceramic composition and microstructure may affect the opposing enamel wear, but that low-fusing temperatures do not necessarily guarantee low enamel wear. Although the clinical relevance of this testing apparatus may be questioned, the testing method was repeatable.
Paulo Francisco Cesar - One of the best experts on this subject based on the ideXlab platform.
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flexural strength and failure modes of layered ceramic structures
Dental Materials, 2011Co-Authors: M Borba, H N Yoshimura, Paulo Francisco Cesar, M D Araujo, Erick De Lima, Jason A Griggs, Alvaro Della BonaAbstract:Abstract Objective To evaluate the effect of the specimen design on the flexural strength ( σ f ) and failure mode of ceramic structures, testing the hypothesis that the ceramic material under tension controls the mechanical performance of the structure. Methods Three ceramics used as framework materials for fixed partial dentures (YZ – Vita In-Ceram YZ; IZ – Vita In-Ceram Zirconia; AL – Vita In-Ceram AL) and two veneering Porcelains (VM7 and VM9) were studied. Bar-shaped specimens were produced in three different designs ( n = 10): monolithic, two layers (Porcelain-framework) and three layers (TRI) (Porcelain-framework-Porcelain). Specimens were tested for three-point flexural strength at 1 MPa/s in 37 °C artificial saliva. For bi-layered design, the specimens were tested in both conditions: with Porcelain (PT) or framework ceramic (FT) layer under tension. Fracture surfaces were analyzed using stereomicroscope and scanning electron microscopy (SEM). Young's modulus ( E ) and Poisson's ratio ( ν ) were determined using ultrasonic pulse-echo method. Results were statistically analyzed by Kruskal–Wallis and Student–Newman–Keuls tests. Results Except for VM7 and VM9, significant differences were observed for E values among the materials. YZ showed the highest ν value followed by IZ and AL. YZ presented the highest σ f . There was no statistical difference in the σ f value between IZ and IZ-FT and between AL and AL-FT. σ f values for YZ-PT, IZ-PT, IZ-TRI, AL-PT, AL-TRI were similar to the results obtained for VM7 and VM9. Two types of fracture mode were identified: total and partial failure. Significance The mechanical performance of the specimens was determined by the material under tension during testing, confirming the study hypothesis.
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effect of temperature and heating rate on the sintering of leucite based dental Porcelains
Ceramics International, 2011Co-Authors: Catia Fredericci, H N Yoshimura, Andre Luiz Molisani, Marcelo Mendes Pinto, Paulo Francisco CesarAbstract:Abstract The aim of this work was to determine the effect of temperature and heating rate on the densification of four leucite-based dental Porcelains: two low-fusion (Dentsply–Ceramco and Ivoclar) and two high-fusion commercial Porcelains (Dentsply–Ceramco). Porcelain powders were characterized by differential thermal analysis (DTA), X-ray diffraction (XRD), particle size distribution, helium picnometry, and by scanning electron microscopy. Test specimens were sintered from 600 to 1050 °C, with heating rates of 55 °C/min and 10 °C/min. The bulk density of the specimens was measured by the Archimedes method in water, and microstructures of fracture surfaces were analyzed by scanning electron microscopy (SEM). The results showed that densification of specimens increased with the increase in temperature. The increase in the heating rate had no effect on the densification of the Porcelains studied. Both high-fusion materials and one of the low-fusing Porcelains reached the maximum densification at a temperature that was 50 °C lower than that recommended by the manufactures.
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influence of leucite content on slow crack growth of dental Porcelains
Dental Materials, 2008Co-Authors: Paulo Francisco Cesar, Carla Castiglia Gonzaga, H N Yoshimura, Fabiana N Soki, V I StyopkinAbstract:Abstract Objectives To determine the stress corrosion susceptibility coefficient, n , of seven dental Porcelains (A: Ceramco I; B: Ceramco-II; C: Ceramco-III; D: d.Sign; E: Cerabien; F: Vitadur-Alpha; and G: Ultropaline) after aging in air or artificial saliva, and correlate results with leucite content (LC). Methods Bars were fired according to manufacturers’ instructions and polished before induction of cracks by a Vickers indenter (19.6 N, 20 s). Four specimens were stored in air/room temperature, and three in saliva/37 °C. Five indentations were made per specimen and crack lengths measured at the following times: ∼0; 1; 3; 10; 30; 100; 300; 1000 and 3000 h. The stress corrosion coefficient n was calculated by linear regression analysis after plotting crack length as a function of time, considering that the slope of the curve was [2/(3 n + 2)]. Microstructural analysis was performed to determine LC. Results LC of the Porcelains were 22% (A and B); 6% (C); 15% (D); 0% (E and F); and 13% (G). Except for Porcelains A and D, all materials showed a decrease in their n values when stored in artificial saliva. However, the decrease was more pronounced for Porcelains B, F, and G. Ranking of materials varied according to storage media (in air, Porcelain G showed higher n compared to A, while in saliva both showed similar coefficients). No correlation was found between n values and LC in air or saliva. Significance Storage media influenced the n value obtained for most of the materials. LC did not affect resistance to slow crack growth regardless of the test environment.
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influence of ph on slow crack growth of dental Porcelains
Dental Materials, 2008Co-Authors: Marcelo Mendes Pinto, Paulo Francisco Cesar, Vinicius Rosa, H N YoshimuraAbstract:Abstract Objectives To evaluate the effect of pH of storage medium on slow crack growth (SCG) parameters of dental Porcelains. Methods Two Porcelains were selected: with (UD) and without (VM7) leucite particles, in order to assess if the microstructure would affect the response of the material to the pH variation. Disc specimens were produced following manufacturers’ instructions. Specimens were stored in artificial saliva in pHs 3.5, 7.0 or 10.0 for 10 days and after that the fatigue parameters ( n : SCG susceptibility coefficient and σ 0 : scaling parameter) were obtained by the dynamic fatigue test using the same pH of storage. Microstructural analysis of the materials was also performed. Results For VM7, the values of n obtained in the different pHs were similar and varied from 29.9 to 31.2. The σ 0 value obtained in pH 7.0 for VM7 was higher than that obtained in the other pHs, which were similar. For Porcelain UD, n values obtained in pHs 7.0 and 10.0 were similar (40.8 and 39.6, respectively), and higher than that obtained in pH 3.5 (26.5). With respect to σ 0 , the value obtained for Porcelain UD in pH 10.0 was lower than those obtained in pHs 3.5 and 7.0, which were similar. Significance The effect of pH on the stress corrosion susceptibility ( n ) depended on the Porcelain studied. While the n value of VM7 was not affected by the pH, UD presented lower n value in acid pH. For both Porcelains, storage in acid or basic pH resulted in strength degradation.
H N Yoshimura - One of the best experts on this subject based on the ideXlab platform.
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flexural strength and failure modes of layered ceramic structures
Dental Materials, 2011Co-Authors: M Borba, H N Yoshimura, Paulo Francisco Cesar, M D Araujo, Erick De Lima, Jason A Griggs, Alvaro Della BonaAbstract:Abstract Objective To evaluate the effect of the specimen design on the flexural strength ( σ f ) and failure mode of ceramic structures, testing the hypothesis that the ceramic material under tension controls the mechanical performance of the structure. Methods Three ceramics used as framework materials for fixed partial dentures (YZ – Vita In-Ceram YZ; IZ – Vita In-Ceram Zirconia; AL – Vita In-Ceram AL) and two veneering Porcelains (VM7 and VM9) were studied. Bar-shaped specimens were produced in three different designs ( n = 10): monolithic, two layers (Porcelain-framework) and three layers (TRI) (Porcelain-framework-Porcelain). Specimens were tested for three-point flexural strength at 1 MPa/s in 37 °C artificial saliva. For bi-layered design, the specimens were tested in both conditions: with Porcelain (PT) or framework ceramic (FT) layer under tension. Fracture surfaces were analyzed using stereomicroscope and scanning electron microscopy (SEM). Young's modulus ( E ) and Poisson's ratio ( ν ) were determined using ultrasonic pulse-echo method. Results were statistically analyzed by Kruskal–Wallis and Student–Newman–Keuls tests. Results Except for VM7 and VM9, significant differences were observed for E values among the materials. YZ showed the highest ν value followed by IZ and AL. YZ presented the highest σ f . There was no statistical difference in the σ f value between IZ and IZ-FT and between AL and AL-FT. σ f values for YZ-PT, IZ-PT, IZ-TRI, AL-PT, AL-TRI were similar to the results obtained for VM7 and VM9. Two types of fracture mode were identified: total and partial failure. Significance The mechanical performance of the specimens was determined by the material under tension during testing, confirming the study hypothesis.
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effect of temperature and heating rate on the sintering of leucite based dental Porcelains
Ceramics International, 2011Co-Authors: Catia Fredericci, H N Yoshimura, Andre Luiz Molisani, Marcelo Mendes Pinto, Paulo Francisco CesarAbstract:Abstract The aim of this work was to determine the effect of temperature and heating rate on the densification of four leucite-based dental Porcelains: two low-fusion (Dentsply–Ceramco and Ivoclar) and two high-fusion commercial Porcelains (Dentsply–Ceramco). Porcelain powders were characterized by differential thermal analysis (DTA), X-ray diffraction (XRD), particle size distribution, helium picnometry, and by scanning electron microscopy. Test specimens were sintered from 600 to 1050 °C, with heating rates of 55 °C/min and 10 °C/min. The bulk density of the specimens was measured by the Archimedes method in water, and microstructures of fracture surfaces were analyzed by scanning electron microscopy (SEM). The results showed that densification of specimens increased with the increase in temperature. The increase in the heating rate had no effect on the densification of the Porcelains studied. Both high-fusion materials and one of the low-fusing Porcelains reached the maximum densification at a temperature that was 50 °C lower than that recommended by the manufactures.
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influence of leucite content on slow crack growth of dental Porcelains
Dental Materials, 2008Co-Authors: Paulo Francisco Cesar, Carla Castiglia Gonzaga, H N Yoshimura, Fabiana N Soki, V I StyopkinAbstract:Abstract Objectives To determine the stress corrosion susceptibility coefficient, n , of seven dental Porcelains (A: Ceramco I; B: Ceramco-II; C: Ceramco-III; D: d.Sign; E: Cerabien; F: Vitadur-Alpha; and G: Ultropaline) after aging in air or artificial saliva, and correlate results with leucite content (LC). Methods Bars were fired according to manufacturers’ instructions and polished before induction of cracks by a Vickers indenter (19.6 N, 20 s). Four specimens were stored in air/room temperature, and three in saliva/37 °C. Five indentations were made per specimen and crack lengths measured at the following times: ∼0; 1; 3; 10; 30; 100; 300; 1000 and 3000 h. The stress corrosion coefficient n was calculated by linear regression analysis after plotting crack length as a function of time, considering that the slope of the curve was [2/(3 n + 2)]. Microstructural analysis was performed to determine LC. Results LC of the Porcelains were 22% (A and B); 6% (C); 15% (D); 0% (E and F); and 13% (G). Except for Porcelains A and D, all materials showed a decrease in their n values when stored in artificial saliva. However, the decrease was more pronounced for Porcelains B, F, and G. Ranking of materials varied according to storage media (in air, Porcelain G showed higher n compared to A, while in saliva both showed similar coefficients). No correlation was found between n values and LC in air or saliva. Significance Storage media influenced the n value obtained for most of the materials. LC did not affect resistance to slow crack growth regardless of the test environment.
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influence of ph on slow crack growth of dental Porcelains
Dental Materials, 2008Co-Authors: Marcelo Mendes Pinto, Paulo Francisco Cesar, Vinicius Rosa, H N YoshimuraAbstract:Abstract Objectives To evaluate the effect of pH of storage medium on slow crack growth (SCG) parameters of dental Porcelains. Methods Two Porcelains were selected: with (UD) and without (VM7) leucite particles, in order to assess if the microstructure would affect the response of the material to the pH variation. Disc specimens were produced following manufacturers’ instructions. Specimens were stored in artificial saliva in pHs 3.5, 7.0 or 10.0 for 10 days and after that the fatigue parameters ( n : SCG susceptibility coefficient and σ 0 : scaling parameter) were obtained by the dynamic fatigue test using the same pH of storage. Microstructural analysis of the materials was also performed. Results For VM7, the values of n obtained in the different pHs were similar and varied from 29.9 to 31.2. The σ 0 value obtained in pH 7.0 for VM7 was higher than that obtained in the other pHs, which were similar. For Porcelain UD, n values obtained in pHs 7.0 and 10.0 were similar (40.8 and 39.6, respectively), and higher than that obtained in pH 3.5 (26.5). With respect to σ 0 , the value obtained for Porcelain UD in pH 10.0 was lower than those obtained in pHs 3.5 and 7.0, which were similar. Significance The effect of pH on the stress corrosion susceptibility ( n ) depended on the Porcelain studied. While the n value of VM7 was not affected by the pH, UD presented lower n value in acid pH. For both Porcelains, storage in acid or basic pH resulted in strength degradation.
