Opaque Layer Firing Temperature and Aging Effect on the Flexural Strength of Ceramic Fused to Cobalt-Chromium Alloy

Purpose: To evaluate the effect of the opaque layer firing temperature and mechanical and thermal cycling on the flexural strength of a ceramic fused to commercial cobalt-chromium alloy (Co-Cr). The hypotheses were that higher opaque layer temperatures increase the metal/ceramic bond strength and that aging reduces the bond strength.Materials and Methods: Metallic frameworks (25 x 3 x 0.5 mm(3); ISO 9693) (N = 60) were cast in Co-Cr and airborne-particle abraded (Al(2)O(3): 150 mu m) at the central area of the frameworks (8 x 3 mm(2)) and divided into three groups (N = 20), according to the opaque layer firing temperature: Gr1 (control)-900 degrees C; Gr2-950 degrees C; Gr3-1000 degrees C. The opaque ceramic (Opaque, Vita Zahnfabrick, Bad Sackingen, Germany) was applied, and the glass ceramic (Vita Omega 900, Vita Zahnfabrick) was fired onto it (thickness: 1 mm). While half the specimens from each group were randomly tested without aging (water storage: 37 degrees C/24 hours), the other half were mechanically loaded (20,000 cycles; 50 N load; distilled water at 37 degrees C) and thermocycled (3000 cycles; 5 degrees C to 55 degrees C, dwell time: 30 seconds). After the flexural strength test, failure types were noted. The data were analyzed using 2-way ANOVA and Tukey's test (alpha = 0.05).Results: Gr2 (19.41 +/- 5.5 N) and Gr3 (20.6 +/- 5 N) presented higher values than Gr1 (13.3 +/- 1.6 N) (p = 0.001). Mechanical and thermal cycling did not significantly influence the mean flexural strength values (p > 0.05). Increasing the opaque layer firing temperature improved the flexural bond strength values (p < 0.05). The hypotheses were partially accepted.Conclusion: Increasing of the opaque layer firing temperature improved the flexural bond strength between ceramic fused to Co-Cr alloy.

Mechanical and thermal cycling effects on the flexural strength of glass ceramics fused to titanium

This study evaluated the effects of mechanical and thermal cycling on the flexural strength (ISO 9693) of three brands of ceramics fused to commercially pure titanium (cpTi). Metallic frameworks of 25 x 3 x 0.5 mm dimensions (N = 84) were cast in cpTi, followed by 150-mu m aluminum oxide airborne particle abrasion at a designated area of the frameworks (8 x 3 mm). Bonder and opaque ceramic were applied on the frameworks, and then the corresponding ceramic (Triceram, Super Porcelain Ti-22, Vita Titankeramik) was fired onto them (thickness: 1 mm). Half of the specimens from each ceramic-metal combination were randomly tested without aging (only water storage at 37 degrees C for 24 hours), while the other half were mechanically loaded (20,000 cycles under 10 N load, immersion in distilled water at 37 degrees C) and thermocycled (3,000 cycles, between 5-55 degrees C, dwell time of 13 seconds). After the flexural strength test, failure types were noted. Mechanical and thermal cycling decreased the mean flexural strength values significantly (p<0.05) for all the three ceramic-cpTi combinations tested when compared to the control group. In all the three groups, failure type was exclusively adhesive at the opaque ceramic-cpTi interfacial zone with no presence of ceramic on the substrate surface except for a visible oxide layer.

Flexural strength of autopolymerizing denture reline resins with microwave postpolymerization treatment

Statement of problem. Microwave postpolymerization has been Suggested as a method to improve the mechanical strength of repaired denture base materials. However, the effect of microwave heating oil the flexural strength of the autopolymerizing denture reline resins has not been investigated.Purpose. This study analyzed the effect of microwave postpolymerization on the flexural strength of 4 autopolymerizing reline resins (Duraliner II, Kooliner, Ufi Gel Hard, and Tokuso Rebase Fast) and 1 heat-polymerized resin (Lucitone 550).Material and methods. For each material, 80 specimens (64 X 10 X 3.3 mm) were polymerized according to the manufacturer's instructions and divided into 10 groups (n = 8). Control group specimens remained as processed. Before testing, the specimens were Subjected to postpolymerization in a microwave oven using different power (500, 5,50, or 650 W) and time (3, 4, or 5 Minutes) settings. Load measurements (newtons) were made at a crosshead speed of 5 mm/min using a 3-point bending device with a span of 50 mill. The flexural strength values were calculated in MPa. Data analyses included 3-way and 2-way analysis of variance and the Tukey Honestly Significant Difference test (alpha=.05).Results. The flexural strengths of resins Duraliner 11 and Kooliner were significantly increased (P=.0015 and P=.0046, respectively) with the application of microwave irradiation using different time/power combinations. The materials Lucitone 550, Tokuso Rebase Fast, and Ufi Gel Hard demonstrated no significant strength improvement compared to the corresponding control. Only after microwave postpolymerization irradiation for 3 minutes at 550 W did Lucitione 550 show significantly higher flexural strength than Tokuso Rebase Fast and Ufi Gel Hard relining resins.Conclusion. Microwave postpolymerization irradiation can be an effective method for increasing the flexural strength of Duraliner II (at 650 W) and Kooliner (at 550 W and 650 W for 5 minutes).

Effect of mechanical cycling on the flexural strength of densely sintered ceramics

Objectives. The aim of this study was to evaluate the effect of mechanical cycling on the biaxial flexural strength of two densely sintered ceramic materials.Methods. Disc shaped zirconia (In-Ceram Zirconia) and high alumina (Procera AllCeram) ceramic specimens (diameter: 15 min and thickness: 1.2 mm) were fabricated according to the manufacturers' instructions. The specimens from each ceramic material (N = 40, n = 10/per group) were tested for flexural strength either with or without being subjected to mechanical cycling (20,000 cycles under 50 N load, immersion in distilled water at 37 degrees C) in a universal testing machine (1 mm/min). Data were statistically analyzed using two-way ANOVA and Tukey's test (alpha = 0.05).Results. High alumina ceramic specimens revealed significantly higher flexural strength values without and with mechanical cycling (647 +/- 48 and 630 +/- 143 MPa, respectively) than those of zirconia ceramic (497 +/- 35 and 458 +/- 53 MPa, respectively) (p < 0.05). Mechanical cycling for 20,000 times under 50 N decreased the flexural strength values for both high alumina andSignificance. High alumina ceramic revealed significantly higher mean flexural strength values than that of zirconia ceramic tested in this study either with or without mechanical cycling conditions. (C) 2005 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Evaluation of the flexural strength of carbon fiber-, quartz fiber-, and glass fiber-based posts

This study investigated the flexural strength of eight fiber posts (one carbon fiber, one carbon/quartz fiber, one opaque quartz fiber, two translucent quartz fiber, and three glass fiber posts). Eighty fiber posts were used and divided into eight groups (n = 10): G1: C-POST (Bisco); G2: ÆSTHETI-POST (Bisco); G3: ÆSTHETI-PLUS (Bisco); G4: LIGHT-POST (Bisco); G5: D.T. LIGHT-POST (Bisco); G6: PARAPOST WHITE (Coltene); G7: FIBERKOR (Pentron); G8: REFORPOST (Angelus). All of the samples were tested using the three-point bending test. The averages obtained were submitted to the ANOVA and to Tukey's test (p < 0.05). The mean values (MPa) of the groups ÆSTHETI-POST - carbon/ quartz fiber post (Bisco) and ÆSTHETI-PLUS - quartz fiber post (Bisco) were statistically similar and higher than the mean values of the other groups. The mean values of the groups C-POST - carbon fiber post (Bisco), LIGHT-POST - translucent quartz fiber post (Bisco), D.T. LIGHT-POST - double tapered translucent quartz fiber post (Bisco), PARAPOST WHITE - glass fiber post (Coltene) and FIBREKOR - glass fiber post (Pentron) were similar and higher than the group REFORPOST - glass fiber post (Angelus). Copyright © 2005 by the American Association of Endodontists.

Effect of a post-polymerization treatments on the flexural strength and vickers hardness of reline and acrylic denture base resins

This study evaluated the effect of water-bath and microwave post-polymerization treatments on the flexural strength and Vickers hardness of four autopolymerizing reline resins (Duraliner II-D, Kooliner-K, Tokuso Rebase Fast-TR and Ufi Gel Hard C-UGH) and one heat-polymerized acrylic resin (Lucitone 550-L), processed using two polymerization cycles (short cycle - 90 minutes at 73°C and 100°C for 30 minutes; and long cycle - 9 hours at 71°C). For each material, thirty specimens (64 x 10 x 3.3 mm) were made and divided into 3 groups (n=10). Specimens were tested after: processing (control group); water-bath at 55°C for 10 minutes (reline materials) or 60 minutes (L); and microwave irradiation. Flexural strength tests were performed at a crosshead speed of 5 mm/min using a three-point bending device with a span of 50 mm. The flexural strengths values were calculated in MPa. One fragment of each specimen was submitted to Vickers hardness test. Data were analyzed by 2-way ANOVA followed by Tukey's HSD test (α=0.05). L microwaved specimens (short cycle) exhibited significantly higher flexural strength means than its respective control group (p<0.05). Water-bath promoted a significant increase (p<0.05) in flexural strength of K and L (long cycle). The hardness of the tested materials was not influenced by the post-polymerization treatments. Post-polymerization treatments could be used to improve the flexural strength of some materials tested.

Influence of thermal and mechanical cycling on the flexural strength of ceramics with titanium or gold alloy frameworks

Objectives: The aim of this study was to evaluate the effect of thermal and mechanical cycling alone or in combination, on the flexural strength of ceramic and metallic frameworks cast in gold alloy or titanium. Methods: Metallic frameworks (25 mm × 3 mm × 0.5 mm) (N = 96) cast in gold alloy or commercial pure titanium (Ti cp) were obtained using acrylic templates. They were airborne particle-abraded with 150 μm aluminum oxide at the central area of the frameworks (8 mm × 3 mm). Bonding agent and opaque were applied on the particle-abraded surfaces and the corresponding ceramic for each metal was fired onto them. The thickness of the ceramic layer was standardized by positioning the frameworks in a metallic template (height: 1 mm). The specimens from each ceramic-metal combination (N = 96, n = 12 per group) were randomly assigned into four experimental fatigue conditions, namely water storage at 37 °C for 24 h (control group), thermal cycling (3000 cycles, between 4 and 55 °C, dwell time: 10 s), mechanical cycling (20,000 cycles under 10 N load, immersion in distilled water at 37 °C) and, thermal and mechanical cycling. A flexural strength test was performed in a universal testing machine (crosshead speed: 1.5 mm/min). Data were statistically analyzed using two-way ANOVA and Tukey's test (α = 0.05). Results: The mean flexural strength values for the ceramic-gold alloy combination (55 ± 7.2 MPa) were significantly higher than those of the ceramic-Ti cp combination (32 ± 6.7 MPa) regardless of the fatigue conditions performed (p < 0.05). Mechanical and thermo-mechanical fatigue decreased the flexural strength results significantly for both ceramic-gold alloy (52 ± 6.6 and 53 ± 5.6 MPa, respectively) and ceramic-Ti cp combinations (29 ± 6.8 and 29 ± 6.8 MPa, respectively) compared to the control group (58 ± 7.8 and 39 ± 5.1 MPa, for gold and Ti cp, respectively) (p < 0.05) (Tukey's test). While ceramic-Ti cp combinations failed adhesively at the metal-opaque interface, gold alloy frameworks exhibited a residue of ceramic material on the surface in all experimental groups. Significance: Mechanical and thermo-mechanical fatigue conditions decreased the flexural strength values for both ceramic-gold alloy and ceramic-Ti cp combinations with the results being significantly lower for the latter in all experimental conditions. © 2007 Academy of Dental Materials.

Effect of radiotherapy on the radiopacity and flexural strength of a composite resin.

The aim of this study was to evaluate the effect of radiotherapy on the radiopacity and flexural strength of composite resin. Forty Z250 composite resin specimens were polymerized using a halogen light-curing unit and divided into 5 groups, in accordance with the radiotherapy dose: G1- without irradiation, G2- 30 Gy, G3- 40 Gy, G4- 50 Gy and GS- 60 Gy Digital images were obtained using a GE 100 X-ray. Radiopacity values were obtained with the Digora digital imaging system and the flexural strength was evaluated with an EMIC universal testing machine. Data were submitted to ANOVA and Tukey 's test. G1 presented the highest radiopacity value, followed by G3, G5, G4 and G2. For flexural strength, G1 presented the lowest value, followed by G2, G5, G3 and G4. Differences were no significant (p>0.05). The commonly used dosage of radiotherapy treatment, did not cause alteration in the radiopacity and flexural strength of resin-based composites.

Influence of bleaching treatment on flexural resistance of hybrid materials.

The aim of this study is to evaluate the flexural resistance of three types of restorative materials: compomer (Freedom), resin-modified glass-ionomer (Vitremer) and composite resin (Esthet-X), observing whether the application of bleaching agent can cause alterations of their flexural properties. Sixty samples were made using a 10 x 1 x 1 mm brass mold, and divided into three groups: G1- Freedom (SDI); G2- Vitremer (3M ESPE); G3- Esthet-X (Dentsply). On half of the samples of each group (10 samples) the bleaching treatment was applied and the other half used as control, was stored in distilled water at a temperature of 37 degrees C. Whiteness HP Maxx bleaching system was applied on the sample surface following the manufacturer's recommendations, simulating the bleaching treatment at the clinic. After this period, a flexural strength (three-point bending) test was conducted using (EMIC DL 1000) machine until the samples fractured. The data were submitted to ANOVA and Tukey tests. Of the restorative materials studied, G3-(87.24 +/- 31.40 MPa) presented the highest flexural strength, followed by G1-(61.67 +/- 21.32 MPa) and G2-(61.67 +/- 21.32 MPa). There was a statistical difference in flexural strength after the bleaching treatment. It was concluded that the use of a beaching agent can promote significant alteration of the flexural strength of these restorative materials.

Assessment of the flexural strength of two heat-curing acrylic resins for artificial eyes

Prosthetic eyes are artificial substitutes for the eyeball, made of heat-curing acrylic resin, serving to improve the esthetic appearance of the mutilated patient and his/her inclusion in society. The aim of this study was to assess the flexural strength of two heat-curing acrylic resins used for manufacturing prosthetic eyes. Thirty-six specimens measuring 64 x 10 x 3.3 mm were obtained and divided into four groups: acrylic resin for artificial sclera N1 (Artigos Odontológicos Clássico, São Paulo, SP, Brazil), heat-cure water technique (GI) and microwave-cured (GII); colorless acrylic resin for prosthetic eyes (Artigos Odontológicos Clássico, São Paulo, SP, Brazil), heat-cure water technique (GIII) and microwave-cured (GIV). Mechanical tests using three point loads were performed in a test machine (EMIC, São José dos Pinhais, PR, Brazil). The analysis of variance and the Tukey test were used to identify significant differences (p < 0.01). Groups GII and GIV presented, respectively, the highest (98.70 ± 11.90 MPa) and lowest means (71.07 ± 8.93 MPa), with a statistically significant difference. The cure method used for the prosthetic eye resins did not interfere in their flexural strength. It was concluded that all the resins assessed presented sufficient flexural strength values to be recommended for the manufacture of prosthetic eyes.

Effect of hydrofluoric acid etching duration on the roughness and flexural strength of a lithium disilicate-based glass ceramic

The aim of this study was to examine the effect of different acid etching times on the surface roughness and flexural strength of a lithium disilicate-based glass ceramic. Ceramic bar-shaped specimens (16 mm x 2 mm x 2 mm) were produced from ceramic blocks. All specimens were polished and sonically cleaned in distilled water. Specimens were randomly divided into 5 groups (n=15). Group A (control) no treatment. Groups B-E were etched with 4.9% hydrofluoric acid (HF) for 4 different etching periods: 20 s, 60 s, 90 s and 180 s, respectively. Etched surfaces were observed under scanning electron microscopy. Surface profilometry was used to examine the roughness of the etched ceramic surfaces, and the specimens were loaded to failure using a 3-point bending test to determine the flexural strength. Data were analyzed using one-way ANOVA and Tukey's test (α=0.05). All etching periods produced significantly rougher surfaces than the control group (p<0.05). Roughness values increased with the increase of the etching time. The mean flexural strength values were (MPa): A=417 ± 55; B=367 ± 68; C=363 ± 84; D=329 ± 70; and E=314 ± 62. HF etching significantly reduced the mean flexural strength as the etching time increased (p=0.003). In conclusion, the findings of this study showed that the increase of HF etching time affected the surface roughness and the flexural strength of a lithium disilicate-based glass ceramic, confirming the study hypothesis.

Biaxial flexural strength of CAD/CAM ceramics.

Aim of the study was to evaluate the biaxial flexural strength of ceramics processed using the Cerec inLab system. The hypothesis was that the flexural strength would be influenced by the type of ceramic. Ten samples (ISO 6872) of each ceramic (N.=50/n.=10) were made using Cerec inLab (software Cerec 3D) (Ø:15 mm, thickness: 1.2 mm). Three silica-based ceramics (Vita Mark II [VM], ProCad [PC] and e-max CAD ECAD]) and two yttria-stabilized tetragonal-zirconia-polycrystalline ceramics (Y-TZP) (e-max ZirCad [ZrCAD] and Vita In-Ceram 2000 YZ Cubes [VYZ]) were tested. The samples were finished with wet silicone carbide papers up to 1200-grit and polished in a polishing machine with diamond paste (3 μm). The samples were then submitted to biaxial flexural strength testing in a universal testing machine (EMIC), 1 mm/min. The data (MPa) were analyzed using the Kruskal-Wallis and Dunn (5%) tests. Scanning electronic microscopy (SEM) was performed on a representative sample from each group. The values (median, mean±sd) obtained for the experimental groups were: VM (101.7, 102.1±13.65 MPa), PC (165.2, 160±34.7 MPa), ECAD (437.2, 416.1±50.1 MPa), ZrCAD (804.2, 800.8±64.47 MPa) and VYZ (792.7, 807±100.7 MPa). The type of ceramic influenced the flexural strength values (P=0.0001). The ceramics ECADa, e-max ZrCADa and VYZa presented similar flexural strength values which were significantly higher than the other groups (PCb and VM IIb), which were similar statistically between them (Dunn's test). The hypothesis was accepted. The polycrystalline ceramics (Y-TZP) should be material chosen for make FPDs because of their higher flexural strength values.

Chemical characterization and flexural strength of a denture base acrylic resin with monomer 2-tert-butylaminoethyl methacrylate

Purpose: The objectives of this study were to investigate the flexural strength (FS) and chemical interaction between 2-tert-butylaminoethyl methacrylate (TBAEMA) and a denture base acrylic resin. Materials and Methods: Specimens were divided into five groups according to the concentration of TBAEMA incorporated in acrylic resin Onda-Cryl (0%, 1%, 2%, 3%, 4%) and were submitted to Fourier transform infrared spectroscopy (FTIR), electron spectroscopy for chemical analysis (XPS-ESCA), and differential scanning calorimetry (DSC) analyses. FS of the specimens was tested, and results were analyzed by ANOVA/Tukey's test (α < 0.05). Results: Different nitrogen ratios were observed on specimens' surfaces: 0.36%, 0.54%, 0.35%, and 0.20% for groups 1%, 2%, 3%, and 4%, respectively. FTIR indicated copolymerization of acrylic resin and TBAEMA, and DSC results demonstrated a decrease in glass transition temperature (Tg). Significant differences were found for FS (p < 0.05). The mean values were 91.1 ± 5.5,A 77.0 ± 13.1,B 67.2 ± 12.5,B 64.4 ± 13.0,B and 67.2 ± 5.9B MPa for groups 0%, 1%, 2%, 3% and 4%, respectively (same superscript letters indicate no significant difference). Conclusions: The incorporation of TBAEMA in acrylic resin resulted in copolymerization and the presence of amine groups on specimens' surfaces, and in decreases of Tg and FS. © 2012 by the American College of Prosthodontists.

Effect of carbamide peroxide bleaching gel on composite resin flexural strength and microhardness

This study investigated the effect of 16% carbamide peroxide (Whiteness Perfect/FGM) on the Vickers microhardness and flexural strength of the restorative composites Filtek Z100 (hybrid), Filtek Z350 (nanofill), Brilliant (micro-hybrid) and Opallis (micro-hybrid). Discshaped (4×2 mm; n=5) and bar-shaped (12×2×1 mm; n=10) specimens of each restorative material were randomly divided into 2 groups: (G1) 16 weeks stored in distilled water; (G2) 16 weeks stored in distilled water, with 16% carbamide peroxide application during 6 h per day for the last 4 weeks. The mechanical properties were evaluated using a Vickers microhardness tester and a mechanical testing machine. Data were analyzed by twoway ANOVA and Tukey's (HSD) post-hoc test (α=0.05). Filtek Z100 presented the highest microhardness value, followed by Filtek Z350 and finally by Brilliant and Opallis (p=0.00). Filtek Z100 and Brilliant exhibited the highest flexural strength value, followed by Filtek Z350 and Opallis (p=0.00). Bleaching treatment decreased significantly microhardness of Brilliant and Opallis (p=0.00). The flexural strength of all studied materials was not affected by the home bleaching (p=0.28).

Surface agents' influence on the flexural strength of bilaminated ceramics

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)