Comparison of two bond strength testing methodologies for bilayered all-ceramics

Objectives. This study compared the shear bond strength (SBS) and microtensile (MTBS) testing methodologies for core and veneering ceramics in four types of all-ceramic systems.Methods. Four different ceramic veneer/core combinations, three of which were feldspathic and the other a fluor-apatite to their respectively corresponding cores, namely leucitereinforced ceramic ((IPS)Empress, Ivoclar), low leucite-reinforced ceramic (Finesse, Ceramco), glass-infiltrated alumina (In-Ceram Alumina, Vita) and lithium disilicate ((IPS)Empress 2, Ivoclar) were used for SBS and MTBS tests. Ceramic cores (N = 40, n = 10/group for SBS test method, N=5blocks/group for MTBS test method) were fabricated according to the manufacturers' instructions (for SBS: thickness, 3 mm; diameter, 5 mm and for MTBS: 10 mm x 10 mm x 2 mm) and ultrasonically cleaned. The veneering ceramics (thickness: 2 mm) were vibrated and condensed in stainless steel moulds and fired onto the core ceramic materials. After trying the specimens in the mould for minor adjustments, they were again ultrasonically cleaned and embedded in PMMA. The specimens were stored in distilled water at 37 degrees C for 1 week and bond strength tests were performed in universal testing machines (cross-head speed: 1mm/min). The bond strengths (MPa +/- S.D.) and modes of failures were recorded.Results. Significant difference between the two test methods and all-ceramic types were observed (P < 0.05) (2-way ANOVA, Tukey's test and Bonferroni). The mean SBS values for veneering ceramic to lithium disilicate was significantly higher (41 +/- 8 MPa) than those to low leucite (28 +/- 4 MPa), glass-infiltrated (26 +/- 4 MPa) and leucite-reinforced (23 +/- 3 MPa) ceramics, while the mean MTBS for low leucite ceramic was significantly higher (15 +/- 2 MPa) than those of leucite (12 +/- 2 MPa), glass-infiltrated (9 +/- 1 MPa) and lithium disilicate ceramic (9 +/- 1 MPa) (ANOVA, P < 0.05).Significance. Both the testing methodology and the differences in chemical compositions of the core and veneering ceramics influenced the bond strength between the core and veneering ceramic in bilayered all-ceramic systems. (c) 2006 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Influence of Different Ceramics on Resin Cement Knoop Hardness Number

This study evaluated: 1) the effect of different ceramics on light attenuation that could affect microhardness, measured as the Knoop Hardness Number (KHN), of a resin cement immediately and 24 hours after polymerization and 2) the effect of different activation modes (direct light-activation, light activation through ceramics and chemical activation) on the KHN of a resin cement.Resin cement Rely X ARC (3M ESPE) specimens 5.0 mm in diameter and 1.0 nun thick were made in a Teflon mold covered with a polyester film. The cement was directly light activated for 40 seconds with an XL 2500 curing unit (3M ESPE) with 650 mW/cm(2), light activated through ceramic discs of Duceram Plus (DeguDent), Cergogold (DeguDent), IPS Empress (Ivoclar), IPS Empress 2 (Ivoclar), Procera. (NobelBiocare), In Ceram Alumina (Vita) and Cercon (DeguDent), having a 1.2 mm thickness or chemically activated without light application. The resin cement specimens were flattened, and KHN was obtained using an HMV 2 microhardness tester (Shimadzu) with a load of 50 g applied for 15 seconds 100 pin from the irradiated surface immediately and after storage at 37 degrees C for 24 hours. Ten measurements were made for each specimen, with three specimens for each group at each time. The data were submitted to ANOVA and Tukey's test (p=0.05). The KHN of the resin cement was not only affected by the mode of activation, but also by the post-activation testing time. The mean KHN of the resin cement for chemical activation and through all ceramics showed statistically significant lower values compared to direct activation immediately and at 24 hours. The KHN for 24 hours post-activation was always superior to the immediate post-activation test except with direct activation. The most opaque ceramics resulted in the lowest KHN values.

Bond strength durability of a resin composite on a reinforced ceramic using various repair systems

Objectives. This study compared the durability of repair bond strength of a resin composite to a reinforced ceramic after three repair systems.Methods. Alumina-reinforced feldspathic ceramic blocks (Vitadur-alpha(R)) (N=30) were randomly divided into three groups according to the repair method: PR-Porcelain Repair Kit (Bisco) [etching with 9.5% hydrofluoric acid + silanization + adhesive]; CJ-CoJet Repair Kit (3M ESPE) [(chairside silica coating with 30 mu m SiO2 + silanization (ESPE(R)-Sil) + adhesive (Visio(TM)-Bond)]; CL-Clearfil Repair Kit [diamond surface roughening, etching with 40% H3PO4 + Clearfil Porcelain Bond Activator + Clearfil SE Bond)]. Resin composite was photo-polymerized on each conditioned ceramic block. Non-trimmed beam specimens were produced for the microtensile bond strength (mu TBS) tests. In order to study the hydrolytic durability of the repair methods, the beam specimens obtained from each block were randomly assigned to two conditions. Half of the specimens were tested either immediately after beam production (Dry) or after long-term water storage (37 degrees C, 150 days) followed by thermocyling (12,000 cycles, 5-55 degrees C) in a universal testing machine (1 mm/min). Failure types were analyzed under an optical microscope and SEM.Results. mu TBS results were significantly affected by the repair method (p=0.0001) and the aging conditions (p=0.0001) (two-way ANOVA, Tukey's test). In dry testing conditions, PR method showed significantly higher (p < 0.001) repair bond strength (19.8 +/- 3.8 MPa) than those of CJ and CL (12.4 +/- 4.7 and 9.9 +/- 2.9, respectively). After long-term water storage and thermocycling, CJ revealed significantly higher results (14.5 +/- 3.1 MPa) than those of PR (12.1 +/- 2.6 MPa) (p < 0.01) and CL (4.2 +/- 2.1 MPa) (p < 0.001). In all groups when tested in dry conditions, cohesive failure in the composite accompanied with adhesive failure at the interface (mixed failures), was frequently observed (76%, 80%, 65% for PR, CJ and CL, respectively). After aging conditions, while the specimens treated with PR and CJ presented primarily mixed failure types (52% and 87%, respectively), CL group presented mainly complete adhesive failures at the interface (70%).Significance. Hydrolytic stability of the repair method based on silica coating and silanization was superior to the other repair strategies for the ceramic tested. (C) 2009 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Effect of Surface Conditioning Modalities on the Repair Bond Strength of Resin Composite to the Zirconia Core / Veneering Ceramic Complex

Purpose: This study evaluated the effect of different surface conditioning protocols on the repair strength of resin composite to the zirconia core / veneering ceramic complex, simulating the clinical chipping phenomenon.Materials and Methods: Forty disk-shaped zirconia core (Lava Zirconia, 3M ESPE) (diameter: 3 mm) specimens were veneered circumferentially with a feldspathic veneering ceramic (VM7, Vita Zahnfabrik) (thickness: 2 mm) using a split metal mold. They were then embedded in autopolymerizing acrylic with the bonding surfaces exposed. Specimens were randomly assigned to one of the following surface conditioning protocols (n = 10 per group): group 1, veneer: 4% hydrofluoric acid (HF) (Porcelain Etch) + core: aluminum trioxide (50-mu m Al2O3) + core + veneer: silane (ESPE-Sil); group 2: core: Al2O3 (50 mu m) + veneer: HF + core + veneer: silane; group 3: veneer: HF + core: 30 mu m aluminum trioxide particles coated with silica (30 mu m SiO2) + core + veneer: silane; group 4: core: 30 mu m SiO2 + veneer: HF + core + veneer: silane. Core and veneer ceramic were conditioned individually but no attempt was made to avoid cross contamination of conditioning, simulating the clinical intraoral repair situation. Adhesive resin (VisioBond) was applied to both the core and the veneer ceramic, and resin composite (Quadrant Posterior) was bonded onto both substrates using polyethylene molds and photopolymerized. After thermocycling (6000 cycles, 5 degrees C-55 degrees C), the specimens were subjected to shear bond testing using a universal testing machine (1 mm/min). Failure modes were identified using an optical microscope, and scanning electron microscope images were obtained. Bond strength data (MPa) were analyzed statistically using the non-parametric Kruskal-Wallis test followed by the Wilcoxon rank-sum test and the Bonferroni Holm correction (alpha = 0.05).Results: Group 3 demonstrated significantly higher values (MPa) (8.6 +/- 2.7) than those of the other groups (3.2 +/- 3.1, 3.2 +/- 3, and 3.1 +/- 3.5 for groups 1, 2, and 4, respectively) (p < 0.001). All groups showed exclusively adhesive failure between the repair resin and the core zirconia. The incidence of cohesive failure in the ceramic was highest in group 3 (8 out of 10) compared to the other groups (0/10, 2/10, and 2/10, in groups 1, 2, and 4, respectively). SEM images showed that air abrasion on the zirconia core only also impinged on the veneering ceramic where the etching pattern was affected.Conclusion: Etching the veneer ceramic with HF gel and silica coating of the zirconia core followed by silanization of both substrates could be advised for the repair of the zirconia core / veneering ceramic complex.

Manufacturing conditioned roughness and wear of biomedical oxide ceramics for all-ceramic knee implants

Background: Ceramic materials are used in a growing proportion of hip joint prostheses due to their wear resistance and biocompatibility properties. However, ceramics have not been applied successfully in total knee joint endoprostheses to date. One reason for this is that with strict surface quality requirements, there are significant challenges with regard to machining. High-toughness bioceramics can only be machined by grinding and polishing processes. The aim of this study was to develop an automated process chain for the manufacturing of an all-ceramic knee implant. Methods: A five-axis machining process was developed for all-ceramic implant components. These components were used in an investigation of the influence of surface conformity on wear behavior under simplified knee joint motion. Results: The implant components showed considerably reduced wear compared to conventional material combinations. Contact area resulting from a variety of component surface shapes, with a variety of levels of surface conformity, greatly influenced wear rate. Conclusions: It is possible to realize an all-ceramic knee endoprosthesis device, with a precise and affordable manufacturing process. The shape accuracy of the component surfaces, as specified by the design and achieved during the manufacturing process, has a substantial influence on the wear behavior of the prosthesis. This result, if corroborated by results with a greater sample size, is likely to influence the design parameters of such devices.

Influence of lanthanum doping on the dielectric, ferroelectric and relaxor behaviour of barium bismuth titanate ceramics

Barium lanthanum bismuth titanate (Ba1−(3/2)xLaxBi4Ti4O15, x = 0–0.4) ceramics were fabricated using the powders synthesized via the solid-state reaction route. X-ray powder diffraction analysis confirmed the above compositions to be monophasic and belonged to the m = 4 member of the Aurivillius family of oxides. The effect of the partial presence of La3+ on Ba2+ sites on the microstructure, dielectric and relaxor behaviour of BaBi4Ti4O15 (BBT) ceramics was investigated. For the compositions pertaining to x ≤ 0.1, the dielectric constant at both room temperature and in the vicinity of the temperature of the dielectric maximum (Tm) of the parent phase (BBT) increased significantly with an increase in x while Tm remained almost constant. Tm shifted towards lower temperatures accompanied by a decrease in the magnitude of the dielectric maximum (εm) with an increase in the lanthanum content (0.1 < x ≤ 0.4). The dielectric relaxation was modelled using the Vogel–Fulcher relation and a decrease in the activation energy for frequency dispersion with increasing x was observed. The frequency dispersion of Tm was found to decrease with an increase in lanthanum doping, and for compositions corresponding to x ≥ 0.3, Tm was frequency independent. Well-developed P(polarization)–E(electric field) hysteresis loops were observed at 150 °C for all the samples and the remanent polarization (2Pr) was improved from 6.3 µC cm−2 for pure BBT to 13.4 µC cm−2 for Ba0.7La0.2Bi4Ti4O15 ceramics. Dc conductivities and associated activation energies were evaluated using impedance spectroscopy.

Compatibility of RuO2 electrodes with PZT ceramics

Because of its high electrical conductivity and good diffusion barrier properties ruthenium dioxide (RuO2) is a good electrode material for use with ferroelectric lead zirconate-titanate (PZT) solid solutions. Under certain conditions, RuO2 can react with PZT to form lead ruthenate (Pb2Ru2O6.5) during processing at elevated temperatures resulting in lead depletion from PZT. The standard Gibbs energies of formation of RuO2 and Pb2Ru2O6.5 and activities of components of the PZT solid solution have been determined recently. Using this data along with older thermodynamic information on PbZrO3 and PbTiO3, the stability domain of Pb2Ru2O6.5 is computed as a function of PZT composition, temperature and oxygen partial pressure in the gas phase. The results show PbZrO3-rich compositions are more prone to react with RuO2 at all temperatures. Increasing temperature and decreasing oxygen partial pressure suppress the reaction. Graphically displayed are the reaction zones as a function of oxygen partial pressure and PZT composition at temperatures 973, 1173 and 1373 K.

Influence of sintering conditions and doping on the dielectric relaxation originating from the surface layer effects in CaCu3Ti4O12 ceramics

Detailed investigations into the dielectric dispersion phenomenon in the giant dielectric constant material CaCu3Ti4O12 (CCTO) around room temperature revealed the existence of two successive dielectric relaxations. In the temperature domain, a new dielectric relaxation was clearly observed around 250K, in addition to the well-investigated dielectric relaxation close to 100K. The effect of sintering and doping (La3+) on the strength of these dielectric relaxations were studied in detail. The sintering temperature as well as its duration was found to have tremendous influence on the dielectric relaxation that was encountered around 250 K. This Maxwell-Wagner (M-W) type of relaxation was found to be originating from the surface layer containing the Cu-rich phase, which was ascribed to the difference in the oxygen content between the surface and the interior of the sample. Interestingly, this particular additional relaxation was not observed in La2/3Cu3Ti4O12, a low dielectric constant member of the CCTO family, in which the segregation of Cu-rich phase on the surface was absent. Indeed the correlation between the new relaxation and the presence of Cu-rich phase in CCTO ceramics was further corroborated by the absence of the same after removing the top and bottom layers. (C) 2007 Elsevier Ltd. All rights reserved.

The significance of brittle reaction layers in fusing of dental ceramics to titanium

This thesis comprises four intercomplementary parts that introduce new approaches to brittle reaction layers and mechanical compatibility of metalloceramic joints created when fusing dental ceramics to titanium. Several different methods including atomic layer deposition (ALD), sessile drop contact angle measurements, scanning acoustic microscopy (SAM), three-point bending (TPB, DIN 13 927 / ISO 9693), cross-section microscopy, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS) were employed. The first part investigates the effects of TiO2 layer structure and thickness on the joint strength of the titanium-metalloceramic system. Samples with all tested TiO2 thicknesses displayed good ceramics adhesion to Ti, and uniform TPB results. The fracture mode was independent of oxide layer thickness and structure. Cracking occurred deeper inside titanium, in the oxygen-rich Ti[O]x solid solution surface layer. During dental ceramics firing TiO2 layers dissociate and joints become brittle with increased dissolution of oxygen into metallic Ti and consequent reduction in the metal plasticity. To accomplish an ideal metalloceramic joint this needs to be resolved. The second part introduces photoinduced superhydrophilicity of TiO2. Test samples with ALD deposited anatase TiO2 films were produced. Samples were irradiated with UV light to induce superhydrophilicity of the surfaces through a cascade leading to increased amount of surface hydroxyl groups. Superhydrophilicity (contact angle ~0˚) was achieved within 2 minutes of UV radiation. Partial recovery of the contact angle was observed during the first 10 minutes after UV exposure. Total recovery was not observed within 24h storage. Photoinduced ultrahydrophilicity can be used to enhance wettability of titanium surfaces, an important factor in dental ceramics veneering processes. The third part addresses interlayers designed to restrain oxygen dissolution into Ti during dental ceramics fusing. The main requirements for an ideal interlayer material are proposed. Based on these criteria and systematic exclusion of possible interlayer materials silver (Ag) interlayers were chosen. TPB results were significantly better in when 5 μm Ag interlayers were used compared to only Al2O3-blasted samples. In samples with these Ag interlayers multiple cracks occurred inside dental ceramics, none inside Ti structure. Ag interlayers of 5 μm on Al2O3-blasted samples can be efficiently used to retard formation of the brittle oxygen-rich Ti[O]x layer, thus enhancing metalloceramic joint integrity. The most brittle component in metalloceramic joints with 5 μm Ag interlayers was bulk dental ceramics instead of Ti[O]x. The fourth part investigates the importance of mechanical interlocking. According to the results, the significance of mechanical interlocking achieved by conventional surface treatments can be questioned as long as the formation of the brittle layers (mainly oxygen-rich Ti[O]x) cannot be sufficiently controlled. In summary in contrast to former impressions of thick titanium oxide layers this thesis clearly demonstrates diffusion of oxygen from sintering atmosphere and SiO2 to Ti structures during dental ceramics firing and the following formation of brittle Ti[O]x solid solution as the most important factors predisposing joints between Ti and SiO2-based dental ceramics to low strength. This among other predisposing factors such as residual stresses created by the coefficient of thermal expansion mismatch between dental ceramics and Ti frameworks can be avoided with Ag interlayers.

Dielectric, pyroelectric and ferroelectric properties of Bi4Ti2.98Nb0.01Ta0.01O12 ceramics

The electrical conductivity and electrical relaxation for ferroelectric Bi4Ti2.98Nb0.01Ta0.01O12 (BTNT) ceramics have been reported in the frequency range 0.1 Hz to 1 MHz and in the 300-550 degrees C temperature range. The electrical data was analyzed in the framework of the dielectric as well as the electric modulus formalisms. The bulk dc conductivity at various temperatures was extracted from the electrical relaxation data. The activation energy associated with the electrical relaxation determined from the electric modulus spectra was found to be 0.93 +/- 0.03 eV, close to that of the activation energy for dc conductivity (1.03 +/- 0.02 eV). It suggests that the movements of oxygen ions are responsible for both ionic conduction as well as the relaxation process. The pyroelectric coefficient was found to be 12 mu C m(-2) K-1 at room temperature which is higher than that of the reported value of pyroelectric coefficient for undoped Bi4Ti3O12 ceramics. (C) 2010 Elsevier B.V. All rights reserved.

Wide Ranged La Modification in CCTO Ceramics Through Sol-Gel: Effect on Microstructure and Dielectric Properties

Sol-Gel method was employed to synthesize pure and wide ranged La-modified CaCu3Ti4O12 ceramics using mixed acetate-nitrate-alcoxide individual metal-ion precursors. SEM pictures revealed that grain size monotonously decreases with the extent of La incorporation. All the prepared ceramics manifested dielectric constant in the range similar to 10(3)-10(4). Dielectric loss was found to decrease with La incorporation and got optimized for 20% La3+ while retaining its high dielectric constant which may be industrially important. Room temperature Impedance spectroscopy suggested that decrease in grain resistance is responsible for reduction in dielectric loss according to Internal Barrier Layer Capacitor (IBLC) model.

Dielectric relaxation in bismuth layer-structured BaBi4Ti4O15 ferroelectric ceramics

The dielectric properties of BaBi4Ti4O15 ceramics were investigated as a function of frequency (10(2)-10(6) Hz) at various temperatures (30 degrees C-470 degrees C), covering the phase transition temperature. Two different conduction mechanisms were obtained by fitting the complex impedance data to Cole-Cole equation. The grain and grain boundary resistivities were found to follow the Arrhenius law associated with activation energies: E-g similar to 1.12 eV below T-m and E-g similar to 0.70 eV above T-m for the grain conduction; and E-gb similar to 0.93 eV below T-m and E-gb similar to 0.71 eV above T-m for the grain boundary conduction. Relaxation times extracted using imaginary part of complex impedance Z `'(omega) and modulus M `'(omega) were also found to follow the Arrhenius law and showed an anomaly around the phase transition temperature. The frequency dependence of conductivity was interpreted in terms of the jump relaxation model and was fitted to the double power law. (C) 2010 Elsevier B. V. All rights reserved.

Crystal structure and electrical properties of CaNaBi2Nb3O12 ceramics

Monophasic CaNaBi2Nb3O12 powders were synthesized via the conventional solid-state reaction route. Rietveld refinement of the X-ray powder diffraction (XRD) data and selected area electron diffraction (SAED) studies confirmed the phase to be a three-layer Aurivillius oxide associated with an orthorhombic B2cb space group. The dielectric properties of the ceramics have been studied in the 300-800 K temperature range at various frequencies (1 kHz to 1 MHz). A dielectric anomaly was observed at 676 K for all the frequencies corresponding to the ferroelectric to paraelectric phase transition as it was also corroborated by the high temperature X-ray diffraction studies. The incidence of the polarization-electric field (P vs. E) hysteresis loop demonstrated CaNaBi2Nb3O12 to be ferroelectric.

Phase stability and dielectric properties of ceramics in the Pb(Zn1/3Nb2/3)O3-Pb(Ni1/3Nb2/3)O3-PbTio3 relaxor ferroelectric system

The perovskite structure in Pb(Zn1/3Nb2/3)O3 can be stabilized by the addition of Pb(Ni1/3Nb2/3)O3 and PbTiO3.Pb(Ni1/3Nb2/3)O3 assists in lowering the sintering temperature and shifting the Curie temperature of ceramics while PbTiO3 helps to optimize the dielectric properties. The phase stability and dielectric properties of several compositions in the Pb(Zn1/3Nb2/3)O3-Pb(Ni1/3Nb2/3)O3-PbTiO3 ternary relaxor ferroelectric system were investigated for possible capacitor applications. The effect of calcining and sintering temperature on the stability of perovskite phase in PZN rich compositions was studied extensively as a function of composition. The boundary line separating perovskite and mixed phases was determined for compositions near PZN. Several compositions can be sintered below 1050°C. The dielectric properties of compositions near the mixed phase boundary showed strong dependence on the percentage of pyrochlore phase. Compositions with a dielectric constant of 12.500 at room temperature have been identified which meet Z5T and Y5U specifications for dielectric constant and tan δ.

Observations on the role of the steel disc counterface during the sliding of various structural ceramics

Sliding wear characteristics and mechanisms of structural ceramics, namely Al2O3, zirconia-toughened alumina, tetragonal zirconia polycrystals (TZP) and Si3N4 against a steel counterface are influenced by mechanical and tribochemical interactions, specific to the combinations studied. The present paper studies the role of the disc in the sliding wear process of the above ceramics. Experiments were conducted at a pressure of 15.5 MPa between 0.1 and 12.0 m s(-1) with ceramic pins sliding against an EN-24 steel disc. Except in the case of TZP, the disc morphology is sensitive to variations in speed rather than to the pin material. The disc track is (i) mildly abraded at low speeds (about 0.1-0.75 m s(-1)), (ii) severely abraded at intermediate speeds (about 1.0-3.0 m s(-1)), (iii) covered with black patches at high speeds (about 4.0-6.0 m s(-1)) and (iv) completely black at very high speeds (about 7.0-12.0 m s(-1)). In the case of TZP, although black patches appear, transfer of TZP onto the disc surface and high wear of TZP occurs at 4.0 m s(-1). The order of the wear of the disc estimated from profilometric measurements is the same for all the ceramics. Except for Si3N4, the onset of wear of the ceramics is associated with the appearance of deep 'V' grooves on either side of the profile of the disc track. This can be explained on the basis of the thermal and hardness variations. Although other interaction products specific to the ceramic pin are present, the formation of iron oxides dominates the wear of the disc.