Vita In-Ceram YZ Research Articles

Comparison of Contrast Ratio, Translucency Parameter, and Flexural Strength of Traditional and "Augmented Translucency" Zirconia for CEREC CAD/CAM System.

Tetragonal zirconia polycrystals (TZP) can be used via CAD/CAM technique as metal replacement for fixed partial dentures. However, its intense white color and high opacity may represent an aesthetic limit. New TZPs with a claimed higher degree of translucency were recently marketed. The aim of the study was to investigate contrast ratio (CR), translucency parameter (TP), flexural strength (σ), Weibull characteristic strength (σ0 ), and Weibull modulus (m) of three "traditional" (IPS e.max Zir-CAD, inCoris ZI, VITA In-Ceram YZ) and two "increased translucency" (inCoris TZI, VITA In-Ceram YZ HT) Y-TZPs. For flexural strength, ISO 6872:2008 was followed. Bars (N = 40) were cut from pre-sintered blocks. Dense-sintering, finishing, and polishing were performed in order to obtain specimens of 15 × 4 × 1.2 mm. Samples were tested with three-point bending setup in a universal testing machine. For CR and TP, specimens (N = 10) were cut perpendicularly to the long axis from pre-sintered blocks. After the dense-sintering, specimens were finished and polished in order to obtain tiles of 12 × 15 × 1 mm. CR and TP were measured with a spectrophotometer equipped with an integrating sphere. No significant difference was found regarding flexural strength. A significant difference was found both for CR and TP among tested groups. VITA In-Ceram YZ HT and inCoris TZI showed the higher translucency. The difference was not statistically significant when compared with VITA In-Ceram YZ, and statistically significant when compared with IPS e.max Zir-CAD and inCoris ZI. The new "augmented translucency" TZPs showed higher translucency and similar flexural strength than "traditional" TZPs. Monolithic zirconia use is partially restricted due to the zirconia low translucency. The new "augmented translucency" zirconia showed a modest but perceptible increase in translucency and a similar flexural resistance, thus increasing the clinically suitable thickness range with optimized aesthetic and resistance. (J Esthet RestorDent 28:S32-S39, 2016).

Five-year clinical outcome of posterior zirconia ceramic inlay-retained FDPs with a modified design

ObjectivesTo evaluate the 5-year clinical outcome of posterior inlay-retained fixed dental prostheses (IRFDPs) with a modified design made from zirconia ceramic (Vita In-Ceram YZ, Vita Zahnfabrik, Bad Säckingen, Germany). MethodsThirty 3-unit IRFDPs were placed in 30 patients. Seven IRFDPs replaced the second premolars (4 in the maxilla, 3 in the mandible), and 23 replaced the first molars (15 in the maxilla, 8 in the mandible). Preparations were performed in accordance with general principles for ceramic inlay restorations and modified with a short retainer-wing bevel preparation within the enamel at the buccal and oral sides. The frameworks were milled from zirconia ceramic, and the pontics were veneered with feldspathic ceramic. After air-abrasion of bonding surfaces, IRFDPs were bonded with an adhesive composite resin. The patients were recalled 6–12 months after placement, and then annually. Kaplan–Meier analysis was used to calculate the survival and complication rates of the IRFDPs. ResultsAfter a mean observation time of 64.4 (SD=17.6) months (min 15, max 95.6), the 5-year cumulative survival of IRFDPs was 95.8%. Debonding was reported for two IRFDPs (6.9%), one of them failed finally after 49.4 months due to repeated debonding. Chipping of the veneering ceramic was reported in three cases (10.5%). Secondary caries were reported in 2 patients (8.1%). Nevertheless, the latter complications did not affect the clinical function of the involved IRFDPs. ConclusionThe 5-year clinical outcome of zirconia-based IRFDPs fabricated in the modified design is encouraging, so that they may represent a treatment alternative to replace posterior single missing teeth, taking into consideration the appropriate case selection.

Comparison of the Effectiveness of Bonding Composite to Zirconia as a Repair Method

Chipping of the veneering porcelain is often reported in the literature. Intraoral repair of chipped veneering porcelain provides an option when the restoration cannot be removed and replaced. This in vitro study investigated the bond strength of two porcelain repair methods to the zirconia ceramic after different aging conditions. A total of 120 (Vita InCeram YZ) samples were divided into two main groups according to the different repair methods (n = 60). The first method was using a porcelain repair kit (Bisco), and the second method was repairing with a universal adhesive (Single Bond Universal Adhesive) and a composite resin (Z100). Each group was divided into two subgroups (n = 30) according to surface modification (with or without airborne particle abrasion). Each group was then divided into three subgroups (n = 10) depending on aging conditions. Shear bond strength tests were performed to measure the adhesion strength between composite and zirconia surfaces. Statistical analysis was performed with 3‐way ANOVA, followed by Tukey HSD test (α = 0.05). Surface conditioning by airborne particle abrasion affected the strength values in the repair kit group compared with conventionally repaired group. Conventionally repaired group showed statistically significant higher bond strength values than repair kit group.

Influence of CAD/CAM zirconia for implant-abutment manufacturing on gingival fibroblasts and oral keratinocytes.

This study investigated the influence of three CAD/CAM zirconia ceramics for implant-abutment manufacturing on cell viability, migration ability, and cytotoxicity of human gingival fibroblasts (HGF) and oral keratinocytes (HOK) in vitro. HGF and HOK were cultured on zirconia ceramic disks (VITA In-Ceram YZ, Ivoclar IPS e.max ZirCAD, Sirona inCoris ZI) and on control disks made of tissue culture polystyrene. Cell viability was analyzed by a MTT assay. Migration ability was detected by a scratch assay. A ToxiLight assay was used to analyze the influence of the tested zirconia ceramics on adenylate kinase (ADK) release and cytotoxicity. At MTT assay, HGF showed an increased cell viability compared to the control after 9 and 12days for all ceramics (p each ≤0.0002) while HOK demonstrated a decreased cell viability after 9 and 12days for all ceramics (p each ≤0.0003). At scratch assay, HGF exhibited for all ceramics decreased relative distances of the scratch wound compared to the control from 24 to 48h (p each <0.0001) with exception of VITA In-Ceram YZ after 48h. HOK showed increased distances compared to the control for all ceramics after 48h (p each <0.0001). At ToxiLight assay, a minimal cytotoxicity of the tested materials could be detected. Overall, significant influences of the investigated CAD/CAM zirconia ceramics on HGF and HOK could be shown. The analyzed zirconia ceramics could influence oral soft-tissue cells that might affect the esthetic outcome after implant placement using CAD/CAM zirconia abutments.

Marginal and Internal Discrepancies of Posterior Zirconia-Based Crowns Fabricated with Three Different CAD/CAM Systems Versus Metal-Ceramic.

The aim of this study was to analyze the marginal and internal fit of metalceramic and zirconia-based crowns. Forty standardized steel specimens were prepared to receive posterior crowns and randomly divided into four groups (n = 10): (1) metal-ceramic, (2) NobelProcera Zirconia, (3) Lava Zirconia, and (4) VITA In-Ceram YZ. All crowns were cemented with glass-ionomer agent and sectioned buccolingually. A scanning electron microscope was used for measurements. Kruskal-Wallis and Wilcoxon signed rank test (α = .05) statistical analyses were conducted. Significant differences (P < .0001) in marginal discrepancies were observed between metal-ceramic and zirconia groups. No differences were found for the axial wall fit (P = .057). Significant differences were shown among the groups in discrepancies at the occlusal cusp (P = .0012) and at the fossa (P = .0062). No differences were observed between surfaces. All zirconia groups showed better values of marginal discrepancies than the metal-ceramic group. Procera Zirconia showed the lowest gaps.

Influence of surface treatment on the resin-bonding of zirconia

ObjectiveTo compare the effect of various surface treatments on the bonding of luting resin cements to zirconia under four-point bending. MethodsBar specimens (n=200) (2mm×5mm×25mm) were prepared from zirconia blocks (VITA In-Ceram YZ, Vita Zahnfabrik) with the cementation surface (2mm×5mm) of groups of 40 treated in one of five ways: airborne particle abrasion with 50μm Al2O3 (GB), zirconia primer (Z-Prime Plus, Bisco) (Z), glaze ceramic (Crystall.Glaze spray, Ivoclar Vivadent)+hydrofluoric acid (GHF), fusion glass-ceramic (Crystall.Connect, Ivoclar Vivadent) (CC), or left untreated as control (C). Within each treatment, bars were cleaned ultrasonically for 15min in ethanol and then deionized water before bonding in pairs with one of two luting resins: Panavia F 2.0, (Kuraray) (P); RelyX U-200 (3M/Espe) (R), to form 10 test specimens for each treatment and lute combination. Mechanical tests were performed and bond strengths (MPa) were subject, after log transformation, to analysis of variance, Shapiro–Wilk and Holm–Sidak tests; also log-linear contingency analysis of failure mode distribution; all with α=0.05. Fracture surfaces were examined under light and scanning electron microscopy. ResultsWhile the effect of surface treatment was significant (p=1.27×10−9), there was no detected effect due to resin (p=0.829). All treatments except CC (30.1MPa×/÷1.44)* were significantly better than the untreated control (24.8MPa×/÷1.35) (p=3.28×10−9). While the effect of GB – which gave the highest mean strength (50.5MPa×/÷1.29) – was not distinguishable from that of GHF (39.9MPa×/÷1.29) (p=0.082), it was significantly better than treatment with either CC or Z (33.1MPa×/÷1.48) (p<0.05). (* After log transformation for analysis and back; asymmetric error bounds as s.d. in log values.) SignificanceThe novel test method design, which has good discriminatory power, confirmed the value of gritblasting as a simple and effective treatment with low operator hazard. It gave the highest bond strengths regardless of the cement type. Glaze layer application followed by hydrofluoric acid-etching on zirconia before cementation might be viable for adhesive zirconia cementation, but represents a much greater hazard as well as having problems with thickness control.

Evaluation of a novel multiple phase veneering ceramic

ObjectivesTo produce a new veneering ceramic based on the production of a multiple phase glass–ceramic with improved performance in terms of strength and toughness. MethodsA composition of 60% leucite, 20% diopside and 20% feldspathic glass was prepared, blended and a heat treatment schedule of 930°C for 5min was derived from differential thermal analysis (DTA) of the glasses. X-ray diffraction (XRD) and SEM analysis determined the crystalline phases and microstructure. Chemical solubility, biaxial flexural strength (BFS), fracture toughness, hardness, total transmittance and coefficient of thermal expansion (CTE) were all measured in comparison to a commercial veneering ceramic (VITA VM9). Thermal shock resistance of the leucite–diopside and VITA VM9 veneered onto a commercial high strength zirconia (Vita In-Ceram YZ) was also assessed. Statistical analysis was undertaken using Independent Samples t-test. Weibull analysis was employed to examine the reliability of the strength data. ResultsThe mean chemical solubility was 6μg/cm2 for both ceramics (P=1.00). The mean BFS was 109±8MPa for leucite–diopside ceramic and 79±11MPa for VITA VM9 ceramic (P=0.01). Similarly, the leucite–diopside ceramic demonstrated a significantly higher fracture toughness and hardness. The average total transmittance was 46.3% for leucite–diopside ceramic and 39.8% for VITA VM9 (P=0.01). The leucite–diopside outperformed the VITA VM9 in terms of thermal shock resistance.Significance This novel veneering ceramic exhibits significant improvements in terms of mechanical properties, yet retains a high translucency and is the most appropriate choice as a veneering ceramic for a zirconia base core material.

Effects of thickness, processing technique, and cooling rate protocol on the flexural strength of a bilayer ceramic system

ObjectiveTo determine whether the thickness, processing technique, and cooling protocol of veneer ceramic influence the flexural strength of a bilayer ceramic system. Materials and methodsSixty-four bar-shaped specimens (20mm×4mm×1mm) of yttria-stabilized tetragonal zirconia (Vita In-Ceram YZ, Vita) were fabricated (ISO 6872) and randomly divided into 8 groups (n=8) according to the factors “processing technique” (P – PM9 and V – VM9), “thickness” (1mm and 3mm), and “cooling protocol” (S – slow and F – fast). The veneer ceramics were applied only over one side of the bar-shaped specimens. All specimens were mechanically cycled (2×106 cycles, 84N, 3.4Hz, in water), with the veneer ceramic under tension. Then, the specimens were tested in 4-point bending (1mm/min, load 100kgf, in water), also with the veneer ceramic under tension, and the maximum load was recorded at first sign of fracture. The flexural strength (σ) was calculated, and the mode of failure was determined by stereomicroscopy (30×). The data (MPa) were analyzed statistically by 3-way ANOVA and Tukey's test (α=0.05). ResultsANOVA revealed that the factor “thickness” (p=0.0001) was statistically significant, unlike the factors “processing technique” (p=0.6025) and “cooling protocol” (p=0.4199). The predominant mode of failure was cracking. SignificanceThe thickness of the veneer ceramic has an influence on the mechanical strength of the bilayer ceramic system, regardless of processing technique and cooling protocol of the veneer ceramic.

Influence of surface treatments on the surface properties of different zirconia cores and adhesion of zirconia-veneering ceramic systems

ObjectiveThe aim of this study was to assess the influence of surface treatments on the surface characteristics of different zirconia cores and the adhesion of the zirconia-veneering ceramic systems by means of strain energy release rate (G-value, J/m2). MethodsThree types of zirconia cores (NANOZR (NZ), Vita In-Ceram YZ (VZ), and IPS e.max ZirCAD (IZ)) were used. The specimens were divided into four groups in each test according to the surface treatment used; Gr 1 (control; no treatment), Gr 2 (sandblasted), Gr 3 (CH2Cl2 for 60min), and Gr 4 (experimental hot etching solution for 60min). AFM, SEM, EDS, and XRD were carried out. Two types of veneering ceramics (Vita VM9 (V9) and IPS e.max Ceram (IC)) were used for testing the adhesion. The G-value (J/m2) was measured with a four-point bending configuration. Following fracture testing specimens were examined with SEM. Data were analyzed using ANOVA and Tukey's test. ResultsNZ treated with the experimental hot etching solution showed the highest Ra values (206.06±9.98nm) compared with the other groups (P<0.05). The greatest amount of monoclinic phase is measured after sandblasting (19.59%) for NZ, followed by VZ (9.3%) and IZ (6.6%). The NZ/V9 (etching for 60min) group showed the highest G-value (36.02±2.80J/m2) among the groups. Mode of failure was mostly cohesive failure within all the bonded veneering ceramic systems. SignificanceThe experimental hot etching solution could be considered as alternative treatment modality to sandblasting for zirconia cores to avoid phase transition at the surface from tetragonal to monoclinic that may be detrimental for the longevity of the zirconia-veneering ceramic restoration.

Effect of surface treatments on the bonding strength of self-adhesive resin cements to zirconia ceramics.

To investigate the effect of surface treatments on the surface properties of yttria-stabilized zirconia ceramics (Y-TZP) and the interfacial bond strength to self-adhesive resin cements. Two types of Y-TZP (Vita In-Ceram YZ [VZ] and IPS e.max ZirCAD [IZ]) were used. The specimens were divided into four groups in each test according to the surface treatment used: Group A (control; no treatment), Group B (airborne-particle abrasion), Group C (CH₂Cl₂ for 60 minutes), and Group D (hot etching for 60 minutes). Scanning electron microscopy, atomic force microscopy, and X-ray diffractometry were carried out. Two types of self-adhesive resin cements (i CEM [IC] and Multilink Speed [MS]) were used for testing the adhesion. The G-value (J/m²) was measured with a four-point bending configuration. Following fracture testing, specimens were examined with a stereomicroscope. Data were analyzed using ANOVA and Tukey test. IZ treated with hot etching showed the highest average surface roughness values (172.5 ± 15.43 nm) compared with the other groups (P < .05). The greatest amount of monoclinic phase was measured after airborne-particle abrasion for VZ (8.9%), followed by IZ (6.1%). Improvements in bond strength values were found in the following order: hot etching > CH2Cl2 > airborne-particle abrasion > no treatment. Most failure modes were adhesive type of failures between ceramics and cement material (68.76%). Adhesion between Y-TZP and self-adhesive resin cements can be improved by the use of CH₂Cl₂ or hot etching surface treatments prior to resin cement application as an alternative technique to airborne-particle abrasion treatment.

Flexural strength and failure modes of layered ceramic structures

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.

Adaptation of all-ceramic fixed partial dentures

Objectives To measure the marginal and internal fit of three-unit fixed partial dentures (FPDs) using the micro-CT technique, testing the null hypothesis that there is no difference in the adaptation between the ceramic systems studied. Methods Stainless steel models of prepared abutments were fabricated to design the FPDs. Ten FPDs were produced from each framework ceramic (YZ – Vita In-Ceram YZ and IZ – Vita In-Ceram Zirconia) using CEREC inLab according to the manufacturer instructions. All FPDs were veneered using the recommended porcelain. Each FPD was seated on the original model and scanned using micro-CT. Files were processed using NRecon and CTAn software. Adobe Photoshop and Image J software were used to analyze the cross-sections images. Five measuring locations were used as follows: MG – marginal gap; CA – chamfer area; AW – axial wall; AOT – axio-occlusal transition area; OA – occlusal area. The horizontal marginal discrepancy (HMD) was evaluated in another set of images. Results were statistically analyzed using ANOVA and Tukey tests ( α = 0.05). Results The mean values for MG, CA, AW, OA and HMD were significantly different for all tested groups ( p < 0.05). IZ exhibited greater mean values than YZ for all measuring locations except for AW and AOT. OA showed the greatest mean gap values for both ceramic systems. MG and AW mean gap values were low for both systems. Significance The ceramic systems evaluated showed different levels of marginal and internal fit, rejecting the study hypothesis. Yet, both ceramic systems showed clinically acceptable marginal and internal fit.

Soak Colored Zirconia Ceramics and its Colorimetric Plate

Objective: To test specimens of soak-colored Vita In-Ceram YZ zirconia ceramics and the colorimetric data of staining solution colorimetric plate. Methods: five sets of specimens were prepared, soaking and coloring them with LL1 to LL5 staining solution for 2 min respectively. Specimens were sintered for 2 h at 1530°C, and grinded one side of the specimens to 1.5 mm in thickness. The colors of the specimens and staining solution colorimetric plate were tested by spectrophotometer in black background. The chromatic aberration between the specimens and colorimetric plate were calculated as well as measured the lightness difference, hue angle difference, and saturation difference. Results: the colorimetric data of the dyed specimens are L: 59.81 ~ 78.93; a: 0.36 ~ 9.36; b: 19.62 ~ 26.91. The color space of the specimens and staining solution colorimetric plate was similar and the chromatic aberration was 4.02-6.96 NBS units. The biggest difference between them was the hue angle difference, mean 7.38, followed by the saturation difference, mean 2.31; minimum lightness difference, mean 2.29. Conclusion: staining solution colorimetric plate was suitable to be colorimetric reference for the color-matching of the basic layer of the ceramic. Proper chromatic aberration leaves color revision space for the translucent porcelain veneer.

Effects of sandblasting on surface character and resin bond of zirconia ceramic

To evaluate the effect of Al2O3 particles sandblasting on the surface roughness, element composition and resin bond durability of zirconia ceramic. Sixty 2.5 mm thick computer aided design and computer aided manufacture (CAD/CAM) zirconia ceramic (Vita Inceram YZ) plates were fired, polished and cleaned. Half of polished ceramic plates was sandblasted with 50 µm alumina particles at 0.3 MPa for 20 s. The surface roughness of polished and sandblasted ceramic surface were measured by 3D-laser scanning microscope, and the surface element weight and atom ratio of the ceramic surface were measured by energy disperse spectroscopy (EDS). Then polished and sandblasted ceramic plates were randomized into six groups. In Group 1 and 2 the polished and sandblasted ceramic plates were bonded irrespectively with conventional resin cement (DUOLINK). In Group 3 and 4 the ceramic plates were bonded with resin cement containing MDP (Panavia F), In Group 5 and 6 the specimens were pretreated with silane coupler acitivated by MDP (Clearfil Ceramic Primer), then bond with Panavia F. The specimens of each test group were then divided into two subgroups, and to received shear test after 0 and 10 000 time thermal cycle. The data was analyzed by one-way ANOVA and independent t test. Comparing with polishing, sandblasting reduced the oxygen atom and weight ratio of zirconia ceramic surface (P < 0.001), and increased the zirconium atom and weight ratio (P < 0.001), meanwhile increased the surface roughness (P < 0.001). The bond strength between ceramic plates and resin cement in all test groups decreased after thermocycling (P < 0.001). All specimen in test group 1 and 2 lost bond, and the bond strength of test group 3 and 5 [(0.59 ± 0.17), (0.89 ± 0.84) MPa] were significantly lower than that of test group 4 and 6 [(14.63 ± 3.03), (16.64 ± 1.90) MPa], and the bond strength of test group 6 were significanlty higher than that of test group 4. Sandblasting improves durability of bond between zirconia ceramic and resin cement containing MDP, not only by increasing the roughness and area of ceramic surface, but also by changing its surface element composition to obtain more chemical bond.

Effect of the microstructure on the lifetime of dental ceramics

Objectives To evaluate the effect of the microstructure on the Weibull and slow crack growth (SCG) parameters and on the lifetime of three ceramics used as framework materials for fixed partial dentures (FPDs) (YZ – Vita In-Ceram YZ; IZ – Vita In-Ceram Zirconia; AL – Vita In-Ceram AL) and of two veneering porcelains (VM7 and VM9). Methods Bar-shaped specimens were fabricated according to the manufacturer's instructions. Specimens were tested in three-point flexure in 37 °C artificial saliva. Weibull analysis ( n = 30) and a constant stress-rate test ( n = 10) were used to determine the Weibull modulus ( m) and SCG coefficient ( n), respectively. Microstructural and fractographic analyzes were performed using SEM. ANOVA and Tukey's test ( α = 0.05) were used to statistically analyze data obtained with both microstructural and fractographic analyzes. Results YZ and AL presented high crystalline content and low porosity (0.1–0.2%). YZ had the highest characteristic strength ( σ 0) value (911 MPa) followed by AL (488 MPa) and IZ (423 MPa). Lower σ 0 values were observed for the porcelains (68–75 MPa). Except for IZ and VM7, m values were similar among the ceramic materials. Higher n values were found for YZ (76) and AL (72), followed by IZ (54) and the veneering materials (36–44). Lifetime predictions showed that YZ was the material with the best mechanical performance. The size of the critical flaw was similar among the framework materials (34–48 μm) and among the porcelains (75–86 μm). Significance The microstructure influenced the mechanical and SCG behavior of the studied materials and, consequently, the lifetime predictions.

Influence of the veneering process on the marginal fit of zirconia fixed dental prostheses

Distortions in the marginal region during manufacture are detrimental to the long-term success of fixed dental prostheses (FDPs). The aim of the present in vitro study was to evaluate changes in marginal fit because of the veneering process of four-unit FDPs made from different zirconia materials. Two groups of FDPs with 10 specimens each were machined from white body zirconia blanks (VITA In-Ceram YZ Cubes, KaVo Everest ZS-Blanks) by means of computer-aided design/computer-aided manufacturing systems and subsequently sintered to their final density. The marginal and internal gaps of the frameworks were determined using a replica technique. Afterwards, frameworks were veneered with the recommended ceramics (VITA VM9, GC Initial Zr), and fitting accuracy was evaluated again. Statistical analyses were performed by Student's t-test with the level of significance chosen at 0.05. With one framework/veneering system (Everest ZS-Blanks/Initial Zr), both marginal gap (P = 0.019) and internal gap (P = 0.001) at the premolar retainer were significantly affected by the veneering process. The resulting distortions were directed towards the lumina of the retainers and the mean values of the measured gaps decreased by about 23.8 mum (marginal gap) and 27.3 mum (internal gap). For the other system (In-Ceram YZ Cubes/VM9), no distortions because of the veneering were found. The veneering of zirconia restorations may lead to significant changes in the marginal fit, while the combination of core and veneering material used influences the resulting distortions.

The effect of low temperature aging on the mechanical property &amp; phase stability of Y-TZP ceramics

STATEMENT OF PROBLEMRecently Yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) has been introduced due to superior flexural strength and fracture toughness compared to other dental ceramic systems. Although zirconia has outstanding mechanical properties, the phenomenon of decrease in the life-time of zirconia resulted from degradation in flexural strength after low temperature aging has been reported.PURPOSEThe objective of this study was to investigate degradation of flexural strength of Y-TZP ceramics after various low temperature aging treatments and to evaluate the phase stability and micro-structural change after aging by using X-ray diffraction analysis and a scanning electron microscope (SEM).MATERIAL AND METHODSY-TZP blocks of Vita In-Ceram YZ (Vita Zahnfabrik, Bad Säckingen, Germany) were prepared in 40 mm (length) × 4 mm (width) × 3 mm (height) samples. Specimens were artificially aged in distilled water by heat-treatment at a temperature of 75, 100, 125, 150, 175, 200, and 225℃ for 10 hours, in order to induce the phase transformation at the surface. To measure the mechanical property, the specimens were subjected to a four-point bending test using a universal testing machine (Instron model 3365; Instron, Canton, Mass, USA). In addition, X-ray diffraction analysis (DMAX 2500; Rigaku, Tokyo, Japan) and SEM (Hitachi s4700; Jeol Ltd, Tokyo, Japan) were performed to estimate the phase transformation. The statistical analysis was done using SAS 9.1.3 (SAS institute, USA). The flexural strength data of the experimental groups were analyzed by one-way analysis of variance and to detect statistically significant differences (α= .05).RESULTSThe mean flexural strength of sintered Vita In-Ceram YZ without autoclaving was 798 MPa. When applied aging temperature at below 125℃ for 10 hours, the flexural strength of Vita In-Ceram YZ increased up to 1,161 MPa. However, at above 150℃, the flexural strength started to decrease. Although low temperature aging caused the tetragonal-to-monoclinic phase transformation related to temperature, the minimum flexural strength was above 700 MPa.CONCLUSIONThe monoclinic phase started to appear after aging treatment above 100℃. With the higher aging temperature, the fraction of monoclinic phase increased. The ratio of monoclinic/tetragonal + monoclinic phase reached a plateau value, circa 75% above 175℃. The point of monoclinic concentration at which the flexural strength begins to decrease was between 12% and 54%.

Shear bond strengths between different zirconia cores and veneering ceramics and their susceptibility to thermocycling

Objectives The purpose of this study was to evaluate the shear bond strength between various commercial zirconia core and veneering ceramics, and to investigate the effect of thermocycling. Methods The Schmitz–Schulmeyer test method was used to evaluate the core–veneer shear bond strength (SBS) of three zirconia core ceramics (Cercon Base, Vita In-Ceram YZ Cubes, DC-Zirkon) and their manufacturer recommended veneering ceramics (Cercon Ceram S, Vita VM9, IPS e.max Ceram). A metal ceramic system (Degudent U94, Vita VM13) was used as a control group for the three all-ceramic test groups ( n = 30 specimens/group). Half of each group ( n = 15) was thermocycled (5–55 °C, 20,000 cycles). Subsequently, all specimens were subjected to shear force in a universal testing machine. Fractured specimens were evaluated microscopically to determine the failure mode. Results The initial mean SBS values in MPa ± S.D. were 12.5 ± 3.2 for Vita In-Ceram YZ Cubes/Vita VM9, 11.5 ± 3.4 for DC-Zirkon/IPS e.max Ceram, and 9.4 ± 3.2 for Cercon Base/Cercon Ceram S. After thermocycling mean SBS values of 11.5 ± 1.7 MPa for DC-Zirkon/IPS e.max Ceram, 9.7 ± 4.2 MPa for Vita In-Ceram YZ Cubes/Vita VM9, and 9.6 ± 4.2 MPa for Cercon Base/Cercon Ceram S were observed. Neither the differences between the SBS values of the all-ceramic test groups nor the influence of thermocycling on all groups were statistically significant. Irrespective of thermocycling the metal ceramic control group (27.6 ± 12.1 MPa, 26.4 ± 13.4 MPa) exhibited significantly higher mean SBS than all three all-ceramic groups tested. The all-ceramic groups showed combined failure modes as cohesive in the veneering ceramic and adhesive at the interface, whereas the metal ceramic group showed predominately cohesive fractures. Significance The results indicated that the SBS between zirconia core and veneering ceramics was not affected by thermocycling. None of the zirconia core and veneering ceramics could attain the high bond strength values of the metal ceramic combination.

In vitro evaluation of low-temperature aging effects of Y2O3 stabilized tetragonal zirconia polycrystals dental ceramics

To investigate the influence of in vitro low-temperature degradation (LTD) treatment on the structural stability of 5 kinds of Y2O3 stabilized tetragonal zirconia polycrystals (Y-TZP) dental ceramics. TZ-3YS powder was compacted at 200 MPa using cold isostatic pressure and pre-sintered at 1050 degrees C for 2 h forming presintered blocks. Specimens were sectioned into 15 mm x 15 mm x 1.5 mm slices from blocks of TZ-3YS, Vita In-Ceram YZ, Ivoclar, Cercon Smart, and Kavo Y-TZP presintered blocks, 18 slices for each brand, and then densely sintered. Specimens were divided into 6 groups and subjected to an accelerated aging test carried out in an autoclave in steam at 134 degrees C, 0.2 MPa, for 0, 1, 2, 3, 4, and 5 h. X-ray diffraction (XRD) was used to identify crystal phases and relative content of monoclinic phase was calculated. Specimens for three-point bending test were fabricated using TZ-3YS ceramics according to the ISO 6872 standard and bending strength was tested before and after aging. The polished and aging specimens of TZ-3YS and Cercon Smart zirconia ceramics were observed by atomic force microscopy (AFM) to evaluate surface microstructure. Tetragonal-to-monoclinic phase transformation was detected for specimens of TZ-3YS, Vita In-Ceram YZ, Ivoclar, and Kavo zirconia ceramics except for Cercon Smart ceramics after aging, and the relative content of monoclinic phase was increasing with the prolonged aging time. TZ-3YS was the most affected material, Kavo took the second, and Vita and Ivoclar were similar. Aging had no significant negative effects on flexural strength of TZ-3YS with average bending strength being over 1100 MPa. The nucleation and growth of monoclinic phase were detected by AFM in surface of Cercon Smart zirconia in which monoclinic phase was not detected by XRD. The results suggest that LTD of dental Y-TZP is time dependent, but the aging test does not reduce the flexural strength of TZ-3YS. The long-term clinical serviceability of dental Y-TZP needs further observation.