Multilayered Zirconia Research Articles

Influence of Layer and Sintering Temperature on the Optical Properties of Multilayered Zirconia Materials.

To evaluate the translucency and color difference of the individual layers of two multi-layered zirconia materials at different sintering temperatures and to compare them with lithium disilicate. Multi-layered zirconia systems with four distinct layers were selected for this study: DD cube ONE ML (4Y-TZP), DD cubeX2 ML (5Y-TZP); and compared with IPS e.max CAD HT (LS2). Plate-shaped A2-shade specimens were obtained from LS2 and individual layers of both zirconia materials. Individual layers were then divided equally into three different sintering temperatures:1300°C, 1450°C, and 1600°C. The TP and ΔE were determined by a spectrophotometer. SEM images were taken. Data was analyzed using SPSS 24.0 software with a p-value ⟨0.05. A significant difference was found in TP and ΔE values amongst all types of ceramic materials. Different sintering temperatures yielded distinct TP and ΔE values when both zirconia materials were tested and compared with LS2. Finally, TP and ΔE values were different amongst the zirconia layers. Sintering temperature, type of ceramic material and different zirconia layers significantly affected the optical properties. Multi-layered zirconia materials possess a unique gradient effect that could efficiently enhance the esthetics of monolithic zirconia restorations. However, the sintering condition should be optimized.

The Effect of Sintering Temperature on Vickers Microhardness and Flexural Strength of Translucent Multi-Layered Zirconia Dental Materials

This study evaluated the effects of the sintering temperature on Vickers microhardness and three-point flexural strength values of two multi-layered zirconia materials. Multi-layered zirconia systems with four distinct layers were selected: DD cube ONE ML (4Y-TZP) and DD cubeX2 ML (5Y-TZP). In total, 96 plate-shaped A2-shade specimens were obtained using individual layers of these two zirconia materials. The individual layers were then divided equally into batches with three different sintering temperatures (1300, 1450, and 1600 °C), and the Vickers microhardness was assessed. Another group of 72 bar-shaped specimens was prepared from the same materials. These were similarly divided into three different sintering temperatures, and the flexural strength was assessed. SEM was used to conduct fractographic analyses. The data were analyzed using SPSS 24.0 software with a p-value < 0.05. The microhardness and flexural strength of 4Y-TZP were higher than those of the 5Y-TZP at all the sintering temperatures. A significant difference was found in the microhardness and flexural strength values between groups sintered at different sintering temperatures (p < 0.05). The highest microhardness and flexural strength values were found at 1450 °C (p < 0.05). The microhardness values of different layers were not significantly different (p > 0.05). The sintering temperature and type of ceramic material significantly affected the microhardness and flexural strength. However, the layers did not significantly affect the microhardness.

Effect of Different Decontamination Methods on Fracture Resistance, Microstructure, and Surface Roughness of Zirconia Restorations-In Vitro Study.

This study aimed to evaluate the effect of seven different decontamination methods (water, ZirCleanTM, 37% phosphoric acid, 9.5% hydrofluoric acid, Al2O3 sandblasting, low-speed dental stone, and high-speed dental stone) on the fracture resistance, microstructure, and surface roughness of monolithic and multilayered zirconia. The as-received and sandblasted zirconia was used as a control. One-way ANOVA and t-test were performed. As-received monolithic zirconia was stronger (856 ± 94 MPa) than multilayered zirconia (348.4 ± 63 MPa). Only phosphoric acid (865 ± 141 MPa) and low-speed dental stone (959 ± 116 MPa) significantly increased the flexural strength of sandblasted monolithic zirconia (854 ± 99 MPa), but all tested decontamination methods except phosphoric acid (307 ± 57 MPa) and Al2O3 (322 ± 69 MPa) significantly increased the flexural strength of sandblasted multilayered zirconia (325 ± 74 MPa). Different decontamination methods did not significantly affect the flexural modulus, but introduced irregularities in the crystal as well as deep surface flaws in both types of zirconia. The surface of sandblasted monolithic zirconia is more resistant to change than multilayered zirconia. Among different decontamination methods, a low-speed dental stone could be beneficial as it significantly increased the surface roughness and fracture resistance of both types of zirconia.

Effect of multiple firings on the color and translucency of monolithic zirconia

The effects of multiple firings on the color and translucency of monolithic zirconia were investigated in this paper. One hundred specimens were milled using three types of monolithic zirconia: multilayered zirconia (UTML, Katana) (UT), highly translucent zirconia (Organic Translucent, R + K) (OT), and nanosized zirconia (DIAZIR ST9810, Zhong Xin Tang Guo Ye) (ST). The group UT was divided into three subgroups: the incisal (UT-I), middle (UT-M), and cervical (UT-C). After sintering (T0), the specimens of each group (n = 20) were repeatedly fired 3 times. The L*, a*, and b* values were measured by using a spectrophotometer at T0, and after the first (T1), second (T2), and third (T3) firings. The translucency parameter (TP), contrast ratio (CR), opalescence parameter (OP), and color difference (∆E00) were calculated and statistically analyzed (α = 0.05). The surface morphologies of the specimens were observed using SEM. Multiple firings significantly affected the OP and the ∆E00 values of the materials tested (both p < 0.001). The ∆E00 values of group ST at T1-T3 were greater than the 50%:50% acceptability threshold (∆E00 > 1.8). Moreover, multiple firings did not exhibit significant effects on the TP and contrast ratio values of any materials (both p > 0.05). The surface topographies of the specimens after multiple firings were quite similar. Changes in opalescence were found for the multilayered zirconia and nanosized zirconia after multiple firings, but the clinical significance was low. Clinically unacceptable color changes were found in the nanosized zirconia after multiple firings, which were attributed to the higher L* values and the lower b* values after multiple firings. However, the optical properties and composition of surface elements of multilayered 5Y-TZP with over three layers need to be investigated in future studies.

Efficacy of try-in paste and resin cement shades in prediction of the Final Color of multilayer Zirconia Veneers (An In-Vitro Study).

Efficacy of try-in paste and resin cement shades in prediction of the Final Color of multilayer Zirconia Veneers (An In-Vitro Study).

Effect of low-temperature degradation treatment on hardness, color, and translucency of single layers of multilayered zirconia

Statement of problemEvaluating the effect of low-temperature degradation (LTD) on multilayered zirconia blocks is important for the long-term life of zirconia restorations. PurposeThe purpose of this in vitro study was to analyze the changes in color, translucency, and hardness of a single layer of multilayered zirconia after an LTD treatment. Material and methodsNinety multilayered 10×10×1.0-mm zirconia specimens (3M Lava Esthetic) were designed using Auto CAD 2006 (Autodesk) and divided into 6 groups (n=15) based on LTD (no treatment, LTD treatment) and the inherent layer type (incisal, transition, and body). The hardness of each specimen was measured using a microVickers hardness tester. The CIELab color coordinates were measured using a spectrophotometer, and the data were used to calculate the color difference and translucency (TP). Data were analyzed using 2-way ANOVA and the Scheffé test (α=.05). ResultsLTD treatment did not alter the hardness of multilayered zirconia (P=.572). A significant difference was found in the hardness between the layers of multilayered zirconia (P<.001). LTD treatment did not alter the b∗ or L∗ values (P=.773, P=.701) but did change the a∗ values (P<.001). On LTD treatment, the a∗ value was found to decrease. The L∗, a∗, and b∗ values differed based on the respective layer within the material (P<.001). As layers progress from the incisal to the body, the L∗ value decreased and the a∗ and b∗ values increased. In all groups, the color difference values were highest in the following order: the incisal and transition layers < the transition and body layers < the incisal and body layers. On LTD treatment, the color difference between the layers decreased. The LTD treatment did not affect the TP value (P=.208), but the TP value for each layer showed a significant difference (P<.001). ConclusionsLTD treatment did not affect the optical properties or hardness of the multilayered zirconia. The hardness of the multilayered zirconia increased from the incisal to the body layer. In multilayered zirconia, the brightness decreased from the incisal to the body layer, and red and yellow color changes were observed. The TP of multilayered zirconia increased from the incisal to the body layer.

Fatigue resistance of monolithic and multilayer zirconia crowns using veneer layering or CAD-on technique.

This study aims to evaluate the fatigue resistance of monolithic zirconia (Yz) and multilayer ceramic structures using the CAD-on technique in different thicknesses. Fifty (N=50) standardized single crowns preparations were made in fiberglass-reinforced epoxy resin (NEMA grade G10), digitalized, and restorations were machined in CAD-CAM, composing 5 groups (n= 10): Control: 1.5 mm (milled zirconia framework + manual layered porcelain); Yz monolithic 1.5 mm; Yz monolithic 1.0 mm; CAD-on 1.5 mm; and CAD-on 1.0 mm (milled zirconia framework 0.5 mm thickness bonded by a low fuse ceramic to a milled lithium disilicate layer of 1.0 mm or 0.5 mm, respectively). The G10 bases were conditioned with 10% hydrofluoric acid; the crowns were air abraded with 110 μm alumina particles; and then luted onto each other with self-adhesive resin cement. A cyclic fatigue test was performed (initial load: 400N for 10,000 cycles, frequency of 20 Hz, step size of 200N) until failure, and the data was submitted to a survival statistical analysis. No failures were observed at Yz monolithic 1.5 mm. High and similar performance was observed for Cad-On groups and Yz monolithic 1.0 mm. The control group depicted the worst behavior. The Weibull modulus of CAD-on 1.5 mm was higher than the control while being similar to the other conditions. Both the monolithic systems and the CAD-on technique showed high and similar fatigue fracture behavior and survival rates, which were also higher than the control bilayer system. Both systems reduced the occurrence of delamination failures, making them suitable for clinical use.

59 - Effect of Aging Treatment on Fracture Properties of Multilayer Zirconia

59 - Effect of Aging Treatment on Fracture Properties of Multilayer Zirconia

Novel model-less fully digital workflow for implant superstructures in an esthetic zone: A technical report.

This report introduces a fully digital workflow for the fabrication of implant superstructures in an esthetic zone using an intraoral scanner (IOS), computer-aided design/computer-aided manufacturing (CAD/CAM) technology, and monolithic multilayer zirconia. Digital impressions of scan bodies and occlusal registration were made in the esthetic zone using an IOS. The provisional restoration in the oral cavity was scanned, and the provisional restoration with an optimized surface morphology of the subgingival contour was scanned outside the oral cavity. These morphological data were integrated into the CAD software to generate a digital cast. The morphology of the final superstructure was generated based on morphological data of the provisional restoration. The final superstructure was fabricated from monolithic multilayer zirconia using a CAM machine, sintered, colored with a stain material, and subsequently bonded to a titanium base using resin cement. The superstructure was successfully fabricated using a model-less, fully digital workflow, and delivered to the patient. No clinical complications were reported. Thus, within the limitations of this report, the novel developed superstructure fabrication techniques can change the clinical and laboratory workflows from analog to digital in the esthetic zone.

Translucent Monolithic, Multi-Layered Zirconia: Matching Esthetics with Strength

High esthetic demand of patients has led to the development of newer tooth-colored restorative materials. Yttria-stabilized Zirconia (3Y-TZP) ceramic is considered an acceptable material for prosthetic rehabilitation due to its high fracture resistance, biocompatibility, biomechanical stability, and better color matching compared to the traditional porcelain fused to metal restorations. Tetragonal stabilized polycrystalline zirconia (TZP: tetragonal zirconia polycrystal) is doped with 3 mol% yttrium oxide (3Y-TZP).The opaque appearance of zirconia is a key challenge in obtaining optimum esthetics. These restorations are typically veneered with a weak glassy phase ceramic to mask the opaque appearance. The risk of delamination and chipping of ceramic veneer from such layered prostheses is a major concern. High masticatory load in posterior teeth, poor framework design, inadequate thickness of ceramic veneer, contamination of zirconia substructure, low elastic modulus and thermal conductive of zirconia compared to veneer porcelain could be some of the factors leading to such catastrophic failures.Various methods have been developed to increase the translucency of zirconia such as increasing the percentage of the cubic phase, increasing sintering temperature, reducing impurities, altering yttria content, and reducing the grain size. With higher yttrium doping, the proportion of cubic phase zirconia is increased by 25 % for 4Y-TZP and 53 % for 5Y-TZP, which allows for improved translucency. However, with the increase in the cubic phase proportion, there is a risk of reduced strength, due to a reduction in the extent of transformation toughening.More recently, new monolithic multi-layer zirconia has been developed with a color gradient from the incisal to the cervical third, miming natural tooth color. Different grades of the translucent blank are available such as High Translucent Multi-layered (HTML), Super Translucent Multi-layered (STML), and Ultra Translucent Multi-layer zirconia (UHTML). Multi-layer zirconia discs consist of different layers with varying degrees of transparency: the outer enamel layer, transitions layers, and an inner body layer. This new innovative multilayer polychromatic zirconia blank allows technicians to work with a nearly universal zirconia blank. However, more researches ensuring the optimum mechanical properties of newer products are necessary before they can be safely used in all clinical scenarios.

Mechanical Properties of New Generations of Monolithic, Multi-Layered Zirconia.

New monolithic multi-layered zirconia restorations are gaining popularity due to their excellent aesthetic properties. However, current knowledge of these newest multi-layer ceramics in terms of mechanical properties is scarce. Three monolithic, multi-layered zirconia materials (Katana, Kuraray Noritake, Japan) were selected for comparison: High Translucent Multi-layered zirconia (HTML), Super Translucent Multi-layered zirconia (STML) and Ultra Translucent Multi-layered zirconia (UTML). Fifteen specimens per group were cut from pre-sintered blocs in each of the four layers (L1, L2, L3, L4) and in different thicknesses (0.4 mm, 0.8 mm and 1.2 mm). Critical fracture load (Fcf) was recorded in 3-point-bending. Flexural strength (σ) in MPa, Vickers hardness (HV) in N/mm2, fracture toughness (KIc) in MPa*m1/2, Weibull Modulus (m) and characteristic Weibull strength (σw) in MPa were assessed. Statistical analysis was performed using ANOVA analysis. FS and KIc were significantly higher (p &lt; 0.05) for Katana™ HTML (652.85 ± 143.76-887.64 ± 118.95/4.25 ± 0.43-5.01 ± 0.81) in comparison to Katana™ STML (280.17 ± 83.41-435.95 ± 73.58/3.06 ± 0.27-3.84 ± 0.47) and UTML (258.25 ± 109.98-331.26 ± 56.86/2.35 ± 0.31-2.94 ± 0.33), with no significant differences between layers and layer thicknesses. The range of indications should be carefully considered when selecting the type of monolithic zirconia for fabrication of dental restorations, as materials widely differ in mechanical properties.

Optical Properties, Microstructure, and Phase Fraction of Multi-Layered Monolithic Zirconia with and without Yttria-Gradient.

The differences in the optical properties of multi-layered zirconia with and without yttria-gradient are not fully understood. This study aimed to evaluate and compare the optical properties, related microstructures, and phase fractions of multi-layered zirconia with and without yttria-gradient. For this, multi-layered zirconia of 5 mol% yttria (5Y) stabilized (Katana STML) and 4Y/5Y stabilized (e.max MT Multi) were cut layerwise, sintered, and analyzed using the opalescence parameter (OP), average transmittance (AT%), translucency parameter (TP), and contrast ratio (CR). The average grain size and phase fractions were obtained from field-emission scanning electron micrographs and X-ray diffraction patterns, respectively. Although the TP values of Katana STML and e.max MT Multi did not show a significant difference (except for transition layer 1), the results of AT and CR showed that the translucency of e.max MT Multi was slightly higher than that of Katana STML (p < 0.05). The opalescence gradient was higher in Katana STML than in the e.max MT Multi. In both zirconia types, translucency increased from the dentin to enamel layer based on the AT, TP, and CR results, while OP decreased (p < 0.05). The higher translucency from the dentin to enamel layer in Katana STML was caused by the pigmentation gradient, while in e.max MT Multi, it was caused by the difference in phase fraction and the pigmentation gradient.

Optical Properties of Five Esthetic Ceramic Materials Used for Monolithic Restorations: A Comparative In Vitro Study

Zirconia has generated tremendous interest in the esthetic materials used for dental restorations. However, using conventional zirconia has some limitations especially in highly esthetically demanding situations, as it lacks the translucency that other ceramic materials possess. This study aimed to evaluate and compare the optical properties (shade, translucency, and opalescence) of three CAD-CAM monolithic multilayer zirconia ceramics (GNX; Ceramill Zolid® Gen-X, ZCP; IPS e.max® ZirCAD, and UPC; Upcera® Esthetic Explore Prime) and one CAD-CAM monolithic multilayer polymer-infiltrated hybrid ceramic (ENM; Vita® Enamic) with a CAD-CAM monolithic lithium disilicate ceramic as control (EMX; IPS e.max® CAD). 200 discs (GNX = 40, ZCP = 40, UPC = 40, ENM = 40, and EMX = 40) were cut, polished, and fully crystallized. Half of the samples for each group were subjected to hydrothermal aging. Descriptive analysis and ANOVA tests were used to compare the groups. Zirconia GNX, ZCP, and UPC groups showed significantly lower optical properties than ENM and EMX groups for both the non-aged and aged samples (p &lt; 0.05). UPC and ENM groups showed a significant decrease in translucency and opalescence after aging (p &lt; 0.05). The optical properties of monolithic multilayer zirconia ceramics were lower than monolithic multilayer polymer-infiltrated hybrid ceramic and lithium disilicate ceramic. Polymer-infiltrated hybrid ceramic was significantly affected by aging.

Durability of cantilever inlay-retained fixed dental prosthesis fabricated from multilayered zirconia ceramics with different designs

PurposeThe purpose of this in-vitro study was to investigate the effect of framework design on fracture resistance and failure modes of cantilever inlay-retained fixed partial dentures (IRFDPs) fabricated from two multilayered monolithic zirconia materials. Materials and methodsSeventy-two natural premolar teeth were prepared as abutments for cantilever IRFDPs using three designs: mesial-occlusal (MO) inlay with short buccal and palatal wings (D1), MO inlay with long palatal wing (D2), MO inlay with long palatal wing and occlusal extension (D3). Full-contoured IRFDPs were fabricated from two monolithic zirconia materials; IPS e.max ZirCAD Prime and Zolid Gen-X. Adhesive surfaces were air-abraded and bonded with MDP-containing resin cement. Specimens were subjected to thermocycling (5–55 °C, 5000 cycles); then, mechanical loading (1.2 × 10⁶ cycles, 49 N). Surviving specimens were loaded until failure in the universal testing machine. All specimens were examined under stereomicroscope, and two samples from each group were evaluated using Scanning Electron Microscope. ResultsMean failure loads were not significantly different between different framework designs or between two materials. However, IPS e.max ZirCAD Prime showed significantly higher failure rate than Zolid Gen-X during dynamic fatigue (p = 0.009). Samples with D1 design showed higher debonding rate, D2 failed mainly by fracture of the palatal wing and debonding, and D3 failed mainly by fracture of the abutment tooth. Debonded restorations showed mainly mixed failures. ConclusionCantilever IRFDPs with framework designs that maximize adhesion to enamel exhibited promising results. IPS e.max ZirCAD Prime was more susceptible to fractures with the long palatal wing design.

Effect of speed sintering of monolithic zirconia with different yttria contents on color and crystal phase.

This study evaluated the color and microstructure of monolithic zirconia crowns with different yttrium oxide (Y2 O3 ) contents treated by conventional or speed sintering. Four types of zirconia ceramics were assessed: two monolayer zirconia, and two multilayer zirconia. The monolithic zirconia crowns were fabricated using a dental computer-aided design/computer-aided manufacturing (CAD/CAM) system and in two shades (A2 and BL). After milling, the zirconia crowns were sintered using either speed sintering or conventional sintering. For each combination of zirconia (4), shade (2), and sintering condition (2), the color parameters were determined at three positions of each of nine crowns using a non-contact dental spectrophotometer. In addition, the zirconia phases in the specimens were quantified using X-ray diffractometry. Significant differences in the ΔE00 values at different measurement positions were observed for the Multi2 crown of the BL shade group. The color difference resulting from conventional and speed sintering programs was not affected by the difference in yttria content of Mono1, Mono2, and Multi1. However, in Multi2, containing 3Y-TZP and 5Y-PSZ, a color change was caused by the use of speed sintering. Therefore, when performing speed sintering with Multi2, it is necessary to select the color in consideration of these results or take measures for staining.

Effect of Staining Drinks on the Color Stability of Grit Blasted and Non-Grit Blasted Monolithic Zirconia: An In Vitro Study

The present study aimed to compare the color stability of different types of zirconia with and without grit blasting (GB) after they were immersed in staining drinks. Two hundred and forty zirconia samples (N = 240) belonging equally to three different types of zirconia (Cercon® xt multilayer, xt extra translucent, and ht high translucent) were used in this study. Forty samples from each zirconia group were roughened with GB, while the other forty remained non-GB (NGB). Eight GB and NGB zirconia samples from each sub-group were immersed in artificial saliva, coffee, protein shake, chlorhexidine mouthwash, and a soft drink. Besides chlorhexidine mouthwash (immersion time: 14 days), the samples were immersed in the liquids for 28 days. A spectrophotometer was utilized to observe the color differences (∆E) at baseline (T0), 7 days post-immersion (T1), 14 days post-immersion (T2), 21 days post-immersion (T3), and 28 days post-immersion (T4). For the multilayer zirconia, the greatest ∆E (8.45 for GB and 5.97 for NGB samples) was observed after immersion in coffee at T4. For the extra translucent zirconia, the greatest ∆E (9.10 for GB and 6.81 for NGB samples) was also observed after immersion into the coffee at T4. For the high translucent zirconia, the greatest ∆E (4.53 for GB and 3.62 for NGB samples) was observed after immersion into the coffee at T4 and T3. Protein shake and soft drink immersion also significantly discolored some zirconia samples. Overall, GB zirconia samples presented with greater ∆E values than their NGB counterparts. It can be concluded that coffee immersion of zirconia samples caused a more significant discoloration (increased ∆E values) than any other liquid. Future clinical studies should be carried out to corroborate the current study’s findings.

Comparing the color match of monolithic CAD-CAM dental ceramics with the VITA Classical shade guide

Statement of problemMatching the shade selected and the final color of a ceramic restoration is challenging, and studies on matching monolithic ceramics to the shade selected are lacking. PurposeThe purpose of this in vitro study was to compare the color match of monolithic lithium disilicate (LDS), zirconia-reinforced lithium silicate (ZLS), presintered zirconia-reinforced lithium silicate (PS-ZLS), polymer-infiltrated ceramic network (PICN), and multilayer zirconia with the 3 modes of the VITA Classical shade guide. Material and methodsThis study was performed on 50 rectangular plates (14×12×1 mm) of 5 types of ceramics with A2 shade (n=10). Zirconia specimens were evaluated in 3 locations: incisal, medial, and cervical thirds. The color coordinates of the specimens of all 7 groups were measured on #3 and #8 Ivoclar Natural Die Color material by using a reflective spectrophotometer. The color coordinates of A2 VITA shade were measured in 5 modes: without backing placed in specimen holder, shade tab on the backgrounds #3 and #8, and 1-mm-thick shade tab on the backgrounds #3 and #8. The color difference of each specimen with 3 modes of A2 shade (without backing and on similar backgrounds) was calculated by using the ΔE00 formula, and comparison among groups was performed by using 2-way ANOVA and Tamhane post hoc tests. The comparison of ΔE00 between the values obtained from backgrounds #3 and #8 was performed by using the independent t test (α=.05). ResultsIn both backgrounds, statistically significant differences were found between the studied groups and VITA shade (P<.001). In most situations, the amount of color difference was lowest for the “shade tab on the backgrounds” mode. On background #3, the highest color difference was related to ZLS (6.48 ±0.23), and the lowest values were observed in the PICN group (1.02 ±0.31). On background #8, the highest color difference was related to ZLS compared with the “without backing” mode (8.62 ±0.27), and the lowest values were reported for ZLS compared with the “shade tab on the backgrounds” mode (1.27 ±0.44). The independent t test showed a statistically significant color difference on the 2 different backgrounds for all situations (P<.001). ConclusionsColor selection of monolithic ceramics with the VITA Classical shade guide is improved by placing the VITA tabs on a similar background. Background color has a significant effect on the final shade of the monolithic ceramics. Choosing the correct color for LDS, ZLS, and PS-ZLS requires more care than for PICN and zirconia.

Mechanical characterization of a multi-layered zirconia: Flexural strength, hardness, and fracture toughness of the different layers

This study compared the flexural strength under monotonic (static - sσ) and cyclic load application (fatigue - fσ), hardness (H) and fracture toughness (KIC) of different layers of a multi-layered zirconia (IPS e.max ZirCAD MT Multi, Ivoclar). Each layer was sectioned, classified into three groups according to yttria content (4-YSZ, 4/5-YSZ and 5-YSZ), and shaped on samples for flexural strength and fracture toughness tests (bars: 1.0 × 1.0 × 11 mm); and Vickers hardness test (plates: 1.5 × 4.0 × 5.0 mm). Flexural strength under monotonic load application (sσ; n = 10) was obtained through two different devices (three-point-bending and ball-in-hole device) and fatigue flexural strength (fσ; n = 15; initial load: 10 N; step-size: 5 N; 10,000 cycles/step) was assessed using a ball-in-hole device under cyclic load application. Vickers hardness test (n = 5), fracture toughness test (n = 10), and additional analyzes (Finite Element Analysis - FEA, Energy-dispersive X-ray spectroscopy - EDS and Scanning Electron Microscopy - SEM) were also performed. No differences were found between the different devices in the monotonic flexural strength test, and FEA showed similar tensile stress distribution for the two devices. 4-YSZ showed higher values of flexural strength under monotonic and cyclic load application modes (sσ = 1114.73 MPa; fσ = 798.84 MPa), and fracture toughness (KIC = 3.90 MPa√m). 4/5-YSZ had an intermediate sσ; however, fσ was similar to 5-YSZ (404.00–429.36 MPa) and KIC similar to 4-YSZ (KIC = 3.66 MPa√m). No statistical differences were found for hardness and Weibull modulus for fatigue flexural strength data. The amount of yttria in the layer compositions increased from 4-YSZ to 5-YSZ, and larger zirconia crystals were observed in the topographic images of 5-YSZ. Failures in the flexural strength and toughness tests started from the face subjected to tensile stress. Different layers of the multi-layered zirconia blank presented distinct mechanical properties. 4-YSZ (cervical layer) presented the highest flexural strength under monotonic and cyclic loads (fatigue), and higher fracture toughness even similar to the transition layer (4/5-YSZ). Hardness was similar between the layers. The ball-in-hole device performed similarly to the three-point bending device and can be used as an alternative to the traditional method.

The Effect of UV Treatment on Surface Contact Angle, Fibroblast Cytotoxicity, and Proliferation with Two Types of Zirconia-Based Ceramics.

UV photofunctionalization of Zirconia-based materials for abutment fabrication is a promising approach that might influence the formation of a sound peri-implant seal, thus promoting long-term soft and hard tissue implant integration. This study aimed to evaluate the effect of UV treatment of test specimens made by two different ZnO2-based ceramic materials on the hydrophilicity, cell cytotoxicity, and proliferation of human gingival fibroblasts (HGFs). Two Zirconia-based materials, high-translucent and ultra-translucent multi-layered Zirconia (Katana, Kuraray Noritake, Japan), were used to prepare a total of 40 specimens distributed in two equally sized groups based on the material (n = 20). The same surface finishing protocol was applied for all specimens, as suggested by the manufacturer. Half the specimens from each group were treated with UV-C light for 48 h. Water contact angle (WCA), fibroblast cytotoxicity, and proliferation were investigated. The WCA values for the high-translucent Zirconia ranged from 69.9° ± 6.4° to 73.7° ± 13.9° for the treated/non-treated specimens and from 79.5° ± 12.8° to 83.4° ± 11.4° for the ultra-translucent multi-layered Zirconia, respectively. However, the difference was insignificant (F(16) = 3.50, p = 0.292). No significant difference was observed for the fibroblast cytotoxicity test. The results for proliferation revealed a significant difference, which was material-dependent (F(8) = 9.58, p = 0.005). We found that UV surface photofunctionalization of ZrO2-based materials alters the human gingival fibroblast cell viability, which might produce favourable results for cell proliferation.

Fracture Load and Fracture Patterns of Monolithic Three-Unit Anterior Fixed Dental Prostheses after In Vitro Artificial Aging-A Comparison between Color-Gradient and Strength-Gradient Multilayer Zirconia Materials with Varying Yttria Content.

(1) Background: Due to advantages such as avoidance of chipping, pulp-friendly tooth preparation and cost reduction, zirconia is increasingly being used monolithically without veneering. Nevertheless, to enable good aesthetics, various multilayer systems have been developed. The aim of this study was to investigate the impact of different zirconia multilayer strategies and yttria levels on fracture load, fracture pattern, stress distribution and surface roughness. (2) Methods: Monolithic three-unit anterior FDPs were made from three different color-gradient zirconia multilayer materials with different yttria levels corresponding to varying strength and degrees of translucency grades (Katana HTML, STML, UTML, Kuraray) and one strength-gradient zirconia multilayer material (Katana YML, Kuraray) and artificially aged in a chewing simulator (1.2 × 106 load cycles, 50 N, 2 × 3000 thermocycles, 5–55 °C). Analyses of fracture load, fracture pattern, fracture surfaces, stress distribution and roughness were performed after the fracture load test. Shapiro–Wilk, Kruskal–Wallis, Mann–Whitney U-tests and one-way ANOVA were used (p < 0.05). (3) Results: Fracture loads of the high strength color-gradient material HTML and the strength-gradient material YML were comparable after 5 years of aging (p = 0.645). Increasing yttria levels resulted in a decrease in fracture resistance of 42–57% (p < 0.05). Surface roughness of different zirconia generations is comparable after polishing and aging. (4) Conclusions: Color-gradient multilayer zirconia materials and new strength-gradient zirconia materials with similar yttria levels in the basal layers show comparable mechanical properties and are suitable for anterior FDPs.