Multilayered Zirconia Research Articles

Effect of different CAD/CAM cutting depths on the post-fatigue load-bearing capacity of novel multilayer zirconia restorations

ObjectivesTo investigate the post-fatigue load-bearing capacity of restorations milled at various cutting depths in a novel strength- and color-gradient multilayer zirconia CAD/CAM disk. MethodsIdentical crowns were divided into 4 groups (n = 25 per group): crowns milled at 3 CAD/CAM cutting depths in multilayer zirconia disks as 3 experiment groups and homogeneous zirconia crowns as a control group. The color differences between various cutting depths were measured. In each group, crowns were tilted at 15° and subjected to fatigue loading for various numbers of cycles (0, 106, 2 × 106, 3 × 106 or 4 × 106, n = 5 per subgroup). All surviving crowns were subsequently submitted to a static fracture test to determine load-bearing capacity. The data were analyzed by ANOVA and Weibull distribution analysis. Failure modes were observed with SEM. ResultsFor a novel multilayer zirconia, a deeper CAD/CAM cutting depth corresponded to a higher load-bearing capacity but a darker color. After 106 cycles of fatigue loading, there was not a significant reduction in fracture load. However, after 4 × 106 cycles, the load-bearing capacity of all crowns decreased significantly by approximately 50%. For multilayer and homogeneous zirconia materials, similar failure mode and Weibull modulus were identified. ConclusionsRestorations can be milled at various CAD/CAM cutting depths in a novel multilayer zirconia disk depending on the durability and esthetic requirements. The load-bearing capacity of multilayer restorations degraded significantly after 4 × 106 cycles of fatigue loading, but not after 106 cycles. Clinical SignificanceFor a novel multilayer zirconia disk, a posterior restoration can be milled from the middle or bottom of the disk to improve its load-bearing capacity. For an anterior restoration, to meet the esthetic requirements, milling the entire thickness of a multilayer disk is recommended.

Translucency evaluation of an ultra-translucent monolithic zirconia and a super translucent multilayer zirconia: a pilot study on the thickness effect

Introduction The increasing application of zirconia as an aesthetic material has led to an evolution with improvement on its optical properties [1]. Nowadays, zirconia presents a compatible translucency with natural teeth. Depending on the clinical situation, you can choose a more translucent or more opaque zirconia. Due to its excellent mechanical properties, it is possible to return the function and aesthetics through a restoration with thicknesses lower than those required by other materials [2]. Materials and methods Twenty specimens of pre-sintered ultra-translucent (UT) monolithic zirconia (Bloomden W00098014UT) and twenty specimens of pre-sintered super translucent (ST) multilayer zirconia (Bloomden W00098016ST- ML-A2) were cut through the computer-aided design/computer-aided manufacturing system (Wieland Dental). For each type of zirconia, four subgroups (n = 5) were defined according to its thickness: 0.5, 1.0, 1.5 and 2.0 mm. All monolithic specimens were coloured with colouring liquid (BloomZir® UT Coping Crown A2) for 2 min. Finally, all zirconia specimens were sintered in the furnace (IMES-Wieland Zeno® Fire) at a temperature range of 1500 − 1550 °C and subsequently submitted to an ultrasonic bath (VGT-2120QTD 20 L) [3]. The values of L*, a* and b* were measured, under natural light (D65), using the spectrophotometer SpectroShade Micro (MHT S.p.A., Arbizzano di Negrar, Itália) at six different locations on a white background (Comission Internationale de l’ Éclairage (CIE) L*=95.6 a*= 0.8, b*= 0.1) and on a black background ((CIE) L *= 13.2, a *= 0.8, b *= −0.7). Translucency was assessed through the contrast ratio (CR) [4] and the translucency parameter (TP) [5]. Data was submitted to descriptive statistical analysis. Results Mean CR values ranged from 0.7 (±0.0) to 0.9 (±0.0) in UT monolithic zirconia and 0.8 (±0.0) to 0.9 (±0.0) in the ST multilayer zirconia. Mean TP values ranged from 14.1 (±0.3) to 26.7 (±0.4) in UT monolithic zirconia and 9.9 (±0.4) to 18.6 (±0.3) in ST multilayer zirconia. As thickness increases, translucency values decreased, in both materials. Discussion and conclusions Overall, ultra-translucent monolithic zirconia was found to be more translucent than the super translucent multilayer zirconia. The translucency showed to decrease when zirconia thickness increases.

Effect of hydrothermal aging on dental multilayered zirconia for monolithic restorations: An in vitro study

The aim of this in vitro study was to investigate the changes in mechanical, optical, and surface properties of multilayered zirconia during hydrothermal aging.One conventional block (Katana Zirconia HT) and three multilayered blocks (Katana Zirconia ML, STML, and UTML) of monolithic zirconia were examined. Bar-shaped specimens were autoclaved at 134°C and 0.2MPa for 0, 5, and 10 h. The Young's modulus, three-point flexural strength, and nanoindentation hardness were measured to evaluate the mechanical properties. The surface roughness, phase distribution, surface microstructure, and elemental composition were measured to analyze the surface properties. The contrast ratio and total transmittance were measured via spectrophotometry to evaluate the optical properties. Statistical differences were analyzed using appropriate ANOVA, Tukey HSD post hoc tests, and independent and paired sample t-tests (α = .05).The monoclinic phase increased gradually after hydrothermal aging. The yttrium and zirconium concentrations decreased, and the oxygen concentration and the surface roughness increased in all specimens (P<.05) after the aging process. All specimens showed significant grain push-out and microcracks. The total transmittance increased, and the contrast ratio and Young's modulus decreased in all specimens (P<.05) after the aging process. The nanoindentation hardness and three-point flexural strength exhibited a decreasing tendency after the aging process. However, there were no statistical differences (P>.05) between the materials. Significant interactions between material grades and hydrothermal aging were found for all the properties studied (P<.001).Microstructural alterations and significant phase transformations were detected on the surface of the multilayered zirconia after hydrothermal aging. The hydrothermal aging led to increased surface roughness, opaqueness, and elasticity of multilayered zirconia. The optical, mechanical, and surface properties of multilayered zirconia were influenced by the grade of the material after hydrothermal aging. Careful consideration of the grade of materials is necessary for the appropriate selection of multilayered zirconia ceramics for monolithic restorations.

Evaluation of fracture strength of two kinds of zirconia all-ceramic crowns with different edge compensation angles

Objective To evaluate the effects of different edge compensation angles on the fracture strength of multilayer zirconia all-ceramic crowns and traditional uniform zirconia all-ceramic crowns. Methods The resin tooth preparation specimen of the mandibular first molar with a knife-edge was fabricated. A 3D digital model of the specimen was obtained by scanning it with a 3D dental model scanner. The 3D digital model was imported into computer aided design (CAD) software, and three 3D digital models of the full crown with the same surface shape are designed with the edge compensation angles of 30°, 45° and 60°, respectively. Then, the designed 3D digital model is imported into computer aided manufacturing (CAM) software. Three kinds of multilayer and homogeneous zirconia all-porcelain crowns with different edge compensation angles were fabricated, 10 each for a total of 60. The fracture load of each crown was measured under the electronic universal testing machine. Results Fracture load of multilayer and uniform zirconia all-ceramic crowns, (4 322.86±610.07) N and (5 914.12±596.80) N in the 30° group, (5 264.82±883.76) N and (5 220.83±563.38) N in the 45° group and (4 900.42±345.41) N and (5 050.22±560.24) N in the 60° group, respectively. The fracture load of multi-layer zirconia all-ceramic crowns in the 30° group was significantly lower than that of homogeneous zirconia all-ceramic crowns(P 0.05). In the multi-layer zirconia all-ceramic crowns: the fracture load of the 30° group was significantly lower than that of the 45° group (P 0.05).In uniform zirconia full crown group: the 30° group was higher than the 45° group, the 30° group was higher than the 60° group (P 0.05). Conclusion The fracture loads of three kinds of uniform and multilayer zirconia all ceramic crowns with different edge compensation angles can meet the clinical requirements. A smaller edge compensation angle is recommended when using traditional zirconia all-ceramic crowns, while 45° is recommended when using multi-layer zirconia all-ceramic crowns.

Effect of margin design of Monolithic Multilayered zirconia Crowns on Internal &amp; Marginal Fit

Effect of margin design of Monolithic Multilayered zirconia Crowns on Internal &amp; Marginal Fit

PERSONALIZED CHOICE OF STRUCTURAL MATERIALS FOR ARTIFICIAL CROWNS FROM THE LEVEL OF MULTI-UNIT ABUTMENT OR TITANIUM PLATFORM FOR DIRECT PROSTHETICS ON DENTAL IMPLANTS

The high prevalence of secondary adentia in the adult population, as well as increased aesthetic requirements of patients has contributed to the development of orthopedic dentistry. Direct prosthetics on dental implants have been increasingly used for replacing defects in the dentition. However, the choice of structural materials for dental implant-supported prostheses is not fully understood. Hence, it remains a debatable issue.&#x0D; Purpose of the study: to justify the optimal structural materials for artificial crowns from the level of a multi-unit abutment or a standard titanium platform for direct prosthetics on dental implants with the use of finite-element analysis of the stress-strain state of the “bone tissue-dental implant-abutment-suprastructure” multidimensional model under the conditions of simulation modeling.&#x0D; Materials and methods. Specialized CAD / CAE software was employed to develop multi-dimensional computer models of biomechanical systems such as “bone tissue-dental implant-abutment-suprastructure” with simulation of direct prostheses on dental implants with the corresponding physical and mechanical properties of structural elements and load conditions. The created 10 simulation models were based on combinations of two types of abutment (standard titanium platform (A1) and multi-unit abutment (A2)), and five structural materials of the crown, including lithium disilicate glass ceramic (KM1), polymer-infiltrated hybrid ceramic (KM2), polymethyl methacrylate (PMMA) (KM3), zirconia (KM4), and multi-layer zirconia (KM5)). The stress-strain state and the bearing capacity of biomechanical systems were assessed with the use of the von Mises stresses analysis and safety factors.&#x0D; Results. During a numerical experiment, there was revealed a complex stress-strain state in “bone tissue - dental implant - abutment - suprastructure” biomechanical systems. The maximum loads were recorded in systems with A1 and A2 type of abutment in the crown models (149.37 MPa and 142.08 MPa, respectively), spongy (4.25 MPa and 4.08 MPa) and the cortical bone (20.58 MPa and 20.61 MPa). The nature of the distribution of the von Mises stresses in the structural elements of systems with A1 and A2 types of abutments was found to be similar for all models under consideration with KM1, KM2, KM4, KM5 structural materials of crowns, except for the system with KM3 suprastructure material.&#x0D; Conclusions. Based on the findings of computer simulation of the stress-strain state of “bone tissue - dental implant - abutment - suprastructure” biomechanical systems, there have been grounded the optimal structural materials for dental implant-supported crowns for direct prosthetics by such abutment as a standard titanium platform and multi-unit abutment. The obtained values of the von Mises stresses analysis and safety factors showed that with external force applied to the dental implant-supported crown the at an angle of 11.5°, the greatest bearing capacity was ensured by biomechanical systems with a standard titanium platform and multi-unit abutment with crown materials including zirconia (safety factors 6.22 and 6.42 respectively), multilayer zirconia (safety factors 5.52 and 5.70) and lithium disilicate glass ceramic (safety factors 2.39 and 2.52).

Multilayer zirconia: Influence of positioning within blank and sintering conditions on the in vitro performance of 3-unit fixed partial dentures

Statement of problemMultilayer zirconia blanks comprise material layers with different optical and mechanical properties. Whether positioning within the blank, as well as variation in the sintering procedure, will lead to restorations with different properties is unclear. PurposeThe purpose of this in vitro study was to test the influence of sintering procedures and positioning in a multilayer blank on the in vitro performance of 3-unit zirconia fixed partial dentures. Material and methodsHuman molars were embedded in acrylic resin and prepared for 3-unit fixed partial dentures. Anatomic contour prostheses were milled from zirconia blanks (ZirCAD Prime 16 mm) in 3 different positions: above (cusp-top at the top of the blank), central (center of the prosthesis in the center of the blank), and bottom (margins at the lower edge of the blank). Sintering time (2:26, 4:25, 9:50 hours:minutes) was varied for the central and bottom prostheses. All prostheses were glazed and adhesively bonded. Thermocycling and mechanical loading was performed at 2×3000×5 °C/55 °C in distilled water for 1.2×106 cycles at a 50-N load. Then, fracture force was determined with a universal testing device by using central loading, a Ø12-mm steel ball, a 1-mm tin foil, and a rate of 1 mm/min. Failure was defined as 10% force drop or acoustic signal (crack). Statistical analysis was performed with 1-way ANOVA and Bonferroni correction (α=.05). ResultsAll fixed partial dentures survived thermocycling and mechanical loading. Fracture forces varied between 1002 ±446 N (above; 9:50 hours) and 1760 ±607 N (central; 9:50 hours). The 1-way ANOVA revealed no statistically significant differences (P=.059) among the groups. Individual significant differences (P=.048) were found between prostheses from positions above, 9:50 hours, and central, 9:50 hours. For normal and long sintering times, fracture forces were highest in the central position. ConclusionsThe sintering process and positioning of restorations within a multilayer zirconia blank have little effect on the mechanical properties of the prostheses.

Wear behavior and microstructural characterization of translucent multilayer zirconia

ObjectiveTo characterize the composition, microstructure and wear properties of a multilayer translucent zirconia relative to the conventional 3Y-TZP. MethodsTwo types of ceramics were evaluated: a multilayer zirconia (MULTI, IPS e.max ZirCAD Multi, Ivoclar Vivadent) and a control 3Y-TZP (IPS e.max ZirCAD LT, Ivoclar Vivadent). Pre-sintered CAD-CAM blocks were cut, ground, sintered and polished to 1 μm finish. The phase fraction and grain size were measured using XRD and FE-SEM. For wear testing (n = 12), square-shaped specimens (16 × 16 × 1 mm) were adhesively bonded to a dentin analog. Sliding wear tests were performed using a spherical zirconia antagonist (r = 3.15 mm), with 30 N load at 1.5 Hz for 500,000 cycles in water. Optical and scanning electron microscopes and 3D laser scanner were used for quantitative wear analyses. Data were analyzed using Student’s t-test (α = 0.05). ResultsFor MULTI, the enamel layer had the highest cubic content and the largest grain size, followed by the two transition layers, and the dentin layer. 3Y-TZP showed the smallest grain size and cubic content. A significant amount of wear was observed in both materials up to 50,000 cycles until it reached a plateau. MULTI showed higher volume loss and greater wear depth than 3Y-TZP (p < 0.01). The higher volume loss was associated with extensive lateral fracture, leading to material spalling from the surface of cubic-containing zirconias. SignificanceThe wear pattern in multi-layered zirconia was more severe than 3Y-TZP. Additionally, the different layers of the multi-layered zirconia had similar wear behavior.

Mechanical properties and translucency of a multi-layered zirconia with color gradient for dental applications

In this work, the properties of yttria-stabilized zirconia-based ceramics, Y-TZP containing Fe2O3 as coloring agent were evaluated. Nanoparticled powder of 3Y-TZP (ZrO2 - 3 mol.% Y2O3) doped with different amounts of Fe2O3 (0.002–0.136 wt%) were compacted into monolithical or multilayered samples and sintered at 1475 °C - 2 h. The samples were characterized by X-ray diffraction analysis (XRD), relative density, scanning electron microscope (SEM). Hardness and fracture toughness in the color interface were investigated using the Vickers indentation method and the biaxial flexural strength was determined by the piston on 3 balls method (P–3B). Furthermore, optical parameters were measured using spectrophotometry in regard to sample thickness and Fe2O3 content. The results indicated a good adhesion between layers, proven by indentation cracks randomly growing between different regions, because the powders used produced very similar morphological characteristics. The different amounts of Fe2O3 studied in this work did not interfere in densification, phase composition, or microstructure of the sintered ceramics. The fracture toughness and flexural strength did not significantly change due to the addition of Fe2O3, presenting values close to 7 MPa m1/2 and 1120–1150 MPa, respectively, in all studied compositions. On the other hand, increasing Fe2O3 contents lead to an increase in the hardness of the material (1280–1330 H V), and higher contrast ratios (CR) with a consequent loss of translucency. Color variation (ΔE) depended also on the thickness of the material.

Comparison between novel strength-gradient and color-gradient multilayered zirconia using conventional and high-speed sintering

ObjectivesTo investigate and compare the mechanical and optical properties of novel strength- and color-gradient multilayered zirconia and the impact of conventional and high-speed sintering. Materials and methodsFollowing zirconia materials were analyzed and compared: the high-speed sintered Katana Zirconia Block STML (4Y-TZP, KZC), the conventionally sintered Katana Zirconia Disc STML (4Y-TZP, KZL) and IPS e. max ZirCAD Prime (5Y-TZP/3Y-TZP, EZL). As control group acted the crystallized lithium disilicate ceramic IPS e. max CAD (ELC). Monolithic single molar crowns were fabricated and half of them were aged in a chewing simulator with human enamel antagonists (1.2 × 106 cycles, 50 N, lateral movement of 0.7 mm, 5/55 °C). The fracture load was tested in a universal testing machine (N = 96/n = 12). The two-body wear was determined using 3D matching of pre- and post-scans (N = 48/n = 12). Translucency (N = 36/n = 10) was evaluated with UV/Vis spectrophotometer. Data was analyzed using Kolmogorov-Smirnov test, one-way ANOVA followed by post-hoc Scheffé test, unpaired t-test and Weibull analysis (p < 0.05). ResultsZirconia groups showed higher fracture load than ELC (p ≤ 0.001). Initially, all zirconia materials ranged in the same values (p > 0.05). After chewing simulation, EZL showed higher fracture load than KZC (p < 0.001) and KZL (p = 0.043). Zirconia materials showed no material loss, whereas the ELC showed the volumetric wear of 0.334 ± 0.34 mm3 and vertical wear of 0.155 ± 0.07 mm. Enamel antagonist wear ranged in the same values (p = 0.083-0.906). The translucency values within each zirconia material showed significant differences between the enamel and the dentin layers (p < 0.001). ConclusionsThe novel strength and color-gradient multilayered zirconia showed higher mechanical properties than lithium disilicate ceramic. The high-speed sintering of zirconia showed neither a negative impact on the fracture load nor on the two-body wear. However, the optical properties and the reliability of zirconia is lower than those of highly translucent lithium disilicate ceramic.

Do different sintering conditions influence bond strength between the resin cements and a currently used esthetic zirconia?

The present research aimed to evaluate the effect of sintering temperature (1300 °C, 1400 °C and 1600 °C) on short-term and long-term SBS values (SBS1 and SBS2, respectively) as well as grain size and surface roughness of a novel multi-layered monolithic zirconia material (Katana STML). One hundred and eighty-six samples (N = 186) of monolithic zirconia were prepared and randomly divided into three groups (n = 62) according to the final sintering temperatures. Two samples from each group were taken before and after sandblasting for scanning electron microscopy (SEM) examination. The surface roughness (Ra) values were determined. Sixty samples for each group were divided into three subgroups according to the resin cement (n = 20) and luting procedures were performed. Half of the specimens for each subgroup (n = 10) were non-aged, while the other half (n = 10) were aged before shear bond strength test (SBSt). One-way analysis of variance (ANOVA), two-way ANOVA and independent samples T-test were used to analyse the data. The sintering temperature, resin cement and their interaction were significant (p ≤ .05) for both aged and non-aged samples. The grain sizes and Ra values of monolithic zirconia significantly increased by the increase of sintering temperature (p ≤ .05). The aging significantly reduced SBS values (p ≤ .05). Sintering temperature and resin cement affected both SBS1 and SBS2 values between resin cement and monolithic zirconia (p ≤ .05). Application of 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) containing primer revealed an increase in long-term SBS values in response to the increase in sintering temperature.

Effects of Khat on Surface Roughness and Color of Feldspathic and Zirconia Porcelain Materials under Simulated Oral Cavity Conditions.

Background and Objectives: Khat chewing is considered as a daily habit that is practiced by more than five million people globally. The effect of khat chewing on the surface roughness and the color stability of natural teeth and the material used in the fabrication of dental prosthesis remains unknown. This study was conducted to explore and compare the effect of khat homogenate (KH) on the surface roughness (Ra) and the average color changes (ΔE*) amongst natural teeth and selected shades from different porcelain types, namely, feldspathic metal ceramic (MC) VM13, computer-aided design/computer assisted manufacture (CAD/CAM) feldspathic (Vitablocs Mark II), and multilayer zirconia (Ceramill Zolid PS) porcelains. Materials and Methods: Seventy samples were prepared from natural teeth, feldspathic MC, CAD/CAM Vitablocs Mark II, and zirconia porcelain. The Ra values were measured using a profilometer and expressed in micrometers, whereas the ΔE* values were measured using VITA Easyshade® V spectrophotometer for all samples before and after frequent immersion and thermocycling in KH for 30 days. The surface topography was used to assess the materials surfaces (glazed or polished) after KH immersion by using a white light interferometry machine. Results: Results revealed that the Ra and the ΔE* values of the different types of tested porcelain were influenced by KH. The order of surface roughness values was glazed or polished MC > polished Zircon > polished Vitablocs Mark II > natural teeth. The lowest ΔE* values were recorded for glazed Vitablocs Mark II and MC, and the values could be arranged as polished zircon > natural teeth > glazed zircon > polished MC > polished Vitablocs Mark II. P values were significantly varied (<0.001) among all the tested groups, except the zircon group (>0.05) for both Ra and ΔE*. Conclusions: KH significantly affected both surface parameter and color of glazed or polished porcelain materials and natural teeth.

Marginal and internal fit of three-unit zirconia fixed dental prostheses: Effects of prosthesis design, cement space, and zirconia type

PurposeThe purpose of this study was to compare the marginal and internal fit of three-unit fixed dental prostheses (FDPs) fabricated using CAD/CAM with two designs, two cement space (CS), and two zirconia types. MethodsA master model with two zirconia abutments and a missing tooth was scanned with an intraoral scanner. FDPs were fabricated with two designs (Full contour: FC, Framework: FW), two zirconia types (multi-layer: L, single-layer: W), and two CS values (30 and 45 μm for L and 30 μm for W). There were six experimental groups. The fit of the FDPs was evaluated using the replica method. The space between an abutment and the FDPs in the marginal (MO), chamfer (CH), axial (AX), and occlusal (OC) areas was measured under an optical microscope and the data was statistically analyzed using three-way ANOVA and Bonferroni test (p < 0.05). ResultsFW-l-45 μm showed a significantly smaller space than those for the FC in MO (p = 0.011), CH (p = 0.001) and AXE (p = 0.003). FW-l-30 μm showed a significantly smaller space than that for the 45 µm in AXE (p = 0.000) and OC (p = 0.016). FW-W-30 µm showed a significantly smaller space than that for the L in MO (p = 0.000), CH (p = 0.000), AXE (p = 0.000), and OC (p = 0.002). ConclusionsThe design and CS of the FDPs affected the fit. FDPs with single-layer zirconia showed better fit than that obtained with multi-layer zirconia.

The Effect of Thermocycling on the Translucency and Color Stability of Modified Glass Ceramic and Multilayer Zirconia Materials.

AimThe aim of this in vitro study was to evaluate the new, multilayered, translucent zirconia and enhanced glass-ceramics to determine if their translucency (TP) and color stability (ΔE) are affected by thermocycling at 10,000, 30,000, and 50,000 cycles.Materials & methodsTwo pre-shaded, multilayer zirconia products: Prettau® 2 Dispersive® (PRT) and Prettau® 4 Anterior® Multi® (PRTA), and two glass-ceramic: IPS e.max CAD® HT (E.max) and Vita Suprinity® HT (VS) were used. All were prepared and sectioned to get plate specimens with dimensions 12.5x14.5x1 mm (n=12) for each material. The L*a*b* values were recorded using a spectrophotometer before and after thermocycling for 10,000, 30,000, and 50000 cycles. The translucencies of the specimens were calculated using the TP formula and the color changes were giving by the color differences ΔE formula at each interval.ResultsOne-way analysis of variance (ANOVA) was used to analyze the data followed by Scheffe’s post-hoc test and multiple paired t-tests (P < 0.05). There was a statistically significant higher TP for E.max before (16.2) and after aging (16.9) (p<0.001**). All the tested groups showed a statistically significant increase in their TP at different intervals. PRT showed significantly higher ΔE (p<0.001**) after 50,000 cycles.ConclusionThere was a mild but significant increase in translucency in both Zirconia and glass-ceramic after thermocycling. In addition, all materials showed a significant color change with time, however, this is not clinically perceptible.

Spectrophotometric examination of the optical effects of monolithic multilayered zirconia with different substrates

ABSTRACT The goal of this study is to examine specific optical effects of multilayered and coloured monolithic zirconia considering thickness and substrates of different colours using one of the most advanced spectrophotometers of the world. Multilayered zirconia specimens were used for the study with the thickness range of 0.5–2.5 mm and six types of substrate materials and three types of metal substrates. Measurements were carried out at Budapest Technical University with a PerkinElmer®Lambda1050UV/Vis/NIR spectrophotometer. The substrate colour and the thickness of zirconia affects the optical results, with special regard to colour perceptibility and acceptability. Monochromatic and multilayer zirconia show both similarities and discrepancies in behaviour, i.e. spectral reflectance and ΔE. Owing to the multi-coloured characteristics of multilayered zirconia the optical effect of the substrate less predictable than in the case of monochromatic zirconia thus requiring more detailed planning and implementation.

Flexural properties, bond ability, and crystallographic phase of highly translucent multi-layered zirconia.

This study investigated the mechanical properties, bond ability, and crystallographic forms of different sites in a highly translucent, multi-layered zirconia disk. Flexural properties, bond ability to resin cement, and phase composition were investigated at three sites of a highly translucent, multi-layered zirconia disk: incisal, middle, and cervical. Flexural strength (FS) and flexural modulus (FM) were measured with static three-point flexural test. Shear bond strength (SB) to resin cement was measured after 24 h storage (37°C). Phase composition under mechanical stress was analyzed using X-ray diffraction. Without air abrasion, FS at the incisal site yielded the lowest value and was significantly lower than the middle and cervical sites. Air abrasion lowered the FS of each site. FM at the incisal site without air abrasion showed the significantly lowest value, and air abrasion increased its FM value. At the middle and cervical sites, their FM values were higher than the incisal site but were not significantly affected by air abrasion. SB value did not show significant differences among the sites. After sintering, cubic zirconia was detected at each site. Rhombohedral phase transformation occurred after mirror polishing. In highly translucent, multi-layered zirconia which was mainly composed of cubic zirconia, rhombohedral phase transformation occurred under mechanical stress and resulted in weakened mechanical properties.

Probing the interfacial strength of novel multi-layer zirconias

ObjectivesThe rapidly increasing use of zirconia-based CAD/CAM multi-layer structures in dentistry calls for a thorough evaluation of their mechanical integrity. This work examines the effect of the multi-layering architecture as well as variations in composition and inclusion of pigments among the layers on the flexural strength of multi-layer zirconias. MethodsA modified 4-point bending test, aided by a Finite Element Analysis (FEA), was used to probe the interfacial strength of 3 classes of yttria-partially-stabilized zirconia: Ultra Translucent Multi-Layer (UTML—5Y-PSZ), Super Translucent Multi-Layer (STML—4Y-PSZ), Multi-Layer (ML—3Y-PSZ). In accord with the size limitation (22-mm height) of CAD/CAM pucks, test samples were prepared in the form of “long” (25×2×3mm) and “short” (17.8×1.5×2mm) beams. Homogeneous beams (both long and short) were produced from either the Enamel (the lightest shade) or Dentin (the darkest shade) layer, whereas multi-layer beams (short beam only) were obtained by cutting the pucks along their thickness direction, where the material components of various shades were stacked. ResultsThe Enamel and Dentin layers exhibited similar flexural strength for a given material class, with ML amassing the highest strength (800–900MPa) followed by STML (560–650MPa) and UTML (470–500MPa). The 3 classes of multi-layer zirconia showed a trade-off between strength and translucency, reflecting different yttria contents in these materials. The failure stress of the cross-sectional multi-layer beams was, however, ∼30% lower than that of their Enamel or Dentin layer counterparts, regardless of material tested. SignificanceThe weakness of interfaces is a drawback in these materials. Additionally, when measuring strength using short beam flexure, friction between the specimen and supporting pins and accuracy in determining loading span distances may lead to major errors.

Comparison of fracture strength and color of zirconia copings according to multi-layer zirconia blocks and sintering method

Comparison of fracture strength and color of zirconia copings according to multi-layer zirconia blocks and sintering method

Comparison of Mechanical Properties of Zirconia Copping by multi-layered zirconia blocks and Design locations

Comparison of Mechanical Properties of Zirconia Copping by multi-layered zirconia blocks and Design locations

Effects of Speed Sintering on Multilayered Monolithic Zirconia

Objective:In dentistry, different products are being developed in order to shorten the chairside but the interactions between these materials needs further investigations. This study aims to investigate the two different short time sintering protocols on monolithic multilayered zirconia’s surface roughness (SR), translucency parameter (TP), and contrast ratio (CR). Material and Methods:Twenty monolithic multilayer zirconia specimens were prepared with the dimension 10x10x1 mm and divided into two sintering groups (speed sintering group 30 min at 1510 0C, high speed sintering group 10 min 1580 0C) and SEM analyzed were performed. Surface roughness tests were performed by using profilometer and optical measurements were performed by using spectrophotometer. The data was statistically analyzed by using Wilcoxen test at the 0.05 probability level.Results:SR values and CR did not show any significant difference at any layer of any group. In all parts of monolithic multilayered zirconia, the difference of TP between sintering groups were statistically significant (P&amp;lt;.05). Conclusion: High speed sintering parameters has promising effects on monolithic multilayered zirconia with combined acceptable optical properties. Because of their different content, different layers show different reactions in terms of contrast ratio and translucency parameters and these changes should be taken into account in treatment planning.