Types Of Zirconia Research Articles

Evaluation of the Bonding Shear Strength between Enamel and Dentin Feldspathic Porcelain and Two Different Monolithic Zirconia with Low and High Translucency.

The utilization of ceramics in the field of dentistry has seen a significant rise owing to their esthetic appeal and excellent functional properties. The use of ceramics in the field of dentistry has witnessed a notable surge, driven by their appealing esthetics and exceptional functional attributes. Zirconia, distinguished by its exceptional mechanical strength, plays a pivotal role in the fabrication of posterior crowns and bridges. Among zirconia variants, monolithic zirconia stands out, where the entire restoration is crafted from zirconia material. In parallel, feldspathic porcelain, chosen for its remarkable resemblance to natural tooth enamel, represents another significant ceramic type. This study aims to evaluate the shear bond strength (SBS) between two types of monolithic zirconia with two types of feldspathic porcelain. Forty-four monolithic zirconia veneered discs with feldspathic porcelain were subjected to SBS testing. The dimensions of the discs were 7 mm in diameter and 5 mm in height (3 mm of zirconia and 2 mm of porcelain). Subsequently, the specimens were subjected to a universal testing machine at a speed of 0.5 mm/min until failure occurred. The type of failure was examined using scanning electron microscopy. One-way analysis of variance (ANOVA), two-way ANOVA, Fisher's test, and multiple Tukey comparisons were used as statistical analyses. The highest SBS was achieved by the high-translucency monolithic zirconia with enamel porcelain group (18.81 ± 3.18 MPa) and the high-translucency monolithic zirconia with dentin porcelain group (17.89 ± 2.75 MPa), followed by the low-translucency monolithic zirconia with dentin porcelain group (15.04 ± 2.24 MPa) and the low-translucency monolithic zirconia with enamel porcelain group (14.33 ± 2.00 MPa), respectively. Additionally, the most common type of failure pattern observed was mixed, followed by adhesive failure. The translucency of the porcelain did not significantly affect SBS, while the type of monolithic zirconia used had a significant impact. Furthermore, there was no discernible relationship between the four groups in terms of the distribution of failure patterns.

In vitro effect of zirconia type on shear bond strength to feldspathic porcelain and wear of the opposing teeth.

Multilayer zirconia has more optical and aesthetic features than regular zirconia. Therefore, its mechanical properties should be compared with monochromatic zirconia. Among the mechanical characteristics that can be checked are the wear of the opposite tooth and the bond to the porcelain. This study assessed the effect of zirconia type (multilayer versus monochromatic) on the shear bond strength (SBS) to feldspathic porcelain and the wear of the opposing teeth. The present in vitro study was conducted in two phases. In the first phase, 15 multilayer and 15 monochromatic zirconia blocks measuring 10×5×5 mm were designed, milled, sintered, veneered with porcelain, and underwent thermocycling. Their SBS was then measured in a universal testing machine. In the second phase, 15 multilayer and 15 monochromatic zirconia blocks were placed in a chewing simulator, and 30 sound premolars served as antagonistic teeth. The magnitude of wear of the buccal cusp of premolars was quantified from a 4-mm reference point after 100000 cycles. Data were analyzed by independent t test (α=0.05). The mean SBS of monochromatic zirconia to porcelain (24.49±3.58 MP) was slightly higher than that of multilayer zirconia (22.98±2.98 MP), but the difference was not significant (P>0.05). The mean wear of the opposing teeth was also slightly higher in the monochromatic group (284.1±66.53 µm) than in the multilayer group (263.2±58.69 µm), but this difference was not significant either (P>0.05). Monochromatic and multilayer zirconia showed comparable SBS to feldspathic porcelain and caused comparable wear of the opposing teeth in vitro. Thus, multilayer zirconia may serve as an alternative to monochromatic zirconia.

How could mouthwashes affect the color stability and translucency of various types of monolithic zirconia? An in-vitro study.

This study aimed to evaluate the color stability and translucency of various types of monolithic zirconia after immersion in chlorhexidine and Listerine mouthwashes. This experimental study was performed on 36 disk-shaped specimens fabricated from low-translucent, high-translucent, and multilayered monolithic zirconia (n = 12 per group). Each group was equally divided and immersed in either 2% chlorhexidine (CHX) or Listerine mouthwash for 2 min daily over 7 days. Changes in color (ΔE) and the translucency parameter (ΔTP) were evaluated and compared. The data were analyzed with one-way ANOVA followed by Tukey's post-hoc tests (α = 0.05). Chlorhexidine caused a significantly lower ΔE and a significantly higher ΔTP in multilayered zirconia compared to the low-translucency (ΔE: P = 0.0027, ΔTP: P<0.001) and the high-translucency zirconia group (ΔE: P<0.001, ΔTP: P = 0.022). Listerine caused a significantly higher ΔE in the high-translucency zirconia group compared to the multilayered zirconia group (P = 0.0165). It also resulted in a significantly higher mean ΔTP in the multilayered zirconia group compared to the low-translucency (P = 0.0003) and high-translucency zirconia groups (P = 0.019). In both mouthwashes, multilayered monolithic zirconia exhibited the highest color stability among the tested materials; albeit with the most pronounced changes in translucency. Meanwhile, high-translucency monolithic zirconia was more prone to discoloration when exposed to both mouthwashes.

Surface Roughness and Bacterial Colonization Of Two Types Of Zirconia (Cubic And Gradient) After Accelerated Hydrothermal Aging. (Comparative In-Vitro Study)

Surface Roughness and Bacterial Colonization Of Two Types Of Zirconia (Cubic And Gradient) After Accelerated Hydrothermal Aging. (Comparative In-Vitro Study)

Translucent Zirconia in Fixed Prosthodontics-An Integrative Overview.

Over the past two decades, dental ceramics have experienced rapid advances in science and technology, becoming the fastest-growing field of dental materials. This review emphasizes the significant impact of translucent zirconia in fixed prosthodontics, merging aesthetics with strength, and highlights its versatility from single crowns to complex bridgework facilitated by digital manufacturing advancements. The unique light-conducting properties of translucent zirconia offer a natural dental appearance, though with considerations regarding strength trade-offs compared to its traditional, opaque counterpart. The analysis extends to the mechanical attributes of the material, noting its commendable fracture resistance and durability, even under simulated physiological conditions. Various zirconia types (3Y-TZP, 4Y-TZP, 5Y-TZP) display a range of strengths influenced by factors like yttria content and manufacturing processes. The study also explores adhesive strategies, underlining the importance of surface treatments and modern adhesives in achieving long-lasting bonds. In the realm of implant-supported restorations, translucent zirconia stands out for its precision, reliability, and aesthetic adaptability, proving suitable for comprehensive dental restorations. Despite its established benefits, the review calls for ongoing research to further refine the material's properties and adhesive protocols and to solidify its applicability through long-term clinical evaluations, ensuring its sustainable future in dental restorative applications.

Er:YAG laser debonding of zirconia and lithium disilicate restorations

Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) restorations of different formulations are being used increasingly in monolithic form for a range of clinical applications. Using rotary instruments to remove such restorations for any purpose is challenging, but they can be removed conservatively with erbium lasers. However, studies on how a laser penetrates different zirconias to break the cement bond between the tooth surface and the zirconia are lacking. The purpose of this in vitro study was to evaluate and compare the time required for an erbium-doped yttrium-aluminum-garnet (Er:YAG) laser to remove different types of zirconia and lithium disilicate crowns. Forty extracted premolar teeth were prepared, scanned, designed, and milled to fabricate 40 computer-aided design and computer-aided manufacturing (CAD-CAM) crowns, which were assigned to 4 groups (n=10): 3mol% Y-TZP, 4mol% Y-TZP, 5mol% Y-TZP, and lithium disilicate as a control. All crowns were bonded to the teeth with a self-adhesive resin cement (Panavia SA Cement Universal). Each specimen was irradiated with an Er:YAG laser with the following parameters: 300mJ, 15Hz, 5.0W, and a 50-microsecond pulse duration (supershort pulse mode). The irradiation time required for crowns to be retrieved successfully was recorded for each specimen. Data were statistically analyzed using analysis of variance and the Tukey honestly significant difference post hoc test (α=.05). The intaglio surfaces of the restorations were analyzed using scanning electron microscopy (SEM). The mean ±standard deviation times in minutes needed for crown debonding were 12.46 ±4.17 for the 3mol% Y-TZP group, 10.30 ±3.33 for the 4mol% Y-TZP group, 4.03 ±1.62 for the 5mol% Y-TZP group, and 2.08 ±0.92 for the lithium disilicate group. A statistically significant difference (P<.05) in the debonding time was found for all investigated groups, expect between the 3mol% and 4mol% Y-TZP groups and between the 5mol% Y-TZP and lithium disilicate groups. SEM analysis of the ceramic surfaces showed no visual damage associated with Er:YAG laser irradiation. Zirconia crown retrieval time with the Er:YAG laser was influenced by the yttria content of the zirconia, with decreasing retrieval time with increasing yttria content. Er:YAG laser debonding of zirconia crowns is a noninvasive, efficient, and rapid approach to the removal of crowns and could be applied in clinical practice.

Zirconia restoration types, properties, tooth preparation design, and bonding. A narrative review.

The purpose of this review was to provide dental professionals with information regarding the various types of zirconia restorations, their mechanical and optical properties, tooth preparation design, and bonding protocol in an effort to enhance the longevity and durability of zirconia restorations. The yttria content of zirconia ceramics determines their classification. The mechanical and optical properties of each type are discussed, with an emphasis on the effect of yttria concentration on the properties of zirconia. The processing and sintering methods are also discussed as they have a direct impact on the properties of zirconia. The design of tooth preparation, specifically occlusal reduction, varies depending on the type of zirconia used in each case. Finally, a protocol for zirconia restoration bonding is described to ensure optimal bonding to the tooth structure. Not all zirconia restorations are the same. The selection of zirconia type based on yttria concentration, processing and sintering methods, tooth preparation design, and adherence to the bonding protocol are all critical to the success and longevity of zirconia restorations. Zirconia restorations are the most commonly used indirect restorative material. The selection of the most appropriate zirconia type based on its yttria content, which determines its strength and translucency, is critical to the success and the longevity of the restoration. Tooth preparation design also influences the strength and translucency of the zirconia. Air-borne particle abrasion, followed by a ceramic primer and resin cement, can ensure a durable bond to the tooth structure.

Effect of High-Speed Sintering on the Optical Properties, Microstructure, and Phase Distribution of Multilayered Zirconia Stabilized with 5 mol% Yttria.

As dental 5 mol% yttria-stabilized (5Y-) zirconia demand high esthetics, it is necessary to clarify how the optical properties are affected by high-speed sintering, which is not yet fully understood. Our study aimed to investigate the effect of high-speed sintering on the translucency and opalescence parameters (TP and OP, respectively), as well as their related microstructure and phase distribution, using two types of multilayered 5Y-zirconia. Multilayered 5Y-zirconia (Cercon xt ML, Lava Esthetic) were cut layer-by-layer, followed by conventional and high-speed sintering. The TP and OP values were subsequently obtained using a spectrophotometer, and field emission scanning electron microscopy images were used to analyze the average grain size. The phase fractions were analyzed using X-ray diffraction. Regardless of the zirconia type, the TP was slightly lowered by high-speed sintering in all the layers except the dentin layer (DL) for Lava Esthetic (p < 0.05). The OP decreased by high-speed sintering in the DL for Cercon xt ML and in all the layers for Lava Esthetic (p < 0.05). The decrease in translucency after high-speed sintering was attributed to a decrease in the yttria-rich t'-phase with low tetragonality, along with an increase in the yttria-lean t-phase with high tetragonality.

Analysis of the effect of thermocycling on bonding cements to zirconia

ObjectiveThe aim of this study was to evaluate the effect of thermocycling on shear bond strength (SBS) of several resin cement materials to different types of zirconia dental ceramics. Materials and Methods120 square shaped disc specimens were fabricated using two types of zirconia blocks (Sagemax and Sirona). Each zirconia group was divided into three sub-groups based on the resin cement bonded to the specimens. Three different self-adhesive resin cements were used (Calibra, Breeze and RelyX). The specimens were further grouped into experimental and control groups (n = 10). The experimental specimens were exposed to a thermo-cycling protocol of 1500 cycles in water bath at 5c and 55c. Specimens were then stored at 37c for 24 h then all specimens underwent SBS test with an Instron machine. Mode of failure was inspected visually and microscopically. Data were statistically analyzed using multivariate analysis of variance followed by one-way analysis of variance, Tukey’s multiple comparison test, student’s t-test for independent samples were used to compare the mean values of SBS in relation to the categorical study variables. ResultsThe mean SBS values of experimental groups were significantly lower than control groups for all the 6 combinations of Zirconia and cement types (p < 0.0001). The higher mean difference (14.29 MPa) was observed in the combination of Sagemax and Rely-X. Rely-X displayed the highest SBS among all the cements while no significant difference was found in mean SBS values of Calibra and Breez cements in all groups. The mean SBS values of Sagemax zirconia were significantly higher than the Sirona with all three types of cements (p < 0.0001) within control groups. Microscopic and visual analysis demonstrated a majority of adhesive mode of failure. ConclusionThermocycling significantly reduced the SBS between the zirconia materials and self-adhesive resin cements tested. The amount of reduction varies according to cement and zirconia types.

Evaluation of the Effect of Two Surface Treatment Methods on Shear Bond Strength between Porcelain Veneer and Two Different Zirconia Blocks

Introduction: The aim of the study was to test the effect of two surface treatment methods on shear bond strength between a porcelain veneer and two different zirconia blocks. Materials and Methods: Sixty disk-shaped zirconia samples (30 samples of Novi brand and 30 samples of Rainbow brand) were used (diameter of 10 mm and thickness of 4 mm). Based on surface treatment, the samples were randomly divided into 3 groups: control, air-particle abrasion, and Zircos-E Etching Solution. Using the metal mold, the porcelain was veneered on the zirconia surface and then fired. Then, all samples were subjected to shear bond strength testing using a universal testing machine at a speed of 1 mm/min until breaking. Results: There was a statistically significant difference between the mean variable shear bond strength of the control group and two other groups, so the shear bond strength in the control group was less than in both groups. And there was no statistically significant difference between the mean variable of shear bond strength in the two groups of “airborne particle abrasion” and “Etching”. There was a statistically significant difference between the mean shear bond strength of the two types of zirconia samples and this amount was lower in Novi than in Rainbow. There was also no interaction between the type of surface preparation and the type of zirconia. Conclusion: It can be concluded that surface preparation with air particle abrasion and etching increases the shear bond strength of zirconia to porcelain veneer and the shear bond strength of zirconia and porcelain veneer is affected by the type of zirconia.

Optical effect of rapid sintering protocols on different types of zirconia

Statement of problemRapid sintering protocols are available for the fabrication of zirconia restorations, but whether rapid sintering influences color or translucency is unclear. PurposeThe purpose of this in vitro study was to investigate the effect of different rapid sintering protocols on the color and translucency of cubic and tetragonal zirconias. Material and methodsSixty disk-shaped specimens of 1-mm-thick cubic (DD CubeX2) and tetragonal (DD Bio ZX2) zirconia were investigated. Specimens of each type of zirconia were divided into three groups: conventional, speed, and superspeed sintering protocols. The conventional group of each zirconia type served as the control for calculating color differences. Translucency for each group was assessed by the translucency parameter and contrast ratio. Two-way analysis of variance was used for statistical analysis of the data (α=.05). ResultsThe translucency of cubic and tetragonal zirconia decreased after speed and superspeed sintering (P<.001). Superspeed sintering resulted in a greater color change than speed sintering (P<.001). ConclusionsRapid sintering protocols produced a significant effect on the color and translucency of cubic and tetragonal zirconias.

Effect of Aging Treatments on Properties of Zirconia with Different Levels of Translucency

Purpose: The aim of this study was to evaluate the effect of low-temperature degradation(L-TD), and weathering process on translucency, surface roughness, biaxial-flexural strength, and crystalline phase identification of zirconia with different levels of translucency. Materials and methods: A total of ninety-six (N= 96) zirconia discs were fabricated in this study. Samples were divided into three groups (n=32 each) according to type of zirconia: IPS EmaxZirCAD of low, medium translucency and Incoris translucent Zirconia of high translucency. Translucency measurements, surface roughness, biaxial flexural strength determination and phase identification were carried out before and after aging. Each group was then sub-divided into 2 subgroups (n=16); (subgroup A): Low-temperature degradation(L-TD) at 134ºC, (subgroup B): Accelerated aging by means of a weathering process (WP). Results: Statistical analysis using two-way ANOVA test revealed that there was a significant effect on translucency parameter (TP), and L-TD showed statistically significantly higher mean TP than WP. L-TD showed significantly lower mean roughness than WP. There was no significant difference between biaxial flexural strength values before aging and after L-TD and WP. There was no phase transformation identified before and after aging indicating resistance to different types of artificial aging. Conclusions: Low-temperature degradation and weathering process affect translucency parameter and surface roughness of zirconiabased materials. Artificial aging doesn’t affect the biaxial flexural strength, and phase identification of different zirconia translucencies.

Effect of Aging Treatments on Properties of Zirconia with Different Levels of Translucency

Purpose: The aim of this study was to evaluate the effect of low-temperature degradation(L-TD), and weathering process on translucency, surface roughness, biaxial-flexural strength, and crystalline phase identification of zirconia with different levels of translucency. Materials and methods: A total of ninety-six (N= 96) zirconia discs were fabricated in this study. Samples were divided into three groups (n=32 each) according to type of zirconia: IPS EmaxZirCAD of low, medium translucency and Incoris translucent Zirconia of high translucency. Translucency measurements, surface roughness, biaxial flexural strength determination and phase identification were carried out before and after aging. Each group was then sub-divided into 2 subgroups (n=16); (subgroup A): Low-temperature degradation(L-TD) at 134ºC, (subgroup B): Accelerated aging by means of a weathering process (WP). Results: Statistical analysis using two-way ANOVA test revealed that there was a significant effect on translucency parameter (TP), and L-TD showed statistically significantly higher mean TP than WP. L-TD showed significantly lower mean roughness than WP. There was no significant difference between biaxial flexural strength values before aging and after L-TD and WP. There was no phase transformation identified before and after aging indicating resistance to different types of artificial aging. Conclusions: Low-temperature degradation and weathering process affect translucency parameter and surface roughness of zirconiabased materials. Artificial aging doesn’t affect the biaxial flexural strength, and phase identification of different zirconia translucencies.

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.

Influence of Restoration Thickness and Resin Cement on Translucency and Color of Different Types of Monolithic Zirconia and Lithium Disilicate Ceramic.

In recent years, high esthetic expectations and natural appearance demands from patients have increased the popularity of ceramic restorations. The purpose of this study was to investigate the influence of restoration thicknesses and different resin cement brands on the translucency and final color of different types of monolithic zirconia and lithium disilicate ceramics. A total of 160 disc-shaped specimens (10-mm diameter; 1 mm, or 1.5 mm thick) were produced using different types of monolithic zirconia (Katana Zirconia UTML, Katana Zirconia ML, Katana Zirconia STML Blocks; Kuraray) and lithium disilicate ceramic (IPS e.max Press, Ivoclar Vivadent) (n = 40 discs per material, with 20 discs per thickness). Two different brands of dual-cured resin cements (RelyX Ultimate, 3M ESPE; and BisCem, Bisco) were applied to the specimen surfaces. The translucency and color changes of the lithium disilicate and monolithic zirconia ceramics were examined before and after cementation using a spectrophotometer. Within the limitations of this in vitro study, the resin cement brand and ceramic thickness variation influenced the translucency and final color of the monolithic zirconia and lithium disilicate ceramic specimens.

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 &amp;lt; 0.001). The ∆E00 values of group ST at T1-T3 were greater than the 50%:50% acceptability threshold (∆E00 &amp;gt; 1.8). Moreover, multiple firings did not exhibit significant effects on the TP and contrast ratio values of any materials (both p &amp;gt; 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.

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.

Surface characteristics assessment among layers of different translucent multilayered dental zirconia related to aging

Considering that the surface characteristics and microstructure are relevant factors that may affect the appearance and strength of a material, this study aims to analyse the differences regarding surface roughness and microhardness among layers of three types of dental zirconia: super-high translucent zirconia Ceramill Zolid fx ML (5Y-TZP), super-translucent zirconia STML (4Y-TZP), and IPS e.max ZirCAD CEREC/in Lab MT Multi (4Y + 5Y-TZP), also evaluating the influence of the surface treatment performed by glazing and polishing-before, respectively after aging-by thermocycling. Forty plate-shape specimens were sectioned from the ceramic blocks with a precision disc, polished and sintered according to the manufacturer’s instructions and then, equally divided - the surface of some was finished by polishing and the others by glazing; from each category was formed a control (polished/glazed) group and one subjected to termocycling (polished/glazed) − 30.0000 cycles in a 5˚C and a 55˚C bath with distilled water in a thermocycler, resulting four groups of ten samples, for a material. The assessment of surface roughness (Ra, Rz) was performed with a contact profilometer, with Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM); Vickers hardness (VH) values were recorded with a microhardness tester. The evaluations of the surfaces were achieved in each area: incisal, medium, cervical. For statistical analyses, paired sample t-Test, unpaired sample t-Test, two-way ANOVA test (α = 0.05), Pearson's correlations were used. Both before and after thermocycling, polishing and glazing, as surface treatment have a significant effect on roughness, respectively on microhardness; no statistical differences were observed among areas, on each polished or glazed surface. On the glazed samples, the values recorded for surface roughness were significant higher and for microhardness-lower, compared with those of the polished group. After thermocycling, microrougness increased for STML and all polished specimens and decreased on glazed surfaces of Ceramill Zolid fx ML and IPS e.max ZirCAD CEREC/in Lab MT Multi. Concerning microhardness, the thermocycling procedure had no significant influence. The super-high translucent material was less affected by aging than the super-high translucent zirconia.

Effect of Sintering Temperature on Flexural Strength of Two Types of Zirconia.

Objectives: Any change in the sintering process can directly affect the micro-structure and properties of zirconia. This study sought to assess the effect of sintering temperature on flexural strength of IPS e.max ZirCAD MO Ivoclar (EZI) and CopraSmile White Peaks Symphony (WPS) zirconia blocks. Materials and Methods: In this in vitro, experimental study, 30 EZI and 30 WPS zirconia blocks measuring 10 x 10 x 1 mm were milled and sintered at 1440, 1500 and 1530°C in three subgroups. The flexural strength of the specimens was measured by a testing machine with piston-on-3-ball method according to ISO2015. Data were analyzed using one-way ANOVA. Results: The mean flexural strength was 1.31±0.49, 1.09±0.24 and 1.29±0.48 MPa in 1440, 1500, and 1530°C subgroups of EZI, and 1.44±0.61, 1.18±0.35, and 1.33±0.54 MPa in 1440, 1500, and 1530°C subgroups of WPS zirconia, respectively. Two-way ANOVA revealed that the effects of zirconia type (P=0.484), temperature (P=0.258) and their interaction (P=0.957) on flexural strength were not significant. Conclusion: Increasing the sintering temperature from 1440°C to 1530°C did not increase the flexural strength of EZI or WPS zirconia.