Flexural strength of monolithic zirconia: Effect of finishing/polishing procedures (original) (raw)
Journal of the Mechanical Behavior of Biomedical Materials, 2016
OBJECTIVES: To test the mechanical and optical properties of monolithic zirconia in comparison to conventional zirconia. MATERIALS AND METHODS: Specimens were prepared from: monolithic zirconia: Zenostar (ZS), DD Bio ZX2 hochtransluzent (DD), Ceramill Zolid (CZ), InCoris TZI (IC) and a conventional zirconia Ceramill ZI (CZI). Contrast ratio (N=75/n=15) was measured according to ISO 2471:2008. Grain sizes (N=75/n=15) were investigated with scanning electron microscope. Fourpoint flexural strength (N=225/n=15/zirconia and aging regime) was measured initially, after aging in autoclave or chewing simulator (ISO 13356:2008). Two-body wear of polished and glazed/veneered specimens (N=108/n=12) was analyzed in a chewing simulator using human teeth as antagonists. Data were analyzed using 2-/1-way ANOVA with post-hoc Scheffé, Kruskal-Wallis-H, Mann-Whitney-U, Spearman-Rho, Weibull statistics and linear mixed models (p<0.05). RESULTS: The lowest contrast ratio values were found for ZS and IC and CZ. IC showed the largest grain size followed by DD and CZI. The smallest grain size was observed for ZS followed by CZ. There was no correlation between grain size and contrast ratio. The aging regime showed no impact on flexural strength. All non-aged and autoclave-aged specimens showed lower flexural strengths than the control group CZI. Within groups aged in chewing simulator, ZS showed significantly lower flexural strength than CZI. CZI showed higher material and antagonist wear than monolithic polished and glazed groups. Glazed specimens showed higher material and antagonist loss compared to polished ones. There was no correlation between roughness and wear. CONCLUSIONS: Monolithic zirconia showed higher optical, but lower mechanical properties than conventional zirconia.
Materials, 2016
The aim of this work was to evaluate the influence of specimen preparation and test method on the flexural strength results of monolithic zirconia. Different monolithic zirconia materials (Ceramill Zolid (Amann Girrbach, Koblach, Austria), Zenostar ZrTranslucent (Wieland Dental, Pforzheim, Germany), and DD Bio zx 2 (Dental Direkt, Spenge, Germany)) were tested with three different methods: 3-point, 4-point, and biaxial flexural strength. Additionally, different specimen preparation methods were applied: either dry polishing before sintering or wet polishing after sintering. Each subgroup included 40 specimens. The surface roughness was assessed using scanning electron microscopy (SEM) and a profilometer whereas monoclinic phase transformation was investigated with X-ray diffraction. The data were analyzed using a three-way Analysis of Variance (ANOVA) with respect to the three factors: zirconia, specimen preparation, and test method. One-way ANOVA was conducted for the test method and zirconia factors within the combination of two other factors. A 2-parameter Weibull distribution assumption was applied to analyze the reliability under different testing conditions. In general, values measured using the 4-point test method presented the lowest flexural strength values. The flexural strength findings can be grouped in the following order: 4-point < 3-point < biaxial. Specimens prepared after sintering showed significantly higher flexural strength values than prepared before sintering. The Weibull moduli ranged from 5.1 to 16.5. Specimens polished before sintering showed higher surface roughness values than specimens polished after sintering. In contrast, no strong impact of the polishing procedures on the monoclinic surface layer was observed. No impact of zirconia material on flexural strength was found. The test method and the preparation method significantly influenced the flexural strength values.
Biaxial Flexural Strength of Different Monolithic Zirconia upon Post-Sintering Processes
European Journal of Dentistry
Objective Different post-sintering processes are expected to be a reason for alteration in the strength of zirconia. This study evaluated the effect of post-sintering processes on the flexural strength of different types of monolithic zirconia. Materials and Methods A total of 120 classical- (Cz) and high-translucent (Hz) monolithic zirconia discs (1.2 mm thickness and 14 mm in Ø) were prepared, sintered, and randomly divided into four groups to be surface-treated with (1) as-glazed (AG); (2) finished and polished (FP); (3) finished, polished, and overglazed (FPOG); and (4) finished, polished, and heat-treated (FPHT) technique (n = 15). Biaxial flexural strength (σ) was determined on a piston-on-three ball in a universal testing machine at a speed of 0.5 mm/min. Statistical Analysis Analysis of variance, and post hoc Bonferroni multiple comparisons were determined for significant differences (α = 0.05). Weibull analysis was applied for survival probability, Weibull modulus (m), and ...
Influence of heating rate on the flexural strength of monolithic zirconia
The Journal of Advanced Prosthodontics, 2019
PURPOSE. Fabrication of zirconia restorations with ideal mechanical properties in a short period is a great challenge for clinicians. The purpose of the study was to investigate the effect of heating rate on the mechanical and microstructural properties of monolithic zirconia. MATERIALS AND METHODS. Forty monolithic zirconia specimens were prepared from presintered monolithic zirconia blanks. All specimens were then assigned to 4 groups according to heating rate as Control, Group 15°C, Group 20°C, and Group 40°C. All groups were sintered according to heating rates with the sintering temperature of 1500°C, a holding time of 90 minutes and natural cooling. The phase composition was examined by XRD analysis, three-point bending test was conducted to examine the flexural strength, and Weibull analysis was conducted to determine weibull modulus and characteristic strength. Average grain sizes were determined by SEM analysis. One-way ANOVA test was performed at a significance level of 0.05. RESULTS. Only tetragonal phase characteristic peaks were determined on the surface of analyzed specimens. Differences among the average grain sizes of the groups were not statistically significant. The results of the three-point bending test revealed no significant differences among the flexural strength of the groups (P>.05). Weibull modulus of groups was ranging from 3.50 to 4.74. The highest and the lowest characteristic strength values were obtained in Group 20°C and Control Group, respectively. CONCLUSION. Heating rate has no significant effect on the flexural strength of monolithic zirconia. Monolithic zirconia restorations can be produced in shorter sintering periods without affecting the flexural strength by modifying the heating rate.
Journal of Prosthodontic Research, 2021
Purpose: This systematic review set out to investigate the influence of chemical composition and specimen thickness of monolithic zirconia on its optical and mechanical properties. Meta-analysis and meta-regression analyzed the effects of variations in percentages of yttrium, aluminum, and specimen thickness of monolithic zirconia. Study selection: The review followed recommendations put forward in the PRISMA checklist. An electronic search for relevant articles published up to October 2019 was conducted in the Pubmed, Cochrane, Scopus, Scielo, and Web of Science databases, with no language limits and articles published in the last 10 years. From 167 relevant articles; applying inclusion criteria based on the review's PICO question, 26 articles were selected for qualitative synthesis (systematic review) and 24 for quantitative synthesis (meta-analysis). Experimental in vitro studies published were selected and their quality was assessed using the modified Consort scale for in vitro studies of dental materials. Results: The variables yttrium, aluminum and thickness were analyzed in random effects models, observing high heterogeneity (>75%), and finding statistically significant influences on the properties of monolithic zirconia (p<0.05). Conclusions: Within the review's limitations, it may be concluded that variations in the percentage of yttrium and aluminum influence the optical and mechanical properties of monolithic zirconia, making it more or less esthetic and resistant in relation to each variable. The clinical implications of these findings can help select the most appropriate type of zirconia to meet the different clinical needs when restoring different regions (posterior or anterior).
Flexural strength, fracture toughness, and translucency of cubic/tetragonal zirconia materials
The Journal of Prosthetic Dentistry, 2018
STATEMENT OF PROBLEM The development of zirconia materials with optimized properties has been rapid, and studies comparing the mechanical and optical properties of recently introduced zirconia with lithium disilicate materials are limited. PURPOSE The purpose of this in vitro study was to compare the mechanical and optical properties of cubic/tetragonal zirconia materials with those of a lithium disilicate ceramic. MATERIAL AND METHODS Specimens were fabricated from 6 different noncolored zirconia materials: Ceramill Zolid FX (CZ), CopraSmile (CS), DD cubeX 2 (DD), NOVAZIR MaxT (NZ), priti multidisc ZrO (PD), and StarCeram Z-Smile (SC), and 1 lithium disilicate ceramic as a control, IPS e.max Press LT A2 (CG). Four-point flexural strength (N=105/n=15) and fracture toughness using the single-edge V-notched beam (N=105/n=15) were examined according to International Organization for Standardization standard 6872:2015. Translucency (N=70/n=10) was evaluated with an ultraviolet spectrophotometer. Grain size (N=6/n=1) of zirconia was investigated by using scanning electron microscopy. Data were analyzed using the Kolmogorov-Smirnov test, multivariate analysis, 1-way analysis of variance, followed by the post hoc Scheffé test and Kruskal-Wallis and Mann-Whitney U tests, and Weibull analysis, using the maximum likelihood estimation method at 95% confidence level (=.05). RESULTS Zirconia materials showed higher mechanical and lower optical properties than CG (P<.001). No differences were observed among the zirconia materials with respect to flexural strength (P=.259) or fracture toughness (P=.408). CG and CS showed significantly higher Weibull modulus than SC and PD. The lowest translucency values were measured for NZ and SC, followed by CS, DD, and PD (P<.001). CZ showed the highest translucency values (P<.001). The lowest grain sizes were found for NZ, DD, and SC; the largest were shown for CS (P<.001). CONCLUSIONS Cubic/tetragonal zirconia showed better mechanical properties than lithium disilicate ceramic. However, the optical properties and the reliability of zirconia are lower than those of lithium disilicate ceramic.
Acta Biomaterialia Odontologica Scandinavica, 2015
Objective: This study investigated the effect of different sintering temperatures and times on the flexural strength and grain size of zirconia. Material and methods: Zirconia specimens (In-Coris ZI, In-Coris TZI, 120 samples) were prepared in a partially sintered state. Subsequently, the specimens were randomly divided into three groups and sintered at different final sintering temperatures and for various durations: 1510 C for 120 min, 1540 C for 25 min and 1580 C for 10 min. Three-point flexural strength (for 120 samples, 20 samples per group) was measured according to the ISO 6872: 2008 standards. The grain sizes were imaged by scanning electron microscopy (SEM) and the phase transitions were determined by X-ray diffraction (XRD). The data were analyzed using one-way ANOVA and Duncan tests (p50.05). Results: The highest flexural strength was observed in ZI and TZI samples sintered at 1580 C for 10 min. The differences between the ZI samples sintered at 1510 C for 120 min and those sintered at 1540 C for 25 min were statistically insignificant. Also, TZI samples sintered at 1510 C for 120 min and those sintered at 1540 C for 25 min also did not show any statistically significant differences. There were no visible differences in the grain sizes between the ZI and TZI specimens. The XRD patterns indicated similar crystalline structure for both materials subjected to the three different procedures. Conclusions: The results of this study showed that experimented high sintering temperature and short sintering time combination increases the flexural strength of zirconia.
Application of Zirconia in Dentistry: Biological, Mechanical and Optical Considerations
Advances in Ceramics - Electric and Magnetic Ceramics, Bioceramics, Ceramics and Environment, 2011
2. Structural bioceramics based in zirconia 2.1 Zirconia Zircon is a shiny gray-white metal, which may look blue-black when in powder form. Zirconia is an oxide which has a high tensile strength, high hardness and corrosion resistance. It is not found as a pure oxide in nature. The main sources of zirconium are zirconate (ZrO 2-SiO 2 , ZrSiO 4) and baddelyite (ZrO 2), and most of the material used is chemically extracted from these two minerals. The zirconate is more abundant, but less pure, requiring significant processing to get zirconia. (Picone & Maccauro, 1999). Baddelyite already contains levels of zirconia ranging from 96.5% to 98.5%. As this mineral shows significant levels, it is known as a source of extreme purity in obtaining zirconium metal and its compounds. Zirconium dioxide (ZrO 2) resulting from baddelyite, which is also known as www.intechopen.com Advances in Ceramics-Electric and Magnetic Ceramics, Bioceramics, Ceramics and Environment 398 zirconia, is a course oxide that presents a monoclinic crystal structure at room temperature. However, the powder can be purified and processed synthetically at high temperatures, forming a cubic structure called cubic zirconia. The resulting material is hard, optically flawless and translucent, usually used for making precious stones or gas sensors, P. ex. (Koutayas et al., 2009). 2.2 Phases of zirconia (monoclic, tetragonal and cubic) The spatial arrangement of the atoms in zirconia is characterized by distinct crystallographic structures, characterizing a property known as polymorphism. Its three phases, or crystal structures, are characterized by specific geometry and dimensional parameters: monoclinic, tetragonal and cubic. (Fig. 1a,b,c). Pure zirconia has a monoclinic structure at room temperature, which is stable up to 1170°C. Between this temperature and 2370°C, tetragonal zirconia is formed, while cubic zirconia is formed at temperatures above 2370°C. After processing, and depending on the cooling process, the tetragonal phase becomes monoclinic at about 970°C. Due to polymorphism, pure zirconia cannot be used at elevated temperatures due to a large volume change (3-5%) which occurs during cooling to the monoclinic phase. This change is sufficient to exceed the elastic and fracture limits, resulting in cracks and flaws in ceramics. (Denry & Kelly, 2008). The transformation of the tetragonal to monoclinic phases can be employed to improve the mechanical properties of zirconia, especially its tenacity. The mechanism involved is known as a booster from transformation. This transformation is martensitic in nature, therefore, a process that occurs by shear without diffusion, ie the atomic position change occurs abruptly at a speed close to the speed of sound propagation in solids. The reverse transition, ie the monoclinic > tetragonal transformation and occurs at approximately 1170° C, while the tetragonal > monoclinic transformation, which occurs during cooling, is observed between 850 and 1000°C, depending on the strain energy. Therefore, the manufacturing of components of pure zirconia is not possible due to spontaneous failure. The addition of stabilizing oxides is important because it allows the maintenance of the tetragonal form at room temperature. (Hannink et al., 2000). Different oxides, such as yttrium oxide (Y 2 O 3), calcium oxide (CaO) or magnesium oxide (MgO), can be added to zirconia to stabilize it, allowing the tetragonal form to exist at room temperature after sintering. The addition of varying amounts of stabilizers allows the formation of partially or fully stabilized zirconia which, when combined with changes in processes, may result in ceramics with exceptional properties such as high flexural strength and fracture toughness, high hardness, excellent chemical resistance and good conductivity ions. A fully stabilized zirconia is obtained by adding sufficient amounts of stabilizing oxides, such as 16mol% magnesia (MgO), 16mol% of limestone (CaO) or 8 mol% yttria (Y 2 O 3). Since the partial stabilization of zirconia is obtained with the same oxides, but in smaller amounts (eg 2 mol% to 3mol% yttria), a multiphase structure is created, which usually consists of tetragonal and cubic zirconia majority / monoclinic precipitated in small amounts. (Picone & Maccauro, 1999). The transformation of tetragonal zirconia into monoclinic is a phenomenon influenced by temperature, vapor, particle size, micro-and macrostructure of the material, and also by the concentration of stabilizing oxides. The critical particle size for the partially stabilized zirconia to be maintained in the tetragonal form at room temperature is 0.2µm to 1μm (for compositions ranging from 2% to 3 mol% yttria), because, under 0.2 micrometres, the transformation to the monoclinic phase is not possible. (Kelly & Denry, 2008). www.intechopen.com Application of Zirconia in Dentistry: Biological, Mechanical and Optical Considerations 399 2.2.1 Monoclinic zirconia The natural form of zirconia, known as baddelyite, contains approximately 2% HfO 2 (hafnium oxide), which is very similar to zirconia in structure and chemical properties. ZR 4 + ions have a coordination number of seven for the oxygen ions occupying tetrahedral interstices, with the average distance between the zirconia ion and three of the seven oxygen ions is 2.07Å. Since the average distance between the zirconium ion and four oxygen ions is 2.21Å, in the structure, one of the angles (134.3°) differs significantly from the tetrahedral value (109.5°). Thus, the structure of the oxygen ion is not planar and a curve occurs in the plane of the four oxygens, and the plane of three oxygens is completely erratic. (Hannink et al., 2000) 2.2.2 Tetragonal zirconia Zirconia in its tetragonal phase has the form of a straight prism with rectangular sides. Ions ZR 4 + have a coordination number of eight, where the shape once again appears distorted due to the fact that four oxygen ions are at a distance of 2.065Å in the form of a tetrahedron plan, and four others are at a distance of 2.455Å in a tetrahedron that is elongated and rotated 90°. (Vagkopoulou et al, 2009).
Dental Materials, 2019
OBJECTIVE To test the impact of zirconia pretreatment and aging on flexural strength and phase structure. METHODS For flexural strength measurements, 180 3Y-TZP 0.25 specimens were fabricated and pretreated: (i) air-abraded (105-m alumina, 0.25MPa), (ii) air-abraded (50-m alumina, 0.25MPa), (iii) air-abraded (30-m silica-coated alumina, 0.28MPa) (iv) non-pretreated. Each pretreated group (n=15) was aged: (a) hydrothermal (134°C, 0.23MPa, 2h) (b) in a mastication simulator (1,200,000×, 5/55°C) and (c) not aged. The fractured specimens were stored dry for 5 years (23°C) for analysis of phase transformation. Additionally, specimens were fabricated from 3Y-TZP 0.25 (n=12) and 3Y-TZP 0.05 (n=8), pretreated (i, ii, iii, iv), and hydrothermally aged. Each air-abrasion method was alternated using 0.05, 0.25 and 0.4MPa pressure. The phase transformation was examined by Raman spectroscopy and surface topography by scanning electron microscope. Data were analyzed using univariate ANOVA with the Scheffé post hoc test and partial-eta-squared ( p ²) (=0.05). RESULTS The highest impact on flexural strength was exerted by the pretreatment ( P ²=0.261, p<0.001), followed by interactions between pretreatment and aging ( P ²=0.077, p=0.033). Non-pretreated and non-aged specimens showed the lowest monoclinic percentage. Hydrothermal aging and 5 years of storage at room temperature increased the monolithic percentage of 3Y-TZP 0.25 . The highest phase transformation was observed in groups air-abraded with 105-m alumina particles. Increasing pressure during the air-abrading process increased the content of the monoclinic phase in zirconia surfaces. SIGNIFICANCE Air-abrasion with 30m silica-coated alumina powder can be recommended for pretreatment of 3Y-TZP 0.25 and 3Y-TZP 0.05 . For air-abrasion using alumina powder lower pressure should be used.