Monoclinic Phase Transformation Research Articles

Fabrication of Multiscale and Periodically Structured Zirconia Surfaces Using Direct Laser Interference Patterning

AbstractThe functionalization of zirconia surfaces by accurate and fast printing of periodical patterns embedding sub‐micrometric features is of great interest to many engineering fields and is yet to be explored. This study aims to assess the influence of the Direct Laser Interference Patterning processing parameters on the morphology and microstructure of zirconia surfaces using a 532 nm 10 ps‐pulsed laser source. Well‐defined linear structures with a period of 3 µm are successfully produced. Depending on the laser parameters, the structures are developed at or below the surface level, with higher depths (≈1 µm) being seen for increasing values of laser fluence and pulse overlap. Line‐like hierarchical structures with smaller interference spatial structures (3 µm period) and higher secondary structures with different periods (18, 15, and 12 µm) and heights (7, 5, and 3 µm, respectively) are also obtained on zirconia surface. Ablated regions presented few traces of molten material, nano‐droplets, and sub‐micrometric (<1 µm) pores, while no (sub) micrometric cracks are detected. A slight amount of tetragonal to monoclinic phase transformation (≈5%) is detected by X‐ray diffractometry. A processability map for ps‐laser processing of zirconia is proposed based on the experimental data.

Microstructure and fracture behaviour of biomimetic Al2O3-ZrO2 composite with 2-levels of structural hierarchy

We report new class of natural nacre-like alumina toughened by zirconia fabricated by the simple two-step approach of unidirectional freeze-casting and spark plasma sintering. The biomimetic alumina-zirconia with a relative density of more than 98 % was achieved by consolidating at temperature of 1300–1425 °C with 50 MPa pressure. The resultant microstructure consists of two levels of structural hierarchy, i.e. level-1: bulk lamellar brick phase (alumina platelets) and level-2: mortar phase (yttria stabilized tetragonal zirconia polycrystals). The increase in volume fraction of zirconia (in tetragonal form) from 0 to 15 vol% was effective in progressively reducing the size of alumina platelets from 12 to 9 μm, and significantly improved the flexural strength of the composite by 60 % (from 172 to 270 MPa). By optimizing the hierarchical architecture from micro to macroscopic level, the structural performance of our synthetic nacre, where strength and toughness of 270 MPa and 13.5 MPa√m respectively are superior to that of natural nacre and many other engineering materials (illustrated in the form of Ashby map). The exceptional damage resistance is rationalized by both intrinsic (stress induced tetragonal to monoclinic phase transformation of zirconia) and extrinsic (crack deflection, crack branching and bridging, multiple cracking, platelets interlocking) toughening mechanisms. For 15 vol% ZrO2 composition, the contribution of intrinsic and extrinsic toughness was quantitatively evaluated as 0.9 ± 0.03 and 4.3 ± 0.07 MPa√m respectively (with experimentally measured toughness at crack initiation as 5.2 ± 0.2 MPa√m).

Nanomechanical and microstructural properties of experimental bilayered zirconia ceramics after hydrothermal aging

Two experimental ceramic systems, 3Y-TZP/5Y-PSZ (3Y/5Y) and 4Y-PSZ/5Y-PSZ (4Y/5Y), underwent analysis before (3Y/5Yi or 4Y/5Yi) and after hydrothermal aging (3Y/5Ya or 4Y/5Ya) to simulate low-temperature degradation (LTD). The samples were sintered and characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy, alongside nanoindentation tests to measure elastic modulus (Em) and hardness (H). Assessments were conducted on the external surfaces and at individual layers on cross-sectioned samples at predetermined regions of interest (ROIs). Degraded superficial regions were observed in the cross-sectional SEM images of the 3Y and 4Y zirconia layers after aging. XRD indicated a tetragonal→monoclinic phase transformation in the aged groups for both 3Y (66 % m-ZrO2) and 4Y (29 % m-ZrO2). Raman spectroscopy revealed monoclinic phase amounts of 86 % for 3Y and 62 % for 4Y in the degradation regions observed in the SEM micrographs. Monoclinic phase peaks were virtually no longer detected in either material beyond a depth of 15 μm. Hydrothermal aging significantly diminished the H and Em values for the 3Y and 4Y zirconia surfaces. For the analysis of different zirconia surfaces within the same subgroup, all pairwise comparisons showed statistically significant differences, except for the values of H of 3Y/5Yi and Em for 4Y/5Yi. Regarding the nanoindentation results of cross-sectioned samples, the aging protocol did not affect the H and Em values of the equivalent ROIs (layers), regardless of the bilayered system. However, significant differences in H values were observed among the ROIs (layers) within the same bilayered system. Despite surface changes, nanomechanical properties remained preserved below the surface and at the interfaces of bilayered materials after aging. Nanoscale H values varied among some layers and interfaces, whereas the Em values exhibited differences across certain surfaces.

Investigations on ion irradiation induced microstructural changes in Gd2O3 nanorods

Ion irradiation induced phase transformations in Gd2O3 nanorods dispersed on TEM grids, are investigated using synchrotron X-ray diffraction and transmission electron microscopy. Ion irradiation induced cubic (C) to monoclinic (B) phase transformation is observed in Gd2O3 nanorods. Gd2O3 nanorods are partially transformed to monoclinic phase at 0.63 dpa (5 × 1016 ions/cm2) itself. The C→B phase transformation is reconstructive type transformation where the role of O-vacancies and diffusion are very important. During He+ ion irradiation, the displacement cascades produced O-vacancies and during the non-melting thermal spike regime, diffusion was assisted and it resulted in the phase transformation. In addition to phase transformation, TEM investigations shows formation of amorphous carbon layer around the nanorods and welding of the nanorods, upon ion irradiation. These observations are explained based on the mechanisms of GOLF (giant onion like fullerene) formation and the localized surface melting during thermal spike.

Novel oxide based anti-corrosion composite coating for gas turbines

In the present study glass-ceramic−8YSZ based multilayered functionally graded corrosion resistant coating was developed for gas turbine applications. Corrosion resistance property of developed coating was evaluated by exposing coating to molten mixture of 80 wt% Na2SO4 + 20 wt% NaCl in air at 1000 °C up to 100 h. It was found that coating morphology was gradually changed with respect to time at 1000 °C. No thermally grown oxide (TGO) layer was observed within different layers of TBC. However, thin reaction film was developed at substrate-coating interface, which helped to increase adherence of coating with substrate. Tetragonal zirconia to monoclinic zirconia phase transformation was not occurred in top coat even after long corrosive salt attack that strengthened TBC system. Developed coating showed good potential to be used as corrosion resistant coating for actual superalloy based gas turbine engine components.

Dental zirconia microwave-sintering followed by rapid cooling protocol

ObjectivesThis study aimed to evaluate the effect of microwave sintering temperature and cooling rate (MS) on 3Y-TZP ceramics and its influence on the ceramic microstructure and mechanical properties. Specifically, to optimize the sintering process, reducing the total sintering time compared to conventional sintering. Materials and methodsEighty-four pre-sintered Y-TZP discs (Vipi block Zirconn, VIPI) (ISO 6872) were divided into seven groups (n = 12) according to the sintering conditions: conventional sintering (CS) at 1530 °C for 120 min and microwave sintering at 1400 °C (MS1400) and 1450 °C (MS1450) for 15 min followed by different cooling conditions: rapid cooling (RC), cooling at 400 °C (C400) and 25 °C (C25). The specimens were submitted to apparent density measurements, X-ray diffraction analysis (XRD), scanning electron microscopy, and biaxial flexural strength test. Data was statistically analyzed through two-way ANOVA, Tukey, Sidak, Dunnett and Weibull (α = 0.05). ResultsAll MS1400 groups presented lower density values than the CS and MS1450 groups. Two-way ANOVA revealed that the MS temperature and cooling rate affected the biaxial flexural strength of the Y-TZP (p < 0.01). Group MS1400RC presented lower biaxial flexural strength values (681.9 MPa) than MS1450RC (824.7 MPa). The cooling rate did not statistically decrease the biaxial strength among the groups submitted to microwave sintering at 1450 °C. XRD analysis showed that the sintering and cooling temperature did not induce tetragonal to monoclinic phase transformation. ConclusionsMicrowave sintering at 1450 °C for 15 min followed by rapid cooling can be a viable fast alternative protocol for Y-TZP sintering, compared with the conventional sintering, reducing the total sintering time by 75% and reducing the energy used for the sintering process without affecting the Y-TZP biaxial flexural strength and relative density compared to the conventional sintering. Moreover, the microwave technique promoted smaller grains and did not induce monoclinic phase formation.

Aging behavior of a 1.5 mol% yttria doped zirconia exhibiting optimized toughness and strength

The aging behavior of a 1.5Y-TZP with 0.25 wt% of alumina exhibiting high mechanical properties was investigated in both water vapor and in air with in situ XRD analysis. The results showed that the material exhibited a high resistance to aging in water vapor at 134 °C compared to 3Y-TZP, which is explained by the addition of alumina and a lower sintering temperature. The aging kinetics were fitted by the Mehl–Avrami–Johnson law, three stages were identified corresponding to predominance of nucleation mechanism for temperatures below 180 °C and above 340 °C and to growth mechanism for intermediate temperatures. It was shown that for the temperature range investigated in water vapor and air, the mechanism was independent on the environment. A strong influence of the cooling rate on the tetragonal to monoclinic phase transformation was observed and discussed using a time–temperature-transformation diagram derived from the aging results in air.

Antibacterial and osteogenic activities of thiolated and aminated yttria-stabilized tetragonal zirconia polycrystal with tolerance to low temperature degradation

The chemical immobilization of silane on yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) surface is promising in improving both osseointegration and antibacterial activity, however, the effect of low temperature degradation (LTD)-induced the tetragonal (t) to monoclinic (m) phase transformation on the chemical bonding and continuous bioactivity remains unclear. In this study, 3-aminopropyltriethoxysilane (APTES) and 3-mercaptopropyltrimethoxysilane (MPTS) were grafted on the Y-TZP surface. Quantum chemistry revealed that Zr–O–Si bonds formed by t/m-ZrO2 both had a strong tendency to undergo hydrolysis in acidic or neutral environments, but were stable in alkaline environments. Inductively coupled plasma mass spectrometry showed that the release of Si increased during weeks 1–3 on both APTES- and MPTS-grafted surfaces, then decreased rapidly on MPTS-grafted surface while maintained a sustain release on APTES-grafted surface until week 4; in particular, the hydrolysis of Zr–O–Si bonds did not accelerated by LTD. X-ray photoelectron spectroscopy showed that LTD-induced reductions in Zr–O–Si bond contents on APTES- and MPTS-grafted surfaces were 0.63% and 1.79%, respectively. In vitro MC3T3-E1 cell experiments confirmed that APTES- and MPTS-grafted Y-TZP surfaces maintained similar adhesion and proliferation before and after LTD. Scanning electron microscopy, laser confocal scanning microscopy, and spread plate assay findings showed favorable anti-Porphyromonas gingivalis (P. gingivalis) effects induced by APTES- and MPTS-grafted t/m-ZrO2 surfaces. Thus, APTES and MPTS both provide LTD-stable and hydrolysis-stable chemical bonding for Y-TZP implants, and t-m phase transformation does not cause detectable effects on Y-TZP bioactivity.

A comparative investigation on micro-channel by using direct laser ablation and liquid-assisted laser ablation on zirconia

In this work, direct laser ablation (DLA), liquid-assisted laser ablation in water (LALA-W) and in ethanol (LALA-E) is applied to fabricate single micro-channels on the zirconia ceramic by using a picosecond laser. To assess the machining ability of them, micro-channels fabricated are characterized and compared the differences in morphology, geometric profile, chemical and phase composition. The morphological results indicate that both LALA-E and DLA can fabricate microchannel with obvious recast layer and cracks, and LALA-W can fabricate microchannel with a porous surface, and almost no recast layer and cracks. The results of geometric characteristics show that LALA-W can fabricated micro-channels with “U” shape profile with 52.74% enhancement in depth compared to that “V” shape by DLA and LALA-E. The XPS results demonstrate that LALA-W can exhibit the smallest oxygen vacancies with 50.01% than that of LDA 53.81% and LALA-E 54.56%. For XRD results, after machining by all three processes, the zirconia ceramic undergoes the tetragonal→monoclinic phase transformation, resulting in an increase in monoclinic phase. While LALA-W exhibits the smallest increase in monoclinic phase from 9.9% to 12.7%, and has the most tetragonal phase content of 58.8%.

Tribological behavior of zirconia ceramic with micro-channels produced by nanosecond laser

Tribological performance of surface can be improved by laser texturing. For this purpose, this paper fabricated the grid-texture composed of micro-channels by nanosecond laser on the zirconia surface. To obtain micro-channel with high-quality, the effect of laser parameter on the morphology and geometry of micro-channels was investigated. The results showed that the laser power has lest effect on the taper angle and the height of pile up. Analysis of chemical properties indicated that a deoxidation reaction by laser irradiating can led to oxygen vacancy decreasing and color darkening, and this color variation can be diminished by the annealing treatment. Analysis of phase properties showed that internal stress resulting from oxygen vacancy decreasing can led to the tetragonal → monoclinic phase transformation. Finally, grid-textures composed by micro-channels with better quality obtained from the experimental results were fabricated to change the tribology of zirconia. Results of wear tests indicated that the coefficient of friction for the laser-treated is higher and more stable than that of untreated. The observation of worn surface indicated that adhered lamellar for laser-treated was less than that on the untreated surface, and abrasive particles can be observed in microgrooves produced by laser, which can decrease ploughing effect to improve the friction stability.

Micromechanical properties of Yttria-doped zirconia ceramics manufactured by direct ink writing

Yttria-doped zirconia ceramics have many applications in a wide range of industries mainly due to their excellent mechanical properties, corrosion resistance and biocompatibility. In this study, micromechanical properties of yttria-doped zirconia produced by Direct-Ink Writing (DIW) were investigated and compared to the ones produced by Cold Isostatic Pressing (CIP). In doing so, mechanical response was assessed at different length scales, from macro- up to submicrometric-, by means of Vickers hardness, nanoindentation, and nanoscratch tests. Microstructure was also characterized by determining grain size, crystal structure and phase tetragonal to monoclinic phase transformation. Results revealed that printed samples displayed 20–25% lower hardness values compared to those exhibited by the respective CIP pairs. Differences in hardness between 3 and 8 mol% yttria content evaluated for CIP samples were slight for printed samples, due to the effect of microstructural defects like porosity, resulting from the processing parameters used. At the local level, such an effect was found to be lower. In this sense, hardness and elastic modulus achieved by nanoindentation were closer, when comparing printed and CIP samples. Scratch tests carried out from 0 to 250 mN revealed that 3 mol% Y2O3 samples developed micro-fracture events in the track length, being the printed samples the ones heavily deformed.

Tribology and in-vitro biological characterization of TiO2 addition on ceria stabilized zirconia-toughened alumina (CSZTA) composite

ABSTRACT The effect of TiO2 addition on tribology and in-vitro biological characteristics of ceria-stabilized zirconia-toughened alumina (CSZTA-TiO2) ceramic composites were examined and presented in this study. Through the powder metallurgy route, the TiO2 added to CSZTA samples were synthesized and sintered (air environment). Additionally, the pin on the disc machine was used to examine the wear characteristics of sintered samples. Adding TiO2 to CSZTA enhances the tribological properties compared to pure ceria-stabilized zirconia-toughened alumina (CSZTA). In addition, the samples (CSZTA and CSZTA-TiO2) were subjected to aging. There is no monoclinic-phase transformation (no degradation) in the CSZTA-TiO2 sample after 100 h of testing, confirming its great resistance to LTD. The bioactivity of developed CSZTA and CSZTA-TiO2 samples was studied using simulated body fluid (SBF). After chemical treatment, it was shown that the composite would create an apatite layer that resembled bone when soaked in a simulated body fluid with ion concentrations equal to human blood plasma. These results suggest that it may generate apatite within a live organism and connect to the bone via the apatite layer.

Optical coherence tomography (OCT) for the analysis of zirconia crystalline phase transformation

This study aimed to validate the Optical coherence tomography (OCT) for the analysis of the transformed zone of two dental zirconia-based materials after hydrothermal ageing and correlate the values with biaxial flexural strength. Kinetics of tetragonal to monoclinic phase transformation (t→m) was calculated. X-ray diffraction (XRD) results showed a sigmoidal transformation rate over time due to the limited X-ray maximum penetration depth. Scanning electron microscope (SEM) and OCT showed a linear relationship between the thickness of the transformed layer and the ageing time. The apparent activation energy was 104.5 kJ/mol and 106.7 kJ/mol (SEM) and 106 kJ/mol and 99.4 kJ/mol (OCT) for the infrastructure and monolithic dental zirconia, respectively. Mechanical strength decreased after 150 h. of ageing at 150 °C for both materials showing a correlation with the depth of the transformed zone observed by OCT. Therefore, both monoclinic phase percentage and the depth of the transformed layer are critical concerning zirconia mechanical properties upon hydrothermal ageing. OCT is a non-destructive, fast, innovative, and accurate method for the analysis of zirconia's t→m phase transformation depth kinetics after hydrothermal ageing.

3D printing of high solid loading zirconia feedstock via screw-based material extrusion

Zirconia ceramic (3Y-TZP) feedstocks with solid loadings from 50 vol% to 68 vol%, in a 60:40 paraffin wax to LDPE ratio binder system, were prepared and printed using a screw-based material extrusion printer. A two-step debinding process involving solvent debinding (cyclohexane + ethanol) and thermal debinding (140 °C–600 °C at 0.2 °C/min) followed by sintering at 1500 °C for 2 h was employed. Tests performed include TGA, density test, Vickers hardness and fracture toughness, XRD, and SEM. The TGA result showed two significant drops in weight starting at 180 °C and 380 °C, which corresponds to the decomposition of paraffin wax and LDPE, respectively. A minimum of 40 wt% of soluble binder was removed from the green sample after solvent immersion for 3 h at 40 °C for solid loadings ≥55 vol%. High solid loading feedstocks produced samples with comparable density, Vickers hardness and fracture toughness, which are 97.5%, ∼12.3 GPa, and ∼5.5 MPa m1/2, respectively; while XRD and SEM shows no adverse tetragonal to monoclinic phase transformation and grain growth, respectively. This study demonstrates that 3D printing of granular 3Y-TZP ceramic feedstock via screw-based material extrusion technique is feasible even with high solid loadings, which is usually difficult to fabricate into flexible filaments and print due to high viscosity.

The Influence of Polishing on the Mechanical Properties of Zirconia—A Systematic Review

Purpose: To systematically review studies that investigated the consequences of various polishing protocols on the mechanical properties of zirconia. The effects on the roughness and crystalline phase transformation were also evaluated. Materials and methods: The Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) was followed. The electronic searches were conducted via OVID MEDLINE (R) and Scopus for publications between 1996 and August 2022. The search strategy was limited to full texts in the English language and in vitro studies. The influences on flexural strength, hardness, fracture strength, fracture toughness, wear resistance, roughness and phase transformation were collected. Various methodologies to measure these properties were also outlined and compared. The risk of bias for included studies was evaluated according to a modified Consolidated Standards of Reporting Trials (CONSORT) checklist. Results: After removing duplicates, the systematic search identified a total of 419 studies. Nineteen studies satisfied the inclusion criteria and were selected for final analysis. Fifteen of the included studies observed the changes in surface roughness along with the mechanical properties and ten studies detected the tetragonal (T) to monoclinic (M) phase transformation. Eight studies also investigated the change in properties after polishing the ground surface. Testing parameters were not consistent among studies due to the varying methods. Conclusions: To a certain extent, polishing influences the strength, hardness, toughness and wear resistance. The damage in some mechanical properties, as well as the roughened surface, from grinding can be restored via an appropriate polishing treatment. The polishing process itself barely induces the transition from the tetragonal to monoclinic phase of zirconia, while this commonly occurs after grinding. If the subsequent polishing is adequate, the transformed monoclinic phase can be eliminated with the removal of the outermost surface layer. In dentistry, polishing is an imperative step to maintain the superior functions and service life of zirconia for patients.

Optimizing the Ferroelectric Properties of Hf1–xZrxO2 Films via Crystal Orientation

This study exploits the coupling of crystallographic and ferroelectric (FE) properties in an effort to enhance the FE performance of Hf1–xZrxO2 (HZO). The proposed scheme involved optimizing the orientation of orthorhombic (O)-phase crystals along the preferred polarization axis by applying an electric pulse during annealing. The proposed electric pulse annealing (EPA) process reduced the need for wake-up treatment; however, it imposed limited changes on the amount of the O-phase and leakage performance, compared with rapid thermal annealing (RTA). Excessively high EPA doses induced an O → M (monoclinic) phase transformation, which sacrificed FE polarization but preserved the wake-up-free-like properties. Our results demonstrate that optimizing the orientation of polycrystalline O-phase may be as important as maximizing the quantity of O-phase for HZO applications.

Effects of transverse compression on the structure and axial tensile properties of polyethylene: A molecular simulation study

This paper investigates the effects of transverse pressure on the structure and axial tensile properties of polyethylene (PE) crystals and fibril (i.e., defective crystal with chain ends) using all-atom molecular dynamics (MD) simulations. The Hugoniot equation of state of the PE crystal is developed using both isotropic and anisotropic compression. To investigate the transverse pressure effects, both the crystal and fibrils models of length 0.02 to 0.2 micro-meter are subjected to axial tensile loading at different levels of transverse pressure from 0.0 to 20 GPa. The tensile stress-strain response and properties are predicted as functions of transverse pressure and fibril length. The MD predicted equation of state agrees well with theoretical Pastine's model and simulation captures orthorhombic to monoclinic phase transformation in anisotropic compression near 22 GPa hydrostatic pressure. Simulation results show that the transverse pressure significantly affects the tensile properties of PE especially for the fibril models by intensifying the inter-molecular interactions and changing the damage modes from chain end slippage to chain scission. In the presence of transverse pressure, the improvement in modulus is predicted to increase by 49% for crystal and 50%–73% for fibril, whereas the tensile strength is increased by 42% for crystal and 263%–600% for fibrils. These predictions provide insight into the response of PE subjected to high velocity impact where the PE structures experience multiaxial loadings at transverse pressure several orders of magnitude greater than the ambient pressure conditions.

Wettability and frictional properties on zirconia surfaces irradiated by femtosecond laser

This study aimed to explore the wettability and tribological performance of zirconia surface by laser irradiating. To investigate the effect of laser parameters, zirconia samples were divided into two groups according to laser power and scanning pitch. The surfaces were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and goniometer. Microcracks were observed from SEM in the laser-irradiated area. The XRD results in turn indicated that the tetragonal → monoclinic (t→m) phase transformation led to microcracks formation. The contact angles (CAs) results demonstrated that the effect of laser powers on wettability was more than that of scanning pitch. With moderate laser power, it is possible to induce micro/nano morphology with best wettability. Hardness tests and friction tests were further performed to investigate the effect of laser irradiation on mechanical properties. The results indicated that the hardness of laser-irradiated showed a slightly increase, expect for the case of the percentage of m phase exceed 50 %. Meanwhile, laser irradiation can slightly reduce the coefficient of friction (COF) of dry friction and increase the COF of wet friction. For wet friction, laser-irradiated microstructure can effectively enhance the adhesion of bone to zirconia. This work may offer a simple method to produce surfaces with controlled wettability and phase transformation by selecting appropriate laser parameters to promote the adhesion of bone to zirconia.

Effect of Sandblasting with Fluorapatite Glass-ceramic Powder and Chemical Primers/Adhesives on Shear Bond Strength of Indirect Repairing Composite to Zirconia.

To investigate the effect of sandblasting with fluorapatite glass-ceramic (FGC) powder on zirconia surface roughness, crystallinity, and shear bond strength (SBS) of indirect repairing composite to zirconia using different primers/adhesives. Zirconia blocks were treated as follows: no treatment (control group), blasting with 30-μm silica-coated alumina (CoJet group), and blasting with FGC powder (FGC group). The surface topography, silica content, roughness, and crystallinity of treated zirconia surfaces were analyzed by a scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), an optical profilometer, and X-ray diffraction (XRD), respectively. Four primers/adhesives (Monobond Plus, Calibra Silane, Futurabond M+, and Scotchbond Universal) were compared to bond precured resin composite to zirconia groups using Multilink Automix resin cement. Bonded specimens were thermocycled for 10,000 cycles and tested in SBS and the modes of failure were recorded. The effect of different surface treatments and primers/adhesives on SBS results were statistically analyzed using two-way ANOVA and Bonferroni post-hoc tests (α=0.05). Both CoJet and FGC groups showed rough surfaces with a higher content of silica in FGC, but less monoclinic crystals, compared to the CoJet group. The highest mean SBS was found in the FGC group treated with Monobond Plus compared to CoJet and Control groups. Adhesive failure was predominant in control groups, while combined failure was found in the CoJet and FGC groups regardless of the primers/adhesives employed. Sandblasting zirconia with FGC powder increased SBS of resin composite to zirconia with lower monoclinic phase transformation compared to CoJet sand. Monobond Plus reported the highest means of SBS values compared to other primers/adhesives.

Strength and phase transformation of different zirconia types after chairside adjustment

Statement of problemLimited evidence is available for the effect of chairside adjustment using diamond instruments on different types of zirconia. PurposeThe purpose of this in vitro study was to evaluate the effect of simulated adjustments on the biaxial flexural strength and phase transformation of 3 different zirconia types. Material and methodsThree zirconia types from the same manufacturer (Katana; Kuraray) were used: High Translucency (3Y-PSZ), Super Translucent Multi Layered (4Y-PSZ), and Ultra Translucent Multi Layered (5Y-PSZ). Thirty disk-shaped specimens (Ø14×1.2 mm) were fabricated according to the International Organization for Standardization (ISO) Standard 6872 from different zirconia types (N=90). Specimens were either left without adjustment (NA), adjusted with Dialite ZR finishing and polishing system (Brasseler) (APol), or adjusted with course diamond instruments only (ADia). The specimens were distributed into 9 groups (n=10): group 3Y-PSZ/NA, group 3Y-PSZ/APol, group 3Y-PSZ/ADia, group 4Y-PSZ/NA, group 4Y-PSZ/APol, group 4Y-PSZ/ADia, group 5Y-PSZ/NA, group 5Y-PSZ/APol, and group 5Y-PSZ/ADia. The biaxial flexural strength of each specimen was measured by using a universal testing machine (Model 4411; Instron) and according to ISO 6872. X-ray diffraction analysis was conducted to quantify the monoclinic phase transformation. Scanning electron microscopy images were obtained to evaluate the fracture pattern. Statistical analysis was performed by using analysis of variance (ANOVA) and Tukey multiple comparison tests for pairwise comparisons (α=.05). ResultsThe mean biaxial flexural strengths ranked from the highest to the lowest were for 3Y-PSZ, 4Y-PSZ, and 5Y-PSZ under any test condition (P=.007). Chairside adjustment with a diamond instrument significantly decreased the flexural strength of all zirconia types (P<.05). No statistically significant difference was found between the effect of APol and ADia on the strength of zirconia 3Y-PSZ (P=.603), 4Y-PSZ (P=.993), and 5Y-PSZ (P=.660). Phase transformation did not occur in the 5Y-PSZ groups. ADia groups had significantly higher phase transformation values regardless of zirconia type (P<.05). ConclusionsThe biaxial flexural strength of zirconia decreased significantly after chairside adjustment with diamond instruments regardless of the yttria percentage. Adjustment with the Dialite ZR finishing and polishing system caused less tetragonal to monoclinic phase transformation than adjustment with a course-grit diamond instrument.