Yttria-stabilized Tetragonal Zirconia Polycrystal Surface Research Articles

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.

Effects of glass-ceramic spray deposition manipulation on the surface characteristics of zirconia dental restorations

A novel glass-ceramic spray deposition (GCSD) method was developed to modify the yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) surface and to enhance the bond strength between Y-TZP and resin cement. Five different experimental groups were characterized, non-treatment (NT), airborne particle abrasion (AB), GCSD without etching (GS), GCSD with 5% HF etching (GSE5), and GCSD with 9.5% HF etching (GSE9), to determine the optimal method for improving the bond strength. Scanning electron microscopy and an argon ion milling system were used to investigate the surface and cross-sectional microstructures. The changes in the surface characteristics of Y-TZP were analyzed via contact angle analysis, atomic force microscopy, X-ray diffraction, and energy-dispersive X-ray spectrometry. The bond strengths were determined using shear bond strength test. The results revealed that GCSD could produce a dense and uniform lithium disilicate glass-ceramic coating layer and infiltrate the Y-TZP surface. This coating resulted in superior micromechanical interlocking and increased hydrophilicity, thereby enhancing the bond strength between Y-TZP and resin cement (P < 0.05). The study findings indicated that GCSD accompanied by 5% HF etching for 100 s is optimal for strengthening the Y-TZP/resin cement bond, thereby providing a novel solution for dental bonding systems.

Improving osteogenic activity of Y-TZP (Yttria-stabilized tetragonal zirconia polycrystal) surfaces by grafting of silanes with different end groups

Poor osteogenesis caused by limited bioactivity is one of the challenges affecting the use of zirconia-based materials as implants. In this study, four representative silanes with different end groups [γ-methacryloxypropyltrimethoxysilane (γ-MPS, with a vinyl end group), methyltrimethoxysilane (MTMS, methyl end), 3-mercaptopropyltrimethoxysilane (MPTS, mercapto end), and 3-aminopropyltriethoxysilane (APTES, amino end)] were grafted on a Y-TZP surface with the purpose of improving its osteogenic activity. Thermodynamic and analytical chemistry results confirmed that the terminal alkoxy groups of the silanes could condense with the hydroxyl groups on the zirconia surface to form covalent Zr–O–Si bonds; in particular, mercapto- terminated silanes were more effective at combining with zirconia than hydrophobic vinyl- and methyl-terminated silanes. Y-TZP modified with mercapto- and amino-terminated silanes showed improved hydrophilicity, which in turn promoted cell adhesion and growth. In vitro cell experiments showed that mercapto- and amino-terminated silanes promoted osteogenic differentiation and mineralization by increasing osteocalcin (OCN) and osterix (OSX) expression levels, while vinyl- and methyl-terminal silanes exhibited inhibitory effects on the collagen type 1 (COL-1), Runt-related transcription factor 2 (Runx2), and OCN expressions. Therefore, grafting mercapto- and amino-terminal silanes is a simple and effective strategy for enhancing the osteogenic potential of Y-TZP implants.

Change of phase transformation and bond strength of Y-TZP with various hydrofluoric acid etching.

ObjectivesThe purpose of this study was to quantify phase transformation after hydrofluoric acid (HF) etching at various concentrations on the surface of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP), and to evaluate changes in bonding strength before and after thermal cycling.Materials and MethodsA group whose Y-TZP surface was treated with tribochemical silica abrasion (TS) was used as the control. Y-TZP specimens from each experimental group were etched with 5%, 10%, 20%, and 40% HF solutions at room temperature for 10 minutes. First, to quantify the phase transformation, Y-TZP specimens (n = 5) treated with TS, 5%, 10%, 20% and 40% HF solutions were subjected to X-ray diffraction. Second, to evaluate the change in bond strength before and after thermal cycling, zirconia primer and MDP-containing resin cement were sequentially applied to the Y-TZP specimen. After 5,000 thermal cycles for half of the Y-TZP specimens, shear bond strength was measured for all experimental groups (n = 10).ResultsThe monoclinic phase content in the 40% HF-treated group was higher than that of the 5%, 10%, and 20% HF-treated groups, but lower than that of TS-treated group (p < 0.05). The 40% HF-treated group showed significantly higher bonding strength than the TS, 5%, and 10% HF-treated groups, even after thermal cycling (p < 0.05).ConclusionsThrough this experiment, the group treated with SiO2 containing air-borne abrasion on the Y-TZP surface showed higher phase transformation and higher reduction in bonding strength after thermal cycling compared to the group treated with high concentration HF.

Effect of hydrofluoric acid-based etchant at an elevated temperature on the bond strength and surface topography of Y-TZP ceramics.

ObjectivesThis study investigated the effects of a hydrofluoric acid (HA; solution of hydrogen fluoride [HF] in water)-based smart etching (SE) solution at an elevated temperature on yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics in terms of bond strength and morphological changes.Materials and MethodsEighty sintered Y-TZP specimens were prepared for shear bond strength (SBS) testing. The bonding surface of the Y-TZP specimens was treated with 37% phosphoric acid etching at 20°C–25°C, 4% HA etching at 20°C–25°C, or HA-based SE at 70°C–80°C. In all groups, zirconia primers were applied to the bonding surface of Y-TZP. For each group, 2 types of resin cement (with or without methacryloyloxydecyl dihydrogen phosphate [MDP]) were used. SBS testing was performed. Topographic changes of the etched Y-TZP surface were analyzed using scanning electron microscopy and atomic force microscopy. The results were analyzed and compared using 2-way analysis of variance.ResultsRegardless of the type of resin cement, the highest bond strength was measured in the SE group, with significant differences compared to the other groups (p < 0.05). In all groups, MDP-containing resin cement yielded significantly higher bond strength values than MDP-free resin cement (p < 0.05). It was also shown that the Y-TZP surface was etched by the SE solution, causing a large change in the surface topography.ConclusionsBond strength significantly improved when a heated HA-based SE solution was applied to the Y-TZP surface, and the etched Y-TZP surface was more irregular and had higher surface roughness.

Y-TZP surface treatments and their effects on the bond strength to resin cement

Aim: This study evaluated the effect of surface treatments of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics on their bond strength to a resin cement. Methods: Seventy zirconia blocks (6 × 6 × 2 mm3, IPS e.max ZirCAD) were assigned into 7 groups (n=10) – as-sintered (AS), no treatment; tribochemical silica coating + silanization (TBS; Cojet-sand; ProSil); airabrasion with 45 μm alumina particles + universal primer (AAP; Monobond®Plus); fusion sputtering (FS); SiO2 nanofilm + silanization (SN; ProSil); FS+SN+ silanization (FSSN; ProSil); FS+SN+Universal Primer (FSSNP; Monobond®Plus). Afterwards, a resin cement (RelyX™ ARC) was applied inside cylinders (Ø = 0.96 mm × 1 mm height) placed on the zirconia surfaces. Microshear bond strength tests (μSBS) were carried out (1 mm/min). Failure and phase transformation analysis were performed. Bond strength data (MPa) were subjected to Kruskal-Wallis/Mann Whitney tests. Results: TBS (27 ± 1.2) and AAP (24.7 ± 0.8) showed higher bond strengths than the other groups, followed by FSSNP (15.5 ± 4.2) and FSSN (13.3 ± 3.6). FS (3.4 ± 0.44) and SN (9.5 ± 2.7) showed the lowest values (p &lt; 0.001). Most of the specimens exhibited an adhesive failure. Conclusion: Air-abrasion by silica-coated alumina particles followed by silanization or by alumina particles followed by universal primer resulted in the highest resin bond strength to zirconia. Fusion sputtering and silica nanofilm deposition induced low strengths. However, when these methods are applied in combination and with a primer (FSSN and FSSNP), higher bond strengths may be achieved. Low bond strengths are obtained when no zirconia treatment is performed.

Micropatterned Silica Films with Nanohydroxyapatite for Y-TZP Implants

This investigation aimed at developing micropatterned silica thin films (MSTFs) containing nanohydroxyapatite (nano-HA) microaggregates that were not completely covered by silica so that they could directly interact with the surrounding cells. The objectives were 1) to evaluate the effect of the presence of 2 films (MSTF with or without nano-HA addition) on the characteristic strength (σ0) and Weibull modulus (m) of a yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) and 2) to evaluate the effect of these 2 films, as applied onto the Y-TZP surface, on the morphology, orientation, and proliferation of MG63 cells. Sol-gel process and soft lithography were used to apply the MSTF onto the Y-TZP specimens. Three experimental groups were produced: Y-TZP, Y-TZP + MSTF, and Y-TZP + MSTF + sprayed nano-HA. All surfaces were characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy and tested for 4-point flexural strength (n = 30) in water at 37 °C. Weibull analysis was used to determine m and σ0 (maximum likelihood method). In vitro biological behavior was performed with human osteoblast-like cells (MG63). Y-TZP was successfully coated with MSFT and MSFT + nano-HA. Scanning electron microscopy micrographs indicated that the microaggregates of nano-HA were not entirely covered by the silica. There was no statistically significant difference among the experimental groups for σ0 and m. In the groups containing the films, the cells were elongated and aligned along the lines. The MSFT + nano-HA group showed significantly higher cell metabolic activity than that obtained for the Y-TZP group at day 7. This investigation was successful in producing an MSTF containing nano-HA microaggregates that remained exposed to the environment. The developed films did not jeopardize the structural reliability of a commercial Y-TZP, as confirmed by the Weibull statistics. The MG63 cells seeded over the films became elongated and aligned along the films’ micropatterned lines. Y-TZP specimens coated with MSTF and nano-HA showed a higher cell metabolic activity and proliferation after 7 d of culture when compared with uncoated Y-TZP.

Effects of whitening dentifrice on yttria-stabilized tetragonal zirconia polycrystal surfaces after simulating brushing

Statement of problemThe changes that occur after brushing yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) are unknown. These changes may favor the retention of microorganisms and chemisorption of water, impairing its longevity. ObjectiveThe purpose of this in vitro study was to evaluate the effects of a whitening dentifrice on Y-TZP surfaces after simulating 10 years of brushing. Material and methodsSeventy-two bar-shaped specimens (20×4×1.2 mm) were divided into 4 groups: storage in distilled water (SW, control), brushing with distilled water (BW), brushing with dentifrice (BD), and brushing with whitening dentifrice (BWD). Brushing was conducted using a linear brushing machine (878400 cycles, 0.98 N, soft toothbrush). The mean roughness (Ra) was analyzed with a profilometer and the superficial topography with scanning electron microscopy (SEM) at baseline and after treatment. Crystalline phases were characterized using x-ray diffraction. Baseline and posttreatment Ra were analyzed using the 1-way ANOVA and Tukey HSD multiple comparison test; the paired t test was used for intragroup comparison (all α=.05). ResultsThe Ra (μm) means (before/after treatment) were SW 0.28/0.28; BW 0.32/0.31; BD 0.28/0.36; BWD 0.30/0.20. No statistically significant difference was found for Ra at baseline (P=.108) than for posttreatment results (P<.001); the BD group had higher Ra values when compared with baseline (P=.019); the BWD group had the lowest values (P<.001). The BD surfaces showed pronounced scratches and detachment of the surface, while BWD showed smoother surfaces; similar crystallographic results among groups were observed. ConclusionsBrushing Y-TZP with conventional dentifrice increased roughness, while brushing with whitening dentifrice reduced roughness. Neither dentifrice changed the crystallographic phases after brushing.

Sol-gel dip coating of yttria-stabilized tetragonal zirconia dental ceramic by aluminosilicate nanocomposite as a novel technique to improve the bonding of veneering porcelain.

The aim of this in vitro study was to evaluate the effect of silica and aluminosilicate nanocomposite coating of zirconia-based dental ceramic by a sol–gel dip-coating technique on the bond strength of veneering porcelain to the yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) in vitro. Thirty Y-TZP blocks (10 mm ×10 mm ×3 mm) were prepared and were assigned to four experimental groups (n=10/group): C, without any further surface treatment as the control group; S, sandblasted using 110 μm alumina powder; Si, silica sol dip coating + calcination; and Si/Al, aluminosilicate sol dip coating + calcination. After preparing Y-TZP samples, a 3 mm thick layer of the recommended porcelain was fired on the coated Y-TZP surface. Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray analysis were used to characterize the coating and the nature of the bonding between the coating and zirconia. To examine the zirconia–porcelain bond strength, a microtensile bond strength (μTBS) approach was chosen. FT-IR study showed the formation of silica and aluminosilicate materials. XRD pattern showed the formation of new phases consisting of Si, Al, and Zr in coated samples. SEM showed the formation of a uniform coating on Y-TZP samples. Maximum μTBS values were obtained in aluminosilicate samples, which were significantly increased compared to control and sandblasted groups (P=0.013 and P<0.001, respectively). This study showed that aluminosilicate sol–gel dip coating can be considered as a convenient, less expensive reliable method for improving the bond strength between dental Y-TZP ceramics and veneering porcelain.

Influence of zirconia surface treatment on veneering porcelain shear bond strength after cyclic loading

The influence of yttria-stabilized tetragonal zirconia polycrystal surface treatment on veneering porcelain shear bond strength after cyclic loading is not fully understood. The purpose of this study was to investigate the influence of yttria-stabilized tetragonal zirconia polycrystal surface treatment on veneering porcelain shear bond strength and cyclic loading on the shear bond strength between the 2 materials. A total of 48 cylinder-shaped yttria-stabilized tetragonal zirconia polycrystal specimens were fabricated with computer-aided design and computer-aided manufacturing (CAD/CAM), sintered for 8 hours at 1500°C, ground with 320-grit diamond paper, and divided into 4 groups (n = 12) according to surface treatment as follows: no treatment/control; heat treatment of 650°C to 1000°C at 55°C/min; airborne-particle abrasion with 50-μm alumina at 0.4 MPa pressure for 10 seconds; or heat treatment after abrasion. A veneering porcelain cylinder was built and fired on the prepared yttria-stabilized tetragonal zirconia polycrystal specimens. The shear bond strength was tested with a universal testing machine. Six specimens from each group were subjected to cyclic loading (10000 cycles, 1.5 Hz, 10 N load) before testing. The mean ± SD ranged from 10.7 ± 15.4 to 34.1 ± 10.0. Three-way ANOVA found no statistically significant (P > .05) effect of surface treatment and cyclic loading on shear bond strength. The Sidak multiple comparisons procedure found that cyclic loading specimens had significantly lower shear bond strength than noncyclic loading specimens after airborne-particle abrasion without heat treatment (P = .013). Within the limitations of this study, the shear bond strength between yttria-stabilized tetragonal zirconia polycrystal and veneering porcelain was not significantly affected by surface treatment. Airborne-particle abrasion without subsequent heat treatment should be avoided as a surface treatment in fabrication methods.

Initial Bacterial Adhesion on Different Yttria-Stabilized Tetragonal Zirconia Implant Surfaces in Vitro

Bacterial adhesion to implant biomaterials constitutes a virulence factor leading to biofilm formation, infection and treatment failure. The aim of this study was to examine the initial bacterial adhesion on different implant materials in vitro. Four implant biomaterials were incubated with Enterococcus faecalis, Staphylococcus aureus and Candida albicans for 2 h: 3 mol % yttria-stabilized tetragonal zirconia polycrystal surface (B1a), B1a with zirconium oxide (ZrO2) coating (B2a), B1a with zirconia-based composite coating (B1b) and B1a with zirconia-based composite and ZrO2 coatings (B2b). Bovine enamel slabs (BES) served as control. The adherent microorganisms were quantified and visualized using scanning electron microscopy (SEM); DAPI and live/dead staining. The lowest bacterial count of E. faecalis was detected on BES and the highest on B1a. The fewest vital C. albicans strains (42.22%) were detected on B2a surfaces, while most E. faecalis and S. aureus strains (approximately 80%) were vital overall. Compared to BES; coated and uncoated zirconia substrata exhibited no anti-adhesive properties. Further improvement of the material surface characteristics is essential.

Composite Resin to Yttria Stabilized Tetragonal Zirconia Polycrystal Bonding: Comparison of Repair Methods

The purpose of the current study was to evaluate different approaches for bonding composite to the surface of yttria stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics. One hundred Y-TZP blocks were embedded in acrylic resin, had the free surface polished, and were randomly divided into 10 groups (n=10). The tested repair approaches included four surface treatments: tribochemical silica coating (TBS), methacryloxydecyldihidrogenphosphate (MDP)-containing primer/silane, sandblasting, and metal/zirconia primer. Alcohol cleaning was used as a "no treatment" control. Surface treatment was followed by the application (or lack thereof) of an MDP-containing resin cement liner. Subsequently, a composite resin was applied to the ceramic surface using a cylindrical mold (4-mm diameter). After aging for 60 days in water storage, including 6000 thermal cycles, the specimens were submitted to a shear test. Analysis of variance and the Tukey test were used for statistical analyses (α=0.05). Surface treatment was a statistically significant factor (F=85.42; p<0.0001). The application of the MDP-containing liner had no effect on bond strength (p=0.1017). TBS was the only treatment that had a significantly positive effect on bond strength after aging. Considering the evaluated approaches, TBS seems to be the best surface treatment for Y-TZP composite repairs. The use of an MDP-containing liner between the composite and Y-TZP surfaces is not effective.

The effect of preparation order on the crystal structure of yttria-stabilized tetragonal zirconia polycrystal and the shear bond strength of dental resin cements

Objectives The purpose of this study was to evaluate the effect of preparation order on the crystal structure of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) and the shear bond strength of dental resin cements. Methods One-hundred fifty pre-sintered Y-TZP cylinders ( Ø 9 mm × 13.5 mm) were prepared and divided into three groups (control group, SBS group and SAS group). Specimens in control group were not treated. Specimens in SBS group were sandblasted and then densely sintered, and specimens in SAS group were sintered in advance, and then sandblasted. The specimens were analyzed by X-ray diffractometry, confocal laser scanning microscopy and Energy dispersive X-ray spectroscopy before and after sandblasting. All specimens were embedded in polytetrafluoroethylene (PTFE) molds using PMMA and each group was divided into five subgroups. The mixed resin cements (Clearfil SA luting cement, Zirconite, Superbond C&B, Rely-X Unicem, and Multilink) were placed onto the Y-TZP surfaces using PTFE molds with Ø 3 mm × 3 mm, followed by storage in distilled water at 37 °C for 24 h, and thermocycling (5000 cycles at 5 °C and 55 °C with a 30 s dwelling time). All specimens were tested for the shear bond strengths with a universal testing machine, and fractured surfaces were evaluated by SEM. Statistical analysis was performed using one-way ANOVA and Scheffé comparison with α = .05. Results Sandblasting of the zirconia significantly increased shear bond strength of resin cements, but the preparation order had no significant influence on the shear bond strength in both test groups. In SEM observation, the natures of the surface faceting of the zirconia grains were totally different between SBS and SAS groups. SBS group exhibited less monoclinic structures than SAS group. Significance Sandblasting of pre-sintered Y-TZP and then sintering may induce favorable proportion of tetragonal structures. This might have positive effect on the clinical performance of zirconia restorations.