Y-TZP Discs Research Articles

In vitro plaque formation model to unravel biofilm formation dynamics on implant abutment surfaces

ABSTRACT Background Biofilm formation on implant-abutment surfaces can cause inflammatory reactions. Ethical concerns often limit intraoral testing, necessitating preliminary in vitro or animal studies. Here, we propose an in vitro model using human saliva and hypothesize that this model has the potential to closely mimic the dynamics of biofilm formation on implant-abutment material surfaces in vivo. Methods A saliva stock was mixed with modified Brain-Heart-Infusion medium to form biofilms on Titanium-Aluminum-Vanadium (Ti6Al4V) and Yttria-partially Stabilized Zirconia (Y-TZP) discs in 24-well plates. Biofilm analyses included crystal violet staining, intact cell quantification with BactoBox, 16S rRNA gene analysis, and short-chain fatty acids measurement. As a control, discs were worn in maxillary splints by four subjects for four days to induce in vivo biofilm formation. Results After four days, biofilms fully covered Ti6Al4V and Y-TZP discs both in vivo and in vitro, with similar cell viability. There was a 60.31% overlap of genera between in vitro and in vivo biofilms in the early stages, and 41% in the late stages. Ten key oral bacteria, including Streptococcus, Haemophilus, Neisseria, Veillonella, and Porphyromonas, were still detectable in vitro, representing the common stages of oral biofilm formation. Conclusion This in vitro model effectively simulates oral conditions and provides valuable insights into biofilm dynamics.

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.

TiO2 nanoparticles added to dense bovine hydroxyapatite bioceramics increase human osteoblast mineralization activity

ObjectivesThis study evaluated the effect of TiO2 nanoparticles + dense hydroxyapatite (HA) on human osteoblast cells (SAOS-2). MethodsParticulate bovine HA powder with or without the addition of either 5 or 8 % TiO2 (HA, HA/TiO2Np5 % or HA/TiO2Np8 %) were pressed into disks (Ø = 12.5 mm; thickness = 1.3 mm) uniaxially (100 MPa) and isostatically (200 MPa/1 min) and sintered at 1300 °C. Y-TZP disks were used as control. The following tests were performed: Scanning Electron Microscopy and Dispersive Energy Spectroscopy (SEM/EDS), Atomic Force Microscopy (AFM), cell viability assay (Alamar Blue-AB) and mineralized matrix deposition (Alizarin Red-AR). AB and AR data were submitted to 2-way ANOVA/Tukey tests and ANOVA/Tukey tests, respectively. ResultsSEM revealed that the surface of HA/TiO2Np5% resembles DPBHA surface, but also contains smaller granules. HA/TiO2Np8% characteristics resembles HA/TiO2Np5% surface, but with irregular topography. Y-TZP showed a typical oxide ceramic surface pattern. EDS revealed Ca, O, and P in all samples. C, O, and Zr appeared in Y-TZP samples. AFM data corroborates SEM analysis. AB test revealed excellent cellular viability for HA/TiO2Np5% group. AR test showed that all groups containing TiO2np had more mineralized matrix deposition than all other groups, with statistically differences between HA/TiO2Np8% and HA cultivated in non-osteogenic medium. Culture in osteogenic medium exhibited much more mineralized matrix deposition by TiO2np groups. SignificanceIn conclusion, the addition of TiO2np showed chemical, superficial, and biological changes in the reinforced materials. HA/TiO2Np5% showed the best results for cell viability and HA/TiO2Np8% for mineralized matrix deposition.

Biocompatibility of ZrO2 vs. Y-TZP Alloys: Influence of Their Composition and Surface Topography.

The osseointegration of implants is defined as the direct anatomical and functional connection between neoformed living bone and the surface of a supporting implant. The biological compatibility of implants depends on various parameters, such as the nature of the material, chemical composition, surface topography, chemistry and loading, surface treatment, and physical and mechanical properties. In this context, the objective of this study is to evaluate the biocompatibility of rough (Ra = 1 µm) and smooth (Ra = 0 µm) surface conditions of yttria–zirconia (Y-TZP) discs compared to pure zirconia (ZrO2) discs by combining a classical toxicological test, morphological observations by SEM, and a transcriptomic analysis on an in vitro model of human Saos-2 bone cells. Similar cell proliferation rates were observed between ZrO2 and Y-TZP discs and control cells, regardless of the surface topography, at up to 96 h of exposure. Dense cell matting was similarly observed on the surfaces of both materials. Interestingly, only 110 transcripts were differentially expressed across the human transcriptome, consistent with the excellent biocompatibility of Y-TZP reported in the literature. These deregulated transcripts are mainly involved in two pathways, the first being related to “mineral uptake” and the second being the “immune response”. These observations suggest that Y-TZP is an interesting candidate for application in implantology.

Sintering mode of a translucent Y-TZP: Effects on its biaxial flexure fatigue strength, surface morphology and translucency.

This investigation evaluated the effect of two sintering modes of a translucent zirconia (Y-TZP) on its surface roughness, topography, phase-transformation (t → m), translucency and biaxial flexure fatigue strength. To do so, 50 Y-TZP discs (Ø=15 mm; thickness=1.2 mm; IPS e.max ZirCAD LT) were prepared and divided into two groups: Standard mode (SM) and Fast mode (FM). Staircase fatigue testing was performed (piston-on-three balls set-up, ISO 6872:2015), as well as surface roughness, profilometry, scanning electron microscopy (SEM-FEG), energy dispersive X-ray spectroscopy (EDX), phase transformation (t → m) using X-ray diffraction analysis (XRD), translucency parameter analysis (TP and TP00 ) and fractography. The results showed no statistical significant differences for roughness parameters (p > 0.05, SM: Ra=0.13 ± 0.02, Rz=1.21 ± 0.26 and RSm=24.91 ± 2.19; FM: Ra=0.14 ± 0.03, Rz=1.32 ± 0.25 and RSm=24.68 ± 2.16) or flexural fatigue strength (SM: 512 (464-560) MPa; FM: 542 (472-611) MPa) between the groups. In addition, similarity in surface morphological features (SEM and profilometry), composition and phases (EDX and XRD) was observed between the firing protocols. Fractography showed that the failure origin occurred on the tensile side. Sintering mode did not affect the TP (F=0.001, p=0.97) and TP00 (F=0.12, p=0.72). Therefore, the fast-sintering mode is suggested as a viable alternative to the standard mode since it does not influence the evaluated surface morphology, microstructure, fatigue strength and translucency of a translucent monolithic zirconia. The fast sintering mode is a viable alternative for zirconia without compromising its topography, microstructure, mechanical performance or translucency.

Comparative Analysis of Biofilm Formation on Materials Used for the Fabrication of Implant Supported Prostheses.

Background:Zirconia and other dental pottery, heat-restored polymethyl methacrylate, titanium and other metal amalgams, or a mix of these materials are utilized to fix inserts. It is important to choose a material that is resistant to bacterial colonization for implant-supported prostheses, but durability and aesthetics are important factors as well.Aim:Biofilm generation on materials used in implant-supported dental prosthesis manufacturing was an objective of this investigation.Methods and Materials:In this study, 90 discs were prepared. These discs were divided into three groups: group PMMA, group Y-TZP, and group CP-Ti. Each group consisted of 30 discs. As helpful materials, 30 discs (D = 15 mm, H = 3 mm) each were created from either monetarily unadulterated titanium (CP-Ti), yttria tetragonal zirconia polycrystal (YTZP), or hotness-restored polymethyl methacrylate (PMMA). The examples were cleaned as per acknowledged practices. The non-contact profilometer (NPFLEX, Bruker, UK) was utilized to survey the surface rougness of each disc, and the outcomes were accounted for as Ra (m). An assortment of gram-negative microbes, including Aggregatibacter actinomycetemcomitans, Tannerella forsythia, Porphyromonas gingivalis, Prevotella intermedia, and Tannerella albicans, were refined close by cleaned discs produced using heat-relieved PMMA, Y-TZP, or CP-Ti to see which type of biofilm is shaped best. CFU/mL was the unit of estimation (state framing units per milliliter).Results:Y-TZP discs have a substantially higher Ra (349 41 m) than PMMA and CP-Ti discs. Some bacteria that have been associated with peri-mucositis and peri-implantitis may be less prevalent on Y-TZP or CP-Ti discs. Biofilm development must be considered while making implant-supported prostheses using Y-TZP and CP-Ti.Conclusion:Y-TZP and CP-Ti are preferred materials for implant-supported prosthesis production because of biofilm development.

Fatigue behavior and colorimetric differences of a porcelain-veneered zirconia: effect of quantity and position of specimens during firing

To evaluate the influence of quantity and positioning of veneered zirconia specimens during firing of porcelain on their fatigue performance and colorimetric differences. Bilayer discs (Ø=15 mm) were made, following ISO 6872 guidelines, using a Y-TZP core (yttria-stabilized tetragonal zirconia polycrystal ceramic; VITA In-Ceram YZ) and a feldspathic veneering material (VITA VM9), being both layers with 0.7 mm thickness. Y-TZP discs were sintered, the veneering material was applied over it, and the bilayer specimens were fired according to two factors (n=20): 'quantity' (1 or 5 samples per firing cycle; G1 and G5 groups respectively) and 'positioning' of the specimens inside the furnace (center or periphery of the refractory tray; G5C and G5P groups, respectively). The CIEL*a*b* parameters were recorded with a spectrophotometer and the color difference (ΔE 00 ) and translucency (TP 00 ) were calculated using CIEDE2000 equations. The step-stress fatigue test was performed with the veneer facing down (region of tensile stress concentration), 10 Hz frequency, initial tension of 20 MPa for 5,000 cycles, followed by steps of 10,000 cycles using a step size of 10 MPa, up to 100 MPa; data from strength and number of cycles for failure were recorded for statistical analysis. Unacceptable color differences (ΔE 00 >1.8) were observed comparing G5C vs. G1 (quantity) and G5C vs. G5P (positioning), meanwhile translucency parameters were not affected. Besides, only the 'quantity' factor influenced the fatigue performance (G1>G5C). None of the tested specimens survived beyond 90N and/or 75000 cycles. The quantity and position of the specimens during firing influence the final color of porcelain-veneered zirconia, and firing one specimen per cycle improved the fatigue performance of the bilayer system.

Processing of Zn-Substituted calcium silicate layers on Y-Tzp bioceramics by dip coating

Ceramic layers based on calcium silicate non-substituted and substituted by Zn with different thickness, were developed by immersing porous Y-TZP disks into SiO2–CaO–ZnO–P2O5 glass suspensions with ZnO contents in the range of 0–20 mol%. The effect of the disk surface porosity and the slip solid loading on the formation of the dip coated layer was investigated. Special emphasis was given to the ZnO content of the dip coating slurries and its influence on the thickness and composition of the sintered layer. The greater chemical stability of the 20 mol% ZnO-substituted glass powder during aqueous colloidal processing resulted in slips with low viscosity values; whereas the high dissolution rate of the glass having 10 mol% ZnO significantly increased the slip viscosity. The liquid entrainment mechanism at the initial stage was accelerated either by using 10 mol% ZnO-substituted glass slips or by increasing the slip solid loading. The casting rate for longer immersion times markedly increased by increasing the surface porosity of Y-TZP disks. Sintered layers with thickness ~30–70% lower were produced using the glass dip coating slip with 20 mol% ZnO in comparison to 10 mol% ZnO. The main crystalline phase of the coated sintered layers was Ca3Si3O9, Ca2ZnSi2O7 and ZnSiO4 for the glasses with 0, 10 and 20 mol% ZnO, respectively.

Yttria-stabilized tetragonal zirconia polycrystal/resin luting agent bond strength: Influence of Titanium dioxide nanotubes addition in both materials

PurposeTo evaluate the shear bond strength (SBS) between Y-TZP and a resin luting agent, after 1 of 2 enhancing strategies with TiO2--nts was applied, either to the resin luting agent or the Y-TZP mass, in different concentrations. MethodsIn the Strategy TiO2-nts on ceramic, the resin luting agent Panavia F2.0™ (Kuraray) and an experimental Y-TZP with added concentrations of TiO2--nts (0%, 1%, 2%, and 5% vol/vol) and a commercial Y-TZP, comprised 5 different groups (n = 10). In the Strategy TiO2-nts on cement, the resin luting agent RelyX U200™ (3 M ESPE) was added with different concentrations of TiO2--nts (0%, 0.3%, 0.6%, 0.9% wt/wt) luted to a commercial Y-TZP, comprising 4 different groups (n = 10). The Y-TZP discs were included in acrylic bases, and a cylinder (3 × 3 mm) of the correspondent luting agent for each respective group was applied over them. After 24 h, specimens were subjected to SBS assessments in a universal testing machine. Field emission scanning electron microscopy and energy dispersive X-ray spectroscopy analyses were also performed on Y-TZP surfaces. Data were analyzed via analysis of variance and Tukey tests (α = 0.05). ResultsTiO2-nts on ceramic influenced the bond strength significantly, but not linearly; TiO2-nts on cement did not influence bond strength when analyzed separately, nor in comparison with the first. ConclusionY-TZP enhancements with TiO2-nts led to a higher SBS with Panavia F2.0, a 5% TiO2--nt concentration presented the highest bond strength. Modified Rely X U200 did not improve SBS.

Effects of 10-MDP Based Primer on Shear Bond Strength between Zirconia and New Experimental Resin Cement.

To date, numerous materials in the dental field are marketed to ensure stable adhesive cementation of zirconia ceramics (Y-TZP). The aims of this study were to assess the shear bond strength of the new experimental cement Surgi Dual Flo’ Zr to Y-TZP compared to Panavia V5 cement, and to evaluate the effect of 10-MDP (10-methacryloyloxydecyl dihydrogen phosphate) containing primer on their bond strength. Twenty composite cylinders and Y-TZP disks were adhesively luted and divided into four groups based on cement type used and application or not of 10-MDP. The groups (n = 5 each) were S 10MDP (Surgi Dual Flo’ Zr with 10-MDP); S no 10MDP (Surgi Dual Flo’ Zr without 10-MDP); P 10MDP (Panavia V5 with 10-MDP); P no 10MDP (Panavia V5 without 10-MDP). Maximum load resistance (ML) and shear bond strength (SBS) were tested and mode of failure qualitative documented via scanning electron microscopy. The data were analyzed with one-way ANOVA, Holm-Sidak method, and Bayesian analysis. ML and SBS were significantly higher in S 10MDP than in S no 10MDP; and in P 10MDP than in P no 10MDP (p < 0.05). No significant differences were found between S 10MDP and P 10MDP; S no 10MDP and P no 10MDP (p > 0.05). Cohesive, adhesive, and mixed failure occurred among the groups. Bond strength between the experimental resin-based cement and Y-TZP was adequate for clinical application when 10-MDP was added. 10-MDP containing primer was effective improving the bond strength to Y-TZP more than the different type of resinous cement.

Effect of glazing application side and mechanical cycling on the biaxial flexural strength and Weibull characteristics of a Y-TZP ceramic

Glaze application on monolithic zirconia (Y-TZP) can be a practical approach to improve the mechanical properties of this material. Objective Our study evaluated the effect of glazing side and mechanical cycling on the biaxial flexure strength (BFS) of a Y-TZP.Methodology Eighty sintered Y-TZP discs (Ø:12 mm; thickness: 1.2 mm - ISO 6872) were produced and randomly assigned into eight groups (n=10), according to the factors “glazing side” (control – no glazing; GT – glaze on tensile side; GC – glaze on compression side; GTC – glaze on both sides) and “mechanical aging” (non-aged and aged, A – mechanical cycling: 1.2×106, 84 N, 3 Hz, under water at 37°C). Specimens were subjected to BFS test (1 mm/min; 1,000 Kgf load cell) and fractured surfaces were analyzed by stereomicroscopy and SEM. Hsueh’s rigorous solutions were used to estimate the stress at failure of glazed specimens. Two-way ANOVA, Tukey’s test (5%), and Weibull analysis were performed.Results The “glazing side”, “mechanical aging” and the interaction of the factors were significant (p<0.05). Groups GC (1157.9±146.9 MPa), GT (1156.1±195.3 MPa), GTC (986.0±187.4 MPa) and GTC-A (1131.9±128.9 MPa) presented higher BFS than control groups (Tukey, 5%). Hsueh’s rigorous solutions showed that the maximum tensile stress was presented in the bottom of zirconia layer, at the zirconia/glaze interface. Weibull characteristic strength (σo) of the GC was higher than all groups (p<0.05), except to GT, GTC-A and GTC, which were similar among them. The fractography showed initiation of failures from zirconia the tensile side regardless of the side of glaze application and fatigue.Conclusion Glazing zirconia applied on both tensile and compression sides improves the flexural strength of Y-TZP, regardless the mechanical aging.

A new approach for Y-TZP surface treatment: evaluations of roughness and bond strength to resin cemen.

Objective This study aims to evaluate the effect of sonochemical treatment on the surface of yttria-stabilized tetragonal zirconia (Y-TZP) before and after the final sintering.Material and Methods Twenty-eight Y-TZP discs were divided into four groups (n=7), according to surface treatment: PRE: pre-sintering sonication with 30% nominal power for 15 min; POS: post-sintering sonication with 30% nominal power for 15 min; JAT: air abrasion with 50-μm alumina particles; and CON: control group with no treatment. The POS and JAT groups were sintered before sonication and the PRE group after sonication. Surface roughness was analyzed using confocal microscopy, after which resin cement cylinders were placed on the surface of the Y-TZP discs and subjected to mechanical microshear bond strength test until fracture. Surface roughness and microshear bond strength values underwent ANOVA and the Tukey tests.Results The surface roughness values for the PRE group (299.91 nm) and the POS group (291.23 nm) were not significantly different (p≥0.05), statistically, and the surface roughness value of the JAT group (925.21 nm) was higher than those of PRE and POS (p=0.007) groups. The mechanical microshear bond strength test showed that there was no statistically significant difference between the groups (p=0.08).Conclusions Therefore, the results showed that sonochemical treatment modifies the Y-TZP surface and is similar to the well-established sandblasting surface treatment regarding the strength of the bond with the resin cement.

Does Luting Strategy Affect the Fatigue Behavior of Bonded Y-TZP Ceramic?

To evaluate the effect of different luting strategies on the fatigue failure load (FFL) and stress distribution of Y-TZP disks luted to epoxy resin substrate. Y-TZP disks (diameter = 10 mm; thickness = 0.7 mm) were assigned to five groups according to the luting strategy (n = 15): CC: no zirconia surface treatment, composite cement; G_CC: application of a thin glaze layer on zirconia followed by hydrofluoric acid etching and silanization, composite cement; Al_CC: air abrasion of the zirconia surface with 125-µm Al2O3 particles, composite cement; Si_CC: tribochemical silica coating (30-µm SiO2 particles), composite cement; ZP: air abrasion of the zirconia surface with 125-µm Al2O3 particles, zinc-phosphate cement. The disks were luted to the epoxy resin substrate. The FFL was evaluated by the step-test method. The load was applied in stages of 10,000 cycles, starting with 600 N, followed by increments of 200 N. Samples were loaded until fracture or to a maximum of 100,000 cycles. FFL data were submitted to Kaplan-Meier (α = 0.05) and Weibull analyses. Conditions simulating a strong and a weak bond between Y-TZP and epoxy resin were evaluated in the finite element analysis (FEA). Luting strategy influenced the FFL (p < 0.001) and the stress distribution of Y-TZP disks. Al_CC (2227 ± 149 N) and Si_CC (2133 ± 235 N) showed the highest FFL values, followed by CC (1800 ± 293 N) and G_CC (1280 ± 147 N), while ZP showed the lowest FFL value (680 ± 101 N). The highest Weibull modulus occurred in Al_CC (18.2). A strong bond reduced the tensile stress concentration in the Y-TZP luting surface, while a weak bond between Y-TZP and the epoxy resin favored the concentration of tensile stresses. Air abrasion with aluminum oxide and silica-coated alumina particles improves the FFL of bonded Y-TZP. Zinc-phosphate cement should be used very carefully in the cementation of zirconia restorations, since it results in lower values of FFL than composite cements.

Effect of Er: YAG Laser, Sandblast and Several Types of Universal Bonding on Shear Bond Strength of Zirconia Ceramic to Composite Resin

The purpose of this study was to investigate the effect of Erbium-doped yttrium aluminium garnet laser laser (Er: YAG laser), sandblast and several universal bonding on the shear bond strength of zirconia ceramic to composite resin. In this experimental study, 96 Y-TZP disks were used. They were divided into six groups based on surface preparation: 1-Er: YAG laser + single bond universal/ 3M, 2-Er: YAG laser + all bond universal/bisco, 3-Er: YAG laser + G-premio bond/GC, 4-sandblast + single bond universal/3M, 5-sandblast + all bond universal/bisco, 6-sandblast + G-Premio bond/GC; in the next step, composite discs were cured on the surface of the zirconia discs and their shear bond strength was evaluated using a mechanical test machine (universal testing machine). Two-way ANOVA showed that the surface preparation had a significant statistical effect on shear bond strength (p< 0.001). There was no association between these two variables with regards to the interaction of bonding and surface preparation (p = 0.064). Tukey's test showed that the shear bond strengths in the sandblast type group did not differ significantly between the groups according to the type of universal bonding, as well as in the Er: YAG laser treated group by type Universal bonding which was not significantly different between the groups of single bond universal and all bond universal, but there was a significant difference between the groups in terms of single bond universal and G-Premio, as well as all bond universal and G-Premio. Based on the results, the preparation of Er:YAG laser is a more appropriate method for increasing bond strength when compared with sandblasting, and among the universal bonding, G-Premio is also more suitable for this purpose. The present data indicate that bond strength of laser preparation and G-Premio adhesive might be reliable for clinical application Keywords: Er: YAG Laser, Sandblasting, Shear bond strength, Universal bonding.

Surface roughness and volumetric contraction of a Y-TZP ceramic sintered by microwave energy and by resistive heating

Objective: The aim of this study was to evaluate a Y-TZP ceramic sintered by a microwave protocol on volume shrinkage and surface roughness. Material and Methods: Twenty four (N=24) Y-TZP discs were fabricated by milling in CAD/CAM for size standardization. The mean final dimensions of the specimens were 15 mm X 1.6 mm. Samples were divided into 2 groups (n=12): conventional resistive heating sintering protocol (C - Control) and microwave sintering protocol (MO - experimental). For the characterization of the specimens, surface roughness (Ra and Rz parameters) was evaluated with a roughness tester, and volume shrinkage was measured with a hand micrometer. Data were statistically evaluated by Student’s t and Mann-Whitney U tests (?=0.05). Results: The roughness results were: 0.25 ?m ± 0.02 (Ra) and 2.68 ?m ± 0.666 (Rz) for the MO samples; 0.26 ?m ± 0.04 (Ra) and 2.73 ?m ± 0.461 (Rz) for the C group (Ra: p = 0.19; Rz: p = 0.81). The shrinkage results was: MO (21.02% ± 2.70) and C (20.10% ± 0.52) (p = 0.274). Conclusion: The conventional and microwave sintering methods were similar regarding surface roughness and volume shrinkage of Y-TZP dental ceramic.KeywordsBioceramics; Microwave sintering; Roughness surface; Zirconia.

Microstructural analysis and reliability of monolithic zirconia after simulated adjustment protocols

ObjectiveTo investigate the microstructural properties and reliability of zirconia partially stabilized by yttrium oxide (Y-TZP) for use in monolithic form (Vita YZ HT, Vita Zahnfabrik, Germany) after different clinical adjustment protocols simulation. One-hundred and sixty two Y-TZP discs of high translucency were divided into 6 groups (n=27), according to simulated adjustments: S-Y-TZP as sintered; G-glazed Y-TZP; DbG-Y-TZP with diamond bur adjustment simulation followed by glaze application; GDb-glazed Y-TZP adjusted with diamond bur; DbDrG-Y-TZP with adjustment simulation with diamond bur and polishing kit (diamond rubber), followed by glaze; GDbDr-glazed Y-TZP with adjustment simulation with diamond bur followed by polishing kit. MethodsAfter monotonic testing under biaxial flexure (n=3), remaining specimens were distributed into 3:2:3 ratio and tested under step-stress accelerated life testing. Specimens were evaluated in a stereomicroscope and SEM. Microstructure was analyzed by X-ray diffraction and mean surface roughness (Ra). Survival data were used to calculate Weibull's beta value (β) and reliability for missions of 300,000 and 600,000 cycles at 200N. Ra data were statistically analyzed by 1-way ANOVA and Tukey’s test (both, a=5%). ResultsThe untreated HT zirconia (S) presented a lower probability of survival after 600,000 cycles at 200N, compared to HT zirconia adjusted with diamond bur and glazed (DbG), and after final polishing with polishing kit (GDbDr). Final polishing with diamond rubber (GDbDr) resulted in a more homogeneous surface compared to glazed samples (G, DbG and DbDrG). SignificanceHT zirconia is more likely to present increased survival when glazed after diamond adjustments (DbG) or when it is finished with polishing kit (GDbDr).

Surface analysis and shear bond strength of zirconia on resin cements after non-thermal plasma treatment and/or primer application for metallic alloys

There is no established protocol for bonding zirconia (Y-TZP) with resin cements. Non-thermal plasma (NTP) may be an alternative for the clinical problems related to adhesion. The purpose of the present study was to characterize the surface of Y-TZP exposed to methane (CH4) NTP or coated with a layer of primer for metal alloys and the association between the two methods and to evaluate the effect of NTP treatment on bond strength between Y-TZP and two resin cements. A total of 235 Y-TZP discs (8×2mm) were distributed into five groups: Co (no surface treatment), Pr (primer), NTP (methane plasma), Pr+NTP and NTP+Pr. The effect of the treatment type on the surface free energy, morphology, topography and chemical composition of the Y-TZP discs was investigated. The discs were cemented to composite resin substrates using Panavia F2.0 or RelyX U200. Shear bond strength (n=10) analyses were performed (1mm/min) before and after thermocycling (5–55°C, 2000cycles) on the bonded specimens. The data were analyzed with one and three-way ANOVAs and Bonferroni tests (α=0.05). NTP reduced the surface energy and roughness of the Y-TZP discs. SEM-EDS and XPS analyses showed the presence of the organic thin film, which significantly improved the bond strength results when Rely X U200 was used, whereas the primer treatment was more effective with Panavia F2.0. Thermocycling significantly reduced the bond strength results of the NTP and Pr+NTP groups cemented with Rely X U200 and the Pr and NTP+Pr groups cemented with Panavia F2.0. Nonthermal plasma improves the bond strength between Rely X U200 and Y-TZP and also seems to have water-resistant behavior, whereas Panavia F2.0 showed better results when associated with primer.

Loading frequencies up to 20 Hz as an alternative to accelerate fatigue strength tests in a Y-TZP ceramic

Considering the interest of the research community in the fatigue behavior of all-ceramic restorations and the time consumed in low-frequency cyclic fatigue tests, this study aimed to investigate the influence of the loading frequency on the zirconia fatigue strength. The biaxial flexural fatigue strength of Y-TZP discs was determined by the staircase approach after 500,000 cycles. The investigated frequencies were 2Hz (control-simulation of the chewing activity; n=20), 10Hz (n=20), 20Hz (n=20), and 40Hz (n=21). The fatigue strength data were analyzed using one-way ANOVA and post-hoc Tukey׳s test (α=0.05). Pearson coefficient (r) was calculated to assess the existence of a correlation between fatigue strength and loading frequency. X-ray diffraction analysis was used to determine the relative amount of monoclinic phase under each fatigue test condition. The fatigue strength was significantly higher for 40Hz group (630.7±62.1MPa) and did not differ among the groups 2Hz (550.3±89.7MPa), 10Hz (574.0±47MPa) and 20Hz (605.1±30.7MPa). Pearson correlation coefficient indicated a significantly moderate correlation (r=0.57) between fatigue strength and loading frequency. The percentage of monoclinic phase was similar among the groups. Therefore, the use of loading frequencies up to 20Hz seems a good alternative to expedite the cycling strength fatigue tests in polycrystalline ceramics without significantly changing the fatigue behavior showed by zirconia in tests employing the frequency of the masticatory cycle.

Interaction of zirconia primers with yttria-stabilized zirconia surfaces

ObjectivesRecently several zirconia primers have been introduced to mediate bonding of dimethacrylate resins to yttria-stabilized zirconia frameworks (Y-TZP). The aim of the study was to evaluate the changes in surface chemistry of Y-TZP frameworks induced by zirconia primer treatments. MethodsPolished Y-TZP discs (Lava, 3M ESPE), ultrasonicated for 10min in ethanol, water-rinsed and air-dried were treated as follows: A: Reference (no treatment), B: Treatment with Z Prime Plus (Bisco), and C: Treatment with Z-Bond (Danville Materials). The primer films formed on Y-TZP surfaces were air-dried, left intact for 5 days (dark storage, 37°C, 40% RH), rinsed with 10ml acetone to remove the loosely bound fractions, air-dried and studied by: (a) reflection optical microscopy, (b) reflection Fourier transform infrared microscopy (RFTIRM) and (c) scanning electron microscopy/energy dispersive X-ray microanalysis (SEM/EDX). ResultsAn amorphous thick film was observed on primed and acetone rinsed Y-TZP surfaces after B treatment, whereas C treatment formed a thinner film with phase-separated aggregates. The RFTIRM study showed that both primers induced carboxylate salt formation on Y-TZP. Phosphate groups in a dissociative form have been identified on Y-TZP, as well, indicating formation of phosphate salts. EDX analysis showed increased C, O and P content on the films, which masked the substrate contributions. SignificanceThe primers tested formed carboxylate and phosphate salts on Y-TZP, promoting thus chemical adhesion. However, the differences in the film forming properties and water solubility between the carboxylate and phosphate salts may affect the strength and the durability of adhesive resin interfaces with Y-TZP, as mediated by these primers.

Durability of Resin-Zirconia Bonds Produced Using Methods Available in Dental Practice.

To evaluate the strength, after artificial aging, of resin-zirconia bonds yielded by methods available in dental practice. Standardized test specimens consisting of composite resin cylinders cemented to Y-TZP disks were assigned to 24 groups (n=20 per group) on the basis of the surface conditioning of the disks and the adhesive used (cement+manufacturer-specific primer). Conditioning methods were: none (control), airborne particle abrasion (50-μm Al2O3 at 0.05, 0.10, or 0.25 MPa), or tribochemical silica coating (Rocatec or CoJet). Panavia 21+Clearfil Ceramic Primer, Multilink Automix+Monobond Plus, BiFix QM+Ceramic bond, or RelyX Ultimate+Scotchbond Universal were used for cementation. Specimens were stored in water at 37°C either for 3 days or for 150 days in conjunction with 37,500 thermocycles before being submitted to a tensile test (crosshead speed: 1 mm/min). Nonparametric ANOVA and post-hoc tests within the same model were applied to the results (α=0.05). Conditioning, cement, aging, and all their interactions significantly affected bond strength (p<0.0001). After storage in water for 3 days, bond strengths ranged between 4 and 45 MPa (values were lowest in the BiFix QM groups). After long-term aging, the best results were obtained for silica-coated (Rocatec) zirconia samples cemented with Panavia 21/Clearfil Ceramic Primer; this was the only group for which bond strengths were >10 MPa. Premature failure of the resin-ceramic bond was usually observed during long-term aging, the only exception being the non-control groups cemented with Panavia. Most bonding strategies failed to create bonds to zirconia with acceptable strength after long-term aging. It might therefore be unwise to rely solely on adhesion for retention of load-bearing Y-TZP restorations.