Yttria Tetragonal Zirconia Research Articles

In-situ nano-silica deposition and air-abrasion with Bioglass 45S5 or aluminium oxide: Effects on methacrylate bonding to yttria-tetragonal zirconia polycrystal

This study aimed at assessing the bonding performance after water storage (24h/6-month) of a methacrylate-based cement applied onto Yttria-Tetragonal Zirconia Polycrystal(Y-TZP) pre-treated using an innovative in-situ silica nanoparticle deposition method and/or air-abrasion with Bioglass 45S5 (BAG) or aluminium oxide (AlO).Pre-sintered blocks of Y-TZP were coated with nano-silica using an experimental in-situ deposition method or used as received (control/silica-free). Air-abrasion was performed with AlO or BAG particles both on silica-coated and control Y-TZP specimens. All the specimens were then analysed using SEM–EDX. Further specimens were treated as described above, bonded using a dual-cure resin cement system and submitted to shear bond strength test after water storage (24h and 6 months). Fracture analysis was subsequently performed using a stereo-microscope.Uniform nano-silica deposition was achieved in the Y-TZP specimens after in-situ silica deposition treatment. However, AlO air-abrasion removed the nano-silica and roughened the Y-TZP surfaces. Conversely, BAG air-abrasion caused partial removal of the nano-silica layer and created only little retention in the control/silica-free Y-TZP specimens. The highest bond strength both at 24h and 6-month water storage was attained with the silica-coated specimens air-abraded with BAG and with those which received no air-abrasion. AlO air-abrasion increased the bond strength (24h) in the Y-TZP specimens compared to the control/silica-free specimens which received no air-abrasion or BAG air-abrasion.The in-situ nano-silica coating method employed in this study may be a suitable, simplified and low-cost approach to provide reliable bond strength to Y-TZP ceramics. No air-abrasion is required after in-situ nano-silica deposition. However, AlO air-abrasion can create micro-retentions on the surface of silica-free Y-TZP ceramics and increases the immediate bond strength of methacrylate-based resin cements.

Effects of different polishing protocols on the surface roughness of Y-TZP surfaces used for custom-made implant abutments: A controlled morphologic SEM and profilometric pilot study

Statement of problemLimited information is available on how to treat the surface of computer-aided design/computer-aided manufacturing (CAD/CAM)-derived implant abutments made of yttria tetragonal zirconia polycrystal (Y-TZP). PurposeThe purpose of this study was to assess and compare 4 different standardized polishing protocols of dental zirconia with a standard handpiece and abrasives and to identify a standardized protocol to obtain a surface roughness of Ra=0.2 μm on dental Y-TZP. Material and methodsForty specimens of Y-TZP were produced and finished with 4 different polishing protocols with standard dental abrasives. Protocol Co used a coarse rubber abrasive, protocol Me used the rubber abrasive of protocol Co plus a medium rubber abrasive, protocol Fi used the polishing sequences of protocol Me plus a fine rubber abrasive, and protocol UF used protocol Me plus ultrafine high-gloss polishing. Ten machined titanium disks served as control (C). Roughness measurement and scanning electron microscopy was performed for each specimen and tested for differences with ANOVA with Bonferroni correction and the Student t test (α=.05). ResultsIn the zirconia groups, Co (Ra 0.29 ±0.38 μm) showed significantly higher Ra values than Me (Ra 0.22 ±0.38 μm; P=.003), Fi (Ra 0.17 ±0.37 μm; P<.001), and UF (Ra 0.07 ±0.06 μm; P<.001). UF showed the significantly lowest Ra values of all zirconia groups (Co and Me: P<.001, Fi: P=.002). Differences between Me and Fi were not significant (P=.116). Comparison of the 4 zirconia surfaces to the control group (C; Ra=0.17 ±0.03) revealed significant differences for Co (P<.001) and UF (P=.006) but not Me (P=1.000) and Fi (P=.055). In comparison with the literature-based optimal roughness of Ra=0.2 μm, significant differences were found for Co, Fi, and UF (P<.05), but not for Me (P=.117). However, the machined titanium surface (C) also showed significantly smoother Ra values than 0.2 μm (P<.05, Student t test). ConclusionsA roughness of Ra=0.2 μm on zirconia can be achieved by following protocol Me, whereas a roughness comparable to machined titanium is present after protocol Fi.

Abrasivity of Yttria Tetragonal Zirconia Polycrystal (Y-TZP) to dental enamel in comparison to noble white high palladium alloy

ObjectivesTo test the wear of enamel against Yttria Tetragonal Zirconia Polycrystals (Y-TZP) in comparison to the wear of enamel against a noble white high Palladium alloy. MethodsA total of 20 specimens were used, 10 of Y-TZP and 10 of High Palladium alloy, both were subjected to 202,800 contacts against an enamel rod 2 × 2 mm in cross section under a mean load of 475.04 g leading to a mean force of 4.66 N in a Wilson Wear Machine. The specimens were kept in Dulbecco's phosphate buffered saline at a pH of 7 and the enamel rods were measured before and after the experiment for loss of enamel height (mm). ResultsThe mean wear caused by the Y-TZP and the High Palladium alloy tested was 0.0912 mm, and 0.0113 mm respectively. This difference was statistically significant (p = 0.012 (p < 0.05)). SignificanceIt is recommended that Y-TZP is not to be used to form the occlusal surfaces of indirect restorations due to its high abrasive potential with respect to dental enamel.

Fracture of Porcelain Fused to Yttria-Tetragonal Zirconia Polycrystals Dental Crowns from Dual-motion Cyclic Loading in Aqueous Condition

Porcelain fused to Y-TZP dental crowns are widely used in dental restorations. The fracture damage from concentrated loading especially under dual-motion cyclic loading-simulating chewing remains doubtful. Flat occlusal surface porcelain/Y-TZP ceramic crowns were fabricated following general dental practice and were supported with dentine-like composite to simulate actual dental restorations. Specimens were subjected to eccentric forces in a Willytic chewing simulator with loads of 5, 7 and 8 Kg delivered by means of steel stylus of 4mm diameter in wet condition. The damage evolution was observed at stepwise increase in cycles of 100,000 cycles each. Force measurements were taken using a 3D force sensor during dynamic loading of simultaneous axial-lateral movements. Localized surface damage which was observed at early stages was halted later after 500,000 cycles with distinctive crack patterns. Radial cracks were observed in three locations; the first location was at the porcelain inner layer under the indentation area. The second location was at the marginal extremists similar to lunar cracks observed when using soft intenders. The third location was the mesiobuccal area between the occlusal and axial sides of the crown. This latter finding may explain the chipping damage of the dental crowns. More interestingly at mesiobuccally area between the occlusal and the axial side of the crown which explain the chipping damage of dental crowns, it was believed that extension of radial cracks from indentation area are the major cause of such failure.

Shear Bond Strength of MDP-Containing Self-Adhesive Resin Cement and Y-TZP Ceramics: Effect of Phosphate Monomer-Containing Primers.

Purpose. This study was conducted to evaluate the effects of different phosphate monomer-containing primers on the shear bond strength between yttria-tetragonal zirconia polycrystal (Y-TZP) ceramics and MDP-containing self-adhesive resin cement. Materials and Methods. Y-TZP ceramic surfaces were ground flat with #600-grit SiC paper and divided into six groups (n = 10). They were treated as follows: untreated (control), Metal/Zirconia Primer, Z-PRIME Plus, air abrasion, Metal/Zirconia Primer with air abrasion, and Z-PRIME Plus with air abrasion. MDP-containing self-adhesive resin cement was applied to the surface-treated Y-TZP specimens. After thermocycling, a shear bond strength test was performed. The surfaces of the Y-TZP specimens were analyzed under a scanning electron microscope. The bond strength values were statistically analyzed using one-way analysis of variance and the Student–Newman–Keuls multiple comparison test (P < 0.05). Results. The Z-PRIME Plus treatment combined with air abrasion produced the highest bond strength, followed by Z-PRIME Plus application, Metal/Zirconia Primer combined with air abrasion, air abrasion alone, and, lastly, Metal/Zirconia Primer application. The control group yielded the lowest results (P < 0.05). Conclusion. The application of MDP-containing primer resulted in increased bond strength between Y-TZP ceramics and MDP-containing self-adhesive resin cements.

Fracture Strength of Aged Monolithic and Bilayer Zirconia-Based Crowns.

The purpose of this study was to evaluate the effect of design and surface finishing on fracture strength of yttria-tetragonal zirconia polycrystal (Y-TZP) crowns in monolithic (1.5 mm thickness) and bilayer (0.8 mm zirconia coping and 0.7 mm porcelain veneer) configuration after artificial aging. Bovine incisors received crown preparation and Y-TZP crowns were manufactured using CAD/CAM technique, according to the following groups (n = 10): Polished monolithic zirconia crowns (PM); Glazed monolithic zirconia crowns (GM); Bi-layer crowns (BL). Crowns were cemented with resin cement, submitted to artificial aging in a chewing simulator (2.5 million cycles/80 N/artificial saliva/37°C), and tested for fracture strength. Two remaining crowns referring to PM and GM groups were submitted to a chemical composition analysis to measure the level of yttrium after aging. One-way ANOVA and Tukey's test (P = .05) indicated that monolithic zirconia crowns presented similar fracture strength (PM = 3476.2 N ± 791.7; GM = 3561.5 N ± 991.6), which was higher than bilayer crowns (2060.4 N ± 810.6). There was no difference in the yttrium content among the three surfaces evaluated in the monolithic crowns. Thus, monolithic zirconia crowns present higher fracture strength than bilayer veneered zirconia after artificial aging and surface finishing does not affect their fracture strength.

Efficacy of surface roughness and bond strength of Y-TZP zirconia after various pre-treatments.

The aim of this study was to evaluate surface roughness (SR) and the influence of various surface treatments (STs) on the veneer ceramic shear bond strength (SBS) to Y-TZP zirconia. STs can improve the bonding properties of zirconia ceramics. However, little is known about the effect of Er,Cr:YSGG laser irradiation on SBS between zirconia and veneer ceramic/resin cement. Eighty ceramic discs of yttria-tetragonal zirconia polycrystals (Y-TZP) were prepared, and specimens were divided into eight groups (n=10): untreated (control), air abrasion, and Er,Cr:YSGG laser irradiation with different energy intensities (1-6 W). Average SR of each specimen was determined with a profilometer, and a veneering ceramic recommended for zirconia was fired into cylinder-shaped Y-TZP specimens. SBS test was performed for each specimen at a crosshead speed of 1 mm/min, and the average means of SBS and SR were calculated. Fracture modes and the surface topography were evaluated with various microscopes after STs. Data were analyzed by using one way analysis of variance (ANOVA) and Tukey honest significant difference (HSD) tests. The highest mean force value was observed in the air abrasion group, and followed by 6 and 5 W laser irradiations, respectively. The difference between control and air abrasion groups was found to be statistically significant (p<0.05). All laser irradiations increased the SBS value, but 1 and 2 W laser irradiations showed no statistically significant differences compared with the control group. However, the SR value for air abrasion group was significantly higher than that of the control group and 1 W (p<0.05), and there were no significant differences between the SR of all the laser groups and the control group. The result of this study showed that STs with air abrasion and high laser energy intensities (3-6W), can improve the bonding properties of Y-TZP zirconia.

Effect of Different Surface Treatment on the Shear Bond Strength between Yttria-Tetragonal Zirconia Polycrystal and Non-10-Methacryloyloxydecyl Dihydrogen Phosphate-Containing Resin Cement

Purpose: To evaluate the effect of different surface treatment methods (yttria-tetragonal zirconia polycrystal [Y-TZP] primers, air-abrasion, and tribochemical surface treatment) on the shear bond strength between (Y-TZP) ceramics and etch-and-rinse non-10-methacryloyloxydecyl dihydrogen phosphate (MDP)-containing resin cements. Materials and Methods: Y-TZP ceramic surfaces were ground flat with 600-grit silicone carbide abrasives paper and then divided into seven groups of ten. They were treated as the following: untreated (control), Monobond Plus (IvoclarVivadent), Z-PRIME Plus (Bisco Inc.), ESPE Sil with CoJet (3M ESPE), air-abrasion, Monobond Plus with air-abrasion, and Z-PRIME Plus with air-abrasion. The surface of Y-TZP specimens was analyzed under a scanning electron microscope (SEM). Non-MDP-containing cements were placed on the surface-treated Y-TZP specimens. After thermocycling, shear bond strength test was performed. Bond strength values were statistically analyzed using one-way analysis of variance and Student-Newman-Keuls multiple comparison test (P Result: The Z-PRIME Plus treatment in combination with air-abrasion produced the highest bond strength (14.94±1.70 MPa) followed by Monobond Plus combined with air-abrasion (10.70±1.71 MPa), air-abrasion (10.47±1.60 MPa), ESPE Sil after CoJet treatment (10.38±0.87 MPa), Z-PRIME Plus application (10.00±1.70 MPa), and then Monobond Plus application (9.25±0.86 MPa). The control (6.70±1.49 MPa) indicated the lowest results (P Conclusion: The shear bond strength between the Y-TZP ceramic and the non-MDP-containing resin cement was the greatest when the surface was treated with air-abrasion and MDP-containing Z-PRIME Plus primer.

A retrospective evaluation of zirconia-fixed partial dentures in general practices: An up to 13-year study

ObjectivesTo evaluate zirconia-based fixed partial dentures (FPDs) after more than 8 years in clinical service. MethodsPatients treated between 2000 and 2004 with zirconia FPDs were identified from the records of a manufacturer of FPD substructures. Of the 45 patients who met the inclusion criteria 30 attended the appointment and 33 FPDs were evaluated using modified California Dental Association (CDA) criteria. In addition, plaque and the bleeding index were registered. Patient satisfaction with the restorations was evaluated using a 10-point visual analog scale (VAS). ResultsAll the FPDs were made using CAD/CAM and hot isostatic pressed yttria-tetragonal zirconia polycrystal (HIPed Y-TZP) ceramic (Denzir) and were placed within general practices. The mean observation period was 9.6±1.6 years (range 3.0–13.1 years). The CDA rating was 90% satisfactory for the surface. Corresponding figures for anatomic form, color and margin integrity were 94%, 100% and 94%, respectively. Regarding surface three (9.7%) FPDs exhibited veneer chipping and were rated ‘not acceptable’. For margin integrity two (6.5%) were rated ‘not acceptable’ because of caries. For anatomic form two (6.1%) were rated ‘not acceptable’ due to two lost FPDs. No significant differences were seen between the FPDs and controls for plaque and bleeding. The Kaplan–Meier survival rate (still in clinical function) was 94%, the success rate (technical events accounted for) 91% and (biological events accounted for) 73%. Based on the VAS the mean value for patient satisfaction was 9.3±1.2. SignificanceNinety-four percent of the FPDs were still in clinical function. HIPed Y-TZP could serve as an alternative for FPD treatments similar to those in the current study.

Low-temperature degradation and defect relationship in yttria-tetragonal zirconia polycrystal ceramic

In this work, the relationship between tetragonal to monoclinic phase transformation and photoluminescence spectrum were studied for 3 mol% yttria-tetragonal zirconia polycrystal samples sintered in air and argon atmosphere at 1500°C. A low-temperature degradation study was conducted under autoclave conditions containing superheated steam at 180°C and 10 bar vapour pressure for periods up to 12 hours. Photoluminescence studies were conducted using a photoluminescence spectroscope with helium–cadmium laser at a wavelength of 325 nm as the excitation source, and the phase content in the zirconia samples was measured using X-ray diffractometer. The studies concluded that argon gas sintered samples have higher structural vacancy than air sintered samples; the argon gas sintered sample showed a more rapid phase transformation than the air sintered sample and also showed that the defect associated with oxygen vacancies in the zirconia lattice increases with increasing aging time.

Densification Behaviour and Mechanical Properties of Aluminium Oxide and Cerium Oxide-Doped Yttria Tetragonal Zirconia Polycrystal Ceramics Using Two-Step Sintering

The densification behaviour, mechanical properties, and microstructure of high-purity Al2O3 and CeO2-doped Y-TZP with different weight percentage varied from 0.3 to 1 wt% were investigated. The samples were pressed uniaxially at 200 MPa into rectangular bars and discs and pressureless-sintered at temperature ranging between 1250°C and 1450°C for 2 h while the microstructure was characterized with a scanning electron microscope (SEM). Two-step sintering process works well for temperature higher than 1400°C and it created most tetragonal phase arrangement for stable structure to delay ageing through phase transformation. The mechanical properties in terms of bulk density, Young’s modulus, Vickers hardness, and fracture toughness were also measured. The results indicate that the addition of dopants accelerated the densification parameters and reinforced and toughened the obtained bodies. The maximum values for the mechanical properties of the Al2O3 and CeO2-doped Y-TZP ceramics were 6.01, 220 GPa, 13.8 GPa, and 7 MPa for density, Young’s modulus, Vickers hardness, and fracture toughness, respectively, which are higher than those of the doped samples.

Effect of Short Time Sintering on the Mechanical Properties of Undoped Zirconia Ceramics

Sintering parameters are undoubtedly among the many factors that influence the mechanical properties and hydrothermal ageing resistance of tetragonal zirconia ceramics. In this research, the effect of using short holding times i.e. (1 min., 30 min. and 1 hour) as compared to the conventional 2 hours during sintering of 3 mol% Yttria Tetragonal Zirconia Polycrystals (3Y-TZP) on the mechanical properties were systematically investigated. The research revealed that holding time of 1 minute and sintered at 1400oC yielded a high relative density (above 95% of theoretical density) and high Young’s modulus (above 180 GPa) without compromising on tetragonal phase stability and mechanical properties. The study also revealed that the bulk density is an important parameter governing the matrix stiffness of 3Y-TZPs and that grain size strongly influences the transformability and consequently, the toughness of 3Y-TZPs. The toughness of the ceramic was observed to increase steeply when grains exceeded 0.52 µm, which has been identified as the critical grain size for toughening.

Posttreatment diagnosis of caries under fixed restorations: A pilot study

Conventional radiographic techniques are insufficient for detecting caries under fixed restorations or for acquiring clear images of the disease. Advanced radiographic techniques such as cone beam computerized tomography may be a solution. The purpose of this study was to assess the viability of detecting and characterizing caries under complete-ceramic and metal-supported crowns by using cone beam computerized tomography. A grade 6 carious molar tooth according to the International Caries Detection and Assessment System criteria was selected. The tooth was prepared, and 3 different crowns were fabricated in a dental laboratory: yttria tetragonal zirconia polycrystal (Y-TZP) ceramic, lithium disilicate ceramic, and metal ceramic. The crowns were placed on the prepared tooth, and each specimen was subjected to cone beam computerized tomography. Opacity values were recorded and evaluated with 2-way ANOVA. Multivariate comparisons (Tukey was performed to assess the mean gray value differences of the materials between caries and dentin, and the Mann-Whitney U test was performed to assess the mean gray value differences between caries and dentin for each material (α=.05). Carious borders and cavities were detected under the 3 ceramic crown specimens with a cone beam computerized tomography radiographic technique. The statistical analysis of the radiopacity mean gray value was at the borderline of significance for the specimen radiographies. Significant differences were found with respect to materials, location, and the interaction between these 2 factors (P<.001). Cone beam computerized tomography can be used as a posttreatment diagnostic technique for detecting caries under high atomic numbered crowns and partial fixed dental prostheses.

Comparison of fatigue resistance and failure modes between metal-ceramic and all-ceramic crowns by cyclic loading in water

ObjectivesTo compare fatigue resistance and fracture mode of metal-ceramic crowns with all-ceramic crowns containing yttria tetragonal zirconia polycrystal (Y-TZP) frameworks under compressive cycling loading in water. MethodsTwenty specimens of ivory were randomized and individually prepared to receive anatomically shaped metal-ceramic (n=10) or veneered Y-TZP all-ceramic crowns (n=10). All steps in production were equivalent to clinical situations. Resistance to fatigue fracture was tested under compressive cyclic loading using a universal testing machine, with a loading frequency of 12Hz using a spherical tungsten carbide indenter (6mm diameter) in distilled water. The maximum compressive load was increased as the number of cycles increased (600,000 cycles at 400N, 200,000 cycles at 600N, 200,000 cycles at 800N and 200,000 cycles at 1000N). The specimens were inspected after each loading sequence for initial failures such as infractions. Final failure was considered as any loss of material which automatically ended the test and the number of cycles until final failure was recorded. Fractographic analysis of the fractured specimens was performed with scanning electron microscopy (SEM). ResultsThe two types of crowns exhibit similar fatigue resistance (P=0.87) to compressive cycling loading under wet conditions. The failure modes as observed with SEM were similar in the two groups and were found in the veneer ceramic, except that three veneered Y-TZP all-ceramic crowns displayed a complete framework fracture. ConclusionsWithin the limitation of this study using simulated oral masticatory function, the results revealed that the fatigue resistance was similar for the two crown types. Clinical significanceIn this study metal-ceramic crowns and veneered Y-TZP all-ceramic crowns showed similar fracture resistance to compressive cycling loading in water. The test conditions were simulating clinical conditions. Thus, the result may predict the long-term clinical performance of these types of crowns.

Biomolecular modification of zirconia surfaces for enhanced biocompatibility

Yttria-tetragonal zirconia polycrystal (Y-TZP) is a preferred biomaterial due to its good mechanical properties. In order to improve the biocompatibility of zirconia, RGD-peptide derived from extracellular matrix proteins was employed to modify the surface of Y-TZP to promote cell adhesion in this study.The surface of Y-TZP specimens was first modified using a hydrothermal method for different lengths of time. The topographies of modified Y-TZP specimens were analyzed by contact angle, XRD, FTIR, AFM, and FE-SEM. The mechanical properties were evaluated using Vickers hardness and three point bending strength. Then, the RGD-peptide was immobilized on the surface of the Y-TZP by chemical treatment. These RGD-peptide immobilized Y-TZP specimens were characterized by FTIR and AFM, and then were cocultured with MG-63 osteoblast cells for biocompatibility assay. The cell morphology and proliferation were evaluated by SEM, WST-1, and ALP activity assay.The XRD results indicated that the phase transition, from tetragonal phase to monoclinic phase, was increased with a longer incubation time of hydrothermal treatment. However, there were no significant differences in mechanical strengths after RGD-peptide was successfully grafted onto the Y-TZP surface. The SEM images showed that the MG-63 cells appeared polygonal, spindle-shaped, and attached on the RGD-peptide immobilized Y-TZP. The proliferation and cellular activities of MG-63 cells on the RGD-peptide immobilized Y-TZP were better than that on the unmodified Y-TZP.From the above results, the RGD-peptide can be successfully grafted onto the hydrothermal modified Y-TZP surface. The RGD-peptide immobilized Y-TZP can increase cell adhesion, and thus, improve the biocompatibility of Y-TZP.

The effect of sandblasting and different primers on shear bond strength between yttria-tetragonal zirconia polycrystal ceramic and a self-adhesive resin cement.

To evaluate the effect of zirconia primers, air-abrasion, and tribochemical surface treatment methods on the shear bond strength between yttria-tetragonal zirconia polycrystal (Y-TZP) ceramic and self-adhesive resin cement. Y-TZP ceramic surfaces were ground flat with 600-grit silicon carbide paper and then divided into seven groups of 10 and treated as follows: untreated (control), Monobond Plus, Z-PRIME Plus, ESPE Sil with CoJet, air-abrasion, Monobond Plus with air-abrasion, and Z-PRIME Plus with air-abrasion. Self-adhesive resin cement was placed onto the treated Y-TZP specimens for each group. All specimens were thermocycled and subjected to a shear bond strength test. Scanning electron microscope images of the fractured areas and x-ray diffraction (XRD) analysis of the surface-treated Y-TZP specimens were performed. Data were statistically analyzed using one-way analysis of variance and the Student-Newman-Keuls multiple comparison test (p<0.05). The Z-PRIME Plus treatment in combination with air-abrasion produced the highest bond strength (16.50±2.26 MPa), followed by air-abrasion (10.56±3.32 MPa), and then Monobond Plus combined with air-abrasion (8.93±3.13 MPa), ESPE Sil after CoJet application (8.54±3.98 MPa), and the Z-PRIME Plus group (8.27±2.79 MPa). The control (3.91±0.72 MPa) and Monobond Plus (4.86±1.77 MPa) groups indicated the lowest results (p<0.05). The XRD results showed the peaks of the monoclinic phase for the air-abrasion and CoJet treatment groups compared with the Y-TZP control. Z-PRIME Plus primer application after air-abrasion presented the best results for improving the bond strength between Y-TZP ceramic and self-adhesive resin cement.

Grain-boundary cation diffusion in ceria tetragonal zirconia determined by constant-strain-rate deformation tests

Ceria tetragonal zirconia polycrystals with a content of 12 mol% ceria (CeTZP) have been tested in compression at constant strain rate between 1150 °C and 1300 °C. An accurate analysis of the stress–strain curves has permitted to determine the value of the grain boundary cation diffusion. The results are compared with those reported in literature for this alloy and yttria tetragonal zirconia polycrystals (YTZP). An isotopic effect is found to correlate both grain boundary diffusion coefficients.

Zirconia dental implants: a clinical, radiographic, and microbiologic evaluation up to 3 years.

To retrospectively evaluate the clinical performance of zirconia endosseous implants. Partially edentulous patients with adequate bone volume to fit yttria tetragonal zirconia polycrystal (Y-TZP) implants at least 3.5 mm wide and 8.0 mm long were included. Full-mouth probing pocket depth (PPDs) and percentage bleeding on probing (BOP) scores around teeth and implant(s) were assessed and compared. Marginal bone loss/gain relative to baseline was measured on intraoral radiographs, and the prevalence and quantities of seven periodontal bacteria were assessed around implants and teeth in the same patient. Seventy-four consecutively treated patients with 121 zirconia implants (66 two-piece implants and 55 one-piece implants) were clinically evaluated after a mean observation period of 18 months. Three implants had failed and had been removed, for a cumulative implant survival rate of 96.5% (± 2.0%) after 3 years. The 118 surviving implants demonstrated healthy mucosal conditions, with low mean PPDs (1.8 ± 0.4 mm) and mean BOP scores (4.1% ± 4.2%). PPD and BOP were statistically significantly lower around implants than around teeth. BOP and PPD around implants and teeth were significantly correlated. Stable marginal bone levels were observed (mean bone loss of 0.1 ± 0.6 mm after 3 years). The frequency of isolation of all marker bacteria was similar at tooth and implant sites. Zirconia endosseous implants can achieve a 3-year implant survival rate in partially edentulous patients, similar to that of titanium implants, with healthy and stable soft and hard tissues.

The use of MDP-based materials for bonding to zirconia

A strong and stable bond between the luting resin and overlying ceramic restoration is critical to longevity, but no technique has been established for how to provide such a bond when the core material is zirconia. The purpose of this study was to evaluate the effect of different materials containing 10-methacryloyloxydecyl dihydrogen phosphate (MDP) on the bond strength to yttria-tetragonal zirconia polycrystal (Y-TZP) ceramic. Forty Y-TZP slices (Lava) were cemented to substrates (8 groups; n=5 in each) with or without the previous application of an experimental primer (0.5% MDP) or an MDP-based adhesive (Clearfil S3 Bond Plus or Scotchbond Universal) with either an MDP (Clearfil SA) or a non-MDP (RelyX Ultimate) luting resin. Specimens were cut, stored in distilled water, and microtensile tested (5 beams per specimen) at 48 hours and again at 6 months after luting procedures. The data were analyzed by 4-way ANOVA (α=.05) and the Tukey test (α=.05). The mode of failure was classified with a stereomicroscope, and the treated surfaces were analyzed with energy-dispersive x-ray spectroscopy. Both adhesive (P<.001) and time (P<.001) significantly affected bond strength. The interaction of any of the factors was not significant. The use of an MDP-containing adhesive and the shorter storage time were associated with higher bond strengths. At 48 hours, an overall incidence of 50.5% of Type 1 mode of failure (adhesive at ceramic/resin interface) occurred, as opposed to 68% after 6 months of water storage. Energy-dispersive x-ray spectroscopy results showed peaks of carbon and phosphorus when MDP-based materials were used. The application of an MDP-based adhesive may improve bond strength to zirconia. However, microtensile bond strength results for all groups did not remain stable over 6 months.

Evaluation of the shear bond strength of resin cement to Y‐TZP ceramic after different surface treatments

The purpose of this study was to evaluate the effect of various surface treatments on the shear bond strength of Y-TZP (Yttria-Tetragonal Zirconia Polycrystal) ceramics with zirconia primer and two different resin cements both containing 10-methacryloyloxydecyl dihydrogen phosphate (MDP). Zirconia blocks (LAVA, 3M ESPE, St. Paul, MN) were polished and assigned to five groups according to the surface treatment: (1) no further treatment (control); (2) airborne abrasion with Al2 O3 particles; (3) Z-PRIME Plus (Bisco, Schaumburg, IL) applied on polished zirconia; (4) Z-PRIME Plus applied on zirconia after airborne abrasion; and (5) tribochemical silica-coating performed with the CoJet system (3M ESPE) followed by application of ESPE®-Sil (3M ESPE). Each group was further divided into one of two resin cements: Panavia F2.0 (Kuraray, Kurashiki, Okayama, Japan) and Clearfil SA Luting (Kuraray). Resin cement placed inside a gel-cap was polymerized on the zirconia surface. Shear bond strength was tested with a universal testing machine at 0.5 mm/min. One-way analysis of variance and paired t-test were done. (p < 0.05), and scanning electron microscope (SEM) images were taken. Zirconia primer applied after airborne abrasion significantly increased the shear bond strength resulting in the highest value for both resin cements. Control groups for both cements showed the weakest value for shear bond strength. No significant differences were found between the shear bond strengths of the individual resin cements applied to zirconia surfaces treated the same way. In conclusion, the combined surface treatment of airborne abrasion followed by a zirconia primer is recommended for zirconia bonding with Panavia F2.0 and Clearfil SA Luting cements.