Zirconia Surface Treatment Research Articles

Effect of repeated laser surface treatments on shear bond strength between zirconia and veneering ceramic

Statement of problemDelamination failure may occur between ceramic frameworks and veneering ceramics, shortening the lifetime of fixed dental prostheses in load-bearing areas. PurposeThe purpose of this in vitro study was to compare the effect of different repeating CO2 laser treatment methods and conventional approaches on the shear bond strength of zirconia frameworks and veneering ceramics. Material and methodsZirconia disks (N=110) were prepared and divided into 5 groups: milling without surface treatment (group M), airborne-particle abrasion (group APA), single laser treatment (group LX1), 2 laser treatments (group LX2), and 3 laser treatments (group LX3). The specimens in the first 2 groups were treated before the framework was coated using the spraying technique. Specimens in the remaining groups were coated with veneering ceramic using the spraying process, and then subjected to laser treatment. Surface roughness and topography, interface properties, phase transformation, shear bond strength, and fracture modes were investigated. Outcomes were analyzed using a profilometer, a scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS), X-ray diffractometry (XRD), a stereomicroscope, and a universal testing machine for mechanical testing. ResultsThe XRD showed that phase transformation from tetragonal to monoclinic occurred after airborne-particle abrasion. This phenomenon was not observed in laser-treated specimens. Groups LX2 and LX3 had the highest surface roughness values, 1.18 ±0.23 μm and 1.21 ±0.22 μm, among all groups, and group LX3 had the highest shear bond strength values for unaged and aged conditions, 32.08 ±2.45 MPa and 31.43 ±2.07 MPa. The mixed-fracture mode was the most common type of fracture observed. ConclusionsThe results indicated that the shear bond strength between the zirconia framework and veneering ceramic was higher after laser surface treatments than after milling alone or after airborne-particle abrasion. Laser treatment methods, particularly LX2 and LX3, could be considered reliable approaches for zirconia surface treatment.

Comparative In Vitro Evaluation Between Zirconia and Veneer Ceramic Materials Using Different Techniques

Zirconia surface treatment using different techniques could be employed to overcome the delamination issue reported between veneering ceramic materials and the corresponding zirconia core. The study subjected yttria partially stabilized zirconia core material to grinding and sandblasting as a first surface treatment. An airbrush gun spraying technique was used to coat a uniform thin layer of veneering ceramic (IPS e.max Ceram and Noritake Cerabien ZR) on the core materials followed by performing laser scanning as a second surface treatment. The specimens were investigated for surface topography, interface analysis, elemental compositions, phase transformation, and fracture mode patterns using profilometer, SEM, EDS, XRD, and stereomicroscope. The impact of laser scanning on the shear bond strength before and after storage of specimens in artificial saliva was also studied. Transformable tetragonal phase to monoclinic was predominant in sandblasted specimens followed by laser scanning with observation of micro-cracks at interface. The grinding followed by laser scanning yielded satisfactory outcomes in terms of the presence of coating property. The phase transformation was not detected through the latter technique. The technique greatly enhanced the roughness property and bond strength values which might be considered as a reliable application to improve the longevity of fixed dental crowns in load bearing areas.

Effect of zirconia surface treatment on its wettability by liquid ceramics

Statement of problemThe wettability of the framework by liquid ceramics is important in ensuring a suitable bond between veneering ceramics and zirconia. PurposeThe purpose of this in vitro study was to examine the dependence of the wetting angle on temperature to determine the transition temperature from nonwettable to wettable states and to calculate the values of the relative wetting forces of the milled surfaces. Material and methodsFifty zirconia cylinders were divided into 5 groups (n=10) and subjected to the following treatments: milling, grinding, polishing, and airborne-particle abrasion with Al2O3 or SiC. After treatment, the specimens were rinsed, dried, and examined with respect to their wettability by liquid ceramics by using the automated Thermo-Wet test bench. The results were statistically analyzed by an ANOVA (α=.05). ResultsThe most rapid wettability was obtained through airborne-particle abrasion with Al2O3 at 930 °C. Additionally, the highest relative bond strength (with respect to the machined surface) was obtained with Al2O3 abrasion. ConclusionsBecause of variations in the wettability of the zirconia surface after different treatment methods, the firing temperature of the ceramic should also vary depending on the type of surface treatment applied. Thus, it is determined individually according to the chosen method.

Effects of the combination of Er:YAG laser and sandblasting on the shear bond strength between zirconia and resin cement

Aim: This study was conducted to determine the bond strength between zirconia ceramic and resin luting cement according to the type of surface treatment applied. Methods: Sixty zirconia cylinders measuring 4 x 4 mm were manufactured and distributed into five experimental groups and a control group (n = 10): G1 - sandblasting with 110 μm aluminum oxide; G2 - sandblasting with 30 μm Rocatec Soft®; G3 - Er:YAG laser irradiation at 400 mJ; G4 - Er:YAG laser combined with sandblasting with aluminum oxide; G5 - Er:YAG laser combined with sandblasting with Rocatec Soft®; G6 - no treatment (Control). The zirconia cylinders were bonded in the center of composite resin cylinders (6 mm diameter) using RelyX Ultimate® cement. Shear strength was measured after thermocycling (6000 cycles and 5-55° C). Data were analyzed using one-way ANOVA and Tukey's post-hoc with a 5% significance level. Results: Group 4 had a significantly higher shear strength than all the other groups, except Group 1. Group 3 had a significantly lower shear strength compared with Groups 1 and 4. Conclusion: Sandblasting with 110μm aluminum oxide particles after laser irradiation may be an effective zirconia surface treatment. The use of Er: YAG laser alone is not effective at increasing the bond between resin cement and zirconia.

Comparative Effectiveness of Multiple Laser Scanning and Conventional Techniques on Zirconia Shear Bond Strength

This study aimed to compare the impact of different laser scanning with that of conventional methods on zirconia surface treatment through evaluation of shear bond strength (SBS) values. One hundred and thirty-two sintered zirconia cubic-samples were prepared and randomly divided into six study groups: milling control (without surface treatment); grinding; sandblasting; and three-times, four-times, and five-times laser scanning groups. The treatment process for the first three groups was performed before the zirconia coating, while the last three groups were treated after zirconia coating with veneer slurry through a spraying technique. In the current study, the surface roughness Ra, contact angle measurement, phase transformation, topography and interfaces, SBS in unaged and aged conditions, and fracture mode patterns of zirconia cores were investigated. The results were analyzed using laser confocal scanning microscopy, drop analyzer, X-ray diffractometry (XRD), scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS), universal testing machine and stereomicroscope. The results indicated that three-times laser scanned specimens presented higher Ra values than the other studied groups. The minimum contact angle value was detected in the mentioned group, while the control group presented the highest value. The XRD showed phase transformation from tetragonal to monoclinic t–m following grinding and sandblasting. However, the laser scanned specimens and the control group preserved the structural integrity of the zirconia core, presenting the tetragonal phase only. The highest SBS values were recorded in specimens treated with three-times laser scanning in the unaged and aged conditions. A mixed fracture was a common fracture pattern among the studied groups. The results confirmed that SBS could be optimized through three-times laser scanning and it provided better adhesion between zirconia and the veneer ceramic material. Multiple scanning processes of more than three times are not recommended for zirconia surface treatment.

Comparison of Shear Strength of Metal and Ceramic Orthodontic Brackets Cemented to Zirconia Depending on Surface Treatment: An In Vitro Study.

Objectives Due to the high demand for all-ceramic restorations, monolithic zirconia restorations are nowadays frequently used. With the demand for adult orthodontic treatments, orthodontists need to be mindful of the quality of their brackets bonding to this type of material, as it requires special conditioning. This study aimed to compare different surface treatments of zirconia when bonding metal or ceramic orthodontic brackets. The objectives are to compare the shear bond strength; the amount of adhesive remaining on the surface of the material; the incidence of adhesive, cohesive, and mixed failures; and the occurrence of zirconia fractures. Materials and Methods Forty monolithic blocks of zirconia of a diameter of 10 mm and a length of 10 mm were prepared and randomly divided into two groups ( n = 20): metallic or ceramic brackets. Each group was subsequently divided into two subgroups ( n = 10) depending on the surface preparation (laser treatment or airborne particle abrasion): SMB (airborne particle abrasion, metal bracket), SCB (airborne particle abrasion, ceramic bracket), LMB (laser; metal bracket), and LCB (laser, ceramic bracket). The samples were tested for shear bond strength using a universal testing machine. The adhesive remnant index and the occurrence of zirconia fractures and different types of failures were assessed by optical and electron microscopy. Statistical Analysis Results were analyzed using analysis of variance. Results The differences were significant between the metallic (SMB, LMB) and ceramic (SCB, LCB) bracket groups with regard to shear bond strength, with respectively 23.29 ± 5.34 MPa, 21.59 ± 4.03 MPa, 20.06 ± 4.05 MPa, and 17.55 ± 3.88 MPa. In terms of surface treatment, no statistical differences were found between the different groups. Conclusion Metal brackets have a greater bond strength than ceramic brackets when cemented to zirconia. The surface treatment of zirconia surface has no influence on the shear bond strength.

Effect of aluminum oxide sandblasting, plasma application and their combination on the bond strength of resin cement to zirconia ceramics

Objective: to evaluate the effect of aluminum oxide sandblasting (AOS), argon plasma application (APL) and their combination (AOS+APL) on the shear bond strength (SBS) of dual-cure resin cement (Panavia F 2.0, Kuraray Noritake) to two zirconiabased ceramics (Lava, 3M ESPE and Katana, Kuraray Noritake). Material and Methods: One hundred twenty zirconia plates (13 mm in length X 5 mm in width X 1 mm in thickness) were prepared and treated according to the following treatments: 1- AOS, 2- APL,3- AOS+APL and 4- no treatment (control). After treatments, resin cement cylinders (1.4 mm in diameter x 1 mm in height) bonded to zirconia surface were obtained by filling up the silicon matrix. The shear bond test was performed following storage of the samples for 24 hours and one year. Bond strength values were recorded in MPa and the data were analyzed by three-way ANOVA and Tukey post-hoc test (preset alpha of 0.05). Results: In general, AOS and AOS+APL showed the higher SBS. After one-year storage, SBS of the resin cement to the Katana zirconia did not reduce, regardless of the zirconia surface treatment. Conclusion: AOS alone was able to increase the SBS of the resin cement to both zirconia ceramics compared to control and SBS remained stable after one year depending on type of zirconia ceramic.KeywordsAluminum Oxide; Ceramics; Plasma; Resin Cements

Effect of zirconia surface treatment, resin cement and aging on the load-bearing capacity under fatigue of thin simplified full-contour Y-TZP restorations

This study investigated the effect of zirconia surface treatment (air-abrasion with aluminum oxide or tribochemical silica coating) and aging on the fatigue behavior of thin monolithic Y-TZP (yttria-stabilized tetragonal zirconia polycrystal) restorations cemented with 2 types of resin cements, containing or not containing MDP, to a dentin-like substrate. Y-TZP ceramic (Zenostar T, diameter (Ø) 10 mm, 0.7 mm thick) and dentin-like discs (Ø 10 mm, 2.8 mm thick) were assigned into eight groups according to three factors: ‘zirconia surface treatment’ (aluminum oxide particles air-abrasion ‘AO’; or tribochemical silica coating via silica-coated aluminum trioxide particles air-abrasion + silanization ‘SC’); ‘MDP-containing resin cement’ (with: Panavia F2.0, ‘MDP’; or without: Multilink Automix, ‘nMDP’); and ‘aging’ (baseline; or aged - 'AG':12,000 thermal cycles + 60 days water storage). Y-TZP intaglio surface was conditioned and dentin-like substrate was etched with hydrofluoric acid prior to bonding. Aging was performed in half of the specimens before the fatigue testing (Staircase, 20 Hz; 250,000 cycles). Fractographic and topographic characteristics were analyzed by stereomicroscope and SEM. Prior to aging, no significant difference was found between the two surface treatments, irrespective to the cement. Samples bonded with resin cement containing MDP had a significant reduction in their fatigue failure load when Y-TZP was air-abraded with aluminum oxide particles and subjected to aging (MDP-AO = 2050.71A; MDP-AO/AG = 1756.67B). Other studied conditions were not affected by aging. Topographic images revealed a rougher surface for aluminum oxide air-abrasion. Fractography supports all failures as a radial crack starting at the Y-TZP intaglio surface. Bonded thin simplified Y-TZP restorations had a high load-bearing capacity, regardless of the studied factors. The MDP-containing resin cement applied on aluminum oxide air-abraded zirconia surface was not enough to maintain the fatigue performance after aging, while higher stability to aging was achieved by treating with the tribochemical silica coating method. When using MDP-free resin cement, the surface treatment and the aging did not impact the fatigue performance.

The impact of laser scanning on zirconia coating and shear bond strength using veneer ceramic material.

Laser scanning is one of the methods that can be used for surface treatments of zirconia. Application of the laser to the surface of zirconia has diverse effects, depending on the type of laser. A carbon dioxide (CO2) laser has high irradiation power and can alter the surface properties. This study investigated the surface coating of zirconia as a core material that subsequently coated with a veneering ceramic (v-c) material. This study compared laser scanning and conventional sintering processes. Various properties including surface topography, interface evaluation, phase transformation, elemental compositions, failure mode patterns, and contact angle were examined through X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analyses. Results were confirmed that the bond strength between the v-c and the substrate recorded through laser scanning was higher than that determined through conventional sintering.

Effects of different finishing/polishing protocols and systems for monolithic zirconia on surface topography, phase transformation, and biofilm formation.

PURPOSEThe purpose of this study was to evaluate the effects of various protocols and systems for finishing and polishing monolithic zirconia on surface topography, phase transformation, and bacterial adhesion.MATERIALS AND METHODSThree hundred monolithic zirconia specimens were fabricated and then treated with three finishing and polishing systems (Jota [JO], Meisinger [ME], and Edenta [ED]) using four surface treatment protocols: coarse finishing alone (C); coarse finishing and medium polishing (CM); coarse finishing and fine polishing (CF); and coarse finishing, medium polishing, and fine polishing (CMF). Surface roughness, crystal phase transformation, and bacterial adhesion were evaluated using atomic force microscopy, X-ray diffraction, and streptococcal biofilm formation assay, respectively. One-way and two-way analysis of variance with Tukey post hoc tests were used to analyze the results (α=.05).RESULTSIn this study, the surface treatment protocols and systems had significant effects on the resulting roughness. The CMF protocol produced the lowest roughness values, followed by CM and CF. Use of the JO system produced the lowest roughness values and the smallest biofilm mass, while the ME system produced the smallest partial transformation ratio. The ED group exhibited the highest roughness values, biofilm mass, and partial transformation ratio.CONCLUSIONStepwise surface treatment of monolithic zirconia, combined with careful polishing system selection, is essential to obtaining optimal microstructural and biological surface results.

Bond and topography evaluation of a Y-TZP ceramic with a superficial low-fusing porcelain glass layer after different hydrofluoric acid etching protocols

Abstract Introduction Despite being one of the most studied ceramics today, zirconia still does not have a well-defined adhesion protocol. Objective Evaluate the influence of different etching times and hydrofluoric acid (HF) concentrations on the zirconia surface and bond strength between a vitrified Y-TZP ceramic and a resin cement. Materials and method The zirconia surface treatments were: sandblasting with silica-coated alumina (Co); glaze application + 5% HF etching for 5s (G5-5s), 10s (G5-10s) or 20s (G5-20s); glaze application + 10% HF etching for 5s (G10-5s), 10 (G10-10s) or 20s (G10-20s) . Then, cement cylinders (3.3 × 3.3 mm) were built up for shear bond test on all specimens. The specimens were subjected to 6000 thermal cycling before the test. Fractures were analyzed by stereomicroscope. Data were statistically analyzed by Kruskal-Wallis and Dunn statistical tests (5%). Extra samples of each group were made to obtain profilometry and scanning electron microscopy (SEM). Result Zirconia-cement bond strength was affected by the ceramic surface treatments (p = 0.001). G10-5s (2.71 MPa) recorded the highest bond strength values, followed by the Co (2.05 MPa) while G5 groups had the lowest bond value. Adhesive failure of the samples predominated. The image analysis revealed G5 groups seem to have a lower roughness when compared to groups treated by 10% HF. The creation of pores in the low-fusing porcelain glass layer surface occurred only when 10% HF was used. Conclusion The low-fusing porcelain glass layer application was able to overcome the sandblasting and obtain a greater adhesive bond to the resinous cement, however, only when 10% HF was used for an interval of 5 seconds.

Effect of hot-etching treatment on shear bond strength of zirconia to resin cement

ABSTRACTThe purpose of this study was to evaluate the effect of hot-etching surface treatment on the shear bond strength between zirconia ceramics and resin cement. Ceramic cylinders were divided randomly into 10 groups (n = 10) according to different surface treatments (blank control; airborne particle abrasion; hot-etching for 10 min; hot-etching for 30 min; hot-etching for 60 min) and whether or not performed thermal cycling fatigue test. Flat enamel surfaces, were prepared from human permanent incisors and were bonded to the zirconia discs. All specimens were subjected to shear bond strength test by a universal testing machine. All data were statistically analysed using one-way analysis of variance and multiple comparison least significant difference tests (α = 0.05). Hot-etching for 60 min treatment produced higher bond strengths than the other treatment. Surface treatment of zirconia with a hot-etching solution might enhance surface roughness and bond strength between zirconia and resin cement.

Effects of bonding area size, surface treatment and specimen configuration on the push out test for assessing bonding and stress distribution to Y-TZP

PurposeTo evaluate the influence of specimen configuration, bonding area and zirconia surface treatment on the push out bond strength to Y-TZP and on the stress distribution using finite element analysis (FEA). Materials and methods240 Y-TZP blocks with a central perforation were assigned to 8 groups (n=30) according to the adhesive area (macro-test: 5 × 5.5 × 4 mm and micro-test: 5 × 5.5 × 1 mm), material inserted in the perforation (resin cement or composite resin) and surface treatment (silanization or tribochemical silica coating+silanization). Push-out bond strength test, failure modes evaluation and FEA were performed. ResultsThree-way ANOVA showed that bond strength was statistically higher for composite resin (p=0.00) and for macro specimens (p=0.00). Surface treatment significantly increased the adhesion, except for ‘resin cement macro-test’ (p=0.00). Finite element analysis showed that the stresses were more homogeneously distributed at the interface of micro-specimens. ConclusionMacro-push out with composite resin or cement does not appear to be promising when evaluating adhesion to zirconia ceramics; micro-push out with composite resin filler is an adequate method; the tribochemical silica coating surface treatment can be evaluated by all tested methods in the current study, except for the macro-test with resin cement condition.

Effect Of Non-Thermal Air Plasma Treatment On Shear Bond Strength Of Adhesive Resin Cement To Zirconia

Purpose: The purpose of the present study was to analyze the effect of non-thermal air plasma treatment on shear bond strength and failure mode of self-adhesive resin cement to zirconia. Materials& Methods: Forty eight zirconia plates were prepared from IPS e.max ZirCad blocks (Ivoclar Vivadent, Schaan, Liechtenstein) and classified into four groups (n=12) according to surface treatment; group CO (control) without any surface treatment, group SD was treated with 50 µm alumina sandblasting, group PL used air atmospheric pressure plasma device (Piezobrush® PZ2, Relyon plasma GMBH, Regensburg, Germany) & group SP which was a combination of 50 µm alumina sandblasting followed immediately with atmospheric plasma treatment. Zirconia specimens were immediately centered with Relay X Unicem (3M ESPE) resin cylinders of 3.7 mm diameter and 2 mm height. Shear bond strength test was performed 8 days after water storage at 37˚C using a computer controlled materials testing machine (Model 3345; Instron Industrial Products, Norwood, USA). A scanning electron microscope (Quanta 250 Field Emission Gun, Netherlands) was used to determine failure mode with all morphological and structural changes. Average surface roughness (Ra) was calculated with different surface treatments. Energy Dispersive X-ray (EDX) analysis was used for chemical changes evaluation. Data were analyzed with one-way ANOVA followed by Tukey’s post hoc test when the ANOVA test was significant. Results: A significant difference between different surface treatments (P=0.010) was recorded with the highest shear bond strength value in SP group and the lowest value with untreated surface CO gp. All groups showed mixed failure mode which was mainly cohesive except for CO gp. Surface roughness was increased with sandblasting and decreased after plazma treatment. EDX analysis showed increase oxygen on plazma treated surface.Conclusion: Non thermal air plasma treatment can be used for increasing zirconia surface treatment especially when accompanied with 50 µm AL2O3 sandblasting.Clinical significant: Non thermal air plasma treatment alone or in combination with sandblasting can be considered as a good clinical protocol for cementing zirconia restorations.

Evaluation of the bond strength and characteristics of zirconia after different surface treatments

Statement of problemNonthermal plasma treatment could increase the bond strength of resin cements to zirconia, but studies are lacking. PurposeThe purpose of this in vitro study was to evaluate zirconia bond strength, surface roughness, and contact angle and to measure the infrared spectrum after different surface treatments. Material and methodsYttria-stabilized tetragonal zirconia polycrystal (Y-TZP; n=9) blocks were sectioned into 36 slices (12×11×3 mm) and divided (n=4) into surface treatment groups as follows: 2 control groups, consisting of airborne-particle abrasion plus primer (APP) and 10% hydrofluoric acid etching plus primer (HFP), and 3 experimental groups consisting of a nonthermal plasma (NP) application; a nonthermal plasma plus primer application (NPP); and a 10% hydrofluoric acid etching plus nonthermal plasma plus primer (HFNPP) application. Each zirconia disk was cemented to a prepolymerized resin block. After cementation, the specimens were sectioned for microtensile strength testing and for surface roughness analysis and contact angle analysis. Results were submitted to analysis of variance and Tukey tests (α=.05). ResultsResults showed no statistically significant differences between the APP and HFNPP groups, but these 2 groups showed statistically better bonding than those of HFP, NP, and NPP. ConclusionsAirborne-particle abrasion resulted in a significant increase in surface roughness compared with the other groups. After nonthermal plasma treatment, the contact angle of the zirconia surface decreased within 48 hours. Nonthermal plasma application for surface treatment of zirconia showed no significant difference in bond strength when compared with airborne-particle abrasion.

Non-thermal plasma increase bond strength of zirconia to a resin cement

Objective: This study investigated the influence of different surface treatments on zirconia surface energy, roughness and microshear bond strength. Material and Methods: Forty eight slices of Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP- VITA In-Ceram® YZ for inLab®) (6.4 x 3.2 x 1.6 mm) were divided into 3 groups according to the surface treatment (n = 16): YTZP_control -untreated; YTZP_plasma -surface treatment with non-thermal oxygen plasma; YTZP_primer - coating with ceramic primer. Surface energy (n = 6) was measured with a goniometer; and surface roughness (n = 10) was analyzed with a 3D profilometer were performed over zirconia surface. On the same specimens of surface roughness, on the treated zirconia's surface, resin cement (PANAVIA V5 - Kuraray Noritake Dental) was built up by inserting the resin cement into Tygon tubes (1 mm of internal diameter X 1 mm length). After 24 h storage, microshear test was assessed. Data were analyzed by one-way ANOVA and Tukey post-hoc test (p < 0.05). Results: Non-thermal oxygen plasma treated specimens exhibited higher statistically significant surface energy (p = 0.00) and bond strength (p = 0.00) when compared to control and primer groups. Roughness test (p = 0.897) could not detect statistical difference among the tested groups. Conclusion: Non-thermal oxygen plasma should be a suitable alternative for zirconia surface treatment prior to luting hence it improved microshear bond strength and provided higher surface energy without affecting surface roughness. Keywords Adhesion; Non-thermal plasma; Surface treatment.

Effect of Resin Luting Systems and Alumina Particle Air Abrasion on Bond Strength to Zirconia.

This study aimed to evaluate the effect of different primer/resin luting agent combinations and alumina air abrasion on the adhesion to zirconia. Eighty blocks (4×4×3 mm) of Lava Frame Zirconia (3M ESPE) were produced and randomly assigned into eight groups (n=10) according to two zirconia surface treatments (untreated or air abrasion with 50-μm alumina particles) and four luting systems (SU: Scotchbond Universal/RelyX Unicem 2; ZP: Z-Prime Plus/Duo-link Universal; MB: Monobond Plus/Variolink II; and AP: Alloy Primer/ED Primer II/Panavia F 2.0). After the conditioning and primer applications, resin luting agents were manipulated and applied on the zirconia, using a matrix, to form a cylinder (2 mm in diameter×2 mm high), followed by photoactivation for 40 seconds. After that, the specimens were stored in distilled water (37 °C) for 120 days and then submitted to shear bond strength testing, followed by failure mode evaluation under an optical microscope (30×). A two-way analysis of variance and Tukey test (α=0.05) were used for data analysis. Alumina air abrasion (Al) promoted higher bond values for the three luting systems, except for SU, which showed the best results without air abrasion, while with air abrasion, Al-SU, Al-ZP, and Al-MB presented higher values compared to Al-AP. We concluded that the alumina air abrasion of zirconia surfaces seemed to be dispensable for the SU group, while air abrasion (topographical alterations) enhanced the adhesion of the ZP, MB, and AP groups.

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.

Evaluation of surface treatments of monolithic zirconia in different sintering stages

PurposeThis study evaluated the effect of surface treatment of zirconia in pre-sintered and post-sintered stages on its surface roughness, phase transformation, and biaxial flexural strength (BFS). MethodsZirconia ceramic discs (n=40) having a final dimensions of 12mm diameter and 1.2mm thickness were milled then divided into three main groups according to the type of surface treatment performed (Group 1 (n=16); air-abrasion using Al2O3 particles, Group 2 (n=16); silica coating using Rocatec soft, and Group 3 (n=8); a control group receiving no surface treatment). Groups 1 and 2 were divided into two subgroups each according to the stage in which the surface treatment was performed (Subgroup A; surface treatment performed in the pre-sintered stage and subgroup B; surface treatment performed in the post-sintered stage). Surface roughness, phase transformation, and biaxial flexural strength (BFS) were later assessed. Data was then analyzed using two-way ANOVA and Tukey post-hoc tests at a significance level of p≤0.05. ResultsSubgroups treated in the pre-sintered stage showed higher mean Ra in μm (1.81±0.36) when compared to the subgroups treated in the post-sintered (0.68±0.07) stage and the control group (0.51±0.10) (p≤0.05). The pre-sintered treated group and the control showed no monoclinic phase while the post-sintered group showed significantly higher portions of monoclinic phase. Regarding BFS the post-sintered treated group had statistically significant higher values in MPa (1228±81) when compared to the pre-sintered treated group (940±101) and the control (1019±82) (p≤0.05). ConclusionsAir abrasion in the pre-sintered stage might be a promising surface treatment method to produce promising surface roughness values of zirconia without subjecting it to early degradation.

Effects of small-grit grinding and glazing on mechanical behaviors and ageing resistance of a super-translucent dental zirconia

ObjectivesThe purpose of this study is to elucidate the effects of small-grit grinding on the mechanical behaviors and ageing resistance of a super-translucent dental zirconia and to investigate the necessity of glazing for the small-grit ground zirconia. MethodsSmall-grit grinding was performed using two kinds of silicon carbide abrasive papers. The control group received no grinding. The unground surfaces and the ground surfaces were glazed by an experienced dental technician. Finally, the zirconia materials were thermally aged in water at 134°C for 5h. After aforementioned treatments, we observed the surface topography and the microstructures, and measured the extent of monoclinic phase, the nano-hardness and nano-modulus of the possible transformed zone and the flexural strength. ResultsSmall-grit grinding changed the surface topography. The zirconia microstructure did not change obviously after surface treatments and thermal ageing; however, the glaze in contact with zirconia showed cracks after thermal ageing. Small-grit grinding did not induce a phase transformation but improved the flexural strength and ageing resistance. Glazing prevented zirconia from thermal ageing but severely diminished the flexural strength. The nano-hardness and nano-modulus of the surface layer were increased by ultrafine grinding. ConclusionsThe results suggest that small-grit grinding is beneficial to the strength and ageing resistance of the super-translucent dental zirconia; however, glazing is not necessary and even impairs the strength for the super-translucent dental zirconia. Clinical significanceThis study is helpful to the researches about dental grinding tools and maybe useful for dentists to choose reasonable zirconia surface treatments.