Effect of zirconia surface treatments on the shear bond strength of veneering ceramic

Evaluation of the Bonding Shear Strength between Enamel and Dentin Feldspathic Porcelain and Two Different Monolithic Zirconia with Low and High Translucency

Introduction

The utilization of ceramics in the field of dentistry has seen a significant rise owing to their esthetic appeal and excellent functional properties. The use of ceramics in the field of dentistry has witnessed a notable surge, driven by their appealing esthetics and exceptional functional attributes. Zirconia, distinguished by its exceptional mechanical strength, plays a pivotal role in the fabrication of posterior crowns and bridges. Among zirconia variants, monolithic zirconia stands out, where the entire restoration is crafted from zirconia material. In parallel, feldspathic porcelain, chosen for its remarkable resemblance to natural tooth enamel, represents another significant ceramic type. This study aims to evaluate the shear bond strength (SBS) between two types of monolithic zirconia with two types of feldspathic porcelain.

Methods and Materials

Forty-four monolithic zirconia veneered discs with feldspathic porcelain were subjected to SBS testing. The dimensions of the discs were 7 mm in diameter and 5 mm in height (3 mm of zirconia and 2 mm of porcelain). Subsequently, the specimens were subjected to a universal testing machine at a speed of 0.5 mm/min until failure occurred. The type of failure was examined using scanning electron microscopy. One-way analysis of variance (ANOVA), two-way ANOVA, Fisher's test, and multiple Tukey comparisons were used as statistical analyses.

Results

The highest SBS was achieved by the high-translucency monolithic zirconia with enamel porcelain group (18.81 ± 3.18 MPa) and the high-translucency monolithic zirconia with dentin porcelain group (17.89 ± 2.75 MPa), followed by the low-translucency monolithic zirconia with dentin porcelain group (15.04 ± 2.24 MPa) and the low-translucency monolithic zirconia with enamel porcelain group (14.33 ± 2.00 MPa), respectively. Additionally, the most common type of failure pattern observed was mixed, followed by adhesive failure.

Conclusion

The translucency of the porcelain did not significantly affect SBS, while the type of monolithic zirconia used had a significant impact. Furthermore, there was no discernible relationship between the four groups in terms of the distribution of failure patterns.

Bonding Effectiveness of Veneering Ceramic to Zirconia after Different Grit-Blasting Treatments

Objective: To determine the effect of grit-blasting before and after sintering on the surface roughness of zirconia and the micro-tensile bond strength of a pressable veneering ceramic to zirconia. Methods: Pre-sintered zirconia blocks (IPS e.max ZirCAD, Ivoclar) were divided into four test groups of three specimens each and a control group ('CTR'; no surface treatment). Pre-S-30, Pre-S-50, and Pre-S-110 were grit-blasted with 30-µm SiO2-coated Al2O3, 50-µm Al2O3 and 110-µm Al2O3 particles, respectively, before sintering. Post-S-30 was grit-blasted with 30-µm SiO2-coated Al2O3 after sintering. For each treatment, the surface roughness was measured (Ra, Perthometer M4P, Mahr Perthen). After sintering the zirconia blocks, a liner was applied and a pressable ceramic (IPS e.max ZirPress, Ivoclar) was heat-pressed. Sixteen microbars were obtained from each block and submitted to micro-tensile bond-strength (µTBS) testing. Data were analyzed with one-way ANOVA. Any correlation between Ra and µTBS was evaluated (Sperman test). Results: Grit-blasting before sintering with 110-µm Al2O3 (RaPre-S-110 = 3.4 ± 0.4 µm), 50-µm Al2O3 (RaPre-S-50 = 2.3 ± 0.5 µm), and 30-µm SiO2-coated Al2O3 (RaPre-S-30 = 1.2 ± 0.2 µm) resulted in significantly higher roughness than grit-blasting after sintering with 30-µm SiO2-coated Al2O3 (RaPost-S-30 = 0.5 ± 0.1 µm). The highest µTBS was measured when the sintered zirconia was grit-blasted with 30-μm SiO2-coated Al2O3 (µTBSPost-S-30 = 28.5 ± 12.6 MPa), which was significantly different from that of specimens that were grit-blasted before sintering (µTBSPre-S-30 = 21.8 ± 10.4; µTBSPre-S-50 = 24.1 ± 12.6; µTBSPre-S-110 = 26.4 ± 14.1) or were not grit-blasted (µTBSCTR = 20.2 ± 11.2). Conclusions: Grit-blasting zirconia before sintering enhanced the surface roughness proportionally to the particle size of the sand used. Grit-blasting with 30-µm SiO2-coated Al2O3 after sintering improved bonding of the veneering ceramic to zirconia. Clinical Significance: As grit-blasting with 30-µm SiO2-coated Al2O3 after sintering improved bonding of the veneering ceramic to zirconia, it may reduce veneering ceramic fractures/chipping.

Effects of Surface-Etching Systems on the Shear Bond Strength of Dual-Polymerized Resin Cement and Zirconia

Adhesion of zirconia is difficult; thus, etching agents using several different methods are being developed. We investigated the effects of surface treatment with commercially available etching agents on the bond strength between zirconia and resin cement and compared them with those achieved using air abrasion alone. We used 100 zirconia blocks, of which 20 blocks remained untreated, 20 blocks were sandblasted, and 60 blocks were acid-etched using three different zirconia-etching systems: Zircos-E etching (strong-acid etching), smart etching (acid etching after air abrasion), and cloud etching (acid etching under a hot stream). Each group was subjected to a bonding procedure with dual-polymerized resin cement, and then 50 specimens were thermocycled. The shear bond strengths between the resin cement and zirconia before and after the thermocycling were evaluated. We observed that in the groups that did not undergo thermocycling, specimens surface-treated with solution did not show a significant increase in shear bond strength compared to the sandblasted specimens (p > 0.05). Among the thermocycled groups, the smart-etched specimens showed the highest shear bond strength. In the short term, various etching agents did not show a significant increase in bond strength compared to sandblasting alone, but in the long term, smart etching showed stability in bond strength (p < 0.05).

Evaluation of bond strength between zirconia milled ceramic material and veneered dental porcelain

This study aimed at examining the bond strength between zirconia and ceramic veneer, following the ISO 9693 guidelines. A total of fifty specimens of zirconia/ceramic-veneer system were produced using two commercial zirconias (VITA YZ-HTWhite and Zolid HT+ White, referred to as Group A and Group B, respectively) and a ceramic-veneering material (Zirkonia 750). The microstructure (via x-ray diffraction analysis, XRD and Secondary Electron mode, SEM) and the mechanical properties (via 3-point bending tests) of the two groups were assessed. Then, experiments were conducted according to the ISO 9693 and conventional protocols applied for producing zirconia/ceramic-veneer restorations. Bond strength values, measured by 3-point bending tests, were 34.42 ± 7.60 MPa for Group A and 31.92 ± 6.95 MPa for Group B. SEM observations of the cohesively fractured surfaces (on the porcelain side) and the examination for normality using the Shapiro-Wilk test suggested the use of Weibull statistical analysis. Median strength (σ50%) for Group A and Group B was 34.76 and 32.22 MPa, while the characteristic strength (σ63.2%) was 35.78 and 33.14 MPa, respectively. The Weibull modulus disparity between groups (12.69 and 13.07) was not significant. Bond strength exceeded the ISO 9693 minimum of 20 MPa, suggesting satisfactory strength for clinical use.

Influence of attaching mechanical retentive devices onto frameworks on fracture resistance of implant-supported zirconia crowns

This study investigated the fracture load of implant-supported zirconia crowns (IZCs), in which indirect composite resin or feldspathic porcelain was layered onto zirconia frameworks with mechanical retentive devices. Three different zirconia frameworks were assessed: attaching mechanical retentive devices on glaze and opaque porcelain materials (GL and OP groups, respectively), and no attaching mechanical retentive devices (ND group). The frameworks were layered using feldspathic porcelain (FP veneer) and indirect composite resin (IC veneer). Fracture load of the specimens was measured. In FP veneer, the GL group recorded the highest fracture load. In the IC veneer, the GL and OP groups had significantly higher fracture load than the ND group. The fracture resistance of IZCs can be enhanced by applying glaze material before attaching mechanical retentive devices for porcelain layering. The mechanical retentive devices effectively yielded mechanical interlocking between the zirconia frameworks and the IC veneer in GL and OP groups.

Shear Bond Strength of Colored and Sandblasted Zirconia to Ceramic Veneers Fabricated by the Pressing and Layering Techniques: An In Vitro Study

Introduction

Porcelain-veneered zirconia (PVZ) restorations are increasingly used due to their optimal esthetics and high strength. However, chipping of porcelain limits the application of PVZ restorations. The aim of this study was to assess the shear bond strength (SBS) of colored and sandblasted zirconia to ceramic veneers fabricated by the pressing and layering techniques.

Materials and Methods

Sixty cubic zirconia specimens (10 × 10 × 2 mm) were assigned to three groups according to their surface treatment: (I) control, (II) sandblasting with 50 μm alumina particles (S), and (III) coloring (C). Each group was subsequently divided into two subgroups according to the porcelain-veneering technique: (I) layering (L) and (II) pressing (P). The specimens underwent 10,000 thermal cycles between 5 and 55°C, and their biaxial SBS was measured in an electromechanical universal test machine (0.5 mm/min with 2.5 kN load cell). The failure mode was also assessed under a stereomicroscope. Three samples were randomly selected from each subgroup (n = 18) for examination of zirconia-phase transformation by X-ray diffraction (XRD). Two-way and one-way ANOVA followed by the post hoc Tukey test were used to analyze statistical differences among the groups and subgroups (α = 0.05).

Results

The sandblasted zirconia with press porcelain (SP) subgroup showed the highest (24.40 ± 8.16 MPa) and the colored zirconia with press porcelain (CP) subgroup showed the lowest (13.76 ±3.62 MPa) SBS. All failures were cohesive. Rate of phase transformation in layered porcelain was significantly lower than that in pressed porcelain (P < 0.01).

Conclusion

The sandblasted group showed the highest and the colored group showed the lowest SBS; the layered group showed higher SBS than the pressed group.

Effect of different interfacial surface treatments on the shear bond strength of veneering ceramic and zirconia core

BACKGROUND

Several interfacial surface treatments of zirconia surfaces have been proposed to improve adhesion to ceramic veneering. However, information regarding the durability and effect of such treatments on the bond strength following such treatments is lacking.

AIM OF THE STUDY

This study aimed to evaluate the shear bond strength between veneering ceramic and zirconia core after different interfacial surface treatments.

MATERIALS AND METHODS

Fifty-two discs (8 mm in diameter and 3 mm in height) were fabricated from zirconia blanks using a microtome cutting machine. Zirconia discs were divided into four groups (n = 13). Group I was subjected to air-borne abrasion using (Al₂O₃), group II was coated by bioglass, group III was coated with ZirLiner, and group IV was subjected to wash firing (sprinkle technique). A cylinder (4 mm in diameter and 3 mm in height) of veneering ceramic was fired on top of the zirconia core. Shear bond strength (SBS) between zirconia core and veneering ceramic was evaluated by using a universal testing machine. The data was collected and statistically analysed using One-Way ANOVA followed by multiple pairwise comparisons using Bonferroni adjusted significance level. The failure modes were assessed using a stereomicroscope for each group.

RESULTS

The highest mean bond strength was recorded in group III (17.98 ± 2.51 MPa), followed by group II (15.10 ± 4.53 MPa), then group I 14.65 ± 2.97 MPa. The lowest mean bond strength was recorded in group IV (13.28 ± 3.55 MPa).

CONCLUSIONS

Surface treatments had an effect on the zirconia-veneer shear bond strength. Liner coating revealed the highest shear bond strength values, significantly higher in comparison to wash firing (sprinkle technique) .

Effect of Nonthermal Plasma on Shear Bond Strength of Translucent Zirconia in Layering Ceramic

Background

Today, various methods are used to increase the bond strength of zirconia in layering ceramics. This study evaluated the effects of nonthermal argon plasma on zirconia shear bond strength to layering porcelain. Materials and Method. In this experimental study, 42 square blocks of zirconia were prepared and randomly divided into three groups (n = 14) according to the applying surface treatment: (1) the control group (without any surface treatment), (2) the plasma-treated group with argon nonthermal plasma, and (3) the air abrasion group with 50 µm Al₂O₃ particles. All samples were layered with porcelain. One sample from each group was evaluated by electron microscopy (SEM) to examine the cross-sectional area of the zirconia-ceramic bond. The rest of the specimens were subjected to thermocycling with 5,000 baths to imitate the aging process in the mouth and then were tested for shear bond strength. The failure pattern of the samples was examined by stereomicroscope. Bond strength data were analyzed by one-way ANOVA test in three groups and Tamhane post hoc test in pairs. The significance level of p-value was considered 0.05.

Results

The shear bond strength of the plasma-treated group was significantly higher than the control group (p = 0.032) but the shear bond strength between the sandblast and the plasma-treated group was not significantly different (p = 0.656). The shear bond strength between the sandblast and the control group was also not significant (p = 0.202). Regarding the mode of failure, failures were mostly adhesive and then mixed. Examination of the samples under SEM showed that the bond area is the thickest in the sandblast group and also the surface roughness is the highest in the sandblast group and the lowest in the control group.

Conclusion

This study demonstrated that the use of nonthermal argon plasma treatment is an effective way to enhance the quality and quantity of shear bond strength between layering porcelain and zirconia.

Shear bond strength of porcelain to milled and stereolithography additively manufactured zirconia with and without surface treatment: An in vitro study

STATEMENT OF PROBLEM

Delamination of veneering ceramic is one of the most common challenges relating to veneered zirconia restorations. Additive manufacturing (AM) is a fast-expanding technology that has gained widespread acceptance in dentistry and is increasingly being used to produce dental restorations. However, information about bonding of porcelain to AM zirconia is lacking.

PURPOSE

The purpose of this in vitro study was to investigate the shear bond strength (SBS) of porcelain to milled and additively manufactured zirconia, and the effect of surface treatment on bond strength.

MATERIAL AND METHODS

A Ø12×5-mm disk was designed virtually to fabricate all specimens, which were divided into 2 groups according to the manufacturing technique: additively manufactured or milled zirconia. The effect of airborne-particle abrasion and a zirconia liner before porcelain application was investigated in both groups. Veneering porcelain was fired into an alumina ring mold on the zirconia surface. SBS was measured by using a universal testing machine at a crosshead speed of 1 mm/min before and after aging (n=10). SBS data were analyzed with 3-way ANOVA (α=.05) RESULTS: A significant difference was found between milled and AM zirconia. The SBS of porcelain to milled zirconia was significantly higher (1.38 MPa) than to AM zirconia (0.68 MPa) (P<.001). The surface treatment of zirconia had no significant effect on porcelain SBS in either group (P=.254), whereas thermocycling significantly reduced the SBS of porcelain to zirconia in both milled and AM groups (P=.001).

CONCLUSIONS

Porcelain bonding to milled zirconia was better than to AM zirconia. Pretreating the zirconia substrate before porcelain application did not improve the porcelain bond.

Effect of Helium Plasma Exposure on Wettability and Shear Bond Strength between the Zirconia Core and Feldspathic Veneering Ceramic: An In Vitro Study

Introduction. The present study aimed to evaluate the effect of helium plasma treatment on the wettability of zirconia surface and on the shear bond strength between the dental zirconia core and feldspathic veneering ceramic. Methods. 128 zirconia specimens were prepared, polished, and then divided into four groups: control, Zr, FC, and Zr/FC. In Zr and Zr/FC groups, the zirconia blocks were treated by helium plasma for 60 s. In FC and Zr/FC, the feldspathic ceramic powder received 60 s of plasma treatment. Then, the feldspathic powder was applied on the zirconia blocks. Half of the specimens in each group were sintered in a tube furnace, and the contact angle between the zirconia core and feldspathic ceramic was measured at different time intervals. The other half were sintered in a ceramic furnace and then subjected to thermocycling. The shear bond strength was measured using a universal testing machine. The failure mode was assessed using a stereomicroscope. Data were analyzed by one-way ANOVA test, and the statistical significance was considered less than 0.05. Results. There was no significant difference in the mean contact angle and the shear bond strength values of the experimental groups ( $P>0.05$ ). The mean contact angle decreased significantly in all groups over time ( $P<0.001$ ). The modes of failure were predominantly mixed in all groups. Conclusion. The helium plasma applied on either dental zirconia core or feldspathic ceramic powder could not improve the zirconia surface wettability and the shear bond strength between the two ceramics.

Effect of different zirconia surface pretreatments on the flexural strength of veneered Y-TZP ceramic before and after in vitro aging

PURPOSE

The investigation of zirconia core surface pretreatments on the flexural strength of bilayered zirconia ceramics before and after artificial accelerating aging.

METHODS

Ninety bar-shaped specimens were manufactured from Yttria Stabilized Tetragonal Zirconia Polycrystal (Y-TZP) and divided in three groups depending on zirconia surface pretreatment before veneering: layering with liner, pretreatment with silane-containing gas flame (SGF) with the Silano-Pen device and alumina air-abrasion. Half of the veneered specimens in each group (n=15) underwent artificial accelerating aging. A 4-point bending test was performed to determine flexural strength. Three specimens from each group were further analyzed using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) before veneering and after fracture (aged and non-aged subgroups).

RESULTS

Alumina air-abrasion was correlated to increased phase transformation from tetragonal to monoclinic zirconia phase. Qualitative analysis revealed that with the majority of the specimens pretreated with the silane-containing gas flame, areas of the veneering material remained firmly attached to the zirconia core after flexural strength testing. There was no statistically significant difference on the flexural strength among the groups before or after aging. Artificial accelerating aging resulted in statistically significant higher flexural strength of the specimens after aging.

CONCLUSION

SGF pretreatment can be an acceptable and feasible alternative method before the veneering of Y-TZP zirconia as it presented slightly higher bond strength compared with alumina air-abrasion which was associated with higher tetragonal to monoclinic (t→m) phase transformation. Accelerating aging leads to an increase of the mechanical properties under in vitro conditions.

Surface characterization of different surface treatments associations with plasma and bonding analysis of Y-TZP and the veneering ceramic

OBJECTIVES

To characterize the surface of zirconia (Y-TZP) submitted to different surface treatments (with and without plasma associations) and to evaluate the shear bond strength (SBS) between veneering ceramic (VC) and Y-TZP after different aging methods.

METHODS

301 Y-TZP specimens were fabricated and distributed into 7 groups: C (control): no treatment; Al: airborne abrasion with 27 μm Al₂O₃ particle; L: liner; P: plasma; Al + L: airborne + liner; Al + P: airborne + plasma; P + L: plasma + liner. The Y-TZP surface was characterized by SEM, EDS, AFM, surface profilometry, surface-free energy (SFE), and XRD. SBS between Y-TZP and VC was verified after three aging protocols: initial, after hydrothermal aging (autoclave for 5 h), or thermal fatigue (30,000 baths - 5-55 °C). One- (profilometry, SFE) and two-way ANOVA (SBS), and Tukey's HSD test were used.

RESULTS

For the plasma groups, a full globular surface coverage was observed (SEM, AFM). Si was found for Al, L, Al + L, and P + L. Roughness was lower for C, P, and Al + P. For SFE, the highest values were found when the liner was applied (>74.59 nm/Nm). The highest monoclinic content was observed for Al + L (6.96%) and Al + P (5.86%). For the initial period, Al and P + L presented the lowest SBS values (<5.85 MPa; P > 0.331). The highest SBS values were found for L, P, and P + L (hydrothermal aging) and for P, L, Al + L, and Al + P (thermal fatigue).

SIGNIFICANCE

Changes in Y-TZP topography and the SBS with the VC were found, according to treatments performed. Plasma treatment improved SBS and did not cause phase transformation.

Analysis of surface conditioning methods on core-veneer bond strength of CAD/CAM zirconia restorations

BACKGROUND

The increased strength of zirconia has resulted in its widespread application in clinical dentistry. Nevertheless, the fracture of veneering porcelains remains one of the key reasons of failure.

OBJECTIVE

The objective of this study was to compare and analyze the influence of surface conditioning methods on the core-veneer bond strength of zirconia restorations.

METHODS

Thirty specimens of zirconia core with sizes 10 × 5 × 5 mm were layered with porcelain of sizes 5 × 3 × 3 mm. On the basis of different surface conditioning methods, four groups were made: Group I: abrasion with airborne alumina particles of 110 μm size, Group II: sandblasting with silica coated alumina particles of 50 μm in size, Group III (modified group): alteration with a coating of zirconia powder prior to sintering, and Group IV (control group): metal core specimens. The shear force of all specimens was tested using a universal testing machine with a 0.5 mm/min crosshead speed. One-way analysis of variance (ANOVA) and Tukey's post hoc pair wise comparison (p= 0.05) were performed to analyze the shear bond strength. A scanning electron microscope was used to assess the fractured specimens.

RESULTS

A statistically significant difference was noted between the groups. The mean value of shear bond strength was 40.25 MPa for Group I, 41.93 MPa for Group II, 48.08 MPa for Group III and 47.01 MPa for Group IV.

CONCLUSIONS

The modified zirconia group and control group demonstrated a significantly higher mean bond strength than that of Group I, where airborne particle abrasion was used. The scanning electron microscope showed that cohesive fracture in the porcelain veneers was the main problem of failure in altered zirconia. The modified zirconia specimens in Group III demonstrated significantly improved values of shear bond strength.

Toughening of highly translucent zirconia by monoclinic ZrO2 and SiO2 particle coating

The mechanical properties of highly translucent partially stabilized zirconia (PSZ) need to be improved; however, improvement of mechanical properties often decreases translucency. To overcome this problem, a monoclinic ZrO₂ (mZrO₂)/SiO₂ dispersion was prepared and applied as a coating material for PSZ. The influence of surface treatment by the mZrO₂/SiO₂ dispersion on the surface topography, crystallography, and mechanical properties of highly translucent PSZ was investigated in this study. Following the treatment, the mechanical strength of highly translucent PSZ improved by 170% compared with control, for the best mZrO₂/SiO₂ dispersion ratio and heating temperature condition, while maintaining its translucency. The proposed coating is promising for improving the mechanical properties of highly translucent PSZ.

Glass coatings to enhance the interfacial bond strength between veneering ceramic and zirconia

The purpose of this study was to investigate the tensile bond strength (TBS) and shear bond strength (SBS) between a zirconia core and fluoroapatite-pressed ceramic after the application of glass 46SP6 and AP40 via the ISO-17095:2013 methodology. Sintered zirconia beams (n = 120) were divided into four groups: (a) control: no treatment; (b) ZirL: IPS-E max ceram ZirLiner coating; (c) glass AP40 coating; and (d) glass 46SP6 coating. A fluoroapatite ceramic (IPS e.max Zir Press, Ivoclar Vivadent) beam was injected perpendicularly on top of each zirconia (Zenostar, Wieland Dental) beam forming a cross-bonded specimen. All groups were sub-divided into two for tensile and shear bond strength tests using a universal testing machine. Data were analyzed using the Kruskal-Wallis, Pearson Chi²_, and Mann-Whitney U test (α = 0.05). The failure modes were measured using a stereomicroscope for each group. Scanning electron and atomic force microscopy were also employed. Zirconia surface modification with glass AP40 showed higher TBS values followed by the ZirL group with statistical differences (p < 0.05). SBS values showed no statistical differences between the groups. AFM analysis showed higher roughness values (Ra) in the 46SP6 and AP40 groups (p < 0.05). Glass coating AP40 exhibited promising bond strength results between zirconia and fluorapatite veneering ceramic, making it better for chemical and mechanical interlocking which may improve bilayered restorations longevity.

Effect of thermal and mechanical cycles on shear bond strength of zirconia core to porcelain veneer under different surface treatments

Background. Due to the fragile nature of all-ceramic restorations, it is necessary to provide an appropriate (core) infrastructure to support the veneering porcelain. The veneer detachment and chipping are disadvantages of these restorations. Several techniques have been proposed to minimize these problems. This study evaluated the effect of thermal and mechanical cycles on the shear bond strength of zirconia core to porcelain veneer under different surface treatments.

Methods. Sixty disk-like zirconium samples were randomly divided into three groups. The first group was polished and veneered with porcelain, without additional surface treatments. The two other groups were subjected to different surface treatments (modified aluminum oxide by silica and activator‒aluminum oxide and primer) and veneering with porcelain. Half of the samples in each group were subjected to 6000 thermal cycles and 20,000 masticatory cycles of 50 N to imitate the intraoral conditions; the other half were placed in distilled water at 37°C until the shear strength test. Each sample was then buried using PMMA in a mounting jig so that the gap between the core and the veneer could be placed upward. Then, they were exposed to shear stress using a universal testing machine at a rate of 1 mm/min until fracture. The maximum force leading to the fracture was recorded.

Results. Comparison of the groups showed that the highest shear bond strength was related to the samples treated with aluminum oxide and primer, without applying thermal and masticatory cycles, which indicated no significant difference from the group treated with aluminum oxide and primer, with thermal and masticatory cycles. The lowest shear bond strengths were related to the polished samples without surface treatment by applying thermal and masticatory cycles (P=0.001), which indicated no significant difference from the untreated group without thermal and masticatory cycles.

Conclusion. Based on the results, treatment with aluminum oxide and primer increased the shear bond strength of zirconia core to porcelain veneer. Thermocycling and masticatory cycles failed to reduce the shear bond strength in all the three groups significantly

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

STATEMENT OF PROBLEM

Delamination failure may occur between ceramic frameworks and veneering ceramics, shortening the lifetime of fixed dental prostheses in load-bearing areas.

PURPOSE

The 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 METHODS

Zirconia 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.

RESULTS

The 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.

CONCLUSIONS

The 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.

Effect of zirconia surface treatment on its wettability by liquid ceramics

STATEMENT OF PROBLEM

The wettability of the framework by liquid ceramics is important in ensuring a suitable bond between veneering ceramics and zirconia.

PURPOSE

The 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 METHODS

Fifty 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).

RESULTS

The 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.

CONCLUSIONS

Because 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.

Can universal adhesive systems bond to zirconia?

OBJECTIVE

To measure the bond strength to zirconia subjected to different surface treatments of universal bonding agents.

MATERIALS AND METHODS

Eighty blocks of zirconia were obtained by CAD/CAM milling. The blocks were embedded into PVC tubes, polished sequentially with increasing granulation sandpapers and divided into two groups according to surface treatment: polished or grit-blasted with alumina particles. Each group was then subdivided by bonding agent employed: Z-Prime Plus (control); Scotchbond Universal; All Bond Universal; and Z-Prime Plus + All Bond Universal. Cylindrical composite resin build-ups were constructed atop the blocks using a two-part metal die. Specimens were stored for 24 hours and subjected to microshear bond strength testing. Statistical analyses were performed by means of the F-test (ANOVA), Student's t and Tukey's test. After sputter coating, zirconia surfaces and adhesive interfaces were analyzed by scanning electron microscopy (SEM).

RESULTS

Bond strength was superior for grit-blasted zirconia. In specimens with this surface treatment, there were no significant differences between experimental groups. On SEM, blasted surfaces exhibited areas of micromechanical retention and adhesive interfaces exhibited areas of zirconia-adhesive interlocking.

CONCLUSION

Universal adhesive systems were able to bond to zirconia. The interlocking promoted by grit-blasting enhanced bond strength.

CLINICAL SIGNIFICANCE

Universal adhesive systems simplify bonding to zirconia and enable intraoral repair of fractures.

Shear Bond Strength Between Zirconia and Veneer Ceramic: Effect of Thermocycling and Laser Treatment

Objective: The purpose of this study is to investigate the effect of various presintering and sintered surface treatments and thermocycling on the bond strength between zirconia and veneer ceramics. Background data: Bond stability between zirconia and veneer ceramic is a major concern, and only limited evidence about its longevity is currently available. Moreover, no study has yet evaluated the influence of thermocycling on the bond strength of veneer ceramic to zirconia after Er,Cr:YSGG laser irradiation at different pulse durations and sandblasting. Materials and methods: In this study, 220 nonsintered zirconia specimens were prepared with CAD/CAM and randomly divided into 2 groups; half of the specimens in each group were stored in water for 1 week, and the other half were thermocycled (5000 cycles) between baths of 5°C and 55°C. Specimens were then divided into five subgroups based on the following surface treatments: control (untreated surface), sandblasting (120 μm Al₂O₃), and Er,Cr: YSGG laser irradiations (3 W-8 Hz, 3 W-15 Hz, and 3 W-20 Hz, MGG 6 laser tip, for 20 sec, distance of 10 mm, water/airflow of 55% and 65%). Morphological assessment was done using atomic force microscopy and scanning electron microscopy, and phase transformation was assessed by X-ray diffractometry. All specimens were then veneered with veneering ceramic, and bond strength test using a universal testing device at a 1 mm/min crosshead speed. Data were evaluated by Kruskal-Wallis variance analysis and the Mann-Whitney U test. Results: There was no significant difference in the bonding strength values among the (p > 0.05). Thermocycling reduced the bond strength, but it was not significant (p > 0.05), except for the presintering 20 Hz group (p < 0.02). Conclusions: Application of thermocycling to sintered zirconia specimens may be detrimental to the shear bond strength of zirconia ceramics. Treating the zirconia surface after sintering is not recommended, due to the decrease in bond strength.

The Use of the Finite Elements Method (FEM) to Determine the Optimal Angle of Force Application in Relation to Grooves Notched into a Zirconia Coping with the Aim of Reducing Load on a Connection with Veneering Ceramic

Objective of Study

To investigate, using the FEM, the influence of different notching angles on a zirconium dioxide coping with the aim of establishing the optimal connection conditions with veneering ceramic.

Materials and Methods

To calculate the stresses in the connection between zirconia coping and veneering ceramic, a model comprising grooves cut perpendicular was adopted. Such a notch profile was used to design the shape and spacing of the grooves on an FEM model simulating a zirconium dioxide coping. For discretization purposes we used twenty-node solid BRICK elements featuring intermediate nodes with three degrees of freedom in each node. The model was divided into 117 745 finished elements and 439 131 nodes. The problem was solved with a GLU type contact. The same load F = 1N divided by the number of nodes on the external surface was applied to each node of the outer surface of the base. In subsequent computing variants the F load changed the orientation by angle α from 0° to 45° every 15°.

Results

The highest level of material strain occurs at angle α = 0°  σ_red  max =309 MPa and the lowest at angle α = 45°  σ_red  max =220 MPa. The highest positive stress pressure occurs at angle α = 0°  p_max=251 MPa, p_min=-354 MPa and the lowest at angle α = 15°, p_max=171 MPa, p_min=-186 MPa. In the case of tangential stresses on the coping-veneering ceramic connection, the highest values were noted at angle α = 15°  τ_max=44,4 MPa and the lowest at angle α = 45°  τ_max=32,7 MPa.

Conclusions

To reduce the load on the zirconia-veneering ceramic connection, the notches should be made at an angle of α = 45°.

Improvement of mechanical properties of Y-TZP by thermal annealing with monoclinic zirconia nanoparticle coating

OBJECTIVE

To assess whether a thermal annealing with a monoclinic zirconia (mZrO₂) nanoparticle coating can improve the reliability of sandblasted yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) and maintain its mechanical strength.

METHODS

Commercially available Y-TZP (Lava Frame, 3M Dental Products) disks were sintered and surface-treated as follows: AS (as sintered, with no treatment); SB (sandblasting); SB-TA (sandblasting followed by thermal annealing at 1000 °C); and SB-mZr-TA (sandblasting followed by thermal annealing at 1000 °C with the mZrO₂ nanoparticle coating). The mZrO₂ nanoparticles of 21 nm in size were prepared by a hydrothermal method, and coated onto Y-TZP sintered disks as a 5 g/L ethanol dispersion. Biaxial flexural strength (S) was measured using the piston-on-three-ball test, and reliability was evaluated by the Weibull modulus (m).

RESULTS

Biaxial flexural tests showed a significant increase in the strength of Group SB (S_SB = 1445 ± 191 MPa) compared with Group AS (S_AS = 1071 ± 112 MPa). The thermal annealing improved the reliabilities of the sandblasted Y-TZP (m_SB-TA = 20.14 and m_SB-mZr-TA = 21.33), as compared with Group SB (m_SB = 7.77). However, the conventional thermal annealing without the mZrO₂ coating caused a significant decrease in the strength of sandblasted Y-TZP (S_SB-TA = 1273 ± 65 MPa). Importantly, the mZrO₂ coating prevented the decrease in the strength caused by conventional thermal annealing (S_SB-mZr-TA = 1379 ± 65 MPa).

SIGNIFICANCE

The thermal annealing with the mZrO₂ nanoparticle coating can improve the reliability of sandblasted Y-TZP and maintain its mechanical strength, which would otherwise be decreased by the conventional annealing process.

Bond strength of heat-pressed veneer ceramics to zirconia with various blasting conditions

Background/purpose

With the technology of dental prostheses and materials progress, the bond durability of the all-ceramic restoration system plays an important role in the oral environment. The purpose of this study was to evaluate the influence of the parameters of blasting on the shear bond strength between zirconia and pressed veneer ceramics.

Materials and methods

Zirconia was blasted with different alumina particle size subjected to two types of applied pressures. Heat-pressed and layered veneer ceramic blocks were served as an experimental group and control group, respectively. The shear strength of specimens after thermocycling for 20,000 times was also investigated to simulate oral environment.

Results

The results indicated that the surface roughness was increased significantly (P < 0.05) with increasing particle size of alumina and blasting pressure. The alumina particle size had statistically significant influence (P < 0.05) on shear strength of heat-pressed groups. Among heat-pressed ceramic specimens, the highest and lowest shear strength could be obtained when 50 μm of alumina was used at pressure of 0.3 MPa and 110 μm of alumina was used at 0.5 MPa, respectively. The negligible effect of thermal cycle on shear strength of heat-pressed groups can be seen.

Conclusion

Blasting with 50 μm of alumina at 0.3 MPa could enhance the bond strength between zirconia and veneer ceramics.

Avaliação da resistência de união de uma cerâmica de óxido de zircônia submetida a tratamentos de superfície por abrasão

Resumo Introdução A cimentação adesiva, com cerâmicas puras, é um passo relevante no estabelecimento da longevidade de trabalhos protéticos, sendo estes os melhores materiais utilizados para a reposição de dentes perdidos, de forma a reabilitar o sorriso. O sistema cerâmico de zircônia não se beneficia do tratamento com ácidos e necessita de diferentes métodos para tratar sua superfície, visando à efetividade na união adesiva. Objetivo Avaliar os resultados de diferentes técnicas de jateamento e aplicação de agente de união desenvolvidas para metais e cerâmica de zircônia (Ceramill ZI®), por meio de ensaio de tração, em dois diferentes tratamentos de superfície. Material e método Foram preparadas 20 amostras de Ceramill Zi® (n = 20), em forma de cilindro, e unidas entre si por meio do cimento resinoso (Multilink®), formando 10 espécimes (n = 10). Formaram-se sete grupos experimentais com os mesmos 10 espécimes e estes receberam dois tratamentos de superfície diferentes: abrasão e aplicação de agentes silânicos de união. Resultado A análise estatística mostrou diferenças significativas na resistência à fratura dos espécimes silicatizados com Rocatec®. Os valores de resistência de união à tração, mensurados em MPa, dos grupos 1 a 7, foram, respectivamente: 2,27; 4,48; 8,06; 8,32; 9,15; 10,56 e 10,70. As médias entre os grupos se apresentam estatisticamente significantes, exceto entre os grupos 3 e 4 e entre 6 e 7. Conclusão Os resultados mostraram que o tratamento da superfície cerâmica baseado no método de silicatização promoveu melhor união nos ensaios com Ceramill ZI® e cimentados com Multilink®.

Novel Coatings on Zirconia for Improved Bonding with Veneer Ceramics

This study aimed to compare the effects of two surface-coating methods on the shear bond strength (SBS) of veneering ceramics (VC) to zirconia. Eighty pre-sintered zirconia cubes were randomly assigned into four study groups: E60S, E60P, N60S, and N60P. The zirconia surface was coated with a mixture of two types of glaze and alumina (<60 μm) by airbrush spraying and fine- brush painting. Surface roughness (Ra), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and SBS measurements (both initial and artificial aged conditions, including one month of water storage) were performed. The Ra results revealed significant differences among all groups (p < 0.001). The N60P group exhibited higher values of Ra (5.717 ± 0.20 µm) and SBS before and after water storage with values of 37.22 ± 4.954 MPa and 34.42 ± 3.977 MPa, respectively. The fine-brush coatings showed significantly higher SBS than that of airbrush coatings, in both initial and artificial conditions. Both coating methods and various coating materials (p < 0.001) produced a significant influence on VC-zirconia SBS. A significant correlation between Ra and SBS (Spearman’s rho = 0.808; p < 0.001) was found. The novel coating by fine-brush painting is a promising surface treatment and an easy technique for obtaining a rougher surface, which subsequently improves the bond strength to VC.

Evaluation of mold-enclosed shear bond strength between zirconia core and porcelain veneer

This study aimed to evaluate the mold-enclosed shear bond strength (ME-SBS) of zirconia to veneering porcelain with different surface treatments. Colored or uncolored zirconia coupons were either highly polished or airborne-particle abraded. The specimens were divided into groups with/without application of liner. Veneering porcelain was fired into an alumina ring mold on the zirconia coupons. The assembled specimens were subjected to the ME-SBS test. The mean ME-SBS for groups ranged from 7-10 MPa with no significant difference (p>0.05). A three-way ANOVA showed that coloring and surface roughening of the zirconia specimen had no significant influence on the ME-SBS value, but liner application exhibited a significant effect with a minor decrease in the MESBS (p=0.049). Surface treatments (coloring, airborne-particle abrasion, and liner application) were found to not cause a significant increase to the zirconia-porcelain bond strength. The application of zirconia liner had a slight negative influence on the ME-SBS results.

Bond strength enhancement of zirconia-porcelain interfaces via Nd:YAG laser surface structuring

OBJECTIVES

The aim of this study was to evaluate the effect of laser surface structuring on the bond strength of feldspar-based porcelain to zirconia, as compared to conventional sandblasting treatment.

MATERIALS AND METHODS

Thirty cylindrical zirconia substrates, previously sintered, were divided in three groups according to the type of surface conditioning: 1) sandblasting with 50 µm Al₂O₃; 2) laser structuring (Ø25 µm holes); and 3) laser structuring (Ø50 µm holes). Porcelain was injected onto the zirconia substrates. X-ray diffractometry (XRD) was used to evaluate the influence of the laser treatment on zirconia crystallographic phases. Shear bond strength test was performed. Micrographs using SEM were used to evaluate the zirconia surface after each surface treatment and to evaluate the fracture surface after the shear test.

RESULTS

The laser-structured groups presented the highest shear bond strength (65 ± 16 MPa and 65 ± 11 MPa, for the 25 µm and 50 µm holes, respectively). The sandblasting samples presented shear bond strength of 37 ± 16 MPa. XRD analysis showed that there was no phase transformation on the thermally affected surface due to laser action. Microcracks were created at some holes due to the high temperature gradient generated by laser.

SIGNIFICANCE

Laser structuring significantly increased (up to 75%) the shear bond strength of zirconia to veneering porcelain as compared to conventional sandblasting treatment. Therefore, laser structuring arises as a surface conditioning method for producing stronger and long lasting zirconia-porcelain interfaces.

Pre-sintered Y-TZP sandblasting: effect on surface roughness, phase transformation, and Y-TZP/veneer bond strength

Sandblasting is a common method to try to improve the Y-TZP/veneer bond strength of dental prostheses, however, it may put stress on zirconia surfaces and could accelerate the t→m phase transformation. Y-TZP sandblasting before sintering could be an alternative to improve surface roughness and bonding strength of veneering ceramic.

[Effect of different surface processes on the bond strength between zirconia framework and veneering ceramic]

OBJECTIVE

To compare the effect of different surface processes on bond strength and microscopic structure using a scanning electron microscope (SEM) and an energy distribution spectrum (EDS) at the bonding interface between zirconia framework and veneering ceramic.

METHODS

WIELAND zirconia core material was cut into 33 rectangular specimens and fired on into rectangular specimens (10 mm×5 mm×5 mm). The specimens were randomly divided into three groups (n=
11). The sandblasting group was sandblasted before firing. The sandblasting and liner coverage group was sandblasted before firing and then sintered with liner coverage after firing. The control group was not processed. All the veneering ceramics (5 mm×
5 mm×5 mm) were fired on into the zirconia substructure by slip-casting technique. One bilayered specimen in each group was prepared for SEM and EDS to examine the bonding conditions. The other specimens were measured for shear force using an electronic universal dynamometer. The data obtained were analyzed by using the statistical software SPSS 17.0.

RESULTS

The values of the shear bond strength test were (13.80±1.54) MPa for the control group, (18.06±0.59) MPa for the sandblasting group, and (21.04±1.23) MPa for the sandblasting and liner coverage group. Significant differences existed among the three groups (P<0.01).

CONCLUSIONS

Abrasion before firing significantly increases the shear bond strength of zirconia to veneering porcelain. The use of porcelain combined with liner increases the shear bond strength.

The Application of a Novel Ceramic Liner Improves Bonding between Zirconia and Veneering Porcelain

The adhesion of porcelain to zirconia is a key factor in the success of bilayered restorations. In this study, the efficacy of a novel experimental liner (EL) containing zirconia for improved bonding between zirconia and veneering porcelain was tested. Four ELs containing various concentrations (0, 3.0, 6.0, and 9.0 wt %) of zirconia were prepared. Testing determined the most effective EL (EL3 containing 3.0 wt % zirconia) in terms of shear bond strength value (n = 15). Three different bar-shaped zirconia/porcelain bilayer specimens were prepared for a three-point flexural strength (TPFS) test (n = 15): no-liner (NL), commercial liner (CL), and EL3. Specimens were tested for TPFS with the porcelain under tension and the maximum load was measured at the first sign of fracture. The strength data were analyzed using one-way ANOVA and Tukey's test (α = 0.05) as well as Weibull distribution. When compared to NL, the CL application had no effect, while the EL3 application had a significant positive effect (p < 0.001) on the flexural strength. Weibull analysis also revealed the highest shape and scale parameters for group EL3. Within the limitations of this study, the novel ceramic liner containing 3.0 wt % zirconia (EL3) significantly enhanced the zirconia/porcelain interfacial bonding.

The effect of grinding and/or airborne-particle abrasion on the bond strength between zirconia and veneering porcelain: a systematic review

Objective: The aim of the study was to make an inventory of current literature on the bond strength between zirconia and veneering porcelain after surface treatment of zirconia by grinding with diamond bur and/or with airborne-particle abrasion.

Material and methods: The literature search for the present review was made following recommended guidelines using acknowledged methodology on how to do a systematic review. The electronic databases PubMed, Cochrane Library, and Science Direct were used in the present study.

Results: Twelve studies were selected. Test methods used in the original studies included shear bond strength (SBS) test, tensile bond strength test, and micro-tensile bond strength test. The majority of studies used SBS. Results showed a large variation within each surface treatment of zirconia, using different grain size, blasting time, and pressure.

Conclusions: Airborne-particle abrasion might improve the bond strength and can therefore be considered a feasible surface treatment for zirconia that is to be bonded. Grinding has been recommended as a surface treatment for zirconia to improve the bond strength; however, this recommendation cannot be verified. A standardized test method and surface treatment are required to be able to compare the results from different studies and draw further conclusions.

Shear bond strength of veneering ceramic to coping materials with different pre-surface treatments

PURPOSE

Pre-surface treatments of coping materials have been recommended to enhance the bonding to the veneering ceramic. Little is known on the effect on shear bond strength, particularly with new coping material. The aim of this study was to investigate the shear bond strength of veneering ceramic to three coping materials: i) metal alloy (MA), ii) zirconia oxide (ZO), and iii) lithium disilicate (LD) after various pre-surface treatments.

MATERIALS AND METHODS

Thirty-two (n = 32) discs were prepared for each coping material. Four pre-surface treatments were prepared for each sub-group (n = 8); a) no treatment or control (C), b) sandblast (SB), c) acid etch (AE), and d) sandblast and acid etch (SBAE). Veneering ceramics were applied to all discs. Shear bond strength was measured with a universal testing machine. Data were analyzed with two-way ANOVA and Tukey's multiple comparisons tests.

RESULTS

Mean shear bond strengths were obtained for MA (19.00 ± 6.39 MPa), ZO (24.45 ± 5.14 MPa) and LD (13.62 ± 5.12 MPa). There were statistically significant differences in types of coping material and various pre-surface treatments (P<.05). There was a significant correlation between coping materials and pre-surface treatment to the shear bond strength (P<.05).

CONCLUSION

Shear bond strength of veneering ceramic to zirconia oxide was higher than metal alloy and lithium disilicate. The highest shear bond strengths were obtained in sandblast and acid etch treatment for zirconia oxide and lithium disilicate groups, and in acid etch treatment for metal alloy group.

Low-Fusing Porcelain Glaze Application on 3Y-TZP Surfaces can Enhance Zirconia-Porcelain Adhesion

Abstract The aim of this study was to assess whether surface treatment improves zirconia-porcelain adhesion. The 3Y-TZP blocks were cut into squares, then polished and sintered. The zirconia surface treatments were performed as follows: no treatment (C); tribochemical silica coating (TBS); glaze application + hydrofluoric acid etching (GA); glaze application + hydrofluoric acid etching + silanization (GAS); deposition of silica nanofilm (NF). After treatments, veneering porcelain cylinders (3.3 x 3.3 mm) were built up on all specimens and fired. Then the specimens were subjected to thermal cycling (6000 cycles), and subjected to shear test. Fractures were analyzed by stereomicroscopy and SEM. Data were statistically analyzed by 1-way ANOVA and Tukey's test (5%). Zirconia-porcelain bond strength was affected by the ceramic surface treatments (p=0.0001). GA (19.5±3 MPa) and GAS (16.2±4 MPa) recorded the highest bond strength values, while control group had the lowest bond value (10.1±4 MPa). Adhesive failure of the samples predominated. Therefore, glaze application as 3Y-TZP treatment before veneering porcelain stratification may enhance zirconia-porcelain adhesion.

Influence of the Conditioning Method for Pre-Sintered Zirconia on the Shear Bond Strength of Bilayered Porcelain/Zirconia

This study evaluated the bond strength of veneering porcelain with an experimental conditioner-coated zirconia. Pre-sintered Y-TZP specimens (n = 44) were divided in two groups based on conditioning type. After sintering, all sample surfaces were sandblasted and layered with veneering porcelain. Additionally, half of the specimens in each group underwent thermal cycling (10,000 cycles, 5–55 °C), and all shear bond strengths were measured. After testing, the failure mode of each fractured specimen was determined. Differences were tested by parametric and Fisher’s exact tests (α = 0.05). The differences in bond strength were not statistically significant. Adhesive fractures were dominantly observed for the non-thermal cycled specimens. After thermal cycling, the conditioner-coated group showed cohesive and mixed fractures (p = 0.0021), whereas the uncoated group showed more adhesive fractures (p = 0.0021). Conditioning of the pre-sintered Y-TZP did not change the shear bond strength of the veneering porcelain, but did improve the failure mode after thermal cycling.

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

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

Veneered Zirconia-Based Restorations Fracture Resistance Analysis

PURPOSE

To examine the effects of the veneering technique on the fracture resistance of zirconia-based crowns.

MATERIALS AND METHODS

An artificial tooth was prepared with a 1.2 mm heavy chamfer finish line and 8° taper. The prepared tooth was scanned using CAD/CAM technology to fabricate 45 cobalt chromium (CoCr) testing dies. One CoCr die was scanned, and 45 zirconia copings were milled and divided according to the veneering technique into three groups of 15 specimens each: layering veneering (LV) using Vita Vm9, overpressing veneering (OV) using Vita Pm9, and digital veneering (DV) using Vita Triluxe forte. The crowns were cemented onto the testing dies using glass ionomer cement. The specimens were thermocycled (3000 cycles, 5° to 55°) then statically loaded (3.7 mm ball, 0.5 mm/min crosshead speed) until failure. Failed crowns were inspected using a magnifier, and failure patterns were identified. One-way ANOVA and multiple comparison Bonferroni tests were applied for statistical analysis of the results.

RESULTS

Means and standard deviations of failure loads were 1200 ± 306 N for the LV group, 857 ± 188 N for the OV group, and 638 ± 194 N for the DV group. The differences in failure loads were statistically significant between all groups (p < 0.05). Failure mode was predominantly cohesive for LV and OV groups, whereas it was predominantly adhesive for the DV group.

CONCLUSIONS

The LV group was superior to other groups in terms of fracture resistance, while the DV group was inferior to the other groups in the same aspect.

Effect of Different Firing Temperatures on Structural Changes in Porcelain

PURPOSE

To study the structural changes occurring in the dental porcelain mass fired at various firing temperatures using scanning electron microscopy (SEM) and X-ray diffraction (XRD) spectroscopy. Also, additional tests, namely compressive strength, abrasion resistance analysis, and the amount of oxides released, were conducted at different firing temperatures.

MATERIALS AND METHODS

Six groups (40 specimens in each group) of porcelain mass were prepared. The dimensions and weight of all the specimens were kept constant. The specimens were then heat treated at different firing temperatures (660°C, 760°C, 860°C, 900°C, 960°C, 990°C). Half of the specimens of each group were subjected to a compressive strength test on a universal testing machine and then finely ground using an electrochemical grinder to prepare for XRD analysis. The other half of the specimens was weighed to analyze the amount of oxides released after each firing cycle. Following this, the specimens underwent an abrasion resistance test on a Nanovea Tribometer. The unaltered surface was scanned using SEM. The data (numerical and graphical) for all the tests were recorded and analyzed using one-way ANOVA and post hoc Tukey test.

RESULTS

The specimens fired at 900°C exhibited superior compressive strength and abrasion resistance. The quantity of oxides released by the specimens fired at 900°C was the least compared to specimens heat treated at the other firing temperatures. XRD analysis proved that the oxide released by the porcelain mass was calcium aluminum chromium oxide. Also, the fewer peaks obtained in the XRD graphs of specimens fired at 900°C signified lesser porosities in the porcelain specimens. SEM analysis depicted a homogeneous mass of porcelain at 900°C.

CONCLUSION

All the above findings validate the objective of studying the physical and internal structural changes of dental porcelain when subjected to an increasing firing temperature gradient. The specimens fired at 900°C exhibited superior strength and abrasion resistance. SEM analysis depicted a homogeneous mass of dental porcelain, implying that firing was complete at 900°C.

Effect of Different Surface Treatments on the Bond Strength of Lithium Disilicate Ceramic to the Zirconia Core

OBJECTIVE

The aim of this study was to evaluate the effect of different surface treatments [sandblasting, Erbium:Yttrium-Aluminium-Garnet (Er:YAG), and femtosecond lasers] on the shear bond strength (SBS) of the CAD-on technique.

BACKGROUND DATA

Although demand for all-ceramic restorations has increased, chipping remains one of the major problems for zirconia-based restorations.

MATERIALS AND METHODS

Forty yttrium-stabilized tetragonal zirconia polycrystalline (Y-TZP) zirconia plates (IPS e.max ZirCAD, Ivoclar Vivadent) were cut, sintered (12.4 × 11.4 × 3 mm) and divided into four groups according to the surface treatments (n = 10): a control group with no surface treatment (Group C), sandblasting with 50 μm Al2O3 (Group S), Er:YAG laser irradiation (Group E), and femtosecond laser irradiation (Group F). Also, 40 cylindrical (5 mm diameter, 2 mm height) lithium disilicate (IPS e.max CAD) veneer ceramics were cut and fused to all zirconia cores by a glass-fusion ceramic and crystallized according to the CAD-on technique. Specimens were subjected to shear force using a universal testing machine. The load was applied at a crosshead speed of 0.5 mm/min until failure. Mean SBS (MPa) were analyzed with one way ANOVA (p < 0.05). The failed specimens were examined under a stereomicroscope at ×20 to classify the mode of failure.

RESULTS

The highest SBS was observed in Group F (36 ± 3.31 MPa), followed by Group S (33.03 ± 5.05 MPa), and Group C (32.52 ± 10.15 MPa). The lowest SBS was observed in Group E (31.02 ± 4.96 MPa), but no significant differences were found between the control and surface treated groups (p = 0.377). All the specimens showed a mixed type of failure.

CONCLUSIONS

Femtosecond laser application increased the bond strength between zirconia-veneer specimens. However, the novel CAD-on technique with no surface treatment also showed high bonding strength. Thus, this technique could prevent ceramic chipping without additional surface treatments.

Modified maximum tangential stress criterion for fracture behavior of zirconia/veneer interfaces

The veneering porcelain sintered on zirconia is widely used in dental prostheses, but repeated mechanical loadings may cause a fracture such as edge chipping or delamination. In order to predict the crack initiation angle and fracture toughness of zirconia/veneer bi-layered components subjected to mixed mode loadings, the accuracy of a new and traditional fracture criteria are investigated. A modified maximum tangential stress criterion considering the effect of T-stress and critical distance theory is introduced, and compared to three traditional fracture criteria. Comparisons to the recently published fracture test data show that the traditional fracture criteria are not able to properly predict the fracture initiation conditions in zirconia/veneer bi-material joints. The modified maximum tangential stress criterion provides more accurate predictions of the experimental results than the traditional fracture criteria.

Influence of Different Post-Plasma Treatment Storage Conditions on the Shear Bond Strength of Veneering Porcelain to Zirconia

This in vitro study investigated whether different storage conditions of plasma-treated zirconia specimens affect the shear bond strength of veneering porcelain. Zirconia plates were treated with a non-thermal atmospheric argon plasma (200 W, 600 s). Porcelain veneering (2.38 mm in diameter) was performed immediately (P-I) or after 24 h storage in water (P-W) or air (P-A) on the treated surfaces (n = 10). Untreated plates were used as the control. Each group was further divided into two subgroups according to the application of a ceramic liner. All veneered specimens underwent a shear bond strength (SBS) test. In the X-ray photoelectron spectroscopy (XPS) analysis, the oxygen/carbon ratios of the plasma-treated groups increased in comparison with those of the control group. When a liner was not used, the three plasma-treated groups showed significantly higher SBS values than the control group (p < 0.001), although group P-A exhibited a significantly lower value than the other two groups (p < 0.05). The liner application negatively affected bonding in groups P-I and P-W (p < 0.05). When the veneering step was delayed after plasma treatment of zirconia, storage of the specimens in water was effective in maintaining the cleaned surfaces for optimal bonding with the veneering porcelain.

Evaluation of shear bond strength of veneering ceramics and zirconia fabricated by the digital veneering method

PURPOSE

The purpose of this study was to evaluate the shear bond strength (SBS) of veneering ceramic and zirconia fabricated by the digital veneering method.

METHODS

A total of 50 specimens were fabricated, i.e., 10 specimens each for the metal-ceramic (control) group and the four zirconia groups. The zirconia groups comprised specimens fabricated by the digital veneering method, the heat pressing method, and hand layering method for two groups, respectively. Furthermore, the shear bond strength was measured with a universal testing machine (Model 3345, Instron, Canton, MA, USA) and statistically analyzed using one-way ANOVA set at a significance level of P<0.05. The corresponding mode of failure was determined from Scanning Electron Microscope (FESEM JSM 6701F, Jeol Ltd., Japan) observations.

RESULTS

One-way analysis of variance (ANOVA) revealed that the metal-ceramic group had the highest SBS (43.62MPa), followed by the digital veneering method (28.29MPa), the heat pressing method (18.89MPa), and the layering method (18.65, 17.21MPa). The samples fabricated by digital veneering had a significantly higher SBS than the other zirconia samples (P<0.05). All of the samples exhibited mixed failure.

CONCLUSIONS

Veneering ceramic with a zirconia core that was fabricated via the digital veneering method is believed to be effective in clinical use since, its shear bond strength is significantly higher than that resulting from the conventional method.