Optimal sandblasting conditions for conventional-type yttria-stabilized tetragonal zirconia polycrystals

Effects of different plasma treatments on bonding properties of zirconia

This in vitro study was to evaluate the effect of different non-thermal atmospheric pressure plasma (NTP) on shear bond strength (SBS) between yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) and self-adhesive resin cement. In this study, The Y-TZP specimens were divided into 4 groups according to the surface treatment methods as follows: Control (no surface treatment), Sb (Sandblasting), AP(argon NTP), and CP(20 % oxygen and 80 % argon combination NTP). Y-TZP specimens were randomly selected from each group to observe and test the following indexes: scanning electron microscope to observe the surface morphology; atomic force microscope to detect the surface roughness; contact angle detector to detect the surface contact angle; energy spectrometer to analyze the surface elements. Then, resin cement (Rely X-U200) was bonded to human isolated teeth with Y-TZP specimens to measure SBS. The results showed that for the SE test, the NTP group was significantly higher than the control group (p < 0.05). The results of the SBS test showed that the SBS values of the NTP group were significantly higher than those of the other groups, regardless of the plasma treatment (p < 0.05). However, there was no significant difference between groups AP and CP in a test of SBS (p > 0.05). This study shows that non-thermal atmospheric pressure plasma can improve the shear bond strength of Y-TZP by increasing the surface energy. The addition of oxygen ratio to argon is more favorable to increase the shear bond strength and is worth further investigation.

Effect of femtosecond laser induced surface patterns on the flexural strength of monolithic zirconia

To investigate how patterns generated by femtosecond (fs) laser and femtosecond laser power affect the surface roughness (Ra) and biaxial flexural strength (BFS) of monolithic zirconia. Eighty disk-shaped zirconia specimens were divided into eight subgroups (n = 10): Control (C), airborne-particle abrasion (APA), 400 mW fs laser (spiral [SP(400)], square [SQ(400)], circular [CI(400)]), and 700 mW fs laser ([SP(700)], [SQ(700)], [CI(700)]). Ra values were calculated by using a surface profilometer. One additional specimen per group was analyzed with scanning electron microscopy and x-ray diffractometry. BFS values were obtained by using the piston-on-3-ball test. One-way ANOVA and either Tukey's HSD (BFS) or Tamhane's T2 (Ra) tests were used to evaluate data (α = 0.05). Regardless of the pattern and power, fs laser groups had higher Ra than C and APA, while SP groups had lower Ra than CI and SQ groups (p ≤ 0.004). For each pattern, Ra increased with higher laser power (p < 0.001), while the laser power did not affect the BFS (p ≥ 0.793). CI and SQ groups had lower BFS than the other groups (p ≤ 0.040), whereas SP groups had similar BFS to C and APA (p ≥ 0.430). Fs laser microstructuring with spiral surface pattern increased the Ra without jeopardizing the BFS of zirconia. Thus, this treatment might be an option to roughen tested zirconia.

Flexural Strength and Morphological Study of Different Multilayer Zirconia Dental Materials

Nowadays, yttria (Y3+)-stabilized ZrO2 (Y-TZP) is the most commonly used material in dental prosthetics. Y-TZP dental ceramics are mainly stabilized via the addition of 3 mol% yttrium oxide (Y2O3). These ceramics exhibit excellent mechanical properties, including high flexural strength, fracture toughness, elastic modulus, etc. Some manufacturers have recently introduced a new class of dental materials with multilayer composition with the aim of combining the advantages of adding more or less Y2O3 to the ceramic composition in one Y-TZP material. The flexural strength values of multilayer Y-TZP may vary depending on the dimensions of the specimen, layer distributions, and especially the layer exposed on the maximum tension side, i.e., loading configuration. Although previous studies have examined the flexural strength of separate Y-TZP layers, capturing the flexural strength of multilayer Y-TZP is still challenging. However, one should keep in mind that multilayer flexural strength is important for clinical indications. The objective of this study is to compare the flexural strength of three distinct multilayer translucent Y-TZP materials made up of layers with different Y3+ contents. Rectangular samples (2 mm × 2 mm × 16 mm) were prepared from CAD/CAM discs using the milling machine Programill PM7 (Ivoclar Vivadent AG). Milled bars were tested for flexural strength in a three-point bending test (ISO 6872:2015) using a universal testing machine (Inspekt Duo 5kN; Hegewald & Peschke, Nossen, Germany) at a crosshead speed of 0.5 mm/min. Representative samples of each type of material were selected for quantitative and qualitative analysis of the microstructure. Representative samples of each type of material were selected for structural, mechanical, and microstructural analyses.

Optimization of surface roughness, phase transformation and shear bond strength in sandblasting process of YTZP using statistical machine learning

Sandblasting process is often applied to roughen the intaglio of yttria tetragonal zirconia polycrystals (YTZP) surfaces for easy and quality adhesion and micro-shear retention with dentine/resin cements. Sandblasting process parameters have shown to influence, at different scales, surface roughness, phase transformation and shear bond strength, all of which are referred, herein, as performance characteristics. This study aimed to find the parametric settings of sandblasting parameters that could simultaneously optimize these performance characteristics, hypothetically testing the probability. YTZP surfaces were sandblasted at different levels of incidence angle (IA), abrasive particle size (AP), pressure(P) and sandblasting time (ST) following the Taguchi method based on the two-level parametric process settings (L8(27)). Surface morphologies, roughness (SR), monoclinic content (MC), and shear bond strength (SS) were characterized by the SEM, average surface roughness, XRD, and shear bond strength tests, respectively. Rough surfaces containing scratches, plastic deformation streaks, micro cracks and pitting were observed. According to the Taguchi method, the same optimum sandblasting parametric setting maximized SR and MC but failed to maximize SS. Subsequently, the principal component analysis embedded in statistical machine learning was applied to find the optimum sandblasting parametric setting that maximized all the performance characteristics. The optimum sandblasting setting of IA = 45°, AP = 110 μm, ST = 20 s and P = 400 kPa predicted the maximum values of SR = 0.773 μm, MC = 36% and SS = 16.6 MPa. Analysis of variance confirmed AP and P as the most influencing parameters affecting all performance characteristics. Finally, these results provide a systematic and comprehensive route for optimizing sandblasting roughening of YTZP surfaces which can be adopted in adhesive dental and orthodontic industry.

Evaluation of mechanical properties of dental zirconia in different milling conditions and sintering temperatures

STATEMENT OF PROBLEM

The dry processing of zirconia has the disadvantage of dust dispersal during milling; thus, wet milling may be preferable. However, research on the mechanical properties of dental zirconia milled under different conditions and sintered at different temperatures is lacking.

PURPOSE

The purpose of this in vitro study was to evaluate changes in the mechanical properties of zirconia specimens after milling under dry and wet conditions at different sintering temperatures.

MATERIAL AND METHODS

Four hundred Ø20.0×1.5-mm presintered zirconia specimens were prepared by using a computer-aided design and computer-aided manufacturing (CAD-CAM) system and divided into 8 groups (n=50) based on the sintering (1230, 1330, 1430, and 1530 °C) and milling conditions (dry or wet). The mechanical properties (Vickers hardness, biaxial flexural strength, and fracture toughness) and physical properties (linear shrinkage and density) were examined. The microstructures of the specimens were observed with a scanning electron microscope. The crystal phases of the sintered green bodies were analyzed by using an X-ray diffractometer. The data were analyzed with descriptive statistics and 1-way and 2-way analyses of variance with Tukey HSD tests (α=.05).

RESULTS

The mechanical properties of all specimens increased with increasing sintering temperature, except for 1530 °C and the dry milling condition. The mechanical properties of the groups fabricated under wet milling conditions were better than those of the groups fabricated under dry milling conditions. Microscopic examination of the structure showed that the porosity decreased with increasing sintering temperature regardless of the milling conditions.

CONCLUSIONS

Higher sintering temperatures increased the mechanical properties (biaxial flexural strength, Vickers hardness, fracture toughness). However, phase transformation from tetragonal to cubic was observed for dry milled specimens sintered at 1530 °C, with decreased mechanical properties. Specimens fabricated by wet milling exhibited better mechanical properties than those fabricated by dry milling.

The effect of surface treatment and low-temperature degradation on flexural strength of additive manufactured zirconia

This study aimed to assess the effect of low-temperature degradation (LTD) and surface treatment on the flexural strength of additive-manufactured (AM) zirconia by comparison to subtractive-manufactured (SM) zirconia. Disc-shaped zirconia specimens were fabricated using AM and SM technology, and each group was assigned to 3 subgroups according to the type of surface treatment: control, sandblasting (SB), and 9% hydrofluoric acid etching (HF). The groups were then further divided into 2 subgroups: unaged and aged. Biaxial flexural strength, crystal phase, surface topography, and surface roughness were measured to evaluate the mechanical properties. Statistical analyses were performed with 3-way ANOVA, followed by the comparison of means with Bonferroni post hoc analyses. The means and standard deviations of the biaxial flexural strength and Weibull parameters were calculated with descriptive statistics. All SM groups showed significantly greater flexural strength than the AM groups (p < .05), and LTD did not affect flexural strength except for the SMHF group (p < .05). After LTD, monoclinic phases (m-phase) were found in all groups, and SEM images showed grain pullout due to zirconia volume expansion in both control groups. Sandblasting significantly affected flexural strength (p < .05), whereas the HF group did not affect flexural strength except in the SMHF group after LTD (p < .05). No significant difference was observed in the surface roughness of AM compared to SM groups conditioned with the same surface treatment regardless of LTD. AM zirconia has comparable mechanical properties to SM zirconia, regardless of low-temperature degradation and surface treatment, which indicates the potential of the AM technique for clinical applications.

Improving Bond Strength of Translucent Zirconia Through Surface Treatment With SiO2-ZrO2 Coatings

BACKGROUND

Translucent monolithic zirconia ceramics have been applied in dental clinics due to their esthetic translucent formulations and mechanical properties. Considering inherent ceramic brittleness, adhesive bonding with resin composite increases the fracture resistance of ceramic restorations. However, zirconia is a chemically stable material that is difficult to adhesively bond with resin.

OBJECTIVES

To investigate the influences of SiO2-ZrO2 coatings on adhesive bonding of zirconia and the surface characterization of those coatings.

METHODS AND MATERIALS

Translucent zirconia discs were classified into groups based on surface treatments: CT (control), SB (sandblasting), C21(SiO2:ZrO2=2:1), C11(SiO2:ZrO2=1:1), and C12 (SiO2:ZrO2=1:2) (n=10). Surface characterization of coatings on zirconia were analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), surface roughness assessment (Ra), X-ray diffraction (XRD), water contact angle (WCA), translucency parameter (TP), and shear bond strength (SBS). Two-way ANOVA for shear bond strength results and ANOVA for Ra and WCA were performed.

RESULTS

SEM images revealed SiO2 islands on zirconia disks coated with SiO2-ZrO2. Surface roughness of C12, C11, and C21 groups was significantly larger than those of groups SB and CT (p<0.05). XRD results showed that phase transformation of zirconia disks was detected only in the SB group. In addition, SiO2-ZrO2 coatings reduced WCA. The translucency decreased only in group C21. Group C11 showed the highest shear bond strength under both aging conditions.

CONCLUSION

SiO2-ZrO2 coating is a promising method to enhance the adhesive resin bonding of translucent zirconia without causing phase transformation of translucent zirconia.

Effect of surface topography and wettability on shear bond strength of Y-TZP ceramic

Zirconia ceramics have been widely used as dental restorations due to their esthetic appearance and high flexural strength. The bonding of zirconia with resin cement should rely on both mechanical and chemical bonds. This study was performed to investigate the effect of zirconia surface topography and its wettability after surface pretreatments on the microshear bond strength (μSBS) of a resin cement. Zirconia slabs were prepared and randomly divided into 5 groups based on the surface treatment as follows: no treatment (control), air abrasion (AB), etching with hydrofluoric acid (F), the mixture of hydrofluoric acid and nitric acid (FN), or the mixture of hydrochloric acid and nitric acid (CN) for 10 min. The specimens were subjected to investigation of surface roughness characteristics [average roughness (Ra), peak-to-valley average distance (Rpv), skewness (Rsk), and kurtosis (Rku)] using atomic force microscopy (AFM) and measurements of surface contact angle (θc) and μSBS of a resin cement. In addition, the area % of the nanoscale surface irregularity (nSI%) was calculated from the AFM images. The effects of nSI%, Ra and θc on the μSBS were analyzed by multiple linear regression analysis (p < 0.05). Multiple regression analysis revealed that the nSI% was the most predominant factor for the μSBS (p < 0.001). A surface with larger nSI%, higher Ra and relatively lower θc was essential for establishing a reliable resin-zirconia bond.

Translucent multi-layered zirconia: Sandblasting effect on optical and mechanical properties

OBJECTIVE

The aim of this study was to evaluate the influence of the sandblasting treatment on the microstructure, optical and mechanical properties of multi-layered translucent zirconia.

METHODS

Samples of yttria-stabilized zirconia were prepared by stratifying four layers (L1, L2, L3 and L4) of ML-type KATANA multi-layered monolithic discs, whose surfaces were then sandblasted with alumina particles (110 µm and 0.2 MPa) in order to evaluate its effect on the presence of different crystalline phases as well as on the optical and mechanical properties of each of the four layers. The optical characterization was carried out by measuring the reflectance spectrum and colorimetric parameters by UV-Vis spectrophotometric analysis and the transmittance curves were indirectly obtained using the Kubelka-Munk model (KM). Microstructural, structural, mechanical and roughness characterizations were also performed using SEM, XRD, biaxial flexural strength B3B, and light interferometry, respectively RESULTS: According to the KM model there are different degrees of translucency between the upper and lower layers of the monolithic discs, but there was no influence of the Al2O3-sandblasting treatment on this optical property. The disk pigmentation causes greater absorption of light below 600 nm, decreasing the transmittance rate to values below 25% in this region of the spectrum. The yellowing index presented higher values for inner disk layers L3 and L4, in agreement with the highest values of the light absorption coefficient K observed for these layers. The roughness of the samples did not change significantly with the surface treatment performed and the sandblasting did not result in new crystalline phases. SEM analysis showed the presence of different grain sizes in all layers analyzed, being related to the co-occurring presence of cubic (c-ZrO2) and tetragonal (t-ZrO2) phases in similar contents (∼ 50 wt%). The Weibull statistical analysis, in turn, showed an increase in the Weibull characteristic stress value (σ0) for most layers subjected to sandblasting, except for the second layer (central region of the disk). It was also verified an increase in the value of the structural reliability of the material (m), referring to the samples of the central region of the disc (L2 and L3 layers) after sandblasting.

SIGNIFICANCE

The pigmentation in the disk causes a decrease of the transmittance rate to values well below 25% in the region of the spectrum 400-600 nm and the inner layers (L3 and L4) have even lower transmittance than the outer layers in this spectrum range. Although the CR index indicates variation related to the Al2O3-sandblasting treatment, the transmittance spectra of KM model show that the sandblasting did not cause a significant change in the transmittance rate of the four analyzed layers. Also, there is no significant difference in the light scattering of the different layers of the disc, either before or after Al2O3-sandblasting treatment.

The Shear Bond Strength of Resin-Based Luting Cement to Zirconia Ceramics after Different Surface Treatments

Due to its unique properties, zirconia is increasingly being used in dentistry, but surface preparation for bonding is difficult because of its polycrystalline structure. This study aimed to determine the effect of a new etching technique (Zircos-E) on Ceramill Zi (Amann Girrbach). The effect of etching and the use of primers (Monobond Plus and MKZ Primer) on the bond strength of zirconia with resin cement (NX3) was assessed. Shear bond strength was evaluated after storage in water for 24 h and after thermal aging (5000 thermocycling at 5 °C/55 °C). A scanning electron microscope (Hitachi S-4700) was used to evaluate the surface structure before and after the Zircos-E system. The roughness parameters were assessed using an SJ-410 profilometer. The etched zirconia surface is more homogeneous over the entire surface, but some localized forms of erosion exist. The etching of zirconia ceramics caused changes in the surface structure of zirconia and a significant increase in the shear bond strength between zirconia and resin cement. The use of primers positively affects the adhesion between resin cement and zirconia. Aging with thermocycler significantly reduced the shear bond strength, with one exception-sandblasted samples with MKZ Primer. Standard ceramic surface preparation, involving only alumina sandblasting, does not provide a satisfactory bond. The use of etching with the Zircos-E system and primers had a positive effect on the strength of the zirconium-resin cement connection.

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.

Mechanical properties of additively manufactured zirconia with alumina air abrasion surface treatment

This study aimed to evaluate the mechanical properties of zirconia fabricated using additive manufacturing technology and compare them to those of zirconia fabricated using subtractive manufacturing technology. Sixty disc-shaped specimens were fabricated for the additive (n = 30) and subtractive manufacturing groups (n = 30), and each group was divided into two subgroups according to their air-abrasion surface treatment: control (n = 15) and air-abrasion groups (n = 15). Mechanical properties including the flexural strength (FS), Vickers hardness, and surface roughness were determined, and the values were analyzed by one-way ANOVA and Tukey's post hoc test (α = 0.05). X-ray diffraction and scanning electron microscopy were used for phase analysis and surface topography evaluation, respectively. The SMA group exhibited the highest FS (1144.97 ± 168.1 MPa), followed by the SMC (944.58 ± 141.38 MPa), AMA (905.02 ± 111.38 MPa), and AMC groups (763.55 ± 68.69 MPa). The Weibull distribution showed the highest scale value (1213.55 MPa) in the SMA group, with the highest shape value in the AMA group (11.69). A monoclinic peak was not detected in both the AMC and SMC groups, but after air abrasion, the monoclinic phase content ([Formula: see text]) reached 9% in the AMA group, exceeding that in the SMA group (7%). The AM groups exhibited statistically lower FS values than those of the SM groups under the same surface treatment (p < 0.05). Air-abrasion surface treatment increased the monoclinic phase content and FS (p < 0.05) in both the additive and subtractive groups, while it increased the surface roughness (p < 0.05) only in the additive group and did not affect the Vickers hardness in either group. For zirconia manufactured using additive technology, the mechanical properties are comparable to those of zirconia manufactured using subtractive technology.

An Overview of the Latest Progress in Internal Surface Finishing of the Additively Manufactured Metallic Components

Fast progress in near-net-shape production of parts has attracted vast interest in internal surface finishing. Interest in designing a modern finishing machine to cover the different shapes of workpieces with different materials has risen recently, and the current state of technology cannot satisfy the high requirements for finishing internal channels in metal-additive-manufactured parts. Therefore, in this work, an effort has been made to close the current gaps. This literature review aims to trace the development of different non-traditional internal surface finishing methods. For this reason, attention is focused on the working principles, capabilities, and limitations of the most applicable processes, such as internal magnetic abrasive finishing, abrasive flow machining, fluidized bed machining, cavitation abrasive finishing, and electrochemical machining. Thereafter, a comparison is presented based on which models were surveyed in detail, with particular attention to their specifications and methods. The assessment is measured by seven key features, with two selected methods deciding their value for a proper hybrid machine.

The Effect of Surface Treatments on Zirconia Bond Strength and Durability

To evaluate the effects of airborne particle abrasion (APA) combined with MDP-containing resin cement, a glass-ceramic spray deposition (GCSD) method on the shear bond strengths (SBSs) and durability of 3 mol% yttrium oxide-stabilized zirconia ceramic (3Y-TZP) compared with lithium disilicate glass ceramics (LDGC). 3Y-TZP disks were randomly treated as follows: for Group APA+MDP, 3Y-TZP was abrased using 50 μm Al₂O₃ particles under 0.1 Mpa and bonded with MDP-containing resin cement; for Group GCSD, 3Y-TZP was treated with the GCSD method, etched by 5% HF for 90 s, silanized and bonded with resin cement without MDP. Group LDGC was bonded as the Group GCSD. X-ray diffraction (XRD), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy dispersive X-ray detector (EDX) were used to analyze the surface chemical and micro-morphological changes of the ceramics before bonding. The bonded ceramic specimens were randomly divided into subgroups, and the SBSs were determined before and after 10,000 thermocycling. The SBSs were analyzed with a one-way ANOVA analysis. Failure modes were determined with optical microscopy and SEM. The XRD, ATR-FTIR and XPS results identified the formation of lithium disilicate and zirconium silicate on 3Y-TZP after GCSD. The SEM micrographs revealed that 3Y-TZP surfaces were roughened by APA, while 3Y-TZP with GCSD and LDGC surfaces could be etched by HF to be porous. The APA treatment combined with MDP-containing resin cement produced the high immediate zirconia shear bond strengths (SBSs: 37.41 ± 13.51 Mpa) that was similar to the SBSs of the LDGC (34.87 ± 11.02 Mpa, p > 0.05), but, after thermocycling, the former dramatically decreased (24.00 ± 6.86 Mpa, maximum reduction by 35.85%) and the latter exhibited the highest SBSs (30.72 ± 7.97 Mpa, minimum reduction by 11.9%). The 3Y-TZP with GCSD treatment displayed the lower zirconia SBSs before thermocycling (27.03 ± 9.76 Mpa, p < 0.05), but it was similar to the 3Y-TZP treated with APA and MDP containing resin cement after thermocycling (21.84 ± 7.03 vs. 24.00 ± 6.86 Mpa, p > 0.05). The APA combined with MDP-containing resin cement could achieve the high immediate zirconia SBSs of those of the LDGC, but it decreased significantly after thermocycling. The GCSD technique could yield the immediate zirconia SBSs similar to those of LDGC before thermocycling, and long-term zirconia SBSs were similar to those of 3Y-TZP treated with APA followed by MDP-containing resin cement after thermocycling. Hence, the GCSD technique could enrich zirconia surface treatments and is an alternative to zirconia surface pretreatment for 3Y-TZP bond durability.

Effects of Particle Abrasion Media and Pressure on Flexural Strength and Bond Strength of Zirconia

OBJECTIVES

To compare the effects of particle abrasion medium and pressure on shear bond strength and biaxial flexural strength of three generations of zirconia (Lava Frame, Lava Plus, and Lava Esthetic) with the goal of optimizing the bond to zirconia.

METHODS

280 discs (14 mm diameter; 1 mm thickness) of each zirconia were milled and sintered. Specimens of each material were randomly distributed into 14 groups (n=20); half were tested for shear bond strength and half were tested for biaxial flexural strength. The specimens were particle abraded on one surface by 2 different media (50 μm alumina particles or 50 μm glass beads) for 10 seconds at three different pressures (15, 30, and 45 psi or 0.1, 0.2, 0.3 MPa). Untreated specimens served as positive control. A tube (1.50 mm diameter) filled with dual cured resin cement (Panavia SA) was placed onto the surface and light cured. Specimens were stored in water (37°C for 24 hours) and shear bond strength was measured in a universal testing machine (Instron). Biaxial flexural strength of each specimen was measured according to ISO 6872. Shear bond strength and biaxial flexural strength were compared individually with a 2-way analysis of variance (ANOVA) for factors surface treatment and zirconia composition.

RESULTS

Significant differences were seen between surface treatments (p<0.01), zirconia composition (p<0.01) and their interaction (p<0.01) for both bond strength and flexural strength. With alumina particle abrasion, higher pressure produced higher bonds for Lava Frame and Lava Plus zirconia while the bond of Lava Esthetic declined with increased pressure. Higher pressure (>0.2 MPa or 30 psi) with alumina decreased biaxial flexural strength with Lava Esthetic zirconia.

CONCLUSIONS

Particle abrasion with alumina produced a significantly better combination of bond strength while maintaining biaxial strength of three zirconia materials than particle abrasion with glass beads. The bond strength also depended upon the pressure of particle abrasion and the generation of zirconia used.

The Effect of Clinical Sandblasting With Different Powders on the Surface Roughness of Cores for Metal-Ceramic Crowns and Their Fracture Resistance After the Addition of Repair Material: An In-Vitro Study

Background One of the most frequently encountered issues with metal-ceramic restorations is the fracture of veneering porcelain. This in-vitro study aims to evaluate the effect of clinical sandblasting with 50 μm aluminum oxide and 30 μm silica-coated particles on the surface roughness of metal cores and the subsequent effect on their fracture resistance after the addition of specific adhesive and packable composite as a repair material. Methodology Metal cores (n = 21) were digitally designed and three-dimensionally printed by selective laser melting (SLM) technique. These cores were randomly divided into three groups. Group A (n = 8) was sandblasted with 50 μm aluminum oxide and veneered with light cure composite. Group B (n = 8) was sandblasted with 30 μm silica-coated particles and veneered with light cure composite. Group C control group (n = 5) was sandblasted in the laboratory with 250 μm aluminum oxide and veneered with porcelain. All specimens were tested for surface roughness by a stylus profilometer. After adding the veneering material, all specimens were subjected to a fracture resistance test through a universal testing machine. Results One-way analysis of variance test showed a significantly higher difference for the specimens sandblasted in the laboratory using 250 μm aluminum oxide. Fracture resistance values showed no significant difference between groups A and B. Conclusions Groups A and B showed no significant difference in surface roughness, but their fracture resistance values were above the acceptable clinical limit. Despite the rough nature of metal cores fabricated by the SLM technique, sandblasting with silica-coated particles may be an effective way to optimize the fracture resistance of the repair material because it provides the basis for chemical adhesion.

Effect of surface treatments on biaxial flexural strength, fatigue resistance, and fracture toughness of high versus low translucency zirconia

BACKGROUND

Mechanical surface treatments can deteriorate the mechanical properties of zirconia. This study evaluated and compared the biaxial flexural strength, fracture toughness, and fatigue resistance of high translucency (HT) to low translucency (LT) zirconia after various mechanical surface treatments.

METHODS

Four hundred eighty zirconia discs were prepared by milling and sintering two HT (Katana and BruxZir) and LT (Cercon and Lava) zirconia blocks at targeted dimensions of 12 mm diameter × 1.2 mm thickness. Sintered zirconia discs received one of the following surface treatments: low-pressure airborne particle abrasion (APA) using 50 µm alumina particles, grinding using 400 grit silicon carbide paper, while as-sintered specimens served as control. Internal structure and surface roughness were evaluated by scanning electron microscope (SEM) and a non-contact laser profilometer, respectively. Half of the discs were tested for initial biaxial flexural strength, while the rest was subjected to 10⁶ cyclic fatigue loadings, followed by measuring the residual biaxial flexural strength. Fractured surfaces were examined for critical size defects (c) using SEM to calculate the fracture toughness (K_IC). The effect of surface treatments, zirconia type, and cyclic fatigue on the biaxial flexural strength was statistically analyzed using three-way analysis of variance (ANOVA) and Tukey HSD post hoc tests (α = 0.05). Weibull analysis was done to evaluate the reliability of the flexural strength for different materials.

RESULTS

The initial biaxial flexural strength of LT zirconia was significantly higher (p < 0.001) than that of HT zirconia in all groups. While low APA significantly increased the biaxial flexural strength of LT zirconia, no significant change was observed for HT zirconia except for Katana. Surface grinding and cyclic fatigue significantly reduced the flexural strength of all groups. High translucency zirconia reported higher fracture toughness, yet with lower Weibull moduli, compared to LT zirconia.

CONCLUSION

LT zirconia has higher biaxial flexural strength, yet with lower fracture toughness and fatigue resistance, compared to HT zirconia. Low-pressure APA has significantly increased the biaxial flexural strength in all zirconia groups except BruxZir. Grinding was deteriorating to biaxial flexural strength and fracture toughness in all zirconia types. Cyclic fatigue has significantly decreased the biaxial flexural strength and reliability of HT and LT zirconia.

Fracture analysis of one/two-piece clinically failed zirconia dental implants

OBJECTIVES

Analyzing factors that may have led to fracture of zirconia implants by macro/micro-fractography.

METHODS

Six one-piece and ten two-piece full-ceramic zirconia implants from two manufacturers, Z-Systems and CeraRoot, were retrieved after clinical failure. The time-to-failure ranged from 3 to 49 months. Optical and scanning electron microscopy (SEM) were used to analyze the fracture planes at the macro- and microscopic level. Treatment planning, surgical protocol, fracture-origin location and characteristic fracture features were assessed.

RESULTS

The fracture of all implants seemed to have been primarily due to overload in bending mode, while the fracture-initiation sites varied for the one- and two-piece implants. The fracture of all one-piece implants originated in the constriction region between two threads in the endosseous implant part. For two-piece implants, the abutment neck, internal abutment-implant connections and inner threads were found to be the main fracture-initiation sites. Surface defects at the root area for one-piece implants and damages at the abutment surface for two-piece implants were connected to the fracture origins. Importantly, the clinical failures of implants were often found to result from combined effects related to patient aspects, treatment planning/protocols, a high bending moment at the weakest link, implant-surface conditions and specific implant designs.

SIGNIFICANCE

This study provided information to be considered for future optimization of treatment planning and the surgical protocol for zirconia implants. Optimization of the surface conditions and the zirconia-starting powder were also suggested.

Adhesive Cementation of Zirconia Based Ceramics-Surface Modification Methods Literature Review

Introduction: The conditioning procedures for glass-based ceramic restorations before adhesive cementation are generally recognized. In the case of polycrystalline ceramics, which include zirconium oxide, there is still no standardized protocol. The aim of this work was to present conditioning methods of the cementation surface of zirconium oxide fixed dentures. The new generation high translucency zirconia has been also considered. Material and method: The following keywords for the PUBMED and EMBASE databases were used: zirconium oxide, zirconium oxide with increased translucency, bond strength, bending strength, surface treatment. The inclusion criteria were original papers in English published between 2015–2021. Results: Out of 1537 publications, 53 articles were selected for the study, covering methods of conditioning zirconium ceramics, including new materials with increased translucency. These procedures were divided into 5 main groups. Summary: Due to the widespread use of zirconia ceramics and the introduction of new zirconia-based materials, the use of a predictable and standardized cementation protocol is one of the most important factors contributing to the long-term clinical success of prosthetic restorations. Therefore, the research showed differences in the properties of the covered materials after conditioning. It suggests the need to create separate conditioning protocols for highly translucent and traditional zirconia.

The effect of nonthermal argon plasma surface treatment on the fracture resistance of monolithic zirconia restorations containing tetragonal and cubic grains

PURPOSE

The aim of this study was to investigate the effect of nonthermal argon plasma (NP) surface treatment on the fracture resistance of monolithic zirconia restorations with different microstructures.

METHODS

Twenty restorations were prepared from each of two tetragonal and two cubic zirconia materials (80 restorations in total). The restorations were then divided into two subgroups (n = 10) for each material according to the surface treatment applied: air abrasion or NP. The surface topography of the treated groups was examined using a scanning electron microscope. All restorations were fixed to metal dies with resin cement, subjected to thermal cycling, and then underwent fracture resistance testing with a universal testing device. Two-way ANOVA and Bonferroni tests were used for statistical analysis of the data (α = 0.05).

RESULTS

The type of surface treatment and the type of zirconia material were shown to significantly affect the fracture resistance of the restorations. The air-abraded groups showed significantly higher fracture resistance (N) than the NP groups (P < 0.001).

CONCLUSION

The results of this study suggest that air abrasion surface treatment has a more favorable effect on the fracture resistance of tetragonal and cubic zirconia restorations than NP surface treatment.

Resin Cement-Zirconia Bond Strengthening by Exposure to Low-Temperature Atmospheric Pressure Multi-Gas Plasma

The purpose of this study was to investigate the effect of gas species used for low-temperature atmospheric pressure plasma surface treatment, using various gas species and different treatment times, on zirconia surface state and the bond strength between zirconia and dental resin cement. Three groups of zirconia specimens with different surface treatments were prepared as follows: untreated group, alumina sandblasting treatment group, and plasma treatment group. Nitrogen (N₂), carbon dioxide (CO₂), oxygen (O₂), argon (Ar), and air were employed for plasma irradiation. The bond strength between each zirconia specimen and resin cement was compared using a tension test. The effect of the gas species for plasma irradiation on the zirconia surface was investigated using a contact angle meter, an optical interferometer, an X-ray diffractometer, and X-ray photoelectric spectroscopy. Plasma irradiation increased the wettability and decreased the carbon contamination on the zirconia surface, whereas it did not affect the surface topography and crystalline phase. The bond strength varied depending on the gas species and irradiation time. Plasma treatment with N₂ gas significantly increased bond strength compared to the untreated group and showed a high bond strength equivalent to that of the sandblasting treatment group. The removal of carbon contamination from the zirconia surface and an increase in the percentage of Zr-O₂ on the zirconia surface by plasma irradiation might increase bond strength.

Effects of Different Air Particle Abrasion Protocols on the Biaxial Flexural Strength and Fractography of High/Ultra-Translucent Zirconia

In this study, the biaxial flexural strength (BFS) and fractography of high/ultra-translucent monolithic zirconia ceramics subjected to different mechanical surface pretreatments were evaluated. A total of 108 disc-shaped samples (12 mm diameter, 1.2 mm thickness) of three zirconia materials (5Y-ZP KATANA Zirconia UTML (ML), 3Y-TZP DD Bio ZX2 (DB), and 5Y-ZP DD cube X2 (DC)) were used. The BFS was investigated after subjecting the samples to surface treatment using air abrasion particles of two types (aluminum oxide or glass microbeads). The data were analyzed using two-way analysis of variance, followed by Scheffe's post hoc test for multiple comparisons. The mean ± standard deviation BFS for DB was highest after treatment with 50 µm Al₂O₃ (1626.05 ± 31.9 MPa), with lower values being observed following treatment with 50 µm glass microbeads (1399.53 ± 24.2 MPa) and in the control sample (1198.51 ± 21.1 MPa). The mean ± standard deviation (SD) BFSs for DC and ML were the highest in the control groups. Surface air abrasion with 50 µm Al₂O₃ particles and 2 bar pressure is recommended for 3Y-TZP translucent zirconia, while no abrasion of 5Y-ZP translucent zirconia ceramic.

Palladium-Induced Temporal Internalization of MHC Class I Contributes to T Cell-Mediated Antigenicity

Palladium (Pd) is a widely used metal and extremely important biomaterial for the reconstruction of occlusions during dental restorations. However, metallic biomaterials can cause serious allergic reactions, such as Pd-related oral mucositis seen in dentistry. Metal allergy is categorized as a type IV allergy and we demonstrated that CD8 T cells play an important role in Pd allergy previously. As TCR of CD8 T cells recognizes MHC class I/peptide complex, the antigen specificity to this complex seems to be generated during Pd allergy. However, it remains unknown if Pd affects the MHC class I/peptide complex. In this study, we investigated the behavior of the MHC class I/peptide complex in response to Pd treatment. We found that PdCl₂ treatment altered peptide presentation on MHC class I and that co-culture with Pd-treated DC2.4 cells induced activation of Pd-responsive TCR-expressing T cell line. Furthermore, PdCl₂ treatment induced temporal MHC class I internalization and inhibition of membrane movement suppressed Pd-induced T cell-mediated antigenicity. These data suggest that Pd-induced MHC class I internalization is critical for generation of antigenicity through a mechanism including differential peptide loading on MHC class I, which results in Pd allergy.

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

Objectives

The purpose of this study was to quantify phase transformation after hydrofluoric acid (HF) etching at various concentrations on the surface of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP), and to evaluate changes in bonding strength before and after thermal cycling.

Materials and Methods

A group whose Y-TZP surface was treated with tribochemical silica abrasion (TS) was used as the control. Y-TZP specimens from each experimental group were etched with 5%, 10%, 20%, and 40% HF solutions at room temperature for 10 minutes. First, to quantify the phase transformation, Y-TZP specimens (n = 5) treated with TS, 5%, 10%, 20% and 40% HF solutions were subjected to X-ray diffraction. Second, to evaluate the change in bond strength before and after thermal cycling, zirconia primer and MDP-containing resin cement were sequentially applied to the Y-TZP specimen. After 5,000 thermal cycles for half of the Y-TZP specimens, shear bond strength was measured for all experimental groups (n = 10).

Results

The monoclinic phase content in the 40% HF-treated group was higher than that of the 5%, 10%, and 20% HF-treated groups, but lower than that of TS-treated group (p < 0.05). The 40% HF-treated group showed significantly higher bonding strength than the TS, 5%, and 10% HF-treated groups, even after thermal cycling (p < 0.05).

Conclusions

Through this experiment, the group treated with SiO₂ containing air-borne abrasion on the Y-TZP surface showed higher phase transformation and higher reduction in bonding strength after thermal cycling compared to the group treated with high concentration HF.

The Effect of Translucency and Surface Treatment on the Flexural Strength of Aged Monolithic Zirconia

Aims

This in vitro study aimed to evaluate the effect of the degrees of translucency in different types of monolithic zirconia as well as the aging and surface treatment with airborne particle abrasion on the flexural strength of monolithic zirconia.

Materials and Methods

Sixty bar-shaped specimens were fabricated from three different types of presintered monolithic zirconia (n = 20 per group) including low translucent (LT) (DD Bio ZW iso, high strength zirconia, Dental Direkt, Germany), high translucent (HT) (DD Bio ZX² 98, high translucent zirconia, Dental Direkt, Germany), and multilayered system (ML) (DD cubeX2®ML, multilayer, cubic zirconia system, Dental Direkt, Germany). Each monolithic zirconia group was equally subdivided according to be either air-abraded with 110 µm aluminium oxide particles or left untreated (control). After thermocycling, the flexural strength was measured by using a universal testing machine. Two-way ANOVA followed by Tukey's post hoc and independent samples t-test were used for the statistical analyses (P < 0.05).

Results

Surface treatment and types of zirconia were found to have a significant interaction (P = 0.010). Having controlled the effect of surface treatment, the flexural strength of HT and LT zirconia was found to be significantly higher than the ML zirconia system (P ≤ 0.001). Airborne particle abrasion could significantly decrease the flexural strength of monolithic zirconia only in ML zirconia (P = 0.002).

Conclusions

Multilayered zirconia system had the lowest flexural strength among all groups. Moreover, the flexural strength of this system was attenuated by surface treatment with airborne particles abrasion.

Effects of ytterbium laser surface treatment on the bonding of two resin cements to zirconia

Monolithic zirconia crowns bonded to zirconia abutments have become more commonly used in the construction of cement-retained implant superstructures. The present study aimed to examine the effects of laser surface treatments on the bond strength of two resin cements to zirconia. Three types of surfaces were examined: untreated, alumina blasted, and ytterbium laser treated; and two types of resin cements: 4-META/MMA-TBB resin cement and composite resin cement. Half of the specimens were subjected to a thermocycling process. Subsequently, a shear bond test was carried out. In addition, surface roughness was measured for each surface type. The results showed that laser treatment increased zirconia surface roughness and that laser treatment significantly increased shear bond strength after the thermocycling of both cement types compared to no treatment. Our experimental results suggested that ytterbium laser surface treatment of zirconia increased the bond strength of resin cements.

Increasing dental zirconia micro-retentive aspect through ultra-short pulsed laser microstructuring: study on flexural strength and crystal phase characterization

Objectives

Although ultra-short pulsed laser (USPL) microstructuring has previously improved zirconia bond-strength, it is yet unclear how different laser-machined surface microstructures and patterns may influence the material’s mechanical properties. Therefore, the aim of this study was to assess the flexural strength of zirconia after different USPL settings creating three different geometrical patterns with structures in micrometer scale.

Methods

One hundred sixty zirconia bars (3Y-TZP, 21 × 4 × 2.1 mm) were prepared and randomly divided into five groups (n = 32): no surface treatment (negative control-NC); sandblasting with Al₂O₃ (SB); and three laser groups irradiated with USPL (Nd:YVO₄/1064 nm/2-34 J/cm²/12 ps): crossed-lines (LC), random-hatching (LR), and parallel-waves (LW). Bars were subjected to a four-point flexural test (1 mm/min) and crystal phase content changes were identified by X-ray diffraction. Surface roughness and topography were analyzed through 3D-laser-profilometry and SEM. Data were analyzed with parametric tests for roughness and Weibull for flexural strength (α = 5%).

Results

LR (Mean[95%CI]: 852.0 MPa, [809.2–894.7]) was the only group that did not show a significantly different flexural strength than NC (819.8 MPa, [796.6–842.9]), (p > 0.05). All laser groups exhibited higher Weibull moduli than NC and SB, indicating higher reliability and homogeneity of the strength data. An increase of monoclinic phase peak was only observed for SB.

Conclusion

In conclusion, USPL created predictable, homogeneous, highly reproducible, and accurate surface microstructures on zirconia ceramic. The laser-settings of random-hatching (12 ps pulses) increased 3Y-TZP average surface roughness similarly to SB, while not causing deleterious crystal phase transformation or loss of flexural strength of the material. Furthermore, it has increased the Weibull modulus and consequently material’s reliability.

Clinical significance

Picosecond laser microstructuring (LR conditions) of 3Y-TZP ceramic does not decrease its flexural strength, while increasing materials realiability and creating highly reproducible and accurate microstructures. These features may be of interest both for improving clinical survival of zirconia restorations as well as enhancing longevity of zirconia implants.

Changes in Crystal Phase, Morphology, and Flexural Strength of As-Sintered Translucent Monolithic Zirconia Ceramic Modified by Femtosecond Laser

Conventional bonding technology suitable for silica-based ceramics is not applicable to zirconia, due to its polycrystalline phase composition, chemical stability, and acid corrosion resistance. The development of an effective treatment to improve its surface roughness and mechanical properties remains an unresolved problem. Therefore, to solve this problem, this in vitro study evaluated the changes in surface morphology and flexural strength of translucent monolithic zirconia surfaces treated with femtosecond laser technology. As-sintered translucent zirconia specimens were subjected to airborne particle abrasion and femtosecond laser treatments, while control group specimens received no treatment. After treatment, the roughness and morphology of the treated zirconia surfaces were examined. The flexural strength and X-ray diffraction of the treated specimens were measured and analyzed. Statistical inferential analysis included one-way analysis of variance at a set significance level of 5%. The surface roughness after femtosecond laser treatment was significantly improved when compared with the control group and the group that received the airborne particle abrasion treatment (p < 0.05). In comparison with the airborne particle abrasion group, the flexural strength of the group that received the femtosecond laser treatment was significantly improved (p < 0.05). The femtosecond laser approach using appropriate parameters enhanced the roughness of the zirconia without reducing its flexural strength; therefore, this approach offers potential for the treatment of zirconia surfaces.

Impact of Sandblasting on Morphology, Structure and Conductivity of Zirconia Dental Ceramics Material

Over the last decade, zirconia (ZrO₂)-based ceramic materials have become more applicable to modern dental medicine due to the sustained development of diverse computer-aided design/computer-aided manufacturing (CAD/CAM) systems. However, before the cementation and clinical application, the freshly prepared zirconia material (e.g., crowns) has to be processed by sandblasting in the dental laboratory. In this work, the impact of the sandblasting on the zirconia is monitored as changes in morphology (i.e., grains and cracks), and the presence of impurities might result in a poor adhesive bonding with cement. The sandblasting is conducted by using Al₂O₃ powder (25, 50, 110 and 125 µm) under various amounts of air-abrasion pressure (0.1, 0.2, 0.4 and 0.6 MPa). There has been much interest in both the determination of the impact of the sandblasting on the zirconia phase transformations and conductivity. Morphology changes are observed by using Scanning Electron Microscope (SEM), the conductivity is measured by Impedance Spectroscopy (IS), and the phase transformation is observed by using Powder X-Ray Diffraction (PXRD). The results imply that even the application of the lowest amount of air-abrasion pressure and the smallest Al₂O₃ powder size yields a morphology change, a phase transformation and a material contamination.

Effect of Acid Mixtures on Surface Properties and Biaxial Flexural Strength of As-Sintered and Air-Abraded Zirconia

The aim of this work was to evaluate the effects of application time of an acid mixture solution on the surface roughness, phase transformation, and biaxial flexural strength of 3Y-TZP after sintering or air abrasion. For the biaxial flexural strength measurement, 220 3Y-TZP disk-shaped specimens were prepared after as-sintering or air abrasion. The etching solution comprised a mixture of hydrofluoric acid, sulfuric acid, hydrogen peroxide, methyl alcohol, and purified water. The samples were divided into 11 subgroups according to the etching times (Control, 1, 2, 3, 5, 8, 10, 12, 15, 20, and 30 min). The results showed that acid treatment on both as-sintered and air-abraded 3Y-TZP surfaces increased the surface roughness. However, it had no significant effects on the monoclinic phase or flexural strength of as-sintered zirconia. The monoclinic phase and flexural strength of air-abraded zirconia increased sharply after air abrasion; however, they gradually decreased after acid treatment, to a similar level to the case of the untreated surface. Surface treatment with acid mixture increased the roughness, but the lack of increase of monoclinic phase is thought to be because the loose monoclinic particles remaining on the surface were removed through the etching process.

Fatigue properties of hollow zirconia implants

The objective of this study was to clarify the fatigue behavior of hollow yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) specimens assuming its use for two-piece implants. The fatigue properties of a solid specimen (which simulated a one-piece implant) and 3 types of hollow specimens (which simulated two-piece implants) were evaluated. Specimens were either solid with a diameter of 4.0 mm (S) or hollow with an inner diameter of 3.0 mm and outer diameters of 4.0 mm (H0.5), 4.5 mm (H0.75), or 5.0 mm (H1.0). For each group, 25 specimens were prepared followed by blast and acid etch treatment. Static fracture and cyclic fatigue tests were conducted by modifying the methods provided in ISO6872. Fracture modes were determined by observing the surfaces under a scanning electron microscope. As a result, the cyclic fatigue load of S and H1.0 were similar, and hollow specimens with outer diameters greater than 0.75 mm displayed the ability to withstand molar occlusal forces.

Effect of Al2O3 Sandblasting Particle Size on the Surface Topography and Residual Compressive Stresses of Three Different Dental Zirconia Grades

This study investigated the effect of sandblasting particle size on the surface topography and compressive stresses of conventional zirconia (3 mol% yttria-stabilized tetragonal zirconia polycrystal; 3Y-TZP) and two highly translucent zirconia (4 or 5 mol% partially stabilized zirconia; 4Y-PSZ or 5Y-PSZ). Plate-shaped zirconia specimens (14.0 × 14.0 × 1.0 mm³, n = 60 for each grade) were sandblasted using different Al₂O₃ sizes (25, 50, 90, 110, and 125 μm) under 0.2 MPa for 10 s/cm² at a 10 mm distance and a 90° angle. The surface topography was characterized using a 3-D confocal laser microscopy and inspected with a scanning electron microscope. To assess residual stresses, the tetragonal peak shift at 147 cm⁻¹ was traced using micro-Raman spectroscopy. Al₂O₃ sandblasting altered surface topographies (p < 0.05), although highly translucent zirconia showed more pronounced changes compared to conventional zirconia. 5Y-PSZ abraded with 110 μm sand showed the highest Sa value (0.76 ± 0.12 μm). Larger particle induced more compressive stresses for 3Y-TZP (p < 0.05), while only 25 μm sand induced residual stresses for 5Y-PSZ. Al₂O₃ sandblasting with 110 μm sand for 3Y-TZP, 90 μm sand for 4Y-PSZ, and 25 μm sand for 5Y-PSZ were considered as the recommended blasting conditions.

Coating method for smooth and reinforced surface layer of highly translucent zirconia

Due to the recent evolution of dental ceramic materials, highly translucent zirconia materials have been developed. While this material has high aesthetics, there is still room for improvement in strength. In this study, we investigated to strengthen the high translucent zirconia material. In the study, monoclinic zirconia (mZrO₂) nanoparticles were used as a coating agent. The surface of the highly transparent zirconia was coated with mZrO₂ nanoparticle dispersion by dipping and sintered. Thereby, the high translucent zirconia could obtain about 1.3 times higher strength than the untreated one. The post-coating method introduced in this study would be effective as a simple and economical method for improving highly translucent zirconia strength.

Impact of sandblasting on the flexural strength of highly translucent zirconia

The objective of this study was to assess the influence of alumina sandblasting on the flexural strength of the latest generation of highly translucent yttria partially stabilized dental zirconia (Y-PSZ). Fully-sintered zirconia disk-shaped specimens (14.5-mm diameter; 1.2-mm thickness) of four Y-PSZ zirconia grades (KATANA HT, KATANA STML, KATANA UTML, all Kuraray Noritake; and Zpex Smile, Tosoh) were sandblasted at 0.2 MPa with 50-μm alumina (Al₂O₃) sand (Kulzer) or left as-sintered (control). For each zirconia grade, the yttria (Y₂O₃) content was determined using X-ray fluorescence (XRF). Surface roughness was assessed using 3D confocal laser microscopy. Micro-Raman spectroscopy (μ-Raman) and X-ray diffraction (XRD) were used to assess potentially induced residual stresses. Biaxial flexural strength (n = 20) was statistically compared by Weibull analysis. Focused ion beam - scanning electron microscopy (FIB/SEM) was used to observe the subsurface microstructure. Fracture surfaces after biaxial flexural strength testing were observed by SEM. KATANA UTML had the highest Y₂O₃ content (6 mol%), followed by KATANA STML and Zpex Smile (5 mol%), and KATANA HT (4 mol%). Al₂O₃-sandblasting significantly increased surface roughness of KATANA UTML and Zpex Smile. μRaman and XRD revealed the presence of residual compressive stress on all Al₂O₃-sandblasted surfaces. FIB/SEM revealed several sub-surface microcracks in the sandblasted specimens. Weibull analysis revealed that Al₂O₃-sandblasting increased the characteristic strength of KATANA HT, KATANA STML, whereas it decreased the strength of KATANA UTML. The strength enhancement after Al₂O₃-sandblasting of KATANA HT was the highest, followed by KATANA STML. For Zpex Smile, the influence was statistically insignificant. The impact of Al₂O₃-sandblasting on the Weibull modulus was controversial. The strength of zirconia after Al₂O₃-sandblasting is determined by the balance between microcrack formation (decreased strength) and surface compressive stress build-up (increased strength).

Influence of Sandblasting Particle Size and Pressure on Resin Bonding Durability to Zirconia: A Residual Stress Study

The influence of residual stress induced by sandblasting the zirconia ceramic surface on the resin bonding to the ceramic is still unclear. The effect of four different sandblasting conditions (with 50 and 110 μm alumina at pressures of 0.2 and 0.4 MPa) on the bonding of adhesive resin cement (Panavia F 2.0) to zirconia (Cercon^® ht) was investigated in terms of residual stress. The surface roughness and water contact angle of the zirconia surfaces were measured. The tetragonal-to-monoclinic (t-m) phase transformation and residual stresses (sin²ψ method) were studied by X-ray diffraction. The resin-bonded zirconia specimens were subjected to shear bond strength (SBS) tests before and after thermocycling (10,000 and 30,000 cycles) (n = 10). As the particle size and pressure increased, the roughness gradually and significantly increased (p = 0.023). However, there were no significant differences in roughness-corrected contact angle among all the sandblasted groups (p > 0.05). As the particle size and pressure increased, the m-phase/(t-phase + m-phase) ratios and compressive residual stresses gradually increased. After thermocycling, there were no significant differences in SBS among the sandblasted zirconia groups (p > 0.05). In conclusion, increased surface roughness and residual stress do not directly affect the resin bonding durability.

Atomic layer deposition SiO2 films over dental ZrO2 towards strong adhesive to resin

Atomic layer deposition (ALD) is a self-limiting nanoscale film deposition technology with the advantages of good stability, consistency and conformability. In this study, we proposed to deposit silica (SiO₂) films over dental zirconium-oxide (ZrO₂) by ALD for better SiO₂ films and higher bond strength between ZrO₂ and resin. To investigate the superiority of film deposited by ALD, other surface modification methods such as sol-gel, vapor phase hydrolysis and electrostatic self-assembly were compared in terms of the short-term and long-term bond strength between ZrO₂ and resin, measured by universal testing machine. Meanwhile, the surface morphology and chemical elemental analysis were characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and Fourier transform infrared spectroscopy (FTIR). Results showed that the SiO₂ films deposited by ALD or electrostatic self-assembly were uniform and consistent while sol-gel and vapor phase hydrolysis formed SiO₂ films with cracks or pores, changing the morphology of ZrO₂. ALD had the best results among all methods and increased the bond strength to 16.49 ± 1.60 MPa and 13.44 ± 1.63 MPa before and after aging respectively, which is expected to improve the long-term success rate of clinical dental ZrO₂ prostheses.

Combined application of femtosecond laser and air-abrasion protocols to monolithic zirconia at different sintering stages: Effects on surface roughness and resin bond strength

This study aimed to investigate the effects of femtosecond laser (Fs) and/or air-abrasion protocols on surface roughness (Ra) of zirconia and resin bond strength. Eighty zirconia samples were randomly divided into eight subgroups according to surface treatment protocols: Control (C), Air-abrasion before sintering (ABS), Air-abrasion after sintering (AAS), Air-abrasion before and after sintering (ABS + AAS), Fs laser before sintering (FBS), Fs laser before sintering + air-abrasion after sintering (FBS + AAS), Fs laser after sintering (FAS), and Fs laser after sintering + air-abrasion after sintering (FAS + AAS). Measurements of Ra values were obtained using a surface profilometer. Surface morphological properties were evaluated with scanning electron microscopy (SEM), and crystallographic changes were examined by X-Ray diffractometry (XRD). Self-adhesive resin cement was bonded to zirconia samples, and shear bond strength (SBS) tests were performed. The data were statistically analyzed by one-way ANOVA, followed by Tamhane tests. The control group displayed the lowest Ra and SBS values among all groups. The highest Ra and SBS values were found in the FBS and FBS + AAS groups. Air-abrasion applied before sintering significantly increased the Ra of specimens. FAS, FAS + AAS, and ABS + AAS groups exhibited higher SBS values than AAS and ABS (p < .05). Air-abrasion applied after Fs laser did not produce any significant change in the Ra and SBS compared to Fs laser alone (p > .05). Femtosecond laser application may be a promising method to enhance the surface roughness of zirconia and improve resin bond strength. Air-abrasion at pre- and post-sintered stages may also be a viable surface treatment option.

Flexural properties, bond ability, and crystallographic phase of highly translucent multi-layered zirconia

This study investigated the mechanical properties, bond ability, and crystallographic forms of different sites in a highly translucent, multi-layered zirconia disk. Flexural properties, bond ability to resin cement, and phase composition were investigated at three sites of a highly translucent, multi-layered zirconia disk: incisal, middle, and cervical. Flexural strength (FS) and flexural modulus (FM) were measured with static three-point flexural test. Shear bond strength (SB) to resin cement was measured after 24 h storage (37°C). Phase composition under mechanical stress was analyzed using X-ray diffraction. Without air abrasion, FS at the incisal site yielded the lowest value and was significantly lower than the middle and cervical sites. Air abrasion lowered the FS of each site. FM at the incisal site without air abrasion showed the significantly lowest value, and air abrasion increased its FM value. At the middle and cervical sites, their FM values were higher than the incisal site but were not significantly affected by air abrasion. SB value did not show significant differences among the sites. After sintering, cubic zirconia was detected at each site. Rhombohedral phase transformation occurred after mirror polishing. In highly translucent, multi-layered zirconia which was mainly composed of cubic zirconia, rhombohedral phase transformation occurred under mechanical stress and resulted in weakened mechanical properties.

Oxygen Plasma Improved Shear Strength of Bonding between Zirconia and Composite Resin

Improving the strength of the bonding of zirconia to composite resins remains a challenge in dental restorations. The purpose of this study was to evaluate the shear strength of the bonding of zirconia to composite resins, thereby verifying the hypothesis that as the power of the non-thermal oxygen plasma increases, the bonding strength of the plasma-treated zirconia is increased. The effects of the oxygen plasma power (100, 200, and 400 W) on the surface structure, chemical composition, and hydrophilicity of the zirconia and the strength of the bonding between zirconia and composite resin were investigated. As a result, after different plasma power treatments, the surface structure and phase composition of zirconia were not different from those of zirconia without treatment. However, the oxygen plasma treatment not only reduced carbon adsorption but also greatly increased the hydrophilicity of the zirconia surface. More importantly, the strength of the bonding between the plasma-treated zirconia and composite resin was significantly higher than that in the corresponding control group without plasma treatment. Regardless of whether the zirconia was pristine or sandblasted, the higher the plasma power, the greater the bond strength obtained. The conclusion is that the oxygen plasma treatment of zirconia can effectively improve the strength of the bonding between the zirconia and composite resin without damaging the microstructure and phase composition of the zirconia.

Effect of Pressure and Particle Size During Aluminum Oxide Air Abrasion on the Flexural Strength of Disperse-Filled Composite and Polymer-Infiltrated Ceramic Network Materials

Esthetic dental computer-aided design/computer-aided manufacturing (CAD/CAM) polymers such as disperse-filled composites (DFC) and polymer-infiltrated ceramic networks (PICN) should be subjected to surface treatment before bonding. However, such treatment can lead to defect formation and a decrease in strength. Therefore, in this study, we compared the flexural strengths of DFC and PICN materials air-abraded with alumina particles of different sizes at different pressures. In addition to Weibull analysis, the samples (untreated and treated) were characterized by scanning electron microscopy and atomic force microscopy. Both DFC and PICN exhibited the lowest flexural strength at large particle sizes and high pressures. Therefore, we optimized the air abrasion parameters to maintain the flexural strength and significantly increase surface roughness. In the case of DFC, the optimal particle size and pressure conditions were 50 µm at 2 bar and 110 µm at 1 bar, while for PICN, the best performance was obtained using Al₂O₃ particles with a size of 50 µm at 1 bar. This study reveals that optimization of the surface treatment process is crucial in the fabrication of high-performance clinical materials for dental restorations.

Effect of Low-Concentration Hydrofluoric Acid Etching on Shear Bond Strength and Biaxial Flexural Strength after Thermocycling

This study evaluated the shear bond strength (SBS) and biaxial flexural strength (BFS) of resin cements according to the surface treatment method using low-temperature hot etching with hydrofluoric acid (HF) on a yttrium-stabilized tetragonal zirconia (Y-TZP) surface; 96 discs and 72 cubes for BFS and SBS tests for Y-TZP were randomly divided into four groups of BFS and three groups of SBS. Specimens were subjected to the following surface treatments: (1) no treatment (C), (2) air abrasion with 50 μm Al₂O₃ particles (A), (3) hot etching with HF at 100 °C for 10 min (E), and (4) air abrasion + hot etching (AE). After treatments, the specimens were coated with primer, and resin cement was applied with molds. The specimens were evaluated for roughness (Ra) via scanning electron microscopy and x-ray diffraction, and the data were analyzed by an analysis of variance (ANOVA) and Kruskal–Wallis tests. Group E produced significantly higher SBS compared to group A and AE before and after thermocycling. The BFSs of all groups showed no significant differences before thermocycling; however, after thermocycling, C and E treatment groups were significantly higher compared to group A and AE. All groups showed phase transformation. Group E was observed lower monoclinic phase transformation compared to other groups.

Influence of alumina air-abrasion for highly translucent partially stabilized zirconia on flexural strength, surface properties, and bond strength of resin cement

Objective

This study aims to evaluate the influence of different air-abrasion pressures and subsequent heat treatment on the flexural strength, surface roughness, and crystallographic phases of highly translucent partially stabilized zirconia (Y-PSZ), and on the tensile bond strength of resin cement to Y-PSZ.

Methodology

Fully sintered zirconia specimens were ground with SiC paper (control) and/or air-abraded with 50 µm particles of alumina at 0.1, 0.15, 0.2, or 0.3 MPa or left as-sintered. After air-abrasion at 0.2 MPa (0.2AB), additional specimens were then heated to 1500°C, and held for one hour at this temperature (0.2AB+HT1h). Flexural strength and surface roughness were evaluated. Crystalline phase identification was also carried out using X-ray diffraction. Bonded zirconia specimens with self-adhesive resin cement were stored in distilled water at 37°C for 24 h, either with or without aging (thermal cycling 4-60°C/20000). Results were analyzed statistically by ANOVA and Tukey-Kramer tests.

Results

The flexural strength decreased with the increase in air-abrasion pressure, while in contrast, the surface roughness increased. The lowest flexural strength and the highest roughness value were found for the 0.2AB and 0.3AB groups, respectively. All groups contained cubic-, tetragonal ( t )-, and rhombohedral ( r )-ZrO₂ phases with the exception of the as-sintered group. Upon increasing the air-abrasion pressure, the relative amount of the r -ZrO₂ phase increased, with a significant amount of r -ZrO2 phase being detected for the 0.2AB and 0.3AB groups. The 0.2AB+HT1h group exhibited a similar flexural strength and t -ZrO2 phase content as the as-sintered group. However, the 0.2AB group showed a significantly higher tensile bond strength (p<0.05) than the 0.2AB+HT1h group before and after aging.

Conclusion

Micromechanical retention by alumina air-abrasion at 0.2 MPa, in combination with chemical bonding of a resin to highly translucent Y-PSZ using a MDP-containing resin cement may enable durable bonding.

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.