scholarly journals Structural and Morphological Evaluation of Presintered Zirconia following Different Surface Treatments

2018 ◽  
Vol 19 (2) ◽  
pp. 156-165 ◽  
Author(s):  
Hasan Skienhe ◽  
Roland Habchi
Keyword(s):  
Surface Roughness ◽  
Phase Transformation ◽  
Treatment Group ◽  
Bond Strength ◽  
Surface Treatment ◽  
Ceramic Powder ◽  
Surface Treatments ◽  
Air Abrasion ◽  
Group Iii ◽  
Morphological Evaluation

ABSTRACT Aim The aim of this study was to evaluate the effect of different surface treatments on roughness, grain size, and phase transformation of presintered zirconia. Materials and methods Surface treatments included airborne particle abrasion (APA) before and after sintering with different particles shape, size, and pressure (50 μm Al2O3, 50 μm glass beads, and ceramic powder). Thirty-five square-shaped presintered yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramic slabs (Zenostar ZR bridge, Wieland) were prepared (4 mm height × 10 mm width × 10 mm length) and polished with silicon carbide grit papers #800, 1000, 1200, 1500, and 2000 to ensure identical initial roughness. Specimens were divided into five groups according to surface treatment: group I (control): no surface treatment; group II: APA 50 μm Al2O3 after sintering; group III: APA 50 μm Al2O3 particles before sintering; group IV: APA 50 μm glass bead particles before sintering; and group V: APA ceramic powder before sintering. Specimens were analyzed using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD) analyses, and tested for shear bond strength (SBS). Data were statistically analyzed using one-way analysis of variance (ANOVA) followed by post hoc tests for multiple comparisons Tukey's test (α ≥ 0.05). Results Air abrasion before sintering significantly increased the surface roughness when compared with groups I and III. The highest tetragonal to monoclinic (t-m) phase transformation (0.07%) was observed in group III, and a reverse transformation was observed in presintered groups (0.01%). Regarding bond strength, there was a significant difference between APA procedures pre- and postsintering. Conclusion Air abrasion before sintering is a valuable method for increasing surface roughness and SBS. The abrasive particles’ size and type used before sintering had a little effect on phase transformation. Clinical significance Air abrasion before sintering could be supposed to be an alternative surface treatment method to air abrasion after sintering. How to cite this article Skienhe H, Habchi R, Ounsi HF, Ferrari M, Salameh Z. Structural and Morphological Evaluation of Presintered Zirconia following Different Surface Treatments. J Contemp Dent Pract 2018;19(2):156-165.

scholarly journals Shear Bond Strength of Composite Repair System to Bilayered Zirconia Using Different Surface Treatments (In Vitro Study)

2020 ◽  
Vol 23 (1) ◽  
Author(s):  
Ahmed Atef Baiomy ◽  
Jihan Farouk Younis ◽  
Ahmed Hassanen Khalil
Keyword(s):  
Bond Strength ◽  
Surface Treatment ◽  
Shear Bond Strength ◽  
Treatment Method ◽  
Surface Treatments ◽  
Repair System ◽  
Cohesive Failure ◽  
Air Abrasion ◽  
Composite Repair ◽  
Mode Of Failure

Objective:  the study is aimed to evaluate the effect of different surface treatment methods on shear bond strength between composite repair system and both of zirconia core and veneering porcelain and analyze the mode of failure between composite repair and ceramic surface. Material and methods: 40 Ceramic discs were fabricated with diameter of 7mm and 3mm thickness and divided according to material into two groups, Zirconia core discs (n = 20) and veneering porcelain discs (n = 20). Specimens were thermocycled and then each group was subdivided according to surface treatment method into 4 equal sub groups (n = 5) ,control subgroup I air abrasion, subgroup II Cojet, subgroup III laser, subgroup IV combination of air abrasion and laser surface treatment. Composite blocks were built up and polymerized on the surface of the specimens and shear bond strength of composite to each specimen was tested using a universal testing machine and mode of failure was evaluated using stereomicroscope. Results: Regardless of ceramic type; there was a statistically significant difference between surface treatments. Cojet recorded the highest mean shear bond strength. Laser showed the highest prevalence of adhesive failure.  Porcelain + Cojet showed the highest prevalence of cohesive failure. Conclusion: Cojet surface treatment provided superior shear bond strength regardless of the ceramic type whether zirconia or porcelain. Porcelain provided superior shear bond strength values in comparison to zirconia regardless of the surface treatment method tested. Porcelain showed higher percentage of cohesive failure that while the mode of failure in zirconia was most commonly adhesive.KEYWORDS Laser; Porcelain repair; Zirconia repair. 

scholarly journals Microtensile Bond Strength of Composite Cement to Novel CAD/CAM Materials as a Function of Surface Treatment and Aging

2017 ◽  
Vol 42 (1) ◽  
pp. 73-81 ◽  
Author(s):  
DP Lise ◽  
A Van Ende ◽  
J De Munck ◽  
LCC Vieira ◽  
LN Baratieri ◽  
...  
Keyword(s):  
Treatment Group ◽  
Bond Strength ◽  
Surface Treatment ◽  
Surface Treatments ◽  
Acid Etching ◽  
Microtensile Bond Strength ◽  
Flowable Composite ◽  
Group 4 ◽  
Cad Cam ◽  
Group 1

SUMMARY Objectives: To evaluate the effect of different surface treatments on the bond strength to a composite and a polymer-infiltrated ceramic CAD/CAM block after six-month artificial aging. Methods and Materials: Two types of CAD/CAM blocks (Cerasmart, GC; Enamic, Vita Zahnfabrik) were cut in slabs of 4-mm thickness, divided into six groups, and subjected to the following surface treatments: group 1: no treatment; group 2: sandblasting (SB); group 3: SB + silane (Si); group 4: SB + Si + flowable composite (see below); group 5: 5% hydrofluoric acid etching (HF) + Si; and group 6: 37% phosphoric acid etching (H3PO4) + Si. Sections of the same group were luted together (n=3: 3 sandwich specimens/group) using a dual-cure self-adhesive cement for all groups, except for the sections of group 4 that were luted using a light-curing flowable composite. After three weeks of storage in 0.5% chloramine at 37°C, the sandwich specimens were sectioned in rectangular microspecimens and trimmed at the interface to a dumbbell shape (1.1-mm diameter). One half of the specimens was subjected to a microtensile bond strength (μTBS) test, and the other half was tested after six months of water storage (aging). Data were statistically analyzed with a linear mixed-effects model for the factors surface treatment, material type, and aging, together with their first-degree interactions (α=0.05). Results: The lowest bond strengths were obtained in the absence of any surface treatment (group 1), while the highest μTBSs were obtained when the surface was roughened by either SB or HF, this in combination with chemical adhesion through Si. Loss in bond strength was observed after six-month aging when either surface roughening or silanization, or both, were omitted. Conclusions: Both the composite and polymer-infiltrated ceramic CAD/CAM blocks appeared equally bonding-receptive regardless of the surface treatment used. Creating a microretentive surface by either SB or HF, followed by chemical adhesion using Si, is mandatory to maintain the bond strength after six months.

Effect of Various Surface Treatments on Ti-Base Coping Retention

2020 ◽  
Vol 45 (4) ◽  
pp. 426-434
Author(s):  
K Kemarly ◽  
SC Arnason ◽  
A Parke ◽  
W Lien ◽  
KS Vandewalle
Keyword(s):  
Bond Strength ◽  
Surface Treatment ◽  
Lithium Disilicate ◽  
Surface Treatments ◽  
Air Abrasion ◽  
Chemical Surface ◽  
Cement Interface ◽  
Mechanical Surface Treatment ◽  
Access Channel ◽  
Mechanical Surface

Clinical Relevance Mechanical surface roughening of the titanium-abutment base is necessary to increase the pull-off bond strength of the lithium disilicate abutment material. Additional chemical surface treatment may further increase the bond strength, but the effects are product specific. SUMMARY Objective: The titanium-cement interface of a Ti-Base implant crown must be able to resist intraoral pull-off forces. The purpose of this study was to evaluate the effect of mechanical and chemical surface treatments of a titanium-abutment base (Ti-Base, Dentsply/Sirona) on the pull-off bond strength of a lithium disilicate abutment coping. Methods and Materials: Ti-Bases were divided into nine groups of 10 copings each that varied in both mechanical surface treatment (none; Al2O3 air abrasion; CoJet silicoating, 3M ESPE) and chemical treatments (none; Monobond Plus, Ivoclar Vivadent; Alloy Primer, Kuraray). Lithium disilicate abutment copings (IPS e.max CAD, Ivoclar Vivadent) were designed and milled. After crystallization, the copings were cemented onto the Ti-Bases with a resin cement (MultiLink Hybrid-Abutment Cement, Ivoclar Vivadent) according to the manufacturer's recommendations. The copings were torqued to a mounted implant, and the access channel was sealed with composite. After 24-hour storage and 2000 thermal-cycles in distilled water, the copings were subjected to a removal force parallel to the long axis of the interface until fracture. Data were analyzed with multiple one-way analyses of variance and Tukey post hoc tests (α=0.05). Results: Significant differences were found between groups based on type of surface treatment (p<0.05). Conclusions: Chemical surface treatment with Monobond Plus and mechanical surface treatment with CoJet silicoating or Al2O3 air abrasion resulted in the greatest pull-off bond strength. Alloy Primer did not provide a statistically significant increased pull-off bond strength when the surfaces were mechanically treated with Al2O3 air abrasion or CoJet silicoating. The lack of any mechanical surface treatment resulted in the lowest pull-off bond strength regardless of the type of chemical surface treatment.

scholarly journals Effect of Air-Abraded Versus Laser-Fused Fluorapatite Glass-Ceramics on Shear Bond Strength of Repair Materials to Zirconia

Materials ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1468
Author(s):  
Alaaeldin Elraggal ◽  
Nikolaos Silikas
Keyword(s):  
Surface Roughness ◽  
Bond Strength ◽  
Surface Treatment ◽  
Shear Bond Strength ◽  
Resin Composite ◽  
Glass Ceramics ◽  
Surface Treatments ◽  
Control Groups ◽  
Yag Laser ◽  
Repair Materials

Zirconia repair could be a feasible alternative option to total replacement in fractured zirconia-based restorations. Maximising the bond strength by enriching zirconia with fluorapatite glass-ceramics (FGC) powder has been addressed and compared to other surface treatments. Besides resin composite, other repair materials have been proposed and compared. Zirconia blocks received different surface treatments (A—sandblasting with tribochemical silica-coated alumina (CoJet). B—sandblasting with FGC powder (FGC), C—fluorapatite glass-ceramic coat+ neodymium-doped yttrium aluminum garnet laser irradiation (FGC + Nd: YAG), and D—no surface treatment). The surface roughness, topography, and crystallinity were investigated by a profilometer, scanning electron microscopy (SEM), and X-ray diffraction (XRD) analyses, respectively. For each surface treatment, three repair materials (feldspathic porcelain, lithium disilicate, and resin composite) were bonded to zirconia with 10, Methacryloyloxydecyl dihydrogen phosphate (MDP)–Monobond Plus/ Multilink Automix. Bonded specimens were thermocycled for 10,000 cycles and tested for shear bond strength (SBS) at a speed of 1 mm/min, followed by the analysis of the mode of failure. FGC + Nd: YAG laser group reported the highest surface roughness and monoclinic content compared to CoJet, FGC, and control groups. The highest mean SBS was found in FGC-blasted zirconia, followed by FGC + Nd: YAG laser and CoJet treated groups. However, the lowest SBS was found in control groups regardless of the repair material. Sandblasting zirconia with FGC powder increased SBS of resin to zirconia with lower monoclinic phase transformation compared to FGC + Nd: YAG or CoJet groups.

scholarly journals Effect of different surface treatments on surface roughness, phase transformation, and biaxial flexural strength of dental zirconia

2021 ◽  
Vol 15 (3) ◽  
pp. 210-218
Author(s):  
Niknaz Yahyazadehfar ◽  
Maryam Azimi Zavaree ◽  
Sayed Shojaedin Shayegh ◽  
Mobin Yahyazadehfar ◽  
Tabassom Hooshmand ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Surface Roughness ◽  
Phase Transformation ◽  
Flexural Strength ◽  
Surface Treatment ◽  
Monoclinic Phase ◽  
Pearson Correlation ◽  
Surface Treatments ◽  
Post Hoc ◽  
And Control

Background. Interfacial failures at the cement‒restoration interface highlights the importance of effective surface treatment with no adverse effect on the zirconia’s mechanical properties. This study aimed to determine the effect of different surface treatments on dental graded zirconia’s surface roughness and certain mechanical properties. Methods. Forty sintered zirconia specimens were randomly divided into four groups (n=10): control (no surface treatment), sandblasting (SA), grinding with diamond bur (GB), and Er,Cr:YSGG laser (LS). Following surface treatment, the surface roughness and surface topography of the specimens were examined. X-ray diffraction (XRD) was conducted. In addition, the biaxial flexural strengths of specimens were evaluated. The data were analyzed using one-way analysis of variance (ANOVA) and post hoc Tukey tests; the Pearson correlation coefficient was calculated between either volumetric percentage of monoclinic phase or roughness and flexural strength of specimens (α=0.05). Results. The GB group exhibited significantly greater surface roughness compared to the other groups (P<0.005). The LS and control groups exhibited a significantly lower volumetric percentage of the monoclinic phase (P<0.001) than the GB and SA treatments. The SA group exhibited significantly higher flexural strength than the control (P=0.02) and GB groups (P<0.01). Furthermore, the Weibull analysis for the LS showed higher reliability for the flexural strength than other treatments. Conclusion. Er,Cr:YSGG laser treatment, with the lowest extent of phase transformation and reliable flexural strength, can be a promising choice for surface treatment of zirconia.

Effect of Er,Cr:YSGG Laser, Air Abrasion, and Silane Application on Repaired Shear Bond Strength of Composites

2013 ◽  
Vol 38 (3) ◽  
pp. E58-E66 ◽  
Author(s):  
SD Cho ◽  
P Rajitrangson ◽  
BA Matis ◽  
JA Platt
Keyword(s):  
Bond Strength ◽  
Aluminum Oxide ◽  
Surface Treatment ◽  
Shear Bond Strength ◽  
Resin Composite ◽  
Silica Coating ◽  
Surface Treatments ◽  
Control Group ◽  
Resin Composites ◽  
Air Abrasion

SUMMARY Aged resin composites have a limited number of carbon-carbon double bonds to adhere to a new layer of resin. Study objectives were to 1) evaluate various surface treatments on repaired shear bond strength between aged and new resin composites and 2) to assess the influence of a silane coupling agent after surface treatments. Methods Eighty disk-shape resin composite specimens were fabricated and thermocycled 5000 times prior to surface treatment. Specimens were randomly assigned to one of the three surface treatment groups (n=20): 1) air abrasion with 50-μm aluminum oxide, 2) tribochemical silica coating (CoJet), or 3) Er,Cr:YSGG (erbium, chromium: yttrium-scandium-gallium-garnet) laser or to a no-treatment control group (n=20). Specimens were etched with 35% phosphoric acid, rinsed, and dried. Each group was divided into two subgroups (n=10): A) no silanization and B) with silanization. The adhesive agent was applied and new resin composite was bonded to each conditioned surface. Shear bond strength was evaluated and data analyzed using two-way analysis of variance (ANOVA). Results Air abrasion with 50-μm aluminum oxide showed significantly higher repair bond strength than the Er,Cr:YSGG laser and control groups. Air abrasion with 50-μm aluminum oxide was not significantly different from tribochemical silica coating. Tribochemical silica coating had significantly higher repair bond strength than Er,Cr:YSGG laser and the control. Er,Cr:YSGG laser and the control did not have significantly different repair bond strengths. Silanization had no influence on repair bond strength for any of the surface treatment methods. Conclusion Air abrasion with 50-μm aluminum oxide and tribochemical silica followed by the application of bonding agent provided the highest repair shear bond strength values, suggesting that they might be adequate methods to improve the quality of repairs of resin composites.

scholarly journals Resin Bonding to a Hybrid Ceramic: Effects of Surface Treatments and Aging

2016 ◽  
Vol 41 (2) ◽  
pp. 171-178 ◽  
Author(s):  
F Campos ◽  
CS Almeida ◽  
MP Rippe ◽  
RM de Melo ◽  
LF Valandro ◽  
...  
Keyword(s):  
Bond Strength ◽  
Surface Treatment ◽  
Hydrofluoric Acid ◽  
Surface Treatments ◽  
Resin Cement ◽  
Control Group ◽  
Air Abrasion ◽  
Microtensile Bond Strength ◽  
Cont Group ◽  
Hybrid Ceramic

SUMMARY The aim of this study was to verify the effects of different surface treatments on the microtensile bond strength between resin cement and a hybrid ceramic. Thirty-two hybrid ceramic slices (8 × 10 × 3 mm) were produced and allocated among four groups according to the surface treatment: Cont = no treatment, HA = 10% hydrofluoric acid applied for 60 seconds, PA = 37% phosphoric acid applied for 60 seconds and CJ = air abrasion with silica particle coated alumina (Cojet Sand, 3M ESPE, 30 μm/2.8 bar). As a control group, eight blocks of feldspathic ceramic (8 × 10 × 3 mm) were etched by hydrofluoric acid for 60 seconds (VMII). After the surface treatments, the ceramic slices were silanized (except the Cont group) and adhesively cemented to composite resin blocks (8 × 10 × 3 mm ) with a load of 750 g (polymerized for 40 seconds each side). The cemented blocks were cut into beams (bonded surface area of ∼1 mm2). Half of the beams were aged (thermocycling of 5°C-55°C/6000 cycles + water storage at 37°C/60 days), and the other half were tested immediately after being cut. Data were analyzed by Kruskal-Wallis and Dunn tests (non-aged groups) and by one-way analysis of variance and Tukey test (aged groups; α=0.05%). The mode of failure was classified by stereomicroscopy. The surface treatment significantly affected the bond strength in each set of groups: non-aged (p=0.001) and aged (p=0.001). Before being aged, samples in the CJ, HA, and PA groups achieved the highest bond strength values. However, after being aged, only those in the HA group remained with the highest bond strength values. Adhesive failure was found most often. In conclusion, hydrofluoric acid etching should be used for surface conditioning of the studied hybrid ceramic.

scholarly journals Effect of surface treatments on push-out bond strength of calcium silicate-based cements to fiber posts

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Amr M. Elnaghy ◽  
Ayman Mandorah ◽  
Ali H. Hassan ◽  
Alaa Elshazli ◽  
Shaymaa Elsaka
Keyword(s):  
Bond Strength ◽  
Surface Treatment ◽  
Glass Fiber ◽  
Calcium Silicate ◽  
Surface Treatments ◽  
The Other ◽  
Fiber Posts ◽  
Glass Fiber Posts ◽  
Push Out ◽  
Effect Of Surface

Abstract Background To evaluate the effect of surface treatments on the push-out bond strength of Biodentine (BD) and white mineral trioxide aggregate (WMTA) to fiber posts. Methods Two brands of fiber posts were used: Reblida post; RP and RelyX post; RX. Each type of post (n = 80/group) was divided into four groups (n = 20/group) and exposed to surface treatment as follows: Control (no treatment), sandblasting (SB), hydrofluoric acid (HF), and TiF4 4 wt/v%. Each group was further subdivided into two subgroups (n = 10/subgroup) based on the type of CSCs used as follows: Subgroup A: BD and Subgroup B: WMTA. Push-out bond strength of BD and WMTA to glass fiber posts was assessed. Data were statistically analyzed using three-way ANOVA and Tukey’s test. A Weibull analysis was performed on the push-out bond strength data. Results BD showed higher bond strength than WMTA (P < 0.001). The push-out bond strength for posts treated with TiF4 4 wt/v% showed greater bond strength than the other surface treatments (P < 0.05). The BD/RP-TiF4 4 wt/v% showed the greater characteristic bond strength (σ0) (15.93) compared with the other groups. Surface treatments modified the surface topography of glass fiber posts. Conclusions The BD/RP-TiF4 4 wt/v% showed greater bond strength compared with the other groups. The TiF4 4 wt/v% surface treatment enhanced the bond strength of BD and WMTA to glass fiber posts than the other treatments. Surface treatment of fiber post with TiF4 4 wt/v% could be used to improve the bond strength with calcium silicate-based cements.

scholarly journals Effect of surface treatments on repair strength, roughness and morphology in aged metal-free crowns

2020 ◽  
Vol 19 ◽  
pp. e206155
Author(s):  
Yançanã Luizy Gruber ◽  
Thaís Emanuelle Bakaus ◽  
Bruna Fortes Bittencourt ◽  
João Carlos Gomes ◽  
Alessandra Reis ◽  
...  
Keyword(s):  
Bond Strength ◽  
Surface Treatment ◽  
Adhesive System ◽  
Surface Treatments ◽  
Metal Free ◽  
Diamond Bur ◽  
Before And After ◽  
Post Test ◽  
Microshear Bond Strength

Aim: The roughness and micromorphology of various surface treatments in aged metal-free crowns and the bond strength of these crowns repaired with composite resin (CR) was evaluated in vitro. Methods: A CR core build-up was confectioned in 60 premolars and prepared for metal-free crowns. Prepared teeth were molded with the addition of silicone, and the laboratory ceromer/fiber-reinforced crowns (SR Adoro/Fibrex Lab) were fabricated. Subsequently, the crowns were cemented and artificially aged in a mechanical fatigue device (1.2 X 106 cycles), then divided into 4 groups (n = 15) according to the surface treatment: 1) phosphoric acid etching (PA); 2) PA + silane application; 3) roughening with a diamond bur + PA; and 4) sandblasting with Al2O3 + PA. After the treatments, the crowns (n = 2) were qualitatively analyzed by scanning electron microscope (SEM) and surface roughness (n = 5) was analyzed before and after the surface treatment (Ra parameter). The remaining crowns (n = 8) received standard repair with an adhesive system (Tetric N-Bond) and a nanohybrid CR (Tetric N-Ceram), and the microshear bond strength (SBS) test was performed (0.5 mm/min). Roughness and SBS data were analyzed by one- and two-way ANOVA, respectively, as well as Tukey’s post-test (α = 0.05). Results: Sandblasting with Al2O3 + PA resulted in the highest final roughness and SBS values. The lowest results were observed in the PA group, whereas the silane and diamond bur groups showed intermediate values. Conclusion: It may be concluded that indirect ceromer crowns sandblasted with aluminum oxide prior to PA etching promote increased roughness surface and bond strength values.

scholarly journals Assessment the Bond Strength of Ceramic Brackets to CAD/CAM Nanoceramic Composite and Interpenetrating Network Composite after Different Surface Treatments

2018 ◽  
Vol 2018 ◽  
pp. 1-6 ◽  
Author(s):  
Mustafa Mehmet Özarslan ◽  
Özlem Üstün ◽  
Ulviye Sebnem Buyukkaplan ◽  
Çağatay Barutcigil ◽  
Nurullah Türker ◽  
...  
Keyword(s):  
Bond Strength ◽  
Surface Treatment ◽  
Hydrofluoric Acid ◽  
Shear Bond Strength ◽  
Surface Treatments ◽  
Interpenetrating Network ◽  
Bonding Performance ◽  
Cad Cam ◽  
Ceramic Brackets ◽  
New Generation

Adult orthodontics may confront problems related to the bonding performance of orthodontic brackets to new generation restorative materials used for crown or laminate restorations. The aim of the present study was to investigate the shear bond strength of ceramic brackets to two new generation CAD/CAM interpenetrating network composite and nanoceramic composite after different surface treatments. Er,Cr:YSGG Laser, hydrofluoric acid (9%), sandblasting (50 μm Al2O3), and silane were applied to the surfaces of 120 CAD/CAM specimens with 2 mm thickness and then ceramic brackets were bonded to the treated surfaces of the specimens. Bond strength was evaluated using the shear bond strength test. According to the results, CAD/CAM block types and surface treatment methods have significant effects on shear bond strength. The lowest bond strength values were found in the specimens treated with silane (3.35 ± 2.09 MPa) and highest values were found in the specimens treated with sandblast (8.92 ± 2.77 MPa). Sandblasting and hydrofluoric acid surface treatment led to the most durable bonds for the two types of CAD/CAM blocks in the present study. In conclusion, different surface treatments affect the shear bond strength of ceramic brackets to CAD/CAM interpenetrating network composite and nanoceramic composite. Among the evaluated treatments, sandblasting and hydrofluoric acid application resulted in sufficient bonding strength to ceramic brackets for both of the CAD/CAM materials.

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