Greater Bond Strength Research Articles

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

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

Effect of fiber spacing on dynamic pullout behavior of multiple straight steel fibers in ultra-high-performance concrete

Abstract In this study, the effects of fiber spacing and loading rate on the pullout behaviors of single and multiple straight steel fibers embedded in ultra-high-performance concrete (UHPC) were investigated. Hence, three different fiber spacings, corresponding to the fiber volume fractions of 1, 2, and 7%, and loading rates, i.e., quasi-static and impacts, were considered. Bundled fiber specimens were also fabricated and tested to examine the fiber bundling effect at both the static and impact loading conditions. The test results indicated that the pullout resistance of straight steel fibers in UHPC improved by increasing the loading rate, regardless of their number, spacing, and bundles. Approximately 33–68% greater bond strengths were obtained in the single fiber specimen compared to the multiple fiber specimens at both the static and impact loads. The fiber bundles deteriorated the static pullout resistance, whereas both positive and negative bundling effects were found on the interfacial bond strength and pullout energy, respectively, under the impact loads. The strongest rate sensitivity on the dynamic increase factors of the pullout parameters, such as bond strength, maximum fiber tensile stress, and pullout energy, was found as the fibers were bundled, followed by the single and multiple fiber specimens. For the case of multiple fiber specimens, the loading rate sensitivity increased by decreasing the fiber spacing in general, such that the multiple fibers with closer spacings, corresponding to 2 and 7% by volume, were more sensitive to the rate of loading than their counterparts with greater fiber spacings.

Bond strength of Biodentine to a resin-based composite at various acid etching times and with different adhesive strategies.

Biodentine® is a bioactive calcium silicate-based material, with better strength parameters, an easier application method and a shorter setting time than mineral trioxide aggregate (MTA). The bond strength between Biodentine and the composite material is essential for the durability of the layered restoration. The objective of this study was to evaluate the bond strength of Biodentine to a resin-based composite at various acid etching times and with different adhesive strategies. In the 1st part of the experiment, the specimens were divided into 2 groups: the adhesive was applied in the total-etch (TE) and self-etch (SE) techniques. In the TE group, 37% orthophosphoric acid was applied after 30 s (TE 30) and 240 s (TE 240). In the SE group, the SE system was applied for 30 s (SE 30) and 240 s (SE 240). In the 2nd part, the SE systems Clearfil® SE Bond and Clearfil S3 Bond Plus were evaluated (the CSE and CS3 groups, respectively). In each group, the adhesive system was applied in 1 (the CSE 1 and CS3 1 subgroups) or 2 layers (the CSE 2 and CS3 2 subgroups). The specimens were subjected to a shear bond strength (SBS) test in a universal testing machine. Shear bond strength was higher after a prolonged etching procedure in the TE (TE 30: 2.51 MPa, TE 240: 9.39 MPa) and SE techniques (SE 30: 5.92 MPa, SE 240: 7.89 MPa). A statistically significant influence was detected in relation to 30 s of surface preparation time for Clearfil S3 Bond Plus (p < 0.001). Greater bond strength was revealed after the application of 1 layer of the Clearfil S3 Bond Plus single-bottle system (CS3 1: 6.42 MPa). The SBS of Biodentine to the composite depends on both the etching time and the mode of application of the adhesive systems. Higher bond strength was obtained for the SE adhesive in a shorter application time.

Effect of MDP-Based Primers on the Luting Agent Bond to Y-TZP Ceramic and to Dentin.

Purpose The aim of this study was to evaluate the influence of multimode MDP-based primers and different application protocols on the bond strength of a representative resin cement to an yttrium stabilized tetragonal zirconia (Y-TZP) ceramic. Materials and Methods The occlusal dentin from 60 human molars was exposed. The teeth and zirconia cylinders (N = 60) (3 mm of diameter; 4 mm of height) were divided into six groups (n = 10) according to the ceramic surface conditioning: (1) air abraded with SiO2 particles; (2) Z-Prime Plus; (3) air abraded with SiO2 particles + Z-Prime Plus; (4) air abraded with SiO2 particles + All-Bond Universal; (5) air abraded with SiO2 particles + ScotchBond Universal Adhesive; and (6) untreated zirconia. The luting agent (Duo-Link cement) was applied on the treated dentin surface. Specimens were stored in water (37°C, 24 h) and tested in shear bond strength. Data were statistically analyzed using 2-way ANOVA and Post hoc Tukey tests (α = 0.05). Results Significant effects of ceramic conditioning were found (p < 0.0001). The specimens sandblasted with silica particles followed by the application of Z-Prime Plus or All-Bond Universal presented greater bond strength values. For the untreated zirconia, several specimens failed prematurely prior to testing. Conclusions Sandblasting with silica particles combined with Z-Prime Plus increased the bond strength.

Influence of chlorhexidine in cavities prepared with ultrasonic or diamond tips on microtensile bond strength

This study evaluated the effect of chlorhexidine (CLX) in cavities prepared with either ultrasound-mounted CVDentUS diamond tips or conventional diamond burs on dentin bond strength after 24 h and 180 days. Forty-eight dentin surfaces from sound third molars were flattened and divided into four groups (n = 12), according to the type of cavity preparation (CVDentUS ultrasound tip or conventional diamond) and with or without 2% CLX (Consepsis) treatment. After application of the adhesive system (Clearfil SE Bond), microhybrid composite resin blocks (Charisma) were made on the dentin surface in increments. After 24 h, the specimens were sectioned into stick-shaped samples with an adhesive interface of approximately 1 mm2. From each tooth, half of the sticks were evaluated after 24 h of storage in distilled water and the other half after 180 days, using a universal testing machine. Three-way analysis of variance showed no significant triple interactions (p = 0.722) or double interactions between factors. Higher bond strength values were observed with the use of ultrasonic tips (p = 0.019), irrespective of whether or not CLX was applied in either time period. No difference in bond strength values was observed in terms of CLX application (p = 0.581). No significant difference in bond strength values was shown after storage for 24 h or 180 days (p = 0.302). In conclusion, the ultrasonic tips promoted greater bond strength to dentin, irrespective of whether or not CLX was applied, and storage time.

Bond strength of a chairside autopolymerizing reline resin to injection-molded thermoplastic denture base resins

PurposeThis study evaluated the shear bond strength of a chairside autopolymerizing reline resin to injection-molded thermoplastic denture base resins. MethodsFour kinds of injection-molded thermoplastic resins (two polyamides, a polyethylene terephthalate copolymer and a polycarbonate) and PMMA, as a control, were tested. The eight types of surface treatment: ((1) no treatment, (2) air abrasion, (3) dichloromethane, (4) ethyl acetate, (5) 4-META/MMA-TBB resin, (6) air abrasion and 4-META/MMA-TBB resin, (7) tribochemical silica coating, and (8) tribochemical silica coating and 4-META/MMA-TBB resin) were applied to each specimen. The chairside autopolymerizing reline resins were bonded to disks of the injection-molded thermoplastic denture base resins. All of the specimens were immersed in water for 4 months and then thermocycled for 10,000 cycles in water between 5 and 55°C. The shear bond strengths were determined. ResultsThe shear bond strengths of the two polyamides treated using air abrasion, dichloromethane and ethyl acetate and no treatment were exceedingly low. The greatest bond strength was recorded for the polyethylene terephthalate copolymer specimens treated with tribochemical silica coating and 4-META/MMA-TBB resin (22.5MPa). The bond strengths of the other injection-molded thermoplastic denture base resins increased using 4-META/MMA-TBB resin. ConclusionsTribochemical silica coating and 4-META/MMA-TBB resin were the most effective surface treatments among all denture base resins tested.

Effect of fluoridated casein phospopeptide-amorphous-calcium phosphate complex, chlorhexidine fluoride mouthwash on shear bond strength of orthodontic brackets: A comparative in vitro study

Objective The aim of the current study was to determine the effects of casein phosphopeptide amorphous calcium-phosphate (CPP-ACP) complex, chlorhexidine fluoride mouthwash on shear bond strengths (SBSs) of orthodontic brackets. Materials and Methods About sixty extracted healthy human premolar teeth with intact buccal enamel were divided into two equal groups to which brackets were bonded using self-etching primers (SEPs) and conventional means respectively. These were further equally divided into three subgroups - (1) control (2) CPP-ACP (3) chlorhexidine fluoride mouthwash. The SBSs were then measured using a universal testing machine. Results SBS of the conventional group was significantly higher than the self-etching group. The intragroup differences were statistically insignificant. Conclusion CPP-ACP, chlorhexidine fluoride mouthwash did not adversely affect SBS of orthodontic brackets irrespective of the method of conditioning. Brackets bonded with conventional technique showed greater bond strengths as compared to those bonded with SEP.

Effect of Selective Etch on the Bond Strength of Composite to Enamel Using a Silorane Adhesive.

An improvement in bond strength to enamel has been demonstrated with the use of phosphoric acid prior to bonding with self-etch methacrylate-based adhesive agents. No research has evaluated the effect of phosphoric-acid etching of enamel with a newer self-etch silorane adhesive. The purpose of this study was to evaluate the shear-bond strength of composite to enamel using the self-etch silorane adhesive compared to other self-etching methacrylate-based adhesives, with or without a separate application of phosphoric acid. Bovine incisors were sectioned using a diamond saw and mounted in plastic pipe. The bonding agents were applied to flattened enamel surfaces with or without the application of 35% phosphoric acid. The bonded tooth specimens were inserted beneath a mold, and composite was placed incrementally and light cured. The specimens were stored for 24 hours and six months in water and tested in shear. Data were analyzed with a three-way analysis of variance (ANOVA) to evaluate the effects of surface treatment, adhesive agent, or time on the bond strength of composite to bovine enamel (α=0.05). Significant differences were found between the groups based on surface treatment (p<0.01) or adhesive agent (p<0.01), but not on time (p=0.19), with no significant interactions (p>0.14). Phosphoric-acid etching of bovine enamel significantly increased the bond strength of the self-etch methacrylate and the silorane adhesives. The methacrylate-based adhesives had significantly greater bond strength to enamel than the silorane adhesive.

An investigation into the effects of metal primer and surface topography on the tensile bond strength between cobalt chromium alloy and composite resin

This study examined the influence of surface preparation and metal primer on the tensile bond strength between cobalt chromium alloy and composite resin. The bond strength between 168 cobalt chromium alloy dumb-bells with one of three test surfaces (beaded, machined or sandblasted) to composite resin were tested. Half of each group were treated with metal primer. The weakest bond strength was produced by the unprimed machined surface, many specimens failing before testing. The metal primer increased the bond strengths of all groups tested. The greatest bond strengths were achieved with the primed beaded and sandblasted surfaces. Within the limits of the study it has been shown that the surface preparation of the cobalt-chromium alloy did influence tensile bond strengths with composite resin and Metal Primer II increased the tensile bond strengths for all groups tested. The sandblasted surface treated with Metal Primer II is recommended for the bonding of composite resin to cobalt chromium alloy.

Bond strength of a resin composite and a resin-modified glass-ionomer cement associated or not with chlorhexidine to eroded dentin

Objective: Even resin composites and glass-ionomer cements are widely used for dental cervical region restorations, under erosive condition they can wear out quickly. This study aimed to compare, by means of bond strength by microshear, the performance of a resin composite (RC) and a resin-modified glass-ionomer cement (RMGIC) to eroded dentin and its association with 2% chlorhexidine up to 6 months. Material and Methods:. Eighty sound third molars teeth were cutt to obtain flat coronal dentin, which were subsequently embedded in self-curing acrylic resin circular molds exposing only this surface available. Teeth were divided into two groups, according to the treatment with the Adper Single Bond 2 + RC Filtek Z250 (Z) or the RMGIC Vitremer (V). Half of the specimens were immersed in artificial saliva-AS for 24 hours (control groups) and half subjected to 3x/1 minute daily immersion in Regular Coca Cola ®-RC for 5 days. Half of the specimens for each described condition were treated with water and half with 2% chlorhexidine for 1 minute prior the restoration. For all groups, the specimens were stored in artificial saliva weekly renewed up to tests. The bonding strength was evaluated by microshear test after 1 month and 6 months . Data, in normal distribution, were analyzed with 3-way ANOVA and Tukey (p &lt;0.05). Results: Challenge factors, materials and time were statistically significant.. Restorations with Z showed significantly higher bond strength compared to V in all situations. There was a reduction in bond strength values over time for all tested conditions. The prior application of 2% chlorhexidine was able to preserve the Z bond strength between 1 and 6 months, but this factor was not statistically significant. Conclusion: For eroded dentin, the use of resin composite seems presents greater bond strength compared to resin-modified glass-material, disregarding their association to chlorhexidine or not.

Bond Strenght of Zirconia Submitted to Different Surface Treatments

Objective: To evaluate the shear bond strength of a recent adhesive system used in the cementation of zirconia. Material and Methods: Overall, 72 zirconia specimens (Zirconzhan) were divided and randomized into 3 groups according to the type of surface treatment: G1 no treatment + adhesive system; G2 blasted with aluminum oxide + adhesive system and G3 tribochemical treatment (Rocatec Plus) + adhesive system. Half of each group (n = 12) had bond strength evaluated on two occasions: 24 hours after cementation, kept stored in distilled water at 37 ° C without thermal cycling, and after thermal cycling (5000 cycles, 5°C-55°C). Data were analyzed by ANOVA with Tukey's post-test (α≤0.05). Results: At first moment, G1 and G3 showed higher bond strength (8.64 ± 3.43 MPa and 6.55 ± 2.27 MPa) compared to G2, with no statistically significant difference between them. After thermal cycling, G3 showed higher bond strength (7.70 ± 1.82 MPa). Conclusion: Initially, only the adhesive system promoted higher bond strength, but after thermal cycling,bond strength decreased. The best treatment to promote high bond strength to zirconia is to associate tribochemical treatment with the adhesive system; most failures observed after thermal cycling were mixed and cohesive, showing a mechanical imbrication of the adhesive system, suggesting that there is no chemical bond; and the surface of the group with greater bond strength after thermal cycling showed more surface irregularities compared to the other groups.

Influence of light intensity on surface-free energy and dentin bond strength of single-step self-etch adhesives.

In this study, we investigated the influence of light intensity on the surface-free energy and dentin bond strength of single-step selfetch adhesives. The adhesives were applied to the dentin surfaces of bovine mandibular incisors and cured with light intensities of 0 (no irradiation), 200, 400, and 600 mW/cm(2). Surface-free energies were determined by measuring the contact angles of three test liquids placed on the cured adhesives. Dentin bond strengths of the specimens were also measured. Polymerization with a higher light intensity resulted in a lower surface-free energy of the cured adhesives. The greatest bond strength was achieved when a light intensity of 400 mW/cm(2) or greater was used. Our data suggest that the surface-free energy and dentin bond strength of single-step self-etch adhesives are affected by light intensity of the curing unit.

Shear bond strength of orthodontic brackets after antioxidant treatment on previously bleached teeth: An in vitro study

Context: Bleaching of the enamel surface reduces shear bond strength. This can be reversed by use of antioxidants prior to bonding of brackets. Aims: The aim of the study was to verify and validate the improvement in bond strength through the application of antioxidant on previously bleached teeth. Materials and Methods: Thirty-six sound maxillary and mandibular premolars extracted for orthodontic purposes were collected and divided into three groups of 12. Specimens in Group 1 were bleached with 35% hydrogen peroxide as a bleaching agent. Specimens in Group 2 were bleached and subsequently treated with 10% antioxidant (sodium ascorbate). Specimens in Group 3 served as a control. All specimens were stored in artificial saliva for 24 h prior to the bonding of orthodontic brackets. After bracket attachment, the samples were stored in distilled water for 1-week and then tested for shear bond strength using an INSTRON testing machine. Results: The data revealed that there was a significant difference between shear bond strengths of the bleached group; bleached + antioxidant group and the control group. Group 2 showed greater bond strength compared with Group 1, but lesser than the bond strength of the control group. Conclusion: The results confirmed the positive effect of antioxidant treatment on the bond strength of orthodontic brackets after tooth bleaching.

Prefabricated veneers - bond strengths and ultramorphological analyses.

To measure the microshear bond strengths (μSBS) of composite resin to the intaglio surface of prefabricated indirect veneers and analyze the FE-SEM ultramorphology of the pretreated intaglio surfaces as well as the fracture modes. Three veneer systems (veneer and respective luting material) were used in this study: two prefabricated veneer types, Cerinate One-hour (CER, DenMat) and Componeer (CMP, Coltene), and a laboratory- made veneer, IPS e.max Press (IPS, Ivoclar Vivadent) used as the control. For each group, 10 veneers were used. After delimitation of the bonding area with a double-faced adhesive tape, 0.8-mm-diameter cylinders of composite luting material were bonded to the pretreated intaglio surface. After polymerization, the specimens were fractured in shear mode using the wire-loop method in a universal testing machine. The pretreated intaglio surface of two extra veneers and four fractured specimens per group were morphologically characterized using FE-SEM. CER resulted in statistically lower mean μSBS (7.1 ± 1.2 MPa) than the other two veneer systems, CMP (15.2 ± 2.5 MPa) and IPS (14.7 ± 1.7 MPa) at p < 0.0001. As seen with the FE-SEM, the intaglio surface of CMP did not display microretentive features, while multiple microretentions were observed in both CER and IPS after HF etching. Within the limitations of this in vitro study, the CMP and IPS veneer systems resulted in greater bond strengths than those of the CER veneer system.

BOND STRENGTH OF CONCRETE WITH THE REINFORCEMENT BARS POLLUTED WITH OIL

Practically, the concrete is usually cast in forms made from wood or steel. These forms are oiled to avoid their adhesion with the hardened concrete material. The reinforced steel bars may be polluted with the oil when they placed over or inside the forms. This pollution may affect the bond between the steel bars used and concrete and consequently the strength of reinforced concrete members will decrease. In present investigation, the bond strength of the oil polluted steel bars with concrete was studied. Tests were conducted on 72 cylindrical concrete specimens with compressive strength of 24 MPa at age of 28 days. Two embedded lengths of steel bars were considered in present tests namely 30 cm and 15 cm with four bar diameters. Based on the current experimental results, it is concluded that the pollution of steel bars with oil does not affect their bond strength if the embedded length of the bars is increased and their diameters are decreased. For these bars the bond strength is greater than the tensile strength. It is observed that the embedded length of the bar inversely affects the deterioration of the bond strength due to the bar pollution. For the polluted and non polluted bars it can be stated that small bar sizes has greater bond strength than large bar sizes if the embedded length is small. The predominant type mode of failure is splitting mode for all the tested specimens and no slip failure occurred in testing all the polluted and non-polluted bars throughout the experiments.

Dentin deproteinization effect on bond strength of self-adhesive resin cements

This study examined the effect of deproteinization on the bond strength between self-adhesive resin cements and dentin surfaces that were untreated (control), acid-etched, or acid-etched and subjected to a post-etch deproteinization treatment. Cylinders of RelyX Unicem or BisCem (n = 6) cement were build-up on the dentin surfaces and tested to determine shear strength. The results were analyzed using two-way ANOVA and Tukey's test (5%). While neither dentin pretreatment improved the bond strength for RelyX Unicem, deproteinization treatments resulted in greater bond strength in BisCem specimens while acid etching alone did not improve the performance of the material.

Shear bond strength of different lingual buttons bonded to wet and dry enamel surfaces with resin modified glass ionomer cement (in vitro comparative study)

Background: This study was aimed to investigate the effect of three lingual button (Nickel free / rectangular base, Nickel free / round base and Composite) and bonding environment, wet and dry enamel surface, on: the shear bond strength (SBS) of light and self-cured Resin Modified Glass Ionomer Cements, and the debonding failure sites. Materials and method: One hundred twenty no-carious, free of cracks maxillary first premolar teeth were selected. Three types of orthodontic lingual buttons were used in this study: Nickel free / rectangular base, Nickel free / round base and Composite buttons. The teeth were divided into two groups of sixty teeth each. One group was used for testing the chemically cured GC Fuji Ortho Resin modified Glass Ionomer (RMGIC), while the other was used for testing the light cured GC Fuji Ortho LC RMGIC. Each was further subdivided into two subgroup; thirty teeth were bonded to wet enamel surface while the other was bonded after drying the enamel surface. Then each ten teeth from each subgroup were bonded with only one type of buttons. The sample was tested for bond strength using the universal testing machine and the Adhesive Remnant Index (ARI) was inspected under the stereomicroscope. Results:The highest (SBS) values were obtained in the Nickel free / round base button with both types of RMGIC in wet and dry environment as revealed by ANOVA test. While t-test revealed that both systems of RMGIC yield relatively lower values of (SBS). Conclusions:The GC Fuji Ortho RMGICs resist shear force in dry better that in wet environment.Nickel free / round base buttons give the greatest shear bond strength among the three types of button.The composite buttons give greater bond strength in dry than in wet environment with both GC Fuji Ortho and GC Fuji Ortho LC RMGICs.

Recycling stainless steel orthodontic brackets with Er:YAG laser - An environmental scanning electron microscope and shear bond strength study.

Aim:To determine the efficiency of erbium: Yttrium aluminum garnet (Er:YAG) laser with Environmental Scanning Electron Microscope (ESEM) and shear bond strength analysis as a method of recycling stainless steel orthodontic brackets and compare with other methods of recycling.Materials and Methods:Eighty samples of extracted premolar teeth bonded to SS brackets were tested for rebonded shear bond strength after recycling by four methods and compared with a control group of 20 samples. These 80 samples were randomized into four groups which were recycled by four methods, namely, sandblasting, thermal method, adhesive grinding by tungsten carbide bur, and Er: YAG laser method. After recycling, ESEM and shear bond strength analysis were used to analyze the efficiency of the recycling methodsResults:Er: YAG laser group was found to be having the greatest bond strength among the recycled brackets (8.33±2.51 followed by the sandblasting at 6.12±1.12 MPa, thermal and electropolishing at 4.44±0.95 MPa, and lastly the adhesive grinding method at 3.08±1.07 MPa. The shear bond strength of Er: YAG laser group was found to be having no statistically significant difference with that of the control group (P>0.05 and had statistical signifance with sandblasting, thermal and electropolishing and adhesive grinding groups at P>0.001. ESEM analysis showed complete removal of adhesive from the brackets recycled with Er: YAG laser which mimicked that of the control group.Conclusion:Er: YAG laser (2940 nm) was found to be the most efficient method for recycling, followed by the sandblasting, thermal, and the tungsten carbide methods, which had the least shear bond strength value and is not fit for clinical usage.

Effects of etching and adhesive applications on the bond strength between composite resin and glass-ionomer cements

ObjectiveThis study determined the effects of various surface treatment modalities on the bond strength of composite resins to glass-ionomer cements. Material and MethodsConventional (KetacTM Molar Quick ApplicapTM) or resin-modified (PhotacTM Fil Quick AplicapTM) glass-ionomer cements were prepared. Two-step etch-rinse & bond adhesive (AdperTM Single Bond 2) or single-step self-etching adhesive (AdperTM PromptTM L-PopTM) was applied to the set cements. In the etch-rinse & bond group, the sample surfaces were pre-treated as follows: (1) no etching, (2) 15 s of etching with 35% phosphoric acid, (3) 30 s of etching, and (4) 60 s of etching. Following the placement of the composite resin (FiltekTM Z250), the bond strength was measured in a universal testing machine and the data obtained were analyzed with the two-way analysis of variance (ANOVA) followed by the Tukey's HSD post hoc analysis (p=0.05). Then, the fractured surfaces were examined by scanning electron microscopy. ResultsThe bond strength of the composite resin to the conventional glass-ionomer cement was significantly lower than that to the resin-modified glass-ionomer cement (p<0.001). No significant differences were determined between the self-etching and etch-rinse & bond adhesives at any etching time (p>0.05). However, a greater bond strength was obtained with 30 s of phosphoric acid application. ConclusionsThe resin-modified glass-ionomer cement improved the bond strength of the composite resin to the glass-ionomer cement. Both etch-rinse & bond and self-etching adhesives may be used effectively in the lamination of glass-ionomer cements. However, an etching time of at least 30 s appears to be optimal.

Influence of recycled coarse aggregates on the bond behavior of deformed bars in concrete

To investigate the bond behavior of deformed bars in recycled aggregate concrete (RAC), 144 tests were performed. In this paper, the following variables were considered: the aggregate size, four types of recycled coarse aggregate (RCA) replacement ratios, two reinforcing bar directions (vertical and horizontal), and two reinforcing bar locations (75 and 225mm from the bottom). In addition, the effect of concrete aging on the bond behavior between the bar and the concrete was evaluated. Based on the test results, the RAC-I specimens (with 20mm of maximum RCA size) had a greater bond strength than the RAC-II specimens (with 25mm of maximum RCA size) under the same RCA replacement ratio. Thus, the bond strength of RCA is affected by the aggregate size because the shape of the RAC is generally spherical. For both RAC-I and -II specimens, as RCA replacement ratio increased, compressive strength showed a tendency to decrease proportionally. In terms of aging, regardless of the RCA replacement ratio, RAC-I pullout specimens showed similar bond strength under the same age although the compressive strength showed a downward trend with the RCA replacement ratio. In view of the top-bar effect, a significant difference was detected between the top and bottom bars at all ages; this does not confirm the provision of the ACI and CSA codes that require all of the top bars to have more than 300mm of concrete below them. In particular, the bond stress was not uniformly distributed along the length of the bar in the RAC-II specimens due to settlement of the coarse aggregates.