Reduction In Bond Strength Research Articles

Corrosion initiation and its effect on bond characteristics and service life of reinforced concrete systems with Cement-Polymer-Composite coated steel rebars

This paper investigates the corrosion and bond characteristics of steel reinforcement with Cement-Polymer-Composite (CPC) coating, which is widely used worldwide to prolong the initiation of corrosion. CPC coating is supposed to be applied on sandblasted or cleaned surface to exploit its full potential. However, CPC coating is generally applied on the rusted or uncleaned surface, which can lead to premature corrosion initiation and associated degradation of the bond between coated steel and concrete. For corrosion studies, 20 lollipop specimens with as-received and sandblasted steels, and with and without CPC coating were cast. These were exposed to chlorides and tested using a recently developed test method based on the linear polarization resistance technique. It was found that as-received, CPC coated steels had 50% less chloride threshold than sandblasted, CPC coated steel. For bond studies, 16 pull-out specimens with CPC coated steel rebars were cast. It was found that even negligible corrosion can lead to ≈50 to 70% reduction in bond strength. This indicates that the corrosion propagation period in the case of CPC coated rebar systems would be negligible. Based on the corrosion and bond results, a new service life model for RC systems with CPC coated steel rebars is proposed. The results highlight that if preventive maintenance is not employed, many structures with CPC coated rebars can experience premature corrosion initiation and significant bond reduction.

Conformational distributions of helical perfluoroalkyl substances and impacts on stability.

Per- and polyfluoroalkyl substances (PFAS) have been widely used the past 70 years in numerous applications due to their chemical and thermal stability. Due to their robust stability, they are environmentally recalcitrant which made them one of the most persistent environmental contaminants. In addition to strong CF bond strength, oleophobicity, hydrophobicity, and high reduction-oxidation (redox) potential of PFAS has led to their inefficient degradation by traditional means. A characteristic of their structure is also their preference to adopt helical conformations along the carbon backbone, contrary to their hydrocarbon analogues. This work investigates the helical nature of perfluoroalkanes through their conformational distributions, especially as a benchmark for determining the impact of polar head groups, heteroatoms, and radical center on helical conformations. Since structure governs reactivity and molecular properties, it is important to assess if minor chemical perturbations in the structure will lead to changes in the conformations. Based on density functional theory calculations and comprehensive conformational distributions, it was concluded that the helicity is a local structural property which changes significantly with the presence of heteroatoms in the perfluoroalkyl chain as well as with the presence of radical centers.

Interfacial Bond Strength and Morphology of Sound and Caries-affected Dentin Surfaces Bonded to Two Resin-modified Glass Ionomer Cements.

To evaluate the shear bond strength and interfacial morphology of sound and caries-affected dentin (CAD) bonded to two resin-modified glass ionomer cements (RMGICs) after 24 hours and two months of storage in simulated body fluid at 37°C. Sixty-four permanent human mandibular first molars (32 sound and 32 with occlusal caries, following the International Caries Detection and Assessment System) were selected. Each prepared substrate (sound and CAD) was conditioned (10% polyacrylic acid) and bonded to Activa BioACTIVE Restorative (Activa) and Fuji II LC (F2LC) as per the manufacturers' instructions. Shear bond strength (SBS) was performed after 24 hours and two months of storage. The interfacial surfaces were examined using a digital microscope and scanning electron microscope (SEM). Three-way ANOVA, Bonferroni post-hoc tests (α=0.05), and independent T-tests were used for multifactorial analysis. Activa exhibited reduced bond strength values to sound and CAD in comparison to F2LC after two time periods (p=0.01). There is a pronounced enhancement in SBS of F2LC when bonded to CAD (p=0.01) after storage, with no statistically significant effect on sound dentin (p=0.309). Activa showed stable SBS to sound and CAD immediately and post-aging (p>0.05). However, the evidence of mineral-like deposits under an SEM attached to the aged, debonded dentin surfaces, thereby obliterating the exposed dentinal tubules, might support the tissue repair potential of Activa. The SBS of Activa was lower than F2LC when bonded to sound and CAD, but the bonding stability and sealing ability is advantageous in minimally invasive therapy, suggesting use with a resin composite coverage when used in stress-bearing areas.

Effects of abutment height and type of cements on bond strength of monolithic zirconia single crowns luted to one-piece zirconia implants.

To test the bond strength of one-piece zirconia implants with either standard or reduced height using different luting agents and pretreatments of the ceramic crowns' inner surfaces. Twenty monolithic CAD/CAM-fabricated zirconia single crowns were cemented onto 10 one-piece zirconia implants with either 5-mm or 4-mm abutment height (Z-Look3 Evo SLM, Z-Systems) using 13 different luting agents. After water storage, the crowns were removed using a specially developed test fixture in a universal testing machine (Z010, Zwick/Roell). The maximum force was recorded (N), and the force per area was calculated (MPa). The statistical evaluation was performed using univariate analysis of variance (SPSS version 25.0, IBM). A mean of 4.19 MPa (SD 2.90) at 5 mm and 3.89 MPa (SD 2.85) at 4 mm was obtained for all luting agents. The highest values were achieved for a resinmodified glass-ionomer cement, with 12.37 MPa (4 mm)/12.00 MPa (5mm). The lowest values were shown for a long-term temporary material, with 0.73 MPa (4 mm)/1.07 MPa (5 mm). Only a polycarboxylate cement (P < .001) and a glass-ionomer cement (P = .006) showed statistically significant differences, in favor of the reduced abutment height. The latter did not significantly reduce bond strength for any of the materials examined. Implants with a reduced abutment height are clinically suitable. Pretreatment of the crowns' inner surfaces with ceramic primer showed to be advantageous.

Adhesive system properties and its behavior under simulated pulpal pressure in sound and caries-affected dentin and aging

This study aimed to evaluate the bond strength (BS) and adhesive interface characteristics of sound (SD) and caries-affected dentin (CAD) in the presence of simulated pulpal pressure (SPP) and after aging in solvents. The study also evaluated the physical and mechanical properties of the adhesive system under solvent challenge. Seventy-two SD and 36 natural CAD human molars were used. Thirty-six sound molars were submitted to artificial formation of caries by pH cycling (artificial CAD). Chemical analysis was performed in FTIR, and the surface microhardness (KHN) was measured. All specimens had SPP (20 cm H 2 0) and were etched with 37% phosphoric acid, and an adhesive system (Scotchbond Universal, 3 M ESPE) and composite resin block was applied. Tooth-resin sticks were randomly divided into groups according to storage time (24 h and 30 days) and solvents: deionized water (W), 99% ethanol (E) and methyl ethyl ketone (MEK). The specimens were submitted to BS testing (0.5 mm/min; 10 kgf), and the adhesive interface was evaluated by SEM. After aging in solvents, the adhesive samples were evaluated using flexural strength (FS), modulus of elasticity (ME), sorption (SR), and solubility (SL). Chemical differences in dentin were observed through mineral content loss in N-CAD and A-CAD were observed in FTIR analysis. N-CAD showed the lowest mean KHN. Dentin, time, interaction dentin-time, and interaction dentin-time-solvent ( p = 0.003 < 0.05) had a statistically significant effect on BS values. The characteristics of the adhesive interface differ among substrates and aging solvents on SEM. Ethanol differed significantly after 30 days with the lowest means values in the analysis of FS, ME, SR, SL. Natural caries-affected dentin, ethanol aging solvent and 30 days of storage time showed to be the most aggressive factors in terms of reducing bond strength, negatively interfering with the quality of the adhesive interface under simulated pulpal pressure. The properties of the adhesive system were more compromised with aging in ethanol.

Influence of mechanical and chemical pre-treatments on the repair of a hybrid ceramic

ObjectivesThis study aimed to investigate the influence of the respective mechanical and chemical pre-treatments on the composite repair of a CAD/CAM hybrid ceramic using a microtensile bond strength test (μTBS). Methods15 CAD/CAM Blocks of Vita Enamic (VE) were randomly sectioned into three mechanical pre-treatments: (1.) Diamond bur (D), (2.) Airborne abrasion (A), (3.) Tribochemical silica coating (T) and subsequently five chemical pre-treatments: (1.) Clearfil SE Bond Bond (B; negative control), (2.) ESPE Sil (S), (3.) Clearfil Ceramic Primer Plus (CPP), (4.) Clearfil Repair (CR) and (5.) Scotchbond Universal (SCB). Per block, n = 20 specimens were sawn. Half of the specimens were randomly selected and subjected to an immediate bond strength test, while the other half was subjected to artificial aging for 6 months 180 days at 37 °C and subsequent thermocycling of 5000 cycles. A μTBS was performed and data (MPa) were compared in one-way and two-way ANOVA and Tukey's HSD. Paired-t-test was used for artificial aging (α = 0.05). Debonded specimens were analyzed of for failure modes with a stereomicroscope (SEM). ResultsThe results of one-way ANOVA for the fifteen fastening procedures after aging indicated significant differences according to SCB-A and CPP-T. Two-way ANOVA after aging observed inferior bond strength for SCB. No differences were observed for mechanical pre-treatments. Artificial aging showed a significant reduction in bond strength on most of the fastening procedures. SignificanceSCB showed the lowest bond strength values besides B, S, CPP, and CR. MDP and silane are both suitable for the repair of VE.

Effect of immersion in NaCl solution on the electrical conductivity and the reduction of the shear bond strength of resin-modified glass-ionomer-cements after current application.

Advancements in dental cements have considerably improved their bond strengths. However, high bond strength often makes the removal of restorations difficult. Thus, smart dental cements that show controllable bond strength are required. A conventional resin-modified glass-ionomer-cement demonstrated a significant reduction in the bond strength after current application. However, for this system, the ions in the cement are released into the oral cavity, resulting in a reduction of the electrical conductivity and in losses of the expected on-demand debonding property. Herein, the effects of immersion in 0.9 and 15% NaCl solutions on the electrical conductivity and debonding properties were investigated. The cement immersed in 0.9% NaCl solution from 1 to 28 days maintained similar bond strength reductions after current application, whereas that in 15% NaCl solution initially showed no bond strength reduction after 1 day but exhibited an increase in the bond strength reduction after immersion for 28 days.

Bond-slip performance of GFRP and steel reinforced beams under wet-dry and freeze-thaw cycles: The effect of concrete type

In this experimental study, the bond-slip performance between glass fibre reinforced polymer (GFRP) bars and three different concrete types, namely normal, self-compacting, and fibre-reinforced concrete under freeze-thaw and wet-dry cycles have been studied. Steel reinforced concrete beams were also tested for comparison purposes. In total, 54GFRP and steel reinforced concrete beams were prepared, conditioned, and tested using RILEM recommendations. 18 specimens were subjected to 200 wet-dry cycles between ambient and 60 ˚C and another 18 specimens were subjected to 200 freeze-thaw cycles between -18 ˚C and 4 ˚C for 150 days. The results showed the bond strength reductions of 12, 3 and 9 % between steel bars and beam specimens cast with normal, self-compacting, and fibre-reinforced concrete, respectively after exposure to 200 wet-dry cycles. However, the corresponding values for GFRP reinforced concrete beams under the same conditioning environment were 1, 1, and 16 % respectively. With respect to freeze-thaw cycles, bond strength of steel reinforced normal, self-compacting, and fibre-reinforced concretes experienced only about 5, 2, and 4 % reductions, respectively, after 200 cycles. The corresponding reduction values for GFRP reinforced beams were insignificant and about 2, 1, and 4%. Steel reinforced beams fail due to the concrete crushing, while GFRP reinforced beams fail due to GFRP surface peeling-off. Generally, GFRP reinforced beams experienced fewer bond strength reductions compared to steel reinforced beams. Also, regardless of concrete type, due to their corrosion vulnerability, steel reinforced beams experienced greater stiffness reductions than that of GFRP reinforced beams when subjected to seawater wet-dry cycles. However, such a difference was not drastic.

Investigation on improving the residual mechanical properties of reinforcement steel and bond strength of concrete exposed to elevated temperature

Concrete and reinforcement steel are essential building materials widely used in composite construction due to their advantages, such as strength, durability and ease of availability. Fire is one of the critical hazards that causes severe damage to the structure and leads to progressive collapse. Due to the intensity of fire exposure, the concrete and reinforcing steel significantly losses their inherent mechanical properties and service life. Minimizing the fire-induced damage and failure are the primary objectives in the design of concrete structures. Therefore, an extensive experimental attempt was undertaken to evaluate the pull out behaviour and also to improve the bond performance of concrete and reinforcement steel when exposed to elevated temperature. A cement based perlite coating was developed as a protective material to safeguard the concrete in the study. All the pull out bond test specimens were heated following the ISO 834 standard fire curve, and subsequently cooled either by air or water. Residual mechanical properties of steel rebar such as yield strength, ultimate strength, elastic modulus, shear and bending capacity were evaluated after the exposure to elevated temperature. Investigations were conducted on pull out specimens to evaluate the bond stress slip behaviour and bond strength of concrete. A detailed physical observation was made on the failed concrete specimens to examine the damage. A drastic reduction in bond strength of concrete and tensile strength of the rebar were observed while increasing the duration of heating. Also, it was observed that the coated specimens exhibited better performance by retaining the bond strength and yield strength of the rebar.

Experimental and simulative study of bonding properties on fiber/epoxy interfaces by digital image correlation (DIC) technique and molecular dynamics

Fiber/epoxy interfacial bonding properties play a vital role in the utilization of fiber reinforced polymer (FRP) bars in concrete because almost all durability deficiencies of FRP-reinforced concrete are attributed to the failure of the fiber/epoxy/concrete interface. This study aims to study the evolution of fiber/epoxy debonding under a simulated concrete pore solution environment, combining a self-developed debonding device and the digital image correlation (DIC) technique. The bonding degradation mechanism of the fiber/epoxy interface was revealed by molecular dynamics (MD) simulation. The results show that the interfacial bonding property between glass fiber (GF) and epoxy was superior to that of basalt fiber (BF), and a more significant bonding degradation was observed in BF after the corrosion of water and chloride ions due to the reduction in the number of H-bonds caused by partial replacement of Si by Al, as concluded from MD simulation. Moreover, the bond stresses of GF and BF were reduced to approximately 15% and 12% after 28 days of corrosion in the simulated concrete pore solutions, respectively. Meanwhile, the reduction in bond strength was more significant in the simulated concrete pore solution of seawater and sea sand concrete (SWSSC).

Metakaolin based geopolymer mortar as concrete repairs: Bond strength and degradation when subjected to aggressive environments

By harnessing the benefits of lowering cost and reducing CO2 emission, employing geopolymer as the repair materials have been gaining interest. This article investigated the bond strength and degradation of metakaolin-based geopolymer mortar subjected to rapid efflorescence exposure, acid attack, freeze-thaw cycles, wet-dry cycles, and heat-cool cycles. The slant shear strength tests evaluated the new-old mortar bond strength. FTIR, XRD, and TGA were conducted to monitor the deterioration of geopolymers. Visual observation and ICP-OES tests were performed to quantify the efflorescence risk. Results showed that acid exposure mainly reduces bond strength by degrading the geopolymer framework. In aggressive environments involving moisture and temperature changes, i.e., freeze-thaw, wet-dry and heat-cool cycles, geopolymers exhibit negligible deterioration. However, the shrinkage induced by water migration and the volume expansion caused by elevated temperatures significantly decrease (up to 90%) the bond strength of geopolymer repair mortar. The negative effect imposed by the efflorescence should not be neglected. A significant bond strength reduction (up to 20%) was observed for geopolymer repair mortar suffering from efflorescence. Samples with higher granulated blast furnace slag (GGBS) addition show lower strength loss, benefiting from their lower efflorescence extent. Stoichiometrically designing the geopolymer repair binder to avoid efflorescence is recommended.

Modelling of bond behavior of deformed bar embedded in concrete after heating to high temperatures: A mesoscale study

A three-dimensional (3D) mesoscale model was established in the present work with considering the heterogeneity of concrete materials and the surface characteristics of deformed steel bars. In the simulation, the interaction between deformed rebar and concrete is taken into account, including mechanical interlocking and frictional resistance. The sequentially coupled thermal-stress analysis procedure was employed to model the process of pull-out of deformed steel bar after cooling from high temperature. Comparison with the results of the pull-out test illustrates the correctness of the mesoscale simulation results. Then, the influence of aggregate types and elevated temperatures on the bond properties were discussed. Considering the simulation results, a calculation formula for the bond stress-slip curve after cooling from high temperature was proposed based on the recommendations in the existing codes for the cases of room temperature. The results show that the reduction of peak bond strength is directly bound up with the heat transfer and mechanical performance of the aggregates. When the deformed rebar is pulled out under the displacement load, the development process of concrete cracks with different aggregates is obviously different. Comparing the results obtained by the calculation formula proposed in the present work with the numerical simulation results, one can notice the good consistency between them, which means the effectiveness of the proposed formula.

Self-adhesive composites - Do they keep what they promise?

Self-adhesive composites promise simplified application and reliable adhesion to dental hard tissues without prior conditioning or application of an adhesive system. Their working principle is based on specific functional monomers. Although they may reach acceptable sealing capability in minimally invasive cavities, study results showed significantly reduced bond strength to enamel and dentin compared to conventional adhesive systems. Thus, the use of self-adhesive composites requires critical individual consideration.

Effect of Alkalization on Physical, Chemical, Morphological and Mechanical Properties of Arial Root Ficus Amplissima Fibre

ABSTRACT Natural fiber’s hydrophilic property leads to reduced bond strength for its incompatibility with the matrix. This problem can be sorted out by treating the surface of the fiber. In this connection, the chemical, physical, thermal, and surface morphological properties of alkali-treated Arial root Ficus Amplissima fiber (ARFAF) have been investigated. By using the TGA, the alkali treatment of ARFAF was optimized, and 5% (w/v) NaOH and 45 min of the soaking period was found to be the best. Optimally treated ARFAF improved the cellulose content from (52.64 wt. %) to (61.67 wt. %) and reduced the hemicellulose from (10.64 wt. %) to (6.22 wt. %), crystallinity index improved from (39%) to (43.33%), tensile strength improved from (250.7 ± 11.26MPa) to (278.4 ± 13.20 MPa), thermal stability improved from (200°C) to (230°C), and it improved the surface topography compared with raw ARFAF.

A comprehensive in vitro study on the performance of two different strategies to simplify adhesive bonding

ObjectiveThe purpose of this study is to compare the bonding performance and mechanical properties of two different resin composite cements using simplified adhesive bonding strategies.Materials and methodsShear bond strength of two resin composite cements (an adhesive cement: Panavia V5 [PV5] and a self‐adhesive cement: RelyX Universal [RUV]) to human enamel, dentin, and a variety of restorative materials (microfilled composite, composite, polymer‐infiltrated ceramic, feldspar ceramic, lithium disilicate and zirconia) was measured. Thermocycle aging was performed with selected material combinations.ResultsFor both cements, the highest shear bond strength to dentin was achieved when using a primer (PV5: 18.0 ± 4.2 MPa, RUV: 18.2 ± 3.3 MPa). Additional etching of dentin reduced bond strength for RUV (12.5 ± 4.9 MPa). On enamel, PV5 achieved the highest bond strength when the primer was used (18.0 ± 3.1 MPa), while for RUV etching of enamel and priming provided best results (21.2 ± 6.6 MPa). Shear bond strength of RUV to restorative materials was superior to PV5. Bonding to resin‐based materials was predominantly observed for RUV.ConclusionsWhile use of RUV with the selective‐etch technique is slightly more labor intensive than PV5, RUV (with its universal primer) displayed a high‐bonding potential to all tested restorative materials, especially to resin.Clinical significanceFor a strong adhesion to the tooth substrate, PV5 (with its tooth primer) is to be preferred because etching with phosphoric acid is not required. However, when using a wide range of varying restorative materials, RUV with its universal primer seems to be an adequate option.

Microstructural evolution, metallurgical reactions, and the mechanical properties of pure titanium and carbon steel sheets bonded via hot-roll diffusion with a nickel interlayer

ABSTRACT This study investigated the microstructural evolution and mechanical properties of titanium-carbon steel bi-metallic composite sheets fabricated via hot-rolling diffusion with a nickel interlayer at temperatures of 800, 850, or 900°C. Scanning electron microscopy and energy-dispersive X-ray spectroscopy revealed layers of NiTi2, NiTi, and Ni3Ti phases at the Ti-Ni interface. We also observed interfacial σ + β Ti and β-Ti phases. Note that the carbon steel-Ni interface revealed no reaction layers or intermetallic compounds under any of the processing temperatures. The highest shear strength (∼470 MPa) was obtained at a processing temperature of 850°C. The highest peel strength (∼21 N/mm) was obtained at a processing temperature of 900°C. Lower bonding temperatures were shown to reduce bond strength by hindering atomic diffusion, whereas higher bonding temperatures led to the formation of excessive intermetallic compounds. Both conditions resulted in joint failure at the Ti-Ni interface and extensive cleavage planes with various alignments on fracture surfaces. Overall, a hot-rolling temperature of 850°C provided the optimal tradeoff between interfacial bonding strength and ductility.

Thick elastomeric coating removal using tailored infrared- and infrared-sonication hybrid technology

We report an innovative, cost-effective, and eco-friendly coating removal technology that removes thick polyurethane-based elastomeric coatings without damaging the underlying metal or glass-polymer composite substrates. The developed technology eliminates the need for chemical- or media-based treatments, thus reducing environmental problems such as releasing toxic gases or suspended solid particles in the air. This was achieved using tailored infrared and infrared-ultrasonication treatments of the coated substrates that caused bond failure at the surface coat-substrate interface by selective absorption of IR and/or impinging of the topcoat with the ultrasonication technique. The degraded interfacial adhesion strength then allowed easy removal of the specialty coating with the application of a pull at a certain angle to the substrate-coating interface. The effect of different operating parameters such as time of irradiation, surface temperature, sonication power/intensity was investigated to determine the optimal conditions for coating removal. The treated and untreated coated samples were characterized by DSC, SEM, FTIR, peel-tester, embedded thermocouple/LABVIEW, and infrared thermography techniques. The energy analysis revealed that the fracture energy component was 4× lower on the treated sample than the untreated sample indicating reduced bond strength, which can be explained based on residual thermal stress generated due to the thermal coefficient mismatch and the interfacial cell dislocation. Also, coating from the treated sample could be removed 1.75× faster than from the untreated sample. Based on the cost analysis, the operation cost for this technology is meager compared to conventional and energy-intensive technologies such as laser ablation.

Microshear bond strength of resin cement to glass-ceramics after intaglio surface staining

Statement of problemApplying stains to the intaglio surface of computer-aided design and computer-aided manufacturing (CAD-CAM) monolithic ceramic restorations has been proposed as an option to help mask darkened substrates. However, little is known about the effects of this procedure on the adhesion between the resin cement and the ceramic. PurposeThe purpose of this in vitro study was to evaluate the effect of intaglio surface staining on the microshear bond strength between 2 CAD-CAM ceramics and a resin cement. Material and methodsLithium disilicate (Gmax) and leucite-reinforced (Gpress) ceramic blocks were sectioned, crystalized when indicated, and polished. They received either none, 1, or 2 layers of ceramic stains and a glaze liquid mixture followed by a firing cycle. The surfaces of groups Gmax0, Gmax1, and Gmax2 were etched with 9% hydrofluoric acid etching (HF) for 20 seconds, and those of groups Gpress0 and Gpress1 were etched for 60 seconds. After rinsing and drying, a ceramic primer was applied and air-dried. Resin cement rods (n=24 per group) were built from a silicone mold. Specimens were stored in distilled water for 24 hours before microshear bond testing. Failure mode was observed under a digital microscope. Data were analyzed by using the Kruskal-Wallis and Mann-Whitney nonparametric tests (α=.05). ResultsIntaglio staining negatively affected the microshear bond strength for both ceramics. A significant difference was observed between Gmax1 (3.5 ±1.73 MPa) and Gmax2 (3.7 ±2.1 MPa) when compared with Gmax0 (14.2 ±4.4 MPa) and also between GPress0 (25.7 ±5.1 MPa) and Gpress1 (1.8 ±2.7 MPa). No difference was observed between 1 and 2 stain layers for Gmax. Most failures were adhesive for Gmax0, mixed for Gpress, and cohesive within the stain layer for experimental groups. ConclusionsIntaglio surface staining with a stain and glaze mixture caused a significant reduction in bond strength between resin cement and both ceramics tested.

Experimental Investigations on Bond Behavior between FRP Bars and Advanced Sustainable Concrete.

In response to resource shortage and carbon dioxide emissions, an innovative type of sustainable concrete containing LC3, seawater, sea sand, and surface-treated recycled aggregates is proposed in this study to replace traditional concrete. To understand the bond properties between the sustainable concrete and CFRP bars, an investigation was conducted on the bond behavior between sand-coated CFRP bars and advanced sustainable concrete. Pull-out tests were carried out to reveal the failure mechanisms and performance of this bond behavior. The results showed that the slip increased monotonically along with the increase in confinement. The bond strength increased up to approximately 15 MPa, and the critical ratio of C/D was reached. The critical ratio approached 3.5 for the Portland cement groups, while the ratio was determined as approximately 4.5 when LC3 was introduced. When the proportion of LC3 reached 50%, there was a reduction in bond strength. A multisegmented modified bond–slip model was developed to describe the four-stage bond behavior. In terms of bond strength and slip, the proposed advanced concrete exhibited almost identical bond behavior to other types of concrete.

Bonding interface and dentin enzymatic activity of two universal adhesives applied following different etching approaches

ObjectivesEtching approaches [37% phosphoric acid, self-etching, 10–3 solution (3% ferric chloride dissolved in 10% citric acid), or 1.4% nitric acid] were evaluated regarding enamel shear bond strength (24 h), dentin microtensile bond strength (24 h and 2 years), failure mode, enzymatic activity of the hybrid layer, and nanoleakage (24 h and 2 years) of Prime&Bond Universal (PBU, Dentsply-Sirona) and Gluma Bond Universal (GBU, Kulzer). MethodsAdhesives were applied on blot-dried (wet-bonding, positive control) or air-dried (remaining groups) dentin after acid-etching (15 s) or in self-etch mode. Enamel and dentin bond strength tests used 160 human teeth (n = 10). Failure mode of tested samples and nanoleakage within the dentin-adhesive interface (n = 5) were analyzed by scanning electron microscopy. Dentin enzymatic activity was investigated by in situ zymography (n = 3). ResultsEnamel bond strengths did not differ statistically among groups. Wet-bonding with 37% phosphoric acid showed similar dentin bond strength compared to 10–3 solution or 1.4% nitric acid at 24 h for both adhesives. None of the etchants inhibited enzymatic activity, and all groups showed dentin bond strength reduction after 2-year storage. GBU showed higher nanoleakage. Experimental etchants did not affect enamel bond strength. Dentin bond strength was not stable after 2 years, despite promising 24-hour results. SignificanceThis study suggests multiple etching approaches to optimize and achieve stable dentin bonding, while also offering in-depth information about the performance of recently released universal adhesive systems.