Reduction In Bond Strength Research Articles

Effect of sodium hypochlorite on adhesive charactersitics of dentin: A systematic review of laboratory-based testing

ObjectiveThe purpose of this review was to systematically summarize the outcomes of laboratory-based studies investigated the effect of sodium hypochlorite application on bond strength of dentin to various materials. DataA comprehensive literature search was conducted using PubMed, Google Scholar, Cochrane Library and OpenThesis database. Then a manual search was also carried out for references from identified articles. SourcesThe search followed the “Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)” statement. Two independent reviewers evaluated the collected studies for their eligibility according to the inclusion and exclusion criteria. Data abstraction and evaluation of risk of bias was then performed. Study selectionA total of 164 articles were assessed for eligibility. Only 69 met the inclusion criteria. Most included studies presented a low (15.9%) to medium (68.1%) risk of bias. Only 15.9% presented high risk of bias. Because of heterogeneity of the included studies, Meta-analysis was not performed. ConclusionThe outcome from low or high risk of bias studies revealed that sodium hypochlorite has no effect on bond strength of coronal or root canal dentin. While that from medium risk studies showed a reduction in bond strength of dentin.

Changes of bond strength properties of hot-dip galvanized plain bars with cement paste after 1 year of curing

This paper studies the effect of the corrosion of hot-dip galvanized steel on the porosity development of cement paste at the interfacial transition zone (ITZ) between the two materials. The corrosion of hot-dip galvanized steel by hydrogen evolution was studied during the curing of cement paste samples stored above the water level (AW = 95% RH) and below the water level (BW). The changes in the corrosion process were recorded via the time – open circuit potential evolution (Ecorr/FeCr18Ni9) of stainless steel plate (recounted to Ecorr/SCE) in cement paste bodies. Total monitoring time for the development of both parameters were 6 days, 4 months and 1 year.Further, the bond strength between plain hot-dip galvanized steel and cement by modified pull-out test was verified. Total time of curing was in this case 6 days, 4 months and 1 year.The corrosion reaction between hot-dip galvanized steel and fresh cement produces hydrogen, which significantly increases the capillary porosity of the cement paste at the interfacial transition zone (ITZ). The resulting capillary pores are not effectively filled by the zinc corrosion products and the porous structure is maintained even after one year of curing.Porosity increase of cement consequently results in reduction of bond strength between plain hot-dip galvanized steel and concrete which remains low even for samples cured for very long exposure time.

Effect of sodium ascorbate on bond strength and metalloproteinases activity in bleached dentin.

AimThis study evaluated the effect of sodium ascorbate (SA) on the proteolytic activity of matrix metalloproteinases (MMPs) and investigated the related effects on the bond strength of bleached dentin.Materials and methodsEighty freshly extracted human third molars were randomly divided according to treatment (bleaching or SA application), type of analysis (microshear or measuring MMP activity), and post-bleaching time to assess bond strength (24 hrs or 30 days). Data from both analyses were subjected to one-way analysis of variance to detect differences among groups, followed by Tukey’s multiple comparison test (p≤0.05).ResultsDental bleaching significantly reduced bond strength values when the adhesive strategy was performed after 24 hrs (despite the SA treatment) or 30 days after the bleaching procedure. However, after 30 days, the bond strength values of the groups who received bleaching or SA application were similar to those of the unbleached group. Dental bleaching caused the activation of MMPs, and SA did not influence this activity.ConclusionIt was concluded that SA does not affect the activity of MMPs or the bond strength in bleached dentin immediately after the bleaching treatment.

Study on the weakening mechanism of anchorage interface under the action of water

In this paper, pull-out tests of bolt are carried out to investigate the relation between water inflow and bolt-resin interface. Then, water intrusion tests and ring shear tests are sequentially conducted on rock-like specimens to investigate the effects of moisture content on the shear bond strength and failure mode of the rock–resin interface. The results suggest that the shear bond strength is markedly affected by water and failure concentrates on the interface between rock and resin after immersion in water. When comparing shear tests results from specimens with different immersion methods, it is evident that the resins have low hydroscopic behavior. It is also evident that rock weakening after water intrusion is the main cause of shear bond strength reduction of the rock–resin interface. During the failure process of dry specimens, there is evidence of a resin bearing stage, a breaking point and a residual stage that dissipates. Also, the applied load plunges after peak stress is achieved in specimens with increasing moisture content.

The effect of surface treatment and thermocycling on the shear bond strength of porcelain laminate veneering material cemented with different luting cements

Aim: The study aimed to evaluate and compare the effect of different surface treatment and thermocycling on the shear bond strength (SBS) of different dual-/light-cure cements bonding porcelain laminate veneers (PLV). Methods: One hundred and twenty A2 shade lithium disilicate discs were divided into three groups based on the resin cement used and on the pretreatment received and then divided into two subgroups: thermocycling and control. The surface treatment were either micro-etched with aluminium trioxide and 10% hydrofluoric acid or etched with 10% hydrofluoric acid only before cementation. Three dual-cure (Variolink Esthetic (I), RelyX Ultimate (II), and RelyX Unicem (III)) and three light-cure (Variolink Veneer (IV), Variolink Esthetic (V), RelyX Veneer (VI)) resin cements were used for cementation. The SBS of the samples was evaluated and analysed using three -way ANOVA with statistical significant set at α=0.05. Results: For all resin cements tested with different surface treatments, there was a statistically significant difference within resin cements per surface treatment (p<0.05). The shear bond strength in the micro-etch group was significant higher than the acid-etch group (p<0.05) There was statistically significant interaction observed between the surface treatment and thermocycling (p<0.05) as well as the cement and thermocycling(p<0.05). It was observed that the reduction in shear bond strength after thermocycling was more pronounced in the acid etch subgroup as compared to the microetch subgroup. However, the interaction between the three factors: surface treatments, thermocycling and resin cements did not demonstrate statistically significant differences between and within groups (p=0.087). Conclusions: Within the limitations of the present study, it acan be concluded that Dual cure resin cements showed a higher Shear bond strength as compared to light cure resin cements. Thermal cycling significantly decreased the shear bond strength for both ceramic surface treatments. After thermocycling, the specimens with 10% HF surface treatment showed lower shear bond strength values when compared to those treated by sandblasting with Al2O3 particles.

Electronic structure, chemical bonding, optical, elastic and dynamical properties of MeB2 compounds: Effect of transition metal Me = Sc, Ti and Zr

In present paper, the electronic structure, chemical bonding, optical, elastic and dynamical properties of MeB2 compounds (Me = Sc, Ti and Zr) have been systematically investigated using the first principles calculations to show the effect of changing transition metal. Studied materials have metallic nature. Their chemical bondings are created by mixture of ionic and covalent character. The optical properties including reflectivity, absorption coefficient, refractive index, extinction coefficient, energy loss function and optical conductivity are deduced from calculated complex dielectric function. Obtained results show that these binaries are promising candidate for the application in optoelectronic devices. All three materials are brittle in nature. Their hardness decreases in order TiB2 → ZrB2 → ScB2 due to the reduction of bond strength. The elastic anisotropy is also demonstrated. ScB2, TiB2 and ZrB2 are dynamically stable due to that there is no negative frequency in their phonon dispersion curve.

Bond strength of deformed bar embedded in steel-polypropylene hybrid fiber reinforced concrete

This paper deals with the bond strength of deformed bar embedded in steel-polypropylene hybrid fiber reinforced concrete (HFRC) matrix. The benefits of hybrid fibers were evaluated through a series of monotonic/cyclic pull-out testing on 72 specimens. The influences of fiber characteristics, i.e. the volume fraction and aspect ratio, on the failure mode and the complete bond-slip responses were analyzed. Upon a simplified spring model, the effects of fiber reinforcement at different loading stages were further discussed. The results showed that for a well-confined HFRC specimen, the cyclic bond response at the pre-peak stage almost approached its monotonic response with slight reduction in the ultimate bond strength. Compared to the specimen made with plain concrete, the introduction of hybrid fibers could exert obvious positive influences on the bond strength, due to the synergetic effects in inhibiting the propagation of cracks at multi-scale and multi-stages. Finally, an analytical model was proposed to estimate the ultimate bond strength, in which the effects of fiber reinforcement, stirrup confinement and geometrical shape of deformed bar were taken into consideration. The model was subsequently well validated by various independent experimental results.

Mechanical compatibility and adhesion between alkali-activated repair mortars and Portland cement concrete substrate

Abstract Alkali-activated materials (AAM) have been widely promoted as potential repair material for Portland-cement concrete (PCC). However, a thorough evaluation of compatibility and adhesion of AAM to PCC substrates and the correlation of these properties to the AAM composition is still required. AAMs obtained from metakaolin (MK) partially substituted (0, 20, 40, 60 and 80 wt%) with blast furnace slag (BFS) and their mechanical compatibility with a representative PCC substrate was investigated. Mortars with equivalent compressive strength and modulus of elasticity (with and without polypropylene fiber reinforcement) were applied onto the substrate and subjected to bond tests (pull-off and bending tests). Results indicate that neat MK-based mortars present excellent adhesion to PCC, but are vulnerable to delamination. The addition of 20% BFS mitigates this issue, by reducing the solution demand and drying shrinkage. Higher contents of BFS (>60%) have reduced bond strength, probably due to high alkalinity.

Bond strength of ceramics heat-pressed onto three dental alloys

Statement of problemThe press-on-metal (PoM) technique has been used as an alternative fabrication method for metal-ceramic restorations. However, how the PoM technique compares with the conventional porcelain layering (CPL) technique under a variety of conditions is unclear. PurposeThe purpose of this in vitro study was to compare the bond strength of 3 alloy substrates with heat-pressed ceramics or conventionally layered porcelain before and after thermocycling. Material and methodsSpecimens (n=5) of Au, Pd, and Ni-Cr alloys were veneered with heat-pressed ceramics or conventionally layered porcelain. The 3-point bend test was conducted according to the International Organization for Standardization standard 9693-1 as bond strength before and after thermocycling. The metal-ceramic interfaces were characterized by field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDS). Two- and 3-way ANOVA followed by the Tukey honestly significant difference (HSD) test were used to analyze the data (α=.05). ResultsSignificantly lower mean bond strength was recorded for the Au and Pd alloys of the PoM group than for those of the CPL group (P<.05). CPL-Au demonstrated the highest bond strength of 50.2 ±2.0 MPa, whereas PoM-Pd showed the lowest bond strength of 31.8 ±2.7 MPa; significant differences were found among all groups (P<.05). After 20 000 thermocycles, CPL-Au showed significantly reduced bond strength value (P<.05). A value of approximately 40 MPa was observed in all groups except for PoM-Pd (26.5 ±1.6 MPa, P<.05). The metal-ceramic interface resulting from the PoM technique revealed 2- to 20-μm pores, with more defects observed in the PoM-Pd group than in any of the other group. ConclusionsDefects and an oxide layer were formed at the metal-ceramic interface during the heat-pressing process, especially for the Pd alloy. After thermocycling, PoM-Pd had the lowest bond strength value, although it exceeded the minimum 25 MPa of the ISO 9693-1 standard. The Au and Ni-Cr alloys exhibited similar levels of porcelain bond strength with both techniques.

Thermal Cycling of Sintered Silver (Ag) Joint as Die-Attach Material

Sintered silver is a promising die-attach material capable of operating at temperatures of more than 200°C. However, while sintering reliably bonds Ag paste on Ag-plated substrate, reliability studies are needed to understand the behavior of this sintered bond on copper and direct bond copper (DBC) substrates. Here, we thermally cycled micron-Ag and nano-Ag joints created via sintering on Cu, DBC, and Ag-plated substrates between − 65°C and 150°C in order to understand their evolving microstructures and reliability. Short periods at high temperature did not oxidize the substrate, but the absence of copper oxides did not prevent adhesive failure of the nano-Ag joint at the Cu interface. We found that Ag filler size influences pore shapes, pore sizes, and shear strength; the micron-Ag joint produced a mixture of irregular and regular spherical pore shapes that reduced bond strength more than the predominantly spherical pores present in the nano-Ag joint.

Shear Bond Strength of Resin Cement to Saliva-Contaminated Metal Alloys after Various Surface Treatments

The bonding ability of resin cement to metal alloys of conventional dental restorations is critical for the retention and long-term survival rate. Contaminated saliva during try-in process which is resistant to simple water rinsing could reduce bond strength. Surface treatment before cementation might have an important role in optimizing resin-metal bond strength. The purpose of this study was to study the effect of surface pretreatment on the shear bond strength of dental base metal alloys after saliva contamination using a self-adhesive resin cement. Forty dental wax patterns (7-mm diameter) were made and cast with dental base metal alloy (Argeloy N.P. (V)). Cast metal specimens were embedded in PVC tube using self-curing acrylic resin and then flattened with 600-grit silicon carbide paper. PVC tube holders were specifically designed for the shear bond strength test device. Forty resin composite specimens were prepared in plastic mold (diameter of 3 mm and depth of 3 mm). The resin composite specimens were treated with sandblasting. Fifty-μm aluminum oxide particle was blasted for 10 seconds from the distance of approximately 5 mm perpendicular to the bonding surface. Metal alloy specimens were immersed in artificial saliva for 1 minute and rinsed with water-spray for 15 seconds. The specimens were also air-dried for 15 seconds. Specimens were divided into four groups, which received one of the following surface treatments: (1) No surface treatment (Control), (2) 37% phosphoric acid, (3) 37% phosphoric acid and then rinsed with 70% ethyl alcohol, and (4) 70% ethyl alcohol. After rinsing and drying, the resin composite specimens were cemented with Panavia SA Cement (Kuraray Noritake Dental Inc., Okayama, Japan) at the center of metal alloy specimens followed by the manufacturer’s instruction. Before testing, the specimens were stored in distilled water at 37oC for 24 hours. For testing, specimens were dried and mounted to universal testing machine (EZ-S, Shimadzu Co., Kyoto, Japan) at the crosshead speed of 1 mm/minute. Failure loads was recorded in Newton (N) and then analyzed to Mega Pascal (MPa). The highest shear bond strength was observed for group 2 and 3. The failure mode in all the materials was adhesive failure which occurred at the resin-metal interface. Within the limitations of this study, phosphoric acid was effective in removing saliva contamination and enhancing bond strength at the resin-dental base metal interface.

Bond strength of orthodontic adhesives to dry and saliva-moistened enamel – a comparative in vitro study

salivamoistened enamel. Design/methodology/approach: One hundred twenty stainless steel brackets were bonded to human mandibular third molars with six materials: Enlight LC® (Ormco Corp), Grengloo® (Ormco Corp), Light Bond® (Reliance Orthodontic Products), Charisma® (Heraeus Kulzer), SmartBond® (Gestenco), and Transbond XT® with MIP® primer (3M Unitek). One half of the specimens in each group (n=10) was bonded to dry enamel, while the other half to saliva-moistened enamel. Bond strength testing was performed with a wire loop loading technique after 30-min incubation in artificial saliva. Failure mode was evaluated using adhesive remaining index (ARI). Findings: No significant differences in bond strength to dry enamel were noted for all composite materials (p&gt;0.05). SmartBond exhibited significantly greater bond strength to moistened enamel (7.10 ± 1.47 MPa) and comparable with other composite materials to dry enamel. Composite materials demonstrated significantly reduced bond strength to saliva-moistened enamel (p&lt;0.001), except for Transbond MIP, whose bond strength was not significantly decreased by saliva contamination (p=0.089). There was not statistically significant difference between bond strength of SmartBond and Transbond to saliva contaminated enamel. A higher incidence of cohesive failures was noted for all materials. Research limitations/implications: Composite light-cured materials provide adequate bond strength to dry enamel. Cyanoacrylate adhesive provides sufficient bond strength only under moist conditions. Transbond XT+MIP has sufficient bond strength to either dry or saliva-moistened enamel. Practical implications: The study evaluated the bonding strength of orthodontic brackets, which is a critical parameter in orthodontics, especially in situations that do not allow for proper isolation from saliva, such as bonding to impacted teeth following surgical exposure. Originality/value: Bond strengths evaluated with loop loading technique in different study environments would help the orthodontist to choose the most effective adhesive for the specific clinical situation.

Effect of surface removal following bleaching on the bond strength of enamel

BackgroundA reduction in bond strength of bleached enamel has been confirmed in the literature. Although limited information is available, it is conceivable that the veneer preparation process may remove the impacted enamel and further eliminate the compromised bond strength between the composite resin and bleached enamel. This study aimed to evaluate the effect of surface removal following bleaching on the micro-shear bond strength (μSBS) of bleached enamel.MethodsForty-eight specimens were prepared from bovine incisors and were randomly divided into 2 groups (n = 24): group B (bleaching with 40% hydrogen peroxide for 2 × 45 min with a 1-week interval) and group C (control group without bleaching treatment). Immediately after receiving the treatments, 0.5 mm of the enamel was removed from the specimen surface, followed by bonding of composite resin to the enamel surface. Each group was further divided into 2 subgroups of 12 specimens each: subgroup T (with 5000 thermocycles in water baths at 5 °C and 55 °C), and subgroup N (without thermocycling). The μSBS values were measured using a universal testing machine and subjected to two-way analysis of variance (α = 0.05). The fracture modes of the specimens were observed using a stereomicroscope.ResultsThe μSBS values of the different groups ranged from 21.42 to 25.21 MPa. Following a surface reduction of 0.5 mm, bleaching treatment and thermocycling did not significantly affect the μSBS values (P = 0.348 and P = 0.507, respectively). No significant interaction was found between the bleaching treatment and thermocycling (P = 0.514). All the groups exhibited a high percentage of mixed failures. Compared with group C, group B exhibited higher percentage of adhesive failure.ConclusionThe results suggested that the bonding procedure could be performed on the bleached enamel following a surface reduction of 0.5 mm immediately after the bleaching treatment.

Reduction Potentials of P450 Compounds I and II: Insight into the Thermodynamics of C-H Bond Activation.

We present a mixed experimental/theoretical determination of the bond strengths and redox potentials that define the ground-state thermodynamics for C-H bond activation in cytochrome P450 catalysis. Using redox titrations with [Ir(IV)Cl6]2-, we have determined the compound II/ferric (or Fe(IV)OH/Fe(III)OH2) couple and its associated D(O-H)Ferric bond strength in CYP158. Knowledge of this potential as well as the compound II/ferric (or Fe(IV)O/Fe(III)OH) reduction potential in horseradish peroxidase and the two-electron compound I/ferric (or Fe(IV)O(Por•)/Fe(III)OH2(Por)) reduction potential in aromatic peroxidase has allowed us to gauge the accuracy of theoretically determined bond strengths. Using the restricted open shell (ROS) method as proposed by Wright and co-workers, we have obtained O-H bond strengths and associated redox potentials for charge-neutral H-atom reductions of these iron(IV)-hydroxo and -oxo porphyrin species that are within 1 kcal/mol of experimentally determined values, suggesting that the ROS method may provide accurate values for the P450-II O-H bond strength and P450-I reduction potential. The efforts detailed here indicate that the ground-state thermodynamics of C-H bond activation in P450 are best described as follows: E0'Comp-I = 1.22 V (at pH 7, vs NHE) with D(O-H)Comp-II = 95 kcal/mol and E0'Comp-II = 0.99 V (at pH 7, vs NHE) with D(O-H)Ferric = 90 kcal/mol.

Dry-bonding to dentin using alternative conditioners based on iron-containing solutions or nitric acid

ObjectivesTo evaluate the effect of experimental conditioners (10–3 solution − 10–3, 6.8% ferric oxalate - FOX, and 1.4% nitric acid - NI) on dentin elastic modulus, flexural strength, bond strength, failure mode, and adhesive interface morphology of two etch-and-rinse adhesives (XP Bond, Dentsply or One-Step, Bisco) applied on etched dry dentin. MethodsSound human third molars were used for the microtensile bond strength test (n = 8), performed at 24 h and after one year of water storage. Failure modes were evaluated by scanning electron microscopy. Dentin bonding interface was analyzed by confocal laser scanning microscopy (n = 3). Adhesive systems were applied on phosphoric acid-etched, wet (positive control) and dry (negative control) dentin, and on etched and dry dentin previously treated with 10–3 (15s), FOX (60s), or NI (15s). Bovine dentin bars (n = 15) were immersed into the conditioning solutions and subjected to a three-point bending test. ResultsXP Bond + 10–3 or NI resulted in lower bond strength than phosphoric acid. One-Step + 10–3 or NI resulted in bond strengths equivalent to the positive control. Experimental conditioners presented no bond strength reduction after one year, regardless of the bonding agent tested. One-Step resulted in more adhesive failures than XP Bond at 24 h, and mixed failures increased after storage. All experimental conditioners promoted hybridization and resin tags formation, except FOX. Dentin elastic modulus was not affected by the conditioners, whereas flexural strength was significantly reduced by FOX. ConclusionsAdequate and stable dentin bonds were achieved when the bonding agents were applied on 10–3 or NI-treated dentin. None of the experimental conditioners reduced dentin elastic modulus, but dentin flexural strength was significantly reduced by FOX-conditioning.

Effects of Ions-Releasing Restorative Materials on the Dentine Bonding Longevity of Modern Universal Adhesives after Load-Cycle and Prolonged Artificial Saliva Aging.

This study aimed at evaluating the microtensile bond strength (MTBS) and fractographic features of dentine-bonded specimens created using universal adhesives applied in etch-and-rinse (ER) or self-etching (SE) mode in combination with modern ion-releasing resin-modified glass-ionomer cement (RMGIC)-based materials after load cycling and artificial saliva aging. Two universal adhesives (FTB: Futurabond M+, VOCO, Germany; SCU: Scotchbond Universal, 3M Oral Care, USA) were used. Composite build-ups were made with conventional nano-filled composite (AURA, SDI, Australia), conventional resin-modified glass ionomer cement (Ionolux VOCO, Germany), or a (RMGIC)-based composite (ACTIVA, Pulpdent, USA). The specimens were divided in three groups and immersed in deionized water for 24 h, load-cycled (350,000 cycles; 3 Hz; 70 N), or load-cycled and cut into matchsticks and finally immersed for 8 months in artificial saliva (AS). The specimens were cut into matchsticks and tested for microtensile bond strength. The results were analyzed statistically using three-way ANOVA and Fisher’s LSD post hoc test (p < 0.05). Fractographic analysis was performed through stereomicroscope and FE-SEM. FTB showed no significant drop in bond strength after aging. Unlike the conventional composite, the two RMGIC-based materials caused no bond strength reduction in SCU after load-cycle aging and after prolonged aging (8 months). The SEM fractographic analysis showed severe degradation, especially with composite applied on dentine bonded with SCU in ER mode; such degradation was less evident with the two GIC-based materials. The dentine-bond longevity may be influenced by the composition rather than the mode of application (ER vs. SE) of the universal adhesives. Moreover, the choice of the restorative material may play an important role on the longevity of the finalrestoration. Indeed, bioactive GIC-based materials may contribute to maintain the bonding performance of simplified universal adhesives over time, especially when these bonding systems are applied in ER mode.

Effect of Argon Plasma Surface Treatment on Bond Strength of Resin Composite Repair.

This study evaluated the effect of argon plasma treatment (PLA) and its combination with sandblasting (SAN), silanization (SIL), and hydrophobic bonding resin (HBR) application on the micro-shear bond strength of water-aged restorative resin composite to a newly placed composite, simulating restoration repair. Forty-five light-cured composite plates (20-mm long × 20-mm wide × 4-mm thick) were fabricated using a hybrid composite and stored at 37°C in distilled water for six months. The aged composite surfaces were treated according to the following experimental groups, varying both treatment and order of application: 1) SAN + SIL + HBR (control), 2) SAN + PLA for 30 seconds + SIL + HBR, 3) SAN + SIL + PLA + HBR, 4) PLA + SIL + HBR, 5) PLA + SIL, 6) PLA + HBR, 7) SIL + PLA + HBR, 8) SIL + PLA, and 9) PLA. After the surface treatments, four fresh resin composite cylinders (1.5-mm high × 1.5-mm diameter) of the same composite were built on each aged composite surface using a silicone mold. After water storage for 24 hours or one year, the specimens were submitted to shear bond strength testing. Data were statistically analyzed by two-way analysis of variance and Tukey's test (5%). Groups 1, 2, and 4 presented significantly higher bond strength means at 24 hours, although group 4 did not differ from group 7. Groups 5, 8, and 9 demonstrated significantly lower means than the other groups. Even though groups 1 and 2 had a significant bond strength reduction after 1 year, they still demonstrated higher bond strength at one year of storage. While PLA application combined with surface treatment methods demonstrated high bond strength results, this treatment alone was not as beneficial as other methods that included SAN, SIL and HBR.

Use of (meth)acrylamides as alternative monomers in dental adhesive systems

Objectives: Methacrylamides are proposed as components for dental adhesive systems with enhanced resistance to hydrolytic and enzymatic degradation. The specific objective of this study was to evaluate the polymerization kinetics, water sorption and solubility, pH-derived degradation and microtensile bond strength of various monofunctional acrylamides and meth(acrylamides) when copolymerized with dimethacrylates. Methods: Base monomers were added at 60 wt%, and included either BisGMA or UDMA. Monofunctional monomers were added at 40 wt%, including one (meth)acrylate as the control, two secondary methacrylamides and two tertiary acrylamides. DMPA (0.2 wt%) and DPI-PF6 (0.4 wt%)/BHT (0.1 wt%) were added as initiators/inhibitor. Polymerization kinetics wwere followed with near-IR spectroscopy in real time. Water sorption (WS) and solubility (SL) were measured following ISO 4049. Monomer degradation at different pH levels was assessed with 1H NMR. Microtensile bond strength (MTBS) was assessed in caries-free human third molars 48 h and 3 weeks after restorations were placed using solvated BisGMA-based adhesives (40 vol% ethanol). Data were analyzed with one-way ANOVA/Tukey’s test (α = 0.05). Results: As expected, rate of polymerization and final degree of conversion (DC) were higher for the acryl versions of each monomer, and decreased with increasing steric hindrance around the vinyl group for each molecule. In general, UDMA copolymerizations were more rapid and extensive than for BisGMA, but this was dependent upon the specific monofunctional monomer added. WS/SL were in general higher for the (meth)acrylamides compared to the (meth)acrylates, except for the tertiary acrylamide, which showed the lowest values. One of the secondary methacrylamides was significantly more stable than the methacrylate control, but the alpha substitutions decreased stability to degradation in acid pH. MTBS in general was higher for the (meth)acrylates. While for all materials the MTBS values at 3 weeks decreased in relation to the 24 h results, the tertiary acrylamide showed no reduction in bond strength. Significance: This study highlights the importance of considering steric and electronic factors when designing monomers for applications where rapid polymerizations are needed, especially when co-polymerizations with other base monomers are required to balance mechanical properties, as is the case with dental adhesives. The results of this investigation will be used to design fully formulated adhesives to be tested in clinically-relevant conditions.

Load capacity predictions of continuous concrete deep beams reinforced with GFRP bars

Nine continuous concrete deep beams reinforced with glass fibre reinforced polymer (GFRP) bars were experimentally tested to failure. Three main parameters were investigated, namely, shear span-to-overall depth ratio, web reinforcement and size effect. The experimental results confirmed the impacts of web reinforcement and size effect that were not considered by the strut-and-tie method (STM) of the only code provision, the Canadian S806-12, that addressed such elements. The experimental results were employed to evaluate the applicability of the methods suggested by the American, European and Canadian codes as well as the previous studies to predict the load capacities of continuous deep beams reinforced with GFRP bars. It was found that these methods were unable to reflect the influences of size effect and/or web reinforcement, the impact of which has been confirmed by the current experimental investigation. Therefore, a new effectiveness factor was recommended to be used with the STM. Additionally, an upper-bound analysis was developed to predict the load capacity of the tested specimens considering a reduced bond strength of GFRP bars. A good agreement between the predicted results and the experimental ones was obtained with the mean and coefficient of variation values of 1.02 and 5.9%, respectively, for the STM and 1.03 and 8.6%, respectively, for the upper-bound analysis.

Adhesion characterisation of Portland cement concrete and alkali-activated binders

Alkali-activated binders (AABs) are investigated for their potential use as repair materials of Portland cement concrete (PCC). The adhesion characterisation of PCC and repair materials using AAB made from fly ash (FA) and Portland cement (PC) activated with sodium hydroxide and sodium silicate solutions, AAB made from FA and calcium hydroxide (CH) activated with sodium hydroxide and sodium silicate solutions, and commercial repair materials (RMs) have been investigated. Test results show that the AAB with additives gives high bond strength which is similar to the use of RMs. Bond strength between PCC substrate and AAB with additives is improved, due to increased reaction products, especially calcium–silicate–hydrate gel. However, the CH replacement at 15% shows a large amount of calcite resulting in a reduction in bond strength. The failure patterns and fracture interface images of the tested specimens also demonstrate the quality of the developed bond strength. It is shown that the interface zone of PCC substrate and AAB is homogeneous with no visible gap between the two bonding surfaces. It is suggested that the AAB with PC as additive can be used as a repair binding material which not only has high bond strength but is also cost-effective.