Adhesive Failure Mode Research Articles

A novel dual surface modification on titanium in dental use: Characterization and topography

This laboratory study aimed to compare, contrast, and evaluate the effect of a novel dual surface modification method on the adhesion strength of resin composite cement to titanium. C.p.‐2 grade titanium samples were silica‐coated, etched with HNO3(69vol %) or a blend of HCl (35vol %) and H3PO4 (85vol %), for 1 h at 80°C. Surface roughness was measured by surface roughness profilometry, topographic analysis by scanning electron microscopy (SEM), atomic force microscopy (AFM), and surface analyses by energy dispersive X‐ray spectroscopy (EDX), X‐ray photoelectron spectroscopy (XPS). Silanization of all specimens was carried out after SEM, EDX, and AFM analysis, before enclosed mold microshear bond strength testing (EM‐μSBS). Adhesion strengths were measured after artificial ageing: 1 day, 1 week, 4 weeks, and 8 weeks by EM‐μSBS testing and failure mode analysis by optical microscopy. Polished titanium was used as a control. The highest surface roughness was observed in titanium samples treated with silica‐coating + HCl‐H3PO4 etching. The elemental composition confirmed the presence of Ti, O, C, with Si and Al in samples treated with silica‐coating. A gradual decrease in EM‐μSBS values was observed in all titanium samples with adhesive and cohesive failure modes. The novel dual surface modification method applied in this study suggests that silica‐coating + HCl‐H3PO4etching strongly affects titanium surface topography and roughness. The presence of Si on silica‐coated surface modified titanium before silanization with an experimental silane has a positive effect on the EM‐μSBS of titanium samples treated with silica‐coating only or silica‐coating + HNO3 etching.

The surface modification effect on the interfacial properties of glass fiber-reinforced epoxy: A molecular dynamics study

Abstract In this work, the effect of common functional groups, namely hydroxyl, formyl, carboxyl, and amine groups on the interfacial behavior of surface-modified glass fiber-reinforced epoxy is investigated at molecular scale. The interfacial properties of the epoxy/silica coated with different functional group systems are quantified by performing pulling test using the steered molecular dynamics simulations. It is found that the system with hydroxyl groups has a relatively lower interfacial interaction, exhibiting an adhesive failure mode. When partial hydroxyl groups are replaced by carboxyl, amine, and formyl groups, respectively, the interfacial interactions are increased and these systems exhibit a cohesive failure mode where failure happens in the epoxy close to interface. A relatively higher force is required for the adhesive debonding, while more energy can be dissipated for the cohesive debonding. Because the increased interfacial interactions can prevent the mobility of polymer chains, and delay the propagation of micropores in the matrix, leading to the epoxy matrix with a high ability of energy absorption. Our work provides an insight into how functional groups affect the interface debonding behavior of glass fiber-reinforced epoxy, offering a guideline for control of the interfacial properties of such composites through surface modification techniques.

Enhanced Interfacial Properties of Carbon Nanomaterial–Coated Glass Fiber–Reinforced Epoxy Composite: A Molecular Dynamics Study

The weak interfacial adhesion has significantly affected the durability, long-term reliability, and performance of glass fiber–reinforced epoxy composites. The coating of graphene and carbon nanotubes on the glass fiber can have a positive effect on the strength, toughness, and thermal insulation performance of glass fiber-reinforced composites. However, the strengthening mechanism of carbon nanomaterial coating on the interfacial adhesion between glass fiber and epoxy has not been fully explored. In this work, the effect of graphene and single-walled carbon nanotubes (SWCNTs) on the interfacial properties of the glass fiber–reinforced epoxy has been investigated at atomistic scale. The graphene and SWCNTs are sandwiched between epoxy and silica to study the debonding behavior of the sandwiched structures. It is found that the interfacial energy is significantly improved with the incorporation of graphene and SWCNTs between epoxy and silica, causing an obvious improvement in adhesion stress for graphene coating and in debonding displacement for SWCNT coating. Compared with the epoxy/silica without coatings where the silica and epoxy detach from the contact surface, the sandwiched structures display different failure modes. The sandwiched structure with graphene coating fails at the epoxy matrix close to the interface, exhibiting a cohesive failure mode because of the relatively stronger interfacial interactions. The structures with SWCNTs fail at the interface between silica and SWCNTs, representing an adhesive failure mode due to the interlocking between SWCNTs and polymer chains. This work provides a theoretical guideline to optimize the interface adhesion of coated glass fiber–reinforced epoxy via structure design and surface modification of coating materials.

Effect of surface roughness of electroplating chromium coated steel on bonding strength of polymer coated steel

The effect of surface roughness of electroplating chromium coated steel on bonding strength of polymer coated steel has been investigated in this paper. The experimental results have shown that the electroplating chromium coated steel with different surface roughness could be obtained through the substrate surface treatment before the electroplating process. The peeling test results have shown that the peeling force of the polymer coated steel would increase with the increase of surface roughness of the electroplating chromium coated steel, but the increase rate would become slow gradually. With the increase of surface roughness of electroplating chromium coated steel, the PET film would be damaged locally and some polymer residues would remain on the electroplating chromium coated steel; when the bonding force is large enough, the plating shedding would occur on the electroplating chromium coated steel. With the appearance of the polymer residues and the occurrence of plating shedding, the failure mode of polymer coated steel would transform from adhesion failure mode to the mixed failure mode.

Shear strength and failure modes of double-lap bi-material CFRP/Ni-Cr alloy joint under severe environmental conditions

This study was systematically conducted to investigate the dependence of mechanical behaviors of double-lap bi-material joints on various environmental conditions, including room temperature dry (RTD), cold temperature dry (CTD), elevated temperature dry (ETD), elevated temperature wet (ETW), salty spray (SS), and thermal shock cycles (TS) conditions. Compared to the RTD condition, the shear strength of the joint under the CTD and TS conditions shows increases of approximately 50.0% and 9.09%, respectively, but lower values are obtained under ETD (18.18%), ETW (72.73%), and SS (27.27%) conditions. Failure modes of lap-joint are analyzed on fractured surfaces and confirmed by finite element simulation in which the cohesive failure mode mainly occurs with the highest distributed stresses. However, an experimental adhesive failure mode partially appears under the ETD, ETW, and SS conditions. Furthermore, as the less prevalent conditions, the dependencies of the shear strength and failure mode on the exposure time under SS and TS conditions are more thoroughly evaluated based on the scanning electron microscope (SEM) and the energy-dispersive X-ray spectroscopy (EDS) to show microstructures and chemical compositions of the fracture surface, respectively. The effects of environmental conditions, particularly under SS and TS conditions, could provide new insight into designing specific bonded joints.

Effect of Curcumin Suspension and Vitamin C on Dentin Shear Bond Strength and Durability. A Pilot Study

Background: Preserving the strength and durability of dentin bonds is a concern of dental researchers and practitioners. Objective: The aim of this study was to investigate the effect of treating etched dentin with vitamin C and curcumin suspension as cross-linking agents on the shear bond strength and durability of a universal dental adhesive. Methods: Extracted human third molar teeth were collected. Fifty-six flat coronal dentin surfaces were divided equally into four groups: (1) treated with adhesives; (2) etched with 37% H3PO4 for 10s before application of adhesives; (3) same as group (2), but with dentin treated with 2.5% curcumin suspension for 60s before the application of adhesive; and (4) same as group (3), but with the use of a 20% vitamin C suspension instead of a curcumin suspension. Filtek Z350XT composite was built for all samples. Half of the samples in each group were subjected to thermocycling. Shear bond strength was measured using a universal testing machine. Scanning electron microscopy was used to investigate the dentinal surfaces after treatment. Results: Treatment with curcumin suspension preserved immediate and long-term bond strength. Conversely, treatment of etched dentin with vitamin C solution significantly reduced the immediate bond strength, but a significant improvement was observed after aging. SEM showed that both cross-linking agents resulted in narrowing or closing of the dentinal tubules, with an adhesive mode of failure. Conclusion: The application of curcumin or vitamin C suspension to acid-etched dentin resulted in different effects on immediate and long-term shear bond strength when using universal adhesives.

Retention Force of Glass Ionomer Based Luting Cements with Posterior Primary Zirconium Crowns - A Comparative in Vitro Study.

To determine the retentive force of three glass-ionomer luting cements used with prefabricated primary zirconium crowns (PPZCs) and to assess whether the retentive force was dependent on cementation material or different PPZCs brands. Four mandibular right second molar PPZCs were selected, one each from four manufacturers-NuSmile®ZR, Sprig Crowns, Cheng Crowns and Kinder Krowns. Silicone impressions of the outer surface of crowns were taken; stone dies prepared and reduced to fit the corresponding brand. 24 alginate impressions of each die obtained and filled with core buildup flowable composite. 96 composite tooth-replicas thus achieved were divided into four groups and further categorized into three subgroups of eight samples based on luting cements used - BioCem, FujiCEM®2 and KetacCem. Samples were thermocycled, placed in artificial saliva for one week followed by assessment of retentive force for crown dislodgment and failure mode. Data was statistically evaluated using two-way ANOVA, HSD (P <0.05). KetacCem had the lowest retentive force while BioCem showed comparatively higher value to FujiCEM®2. Adhesive failure modes were predominant with cement mainly adhering to crown's internal surface. Resin-based GI cements offered superior retention than conventional GI cements for PPZCs and retentive force was dependent on cement type.

Comparison of two adhesive systems of various polyetheretherketone (PEEK) composites on the shear bond strength

Aim: In this in vitro study, the effect of two adhesive systems applied to surfaces of different polyether-ether-ketone (PEEK) composites on the shear bond strength (SBS) of a composite resin was compared.&#x0D; Methodology: Eighty PEEK specimens were divided into four groups (n=20): Unfilled PEEK (UF), carbon-fiber-reinforced PEEK (CFR), glass-fiber-reinforced PEEK (GFR), and ceramic-reinforced PEEK (CR). Each group was further divided into two subgroups (n=10): Visio.link (VL) and Single Bond Universal (SB). The specimens with 8-mm diameter and 5-mm thickness were prepared. SBS was examined using a universal testing machine. Results were statistically analyzed by multivariate analysis of variance and Tukey’s post-hoc test. Failure modes were analyzed using a stereomicroscope at 20× magnification. Surface properties were examined by scanning electron microscopy. The surface properties of the specimens were examined by scanning electron microscopy (SEM). &#x0D; Results: Effect of different PEEK and adhesive systems on SBS was found to be statistically significant (p&lt;0.05). SBS values for CFR-VL and UF-VL groups were statistically more significant than those for CFR-SB and UF-SB groups (p=0.001). SBS values for the GFR-VL group were statistically more significant than that for the UF-VL group (p=0.001). SBS values for the CF-SB group were statistically more significant than those for CFR-SB and CFR-SB groups (p=0.001). Failure modes were examined using a stereomicroscope at 20× magnification, and adhesive and mixed failure modes were observed.&#x0D; Conclusion: PEEK composites with different contents and properties can be used in fixed prosthetic restorations. However, additional experimental and clinical studies are required to investigate different PEEK frameworks and composite veneers.&#x0D; &#x0D; How to cite this article: Demirci F, Tekin S. Comparison of two adhesive systems of various polyetheretherketone (PEEK) composites on the shear bond strength. Int Dent Res 2021;11(2):54-61. https://doi.org/10.5577/intdentres.2021.vol11.no2.1&#x0D; &#x0D; Linguistic Revision: The English in this manuscript has been checked by at least two professional editors, both native speakers of English.

Effect of Sputter Deposition on the Adhesion and Failure Behavior between Cu Film and Glassy Calcium Aluminosilicate: A Molecular Dynamics Study

Understanding the physical vapor deposition (PVD) process of metallic coatings on an inorganic substrate is essential for the packaging and semiconductor industry. In this work, we investigate a Copper (Cu) film deposition on a glassy Calcium Aluminosilicate (CAS) by PVD and its dependence on the incident energy. Molecular dynamics simulation is adopted to mimic the deposition process, and pure Cu film is grown on top of CAS surface forming intermixing region (IR) of Cu oxide. In the initial stage of deposition, incident Cu atoms are diffused into CAS bulk and aggregated at the surface which leads to the formation of IR. When the high incident energy, 2 eV, is applied, 20% more Cu atoms are observed at the interface compared to the low incident energy, 0.2 eV, due to enhanced lateral diffusion. As the Cu film grows, the amorphous thin Cu layer of 1 nm is temporarily formed on top of CAS, and crystallization with face-centered cubic from amorphous structure follows regardless of incident energy, and surface roughness is observed to be low for high incident energy cases. Deformation and failure behavior of Cu-CAS bilayer by pulling is investigated by steered molecular dynamics technique. The adhesive failure mode is observed, which implies the bilayer experiences a failure at the interface, and a 7% higher adhesion force is predicted for the high incident energy case. To find an origin of adhesion enhancement, the distribution of Cu atoms on the fractured CAS surface is analyzed, and it turns out that 6.3% more Cu atoms remain on the surface, which can be regarded as a source for the high adhesion force. Our findings hopefully give the insight to understand deposition and failure mechanisms between heterogeneous materials and are also helping to further improve Cu adhesion in sputter experiments.

Discharge Plasma Treatment as an Efficient Tool for Improved Poly(lactide) Adhesive-Wood Interactions.

Poly(lactide) (PLA) films obtained by thermoforming or solution-casting were modified by diffuse coplanar surface barrier discharge plasma (300 W and 60 s). PLA films were used as hot-melt adhesive in joints in oak wood. It was demonstrated that lap shear strength increased from 3.4 to 8.2 MPa, respectively, for the untreated and plasma-treated series. Pull-off tests performed on particleboard for the untreated and treated PLA films showed 100% cohesive failure. Pull-off strength tests on solid oak demonstrated adhesion enhancement from 3.3 MPa with the adhesion failure mode to 6.6 MPa with the cohesion failure mode for untreated and treated PLA. XPS revealed that carbonyl oxygen content increased by two-to-three-fold, which was confirmed in the Fourier-transform infrared spectroscopy experiments of the treated PLA. The water contact angle decreased from 66.4° for the pristine PLA to 49.8° after treatment. Subsequently, the surface free energy increased from 47.9 to 61.05 mJ/m2. Thus, it was clearly proven that discharge air plasma can be an efficient tool to change surface properties and to strengthen adhesive interactions between PLA and woody substrates.

Cohesive and adhesive degradation in PET-based photovoltaic backsheets subjected to ultraviolet accelerated weathering

Delamination between layers in photovoltaic (PV) backsheets is often reported in the literature, causing voids that can collect moisture, diminish module backside heat dissipation, and reduce the backsheet’s effectiveness as a physical barrier. While backsheets with weathering-resistant fluoropolymer outer layers have traditionally been used in modules, more recent backsheets using non-fluoropolymer outer layers, such as polyethylene terephthalate (PET), have been developed. These backsheets have shown signs of premature degradation, and their adhesion degradation, in particular, has not been widely studied. In the present work, the single cantilever beam (SCB) adhesion test was used to quantify the adhesion energy in two commercially available PET-based backsheets. To study the effect of minor changes in formulation, the backsheets were obtained from same manufacturer and product line but during different years. To study the effect of environmental variables on adhesion degradation, the backsheets were subjected to artificial weathering at controlled temperature, humidity, and ultraviolet (UV) radiation in an indoor weathering chamber, and the adhesion energy was quantified at several intervals of exposure time. Layering structure, composition, and adhesion failure mode were compared between the backsheets, using Raman and infrared spectroscopy and thermogravimetric analysis. The results show a large difference in initial (unexposed) adhesion energy between the backsheets, despite very similar structures and compositions. Following exposure, adhesion energy dropped significantly, primarily due to thermo-hydrolytic degradation of the polyurethane (PU)-based adhesive layers. Significant UV-induced adhesion degradation of the PET outer layer surface was also observed. The study represents an important step in understanding adhesion degradation in PET-based backsheets, suggesting ways in which adhesion integrity – and, correspondingly, module service life – can be improved.

Single-Lap Joints Bonded with Epoxy Nanocomposite Adhesives: Effect of Organoclay Reinforcement on Adhesion and Fatigue Behaviors

Organoclay, such as organo-modified montmorillonite (MMT), is one of the potential filler candidates in the preparation of epoxy nanocomposite adhesives for automotive and civil engineering industries. However, there is no systematic research on the effect of organoclay reinforcement on its adhesion and fatigue behaviors in shear loading. Here, single-lap joints (SLJs) of stainless steel substrates bonded with epoxy/MMT nanocomposite adhesives, consisting of diglycidyl ether of bisphenol A and poly(oxypropylene) diamine with various weight contents of a commercialized MMT filler, were prepared. The dispersity of MMT and bulk mechanical properties were investigated by wide-angle X-ray scattering/diffraction, the uniaxial tensile test, and dynamic mechanical analysis. The lap shear strengths and failure modes were investigated based on the single-lap shear test, and the joint durability was examined by using the fatigue test with various shear stress levels. Through the incorporation of the MMT fillers in epoxy resins, the lap shear strengths increased from 25 to 40 MPa, the failure modes changed from adhesive failure mode to cohesive one, and the fatigue lifetimes prolonged with the addition of a small amount of MMT.

A new mussel-inspired highly self-adhesive & conductive poly (vinyl alcohol)-based hydrogel for wearable sensors

Poly (vinyl alcohol) (PVA) hydrogel with nontoxicity, good biocompatibility and high mechanical strength was promising for wearable sensors. However, the traditional freezing/thawing or borax crosslinking method consumed large number of hydroxyl groups in PVA chains, causing insufficient self-adhesiveness of hydrogel. Herein, inspired by mussel-adhesive mechanism, we innovatively introduced carboxyl groups into PVA chains and fabricated PVA-COOH /polydopamine (PDA) hydrogel by incorporation with PDA as crosslinking agent. The formation mechanism of the hydrogel was confirmed through FTIR and 13C NMR analysis. With increasing PDA content, the crosslinking density increased significantly and the dense networks formed by dual covalent/hydrogen bonding. The hydrogel exhibited impressive stretchability and extremely high adhesiveness. It could adhere to both hydrophilic and hydrophobic surface, and the adhesion strength to metal/ rubber/pigskin reached as high as 158.26 kPa/149.86 kPa/56.67 kPa, respectively, attributing to the incorporated enough free catechol/quinone group, carboxyl/hydroxyl group and newly formed amide group in hydrogel, while the adhesion failure mode consisted of both interface failure and matrix failure of hydrogel, which consumed high energy under stress. Furthermore, the hydrogel showed conductive with high strain sensitivity, which could steadily and repeatedly monitor large-scale and subtle limb motions, exhibiting significant and diverse potential in wearable strain sensors.

Effect of using multiwall carbon nanotube reinforced epoxy adhesive in enhancing glass fiber reinforced polymer composite through cocure manufacturing technique

AbstractThe high‐performance epoxy‐based cocure manufacturing technique has been used to join composite structures such as wings, frames, and ribs in aerospace applications. The present study aims to examine the influence of multiwall carbon nanotubes (MWCNTs) addition on mechanical and free vibrational behavior of glass fiber reinforced polymer composites fabricated through cocure manufacture technique. The experimental results revealed that the addition of 1 wt.% of MWCNTs enriched the tensile and flexural properties of cocured composites by 27.8% (344 Mpa) and 26.16% (379.12 Mpa), respectively. Shear analysis depicted that 0.25 wt.% MWCNT reinforcement significantly enhanced the shear strength of cocured lap joints by 63.8% (16.79 MPa). The scanning electron microscopy and atomic force microscopy indicated that homogenous dispersion of MWCNTs enriched the interfacial bonding, deviated the crack path, and formed uneven surfaces. A comparison between the failure mode of neat and modified adhesive demonstrated the effective presence of MWCNTs in changing the adhesive failure mode of cocured composite to cohesive. Thus, it enhanced the failure strength of cocured composites. The experimental free vibrational analysis affirmed that addition of 1 wt.% MWCNTs enhanced the fundamental natural frequency whereas, lower wt.% MWCNT addition increased the cocured composites' inherent damping due to higher‐level formation of agglomeration area in the composite. Thus, it increased the stress level and minimized the bonding between fiber and matrix.

Experimental and numerical evaluations of composite concrete-to-concrete interfacial shear strength under horizontal and normal stresses.

Effects of different surface textures on the interface shear strength, interface slip, and failure modes of the concrete-to-concrete bond are examined through finite element numerical model and experimental methods in the presence of the horizontal load with ‘push-off’ technique under different normal stresses. Three different surface textures are considered; smooth, indented, and transversely roughened to finish the top surfaces of the concrete bases. In the three-dimensional modeling via the ABAQUS solver, the Cohesive Zone Model (CZM) is used to simulate the interface shear failure. It is observed that the interface shear strength increases with the applied normal stress. The transversely roughened surface achieves the highest interface shear strength compared with those finished with the indented and smooth approaches. The smooth and indented surfaces are controlled by the adhesive failure mode while the transversely roughened surface is dominated by the cohesive failure mode. Also, it is observed that the CZM approach can accurately model the interface shear failure with 3–29% differences between the modeled and the experimental test findings.

Electrochemical Surface Structuring for Strong SMA Wire-Polymer Interface Adhesion.

Active hybrid composites represent a novel class of smart materials used to design morphing surfaces, opening up new applications in the aircraft and automotive industries. The bending of the active hybrid composite is induced by the contraction of electrically activated shape memory alloy (SMA) wires, which are placed with an offset to the neutral axis of the composite. Therefore, the adhesion strength between the SMA wire and the surrounding polymer matrix is crucial to the load transfer and the functionality of the composite. Thus, the interface adhesion strength is of great importance for the performance and the actuation potential of active hybrid composites. In this work, the surface of a commercially available one-way effect NiTi SMA wire with a diameter of 1 mm was structured by selective electrochemical etching that preferably starts at defect sites, leaving the most thermodynamically stable surfaces of the wire intact. The created etch pits lead to an increase in the surface area of the wire and a mechanical interlocking with the polymer, resulting in a combination of adhesive and cohesive failure modes after a pull-out test. Consequently, the force of the first failure determined by an optical stress measurement was increased by more than 3 times when compared to the as-delivered SMA wire. The actuation characterization test showed that approximately the same work capacity could be retrieved from structured SMA wires. Moreover, structured SMA wires exhibited the same shape of the stress-strain curve as the as-delivered SMA wire, and the mechanical performance was not influenced by the structuring process. The austenite start As and austenite finish Af transformation temperatures were also not found to be affected by the structuring process. The formation of etching pits with different geometries and densities was discussed with regard to the kinetics of oxide formation and dissolution.

Retrofitting of RC beams using FRP techniques: a review

In structural and civil engineering, reinforced concrete structures are susceptible to inordinate loadings such as earthquake disasters, terrorist attacks and accidental impacts. This prompts an increasing desire to strengthen as well as enhance the fatigue performance and extend the ability of fatigue life of reinforced concrete structural components especially beams. Since 2003, Iraq has suffered major damage to the structural buildings, so it has become an important issue to study the existing concrete structures. Among the different techniques of rehabilitation of existing structures, fibre reinforced polymer (FRP) as an external bonding has been considered as a popular one. This paper reviews several features of Reinforced concrete (RC) beams strengthened with FRP. Also this paper aims to impart a comprehensive insight on adhesive curing, surface arrangement, and failure modes of RC beams modified with FRP. This effect of FRP for enhancing the techniques of rehabilitation is a three-fold task, to strengthen and retrofit of concrete structures, to extend the fatigue life of the structural element, and eliminates the crack growth rate.

Shear bond strength of acid and laser conditioned enamel and dentine to composite resin restorations: An in vitro study.

ObjectiveTo compare the shear bond strength of enamel or dentin conditioned with either Er,Cr:YSGG (erbium, chromium: yttrium–scandium–gallium–garnet) laser or phosphoric acid to composite resin restoration.Material and methodsForty posterior human extracted teeth were used. After mesiodistal sectioning of the teeth crowns, the samples were randomly divided into two groups—in the first group (E), bonding was performed on the enamel after roughening and in the second group (D), the enamel was removed and bonding was performed on the dentin. These groups were further randomly divided into two subgroups according to the type of etching (n = 20 each). In the acid‐etched groups (EA and DA), the surfaces were etched with 37% phosphoric acid. In the laser‐conditioned groups (EL and DL), the surfaces were conditioned with Er,Cr:YSGG laser. Total‐etch adhesive system was used to bond all the 80 specimens resin composite. The composite was vertically light‐cured, and the specimens were subjected to a shear bond strength test. Modes of bond failure were determined with a stereomicroscope.ResultsThe highest shear bond strength was observed for the DA group (16.25 ± 1.10 MPa, p < 0.0001), whereas the lowest was observed for the DL group (8.56 ± 0.67 MPa). The adhesive failure mode was the most frequently observed in all groups.ConclusionsThe shear bond strength of composite resin bonded to enamel and dentin etched with phosphoric acid was higher than when conditioned with Er,Cr:YSGG laser. Thus, laser conditioning is not recommended.

Comparative evaluation of 6% cranberry, 10% green tea, 50% aloe vera and 10% sodium ascorbate on reversing the immediate bond strength of bleached enamel: In vitro study

ObjectivesThe present study aimed to assess antioxidant activity of herbal antioxidants namely 6% cranberry extract, 10% green tea, 50% aloe vera and 10% sodium ascorbate and their effect on reversal of bond strength in bleached enamel. Materials and methodFrom one hundred and twenty extracted maxillary central incisors enamel blocks of 5 ​× ​5 ​mm were prepared and arbitrarily divided into six experimental groups (n ​= ​20): Group A: no bleaching, Group B: only bleaching protocol, Group C – bleaching ​+ ​6% cranberry extract solution, Group D – bleaching +10% Green Tea extract, Group E − bleaching ​+ ​50% aloe vera extract, Group F – bleaching ​+ ​10% Sodium Ascorbate. After bleaching antioxidants were applied for 10 ​min and were subjected to bonding procedures. The specimens were sectioned into 120 small strips of size (1 ​× ​1 ​× ​8 ​mm). Sixty sticks were analyzed to micro tensile bond strength using Universal testing machine and fractured segment were observed for failure modes (Adhesive, Cohesive and Mixed) under stereomicroscope. Remaining 60 sticks were observed for interface gap between tooth and composite resin under SEM. The %AA (antioxidant activity) was assessed with spectrophotometric analysis. ResultsData was statistically analyzed using ANOVA and Post Hoc Tukey’s test. Group A (91.68 ​± ​2.24 Mpa) showed higher mean micro tensile bond strength versus group D (82.14 ​± ​1.45 Mpa), followed by group E (75.26 ​± ​1.92Mpa), group F (63.89 ​± ​1.95Mpa), group C (57.58 ​± ​1.96 Mpa) and least in group B (31.5 ​± ​1.27 Mpa). The %failure mode inferred maximum adhesive mode of failure (86.25%). ConclusionAll the four antioxidants were able to reverse the compromised bond strength comparatively after bleaching maximum being green tea followed by aloe vera, sodium ascorbate, and minimum in cranberry. Clinically significance-Easily available, biocompatible, cost effectual, and potent herbal antioxidants could be used considerably for immediate esthetic cases where time is a restricting factor.

Bondline strength of glued-in threaded rods in new and ancient chestnut (Castanea sativa Mill.) wood

Glued-in rods (GIR) are being increasingly used in connections of new timber structures, complying with design rules mostly based on tests with new softwood specimens. However, the system also shows great potential for use in strengthening and rehabilitation of ancient timber structures, in which hardwoods were often used, namely in the Central and Southern European countries. Aiming at contributing to the scarce information available for these particular applications, an experimental program is carried out, consisting of the production and testing of both new and ancient chestnut timber specimens, the latter cut out from beams of demolished buildings. Given the limited number of specimens available, the bonding length was selected as the only variable parameter, although the hole diameter, the bond line thickness and others also play a relevant role on the behaviour of these connections. The relevant dimensions were set in order to preclude the steel yielding failure mode, desirable in actual applications, to favour the cohesive or adhesive failure modes at the wood-adhesive interface and the timber splitting failure mode, where most of the unanswered issues stand. All specimens were first tested with a pull-pull setup, and the unfailed sides were later tested in pull-push mode. The results were compared to the estimates provided by some of the existing design methods proposed in the literature.