Bond Strength Measurements Research Articles

Predicting the bond strength between steel wire and mortar based on interfacial porosity and shrinkage

The interfacial bond strength, which is the key to predict pullout behavior of steel fiber/wire/rebar embedded in cement-based matrix, is usually determined by pullout tests. However, precise pullout test is difficult to be conducted, especially for steel fiber, due to the high accuracy requirements for equipment and operation process. In the present paper, a prediction model on interfacial bond strength between steel wire and cement mortar was developed, based on the interfacial porosity and matrix shrinkage, without conducting pullout test. Firstly, Backscattered Electron test was conducted to determine the interfacial porosity of the steel wire, Nanoindentation test was carried out to determine the elastic modulus of the interfacial zone, restraint ring test was conducted to determine the effective shrinkage deformation of the matrix. The results show that lower interfacial porosity causes higher elastic modulus of interfacial zone, the relationship between interfacial porosity and elastic modulus can be described by a first order fractional function. Then, the extrusion stress between streel wire and matrix was calculated based on the shrinkage deformation of matrix and elastic modulus of interfacial zone. Finally, the frictional bonding strength of interface was calculated based on the extrusion stress and friction coefficient. The calculated frictional bonding strengths for steel wire embedded in mortar with water-cement ratios of 0.25, 0.35, 0.45 and 0.55 are 4.24 MPa, 3.52 MPa, 2.81 MPa and 2.45 MPa, which are in good agreement with the measured bond strengths by pullout test. The prediction model can be extended to predict the pullout behavior of smooth plain steel fibers/wires/rebars in cement-based material.

The effect of mechanical and chemo-mechanical temporary cement cleaning methods on shear bond strength with self-adhesive resin cement (an in-vitro study)

BackgroundAdhesive tooth-colored restorations are strongly dependent on the substrate surface cleanliness to allow intimate contact between resin cement and dentin surface, so several methods were adopted for the total cleaning of temporary cement residues. This study aimed to assess the effect of mechanical and chemo-mechanical cleaning methods of temporary cement on the immediate shear bond strength of self-adhesive resin cement to dentin surface.MethodsForty freshly extracted lower first premolars were cut to expose a flat dentin surface. Discs of temporary crown composite resin material were constructed and cemented to the flat dentin surface using resin-based and non-eugenol temporary cement then stored at room temperature in distilled water. Dividing of samples into two groups according to the method of temporary cement cleaning. Group I (n = 20) mechanical cleaning using the rotary instrument, and group II (n = 20) chemo-mechanical cleaning using chlorhexidine-containing scrub. CAD/CAM reinforced Composite discs were bonded to the dentin surface using self-adhesive composite resin cement, then measurement of shear bond strength was done using a universal testing machine. Further analysis of failure mode after debonding was performed by Scanning electron microscope.ResultsNo statistically significant difference was found between the mean shear bond strength of the two cleaning methods (P-value = 0.636). Regardless of the cleaning method, the group cemented with resin-based temporary cement showed statistically significantly higher mean shear bond strength than non-eugenol temporary cement (P-value = 0.048).ConclusionBoth cleaning methods (mechanical and chemo-mechanical) applied in this study were effective in cleaning temporary cement remnants from the dentin substrate surface with statistically significant differences between results of shear bond strength with significantly higher values recorded with resin-based temporary cement.

In-vitro comparison of bonding time and strength of adhesive pre-coated and standard metal orthodontic brackets

To compare the shear bond strength and bond time of 3M Unitek's APC (Adehesive Pre-Coated) Flash-Free™system applied to metal brackets. An in vitro study was performed on 40 extracted sound human premolar teeth randomly divided into two groups (20 per group) bonded either with Adhesive Pre-Coated Flash-Free metal brackets or metal brackets coated manually with Transbond XT™ light-cure adhesive. Bonding time was measured using a stopwatch. Thermoycling was performed on the samples (500 cycles) to simulate the oral environment between baths of 5°C and 55°C distilled water. Debonding shear bond strength measurements were performed in an Instron universal testing machine. The APC Flash-Free group bonded in significantly (p<0.001) less time (mean 34.06s/tooth) than the manually coated group (mean 55.14s/tooth). Shear bond strength of the manually coated group was significantly (p<0.001) higher (mean 13.32 MPa) than the APC Flash-Free group (mean 10.95 MPa). The APC Flash-Free free system is efficient and allows for reduced chair time during the bonding appointment while attaining a mean shear bond strength of 10.95MPa, which is higher than the minimum shear bond strength of between 4MPa and 7MPa1

The Local Vibrational Mode Theory and Its Place in the Vibrational Spectroscopy Arena

This Feature Article starts highlighting some recent experimental and theoretical advances in the field of IR and Raman spectroscopy, giving a taste of the breadth and dynamics of this striving field. The local mode theory is then reviewed, showing how local vibrational modes are derived from fundamental normal modes. New features are introduced that add to current theoretical efforts: (i) a unique measure of bond strength based on local mode force constants ranging from bonding in single molecules in different environments to bonding in periodic systems and crystals and (ii) a new way to interpret vibrational spectra by pinpointing and probing interactions between particular bond stretching contributions to the normal modes. All of this represents a means to work around the very nature of normal modes, namely that the vibrational motions in polyatomic molecules are delocalized. Three current focus points of the local mode analysis are reported, demonstrating how the local mode analysis extracts important information hidden in vibrational spectroscopy data supporting current experiments: (i) metal-ligand bonding in heme proteins, such as myoglobin and neuroglobin; (ii) disentanglement of DNA normal modes; and (iii) hydrogen bonding in water clusters and ice. Finally, the use of the local mode analysis by other research groups is summarized. Our vision is that in the future local mode analysis will be routinely applied by the community and that this Feature Article serves as an incubator for future collaborations between experiment and theory.

Adhesion to a CAD/CAM Composite: Causal Factors for a Reliable Long-Term Bond.

Computer aided design/manufacturing (CAD/CAM) technology has become an increasingly popular part of dentistry, which today also includes CAD/CAM resin-based composite (RBC) applications. Because CAD/CAM RBCs are much more difficult to bond, many methods and attachment materials are still being proposed, while the best application method is still a matter of debate. The present study therefore evaluates causal factors for a reliable long-term bond, which includes the surface preparation of the CAD/CAM RBC, aging and the type of luting material. The reliability of the bond was calculated, and supplemented by fractography to identify fracture mechanisms. Five categories of luting materials were used: (1) temporary zinc phosphate cement, (2) glass ionomer cement (GIC), (3) resin-modified GIC, (4) conventional adhesive resin cement (ARC), and (5) self-adhesive RC. Half of the CAD/CAM RBC surfaces (n = 200) were sandblasted (SB) with 50 µm aluminum oxide, while the other half remained untreated. Bond strength measurements of the 400 resulting specimens were carried out after 24 h (n = 200) or after additional aging (10,000 thermo-cycles between 5 and 55 °C) (n = 200). The data were statistically analyzed using one- and three-way ANOVA followed by Games-Howell post-hoc test (α = 0.05) and Weibull analysis. Aging resulted in a significant decrease in bond strength primarily for the conventional cements. The highest bond strengths and reliabilities were recorded for both ARCs. SB caused a significant increase in bond strength for most luting materials, but also caused microcracks in the CAD/CAM RBC. These microcracks might compromise the long-term reliability of the bond in vivo.

High temperature abradable sealing coating for SiCf/SiC ceramic matrix composites

A study of porous YSZ abradable sealing coating (ASC) plasma-sprayed onto SiCf/SiC ceramic matrix composites (CMC) through the compatibility of intermediate layers is reported. The multilayer Si/Yb2Si2O7/LaMgAl11O19 thermal-environmental barrier coating (T-EBC) is served as intermediate layers in consideration of its ability to protect the CMC from recession and ease the misfit of the thermal expansivity. Isothermal exposure and thermal shock tests were conducted at 1200°C and led to the decomposition of t'-ZrO2 phase to t-ZrO2 and c-ZrO2 phases in YSZ topcoat, the formation of mud-cracks throughout the entire coating structure and thermally grown oxide (SiO2), with following an Yb2Si2O7 reaction layer. The measured bond strength of the coated samples was 5.47 ± 0.85 MPa, and the fracture position mainly happened inside the CMC substrate. The Superficial Rockwell Hardness (HR15Y) considered to be an important factor in abradability increased by only 1.34% after 1200°C isothermal exposure for 100 h, showing excellent high temperature hardness stability. The abradability of the ASC was investigated by a sliding wear test, the fatigue wear mainly occurred in worn scar when encountering Si3N4 ceramic ball with high hardness and low thermal conductivity, while adhesive wear occurred when GCr15 steel ball with low hardness and high thermal conductivity are encountered.

Influence of Surface Conditioning on Bonding Polyetherketoneketone to Dental Ceramic

This study researched the effects of different surface conditioning techniques on the bond strength of polyetherketoneketone (PEKK) with lithium disilicate glass-ceramic material. Total of 105 test specimens were prepared from PEKK discs and randomly distributed into 5 experimental groups (n = 21) to which different surface conditioning techniques were applied. [Group A: sandblasting + SR Connect adhesive agent (SRC), Group B: dichloromethane (DCM) + SRC, Group C: methyl methacrylate (MMA) and DCM mixture + SRC, Group D: sandblasting + DCM + SRC, Group E (control): sandblasting + Pekk Bond adhesive agent (PB).] Surface roughness values of PEKK test specimens were measured. They were bonded to lithium disilicate glass-ceramic test specimens with resin cement. Half of them were subjected to thermomechanical aging. Shear bond strength measurements were made. Among the A, B, C, D, and E groups, a statistically significant difference was observed in terms of the surface roughness values (p < 0.001). Statistically significant differences were obtained among the thermomechanical aging groups (p < 0.001) and among the non-thermomechanical aging groups (p = 0.012) in terms of shear bond strength. Group D and Group E demonstrated clinically acceptable bond strength values when bonding PEKK material with lithium disilicate glass-ceramic material.

Push-Out Bond Strength and Dentinal Penetration of a Novel Herbal-Based Pulp Capping Agent: An In vitro Study

Background: Pulp capping agents should have proper sealing effect to enhance dental pulp tissue healing.&#x0D; Aim: The purpose of this study was to compare the effectiveness of grape seed extract (GSE) and Mineral trioxide aggregate (MTA) to penetrate to dentin and their push-out bond strength at two time intervals (1 and 3 months) when used as pulp capping agents either singly or combined to each other.&#x0D; Materials and Methods: This study was conducted on 120 human single-rooted anterior teeth. Sixty dentin discs were randomly divided into three groups (n=20) based on the material used; MTA, GSE, and a combination of MTA and GSE. A universal testing machine was used to determine the push-out bond strength for one and three months. At the same time intervals, extra 60 teeth with the same groups were utilized to quantify the degree of capping material penetration within the dentinal tubules using scanning electron microscopy (SEM). ANOVA with multiple comparison Post hoc test was used to evaluate the data where the p value was &lt; 0.05.&#x0D; Results: MTA had the highest push-out bond strength and penetration depth measurement into dentinal tubules at one month, followed by MTA combined with GSE, while GSE had the lowest push-out bond strength and penetration depth measurement. Nevertheless, GSE had the greatest values in both tests at 3 months, followed by MTA, while MTA coupled with GSE had the lowest value in both tests.&#x0D; Conclusion: Push out bond strength and dentinal penetration depth were improved with time except for the MTA group testing its dentinal penetration depth. GSE shows good push out bond strength and dentinal penetration depth.

Bonding in nitrile photo-dissociating ruthenium drug candidates-A local vibrational mode study.

In this work, we investigated bonding features of 15 ruthenium(II) nitrile complexes of the type [Ru(tpy)(L)-(CH3CN)]n+, containing the tridentate tpy ligand (tpy = 2,2':6',2″-terpyridine) and various bidentate ancillary ligands L; 12 compounds originally synthesized by Loftus et al. [J. Phys. Chem. C 123, 10291-10299 (2019)] and three new complexes. We utilized local vibrational force constants derived from the local mode theory as a quantitative measure of bond strength complemented with the topological analysis of the electron density and the natural bond orbital analysis. Loftus et al. suggested that nitrile dissociation occurs after light induced singlet-triplet transition of the original complexes and they used as a measure of nitrile release efficiency quantum yields for ligand exchange in water. They observed larger quantum yields for complexes with smaller singlet-triplet energy gaps. The major goal of this work was to assess how the Ru-NC and Ru-L bond strengths in these 15 compounds relate to and explain the experimental data of Loftus et al., particularly focusing on the question whether there is a direct correlation between Ru-NC bond strength and measured quantum yield. Our study provides the interesting result that the compounds with the highest quantum yields also have the strongest Ru-NC bonds suggesting that breaking the Ru-NC bond is not the driving force for the delivery process rather than the change of the metal framework as revealed by first results of a unified reaction valley approach investigation of the mechanism. Compounds with the highest quantum yield show larger electronic structure changes upon singlet-triplet excitation, i.e., larger changes in bond strength, covalency, and difference between the singlet and triplet HOMOs, with exception of the compound 12. In summary, this work provides new insights into the interplay of local properties and experimental quantum yields forming in synergy a useful tool for fine tuning of existing and future design of new nitrile releasing ruthenium compounds. We hope that this work will bring theoretical and experimental studies closer together and serves as an incubator for future collaboration between computational chemists and their experimental colleagues.

Effect of Corrosion on Bond Strength of Tension Lap-Splices

This study aimed to investigate the effect of corrosion on the bond strength of tension lap splices in reinforced concrete beams. The test variables were the corrosion level (0%, 2.5% and 5.0%) and the concrete cover to bar diameter (c/d) ratio (c/d=1.5, 2.0, and 2.67). The observed failure mode was splitting of the concrete cover on the tension side. An accelerated corrosion technique was used to corrode the reinforcing lap-spliced bars in a reasonable time frame. Corrosion did not affect failure mode but caused a reduction in the ultimate strength and deflection at failure. The bond strength was reduced by 15% to 26% at 2.5% corrosion level and by 21% to 38% at 5% corrosion level depending on the c/d ratio. A model was proposed to predict the bond strength of corroded tension lap-splices in concrete. The model results correlated well with the measured bond strength.

Mechanical Properties of SDR™ and Biodentine™ as Dentin Replacement Materials: An In Vitro Study

The aim of this study is to evaluate the shear bond strength of nanohybrid composite resins (NCR) and microhybrid composite resins (MCR) placed over three different dentin replacement materials: SDR-Smart Dentin Replacement™, Biodentine™, and resin-modified glass ionomer cement (RMGIC). Thirty acrylic blocks (50 mm × 20 mm × 15 mm), each with a central hole, were prepared, which were randomly distributed into three equal groups, each corresponding to one of the three dentin replacement materials-SDR, Biodentine, and RMGIC. The central holes were then filled with these materials. After setting and application of the respective adhesive system, the specimens were further divided into two subgroups each of NCR or MCR. The respective composite material was then applied to the dentin replacement materials using a cylindrical plastic matrix. Shear bond strength was tested on a universal testing machine (Instron 3366), at a crosshead speed of 1.0 mm/minute. SDR attained consistently higher shear bond strength (means: 21.18, 22.19 Mpa) values than RMGIC and Biodentine, with both types of composite resins (MCR and NCR), which were statistically significant (p <0.001). When considering the means of the shear bond strength measurements obtained by the two types of the composite resin, no significant difference (p <0.05) was found between them with all three types of dentin replacement materials. There is no significant difference in the bond strengths achieved between MCR and NCR to the different dentine replacement materials. Hence, either type of composite resin may be expected to achieve similar bond strengths to the underlying substrate. SDR™ is a suitable dentine replacement material for placing below a composite resin veneer as it can achieve immediate higher bond strengths. SDR can be used as an effective bulk fill material in deep dentinal caries which can be capped with composite resins.

Influence of surface roughness of substrate on corrosion behavior of MAO coated ZM5 Mg alloy

In this study, micro-arc oxidation (MAO) coatings were formed on ZM5 Mg alloy substrate with different surfaces roughness. Therefore, the influence of surface roughness on the corrosion failure progress and mechanism of the MAO coated ZM5 Mg alloy has been investigated. The microstructure, bonding strength, and corrosion resistance of the MAO coatings were studied by SEM, LSCM, bonding strength measurement, and electrochemical test. The results showed that the surface roughness affects the porosity and bonding strength of the coatings. While it had little effect on the thickness and chemical composition of the MAO coating. Due to the high surface porosity, the coating of the grooved sample had poor corrosion resistance in the initial immersion. But, after a long-time immersion, the grooved sample was still protected by the coating, while the smooth sample showed severe damage. The strong bonding strength between the coating and groove sample was the key factor for enhancing the corrosion resistance of MAO coated ZM5 Mg alloy.

Application of neuro-fuzzy estimation in prediction of shear bond strength between concrete layers through the efficient laser roughness analyzer

To ensure the monolithic behavior of reinforced concrete composite parts, the bond strength at the interface between concrete layers cast at various ages must be high. Reinforced concrete composite members include precast beams with cast-in-place slabs, bridge decks strengthened by adding a new concrete layer, and repair and strengthening of existing concrete structural members by adding a new concrete layer. in this study, the shear bond strength (SBS) of reinforcing steel on Portland cement and a hybrid cement including slag and Portland cement activated with sodium carbonate is investigated. The pull-out test was used to determine SBS; also a subsequent test data is evaluated using ANFIS, as well as surface classification utilizing a laser roughness analyzer designed particularly to assess the roughness of the concrete substrate. As a result, this research tried to create an in situ non-destructive approach for assessment of concrete surfaces and its influence on shear bond strength measurement of the concrete layers. All test data is analyzed using an adaptive neural fuzzy inference system (ANFIS) to classify the different input variables for determining the shear bond strength between concrete layers using the mean and maximum surface roughness (SR) height parameters Ra and Rt in X and Y direction. ANFIS was used to optimize the process based on five processing parameters. Skillful prediction could play a pivotal role in the optimal conditions during laser cutting process. Based on results, laser speed is the most influential on the Ra in X and Y direction (RMSE: 0.3255, RMSE: 0.6869, respectively). The most influential parameter on the Rt in X direction is laser power (RMSE: 1.5611), while the most influential parameter on the Rt in Y direction is laser speed (RMSE: 2.0781), resulting that the roughness of the substrate surface highly affects the shear bond strength of concrete interfaces.

Development of MEMS Acoustic Sensor With Microtunnel for High SPL Measurement

The fabrication of piezoelectric ZnO-based micro-electro-mechanical systems (MEMS) acoustic sensor has been reported. The sensor structure consists of a piezoelectric ZnO film deposited between two Al electrodes on a thin silicon diaphragm. A microtunnel is fabricated in the sensor structure using novel approach. This microtunnel is used to protect the diaphragm and determine the lower cut-off frequency of device. The approach presented in this paper completely removed a serious problem of microtunnel blockages during fabrication of sensors. In the developed process, the acoustic sensor fabricated using silicon-on-insulator and the Pyrex glass wafers are diced separately with same chip dimensions. Finally, both Pyrex glass and acoustic sensor chips are fitted in a jig for alignment and then anodically bonded. In reference to microtunnel blockages, the yield of the present technique is obtained as almost 100%. Also, the technique will serve as a cost-effective alternative to the present practice. The developed technique can also be used in manufacturing of similar devices where the microtunnels or microchannels are required in device structure. The technological development is supported by extensive atomic force microscopy (AFM), field emission scanning electron microscopy, Raman spectroscopy, and X-ray diffraction studies of ZnO film; glass-to-silicon bond strength measurement; resonance frequency measurement by laser doppler vibrometer; response characterization of the fabricated sensor, and scanning electron microscopy of microtunnel mouth to demonstrate the feasibility and yield of the process.

Comparison of Retention between Two Dental Root Canal Core Build Up Materials and Silanized and Non-Silanized Glass Fibre Posts: An Invitro Study

Background: Various resin-based core builds up materials are commercially available in market but their clinical use should follow recommendations of bond strength measurement studies. Objective: to evaluate the retention between two commercially available core build up materials and silanized and non-silanized glass fibre posts. Methodology: The retention between two commercially available core build up materials (Core X Flow and Light Core) and Silanized and Non- Silanized glass fiber posts with ten samples in each group were assessed using ‘pull out test’ in universal testing machine. Student’s unpaired ‘t’ test was used for inter group comparison by fixing significance level at p ≤ 0.05. Results: The retention force was higher in silanized fibre post group compared to non-silanized posts (p=0.02). Among the silanized posts, the retention force was significantly higher in CORE X FLOW group compared to LIGHT CORE group (p=0.03). Conclusion: The retention of posts improved with silanization. With silanization, the retention force was significantly higher with ‘CORE X FLOW’ compared to ‘LIGHT CORE’ core build up material.

Influence of Substituents in the Benzene Ring on the Halogen Bond of Iodobenzene with Ammonia.

The effects on the C-I⋅⋅N halogen bond between iodobenzene and NH3 of placing various substituents on the phenyl ring are monitored by quantum calculations. Substituents R=N(CH3 )2 , NH2 , CH3 , OCH3 , COCH3 , Cl, F, COH, CN, and NO2 were each placed ortho, meta, and para to the I. The depth of the σ-hole on I is deepened as R becomes more electron-withdrawing which is reflected in a strengthening of the halogen bond, which varied between 3.3 and 5.5 kcal mol-1 . In most cases, the ortho placement yields the largest perturbation, followed by meta and then para, but this trend is not universal. Parallel to these substituent effects is a progressive lengthening of the covalent C-I bond. Formation of the halogen bond reduces the NMR chemical shielding of all three nuclei directly involved in the C-I⋅⋅N interaction. The deshielding of the electron donor N is most closely correlated with the strength of the bond, as is the coupling constant between I and N, so both have potential use as spectroscopic measures of halogen bond strength.

Latent cure epoxy resins for reliable joints in secondary-bonded composite structures

In high-performance polymer matrix composite assemblies, adhesive bonding is generally superior to mechanical fastening in structural performance and manufacturing efficiency. However, adhesive bonds are susceptible to minute levels of contamination accumulated during assembly that can lead to unpredictable, weak bonds. Current methods of measuring bond strength are all destructive mechanical tests. To overcome these challenges, redundant load paths (e.g., mechanical fasteners) are often implemented in secondary-bonded, primary-structures, which can greatly reduce structural performance. This study investigated reformulated aerospace epoxy matrix resins with stoichiometric offset to inhibit cure of the matrix resin prior to assembly. Inhibited resins can reflow and mix across the joint interface , which eliminates the material discontinuity and forms a homogenous joint with reliable fracture properties . The goal of this study was to develop and demonstrate secondary composite assemblies that are mechanically and microscopically indistinguishable from a co-cured composite joint. This article describes the development of latent epoxy resins, the fabrication of test articles, and the mechanical properties measured from experimental joints compared with conventional, co-cured laminates. Methods of in-line quality control using and infrared spectroscopy and post-assembly forensics are also described. The final mode-II fracture toughness measured from precracked AERoBOND specimens was similar to that measured from co-cured laminates indicating that later cure epoxy materials could be a suitable replacement for secondary bonding. • Methods enable rapid assembly of thermoset composites with the simplicity of secondary bonding and reliability of co-cure. • Epoxy based resins were formulated with offset stoichiometry: epoxy rich and hardener rich. • End-notched flexure tests indicated that joints with offset stoichiometry matched or exceeded co-cured joint performance. • Infrared spectroscopy and ultrasonic inspection were viable means of inline quality control before and after assembly.

CYCLIC FATIGUE RESISTANCE OF ROTATE, EDGEFILE PLATINUM, AND K3XF FILES EXPOSED TO INTRACANAL TEMPERATURE IN AN S-SHAPED CANAL

Aim: To evaluate the bond strength of resin-based sealer to dentin after using different final irrigation solutions, one of which is alexidine dihydrochloride (ALX). Material and method: A total of 90 human maxillary central teeth were used. The groups were designed according to the final irrigation solution applied, as follows: Group 1: 17% ethylenediamine tetra-acetic acid (EDTA), Group 2: QMix, Group 3: 2% chlorhexidine gluconate (CHX) , Group 4: 1% ALX, and Group 5: Distilled water (Control group). All canals were obturated with gutta-percha and AH Plus. For bonding strength measurement, three horizontal sections of 2 mm thickness were obtained from each sample towards the coronal to apical. Push-out force was applied until bond failure occurred. Modes of failure were classified by examining each sample using a stereomicroscope as follows: adhesive (sealer-dentin or sealer-gutta-percha interface), cohesive (failure within sealer or dentin), mixed (failure in both the sealer and dentin). The Kruskal-Wallis H test was used for comparison among the groups (p < 0.05). Results: The mean highest values were obtained from the coronal, middle and apical regions, respectively (p < 0.05). The highest significant values for bonding strength was obtained in the EDTA group and the lowest in the control group (p < 0.001). There are no statistical differences among QMix, CHX and ALX groups, except for the coronal third, where the bond strength for the QMix was higher compared to the other two groups (p=0.001). All samples showed the cohesive failure type in most. Conclusion: Bonding strength is high when EDTA is used in any of the three parts of the root canal. ALX showed similar bond strengths to CHX. Key Words : AH Plus, alexidine, bond strength, chlorhexidine, EDTA, Qmix

Substituted hydrocarbon: a CCSD(T) and local vibrational mode investigation

Substituent effects on the carbon–carbon bonds of hydrocarbons have been a topic of interest within the past seven decades as resultant information would enable one to tune the activity of CC bonds. However, current assessments of the C≡C, C=C, and C−C bond strength of acetylene, ethylene, and ethane as well as their derivatives rely on indirect measures such as bond length and bond dissociation enthalpy. In this work, we introduce a quantitative measure of the intrinsic strength of C≡C, C=C, and C−C bonds for a set of 40 hydrocarbon systems consisting of 3 parent structures, 36 hydrocarbon derivatives involving CF3, CH3, CHO, F, NH2, or OH groups, and a conjugated system, based on vibrational spectroscopy. Local mode force constants (CC) were computed at the CCSD(T)/cc-pVTZ level of theory for systems 1–32 and 34–40 and CCSD(T)/cc-pVDZ for 33. From (CC), we derived related bond strength orders BSO n(CC) in order to provide quantitative measures of intrinsic bond strength. Topological electron density and natural population analyses were carried out as to analyze the nature of these bonds and complement bond strength measures. For substituted hydrocarbon systems, we found the strengthening/weakening of the CC bonds occurs as the covalent nature of the bond increases/decreases by means of varying charge delocalizations. Our findings provide new guidelines for desirably modulating C≡C, C=C, and C−C bond strength and for the design of prospective pathways for bond cleavage reactions.

Electron work function as an indicator for tuning the bulk modulus of MC carbide by metal-substitution: A first-principles computational study

Bulk modulus (B) is a measure of atomic bond strength, affecting the mechanical behavior of materials, especially for ceramic materials having little plastic deformation. Tailoring B of ceramic materials can be achieved by element-substitution. However, such tailoring is more or less based on the trial-and-error approach. We investigated the correlation between electron work function (EWF) and B of transition metal (TM)-substituted MC carbides through first-principles calculation. It was shown that TMs with higher EWFs generally resulted in higher bulk modulus, demonstrating that EWF is a promising guiding parameter for selecting effective substitutes.