Adhesive Failure Mode Research Articles

Interfacial bond strength and failure modes of traditional and modern repair materials for historic fibrous plaster

Many culturally important historic buildings contain fibrous plaster ceilings. The collapse at London’s Apollo Theatre in 2013, which injured 88 people, highlighted the importance of inspecting and restoring ceilings effectively. This study focuses on traditional and modern materials which are applied to the topsides of existing historic fibrous plaster ceiling elements during repair and maintenance. Fibrous plaster ceilings are commonly suspended from primary or secondary structural roof members using fibrous plaster wadding ties or ‘wads’. The application of additional repair material requires the formation of an interface, defining the strength of the repair. Properties of this interface were evaluated through a novel methodology employing pull-off tests’ of approximately 200 specimens consisting of Alpha plaster, Beta plaster, Jesmonite and Aramid gel. Notably, the effect of fibrous reinforcement, and compatibility with historic and degraded material was also investigated. This study has enabled quantification of interfacial properties and evaluated cohesive and adhesive failure modes. Importantly, the extent of redundancy within historic plaster ceiling practice has been demonstrated, with pull-off occurring from 0.5 kN to 2 kN loading, and the ductile behaviour of repair materials evaluated. Results highlight the importance of surface condition, with clean surfaces exhibiting double the tensile loading capacity compared to soiled (dirty) surfaces representative of those encountered on-site. The significance of this study lies in the quantification of repair material performances and consideration of variations in performance, methodology and in-situ environmental factors. Impact stems from the ability of practitioners to make informed decisions relating to adhesion performance when carrying out repairs. A key outcome is more effective preservation of historic elements in heritage buildings, higher levels of safety and serviceability.

Analysis of the effect of thermocycling on bonding cements to zirconia

ObjectiveThe aim of this study was to evaluate the effect of thermocycling on shear bond strength (SBS) of several resin cement materials to different types of zirconia dental ceramics. Materials and Methods120 square shaped disc specimens were fabricated using two types of zirconia blocks (Sagemax and Sirona). Each zirconia group was divided into three sub-groups based on the resin cement bonded to the specimens. Three different self-adhesive resin cements were used (Calibra, Breeze and RelyX). The specimens were further grouped into experimental and control groups (n = 10). The experimental specimens were exposed to a thermo-cycling protocol of 1500 cycles in water bath at 5c and 55c. Specimens were then stored at 37c for 24 h then all specimens underwent SBS test with an Instron machine. Mode of failure was inspected visually and microscopically. Data were statistically analyzed using multivariate analysis of variance followed by one-way analysis of variance, Tukey’s multiple comparison test, student’s t-test for independent samples were used to compare the mean values of SBS in relation to the categorical study variables. ResultsThe mean SBS values of experimental groups were significantly lower than control groups for all the 6 combinations of Zirconia and cement types (p < 0.0001). The higher mean difference (14.29 MPa) was observed in the combination of Sagemax and Rely-X. Rely-X displayed the highest SBS among all the cements while no significant difference was found in mean SBS values of Calibra and Breez cements in all groups. The mean SBS values of Sagemax zirconia were significantly higher than the Sirona with all three types of cements (p < 0.0001) within control groups. Microscopic and visual analysis demonstrated a majority of adhesive mode of failure. ConclusionThermocycling significantly reduced the SBS between the zirconia materials and self-adhesive resin cements tested. The amount of reduction varies according to cement and zirconia types.

To Evaluate and Compare the Effect of Various Surface Treatment Modalities on Shear Bond Strength of Composite to Polyetherketoneketone and SEM Analysis: An In vitro Study

Abstract Context: It is a challenge to bond resin materials with polyetherketoneketone (PEKK). To increase the bond strength, surface treatments using chemical adhesion, mechanical adhesion, or a combination of both can be used. Aims: The objective of the present study was to evaluate and compare the shear bond strength of PEKK to the composite resin after various surface treatments and to evaluate the fracture mode analyses. Materials and Methods: One hundred and twenty PEKK specimens were randomly divided into four groups (n = 30) after three different surface treatments (95% sulfuric acid etching, airborne abrasion with 110 μm aluminum-oxide, and 99% acetone). With the help of polytetrafluorethylene tube, resin composite (3M ESPE) was bonded on all the specimens, thermocycled, and subjected to shear bond strength testing. Thereafter, 15 samples from each group were assessed for fracture mode analyses using a scanning electron microscope. Statistical Analysis Used: Mean, Standard deviation, one-way analysis of variance (ANOVA) f-test, post hoc Tukey’s test. Results: Statistical analysis using one-way ANOVA f-test revealed that the results were significant with a P &lt; 0.05 with the maximum value obtained in the case of air abraded group and the minimum value obtained in the case of the untreated group. Adhesive failure mode was the most common among the air-abraded group. Conclusions: The mechanical surface treatment group (air abrasion) showed higher shear bond strength than the chemical surface treatment groups (sulfuric acid and acetone). The mixed-type fracture mode was most commonly noted in the air-abraded group.

Lap Shear Strength Assessment of Acetone Welded 3D-Printed ABS Polymer

Fused Deposition Modeling (FDM) is one of the most common polymer 3D printing technologies used in many applications today. However, limited volume capacity for 3D printing large parts or components is the usual downside of this technology, especially desktop 3D printers. Hence, to offset this limitation, the 3D-printed parts are often designed in multiple pieces and assembled after printing, which requires post-processing called cold welding. Such welds are also quite strong but not as strong as a single-piece print. Therefore, finding suitable parameters or settings that can provide substantial strength for cold-welded 3D-printed parts will be beneficial. This study aims to determine the failing behavior and shear strength of ABS FDM 3D-printed single-lap joint using ABS glue as adhesive. Specimens were printed with varying raster angles (+45o/-45o and 0o/90o) and layer thickness (290 μm, 190 μm, and 90 μm) to investigate the effects on the adhesion or shear strength and failure mode of the acetone welded 3D-printed joints. Results show that raster angle and layer thickness significantly affected the shear strength of acetone welded materials. Single-lap joint test sample printed with +45o/-45o raster angle reveals higher shear strength than specimens printed with 0o/90o raster angle. Results also indicated that the gaps between the raster and voids between adjacent filaments of 3D-printed parts affects the adhesion and failure mode of a single-lap joint.

Glass ceramics behave like selectively etched enamel on interfaces produced with self-adhesive/ self-curing resin cement

This work aimed at analyzing the bond strength of different ceramic compositions and dental substrates to a self-adhesive/curing resin cement to determine the reliability of the bonded interfaces. The study groups were Lithium Disilicate (LD), Zirconia reinforced Lithium Silicate (ZLS), Conventional Yttria-stabilized Polycrystalline Tetragonal Zirconia (Y-TZP C), Translucent Yttria-stabilized Polycrystalline (Y-TZP T), Selective Etched Enamel (E + E); unetched Enamel (E); and Dentin (D). Twenty 2 mm thick slice specimens of each group were obtained from a cutting machine, under high speed and refrigeration, followed by polishing and inclusion in PVC tubes with acrylic resin, with their flat surfaces exposed. The self-adhesive/curing resin cement was inserted in a plastic matrix on the surface of each specimen, resulting in cylinders with an internal 1.40 mm diameter x 1 mm height. The specimens were subjected to microshear bond strength test. Qualitative failure analysis was performed by stereomicroscope and scanning electron microscope (SEM). Weibull statistical analysis was performed to obtain the following metrics: probability of failure, Weibull modulus (m) (reliability) and characteristic strength (σ0). The E + E group achieved the highest median value (24.88 MPa), lower probability of failure, greater reliability, and greater characteristic strength among all the study groups. ZLS presented the highest bond strength values (20.07 MPa) and characteristic strength but also the highest data variability. LD group presented greater reliability among ceramic materials. Dentin presented the lowest median (4.51 MPa) among all substrates evaluated. The adhesive failure mode was predominant among the failure types. Adhesive interfaces of glass ceramics presented higher characteristic strength, lower probability of failure and greater reliability, being similar to selectively etched enamel.

Reliability of an Innovative Slab Shear versus Microtensile Bond Strength Test: Mechanical and Finite Element Analysis.

The aim of this study was to evaluate the efficiency of slab shear bond strength test (Slab_SBS) versus the microtensile in evaluation of the bond strength of different substrates. Forty-eight extracted caries-free human third molars were utilized for teeth specimens' preparation. After flattening of all molars' occlusal table, the specimens were divided into two groups based on the type of utilized restorative material: nanohybrid resin composite and resin-modified glass ionomer (RMGI). Each group was further subdivided into three subgroups according to the subsequently applied bond strength test and specimen width; microtensile bond strength test (μTBS), Slab_SBS [2 mm] and Slab_SBS [3 mm]. Both testing methods were additionally applied on CAD/CAM specimens, nanohybrid resin composite blocks (composite-to-composite), and ceramic blocks (ceramic-to-ceramic). CAD/CAM specimens were prepared and cemented and then sectioned and subdivided as followed for teeth specimens' preparation. Pretest failures (PTF), bond strength, and failure mode of each specimen were recorded. Representative three-dimensional (3D) finite element analysis (FEA) models were developed to simulate μTBS and Slab_SBS specimens. Data were statistically analyzed using Shapiro-Wilk test and Weibull analysis. Pretest failures were only noted in the μTBS subgroups. Slab_SBS provided comparable bond strength to the μTBS of all substrates with adhesive mode of failure. Slab_SBS is easier to prepare with consistent and predictable outcome with no pretest failures during specimen preparation and better stress distribution.

Influence of Phosphoric Acid Etching on Bond Strength for Calcium Silicate-Based Sealers

IntroductionThis study evaluated the microtensile bond strength of calcium silicate-based sealers and epoxy resin-based sealer, depending on the use of phosphoric acid (PA) etching before immediate resin restoration. MethodsExposed dentin surfaces of extracted human third molars were randomly assigned to 3 groups depending on sealer type (AH Plus [Dentsply DeTrey], CeraSeal [Meta Biomed Co.], and EndoSeal MTA [Maruchi]). Half of the samples were treated with PA for 30 seconds, and the other half were cleaned with water. Completely untreated specimens were used as controls. Self-etching adhesive (Clearfil SE Bond, Kuraray) was applied and composite resin (Tetric N-Ceram, Ivoclar Vivadent) was used to create build-ups. After 24 hours, the microtensile bond strength was measured (EZ Test, Shimadzu Co.). The failure mode was determined by light microscopy and scanning electron microscopy. One-way analysis of variance with the Bonferroni correction was used to analyze the data (P < .05). ResultsThe bond strength of the water-washed dentin surfaces in the calcium silicate-based sealer groups did not differ significantly from those of the control surfaces but the PA-pretreated surfaces exhibited relatively low-bond strength. The AH Plus-treated group had lower bond strength than the control group when no PA treatment was applied, but PA treatment restored the bond strength. The adhesive failure mode was most frequently found in the AH Plus group without PA etching. ConclusionsWhen a water-soluble calcium silicate-based sealer is used, sufficient bond strength can be obtained by washing with water alone, with no need for PA use.

Joining of carbon fiber reinforced polymer/titanium stacks using directed energy deposition additive manufacturing

In this work, we successfully fabricated CFRP/Ti stacks with reliable interfacial bonding using the directed energy deposition (DED) additive manufacturing (AM) technique. Compared to traditional laser welding, the DED process can produce a smaller penetration depth due to the ejection of feedstocks into the melt pool. Such an additive process also enables the multilayer deposition of three-dimensional (3D) Ti alloys with a designed structure to coalesce with the CFRP plate. This study utilized numerical modeling and experiments to uncover the interface formation mechanisms and bonding performance of CFRP/Ti stacks fabricated at different laser powers. The cross-sectional morphologies of CFRP/Ti stacks were observed by an optical microscope (OM) and a scanning electron microscope (SEM). Physical gaps and pores existed along CFRP/Ti interface and within CFRP substrates, respectively. The bonding performance of overall CFRP/Ti stacks was also assessed by lap shear tensile testing. The lap shear tensile strength increased first and then decreased with laser power. The fracture failure of CFRP/Ti interface was characterized by a SEM and X-ray photoelectron spectroscopy (XPS), which indicated the mixed adhesion and cohesion failure mode of DED-joint stacks. This work provides a novel CFRP/Ti stack joining paradigm through DED, paving the way for AM of multi-material lightweight components.

A new adhesion concept based on a dual surface modification for resin Ti adhesion

The objective of this resin Ti adhesion study was to compare and contrast the effect of two novel dual surface modification methods on the surface morphology, changes in surface chemistry and to evaluate their enclosed mold micro-shear bond strength variation on artificial ageing. A total amount of 168 c.p. grade 2 titanium specimens were first manually polished, then 24 of them were randomly selected as control specimens. To study the effect of dual surface modification (silicatization followed by etching), 72 polished titanium specimens were silicatized (Rocatec™ Plus, 3M ESPE, 110 μm silica-coated alumina powder) according to the manufacturer’s protocol and then 36 of the silicatized specimens were etched with a blend of HNO3–HCl at 60 °C for 2 mins. The reversed dual surface modification (etching followed by silicatization) was done for the remaining 72 titanium specimens. They were first etched with a blend of HNO3–HCl at 60 °C for 2 mins, and then 36 of the etched specimens were silicatized with the same protocol as mentioned above. As a final treatment one third of all differently modified sample groups were silanized by Monobond™ Plus (Ivoclar Vivadent), and the other third with an experimental silane primer blend, 1.0 vol% 3-acryloxypropyltrimethoxysilane + 0.3 vol% 1,2-bis-(triethoxysilyl)ethane. One third of each sample groups was left without silanization. SEM, EDX, XPS, AFM, and surface roughness profilometry were conducted to study the effects of different surface modifications. Two enclosed mold resin stubs were bonded on each surface treated titanium specimens to evaluate the enclosed mold micro-shear bond strength. The specimens were artificially aged for 1 day, 1 week, 4 weeks, and 8 weeks, followed by adhesion strength testing and failure mode analyses. SpeedCem™ (Ivoclar Vivadent) was used as resin cement. The highest surface roughness was detected on the titanium specimens, silicatized and followed by etching with and without silanization (group E), while the lowest surface roughness was observed in two groups, silanized polished titanium (group A, control) and etched polished titanium with and without silanization (group C). The surface roughness of titanium only silicatized (group B) and specimens silicatized after etching (group D) exhibited similar surface roughness, higher than groups A and C, but lower than group E. These results were supported by the SEM images and AFM analysis. The EDX and EM-μSBS analyses pointed out that specimens which had higher [Si] and [Al], exhibited higher EM-μSBS values. The highest EM-μSBS values were observed in Ti specimens which were silicatized only or those which were silicatized after etching, i.e., groups B and D. Adhesive and mixed mode of fractures were observed in the specimens after EM-μSBS tests. A novel approach of silicatized titanium surface after etching might prevent the removal of embedded SiO2 and Al2O3, allowing the formation of a durable chemical bond with a silane blend.

Effects of Er:YAG and Er,Cr:YSGG laser irradiation and adhesive systems on microtensile bond strength of a self-adhering composite.

This study was aimed to evaluate the effects of Er:YAG and Er,Cr:YSGG laser irradiation and adhesive systems on the microtensile bond strength of Fusio Liquid Dentin (FLD) which is a self-adhering composite (SAC). Twenty-four freshly extracted human molar teeth were collected, and the enamel was removed from the occlusal surface to obtain a flat dentin surface. Twenty-four teeth were randomly divided into eight groups: Group 1: only Fusio Liquid Dentin (FLD) (Petron Clinical, Orange, California, USA) was applied to the dentin surface; Group 2: 37% Phosphoricacid (i-GEL, Medicinos Linija UAB, Lithuania) + FLD; Group 3: Single Bond Universal (SBU) (3M ESPE, Germany) + FLD; Group 4: Adper Easy One (AEO) (3M ESPE, Germany) + FLD; Group 5: Er:YAG laser + AEO + FLD; Group 6: Er:YAG laser + SBU + FLD; Group 7: Er,Cr:YSGG laser + AEO + FLD; and Group 8: Er,Cr:YSGG laser + SBU + FLD. After thermocycling, 1 × 1 mm2 sticks were used for the µTBS test (n = 10). Two sticks per group were used for SEM analysis. Fractured sample surfaces were evaluated using a stereomicroscope. Group 8 showed the highest µTBS value (13.70MPa), whereas Group 1 showed the lowest μTBS value (5.60MPa). There were no significant differences between Groups 2, 3, and 4 (P = 0.324), but Groups 5-8 showed statistically significant results that were higher than Groups 1-4 (P = 0.012). Adhesive failure mode was predominant followed by mixed failure. The evaluation of bonding of the FLD to dentin showed that the combined use of Er:YAG and Er,Cr:YSGG lasers with SBU and AEO on dentin surfaces improved the dentinal bond strength of the FLD.

Bond Strength and Failure Mode of Glass Fiber Posts with Different Surface Treatments Prior to Silanization: An In Vitro Comparative Study.

The use of chemical agents in the surface treatment of glass fiber posts can improve their bond strength to the root canal. The aim of this study was to assess the bond strength and failure mode of glass fiber posts that received different surface treatments prior to silanization. In this cross-sectional and in vitro experimental study, 50 human lower premolar roots were randomly divided into five groups and subsequently prepared to receive the cementation of a fiberglass post prior to silanization. They were distributed as group 1 (with 24% hydrogen peroxide), group 2 (with 37% phosphoric acid), group 3 (with 1.23% acidulated phosphate fluoride for 2 minutes), group 4 (with 1.23% acidulated phosphate fluoride for 6 minutes), and group 5 (without pretreatment). After cementation, the roots were sectioned into two discs for each cervical, middle, and apical region. Bond strength was assessed using the push out technique. Adhesive, mixed, and cohesive failure modes were also assessed. For data analysis, ANOVA and Tukey's post hoc tests were used, as well as Pearson's chi-square test. A significance of P < 0.05 was considered in all statistical analyses. When comparing the bond strength of root regions, significant differences were obtained in groups pretreated with phosphoric acid (P = 0.018) and acidulated phosphate fluoride for 2 and 6 minutes (P = 0.001 and P = 0.000, respectively). Furthermore, significant differences were obtained between posts treated only with silane and those that received phosphoric acid pretreatment (P = 0.006) and acidulated phosphate fluoride for 6 minutes (P = 0.001). Significant association of mixed failure mode was observed with hydrogen peroxide (P = 0.014) and phosphoric acid (P = 0.006) pretreatments. Cohesive failure was significantly associated with acidulated phosphate fluoride pretreatment for 2 minutes (P = 0.032) and with posts that did not receive treatment prior to silanization (P = 0.000). Posts treated only with silane and pretreated with hydrogen peroxide and acidulated phosphate fluoride for 2 minutes presented significantly higher bond strength with respect to those pretreated with phosphoric acid and acidulated phosphate fluoride for 6 minutes. However, acidulated phosphate fluoride for 2 minutes and silane were associated with a better bonding type.

Assessment Of Shear Bond Strength And Failure Modes Between The Base And Bulk Resin Restorative Materials; An In Vitro Comparative Study

Objective: To assess the comparative shear bond strength and failure modes between the base and bulk Resin restorative materials.Place of Study: Dental Materials Testing Laboratory, Dr. Ishrat-ul-Ibad Khan Institute of Oral Health Sciences, Karachi.Study Design: In Vitro, Experimental StudyDuration of Study: One week (August 2021)Methodology: This experimental material research was conducted at the Dental Materials Test site, Dr. Ishrat-ul-Ibad Khan Institute of Oral Health Sciences, Karachi. Using convenient sampling a total of 16 samples were prepared, eight had Z350 (Material A) while the other eight used Ceram X (Material B) as bulk restorative material sandwiched with GIC as the base material. Samples were made using two sheets of polytetrafluoroethylene mold. Every single sheet contained holes that were 4×2 mm (diameter X thickness). Firstly, these samples were placed in distilled water and later for complete polymerization in the incubator. After this, they were thermo cycled and ultimately checked for shear bond strength.Results: Material A presented the mean value of 148.522±113.928 with single mixed and all other adhesive failure modes, whereas, Material B showed single cohesive failure and the rest of the adhesive failures with a mean of 6062,76±2547,18. Conclusion: Sufficient bonging strengths were observed between the base and bulk resin restorative materials using the sandwich technique, however, Nano-composite “Ceram X” has demonstrated slightly better shear bond strength in comparison to Z350. In addition, adhesive failure in both groups clearly indicated the lack of an adhesive system in between the sandwich material.

Oxynitride c-Al0.7Cr0.3OxN(1-x) arc-PVD hard-coatings, processing, mechanical properties & stability at high temperatures

Crystalline fcc Al0.7Cr0.3OxN(1-x) oxynitride-based dense coatings were deposited in a semi-industrial coater using the arc-PVD technique. The microstructural analysis of the as-coated oxynitrides showed the increased formation of defects such as porosity, droplets, and pinholes upon the O-raise during deposition, while the columnar-like features oriented in the (200) direction were maintained. Meanwhile, the c-Al0.7Cr0.3N reference nitride coating presented a similar microstructure but was mostly texturized in the (111) direction, maintaining the fcc crystal structure. These microstructural characteristics correlated well with the mechanical response of both nitrides. In the c-Al0.7Cr0.3N, significant plastic deformation was registered compared to the c-Al0.7Cr0.3OxN(1-x) coating. However, the interface mismatch did not affect the adhesion strength of the oxynitride. Upon treatment at 950 °C, the c-Al0.7Cr0.3N nitride displayed increased average roughness due to the oxidation and formation of plate-like oxides, probably an α-(CrAl)2O3 phase, while tiny oxide whiskers grow on the c-Al0.7Cr0.3OxN(1-x) coating. The presence of other oxide phases upon thermal treatment was identified. Only slight changes in the nano-hardness & elastic modulus are registered on the thermally treated coatings at 950 °C, which is confirmed by the/E (elastic strain to failure) parameter analysis, indicating that the thermal treatment for the c-AlCrN and the c-AlCrON coatings did not affect their cracking behavior. However, in the as-coated state, the c-AlCrON shows less tendency to form cracking than the c-AlCrN. This cracking behavior agrees with what was found in the scratch testing, supporting the idea that O increases the cracking resistance in the c-AlCrON and results in mixed cohesive + adhesive failure modes in this oxynitride.

Effects of interlayer bias voltage on the mechanical properties of tetrahedral amorphous carbon films

Tetrahedral amorphous carbon (ta-C) films with bias-regulated (namely from −50 V to −200 V) Ti interlayers were prepared on AISI 440C stainless steel substrates, followed by systematic investigation on the microstructure, mechanical, and adhesion properties of such films. In addition, molecular dynamics simulation has been employed to study the formation of Ti films deposited with different incident energy, which was found to be influenced by the bias voltage significantly. The experimental results demonstrated that varying bias voltage on the Ti interlayer exerted minor influence on the sp3C fraction and mechanical properties of ta-C films. Molecular dynamics simulations showed further support for the experimental results. The Ti interlayer exhibited the amorphous-like microstructure, and increasing Ti-atom incident energy resulted in increasing Ti/Fe interlayer thickness and a firstly rising and then descending Fe/Ti interfacial bonding strength. The adhesive failure mode can be divided into buckling crack and interfacial spallation, which was primarily attributed to the tensile-to-compressive transformation of the Ti-interlayer internal stress. Optimised adhesion property of ta-C films can be achieved with a Ti-interlayer bias voltage of ∼ -100 V.

Push-Out Bond Strength of Endodontic Posts Cemented to Extracted Teeth: An In-Vitro Evaluation.

(1) Background: An ideal bond strength between endodontic posts and root canal dentin is essential for optimal retention and good prognosis. This study aimed to evaluate the push-out bond strength (PBS) of prefabricated fiber and metal posts, luted with resin cement to natural dentin. (2) Methods: Extracted premolars with similar root dimensions were assigned into two groups of 30 each for the metal and fiber posts. Teeth were mounted in acrylic blocks exposing 2 mm of the coronal root. Teeth were subjected to endodontic treatment and post-space preparations. Two groups were further subdivided into three sub-groups (n = 10) according to the size of the posts (# 4, 5 and 6). Posts were cemented with resin cement. Specimens were sectioned into 4 mm slices and subjected to the PBS test. (3) Results: The mean PBS was similar for the metal and fiber posts bonded with resin cement, showing a statistically significant result. An increase in post size increased the bond strength initially, but a further increase in size did not show any marked difference. A total of 71.66% of tested specimens failed with the adhesive failure mode. (4) Conclusions: Metal posts showed slightly higher retention compared to the fiber posts, although the p-value was similar for both types. An increase in the size of posts showed increased retention. The most common mode of failure was adhesive failure between cement and dentin.

A comparison of the shear bond strength between magnet keepers and composite resin after using two abrasive metal surface treatments; sandblasting and tribochemical silica coating (CoJet System®).

Traditionally when magnetic attachments are used to retain overdentures, the keeper element is incorporated into gold copings, which often uses the root canal to gain additional retention to the tooth. This procedure may inevitably incur additional expense, laboratory and chair side time. The availability of magnetic attachments to patients may subsequently be limited. This study was conducted to compare the shear bond strength of magnet keepers to a commonly used composite resin following two abrasive metal surface treatments; sandblasting and tribochemical silica coating (CoJet System®). Sixty stainless steels (AUM20) keepers designed for magnetic attachments were embedded in acrylic blocks. Specimens were then divided into two groups of 30 specimens each. The first group was sandblasted with alumina and the second group was treated using the CoJet system. The composite resin was bonded to each magnet keeper and cured. Shear bond strengths were determined for each surface treatment after 24 hours storage in distilled water at 37C° (0 thermocycle), 500 thermocycling, and one-week storage in distilled water at 37C°. The shear bond strength was recorded for each specimen using a universal testing machine and statistical analysis of shear bond strength values within each group of surface treatment was compared using paired T-test. Independent T-test was used to compare the shear bond strengths of sandblasted keeper surfaces with those treated with the CoJet system®. The strongest shear bond strength was obtained with samples treated with CoJet system®. Between groups comparison showed that significant differences were found in the shear bond strength mean values at 0 thermocycle and one week water storage (p=0.001 and p=0.006). The values of shear bond strength recorded by the two treatments exceeded the maximum retentive force required to pull magnet attachment from its keeper. Most of the specimens tested exhibited adhesive failure mode. Within the limitation of this study, it is concluded that using the CoJet surface treatment on the surfaces of magnet keepers is effective for bonding the magnet keepers with the composite resin examined

Assessment of Caries-Affected Dentin Adhesive Interface Treated with Contemporary Conditioning Techniques.

Objective: The aim of this study was to assess shear bond strength (SBS) and failure analysis of adhesion of composite resin (CR) to caries-affected dentin (CAD) pretreated with the Er,Cr:YSGG (ECY) laser, photodynamic therapy (PDT), and etch and rinse (ER) used for cavity disinfection. Materials and methods: Methods used in this study included scanning electron microscopy (SEM), SBS analysis, failure analysis, and digital microscopy. The methods were adopted to assess bond integrity, CAD interface, smear layer, and hybridization. Thirty human third molars assessed clinically and having scores of 4 and 5 based on International Caries Detection and Assessment System (ICDAS) criteria were inspected. Infected dentin was removed. Dentin that was hard and stained pink was categorized as CAD. Ten samples were used in each group for pretreatment of CAD. Ten samples of healthy dentin [sound dentin (SD)] were collected separately and taken as controls. Samples were divided into the following groups: group 1: SD+ER; group 2: CAD+ER; group 3: CAD+ECY; and group 4: CAD+PDT after the pretreatment bonding agent was applied and the restorative procedure was performed using CR. Results: CAD conditioned with PDT before bonding to CR demonstrated the lowest SBS values (11.22 ± 0.77 MPa), whereas the highest SBS values were observed in the SD surface treated with ER (18.25 ± 1.22 MPa). In CAD and SD pretreated with ER, majority of failure modes were cohesive failure and admixed failure, whereas in CAD pretreated with PDT and the ECY laser, the adhesive failure mode was pertinent. Conclusions: The use of the ECY laser and PDT on CAD for cavity disinfection does not have potential for application in clinical settings as it decreases bond integrity of CR. Moreover, the ER pretreatment method for CAD and SD remains the gold standard.

In-situ investigation of temperature-dependent adhesive properties and failure modes in composite bonded joints

This paper presents an experimental investigation into the thermomechanical properties and failure modes of toughened epoxy adhesives and composite-to-aluminum bonded joints in high and low temperature conditions. First, nondestructive evaluation techniques were utilized to characterize the inherent defect morphology of bulk adhesives and the bonded joint interface. This was followed by quasi-static tensile testing conducted over a temperature range of −37 °C to 57 °C. The damage mechanisms and failure modes were investigated using in-situ digital image correlation (DIC) and high-resolution camera. The information from the morphology characterization studies was also used to reconstruct high-fidelity geometries of the test specimens for finite element (FE) analysis. The elastic properties and tensile strength of bulk adhesive test specimens showed significant deterioration while exhibiting considerable ductility at higher temperatures. DIC and FE analysis revealed the strong influence of size and distribution of defects on the material properties and damage localization. In addition, post-fracture surface characterization of the adhesively bonded specimens revealed failure modes ranging between adherent-dominant to adhesive-dominant modes at low and high-temperature conditions.

A study on the effect of process parameters on the joint strength and leak tightness in electromagnetically assisted adhesive Cu-SS tube-to-tube joining through statistical analysis

This work studies an improved hybrid joining technique combining electromagnetic forming and adhesive joining to create a leak-tight Cu-SS tube-to-tube joint named as electromagnetically assisted adhesive joining (EAAJ). An experimental investigation is performed considering three discharge energy (3.9 kJ, 4.4 kJ and 5.0 kJ), four adhesive application lengths (20 mm, 15 mm, 10 mm and 5 mm), three adhesives (Loctite 638, Loctite 567, and Loctite SI 596) and four curing times (24 h, 48 h, 96 h and 120 h) ad process parameters. The mechanical properties of the joints are investigated using testing techniques like pull-out, compression, and micro-hardness tests. An increase in joint strength is observed with the decrease in adhesive application length and increase in curing time. Maximum joint strength, 90% of the base copper tube strength, is obtained in the case of Loctite 638, with 5 mm of adhesive application length, 5.0 kJ of discharge energy and 96 h of curing time. Furthermore, a three-way analysis (3-way ANOVA) of variance technique is implemented to calculate the contribution of the three factors (discharge energy, adhesive application length, type of adhesives) on the joint strength. A cohesive and adhesive failure mode combination leading to sliding failure mode is observed as a joint failure mechanism during pull-out and compression testing. A leak testing setup has been developed to investigate the joint's leak tightness by an air pressure decay test. An increment in leak tightness by 1000 times is observed in 638 EAAJ samples compared to samples joined without adhesives. A 3-way ANOVA analysis is also performed to calculate the contribution of different factors on leak tightness of the joint. Micro-hardness is observed to be increased near the joint interface compared to the base metal. Deformation analysis has highlighted the impact of field shaper slit causing a non-uniformity in radial deformation in the circumferential direction and leading to non-uniform circumferential accumulation of adhesive.

Reflectance Transformation Imaging for the quantitative characterization of experimental fracture surfaces of bonded assemblies

Controlling failure modes is an important issue for the development of bonded assemblies of multi-material structures in industry. The analysis of the failure modes of bonded assemblies, and in particular the evaluation of the adhesive/cohesive failure rate, constitute a significant issue. Generally, it is considered in industrial applications that obtaining a cohesive fracture makes it possible to generate better predictions regarding the rupture of the adhesive joints, even if recent work has shown that a good prediction of the mechanical behavior can also be obtained when adhesive or mixed failure modes occur. Currently, these evaluations are carried out by experts by means of a visual analysis, either directly on the fracture surfaces, or sometimes from high-resolution microscopy. The approach presented in this paper aims to set out a methodology based on the Reflectance Transformation Imaging technique for the objective characterization of experimental fracture surfaces of bonded assemblies. We show how this imaging technique can be used to quantify objective surface features, and how these local descriptors can be used to estimate and map out the failure mode on the fracture surfaces.