Adhesive Mode Research Articles

JOINT STRENGTH OF MIXED SILYL MODIFIED POLYMER-EPOXY ADHESIVE ON SINGLE LAP JOINT ETCHED ALUMINUM

Currently, aluminum alloy is widely used in an automotive structure such as bus body materials due to decreasing the structure weight and fuel consumption. In this structure, there are tens or even hundreds of joints to meet the engineering design. Because of its advantages, the adhesive joint is usually chosen. Aluminum is stiff enough, but it can deform easily. Due to its deformability, cracks will occur easily on the aluminum adhesive joint if it is joined using strong and stiff adhesive. Otherwise, it will be very weak if it is joined using flexible adhesive. The mixture of the strong adhesive, epoxy (EP) and the ductile adhesive, silyl modified polymer (SMP) was proposed for joining aluminum. This study aims to evaluate the effect of the composition of mixed adhesive and its thickness on the strength of single lap joint (SLJ) etched aluminum. Before joining process, the aluminum surface was treated by sandpapering (SDP), and then chromic-sulphuric acid (CSA) etch. The composition variations of mixed adhesive were 100%EP, 75%SMP:25%EP, 50%SMP:50%EP, 25%SMP:75%EP, and 100%SMP. Mixed adhesives were prepared by using a stirrer with a spatula for 4-6 minutes at 60 rpm. SLJ specimens were manufactured through bonding of two aluminum sheets surface with an adhesive and giving 0.1 MPa pressure. The thickness adhesive was varied of 0.2 mm, 0.4 mm, and 0.6 mm. Specimens got a post-curing process at 100oC for 100 minutes. The shear tests were performed to evaluate the strength of SLJ. The experimental result showed that the surface treatments of SDP and CSA give higher porosity on the adherend surface. The highest strength and elasticity modulus were achieved by joint of 25%SMP:75%EP mixed adhesive joints. The addition a few of SMP adhesive in EP adhesive and adherend surface treatment increases the joint strength. All of the joints have mixed failure mode except the 100%EP adhesive joint has an adhesive failure mode.

Effect of universal adhesive etching modes on bond strength to dual-polymerizing composite resins

Statement of problemInformation is lacking as to the effect on bond strength of the etching modes of universal adhesives when they are used to bond dual-polymerizing composite resins to dentin. PurposeThe purpose of this in vitro study was to investigate the bonding of dual-polymerizing foundation composite resins to dentin when universal bonding agents are used in self-etch or etch-and-rinse modes. Material and methodsSixty caries-free, extracted third molar teeth were sectioned transversely in the apical third of the crown and allocated to 12 groups (n=5). Three different bonding agents (Scotchbond Universal, OptiBond XTR, All-Bond Universal) were used to bond 2 different dual-polymerizing composite resins (CompCore AF or CoreFlo DC) to dentin, using 2 different etching approaches (etch-and-rinse or self-etch). The specimens were sectioned into sticks (1×1×8 mm) with a precision saw. The bond strength of the specimens was tested under microtensile force at a crosshead speed of 0.5 mm/min. The data were analyzed using a 3-way ANOVA, a Games-Howell post hoc comparisons model, and Student t tests with Bonferroni corrections (α=.05). ResultsIn the overall model, the composite resin used had no effect on bond strength (P=.830). The etching protocol by itself also did not have a significant effect (P=.059), although a trend was present. The bonding agent, however, did have an effect (P<.001) on bond strength. Also, a significant interaction effect was found for the bonding agent and etching protocol on bond strength (P<.001). The etching protocol influenced the bond strength when Scotchbond Universal (P<.008) and All-Bond Universal (P<.004) were used but not when OptiBond XTR was used (P=1.00). A self-etch protocol provided significantly higher bond strength when Scotchbond Universal was used, whereas with All-Bond Universal, an etch-and-rinse protocol, provided higher bond strength. ConclusionsWhen universal bonding agents were used to secure dual-polymerizing composite resins to dentin, no single etching protocol is better than another. Depending on which bonding agent is being used, one etching mode may perform better.

Time series analysis of tool wear in sheet metal stamping using acoustic emission

Galling is an adhesive wear mode that often affects the lifespan of stamping tools. Since stamping tools represent significant economic cost, even a slight improvement in maintenance cost is of high importance for the stamping industry. In other manufacturing industries, online tool condition monitoring has been used to prevent tool wear-related failure. However, monitoring the acoustic emission signal from a stamping process is a non-trivial task since the acoustic emission signal is non-stationary and non-transient. There have been numerous studies examining acoustic emissions in sheet metal stamping. However, very few have focused in detail on how the signals change as wear on the tool surface progresses prior to failure. In this study, time domain analysis was applied to the acoustic emission signals to extract features related to tool wear. To understand the wear progression, accelerated stamping tests were performed using a semi-industrial stamping setup which can perform clamping, piercing, stamping in a single cycle. The time domain features related to stamping were computed for the acoustic emissions signal of each part. The sidewalls of the stamped parts were scanned using an optical profilometer to obtain profiles of the worn part, and they were qualitatively correlated to that of the acoustic emissions signal. Based on the wear behaviour, the wear data can be divided into three stages: - In the first stage, no wear is observed, in the second stage, adhesive wear is likely to occur, and in the third stage severe abrasive plus adhesive wear is likely to occur. Scanning electron microscopy showed the formation of lumps on the stamping tool, which represents galling behavior. Correlation between the time domain features of the acoustic emissions signal and the wear progression identified in this study lays the basis for tool diagnostics in stamping industry.

Experimental study of the effect of pre‐bond contamination with de‐icing fluid and ageing on the fracture toughness of composite bonded joints

AbstractThe scope of the present work is to experimentally investigate the effect of pre‐bond contamination with de‐icing (DI) fluid and the combined effect of DI fluid and hygrothermal ageing on the fracture toughness of carbon fibre reinforced plastic bonded joints. These scenarios could occur in the implementation of an adhesively bonded patch repair in a composite aircraft structural part. To this end, mode I and mode II fracture toughness tests were conducted on contaminated specimens and mode II fracture toughness tests on contaminated/aged specimens. Three levels of contamination with a de‐icer were considered. The hygrothermal ageing conditions applied until saturation are 70°C/85% relative humidity. The experimental results reveal a detrimental effect of DI fluid on both mode I and mode II fracture toughness of the bonded joints. With increasing the contamination level, the mode I and mode II critical energy release rates decrease. Under mode I loading, the specimens failed mainly in light‐fibre‐tear mode, while under mode II loading, in adhesive failure mode. Hygrothermal ageing decreased further the mode II fracture toughness of the specimens and increased the adhesive failure mode. The present study reveals that the pre‐bond DI contamination and after‐bond ageing could critically degrade the strength of adhesively bonded patch repairs.

Effect of Nanostuctured Hydroxyapetite Incorporation into a Resin Composite on Shear Bond Strength to Dentin and Interfacial Micromorphology after Storage in Different Media

Aim: This study was designed to evaluate the effect of incorporation of hydroxyapatite nanorods into a resin composite restorative material and dental adhesive on shear bond strength to dentin and interfacial micromorphology after storage in different media. Materials and Methods: Ninety natural premolars (N=90) were selected for this study and randomly divided into three main groups (n =30) according to the material used (A), where A1: the resin composite restorative material reinforced with hydroxyapatite nanorods. A2: Adhesive resin material with incorporated hydroxyapatite nanorods, while A3: Resin composite (without nano-hydroxyapatite) as control group. Each group was subdivided into three subgroups (n=10) according the storage media (B) either Acid (B1), artificial saliva (B2) or distilled Water (B3).All specimens were thermocycled then stored at room temperature and kept under each of the above mentioned media for 3 hours every day over 30 days (one month). All samples were individually and horizontally mounted on a Universal testing machine loaded to failure at cross head speed of 0.5 mm/ min then Shear bond strength was calculated. The fractured specimens were tested under scanning electron microscope to examine the dentin adhesive interface and mode of failure. Data were analyzed using one-way analysis of variance (ANOVA) and Tukey’s post hoc significance difference tests. Differences were considered significant at P<0.05. Results: There was a statistically significant difference between groups (p ≤0.05). Adhesive resin with incorporated hydroxyapatite nanorods recorded statistically significant mean highershear bond strength (6.33±1.53, 11.35±0.78 and7.97±0.57) after storage in (acid, artificial saliva, distilled water), followed by resin composite incorporates nanorods

Comparative potential assessment of solid lubricants on the performance of poly aryl ether ketone (PAEK) composites

Poly aryl ether ketone (PAEK) is known as a high performance polymer superior to PEEK (poly ether ether ketone) in many aspects such as temperature stability, tribo-performance etc. Recently few efforts are put to enhance the tribo-potential of PAEK by developing composites containing short fibers of carbon and glass and most favored lubricants such as graphite, PTFE (poly tetrafluoroethylene), hexa boron nitride (hBN) etc. The wear and friction got significantly reduced to the extent that the composites showed very high potential as bearing materials for harsh operating conditions.Mica and boric acid (BA) are known as very good solid lubricants (SLs) with layer lattice structures. Potassium titanate (KT) powder also has been very popular ingredient of friction materials responsible for increasing wear resistance (WR) and reducing friction fluctuations. It is, however, never explored in bearing materials for enhancing tribo-potential.Keeping this in view, a series of composites was prepared by injection molding with identical parent composition but differing in type of solid lubricants (hBN, KT, BA and Mica). The tribo-performance was evaluated in adhesive wear mode on tribometer under severe operating conditions (700–900 N, velocity 1.63–3.5m/s). Composites exhibited very low specific wear rates (K0) (2–8×10–16m3/Nm) and very low coefficient of friction (µ) (0.04–0.08), which decreased with load and velocity. KT proved to be the most performing filler, while Mica was least effective followed by BA. Worn surface analysis by SEM (Scanning electron microscopy) and EDAX (energy dispersive x-ray) helped to understand wear mechanisms.

Effect of self etching ceramic primer and universal adhesive on bond strength of lithium disilicate ceramic

The clinical success of ceramic restorations is affected by the ceramic bonding procedure. The objective of the study was to evaluate the effect of different surface treatments, including the use of self-etching ceramic primer (SECP), on resin cement-glass ceramic bond strength. Thirty lithium disilicate ceramic (LDC) rectangles (3 mm × 3 mm × 8 mm) were fabricated Specimens were randomly assigned into three experimental groups (n = 10) according to the surface treatment: Group 1-hydrofluoric acid [HF acid]+ silane + universal adhesive; Group 2-HF + universal adhesive; Group 3-SECP + universal adhesive. All specimens were stored in distilled water for 24 h at 37 °C and shear bond strength (SBS) was tested at a crosshead speed of 0.5 mm (Universal Testing machine-Instron). Failure modes were evaluated using a digital microscope for all specimens. Analysis of variance and the Tukey post hoc tests using SPSS (Version 22.0, IBM, New York, USA) were used to analyze data. The SBS of groups 1 (19.74 ± 1.28 MPa) and 3 (21.11 ± 2.07 MPa) were significant higher than group 2 (14.80 ± 1.94 MPa). The SBS values for specimens in groups 1 (19.74 ± 1.28 MPa) and 3 (21.11 ± 2.07 MPa) were comparable. Adhesive, mixed and cohesive failure modes were observed and mixed failure was the most common in all groups. Therefore, the use of SECP and universal adhesive is recommended as an alternative to the use of HF acid in combination with ceramic primer while bonding to LDC.

DENTIN BOND EFFICACY OF COMPOSITE RESIN RESTORATIONS USING RESIN INFILTRANT

Aim: To evaluate the bond efficacy of direct resin composite restorations bonded by three different dentin adhesives an etch-and-rinse, self-etch and resin infiltrant (ICON) using microtensile bond strength testing and Analyze their failure mode. Methodology: Thirty molar teeth were selected and thoroughly cleaned. Each tooth was vertically embedded into self-curing acrylic resin up to the level of the cervical line. The occlusal enamel of teeth was removed perpendicular to the long axis of teeth to expose flat dentin surface at a standardized depth. The teeth were divided into three main groups of 10 teeth each; using Etch and rinse adhesive system control group A1 (All-bond Universal, Bisco), self-etch adhesive system group A2 (All-bond Universal, Bisco) and resin infiltrant group A3 (Icon). Direct resin composite nano-hybrid universal composite (FiltekTM Z250 XT, 3M ESPE) cores were build up on the flat dentin surfaces treated with different adhesive systems. The restored teeth were subjected to thermo-cycling at 5°C and 55°C for 2000cycle. Then each tooth was mounted on the cutting machine, sectioned into a series of 1 mm thick. The sticks were stressed to failure under tension using Universal Testing Machine to record the microtensile bond strength. The fractured sticks were evaluated for bond failure mode under a stereomicroscope at 40X magnification to detect the mode of failure. The collected data were submitted to ANOVA and Tukey’s test. Results: Etch-and-rinse (A1) control group showed the highest significant mean Microtensile bond strength (MPa) followed by Self-etch adhesive (A2) followed by Resin infiltrant (ICON) (A3) at p≤0.001. The result of the stereomicroscopic examination revealed adhesive and cohesive failure mode in composite. The predominant mode of failure using resin infiltrant group A3 (Icon) and self-etch adhesive system group A2 group was adhesive failure with a higher percentage in resin infiltrant A3 (Icon) group 100%. On the other hand cohesive in composite is the predominant mode of failure using the Etch and rinse adhesive system group A1 80%. Conclusion: The use of resin infiltrant (Icon) as an adhesive material impaired efficacy of the microtensile bond strength of direct resin composite to sound dentin .

Study on Tensile Mechanical Behavior of Composite T-Joints

Based on three kinds of composite T-joints with different connection way for tension test outside the plane, it was obtained contrastively that how the ordinary adhesive, Z-pin reinforcement and stitching reinforcement three different fitting influence tensile strength, damage failure process and failure mode of composite T-joints. The test results showed that compared with ordinary adhesive connection mode, tensile strength of the Z-pin reinforcement and stitching reinforcement T-joints increased by 13.6% and 11.4%, respectively; and the largest deformation increased by 19.2% and 15.1%, respectively. After reaching maximum load condition, the ordinary adhesive T-joints had brittle failures, but Z-pin reinforcement and stitching reinforcement T-joints all showed that the ductile damage behavior, corresponding to the load-displacement curve appeared saw-tooth wave platform. Obviously, the Z-pin reinforcement T-joints had the most significant reinforcement effect on tensile properties of composite laminates T-joints.

The Bonding Performance of a Universal Adhesive to Artificially-created Caries-affected Dentin.

To evaluate the bonding performance of a universal adhesive to sound and artificially-created caries-affected dentin, using either the etch-and-rinse or self-etch strategy. Flat midcoronal dentin surfaces from 48 third molars were randomly assigned to eight groups according to the substrate (sound dentin and artificially-created caries-affected dentin [pH cycling for 14 days]) and the adhesive or application mode (Scotchbond Universal: self-etch or etch-and-rinse strategies; Adper Single Bond 2 and Clearfil SE Bond, a two-step etch-and-rinse adhesive and a two-step self-etch adhesive as controls, respectively). Then, composite blocks were constructed, the specimens were further stored in water for 24 h, and composite-dentin sticks were prepared (0.8 mm2) and tested under tension at 1.0 mm/min. Data were analyzed with two-way ANOVA and Tukey's test (α = 0.05). All adhesives tested on artificially-created caries-affected dentin presented similar μTBS (p > 0.05), and inferior bonding performance when compared to sound dentin (p = 0.000). On sound dentin, Scotchbond Universal presented higher bond strengths when applied in the etch-and-rinse than self-etch mode, but comparable bond strength in each application mode in relation to the respective control adhesive (p = 0.04). Scotchbond Universal can be used in different application modes when bonded to artificially-created caries-affected dentin; however, the etch-and-rinse strategy improves its bonding ability to sound dentin. Moreover, Adper Single Bond 2 and Clearfil SE Bond presented similar bond strengths, regardless of the dentin condition and comparable performance in relation to each strategy of Scotchbond Universal.

Influence of nano-structured alumina coating on shear bond strength between Y-TZP ceramic and various dual-cured resin cements.

PURPOSEThe purpose of this study was to evaluate the effect of nano-structured alumina surface coating on shear bond strength between Y-TZP ceramic and various dual-cured resin cements.MATERIALS AND METHODSA total of 90 disk-shaped zirconia specimens (HASS CO., Gangneung, Korea) were divided into three groups by surface treatment method: (1) airborne particle abrasion, (2) tribochemicalsilica coating, and (3) nano-structured alumina coating. Each group was categorized into three subgroups of ten specimens and bonded with three different types of dual-cured resin cements. After thermocycling, shear bond strength was measured and failure modes were observed through FE-SEM. Two-way ANOVA and the Tukey's HSD test were performed to determine the effects of surface treatment method and type of cement on bond strength (P<.05). To confirm the correlation of surface treatment and failure mode, the Chi-square test was used.RESULTSGroups treated with the nanostructured alumina coating showed significantly higher shear bond strength compared to other groups treated with airborne particle abrasion or tribochemical silica coating. Clearfil SA Luting showed a significantly higher shear bond strength compared to RelyX ARC and RelyX Unicem. The cohesive failure mode was observed to be dominant in the groups treated with nano-structured alumina coating, while the adhesive failure mode was prevalent in the groups treated with either airborne particle abrasion or tribochemical silica coating.CONCLUSIONNano-structured alumina coating is an effective zirconia surface treatment method for enhancing the bond strength between Y-TZP ceramic and various dual-cured resin cements.

Effects of silver nanoparticles on the bonding of three adhesive systems to fluorotic enamel.

The objective was to evaluate the effect of adding silver nanoparticles into three commercial adhesive systems (Excite™, Adper Prompt L-Pop™ and AdheSE™). Nanoparticles were prepared by a chemical method then mixed with the commercial adhesive systems. This was later applied to the fluorotic enamel, and then micro-tensile bond strength, contact angle measurements and scanning electron microscopy observations were conducted. The commercial adhesive systems achieved the lowest micro-tensile bond strength (Excite™: 11.0±2.1, Adper Prompt L-Pop™: 14.0±5.4 and AdheSE™: 16.0±3.0 MPa) with the highest adhesive failure mode related with the highest contact angle (46.0±0.6º, 30.0±0.5º and 28.0±0.4º respectively). The bond strength achieved in all the experimental adhesive systems (19.0±5.4, 20.0±4.0 and 19.0±3.5 MPa respectively) was statistically higher (p<0.05) than the control and showed the highest cohesive failures related to the lowest contact angle. Adding silver nanoparticles in order to decrease the contact angle improve the adhesive system wetting and its bond strength.

Surface modification for bonding between amalgam and orthodontic brackets.

OBJECTIVE:Testing of methods to enhance the shear bond strength (SBS) between orthodontic metal brackets and amalgam by sandblasting and different primers.MATERIALS AND METHODS:Three hundred samples of amalgam restorations (KerrAlloy®) were prepared in self-cured acrylic blocks, polished, and divided into two groups: nonsandblasted and sandblasted. Each group was divided into five subgroups with different primers used in surface treatment methods, with a control group of bonded brackets on human mandibular incisors. Following the surface treatments, mandibular incisor brackets (Unitek®) were bonded on the amalgam with adhesive resin (Transbond XT®). The SBS of the samples was tested. The adhesive remnant index (ARI) and failure modes were then determined under a stereo-microscope. Two-way analysis of variance, Chi-square, and Kruskal–Wallis tests were performed to calculate the correlations between and among the SBS and ARI values, the failure modes, and surface roughness results.RESULTS:There were statistically significant differences of SBS among the different adhesive primers and sandblasting methods (P < 0.05). The sandblasted amalgam with Assure Plus® showed the highest SBS (P < 0.001). Samples mainly showed an ARI score = 1 and mix-mode failure. There was a statistically significant difference of surface roughness between nonsandblasted amalgam and sandblasted amalgam (P < 0.05), but no significant differences among priming agents (P > 0.05).CONCLUSIONS:Using adhesive primers with sandblasting together effectively enhances the SBS between orthodontic metal brackets and amalgam. The two primers with the ingredient methacryloxydecyl dihydrogen phosphate (MDP) monomer, Alloy Primer® and Assure Plus®, were the most effective. Including sandblasting in the treatment is essential to achieve the bonding strength required.

Effect of Intra-Canal Calcium Hydroxide Remnants on the Push-Out Bond Strength of Two Endodontic Sealers.

Introduction:The aim of this study was to evaluate the effect of intra-canal calcium hydroxide (CH) remnants after ultrasonic irrigation and hand file removal on the push out bond strength of AH-26 and EndoSequence Bioceramic sealer (BC Sealer). Methods and Materials:A total of 102 single-rooted extracted human teeth were used in this study. After root canal preparation up to 35/0.04 Mtwo rotary file, all the specimens received CH dressing except for 34 specimens in the control group. After 1 week, the specimens with CH were divided into 2 groups (n=34) based on the CH removal technique; i.e. either with ultrasonic or with #35 hand file. Then specimens were divided into two subgroups according to the sealer used for root canal obturation: AH-26 or BC Sealer. After 7 days, 1 mm-thick disks were prepared from the middle portion of the specimens. The push out bond strength and failure mode were evaluated. Data were analyzed by the two-way ANOVA and Tukey’s post hoc tests. Results:The push out bond strength of both sealers was lower in specimens receiving CH. These values were significantly higher when CH was removed by ultrasonic (P<0.05). The dominant mode of failure in all subgroups was of mixed type except for the BC Sealer specimens undergoing CH removal with hand file which dominantly exhibited adhesive mode of failure. Conclusion:CH remnants had a negative effect on the push out bond strength of AH-26 and BC Sealer. Ultrasonic irrigation was more effective in removing CH.

Formations of AZ91/Al2O3 nano-composite layer by friction stir processing

Abstract Composite layers containing ~0.8 %vol Al 2 O 3 nanoparticles were produced on AZ91 magnesium alloy by friction stir processing (FSP). The treated layers were characterized using optical and scanning electron microscopes, as well as microhardness and wear testing units. It was noticed that, by reducing the rotational speed and increasing the travel speed, the grain size of the treated layer reduces and its hardness increases. In addition, the presence of nano Al 2 O 3 reduces the grain sizes of the layers further and increases their hardness. Furthermore, FSP of AZ91 with Al 2 O 3 particles improved the wear resistance significantly and changed the wear mechanism from oxidation and adhesive mode in the as-received AZ91 to oxidation and abrasive in the FSPed specimens. Finally, the rotational speed of 800 rpm and the travel speed of 40 mm/min were the optimum parameters for achieving a suitable composite layer with the highest hardness and wear resistance among the treated layers.

Bond Strength of Self-adhesive Resin Cement to Different Root Perforation Materials

IntroductionDifferent materials have been used for intervening in root perforations. These materials are often in contact with resin cements used for cementation of intraradicular retainers. The aim of this study was to evaluate the bond strength of self-adhesive resin cement to different materials used to treat root perforations (mineral trioxide aggregate [MTA], Portland cement [PORT], and glass ionomer cement [GIC]). MethodsFour discs (10 × 1 mm) of each material (the MTA, PORT, and GIC groups) were embedded into polyvinyl chloride tubes using acrylic resin, ground, and polished until a flat surface was exposed. Afterward, 4 silicone molds were used to prepare self-adhesive resin cement cylinders (0.7 × 1 mm) on each disc surface (N = 16). The specimens were stored in deionized water at 37°C for 24 hours and subjected to a microshear test. Then, the failure modes were examined. Data were submitted to statistical analysis (α = 0.05). ResultsThe MTA and GIC groups showed significantly higher microshear bond strength values (3.36 ± 1.56 and 2.90 ± 1.49 MPa, respectively) than the PORT group (1.39 ± 0.77 MPa) (P < .05). Only adhesive failure modes were observed. ConclusionsWhen PORT was used as a root perforation material, GIC should be used as a base over it to improve shear bond strength with self-adhesive resin cement.

Friction Coefficient and Worn Surface of Ferromagnetic Materials under Magnetic Fields

Several machine components including a part of electrical circuit box, an electrical motor and an automotive part were common ferromagnetic materials used under the magnetic fields. In the general, their friction had occurred in the magnetized materials during operation. The friction coefficient of the sample under magnetic fields was different from the sample without magnetic field treatment. Its friction coefficient had correlation with wear behavior of specimens. The wear protection procedures for the ferromagnetic parts during operation are recognized different from others without magnetization. Its friction coefficient was thus used to measure the wear characteristics with a ball on disc friction tester. The microstructure of wear trace and debris was investigated by scanning electron microscope. From the results, the magnetic fields affected the change of friction coefficient. The friction coefficient was decreased with an increasing magnetic intensity. This was because the wear debris was induced and thus decreased the adhesive wear mode during friction test.

Dentin-composite bond strength measurement using the Brazilian disk test

ObjectivesThis study presents a variant of the Brazilian disk test (BDT) for assessing the bond strength between composite resins and dentin. MethodsDentin-composite disks (ϕ 5mm×2mm) were prepared using either Z100 or Z250 (3M ESPE) in combination with one of three adhesives, Adper Easy Bond (EB), Adper Scotchbond Multi-Purpose (MP) and Adper Single Bond (SB), and tested under diametral compression. Acoustic emission (AE) and digital image correlation (DIC) were used to monitor debonding of the composite from the dentin ring. A finite element (FE) model was created to calculate the bond strengths using the failure loads. Fracture modes were examined by scanning electron microscopy (SEM). ResultsMost specimens fractured along the dentin-resin composite interface. DIC and AE confirmed interfacial debonding immediately before fracture of the dentin ring. Results showed that the mean bond strength with EB (14.9±1.9MPa) was significantly higher than with MP (13.2±2.4MPa) or SB (12.9±3.0MPa) (p<0.05); no significant difference was found between MP and SB (p>0.05). Z100 (14.5±2.3MPa) showed higher bond strength than Z250 (12.7±2.5MPa) (p<0.05). Majority of specimens (91.3%) showed an adhesive failure mode. EB failed mostly at the dentin-adhesive interface, whereas MP at the composite-adhesive interface; specimens with SB failed at the composite-adhesive interface and cohesively in the adhesive. ConclusionsThe BDT variant showed to be a suitable alternative for measuring the bond strength between dentin and composite, with zero premature failure, reduced variability in the measurements, and consistent failure at the dentin-composite interface. Clinical significanceThe new test could help to predict the clinical performance of adhesive systems more effectively and consistently by reducing the coefficient of variation in the measured bond strength.

Fatigue resistance of monolithic CAD/CAM ceramic crowns on human premolars

The aim of this study was to determine the fatigue strength of two contemporary crown ceramics, lithium disilicate e.max® CAD (LD) and polymer-infiltrated ceramic Enamic® (PIC) and examine their failure mode. Twenty extracted human maxillary premolars were divided into two groups. The teeth were prepared and restored with either LD or PIC crowns. The restored teeth were subjected to cyclic chewing simulation (9Hz). The sinusoidal loading was started with 500N followed by a stepwise increase of 100N for every 100,000 cycles until fracture occurred or, alternatively, after one million cycles. The Kaplan-Meier survival analysis was applied on fatigue loadings. Differences in the failure modes were analyzed by Fisher Exact tests. The average failure load of LD group was 1400N (904,728 cycles) with 70% survival rate, while the average failure load of PIC group was 870N (378,167 cycles) with 0% survival. Regarding the failure mode in both test groups, the crowns tended to fail above the cemento-enamel junction (CEJ) and both combined adhesive and cohesive failure mode were commonly observed rather than cohesive failure. No significant difference was found between the test groups. The failures were initiated from a contact point or central fossa. The fatigue resistance of LD crowns on premolars was significantly higher than the PIC ceramic crowns.

Improving the Adhesion Resistance of the Boride Coatings to AISI 316L Steel Substrate by Diffusion Annealing

In this study, new results about the practical adhesion resistance of boride coating/substrate system formed at the surface of AISI 316 L steel and improved by means of a diffusion annealing process are presented. First, the boriding of AISI 316 L steel was performed by the powder-pack method at 1173 K with different exposure times (4-8 h). The diffusion annealing process was conducted on the borided steels at 1273 K with 2 h of exposure using a diluent atmosphere of boron powder mixture. The mechanical behavior of the boride coating/substrate system developed by both treatments was established using Vickers and Berkovich tests along the depth of the boride coatings, respectively. Finally, for the entire set of experimental conditions, the scratch tests were performed with a continuously increasing normal force, in which the practical adhesion resistance of the boride coating/substrate system was represented by the critical load. The failure mechanisms developed over the surface of the scratch tracks were analyzed; the FeB-Fe2B/substrate system exhibited an adhesive mode, while the Fe2B/substrate system obtained by the diffusion annealing process showed predominantly a cohesive failure mode.