Significant Reduction In Bond Strength Research Articles

Flexural performance and damage of reinforced fly ash and slag-based geopolymer concrete after coupling effect of freeze-thaw cycles and sustained loading

To better represent field conditions, the bending performance of reinforced geopolymer concrete (GPC) beams after the coupling effect of freeze-thaw cycling and sustained flexural load was investigated. Two types of GPC (G10 and G50) with different content of fly ash and slag were included and compared with ordinary Portland cement concrete (OPC). The mechanical strength of concrete and bond strength of rebars in concrete before and after freeze-thaw cycles were measured. It was found that the frost resistance of G10 was the weakest followed by OPC and G50. Three scenarios of bending tests on reinforced concrete beams were included: (1) control (without freeze-thaw damage); (2) individual freeze-thaw cycling; (3) coupling effect before bending. Rebound tests were conducted to evaluate frost damages at different areas of the beams as the base to analyze bending behaviors of the beams. The failure mode, load-displacement(strain) relationship, ultimate flexural strength, and bending stiffness of beams from bending tests are analyzed. All beams in scenario (1) were dominant in flexural failure. For scenario (2), G10 and G50 failed in debonding failure due to significant reduction in bond strength, while OPC failed in diagonal tension failure as OPC could sustain bond stiffness, thus preventing debonding failure. For scenario (3), damages in GPC were exacerbated, while damages in OPC were limited.

Behavior of high strength reinforcing steel rebars after high temperature exposure: Tensile properties and bond behavior using pull-out and end beam tests

High strength reinforcing steel (HSRS) is increasingly being adopted in the construction industry in North America due to its high load-carrying capacity, yet their behavior relative to normal grade rebars under external hazard events such as fire exposure still need further research. In current work, the first goal is to investigate the residual tensile properties of different types of HSRS and normal rebars including ASTM A706, A615, A1035CS, and A1035CM with grades of 420, 550, and 690 before and after high temperatures (350 °C and 700 °C), that simulates residual capacity after different levels of fire exposure. The second goal is to explore the residual bond strength of these rebars using both pull-out and end-beam tests after heat exposure, facilitating a comparison among test methods and evaluating their reliability under fire hazard conditions. The tensile test results indicated insignificant changes in the mechanical properties of all rebars after 350 ℃ heat exposure. However, there was a significant reduction of more than 30% in both yield and ultimate strength after 700 ℃ heat exposure for high grades like grade 690 of ASTM A1035. Among all rebar types and grades, only grade 420 of ASTM A706 retained most of its ductility and strength, making it the most reliable rebar among those tested against fire hazards. In the bond tests, splitting failure was observed at both ambient and after 500 °C heat exposure. Heat exposure resulted in a 73% reduction in bond strength across all rebars for the pull-out tests, with no significant variations between rebar types. On the other hand, end-beam tests indicated a 12.6% average reduction in bond strength with a 9% improvement in bond behavior for ASTM A706 grade 420. However, for ASTM A1035 CS grade 690 and ASTM A706 grade 550 there were slight reductions in bond behavior, with decreases of 9% and 14%, respectively. Compared to the end-beam test, the pull-out test results in a significant reduction in bond strength due to its high dependency on excessive compressive strength reduction resulting in brittle splitting failure. Based on comparison with empirical models, it is recommended not to use models derived from pull-out tests to estimate bond strength, as they tend to overestimate it. Instead, empirical models based on end-beam tests are recommended, since they show consistency with test results. It should be noted that although the bond strength based on splitting failure is primarily dependent on concrete properties, changes were observed in the bond behavior among different rebars, which can be attributed to changes in friction at the interface due to morphological changes in the rebar surface after heat exposure, as well as potential variations in thermal expansion properties, which need further research.

Influence of Application Modes on Increasing Bond Strength Longevity of Self-etching and Universal Adhesive Systems to Enamel.

The present study aimed to evaluate the influence of application mode on the short-term microshear bond strength longevity of self-etching and universal adhesive systems to enamel, the failure mode, and the resulting enamel surface micromorphology. Ninety enamel surfaces were obtained from sound third molars, planed, and randomly assigned to nine groups, according to the application mode and the adhesive system (n=10). There were three primer application modes: according to the manufacturer's recommended application time (control), using double the application time recommended for the primer and selective enamel etching. The adhesive systems used were: Clearfil SE Bond (Kuraray), FL-Bond II (SHOFU), and Futurabond U (Voco). At least two resin-bonded composite cylinders (Grandioso Light Flow, Voco) were placed on each enamel surface, and then evaluated for microshear bond strength at 24 hours and 180 days of storage in solution body fluid (SBF) at pH 7.4. Failure modes were evaluated with a stereoscopic microscope at 20× magnification. A micromorphological analysis of the enamel surface was performed under a scanning electron microscope at 5000× magnification before and after the treatments. Mixed models for repeated measures over time showed significant interaction among application modes, adhesive systems, and time periods (p=0.0331). The bond strength of FL-Bond II adhesive to enamel observed after performing selective enamel etching was significantly higher than that observed after applying the control treatment (p=0.0010) at both 24 hours and 180 days. However, no significant difference was observed between the application of this same adhesive at double the time recommended by the manufacturer and the other two application modes (p>0.05). There was also no significant difference in the microshear bond strength for the enamel treatments applied using Clearfil SE Bond and Futurabond U (p>0.05). A significant reduction in bond strength to enamel was observed at the 180-day storage time for all the adhesive systems when selective enamel etching was performed (p<0.0001). No significant association was observed between the adhesive system failure mode and the enamel treatments (p=0.1402 and p=0.7590 for 24 hours and 180 days, respectively). The most prevalent failure was the adhesive type.

Bond behaviour evaluation between steel reinforcement and self-healing concrete containing non-axenic biomasses

Although steel reinforcements are used to withstand tensile forces in concrete, cracks are an unavoidable phenomenon. The presence of cracks, in fact, increases the risk for lowering the service life and durability of concrete structures. A critical issue occurs when due to splitting forces, cracks appear in concrete along the tensioned rebars which damage the bonding between the steel and concrete matrix. As a mitigation plan, the cracks should be healed at short notice and the bonding has to be recovered by the potential use of healing agents. This paper aims to investigate the bond behaviour of steel reinforcement in self-healing concrete. Two biomasses were employed as healing agents namely HTN (bacteria-based) and YEAST (fungi-based). The fresh and hardened properties of the normal and self-healing concretes were initially evaluated. The bond properties were investigated by performing pull-out tests on three different states of concrete: uncracked, cracked, and healed. Results revealed that the additions of biomasses did not induce negative effects on the compressive strength of hardened concrete. Moreover, the average bond strength of uncracked concretes containing HTN and YEAST improved by 20% and 8%, respectively, as compared with normal concrete. The introduction of a crack caused a significant reduction in bond strength regardless of the addition of healing agents. Nevertheless, it was found that the bond strength was slightly recovered after healing under water immersion.

Influence of mechanical and chemical pre-treatments on the repair of a hybrid ceramic

ObjectivesThis study aimed to investigate the influence of the respective mechanical and chemical pre-treatments on the composite repair of a CAD/CAM hybrid ceramic using a microtensile bond strength test (μTBS). Methods15 CAD/CAM Blocks of Vita Enamic (VE) were randomly sectioned into three mechanical pre-treatments: (1.) Diamond bur (D), (2.) Airborne abrasion (A), (3.) Tribochemical silica coating (T) and subsequently five chemical pre-treatments: (1.) Clearfil SE Bond Bond (B; negative control), (2.) ESPE Sil (S), (3.) Clearfil Ceramic Primer Plus (CPP), (4.) Clearfil Repair (CR) and (5.) Scotchbond Universal (SCB). Per block, n = 20 specimens were sawn. Half of the specimens were randomly selected and subjected to an immediate bond strength test, while the other half was subjected to artificial aging for 6 months 180 days at 37 °C and subsequent thermocycling of 5000 cycles. A μTBS was performed and data (MPa) were compared in one-way and two-way ANOVA and Tukey's HSD. Paired-t-test was used for artificial aging (α = 0.05). Debonded specimens were analyzed of for failure modes with a stereomicroscope (SEM). ResultsThe results of one-way ANOVA for the fifteen fastening procedures after aging indicated significant differences according to SCB-A and CPP-T. Two-way ANOVA after aging observed inferior bond strength for SCB. No differences were observed for mechanical pre-treatments. Artificial aging showed a significant reduction in bond strength on most of the fastening procedures. SignificanceSCB showed the lowest bond strength values besides B, S, CPP, and CR. MDP and silane are both suitable for the repair of VE.

Metakaolin based geopolymer mortar as concrete repairs: Bond strength and degradation when subjected to aggressive environments

By harnessing the benefits of lowering cost and reducing CO2 emission, employing geopolymer as the repair materials have been gaining interest. This article investigated the bond strength and degradation of metakaolin-based geopolymer mortar subjected to rapid efflorescence exposure, acid attack, freeze-thaw cycles, wet-dry cycles, and heat-cool cycles. The slant shear strength tests evaluated the new-old mortar bond strength. FTIR, XRD, and TGA were conducted to monitor the deterioration of geopolymers. Visual observation and ICP-OES tests were performed to quantify the efflorescence risk. Results showed that acid exposure mainly reduces bond strength by degrading the geopolymer framework. In aggressive environments involving moisture and temperature changes, i.e., freeze-thaw, wet-dry and heat-cool cycles, geopolymers exhibit negligible deterioration. However, the shrinkage induced by water migration and the volume expansion caused by elevated temperatures significantly decrease (up to 90%) the bond strength of geopolymer repair mortar. The negative effect imposed by the efflorescence should not be neglected. A significant bond strength reduction (up to 20%) was observed for geopolymer repair mortar suffering from efflorescence. Samples with higher granulated blast furnace slag (GGBS) addition show lower strength loss, benefiting from their lower efflorescence extent. Stoichiometrically designing the geopolymer repair binder to avoid efflorescence is recommended.

Microshear bond strength of resin cement to glass-ceramics after intaglio surface staining

Statement of problemApplying stains to the intaglio surface of computer-aided design and computer-aided manufacturing (CAD-CAM) monolithic ceramic restorations has been proposed as an option to help mask darkened substrates. However, little is known about the effects of this procedure on the adhesion between the resin cement and the ceramic. PurposeThe purpose of this in vitro study was to evaluate the effect of intaglio surface staining on the microshear bond strength between 2 CAD-CAM ceramics and a resin cement. Material and methodsLithium disilicate (Gmax) and leucite-reinforced (Gpress) ceramic blocks were sectioned, crystalized when indicated, and polished. They received either none, 1, or 2 layers of ceramic stains and a glaze liquid mixture followed by a firing cycle. The surfaces of groups Gmax0, Gmax1, and Gmax2 were etched with 9% hydrofluoric acid etching (HF) for 20 seconds, and those of groups Gpress0 and Gpress1 were etched for 60 seconds. After rinsing and drying, a ceramic primer was applied and air-dried. Resin cement rods (n=24 per group) were built from a silicone mold. Specimens were stored in distilled water for 24 hours before microshear bond testing. Failure mode was observed under a digital microscope. Data were analyzed by using the Kruskal-Wallis and Mann-Whitney nonparametric tests (α=.05). ResultsIntaglio staining negatively affected the microshear bond strength for both ceramics. A significant difference was observed between Gmax1 (3.5 ±1.73 MPa) and Gmax2 (3.7 ±2.1 MPa) when compared with Gmax0 (14.2 ±4.4 MPa) and also between GPress0 (25.7 ±5.1 MPa) and Gpress1 (1.8 ±2.7 MPa). No difference was observed between 1 and 2 stain layers for Gmax. Most failures were adhesive for Gmax0, mixed for Gpress, and cohesive within the stain layer for experimental groups. ConclusionsIntaglio surface staining with a stain and glaze mixture caused a significant reduction in bond strength between resin cement and both ceramics tested.

An in-vitro investigation of the bond strength of experimental ion-releasing dental adhesives to caries-affected dentine after 1 year of water storage

ObjectiveThe aim of this study was to evaluate the bonding performance after 1 year storage of an experimental dental adhesive containing analogues of phosphoproteins and fluoride-doped bioglass (EXP), applied in self-etching (SE) or etch & rinse (ER) mode, to caries-affected dentine after selective caries removal. Materials and MethodsFifty human molars with dentine carious lesions were excavated selectively using CarisolvTM gel and then connected to simulated pulpal pressure system. Teeth were divided randomly into five groups based on the tested materials: EXP-SE, EXP-ER, a resin-modified glass-ionomer cement (RMGIC), a three-step adhesive system (OPT) and a universal adhesive applied in SE mode (UA-SE). The specimens were submitted to different analytical tests (μTBS, SEM fractographic analysis and dye-enhanced confocal microscopy) at baseline (T0) and after 1 year (T1). ResultsAt T0 there was no difference in bond strength between the tested materials (p>0.05). At T1, EXP-SE and EXP-ER were the only materials to show no significant reduction in bond strength (p<0.05). The SEM showed a clear presence of minerals deposited on the dentine surface after bonding in the EXP-SE and EXP-ER groups. The specimens restored with RMGIC showed no exposure of the dentine surface after failure. The OPT and UA-SE specimens showed clear signs of degradation at the interface. Confocal microscopy imaged mineral precipitation at the interface of the EXP groups. ConclusionConventional adhesives may have inadequate bonding performance with evident degradation at the dentine-bonded interface over time. Although the RMGIC may present a drop in bond strength after prolonged storage, the bonding interface may result less affected by degradation over time. Innovative ion-releasing adhesives may remineralise the caries-affected dentine and achieve a stable bond over time. Clinical significanceGIC-based materials may represent an appropriate dentine replacement material after selective chemo-mechanical caries removal rather than conventional adhesive systems.

In Vitro Performance of Different Universal Adhesive Systems on Several CAD/CAM Restorative Materials After Thermal Aging.

To evaluate the microshear bond strength (mSBS) of 10 universal adhesive systems applied on five different CAD/CAM restorative materials, immediately and after thermal aging. Five CAD/CAM materials were selected: 1) feldspathic glass ceramic (FeCe); 2) pre-polymerized reinforced resin composite (ReRC); 3) leucite-reinforced glass ceramic (LeGC); 4) lithium disilicate (LiDi); and 5) yttrium-stabilized zirconium dioxide (ZiDi). For each material, 15 blocks were cut into four rectangular sections (6 × 6 × 6 mm; n=60 per group) and processed as recommended by the respective manufacturer. For each indirect material, the following adhesive systems were applied according to the respective manufacturer's instructions: 1) AdheSE Universal [ADU]; 2) All-Bond Universal [ABU]; 3) Ambar Universal [AMB]; 4) Clearfil Universal Bond [CFU]; 5) Futurabond U [FBU]; 6) One Coat 7 Universal [OCU]; 7) Peak Universal Bond [PUB]; 8) Prime&Bond Elect [PBE]; 9) Scotchbond Universal Adhesive [SBU]; 10) Xeno Select [XEN, negative control]. After the application of the adhesive system, cylinder-shaped transparent matrices were filled with a dual-curing resin cement (NX3) and light cured. Specimens were tested in shear mode at 1.0 mm/min (mSBS), after 24 hours and 10,000 thermal cycles (TC). All data were submitted to statistical analysis (α=0.05). For FeCe, there was no significant decrease in mean mSBS for AMB, FBU, and SBU after TC when compared at 24 hours. For ReRC, AMB and SBU showed higher mean mSBS when compared to CFU and XEN, after 24 hours and TC. For LiDi, FBU and OCU showed higher mean mSBS when compared to CFU and XEN, after 24 hours and TC. For LeGC, AMB and PUB showed higher mean mSBS when compared to XEN, after 24 hours and TC. For ZiDi, OCU and SBU showed higher mean mSBS when compared to XEN, after 24 hours and TC. In addition, PBE and XEN showed the lowest mean mSBS after TC with higher percentage of bond strength reduction. The mean mSBS among the different universal adhesives varied widely for each CAD/CAM material used. In addition, most universal adhesives underwent a statistically significant bond strength reduction after TC.

Nanofiller Particles and Bonding Durability, Water Sorption, and Solubility of Universal Adhesives

The aim of this study was to evaluate the influence of nanofiller particles in simplified universal adhesive on the long-term microtensile bond strength and silver nitrate up-take, as well as water sorption and solubility. Commercial adhesives Ambar Universal (FGM) in nanofilled-containing version (filled) and same lot without fillers (unfilled) were donated and applied by means of etch-and-rinse strategy. Microtensile bond strength was surveyed after 24-hours or 1-year water storage. Silver nitrate uptake was assayed using scanning electron microscopy (SEM). Water sorption and solubility experiments were performed based on ISO 4049:2009. Statistical analysis was performed using two-way ANOVA and Tukey test (p<0.05). The bond strength of both the adhesives were statistically similar at 24 hours (p>0.05), but the filled group attained significant bond strength reduction after aging when compared to initial bond strength (p<0.001). Conversely, unfilled adhesive presented stable adhesion after 1-year storage (p=0.262). Silver nitrate uptake was similar for both adhesives, with little silver impregnation at the hybrid and adhesive layers. Water sorption was higher with filled adhesive compared to the unfilled one (p=0.01). Conversely, solubility was higher in unfilled in comparison to filled one (p=0.008). The presence of nanofillers in universal adhesive achieves higher water sorption and dentin bond degradation, which did not occur in the unfilled adhesive.

Reparo em resina composta usando adesivo universal melhora a estabilidade da união

Repair in resin-based composite is a procedure that has shown good results, when properly indicated. In cases of fracture or stainning, the total removal of the restoration can cause unnecessary wear on the dental element. This study evaluated the aging effect on the bond strength of a universal adhesive containing silane, and/or application of silane separately for composite repairs. Resin composite blocks were thermocycled and divided according to adhesion protocol (n=10): silane(Sil), conventional adhesive(CA), universal adhesive(UA), Sil+CA(SilCA), and Sil+UA(SilUA). Layers of resin composite were added and blocks were sectioned and divided into 2 subgroups: 24h and 4 months of water storage. Microtensile bond strength test was performed and data were statistically analyzed (a = 0.05). After 4months of aging SilCA and SilUA showed a significant bond strength reduction, while for UA the bonding remained stable.

Effects of radiation therapy on the dislocation resistance of root canal sealers applied to dentin and the sealer-dentin interface: a pilot study.

ObjectivesThis study evaluated and compared the effects of radiation therapy on the dislocation resistance of AH Plus and BioRoot RCS applied to dentin and the sealer-dentin interface.Materials and MethodsThirty single-rooted teeth were randomly assigned to 2 groups (n = 15 each): AH Plus (Dentsply DeTrey) and BioRoot RCS (Septodont). Each group was subdivided into control and experimental groups. The experimental group was subjected to a total radiation dose of 60 Gy. The root canals of all samples were cleaned, shaped, and obturated using the single-cone technique. Dentin slices (1 mm) were sectioned from each root third for the push-out test and scanning electron microscopy (SEM) was done to examine the sealer-dentin interface. The failure mode was determined using stereomicroscopy. Bond strength data were analyzed by the independent t-test, 1-way analysis of variance, and the Tukey post hoc test (α = 0.05).ResultsSignificantly lower bond strength was observed in irradiated teeth than non-irradiated teeth in the AH Plus group (p < 0.05). The BioRoot RCS group showed no significant reduction in bond strength after irradiation (p > 0.05) and showed a higher post-irradiation bond strength (209.92 ± 172.26 MPa) than the AH Plus group. SEM revealed slightly larger gap-containing regions in irradiated specimens from both groups.ConclusionsThe dislocation resistance of BioRoot RCS was not significantly changed by irradiation and was higher than that of AH Plus. BioRoot RCS may be the sealer of choice for root canal treatment in patients undergoing radiation therapy.

Weakening the bond strength of luting agents could be a goal in implant retained prosthetics

Aim of the study: The current study was conducted to provide a simple practical technique to relatively weaken the bond strength of E.max Press copings retained to zirconia implant abutment models. This technique should facilitate crown retrieval from onto implant abutments without affecting the integrity of the ceramic crowns, abutment or the implant’s integration, yet, the crown is still well retained during service.Materials and methods: Twenty four zirconia implant abutment models were specially fabricated for the current study, to which 24 e.max press copings were cemented. According to the cementation technique, the samples were divided into four groups, 6 samples each. In Gp A, copings were cemented with a temporary resin luting cement without any surface treatment to the abutment models or the intaglio surfaces of the copings. In Gp B, abutments’ surfaces as well as intaglio surfaces of the copings were treated according to manufacturers’ instructions before cementation with permanent resin luting cement. In Gp C, abutments’ surfaces were coated with a single coat of fresh whole saliva before cementing copings with the permanent resin luting cement. In Gp D, same as in Gp C with replacement of saliva with single coat of glycerin. All assemblies were then subjected to aging through thermocycling for 5000 cycles.All assemblies were then tested for retention of coping cemented to the zirconia implant abutment models and failure surfaces were then examined by stereomicroscope to detect the mode of failure.Results: All samples in Gp A failed before any mechanical testing. Gp C reviled insignificant bond strength results compared to Gps B and D. However, Gp D showed significant reduction in bond strength compared to Gp B.Conclusions: Glycerin coating of zirconia implant abutments before use of permanent resin luting cement would be a good technique to retain crown in place for longer time, yet still liable to easy retrieval.

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

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

Influence of povidone-iodine on micro-tensile bonding strength to dentin under simulated pulpal pressure

BackgroundPrevious studies had reported that bond strength deteriorate over time following the dentin surface pretreatment with chlorhexidine. Therefore, further investigations are needed to evaluate the effect of other materials such as povidone iodine.The purpose of this study was to investigate the effects of 10% povidone-iodine pretreatment on the resin-dentin micro-tensile bond strength of a single bond adhesive system in permanent teeth over time, and compare it with 2% chlorhexidine.MethodsFlat dentin surfaces were prepared in 63 extracted permanent teeth. Teeth were randomly assigned to a 10% povidone-iodine pretreatment, a 2% chlorhexidine pretreatment, or a control group. Composite resin blocks were built up over treated surfaces under pulp pressure simulation. The prepared specimens were assigned to three storage time, 24 h, 1 week, and 2 months. Samples were vertically sectioned to obtain specimens of 0.7 to 1.2 mm2 cross-sectional area.ResultsNo significant reduction of bond strength of povidone iodine group was found among the three storage times (p = 0.477). A significant reduction of bond strength for both chlorhexidine and control groups was found in the three storage times (p < 0.001).ConclusionPovidone iodine pretreatment of etched dentin was effective in reducing the loss of bond strength over time, while the chlorhexidine pretreatment and negative control showed significant deterioration in micro-tensile bond strength over time in permanent teeth.

Effects of Polyacrylic Acid Pre-Treatment on Bonded-Dentine Interfaces Created with a Modern Bioactive Resin-Modified Glass Ionomer Cement and Subjected to Cycling Mechanical Stress.

Objectives: Resin-modified glass ionomer cements (RMGIC) are considered excellent restorative materials with unique therapeutic and anti-cariogenic activity. However, concerns exist regarding the use of polyacrylic acid as a dentine conditioner as it may influence the bonding performance of RMGIC. The aim of this study was to evaluate the effect of different protocols for cycling mechanical stress on the bond durability and interfacial ultramorphology of a modern RMGIC applied to dentine pre-treated with/without polyacrylic acid conditioner (PAA). Methods: The RMGIC was applied onto human dentine specimens prepared with silicon-carbide (SiC) abrasive paper with or without the use of a PAA conditioner. The specimens were immersed in deionised water for 24 h then divided in 3 groups. The first group was cut into matchsticks (cross-sectional area of 0.9 mm2) and tested immediately for microtensile bond strength (MTBS). The second was first subjected to load cycling (250,000 cycles; 3 Hz; 70 N) and then cut into matchsticks and tested for MTBS. The third group was subjected to load cycling (250,000 cycles; 3 Hz; 70 N), cut into matchsticks, and then immersed for 8 months storage in artificial saliva (AS); these were finally tested for MTBS. The results were analysed statistically using two-way ANOVA and the Student–Newman–Keuls test (α = 0.05). Fractographic analysis was performed using FE-SEM, while further RMCGIC-bonded dentine specimens were aged as previously described and used for interfacial ultramorphology characterisation (dye nanoleakage) using confocal microscopy. Results: The RMGIC applied onto dentine that received no pre-treatment (10% PAA gel) showed no significant reduction in MTBS after load cycling followed by 8 months of storage in AS (p > 0.05). The RMGIC–dentine interface created in PAA-conditioned SiC-abraded dentine specimens showed no sign of degradation, but with porosities within the bonding interface both after load cycling and after 8 months of storage in AS. Conversely, the RMGIC–dentine interface of the specimens with no PAA pre-treatment showed no sign of porosity within the interface after any of the aging protocols, although some bonded-dentine interfaces presented cohesive cracks within the cement after prolonged AS storage. However, the specimens of this group showed no significant reduction in bond strength (p < 0.05) after 8 months of storage in AS or load cycling (p > 0.05). After prolonged AS storage, the bond strength value attained in RMGIC–dentine specimens created in PAA pre-treated dentine were significantly higher than those observed in the specimens created with no PAA pre-treatment in dentine. Conclusions: PAA conditioning of dentine prior to application of RMGIC induces no substantial effect on the bond strength after short-term storage, but its use may increase the risk of collagen degradation at the bonding interface after prolonged aging. Modern RMGIC applied without PAA dentine pre-treatment may have greater therapeutic synergy with saliva during cycle occlusal load, thereby enhancing the remineralisation and protection of the bonding interface.

Effect of Different Adhesive Strategies and Time on Microtensile Bond Strength of a CAD/CAM Composite to Dentin.

The aim of this study was to evaluate the effect of adhesive strategy and time on the microtensile bond strength of a computer-aided design/computer-aided manufacturing (CAD/CAM) composite to dentin. Sixty CAD/CAM composite blocks were bonded to human dentin with simplified bonding agents using etch-and-rinse and self-etching approaches and amine-based and amine-free resin cements, with and without the application of a dual-cure activator (DCA; n=10): SBP-ARC (Adper Single Bond Plus + RelyX ARC), SBP-RXU (Adper Single Bond Plus + RelyX Ultimate), SBP-DCA-RXU (Adper Single Bond Plus + DCA + RelyX Ultimate), SBU-ARC (Scotchbond Universal + RelyX ARC), SBU-RXU (Scotchbond Universal + RelyX Ultimate), and SBU-DCA-ARC (Scotchbond Universal + DCA + RelyX ARC). Each specimen was light cured for 40 seconds under load and stored in distilled water at 37°C for seven days. Stick-shaped specimens (1.0 mm2) were obtained. Half of the specimens underwent microtensile bond strength testing, and the other half were subjected to the same tests after six months of storage. Failure mode was determined using an optical microscope (40×). The data were analyzed by a two-way analysis of variance followed by the Games-Howell test and Student t-test (preset alpha of 0.05). After seven days, SBU-RXU presented the highest mean bond strength, statistically different from only SBU-ARC (p<0.05). Most of the groups exhibited a statistically significant reduction in bond strength after 6 months (p<0.05), except SBP-RXU and SBU-ARC (p>0.05). The adhesive strategy, with different associations between adhesive systems and resin cements, as well as the use of a DCA, affected the bond strength of both amine-free and amine-based resin cements to a CAD/CAM composite.

Improved estimate and accurate measurement of thermal stresses in FRP tendon

There is distinctive difference in the coefficient of thermal expansion (CTE) between fiber reinforced polymer (FRP) bar and surrounding mass, which may generate great transverse thermal pressure at their interface and cause significant reduction in bond strength of FRP tendon. However, the transverse thermal pressure predicted from previous analytical model has marked deviation from that obtained from experiment test. This paper presents an improved analytical model to exactly analyzing the transverse thermal pressure at the interface of FRP bar/surrounding mass and the three-dimensional thermal stresses of FRP bar. Then accurate measurement using fiber Bragg grating (FBG) sensor is conducted to obtain the transverse thermal pressure that agrees well with our theoretical result. Our work may be helpful in improving the thermal compatibility and bond performance of FRP tendon.

Influence of Protease Inhibitors on Bond Degradation of Self-Etch Adhesive Systems to Caries-Affected Dentin: An &amp;lt;i&amp;gt;in Vitro&amp;lt;/i&amp;gt; Study

Background: A decline in pH and dissolution of the inorganic content of the dental tissues are followed by exposure of the organic portion of the tooth, which, in dentin, is largely composed of collagen fibres. These unprotected fibres are then degraded by metalloproteinases and cysteine cathepsins, proteolytic enzymes present in dentin. We evaluated the influence of protease inhibitors on the bond strength of a self-etch adhesive system to caries-affected dentin. Eighty permanent third molars were selected for the study. Dentinal caries were induced artificially by the microbial method and the teeth were divided in four groups: G1—application of Clearfil SE Bond adhesive system (CL); G2—2% chlorhexidine (CLX) + CL; G3—sodium bicarbonate (BIC) + CL; G4—BI + CLX + CL. Bond strength was assessed immediately and at six months. During the six months, the specimens were stored in distilled water. Microtensile bond strength testing was performed. On immediate testing, there was no significant difference in bond strength across the control, BIC, and CLX groups. The combination of BIC + CLX, however, led to an immediate, significant reduction in bond strength. After six months, bond strength was reduced in all groups. The highest bond strength was obtained in the control group (P 0.05). Most fractures were adhesive, both immediately and at six months. We concluded that the cavity pretreatment with 2% CLX or 2% BIC did not have an immediate negative impact on bond strength of the Clearfil SE Bond system. After specimens were stored for six months in water, their bond strength of specimens was reduced in all groups. This reduction was the greatest in the groups exposed to the inhibitors.

Pretreatment with Sodium Fluoride Maintains Dentin Bond Strength of a Two-Step Self-Etch Adhesive after Thermal Stressing.

To evaluate the effect of sodium fluoride and chlorhexidine digluconate on the composite-dentin bond strength of a self-etch adhesive after thermocycling. Eighteen human third molars were prepared to expose a flat dentin surface and were divided into 3 groups (n = 6) according to the 3 cavity cleaning solutions: distilled water, 2% chlorhexidine digluconate (CHX), or 1.23% sodium fluoride (NaF). Solutions were rubbed onto dentin surfaces for 60 s, followed by bonding with Clearfil SE Bond, and a 5-mm-thick composite crown buildup. Bonded teeth were stored in distilled water for 24 h and then longitudinally sectioned to obtain bonded sticks. Half of the specimens were immediately tested in tension at 0.5 mm/min, while the remaining specimens were tested after 60,000 thermal cycles. Data were analyzed using two-way ANOVA and the Holm-Sidak method. There was no significant difference between the groups after 24 h (p > 0.05). Thermocycling resulted in significant bond strength reduction for distilled water and CHX (p < 0.05). When 24 h bond strengths were compared to the thermocycling group, NaF maintained its bond strength (p > 0.05), while significant reductions were observed for distilled water and CHX (p < 0.05). Pretreatment with NaF maintained the bond strength of Clearfil SE Bond to dentin after 60,000 thermal cycles, but pretreatment with CHX did not.