Months Of Immersion In Water Research Articles

Glass flakes for enhancing mechanical properties of glass/epoxy composites

The purpose of this study is to improve composite mechanical properties by reducing the degradation induced by seawater in glass fibre/epoxy composites. To do this, glass flakes (50 µm in size) were placed on the surfaces of the glass fibre/epoxy composite material using various ratios (5%–15%). Glass flakes were introduced into composite materials that were exposed to seawater for a period ranging from 0 to 12 months, and changes in bending, tensile, impact, compression, and compression after impact strengths were assessed. Flexural tests revealed that the gel coat and glass flakes increased their loads by up to 24% and 23% after 6 and 12 months of water immersion, respectively. Tensile tests indicated that lower tensile strength loss occurred as the glass flake ratio rose. As the immersion duration increased, the effect of glass flakes became more evident in terms of tensile strength. Composites containing glass flakes showed greater impact strength load values in both 20 and 30 J impacts compared to the control sample. The use of glass flakes improved the residual strength values because it prevented water penetration. The control sample retained up to 50% of its compressive strength, while the 15% glass-flake reinforcement promoted retention to 56%.

Compressive Strength and Porosity Evaluation of Innovative Bidirectional Spiral Winding Fiber Reinforced Composites.

The aim of this in vitro study was to investigate the compressive strength and the bulk porosity of a bidirectional (bFRC) and an experimental bidirectional spiral winding reinforced fiber composite (bswFRC). Cylindrical-shape specimens were prepared for each material group and processed for the evaluation of compressive strength after different storage conditions (dry, 1 and 3 months) in distilled water at 37 °C. The specimens were also assessed for the degree of bulk porosity through X-ray tomography. A scanning electron microscope (SEM) was used to determine the fracture mode after a compressive strength test. Data were statistically analyzed using Two-Way Analysis of Variance (ANOVA). A significantly lower compressive strength was obtained in dry conditions, and after 1 month of water immersion, with the specimens created with bFRC compared to those made with bswFRC (p < 0.05). No significant difference (p > 0.05) was found between the two groups after 3 months of water immersion. However, the presence of water jeopardized significantly the compressive strength of bswFRC after water storage. The type of fracture was clearly different between the two groups; bswFRC showed a brutal fracture, whilst bFRC demonstrated a shear fracture. The bswFRC demonstrated higher pore volume density than bFRC. In conclusion, bswFRC is characterized by greater compressive strength compared to bFRC in dry conditions, but water-aging can significantly decrease the mechanical properties of such an innovative FRC. Therefore, both the novel bidirectional spiral winding reinforced fiber composites (bswFRC) and the bidirectional fiber reinforced composites (bFRC) might represent suitable materials for the production of post-and-core systems via CAD/CAM technology. These findings suggest that both FRC materials have the potential to strengthen the endodontically treated teeth.

Preparation of basalt fibers grafted with amine terminated urea-based oligomer and its application in reinforcing conventional glass ionomer cement

The purpose of this study was to improve interfacial interaction between basalt fibers (BF) and glass ionomer cement (GIC) matrix with grafting amine terminated urea-based oligomer (DIEDA) onto the surface of BF. The DIEDA-BF was prepared by the reaction between 3-aminopropyl- triethoxysilane (APS) modified BF with Isophorone diisocyanate (IPDI) and followed with ethylenediamine (EDA). The reaction was repeated to obtain three generations of DIEDA-BF which were marked as DIEDA-BF-G1, DIEDA-BF-G2, and DIEDA-BF-G3, respectively. X-ray photoelectron spectroscopy (XPS) was used to characterize DIEDA-BF. 3D morphology analysis was taken to investigate the variation of BF after being treated with EDA. Three-point bending-test, compressive strength (CS) test, and fracture toughness (FT) were used to evaluate the reinforcement effect of DIEDA-BF on commercial GIC (GC Fuji IX). Water sorption (WS) and solubility (SL) were measured according to the mass variation at fixed time intervals. The changes of flexural strength (FS) and modulus (FM) after water immersion were used to evaluate the water-aging resistance of DIEDA-BF reinforced GIC. Pure GIC and APS reinforced GIC (APS-GIC) were used as double control groups. The XPS analysis indicated that DIEDA was successfully grafted onto the surface of BF. 3D morphology analysis revealed that BF could be corroded in EDA, thus DIEDA-BF-G3 had lower N content on the surface than DIEDA-BF-G2. The results of mechanical tests showed that DIEDA-BF-G1 and DIEDA-BF-G2 had the best reinforcement effect. The DIEDA-BF-G1 reinforcement GIC (DIEDA-BF-G1-GIC) was chosen for WS, SL, and water aging resistance test further. The results showed that all fiber reinforced GICs had higher WS than pure GIC, and the relationship in SL between fiber reinforced GICs and pure GIC varied with immersion time. The FS of DIEDA-BF-G1-GIC decreased after one week of water immersion, and had no variation after prolonging the immersion time. After three months of water immersion, DIEDA-BF-G1-GIC still had much higher FS than pure GIC and APS-BF-GIC. DIEDA could improve the interfacial interaction between BF and GIC matrix. After long term of water immersion, DIEDA-BF reinforced GIC still had FS higher than 50 MPa, which even met the ISO requirement in FS for dental resin composite. Therefore, GIC/DIEDA modified BF composite had potential to be used in stress bearing areas in dentistry.

Assessment of interfacial fracture energy between concrete and CFRP under water immersion conditions

The interfacial fracture energy is a critical parameter for the bond between carbon fiber reinforced polymer (CFRP) plate and concrete, and is significantly influenced by the ingress of moisture. Exploiting the single-lap shear test, this paper studies the effect of water immersion on the interfacial fracture energy experimentally and analytically by taking into account the impacts of immersion time, concrete compressive strength, and concrete surface roughness. The results indicates that: 1) water immersion transforms the failure mode from concrete cohesive failure to debonding of the adhesive layer from the concrete substrate. 2) the interfacial fracture energy considerably drops in the first six months of immersion in water and then levels off; 3) the reduction of the interfacial fracture energy depends on the compressive strength of the concrete substrates. A higher compressive strength of concrete leads to a more significant reduction; 4) the impact of water immersion on the mechanical interlocking of concrete with epoxy is negligible. Finally, based on the reduction mechanism of the breakage of the van der Waals interactions and hydrogen bonding between SiO2 groups of concrete and hydroxyl groups (–OH) of epoxy with ingress of water, an analytical model is proposed for predicting the interfacial fracture energy.

Investigation of Biocidal Effect of Microfiltration Membranes Impregnated with Silver Nanoparticles by Sputtering Technique.

Silver nanoparticles were loaded in microfiltration membranes by sputtering technique for the development of biocidal properties and biofouling resistance. This technology allows good adhesion between silver nanoparticles and the membranes, and fast deposition rate. The microfiltration membranes (15 wt.% polyethersulfone and 7.5 wt.% polyvinylpyrrolidone in N,N-dimethylacetamide) were prepared by phase inversion method, and silver nanoparticles were deposited on their surface by the physical technique of vapor deposition in a sputtering chamber. The membranes were characterized by Field Emission Scanning Electron Microscopy, and the presence of silver was investigated by Energy-Dispersive Spectroscopy and X-ray Diffraction. Experiments of silver leaching were carried out through immersion and filtration tests. After 10 months of immersion in water, the membranes still presented ~90% of the initial silver, which confirms the efficiency of the sputtering technique. Moreover, convective experiments indicated that 98.8% of silver remained in the membrane after 24 h of operation. Biocidal analyses (disc diffusion method and biofouling resistance) were performed against Pseudomonas aeruginosa and confirmed the antibacterial activity of these membranes with 0.6 and 0.7 log reduction of viable planktonic and sessile cells, respectively. These results indicate the great potential of these new membranes to reduce biofouling effects.

Self-healing adhesive with antibacterial activity in water-aging for 12 months

ObjectiveSecondary caries and micro-cracks are the main limiting factors for dentin bond durability. The objectives of this study were to develop a self-healing adhesive containing dimethylaminohexadecyl methacrylate (DMAHDM) and nanoparticles of amorphous calcium phosphate (NACP), and investigate the effects of water-aging for 12 months on self-healing, dentin bonding, and antibacterial properties for the first time. MethodsMicrocapsules were synthesized with poly (urea-formaldehyde) (PUF) shells containing triethylene glycol dimethacrylate (TEGDMA) and N,N-dihydroxyethyl-p-toluidine (DHEPT). The adhesive contained 7.5% microcapsules, 10% DMAHDM, and 20% NACP (all mass). Specimens were water-aged at 37 °C for 1 day to 12 months. Dentin bond strength was measured using extracted human teeth. A single-edge-V-notched-beam (SEVNB) method was used to measure fracture toughness KIC and self-healing efficiency. A dental plaque microcosm biofilm model was used with human saliva as inoculum. ResultsThe microcapsules + DMAHDM + NACP group showed no decline in dentin bond strength after water-aging for 12 months, which was significantly higher than that of other groups without DMAHDM (p < 0.05). A self-healing efficiency of 67% recovery in KIC was obtained even after 12 months of water immersion, indicating that the self-healing ability was not lost in water-aging (p > 0.1). The bacteria-killing ability of this adhesive did not decline from 1 day to 12 months (p > 0.1), with biofilm CFU reduction by 3–4 orders of magnitude after the resin was water-aged for 12 months, compared to control resin. SignificanceThis novel adhesive with triple merits of self-healing, antibacterial and remineralization functions showed an excellent long-term durability in water-aging for 12 months. This multifunctional adhesive has the potential for dental applications to heal cracks, inhibit bacteria, provide ions for remineralization, and increase the restoration longevity.

Microtensile bond strength, 4-point bending and nanoleakage of resin-dentin interfaces: Effects of two matrix metalloproteinase inhibitors.

Chronic degradation of hybrid layer collagen by matrix metalloproteinases (MMPs) jeopardizes resin-dentin interfacial integrity and limits the durability of dental restorations. The 4-point bending strength (BS) is a valid but uncommon method of testing the mechanical behavior of resin-dentin interfaces. The present study aims to analyze the influence of two matrix metalloproteinase inhibitors on microtensile bond strength (µTBS), BS and nanoleakage. A total of 48M were divided into three groups according to bonding procedure. Teeth were horizontally sectioned to produce a flat dentin surface. In the control group, etch-and-rinse Prime&Bond One (Dentsply) bonding was used; in the self-etch group, methacryloyloxydodecylpyridinium bromide (MDPB)-containing Clearfil SE Protect (Kuraray) was used; and in the benzalkonium chloride (BAC)-etch group, BAC-etchant (Bisco) was used. A Ceram.X-One (Dentsply) composite was built as three successive layers and was light-cured. Samples were sectioned to produce microrods that were randomly divided into two groups for analysis at baseline and after 6 months of water immersion (n = 32), plus one slab for nanoleakage analysis (n = 8) via scanning electron microscopy (SEM) and digital image analysis (Fiji). Data were analyzed using the Weibull distribution and a mixed-model ANOVA with a post hoc Tukey test. All groups showed deterioration of the initial bonds. The self-etch group had a worse baseline µTBS than the control but had the best BS after aging. BAC-etch did not improve bond stability of etch-and-rinse adhesive. The µTBS and BS test results after aging were moderately correlated. Mixed fractures prevailed with regard to µTBS, whereas adhesive fractures dominated with regard to BS. Nanoleakage was not eliminated in any group and increased after aging. MDPB self-etch resisted bond degradation better than etch-and-rinse adhesives, even after BAC-etching. Integrating BS in studies of µTBS and nanoleakage might provide more clinically relevant outcomes for predicting the performance of dental adhesives.

An in vitro investigation of pre‐treatment effects before fissure sealing

Fissure sealants prevent occlusal caries in permanent molars. Enamel preparation methods are used before fissure sealing. To investigate effects of bioglass air-abrasion pre-treatment with and without an adhesive, on fissure enamel of permanent teeth, with respect to etchability, microleakage and microtensile bond strength. Half of the occlusal surfaces of 50 extracted premolars underwent bioglass air-abrasion. Dye was applied to the entire occlusal surface. Photographs were taken to score etched surface by dye uptake. Adhesive was applied to 25 of the bioglass-treated areas and all teeth were fissure sealed, sectioned, and evaluated using confocal microscopy. Buccal and lingual surfaces of a further eight premolars were acid-etched and randomly received: air-abrasion, adhesive, both, or none before sealant application for microtensile bond strength measurement in half of the samples immediately and half following 6 months of water immersion. Linear mixed models and multinomial logistic regression were used (P = 0.05). Bioglass air-abrasion significantly improved enamel etchability and reduced microleakage. The addition of an adhesive made no difference to either microleakage or microtensile bond strength. The combination of bioglass abrasion and adhesive led to more cohesive, rather than adhesive, failure. Bioglass air-abrasion improved enamel etchability and reduced microleakage irrespective of the adhesive use but neither pre-treatment affected the microtensile bond strength.

Influence of storage time in water on the integrity of adhesive interface in resin composite restorations

When immersed in oral fluids, water absorption by the restorative resin composite material can occur, which is identified by some researchers as one of the causes of loss of aesthetic features and reduction of mechanical properties over time. On the other hand, some authors have suggested that the fluids sorption may contribute to the reduction of shrinkage stress generated at the adhesive interface and reduce the width of gaps. The aim of this study was verifying if the storage time in water of restorations carried out with different filling techniques could influence on the integrity of tooth-restoration adhesive interface. Eighteen cavities were built in bovine incisors and they were divided into 3 groups after the adhesive procedure: group B (“Bulk”) received one single increment of light-cured resin composite; group I (“Increments”) received the same composite in three oblique increments; and the group B+S (“Bulk + Self-cured resin composite”). The last one firstly received a flowable, self-cured resin composite, and then, it was inserted one single increment of light-cured composite. After 48 h of storage, the restorations were sliced, the first measurement was accomplished, and the analysis of the adhesive interface was made each 30 days over nine months of immersion in water. The results were subjected to a split-plot analysis of variance and Tukey’s test. It was not verified significant influence of immersion time in water on the gap width, or regular increase or decrease of percentage interface free of gaps over time for any of three filling techniques. Some hypothesis could explain this occurrence, such as gain of mass without significant increase in the volume; the expansion of restoration in directions that did not contributed to the gaps closure; and the simultaneous occurrence of hygroscopic expansion and hydrolytic degradation of the resin processes.

Mechanical and physical properties of silorane and methacrylate-based composites

ObjectivesThis study measured the degree of conversion (DC), sorption, solubility and microhardness of methacrylate (Filtek Z250 and Filtek Z350XT) and silorane-based composites (Filtek P90). MethodsDC was measured using near infrared spectroscopy immediately and 24h after the photoactivation. Sorption and solubility measurements were performed after 24h, 4 weeks and 12 weeks of storage in water. Knoop microhardness was measured after 24h and after thermal cycling. The data were statistically analyzed using ANOVA followed by Tukey's, Tamhane or paired t-tests (α=0.05). ResultsThe DC for P90 (37.22±1.46) was significantly lower than the Z250 (71.44±1.66) and Z350 (71.76±2.84). Water sorption was highest in the Z250 and lowest in the P90. All the tested composites exhibited similar values after 24h of immersion, and no significant differences were observed. No significant differences were observed between the solubilities of the P90 composite (12 weeks) and the Z250 or Z350 composites (4 weeks). KHN values were less elevated for the P90 composite and similar for the Z250 and Z350 composites. An effect of thermal cycling on KHN values was observed for all the composites (p<0.001). ConclusionsSilorane produced the lowest DC and KHN values and exhibited lower water sorption and solubility compared to methacrylate-based composites. These differences suggest that silorane composites exhibit better hydrolytic stability after 3 months of water immersion compared to conventional methacrylate-based composites. Clinical significanceSilorane had higher hydrolytic stability after 3 months of water immersion than the methacrylate-based resins, despite the lower values of DC and KHN recorded.

The effect of load cycling on nanoleakage of deproteinized resin/dentin interfaces as a function of time

Objectives To evaluate the effects of cyclic loading on nanoleakage as a function of time at resin–dentin interfaces with and without removal of collagen. Methods Bovine flat mid-coronal dentin received one of the following surface treatments: (1) acid-etch or (2) acid etched + 5% NaOCl for 2 m. The teeth were then bonded with Single Bond (3M ESPE), Scotchbond Multi-Purpose (3M ESPE), One-Step Plus (Bisco) or All-Bond 2 (Bisco) adhesive systems and restored with Z250 composite. Half of the bonded teeth were randomly assigned to receive 200,000 cycles of loading at 50 N. Teeth were sectioned into 1 mm × 1 mm thick slices and stored in distilled water for 24 h and 6 months. After water storage, beams were prepared for nanoleakage evaluation and observed under the SEM. Data were statistically analyzed using three-way ANOVA and Fisher's PLSD test ( p < 0.05). Results Use of NaOCl did not affect nanoleakage at the interface of all adhesive systems ( p > 0.05) when compared to their respective controls. After 6 months of immersion in water, except for One Step Plus, collagen-depleted groups and control groups presented similar leakage values. After cyclic loading, the deproteinized group revealed a higher degree of silver nitrate deposits when compared to the control group ( p < 0.05). All four adhesive systems presented a high degree of silver nitrate deposits after 6 months of water storage. Significance The hybrid layer is important as a stress-absorbing layer and it may not represent the weak link for initiation of the nanoleakage phenomenon.

Synthesis, characterization and biocidal properties of epoxy resins containing quaternary ammonium salts

Quaternary ammonium salts (QAS) were covalently-bound to epoxy resins of different DP in two steps: addition of a N,N-dialkylaminoethanethiol followed by the quaternization of the tertiary amine by an alkylbromide (C8H17Br to C14H29Br). The products were characterized by 1H NMR spectroscopy. The QAS-containing oligomers were used as polyols to prepare polyurethane (PU) films by reaction with a triisocyanate. The films show a good bactericidal activity against Escherichia coli, which is preserved after 6 months of immersion in water.

Characterization and inhibitory effect of antibacterial dental resin composites incorporating silver-supported materials.

Resin composites with antibacterial activity may be useful for preventing the secondary caries frequently seen around restorations. The purposes of this study were to investigate antibacterial light-activated dental resin composites incorporating each of two silver-supported antibacterial materials and evaluate their long-lasting inhibitory effect against Streptococcus mutans. Two types of silver-supported antibacterial materials, Novaron (N) and Amenitop (AM) were used. These antibacterial materials were incorporated into TEGDMA-UDMA-based light-activated resin composites, and the antibacterial activities and mechanical properties of these composites, and also the release of silver ions, were examined. Two silver-supported antibacterial materials inhibited the growth of the major oral pathogen S. mutans. The minimum inhibitory concentration in suspensions of N and AM against S. mutans was 40 microg/mL and 30 microg/mL, respectively. Composites incorporating 5 wt % (N-5) or more of Novaron and 7 wt % (AM-7) or more of Amenitop inhibited the growth of S. mutans after immersion in water for 6 months. There was no or extremely little release of silver ions from the N-5 and AM-7 composites after 1 day or after 6 months of immersion in water. No significant difference in either compressive or flexural strength was observed between the control and the N-5 composites after 1 day or after 6 months of storage in water. However, for the AM-5 composite, there was a significant difference in both strength parameters between the two immersion periods. These results indicate that a light-activated dental resin composite incorporating silver-supported antibacterial material such as Novaron may be useful clinically because of its long-lasting inhibitory effect against S. mutans and its favorable mechanical properties.

Inhibitory Effect of Antibacterial Resin Composite against Streptococcus mutans

Dental resin composites with antibacterial activity may be useful for preventing the secondary caries frequently seen around restorations. Three types of silver–supported antibacterial materials (Novaron, Amenitop and AIS) inhibited the growth of the major oral pathogen Streptococcus mutans. Minimum inhibitory amounts in suspensions of Novaron, Amenitop and AIS against S. mutans were 40, 30 and 400 μg/ml, respectively. These antibacterial materials were incorporated into TEGDMA–UDMA–based light–activated resin composite, and the antibacterial activities of these composites were examined. Composites incorporating 5 wt% (N–5) or more of Novaron and 7 wt% (AM–7) or more of Amenitop inhibited the growth of S. mutans, whereas composites incorporating up to 10 wt% of AIS did not. No significant difference in either compressive or flexural strength was observed between the control and N–5 composites after 1 day and 6 months of storage in water. However, for AM–5 composite, there was a significant difference in either strength parameter between the two immersion periods. There was no or extremely little release of silver ions from the N–5 and AM–5 composites after 1 day or 6 months of immersion in water. These results indicated that a light–activated resin composite incorporating silver–supported antibacterial material such as Novaron may be clinically useful due to its inhibitory effect against S. mutans and favorable mechanical properties.

The durability of adhesion to phosphoric acid etched, wet dentin substrates

Objective. The purpose of this study was to investigate the influence of remaining non-resin-impregnated, phosphoric acid demineralized dentin upon the long-term durability of specimens that were wet-bonded to bovine dentin substrates. Methods. Prepared bovine dentin samples were etched with 65% phosphoric acid then rinsed with water and kept wet during application of 5 wt% 4-methacryloyloxyethyl trimellitate anhydride (4-META) in acetone primer. This was followed by application of a photocured dentin-bonding agent consisting of 4-methacryloyloxyethyl trimellitate anhydride/triethyleneglycol dimethacrylate - camphorquinone/ N-phenylglycine (4-META/TEGDMA-CQ/NPG). The tensile bond strength (TBS) of bonded specimens was determined after immersion in 37°C water for various time intervals. Generated data were analyzed for statistical significance by one-way ANOVA and Duncan's New Multiple Range Test ( p<0.05). The dentin side of the tensile-load-fractured specimens was examined under optical and scanning electron microscopes (SEM). Results. TBS decreased from 6.6±1.0 MPa after 1-day water immersion to 3.4±1.7 MPa after 1 month of water immersion. After 6 months of water immersion, TBS was found to be 3.9±0.9 MPa and this decreased to 2.0±1.0 MPa for specimens immersed in water for 1 year, a statistically significant difference ( p<0.05). Optical microscopic and SEM observations disclosed failure patterns within demineralized, non-resin-impregnated dentin that increased with the period of water immersion. Significance. The bond durability to wet dentin was poor when demineralized dentin was not resin-impregnated, resulting in exposure of collagen fibrils which hydrolyzed during long periods of water immersion.

Influence of binder type on anodic dissolution of steel embedded in cement pastes

Influence of binder type on anodic dissolution of steel embedded in cement pastes with and without chloride is investigated by examination of anodic polarization curves. The results indicate that the formation of passive layer on steel embedded in cement paste is dependent on the type of binder used. In situation of chloride ion present in the mixing water, passive range is still observed at a concentration of 0.08 M NaCl. In the case of penetrating chloride, passive range of steel is either severely limited or not observed after 6 months of immersion in water with 0.02 M NaCl.

New Composite Insultation

New composite materials such as laminated tapes were applied to high voltage cables. Plastic films laminated with kraft papers were developed for the high voltage oil-filled cables to improve the dielectric properties. The 500 kV oil-filled cables insulated with these laminated papers were also developed and tested with good results. Lead foil, laminated with plastic film, was developed for the water-impervious layer of XLPE cable to improve its reliability. It was confirmed that bow-tie trees were observed in the conventional XLPE cable after six months of water-immersion, but the water impervious XLPE cable retained its original performance.