Impact of conditioning regimens and time on adhesion of a fiber post to root dentin using two resin cements

The aim of this study was to evaluate the influence of irrigation protocols on the bond strength of a glass fiber post bonded to dentin using two resin cements. In 200 root-filled teeth, post space was prepared and divided into five groups (n?=?40) based on the irrigation protocol: group 1 (3% sodium hypochlorite), group 2 (3% sodium hypochlorite – 17% Ethylene diamine tetraacetic acid), group 3 (a mixture of sodium hypochlorite and etidronic acid), group 4 (sodium hypochlorite – QMix), and group 5 (distilled water). Samples were subdivided into two subgroups (n?= 10) and fiber posts were cemented using subgroup A (Self-adhesive dual-cure resin cement; SEA) or B (dual-cure resin cement following an etch-and-rinse protocol, ER). Push-out bond strength was performed after 24 h and four months (n?= 10) and failure modes were categorized. Statistical analysis of data was carried out by appropriate analyses (p < 0.05). The irrigation protocol and the resin cement had a significant impact on push-out bond strength. Subgroup A group showed lower bond strength than B at both time periods when 3% NaOCl–17% EDTA and 1:1 mixture of 6% NaOCl + 18%EA protocols were used. Three percent NaOCl used in combination with 17% EDTA or QMix significantly decreased the push-out bond strength of ER at the end of four months (p < 0.05). In conclusion, dual-cure resin cements bonded with etch-and-rinse protocol showed highest bond strength when a mixture of NaOCl and etidronic acid was used as root canal irrigant. These values were differentially influenced by time.     

Influence of post-curing temperature on the structure,properties, and adhesion of vinyl ester adhesive

Vinyl ester (VE) resins are widely used as thermoset adhesives in structural joints and composites, but complete curing under environmental conditions is not produced. The existing literature dealing with the effect of post-curing on the structure, viscoelastic, mechanical, and adhesion properties of VE resin is scarce. Therefore, in this study, VE resin was subjected to different post-curing temperatures (50–140 °C) for one hour, and the changes in structure and properties were assessed. The degree of cross-linking of the VE resin depended on the post-curing temperature and cure started to be completed above 100 °C, a temperature close to the glass transition temperature (115 °C) of the completely cross-linked polymer. Furthermore, gel formation in VE resin was evidenced for post-curing temperature below 100 °C. In order to fully cross-link the VE resin, post-curing at 140 °C for one hour was necessary, and it was evidenced by an increase in the glass transition temperature and in the mechanical properties; an increase in adhesion to cold rolled steel was obtained although the shear strength was lower than in the joint produced with the non-post-cured VE resin.     

Shear bond strengths of six different porcelain laminate veneer materials cemented to enamel with two different MDP-containing resin cements

Purpose: To compare the shear bond strengths of six different porcelain laminate veneer (PLV) materials cemented to enamel with two different MDP-containing resin cements. Materials and methods: Totally 120 disc specimens were fabricated with In-Ceram alumina (ICA), Turkom-Cera^TM (TCR), IPS Empress (IPS), IPS Empress-II (IPS2), Finesse (FNS), and Ceramco-3 (CER) ceramic systems (n = 20). Sixty specimens were cemented with self-adhesive resin cement (Clearfil SA), and 60 specimens were cemented with self-etch resin cement (Panavia F2.0) to enamel. Thus, 120 PLV–enamel specimens were assigned to 12 experimental groups (ICA/Pv, ICA/Cf, TCR/Pv, TCR/Cf, IPS/Pv, IPS/Cf, IPS2/Pv, IPS2/Cf, CER/Pv, CER/Cf). Shear force was applied on PLV–enamel interfaces until failure. Obtained data were statistically analyzed with ANOVA and t-tests. Results: Obtained shear bond strength values (SBSV) ranged as follows, respectively; TCR/Cf (7.70 MPa), FNS/Cf (7.57 MPa), TCR/Pv (6.91 MPa), ICA/Pv (5.05 MPa), CER/Pv (4.75 MPa), IPS2/Cf (4.66 MPa), FNS/Pv (4.43 MPa), IPS2/Pv (3.97 MPa), CER/Cf (3.82 MPa), IPS/Pv (3.62 MPa), ICA/Cf (3.59 MPa), IPS/Cf (3.11 MPa). Highest SBSV were obtained in TCR groups (7.70 MPa for TCR/Cf and 6.91 MPa for TCR/Pv) and lowest SBSV were obtained in IPS groups (3.11 MPa for IPS/Cf and 3.62 MPa for IPS/Pv) in both resin cements. No significant bond strength difference was found between two resin cements. Conclusions: TCR groups showed highest SBSV; lowest SBSV were obtained with both IPS PLVs. The resin cement type did not significantly affect the bond strength value of a ceramic type, except for the Finesse system.     

Repair bond strength of resin composite with experimental primers – effect of formulation variables

The aim of this study was to prepare experimental resin-based primers with varied components (silane – S, polyacrylic acid – PA, or methacrylic acid – MA) and evaluate their repair bonding ability to resin composite. Primers were prepared containing methacrylate monomers, acidic monomer, ethanol, photoinitiators and 0, 10, or 20 wt% of S, PA, or MA. Degree of C=C conversion and pH were measured. Composite blocks (Opallis, FGM) were aged by 5000 thermal cycles and composite cylinders (repairs) were built up on their surfaces. The cylinders were tested under shear stress after 24 h. Failure modes were classified under magnification. Data were statistically analyzed at α = 0.05. Primers containing MA were the most acidic compositions, whereas S-containing primers were less acidic. Incorporation of 20 wt% of the varied components decreased C=C conversion. PA-based primers had higher C=C conversion than MA-based materials. Repair bond strength results were dependent on the component added and its concentration. MA-based primers presented higher bond strength than primers containing PA. Cohesive failures within composite were predominant for S-based primers, whereas mixed failures were more prevalent for PA-based primers. In conclusion, the overall best repair abilities were observed for primers containing 10 wt% of the components tested.     

Fabrication and mechanical analysis of mimosa tannin and commercial flax fibers biocomposites

Composites were prepared by impregnating commercial nonwoven and unidirectional flax fibers mats, with a mimosa tannin/hexamine resin without addition of NaOH as it was described in previous papers and with improved results. The influence of various parameters was observed: the curing cycle including temperature, time, pressure, the moisture content, and the number of fiber mats the composites were made of. A new two-step method was investigated: full drying of the pre-impregnated mats for storage first and then rehydratation just before pressing. The composites obtained gave good modulus of elasticity and tensile strength in traction as well as a good resistance to water swelling for composites prepared with 50% matrix resin/50% natural fibers. Best results appear to be obtained using a slow curing at low temperature (130?°C for 35?min) with moisture content of 20% on dry material.     

Synthesis and characterization of diphenylsilanediol modified epoxy resin and curing agent

A series of diphenylsilanediol modified epoxy resins and novel curing agents were synthesized. The modified epoxy resins were cured with regular curing agent diethylenetriamine (DETA); the curing agents were applied to cure unmodified diglycidyl ether of bisphenol A epoxy resin (DGEBA). The heat resistance, mechanical property, and toughness of all the curing products were investigated. The results showed that the application of modified resin and newly synthesized curing agents leads to curing products with lower thermal decomposition rate and only slightly decreased glass transition temperature (T_g), as well as improved tensile modulus and tensile strength. In particular, products cured with newly synthesized curing agents showed higher corresponding temperature to the maximum thermal decomposition rate, comparing with products of DGEBA cured by DETA. Scanning electron microscopy micro images proved that a ductile fracture happened on the cross sections of curing products obtained from modified epoxy resins and newly synthesized curing agents, indicating an effective toughening effect of silicon–oxygen bond.     

Synthesis and Characterizations of Melamine-Based Epoxy Resins

A new, easy and cost-effective synthetic procedure for the preparation of thermosetting melamine-based epoxy resins is reported. By this innovative synthetic method, different kinds of resins can be obtained just by mixing the reagents in the presence of a catalyst without solvent and with mild curing conditions. Two types of resins were synthesized using melamine and a glycidyl derivative (resins I) or by adding a silane derivative (resin II). The resins were characterized by means of chemical-physical and thermal techniques. Experimental results show that all the prepared resins have a good thermal stability, but differ for their mechanical properties: resin I exhibits remarkable stiffness with a storage modulus value up to 830 MPa at room temperature, while lower storage moduli were found for resin II, indicating that the presence of silane groups could enhance the flexibility of these materials. The resins show a pot life higher than 30 min, which makes these resins good candidates for practical applications. The functionalization with silane terminations can be exploited in the formulation of hybrid organic-inorganic composite materials.     

镁铝水滑石焙烧产物对甲基橙溶液的吸附性能

本文研究了Mg-Al-LDHs焙烧产物(LDO)对甲基橙的吸附性能并讨论了焙烧温度和吸附温度对反应的影响.结合XRD表征结果得到450℃焙烧产物在吸附甲基橙溶液后,恢复为LDHs层状结构;其对甲基橙溶液的吸附主要是层间吸附,即甲基橙可进入Mg-Al水滑石层间;此外,还对吸附动力学进行了讨论,结果表明:LDO对甲基橙的吸附符合准二级动力学模型.     

腰果酚改性甲阶酚醛树脂的合成及其泡沫性能研究

用腰果酚代替部分苯酚改性酚醛树脂,制备可发性甲阶酚醛树脂。并讨论了腰果酚替代量对改性酚醛树脂性能及其泡沫性能的影响,通过红外光谱仪、热重分析仪对树脂结构及热稳定性进行表征,运用万能电子试验机对甲阶酚醛树脂泡沫的力学性能进行了研究。结果表明:当腰果酚替代量为10%时,制得的树脂黏度为4650mPa·s,树脂中游离苯酚含量从6.72%降为5.45%,游离甲醛含量从1.17%降为0.68%,甲阶酚醛树脂泡沫压缩强度达到最大值0.20MPa,但树脂热稳定性及甲阶酚醛树脂泡沫阻燃性有所下降。     

Effect of ligand chain length on hydrophobic charge induction chromatography revealed by molecular dynamics simulations

Hydrophobic charge induction chromatography (HCIC) is a mixed-mode chromatography which is advantageous for high adsorption capacity and facile elution. The effect of the ligand chain length on protein behavior in HCIC was studied. A coarse-grain adsorbent pore model established in an earlier work was modified to construct adsorbents with different chain lengths, including one with shorter ligands (CL2) and one with longer ligands (CL4). The adsorption, desorption, and conformational transition of the proteins with CL2 and CL4 were examined using molecular dynamics simulations. The ligand chain length has a significant effect on both the probability and the irreversibility of the adsorption/desorption. Longer ligands reduced the energy barrier of adsorption, leading to stronger and more irreversible adsorption, as well as a little more unfolding of the protein. The simulation results elucidated the effect of the ligand chain length, which is beneficial for the rational design of adsorbents and parameter optimization for high-performance HCIC.