Bonding ability of self-adhesive resin-cements after dentin biomodification with hyaluronic acid

Purpose: The present study evaluated the influence of the hyaluronic acid (HA) on the bonding ability of self-adhesive resin cements to dentin regarding the bond strength. Eighty bovine incisors were ground flat to obtain a 2-mm thick slices which received conical preparations. The specimens were randomly distributed into 4 groups (n = 15) according to the dentin pretreatment (1 – control: untreated dentin; 2 – application of HA) and the evaluation time (1 – control: immediate evaluation; 2 – hydrolytic degradation: 6 months of storage in water at 37 °C). Preparations received the application of a self-adhesive resin cement (RelyX U200 or MaxCem Elite). Push-out bond strength test was conducted (0.5 mm/min). The bond strength data was submitted to two-way ANOVA/Tukey’s test (α = 0.05). For U200, no significance was observed when comparing the immediate (24 h) and 6 months means for the control groups (unexposed specimens). Previous application of HA to dentin significantly reduced the bond strength of U200 to dentin in both evaluation times (p < 0.05). HA had no significant influence on the push-out bond strength means for the cement MAX in both evaluation times (p > 0.05). The type 1 failure mode (adhesive mode) occurred in 100% of the specimens, irrespective of the dentin treatment or evaluation times. Pretreatment of dentin with HA produces a material-dependent influence on the push-out bond strength. The bonding ability of RelyX U200 is negatively influenced by the pretreatment of dentin with HA, whereas the biomodification of dentin with this bioactive agent causes no impact for the cement MaxCem Elite.     

Long-term bond strength of fiber posts cement to dentin with self-adhesive or conventional resin cements

The aim of this study was to evaluate the immediate and the long-term push-out bond strength of glass fiber posts (GFP) cemented with conventional or self-adhesive dual-curing resin cements, at different root depths. Prior to cementation, the GFP (Reforpost #3, Angelus) were etched with 37% phosphoric acid for 30 s followed by silane for 1 min. Thirty canine roots were divided into two groups (n = 15) according to resin cement type: ARC – dual resin cement (RelyX ARC/3M ESPE) combined with an three-step etch-and-rinse adhesive (Adper Scotch Bond Multi-Purpose Plus 3M/ESPE) or U200 – self-adhesive resin cement (RelyX U200/3M ESPE). The manufacturer’s instructions were followed. After 48 h, the roots were cross-sectioned at three different depths, resulting in serial slices corresponding to the cervical, middle, and apical root thirds. Slices were randomly divided into two groups, according to the period of water storage prior to push-out bond strength analysis: 48 h or 180 days. The data (MPa) were analyzed using three-way ANOVA for randomized blocks (p < 0.05), which showed no significant interaction between the three factors (p = 0.716). The main study factors were also proven not significant (cement: p = 0.711; time: 0.288; root third: p = 0.646). In conclusion, root depth, cement type (self-adhesive or conventional), and storage in water for 180 days did not influence the bond strength of GFP to intracanal dentin.     

Effect of cyclic loading and resin cement type used for luting fiber posts on bond strength at different root levels of crown-restored human teeth

Objective: This study aimed to evaluate the bond strength (BS) of glass fiber posts (GFP) at different root levels when luted with conventional or self-adhesive cements in crown-restored human premolars subjected, or not, to cyclic mechanical loading.

Materials and Methods: Sixty lower premolar roots were endodontically treated and prepared for a GFP system. Half of the roots (n = 30) had their posts cemented with a self-adhesive resin cement, while the remaining roots followed a three-step conditioning method: acid etch, bonding agent, and a conventional resin cement. Metal crowns were luted onto the post-core preparations and the specimens were embedded to simulate the periodontium. Half of the specimens from each group (n = 15) were submitted to cyclic loading simulations (130 N; 2.0 Hz) and then sections were obtained from each root for the pushout BS test.

Results: Independently of the cyclic loading and the root level tested, the conventional resin cement provided significantly higher values of BS (p = 0.002). For either cement or either root level, cyclic loading caused a significant decrease in BS values (p = 0.023). The Tukey test indicated that, regardless of the resin cement used or the cyclic loading, BS was highest at the middle and cervical thirds of the root (p = 0.026), and their values did not differ between themselves.

Conclusions: When used for luting GFP, self-adhesive resin cement resulted in lower pushout BS than the conventional counterpart, with cyclic loading causing a decrease in BS of the GFP to dentin for both resin cements.     

Phase diagram prediction for a blend of Poly(2,6-dimethyl-1,4-phenylene ether) (PPE)/epoxy resin during reaction induced phase separation

The phase behavior of a Poly(2,6-dimethyl-1,4-phenylene ether) (PPE)/diglycidyl ether of bisphenol A type epoxy (DGEBA)/diethyltoluenediamine (DETDA) blend during reaction induced phase separation is predicted using Flory-Huggins theory. DGEBA and DETDA are treated as a single pseudo-component in order to reflect the crosslinking polymerisation that occurs between them, and both the PPE and the DGEBA/DETDA pseudo-component are treated as polydisperse. The Flory-Huggins χ parameter was determined by measuring the extent of reaction at the on-set of phase separation for different compositions and temperatures and comparing the results with theory. The χ parameter is then used to determine the coexistence curves as a function of conversion of the DGEBA/DETDA pseudo-component, from which the extent of reaction at which vitrification occurs is predicted. The model is shown to be in good agreement with experimental results.     

Cure Kinetics and Thermal Property of Bisphenol-S Epoxy Resin and Phthalic Anhydride

Abstract

The cure kinetics of bisphenol-S epoxy resin (BPSER) and curing agent phthalic anhydride, with N,N-dimethyl phenzylamine as an accelerator, were studied by means of differential scanning calorimetry (DSC). Analysis of DSC data indicated that an autocatalytic behavior showed in the first stages of the cure. The autocatalytic behavior was well described by the model proposed by Kamal including two rate constants, k1 and k2, and two reaction orders, m and n. The overall reaction order, m + n, is in the range 2～3. The activation energies for k1 and k2 were 111.69 and 80.47 KJ/mol, respectively. Diffusion control was incorporated to describe the cure in the latter stages. The glass transition temperatures (T_gS) of the BPSER/anhydride samples isothermally cured partially were determined by means of torsional braid analysis (TBA). and the results showed that the reaction rate increased with increasing T_g in terms of the rate constant, but decreased with increasing conversion. The T_g of completely cured BPSER/anhydride system is about 40 K higher than that of BPAER. The thermal degradation kinetics of this system was investigated by thermogravimetric analysis (TGA). It illustrated that the thermal degradation of the BPSER/phthalic anhydride has n-order reaction kinetics.     

Nonevaporable water from neat OPC and replacement materials in composite cements hydrated at different temperatures

Pastes of two neat OPC and three blended cements using GGBFS (60%), PFA (30%) and a volcanic ash (23%), were cured for up to 1 year at five temperatures. The degree of hydration of the OPCs was estimated by quantitative X-ray diffraction analysis and by measurements of nonevaporable water by thermogravimetry. A correlation between the results from these techniques is presented for the neat OPCSs. The correlation was used to estimate the contribution to the nonevaporable water from the cement replacement material fraction for the blended cements. According to the estimated data, the slag displayed a hydraulic nature retaining significant amounts of water in its hydrates, the slag nonevaporable water values as function of time varied with temperature and the patterns were similar to those of degree of hydration of the neat cement. The data estimated for the two pozzolanic materials indicated that their hydrates retained small amounts of water in spite of the CH consumption.     

Atomistic molecular simulations of structure and dynamics of crosslinked epoxy resin

Many excellent thermal and mechanical performances of cured epoxy resin products can be related to their specific network structure. In this work, a typical crosslinked epoxy resin was investigated using detailed molecular dynamics (MD) simulations, in a wide temperature range from 250 K to 600 K. A general constant-NPT MD procedure widely used for linear polymers failed to identify the glass transition temperature (T_g) of this crosslinked polymer. This can be attributed to the bigger difference in the time scales and cooling rates between the experiments and simulations, and specially to the highly crosslinked infinite network feature. However, by adopting experimental densities appropriate for the corresponding temperatures, some important structural and dynamic features both below and above T_g were revealed using constant-NVT MD simulations. The polymer system exhibited more local structural features in case of below T_g than above T_g, as suggested by some typical radial distribution functions and torsion angle distributions. Non-bond energy, not any other energy components in the used COMPASS forcefield, played the most important role in glass transition. An abrupt change occurring in the vicinity of T_g was also observed in the plots of the mean squared displacements (MSDs) of the crosslinks against the temperature, indicating the great importance of crosslinks to glass transition. Rotational dynamics of some bonds in epoxy segments were also investigated, which exhibited great diversity along the chains between crosslinks. The reorientation functions of these bond vectors at higher temperatures can be well fitted by Kohlrausch-Williams-Watts (KWW) function.     

热机械分析仪测定PMMA玻璃化温度测定条件的研究

采用热机械分析法(TMA)测定了聚甲基丙烯酸甲酯(PMMA)的玻璃化温度(Tg),讨论了升温速率和负荷对PMMA板材Tg的影响。结果表明:升温速率越大,所测的Tg值就越高;样品所受负荷的不同会对所测的Tg值有影响,但影响没有规律性;当升温速率为15℃/min时,测试不受负荷影响。     

Quantitative structure-property relationships for composites: prediction of glass transition temperatures for epoxy resins

The glass transition temperatures of nine stoichiometric resin systems of tetraglycidyl-4,4′-diamino-diphenylmethane (TGDDM), triglycidyl p-amino phenol and diglycidyl ether of bisphenol A with 4,4′-diaminodiphenylsulphone (DDS), diethyl-toluenediamine and dimethylthiotoluenediamine were calculated using group interaction modelling (GIM) and atomic additivity (AA) methods. The input parameters were generated from kinetics simulation, which outputs the structure information for the cured systems. The modelling parameters were also applied to four non-stoichiometric systems of TGDDM and DDS. The predicted values from GIM were in good quantitative agreement with measured results from temperature modulated differential scanning calorimetry for all systems studied. Compared to GIM, the AA method gave inferior predictions for the highly crosslinked systems, especially for those, where epoxy was in excess.     

Disruption of self-assembly and altered mechanical behavior in polyurethane/zinc oxide nanocomposites

The addition of less than 1 vol%, 33 nm zinc oxide nanoparticles into a polyurethane matrix resulted in approximately 40% decrease in the Young's modulus, 80% decrease in strain at fracture, and 50% decrease in the storage modulus, but at the same time resulted in an ∼11 °C increase in the glass transition temperature of the polymer. These results appear to contradict the general principle observed for many polymeric systems, where higher glass transition temperature generally means higher elastic modulus. Detailed experiments with FTIR, DMTA, FE-SEM, and AFM indicated that the addition of ZnO nanoparticles disrupts the phase separation in the polymer, resulting in weaker mechanical properties. The special interaction between the particles and polymer possibly constrains the mobility of polymer chains, which increases the glass transition temperature. The most likely reason for the disruption and the nature of the interaction is the reaction between the surface hydroxyl groups of the zinc oxide nanoparticles and the isocyanate groups of the polyurethane pre-polymer.     

PPO/EP复合材料的玻璃化转变温度及其测试方法

介绍了玻璃化转变温度(Tg)的内涵及其主要测试方法;以聚苯醚/环氧树脂(PPO/EP)为研究对象,分别采用DSC法和DMA法测定其Tg值,并讨论了两种测试方法的异同。结果表明:两种测试方法的测试条件、测试精度及影响测试结果的因素是不同的。在给出某一种高聚物的Tg时须注明测试方法和条件。     

双酚F环氧/聚甲基丙烯酸甲酯互穿网络的研究

合成了双酚F环氧树脂(BPFER),测定了其环氧值。用同步法制备了不同配比的双酚F环氧树脂/聚甲基丙烯酸甲酯互穿聚合物网络(BPFER/PMMAIPN),讨论了配比对IPN的力学性能和热性能的影响。用透射电子显微镜对IPN进行了形态分析。     

MPS-SiO2/PS核壳型复合粒子的形态与玻璃化转变温度研究

以正硅酸乙酯为原料，调节pH值为碱性，通过溶胶-凝胶工艺制备单分散SiO2球，用偶联剂甲基丙烯酰（3-三甲氧基硅烷）丙酯（MPS）进行改性，得到MPS-SiO2球形粒子。以MPS—SiO2球为种子，苯乙烯为壳单体，乳液聚合法制备核壳结构的MPS-SiO2／PS复合粒子。透射电镜观察复合粒子形态的结果表明，MPS—SiO2球粒径为200nm左右时，得到覆盆子状核壳结构；MPS-SiO2球粒径为80nm左右时，得到包含多个MPS—SiO2球的多核壳结构。差示扫描量热法考察MPS-SiO2／PS复合粒子玻璃化转变温度（Tg）的结果表明，随着MPS—SiO2球含量增加，复合粒子的Tg增加；随着MPS-SiO2球粒径减小，复合粒子的Tg也有所增加。     

Electrical characterizations of PZT ceramics in large frequency and temperature ranges

Electrical properties of PbZr_0.75Ti_0.25O₃ ceramics have been characterized. The measurements have been made in frequency ranging from 20 to 2.10⁹ Hz and between 20 and 730 °C for low and medium frequencies. Typically at room temperature, the dielectric constant ′ is higher than 500 at 1 MHz whereas the loss tangent is close to 0.01. From ′(T) measurements, the Curie temperature of our sample has been determined at 320 °C. In the paraelectric state, ′(T) follows the empirical Curie–Weiss law near the phase transition which is of second order type. The increase of ′ observed at high temperatures and low frequencies in the paraelectric state are explained: this abnormal behavior is due to the migation of oxygen ions towards the electrodes, creating an additional non-ferroelectric interface which generates a Maxwell–Wagner effect.     

MPS-SiO_2/PS核壳型复合粒子的形态与玻璃化转变温度研究

以正硅酸乙酯为原料,调节pH值为碱性,通过溶胶-凝胶工艺制备单分散SiO2球,用偶联剂甲基丙烯酰(3-三甲氧基硅烷)丙酯(MPS)进行改性,得到MPS-SiO2球形粒子。以MPS-SiO2球为种子,苯乙烯为壳单体,乳液聚合法制备核壳结构的MPS-SiO2/PS复合粒子。透射电镜观察复合粒子形态的结果表明,MPS-SiO2球粒径为200 nm左右时,得到覆盆子状核壳结构;MPS-SiO2球粒径为80 nm左右时,得到包含多个MPS-SiO2球的多核壳结构。差示扫描量热法考察MPS-SiO2/PS复合粒子玻璃化转变温度(Tg)的结果表明,随着MPS-SiO2球含量增加,复合粒子的Tg增加;随着MPS-SiO2球粒径减小,复合粒子的Tg也有所增加。     

Adhesion of resin cements to contaminated zirconia resin cements on zirconia: effect saliva-contamination and surface conditioning

This study evaluated the adhesion of resin cements to zirconia after saliva contamination using resin cements with different chemistries. Zirconia discs (N?=?240, n?=?10 per group) were randomly divided into three groups: (a) C: No contamination (Control), (b) S: Contamination with saliva, (c) S?+?AA: Contamination with saliva followed by air-abrasion (CoJet). While half of the specimens were not conditioned, the other half were conditioned with 37.5% H₃PO₄ for 60?s. After rinsing, all specimen surfaces were silanized (Monobond Plus). Resin cements based on either methacrylate (Variolink II–VL) or MDP monomer (Panavia 21-PN) were polymerized on the substrates. The specimens were randomly divided into two further groups to be tested either after (a) 24?h dry storage at 37?°C or (b) thermocycling (×5000, 5–55?°C). Microshear bond (MSB) tests were conducted in a Universal Testing Machine and failure types were analyzed. Data were analyzed using Univariate analysis and Tukey’s tests (alpha = 0.05). While saliva contamination, 37.5% H₃PO₄ application (p?<?.001) and aging (p?<?.05) significantly affected the bond results, cement type did not show significant difference after aging (p?>?.05). Adhesive strength of PN (1.2–4.4?MPa) on saliva contaminated and etched zirconia was more stable than that of VL (0–2.8?MPa). After aging, bond strength results decreased the most with VL (3–100%) compared to PN (32–71%) but the decrease was less in the air-abraded groups after aging (VL: 3%; PN: 32%). Exclusively adhesive failures were experienced in all groups.     

Enhanced thermal stability of piezoelectricity in lead-free (Ba,Ca)(Ti,Zr)O3 systems through tailoring phase transition behavior

Good thermal stability in lead-free BaTiO₃ ceramics is important for their applications above room temperature. In this study, thermal stable piezoelectricity in lead-free (Ba,Ca)(Ti,Zr)O₃ ceramics was enhanced by tailoring their phase transition behaviors. Comparison between (1-x)Ba(Ti_0.8Zr_0.2)O₃-x(Ba_0.65Ca_0.35)TiO₃ and (1-y)Ba(Ti_0.8Zr_0.2)O₃-y(Ba_0.95Ca_0.05)TiO₃ revealed that latter system at y?=?0.80 had much better thermal stable piezoelectric coefficient than the former at x?=?0.45. Both systems crystalized in tetragonal to orthorhombic phase boundary at room temperature. The phase transition temperature and degree of diffusion were adjusted by Ca and Zr ions contents and demonstrated great influence on temperature dependent dielectric permittivity, hysteresis loops, and in-situ domain structures. The improved thermal stability of (1-y)Ba(Ti_0.8Zr_0.2)O₃-y(Ba_0.95Ca_0.05)TiO₃ prepared at y?=?0.80 was linked to its higher paraelectric to ferroelectric phase transition temperature (T_m?=?115.7?°C) and less degree of diffusion (degree of diffusion constant γ?=?1.35). By comparison, (1-x)Ba(Ti_0.8Zr_0.2)O₃-x(Ba_0.65Ca_0.35)TiO₃ prepared at x?=?0.45 revealed T_m?=?81.3?°C and γ?=?1.65. Overall, these findings look promising for future stimulation of phase transition behaviors and design of piezoelectric materials with good thermal stabilities.     

The thermochromic characteristics of Zn-doped VO2 that were prepared by the hydrothermal and post-annealing process and their polyurethane composite films

In this paper, Zn-doped VO₂ nanoparticles have been successfully fabricated by a two-step hydrothermal-annealing process, and the thermally induced visible light transmittance enhancement of Zn-doped VO₂ has been studied for the first time. It is found that Zn-doped VO₂ not only exhibits excellent solar modulation ability (ΔT_sol = 15.27%) but also can reduce the phase transition temperature and increase the visible light transmittance after the heat-induced phase transition (ΔT_lum=+5.78%). Moreover, with the increase of Zn doping concentration, the phase transition temperature (T_c) and phase transition hysteresis (ΔT) both decrease. It is shown that the Zn-doped VO₂-PU films not only have good solar light modulation ability and properties of improving visible light transmission after phase transition, but also have good durability. The research result is of great significance for improving the visible light transmittance after phase transition and realizing the practical application of VO₂ in the field of smart windows.     

Influence of alternating sequential fraction on the melting and glass transition temperatures of ethylene-tetrafluoroethylene copolymer

The melting (T_m) and glass transition (T_g) temperatures of a series of ethylene (E)-tetrafluoroethylene (TFE) copolymer (ETFE) have been found to show unique dependence on the TFE content with the minimal and maximal points. These behaviors have been interpreted successfully on the basis of the degree of alternation of E and TFE monomeric units along the skeletal chain. The melting point of a perfectly alternating copolymer is estimated to be 295 °C on the basis of the dependence of T_m using a modified Flory’s equation. The corresponding T_g was estimated as 145 °C by applying a modified Gibbs-Damnation’s equation.