Effect of dentinal surface preparation on the bonding of self-adhesive luting cements

The purpose of the present study was to evaluate the bond strength and the interaction morphology of self-adhesive resin luting cements (SLCs) to dentin prepared with different methods. Four SLCs were used: RelyX U100^®, RelyX U200^®, Clearfil SA Luting^®, and SmartCem2^®. A flat dentin surface of 40 human molars was exposed and each tooth was sectioned in four tooth-quarters, which were distributed into four groups according to the SLC used to cement indirect resin composite restorations. The tooth-quarters of each group were then distributed in four subgroups according to the method used for dentin preparation: flat-ended cylindrical fine-grit diamond, flat-ended cylindrical median-grit diamond, flat-ended cylindrical plain-cut tungsten carbide, or abraded with #600-grit SiC paper (control). The restored tooth-quarters were sectioned to obtain beams (0.8?mm²) and submitted to the microtensile bond strength test (n?=?10). The results were analyzed using two-way ANOVA/Tukey (α?=?0.05). Forty-four additional teeth were used for micromorphological investigation of the SLC/dentin interface and of the topographic aspect of the dentin surfaces after application of the SLCs. Only the bond strength of RelyX U200 was significantly influenced by the surface preparation. No interference was identified on the micromorphological aspect of the bonding interfaces. The topographic investigation of the dentinal surfaces showed that the SLCs were not able to effectively remove the smear layer and etch the underlying dentin, irrespective of the preparation method. So, the interference of the dentin preparation on the bond strength of SLCs is material dependent, but don’t influence the micromorphologic aspect of the interaction zone.     

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.     

Role of strontium substitution in spray drying of hydroxyapatite: A comparative study on physical properties

Spray drying (SD) has the ability to tailor granule size and morphology, thus, it is used for producing hydroxyapatite (HA) granules. Recently, Sr functionalized HA (SrHA) has been recommended owing to its improved biological properties. The aim of this article was to produce SrHA granules with the combination of nanoparticle synthesis and spray-drying. The effects of substitution on the physical properties of SrHA nanoparticles and spray-dried granules were investigated. TEM analyzes revealed that Sr substitution reduced the mean size of HA nanoparticles from 4.59 nm to 2.31 nm. Besides, Sr substitution increased the viscosity of the prepared slurry for spray drying, which may be attributed to the smaller nanoparticle sizes. The reduced nanoparticle size caused to the agglomeration of the SrHA more than the pure HA nanoparticles. Moreover the 16 mol % Sr substituted HA (16SrHA) slurry were quickly hardened, which hampered the feeding of the slurry to the SD system; eventually the atomizer was blocked. The increase in the viscosity increased the mean granule size of HA from 41.53 µm to 49.18 µm. HA and 8SrHA granules presented HA phase dominantly after the heat treatment at 1000°C, while, 16SrHA decomposed to TCP according to RAMAN and XRD investigations.     

Effects of ingredients on thermal and mechanical properties of acrylic bone cements

There is a very delicate relation between the amounts of all the ingredients present in the cement composition and the properties of the product. In this study, homogeneous poly(methyl methacrylate) (PMMA) microspheres were prepared by suspension polymerization technique, and used in cement formulations. Various acrylic cements with different compositions were prepared by using PMMA microspheres, methyl methacrylate (MMA) monomer, radiopaque agent of barium sulfate (BaSO₄), inorganic particles of hydroxyapatite (HA), initiator and chain stopping agent of 1‐dodecyl mercaptan (DDM). The effects of these additives on mechanical and thermal properties of the resultant cements were examined. Addition of 8% HA relative to the solid parts caused an increase in both tensile and compressive strengths from 20.40 to 25.20 MPa, and from 84.04 to 89.57 MPa, respectively, while curing temperature was decreased about 3 degrees. Chain stopping agent of DDM caused a sharp decrease about 30 degrees in the curing temperature. Radiopaque agent of barium sulfate caused inverse effect on mechanical and thermal properties. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of the matrix microstructure on the mechanical properties of CVI-infiltrated carbon fiber felts

The correlation between the matrix microstructure and the mechanical properties of CVI-infiltrated carbon fiber felts was studied by optical microscopy, scanning electron microscopy, and three-point bending tests. The results of these investigations show a correlation between (a) the content of highly textured pyrocarbon in the matrix and the quasi-ductile fracture behavior of the samples and (b) the thickness of the low textured pyrocarbon layers beneath the fibers and the measured flexural strengths. Fractographic investigations using SEM showed that toughness increase results from multiple crack deflections at the interface between numerous ‘sublayers’ forming the highly textured pyrocarbon. The increase of flexural strength could be explained by a thicker, so called ‘virtual’ fiber.     

Effect of polymerization conditions on polyacetylene morphology

In an effort to optimize the synthesis of polyacetylene we have studied the evolution of its morphology by scanning electron microscopy (SEM) and also determined the density of the polymer. Both results are correlated and discussed.     

Kinetic effect of hydroxyapatite types on the polymerization of acrylic bone cements

The effect of type and amount of hydroxyapatite on the setting kinetics of an experimental bone cement based on poly(methyl methacrylate-co-styrene) was studied. The average molecular weights of the polymeric beads synthesized were determined by SEC and the average particle size was determined by Optical Microscopy. Three types of hydroxyapatites were synthesized in the laboratory and then characterized by ICP, FTIR and X-ray diffraction. To obtain more compatible fillers, the hydroxyapatites were treated with 3-trimethoxysilylpropylmethacrylate. Bone cements formulations filled with 0, 10, 30, and 50 weight % of hydroxyapatite powders were prepared and the kinetics of setting was followed by Differential Scanning Calorimetry. The presence of hydroxyapatite decreased the reaction rate and increased the degree of conversion, which could be beneficial for the long time stability of the implant.     

Influence of magnesium and silver ions on rheological properties of hydroxyapatite/chitosan/calcium sulphate based bone cements

Rheology of bioceramic bone cements is usually described as properties of ceramic slurries, neglecting the self-setting character of these materials. In our studies calcium sulphate based bone cements with Ag⁺, Mg²⁺ and Mg²⁺/CO₃^2- modified hydroxyapatite were investigated. Despite of expectations, it has been proven that the presence of magnesium ions significantly influence the rheological properties of cement pastes. Changes in rheological properties were connected with (I) chemical interactions between Mg²⁺ and sulphate ions (II) chemical interaction between Mg²⁺ and chitosan. These effects were not observed for silver additive. Most of the developed calcium sulphate based pastes, except material containing MgHA and chitosan, have been categorized as thick pastes applicable with the spatula. It has been found that the chitosan present around and at the calcium sulphate grains acted as a lubricant and prolong the period of quasi-constant viscosity of the pastes.     

The effect of resin formulation on the cellular morphology and mechanical properties of phenolic foams

In the present study, the effects of blowing agent concentration, surfactant, and resin viscosity on the cellular structure, density, and compressive strength of phenolic foams were investigated. The mechanism of foaming was studied by thermal analyses, as well. The scanning electron microscopy was performed to investigate the morphology of foams. The presence of surfactant was essential to obtain a foam structure. By increasing the amount of blowing agent in the formulation, the bubbles became larger. The variation of the resin viscosity had the sharp effect on the cell size and its distribution so that the cell size dropped from 108 to 77 μm in the sample with the highest viscosity. The mechanical properties were significantly affected by foam structure as well as the cell uniformity. By decreasing the average cell sizes, the compression strength and modulus were improved up to more than 60%. Finally, the optimum values for viscosity of resin and, blowing agent, and surfactant concentrations were obtained. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48331.     

羟基磷灰石增强环氧树脂结构胶的力学性能研究

采用羟基磷灰石(HA)对环氧树脂结构胶进行改性。对改性后结构胶的力学性能进行测试。实验表明:随着HA的掺量增加,环氧结构胶的压缩强度、冲击强度、粘钢剪切强度提高、拉伸强度略有降低;当羟基磷灰石的掺量为5％时。环氧树脂结构胶的压缩强度、冲击强度分别为92MPa、6．8kJ／m2,比纯环氧树脂基体提高28％和70％;当羟基磷灰石的掺量为7％时,环氧树脂结构胶的粘钢剪切强度为26．4MPa．比纯环氧树脂基体提高55％,羟基磷灰石对环氧树脂有较好的增强增韧作用。     

半水磷石膏固化原状磷石膏制备胶凝材料及性能研究

以原状磷石膏（RPG）为基材,通过单因素实验研究了原状磷石膏（RPG）与β-半水磷石膏（HPG）相对掺量以及生石灰、水泥、硅灰3种掺合料对磷石膏基复合胶凝材料（PGBM）抗压强度、抗折强度及软化系数的影响规律以及作用机理。结果表明：HPG、生石灰、水泥、硅灰相对掺量的增加均能有效提高PGBM的强度及软化系数,其中硅灰的作用最为明显。但是,当生石灰和水泥的掺量（以质量分数计）分别大于4%和6%时,对PGBM耐水性能的改善不明显。当RPG与HPG相对掺量（质量分数比）为7∶3,生石灰、水泥、硅灰掺量（以质量分数计）分别为4%、12%、5%时,试件28 d抗压强度和软化系数分别可以达到26.29 MPa和0.79。微观分析表明：各掺合料主要通过水化产物填充率影响RPG颗粒之间的接触强度,进而对PGBM的强度和耐水性产生影响。     

The mode of occurrence of chlorine in high volatile bituminous coals from the Asturian Central coalfield

The occurrence of chlorine in two high volatile bituminous coals from the Asturian Central coalfield, with a chlorine content about 0.1 wt % has been discussed. The methodology used is based on obtaining the chlorine distribution in different densimetric fractions in gravimetric solutions free of chlorides. It allows the separation of elements that could be bonded to chlorine to study their likely association. Additional information has been obtained by carrying out studies on the solubility in water, and the relation of chlorine with alkaline and alkaline-earth elements. Direct evidence of the presence of chlorine and its chemical association has been gained by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). From the results it may be concluded that in the coals studied chlorine is mainly localized in the coal matrix associated to organic matter.     

Thermo-oxidative ageing and its effect on the network structure and fracture mode of natural rubber vulcanizates

The changes in network structure and fracture mode of unfilled and filled natural rubber vulcanizates, during ageing at 100°C have been studied by chemical analyses and scanning electron microscopy. The fall in properties during ageing is caused mainly by chain scission. The increase in crosslink density during the initial periods of ageing causes an increase in modulus and tensile strength. Carbon black accelerates ageing, probably by surface catalysis. The simple network structure of efficiently vulcanized rubber results in better retention of properties during ageing. Antioxidant retards ageing. The extent of degradation of vulcanizates is reflected in the nature of the fracture surfaces. The roughness of the tensile fracture surface is affected to varying degrees depending upon the ageing resistance of the vulcanizates. However, in tear, the mode of fracture propagation is affected by ageing.     

Gauge length effect on the tensile properties of leather

Tensile properties are important basic characteristics of materials and influence their end‐use and performance. More importantly, in the case of leather due to end‐use applications such as shoe uppers, automotive and furniture upholstery, mechanical properties such as tenacity are of extreme importance. Therefore, fundamental studies on the tensile properties of leather are needed. In this study, an attempt has been made to examine the effect of gauge length (GL) on the tensile properties of shoe upper leather. Two different specimens in the form of rectangular and dumbbell shapes have been cut from parallel and perpendicular directions to the body axis of the leather and have been tested. Results showed that the maximum breaking load and the percentage extension at break decreased with the increase in GL. Rectangular specimens showed a 30% decrease in maximum breaking load and a 13% decrease in percentage extension at break, while dumbbell specimens showed reductions in the order of 28 and 6%, respectively, as the GL increased from 9.53 cm to 23.5 cm. Highly varying supramolecular architecture of the collagen matrix and the frictional slippage caused by the free ends present in the collagen fibrils, which induce a weak‐link effect similar to the one found in cotton fibers and yarns, are considered to be the probable reasons for this behavior. A limited scanning electron microscopic study has been undertaken to pictorially represent the breakage of leather at different GLs. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1202–1209, 2006     

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.     

碳纤维增强水泥/混凝土材料力学性能的若干研究

本文通过对水泥基体掺入碳纤维进行研究，得出了复合体抗压强度、劈拉强度与碳纤维掺量的关系。同时文中还利用聚丙烯腈纤维作对比研究，得出目前碳纤维作为增强体的优缺点，为碳纤维增强水泥基复合材料的推广应用提供更多的实验依据。     

Digital light processing stereolithography of hydroxyapatite scaffolds with bone-like architecture,permeability, and mechanical properties

This work deals with the additive manufacturing and characterization of hydroxyapatite scaffolds mimicking the trabecular architecture of cancellous bone. A novel approach was proposed relying on stereolithographic technology, which builds foam-like ceramic scaffolds by using three-dimensional (3D) micro-tomographic reconstructions of polymeric sponges as virtual templates for the manufacturing process. The layer-by-layer fabrication process involves the selective polymerization of a photocurable resin in which hydroxyapatite particles are homogeneously dispersed. Irradiation is performed by a dynamic mask that projects blue light onto the slurry. After sintering, highly-porous hydroxyapatite scaffolds (total porosity ~0.80, pore size 100-800 µm) replicating the 3D open-cell architecture of the polymeric template as well as spongy bone were obtained. Intrinsic permeability of scaffolds was determined by measuring laminar airflow alternating pressure wave drops and was found to be within 0.75-1.74 × 10⁻⁹ m², which is comparable to the range of human cancellous bone. Compressive tests were also carried out in order to determine the strength (~1.60 MPa), elastic modulus (~513 MPa) and Weibull modulus (m = 2.2) of the scaffolds. Overall, the fabrication strategy used to print hydroxyapatite scaffolds (tomographic imaging combined with digital mirror device [DMD]-based stereolithography) shows great promise for the development of porous bioceramics with bone-like architecture and mass transport properties.     

Influence of apple flavor absorption on physical and mechanical properties of poly(ethylene terephthalate) films

Poly(ethylene terephthalate) (PET) films (280‐μm film thickness), which are used in food packaging, were immersed into 160‐ and 320‐ppm apple flavor solution for 14, 28, and 56 days at 5, 25, and 40°C, respectively. At the end of this period, the changes in the PET films were investigated by measuring the mechanical and physical properties. The mechanical properties were determined by examining changes in the Young's modulus. The changes in the physical properties were investigated by Fourier transform IR spectroscopy and scanning electron microscopy (SEM). The formation of microcracks in the structure of PET films was observed by SEM. According to the results of those investigations, the apple flavor affects PET films, even at very low concentrations and temperatures. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1802–1807, 2006     

The effect of trivalent metal nitrates on the properties of dental cements made from poly(acrylic acid)

Addition of either Al(NO₃)₃ or Fe(NO₃)₃ to zinc polycarboxylate and glass polyalkenoate dental cements has been shown to cause an acceleration to their setting reactions. In the case of Fe(NO₃)₃, the reaction was so fast that cements could not be mixed, but Al(NO₃)₃ had a less severe effect, and cements containing various amounts of this additive were prepared. Their compressive strength at 24 h was lower than for the original cements, with zinc polycarboxylate being more affected than the glass polyalkenoate. Both cements are made from poly(acrylic acid), and infrared spectroscopy showed that both Al(NO₃)₃ and Fe(NO₃)₃ form adducts with this polymer, the interaction of aluminum with the polymer being significantly different from that of the iron (III) species. The binding by Al(NO₃)₃ was also shown to reduce the pH of a poly(acrylic acid) solution. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2353–2359, 1998     

Effect of silicon and heat-treatment temperature on the morphology and mechanical properties of silicon - substituted hydroxyapatite

The precipitation method was used to synthesize silicon-substituted hydroxyapatite with different Si contents of 0.4, 0.8 and 1.6 wt.% (0.4, 0.8 and 1.6Si-HA) using silicon acetate [Si(OCOCH₃)₄] as a Si source. As-synthesized hydroxyapatite (HA) and Si-HA powders/bulks were heat-treated at different temperatures of 1150, 1200 and 1250 °C for 1 h. Pure 0.4Si-HA and 1.6Si-HA were obtained after heat-treatment at all temperatures, whilst α-TCP phase was formed in the 0.8Si-HA sample after heat-treatment at 1250 °C. SEM observation clearly showed that the substitution of Si in HA inhibited the grain growth of Si-HA even at high heat-treatment temperatures (1200 or 1250 °C). The highest diametral tensile strength (DTS) of 15.93 MPa was obtained in the 1.6Si-HA sample after heat-treatment at 1250 °C.