Ion migration from fluoride-releasing dental restorative materials into dental hard tissues

This study was carried out in order to determine the extent to which ions released from fluoride-containing dental restoratives migrated through the enamel and dentine of extracted teeth. A total of 40 permanent human 3rd molars were used. They were extracted for orthodontic reasons, and employed within 1 month of extraction. A cervical (Class V) cavity was prepared in each tooth, then filled with one of: a conventional glass-ionomer, a resin-modified glass-ionomer, a polyacid-modified composite resin (“compomer”) or a fluoride-releasing resin composite. Ten samples were prepared per material. After 1 month, five specimens per material were prepared and examined under SEM/EDX. Concentrations of sodium, aluminium, strontium, fluorine, magnesium, silicon, phosphorus and calcium were determined within the tooth. After 18 months, the remaining five specimens for each material were prepared and studied in the same way. The greatest extent of ion migration into the tooth was found with the conventional glass-ionomer and least migration was found for the fluoride-releasing composite, which showed no evidence of fluoride migration at all. Levels of migrating ions were generally higher in the 18 month specimens than in the 1 month specimens, and also higher in the dentine than in the enamel. Ions released by restorative dental materials have been shown conclusively for the first time to be capable of migrating into the enamel and dentine surrounding the restoration. The conventional glass-ionomer showed the highest level of ion migration whereas the fluoridated composite resin showed little if any ion migration. This suggests that the conventional glass-ionomer has the greatest caries inhibiting effects of all the materials tested, and the fluoridated composite the least.     

Mechanical properties of a permanent dental restorative material based on calcium aluminate

This paper deals with some important mechanical properties (hardness, dimensional stability, compressive and flexural strength) of an experimental version of a translucent calcium aluminate dental restorative material. All samples investigated have been made from pre-pressed tablets, with a compaction degree of approximately 60%, hydrated using a 0.15 wt % Li salt solution as an accelerator. The samples were stored in water at 37 degrees C between the measurements. As reference materials one composite, Tetric Ceram, and one glass ionomer, Fuji II, were used with specimens prepared according to the manufacturer's recommendations. For the reference materials some of the properties were published data. The results show that the calcium aluminate material has sufficient mechanical properties to be used as a permanent dental restorative taking as a reference the ISO 9917 and the ISO 4049 as well as the reference materials. In addition the results indicate that the mechanical properties are controlled by the microstructure, which is mainly determined by the grain size of the filler.     

Calculation of the shrinkage-induced residual stress in a viscoelastic dental restorative material

A procedure able to describe the curing process of a particulate composite material used in a dental restoration is developed in the ANSYS environment. The material under concern is a multifunctional methacrylate-based composite for dental restoration, activated by visible light. The model accounts for the dependence of the viscoelastic functions on temperature and degree of cure. Three geometries have been considered in the analysis that are representative of three different classes of dental restoration and mainly differ by the C (constrained)-factor, (i.e. the bounded to unbounded surface ratio). It was found that the temperature could give a necrosis in the vicinity of the tooth nerve and that the average stress at the interface between the composite and the tooth scales exponentially with the C-factor. The residual stress at the dental restoration interface is also compared with the uniaxial tensile strength of twelve commercially available composite materials: it clearly appears that the level of residual stress may overcome the strength of the composite, especially at high C-factors.     

Synthesis of fluoride-releasing carbonate apatites for bone substitutes

Fluoride (F⁻)-substituted B-type carbonate hydroxyapatite (CHAP) powders were prepared for application as bone substitute materials having the ability to enhance bone formation and to suppress bone resorption due to the therapeutic effect of F⁻. F⁻ was adsorbed on CHAP in a sodium fluoride solution followed by heating at 700°C in carbon dioxide flow to substitute F⁻ for the hydroxyl ion in the CHAP structure. The F⁻ contents in the F-substituted CHAP powders were 16–22 times greater than that in normal adult human bones. The carbonate ion contents in the F-substituted CHAP powders corresponded to or were higher than that in normal adult human bones. F-substituted CHAP powder with CO₃²⁻ and F⁻ contents of 11.03 and 0.66 wt%, respectively, slowly released F⁻ in a physiological salt solution to a sufficiently high F⁻ level. The F⁻ concentration slowly increased and reached 67.20 ± 4.81 μg l⁻¹, which was 1.5–9.3 times higher than that in the body fluid of normal adult humans, near the therapeutic window of F⁻, and far lower than the estimated toxic level. Therefore, the F-substituted CHAP can promote bone formation. The present F-substituted CHAP has the advantage of slow F⁻ release over sodium fluoride and sodium monofluorophosphate which are highly soluble salts and cannot be sintered into a ceramic body.     

Curing of visible light-activated dental restorative composites

FTIR spectroscopy and microhardness measurements were employed to follow the degree of curing of visible light activated dental composites. The observed dependence of curing on grade and shade of the materials, exposure time and depth from the light exposed surface have been discussed. Immediately after curing, it was found that direct correlation of microhardness values with that of double bond conversion estimated by FTIR technique could not be established.     

Glass-ionomer dental restorative: Part I: a structural study

A structural study of glass-ionomer cement (GIC) dental restoratives has been completed. Transmission electron microscopy, selected area electron diffraction, and X-ray diffraction studies indicate domain-like microstructure in a new experimental material, whereas a featureless amorphous gel-like microstructure exists in the conventional GIC. Nuclear magnetic resonance studies were also conducted. The new experimental GIC contains domains of (i) bonelike material (apatite), (ii) mesoporous material and (iii) other framework structures (aluminium phosphate in the high cristobalite structure), with its setting chemistry a restructuring of the aluminosilicate glass around the template of poly(acrylic acid). Conventional glass-ionomer cement may set by a similar but slower process. Leaching properties of glass-ionomer cements are also explained.     

Dielectric analysis of light-curing dental restorative materials—a pilot study

This study tested the potentiality of dielectric analysis (DEA) for determining the reaction performance of light-curing dental resins. The influence of polymerisation conditions and material properties on the ion viscosity were investigated within a current field. The restoratives were light-cured for 20, 40 or 60 s in a layer thickness between 1, 2 , or 3 mm with a varying distance between curing light and specimen of 1, 3 or 5 mm. The tests were performed at 25°C/37°C with different polymerisation modes. Nine restoratives (two composites and their derivate flowables, two ormocers, one compomer, one nano-filled composite and one siloran) were investigated. The ion-viscosity-time graph was analysed to characterize reaction velocity and polymerisation conversion. The slope of the ion viscosity decreased with increasing distance between polymerisation light and specimen. The time of exposure affected the affinity and the conversion, with a polymerisation maximum at 40 s. A relation between thickness and reaction time and between polymerisation modus and conversion/velocity was found. The temperature influenced the reaction affinity. Different materials showed an individual curing performance. DEA-monitoring of the ion viscosity gives principal insight in the polymerisation reaction of light curing materials. Further investigations are necessary for identifying the relation between ion viscosity and polymerisation.     

Time-dependent strength and fatigue resistance of dental direct restorative materials

Elastic modulus (EM), initial fracture strength (FS) and flexural fatigue limit (FFL) of dental restorative materials were measured in a simulated oral environment to correlate mechanical response under the influence of water with the chemical nature of the test materials under investigation. One resin composite (RC; Tetric Ceram, Ivoclar-Vivadent Corp., Liechtenstein), an ion-leaching resin composite (ILRC; Ariston pHc, Ivoclar-Vivadent Corp., Liechtenstein) a compomer (CO; Dyract AP, Dentsply Corp., USA) and a glass-ionomer cement (GIC; Ketac Molar, 3MEspe Corp., Germany) were tested. Static EM, FS and dynamic FFL experiments were performed. The FFL was determined under cyclic loading for 10(5) cycles in terms of a staircase approach. The materials were stored for 1, 8, 30, 90 and 180 days in 37 degrees C distilled water, respectively. The RC degraded over time due to water adsorption followed by failure within the resin matrix. The ILRC suffered from a pronounced decrease in FS as well as in FFL due to a constant ion-leaching and macroscopic crack growth. CO failed over time due to resin-filler interface cracking. The GIC exhibited improved mechanical performance over time due to a post-hardening mechanism. The results reveal the necessity for substantial preclinical evaluation of direct restorative materials. The material parameters under investigation are capable of predicting clinical performance over time.     

纳米二氧化锰的可控制备及其电化学储能机理研究

通过添加十二烷基溴化氨(CTAB)利用液相沉淀法制备了不同形貌的纳米二氧化锰,用扫描电镜、X射线衍射、孔结构以及循环伏安法等分析研究了CTAB添加量对二氧化锰形貌和电化学性能的影响.结果表明,随着CTAB添加量的增加,二氧化锰形貌从长棒状到均匀球状发生规律变化,此外随着颗粒尺寸变小,二氧化锰比容量从162F/g提高到了...     

Synthesis and characterizations of Ni-Fe@spinel oxide core-shell nanoparticles

Core-shell Ni-Fe@ferrite nanoparticles with an average diameter of 14 nm and shell thickness of 3 nm were synthesized through a redox-transmetalation process. The alloy core and spinel oxide shell were verified by X-ray photoelectron spectroscopy, X-ray diffraction, and transmission electron microscopy. The hydrophobic oleylamine molecules on the surface were replaced by hydrophilic meso-2,3-Dimercaptosuccinic acid to make the nanoparticles to be water-soluble. X-ray diffraction study of the as-prepared core-shell nanoparticles indicates that they remained face centered cubic alloy core and spinel shell form in air. Magnetic measurements indicate that the core-shell nanoparticles exhibit superparamagnetic and exchange bias characteristics at 300 K and 5 K, respectively.     

CdS量子点的制备和光学性质

以醋酸镉、硫粉为原料制备CdS量子点,研究了硫的加入量对其光学性质的影响,结果表明:合成的CdS量子点粒径均匀,分散性较好,随着硫加入量的增加CdS量子点的粒径增大;反应中过量的硫能有效地填补硫空位,从而抑制表面态发光,同时,ODA的修饰也能有效地钝化表面态,减小表面态的发光强度.     

Synthesis and characterizations of manganese ferrites for hyperthermia applications

In the last few years, magnetic nanoparticles have turned out to offer great potential in biomedical applications. This study was focused on Mn_xFe_1−xFe₂O₄ ferrite particles series with x ranging between 0 and 1. Manganese ferrites nanoparticles were prepared by co-precipitation method that allows a good control of their shape and size. The X-ray analysis indicated a crystallite size of the particles in the nanometers domain increasing with the Mn cation substitution level. Average grain size of the nanoparticles calculated from transmission electron microscopy images of the samples was ranging between 10.5 and 19.0 nm suggesting that the majority of the nanoparticles are monodomain. The hydrodynamic diameter of the water dispersed nanoparticles measured by dynamic light scattering was ranging between 60 and 105 nm proving the tendency of agglomeration. Vibrating sample magnetometer measurement confirmed the superparamagnetic behavior of the powders. The magnetic properties were analyzed considering the proposed cation distribution and Yafet–Kittel angles, while the specific absorption rate (SAR) measurement at 1.95 MHz frequency confirmed the influence of substitution level on magnetic properties and thermal transfer rate. From our results the highest value for specific absorption rate was 148.4 W g⁻¹ for Mn₂Fe₂O₄ at an AC field of 4500 A m⁻¹.     

4-叔丁基苯乙烯/三元乙丙橡胶悬浮共聚树脂的制备及表征

以EPDM(三元乙丙橡胶)、tBS(4-叔丁基苯乙烯)为单体,BPO(过氧化苯甲酰)为引发剂,DVB(二乙烯苯)为交联剂,明胶和磷酸三钙为分散稳定剂,甲苯和环己烷为溶剂,采用悬浮法合成新型功能高分子材料P(tBS/EPDM).采用SEM、FTIR、DSC等方法对其结构和性能进行表征,结果表明:所合成的粒状树脂中存在小而均匀的多孔结构,具有较高的比表面积.P(tBS/EPDM)对油品具有良好吸收性能,对四氯甲烷的最大吸油率为51.68g/g,氯仿35g/g,环己烷25.83g/g,煤油27.50g/g,甲苯22.8g/g,对甲苯和煤油最大吸油速率为66.64和199.93h-1.     

Synthesis and characterizations of nanoribbons and monodispersed nanocrystals of CuBr

Nanoribbons and monodispersed nanocrystals of CuBr have been prepared by a simple reaction between CuO suspension, NH₂OH·HCl and KBr in the presence of deionized gelatin at 10 °C. The products were characterized by X-ray powder diffraction, transmission electron microscopy and UV-vis absorption spectroscopy. The sizes of the monodispersed nanocrystals of CuBr were estimated by Debye-Scherrer formula according to XRD spectrum.     

新型药物载体材料——端羟基聚(丙交酯-co-对二氧环己酮)的合成与表征

聚乳酸(PLA)作为药物载体材料存在因疏水性强而导致的药物释放速率难控以及在循环系统中停留时间短等问题.研究表明,在PLA中引入乙醇酸(GA)可提高材料降解速率,引入聚乙二醇(PEG)则可延长共聚物在循环系统中的停留时间.研究以丙交酯(LA)和对二氧环己酮(PDO)为主要原料,在辛酸亚锡-乙二醇共引发体系的存在下,通过熔融开环聚合制备出了端羟基聚(丙交酯-co-对二氧环己酮)(HO-P(LA-co-PDO)-OH).这种同时具有PLA、GA和EG结构单元的大分子二醇可望成为一种降解速率可控、在循环系统中停留时间可调的新型药物载体材料.采用DSC、~1H NMR、~(13)C NMR和GPC-MALLs等对其结构和热学性能进行了表征.分子量检测结果表明,HO-P(LA-co-PDO)-OH的分子量随原料中PDO/LA摩尔比的减小而增大.     

Synthesis,morphology and device characterizations of a new organic semiconductor based on 2,6-diphenylindenofluorene

A new organic semiconductor, 2,6-diphenylindenofluorene (DPIF), was synthesized in four steps with a high overall yield of 49.3%. The morphology of thin films of DPIF that were formed under different substrate temperatures was examined by atomic force microscopy and X-ray diffraction analysis. Two different crystalline phases were found to exist depending on the deposition conditions. The DPIF thin film emits around 500–530 nm, while the OLED based on DPIF emits green light with a maximum output over 150 Cd/m² under 35 V. Two typical transistor devices, thin-film transistor (TFT) and semiconductor-metal-semiconductor (SMS) transistor, were fabricated and characterized. DPIF shows a weak n-type character from the TFT device measurement, while SMS transistors using DPIF as an emitter behave like permeable-base transistors with low operating voltages in both common-base and common-emitter modes and a feature of current amplification. Our results demonstrate however, that further research efforts are necessary in order to prevent the observed instabilities. These are quite important, considering that the common-emitter mode is widely used in applications requiring not only switching capability, but also current amplification.     

一种新型红色长余辉材料的制备及其发光性能

采用高温固相法制备出Sr3Al2O6∶Eu3x+红色荧光材料,可被可见光激发。在392和463nm激发下的线状发射峰,可归属为Eu3+离子的5DJ(J=0,1,2,3)→7FJ(J=0,1,2,3,4,5)跃迁,以612和617nm附近对应于5D0→7F2的电偶极跃迁发光最强。随着Eu3+掺杂量的增加,612nm附近发射峰相对减弱,而617nm处的发射峰相对增强,当x值为0.16时,样品发光强度最大。将所制样品与蓝、紫色长余辉材料混合,在停止光照后,利用长余辉材料所发出的光作为激发光源,使样品能够继续发射红光,从而得到一种新型的红色长余辉材料。     

一种新型红色磷光材料的合成及光物理性能研究

以2-甲基苯并噻唑、苯甲醛为原料,通过与三氯化铱配合,得到一种新型红色金属铱(Ⅲ) E-2-苯乙烯基苯并噻唑(SBT)乙酰丙酮(acac)配合物(SBT)2Ir(acac).通过质谱、核磁、红外光谱对其结构进行了表征,并对其光致发光性能进行了研究.研究结果表明:配合物(SBT)2 Ir(acac)在428和471nm处的紫外吸收属于单线态和三线态金属铱到配体的电荷转移吸收(1MLCT和3MLCT);在632nm处有强的金属配合物三线态磷光发射;(SBT)2Ir(acac)金属配合物的EHOMO=-4.8 eV,ELUMO=-2.5eV,磷光量子效率Φ (SBT)2Ir(acac) =0.19.(SBT)2Ir(acac)可能是一种极有潜力的电致磷光材料.