Studies on the radiopacity of experimental dental composite resins containing admixed SiO2−ZrO2 fillers

To produce radiopaque silica (SiO₂)-based fillers, zirconia (ZrO₂) powders were mechanically added to SiO₂ powders with ZrO₂ content up to 40 wt%. We evaluated the radiopacity of experimental composite resins consisting of (Bis-GMA + TEGDMA + CQ + DMAEMA) monomer mixture (25 wt%) and admixed SiO₂–ZrO₂ fillers (75 wt%), and compared their radiopacity with those of human dentin and enamel. It became confirmed that the radiopacity of experimental composite resins increased linearly with zirconium content, while the composite resin containing 80 wt% SiO₂-20 wt% ZrO₂ filler possessed radiopacity similar to that of human enamel. It was proved that the radiopacity of the composites could be precisely controlled by adjusting ZrO₂ content in SiO₂–ZrO₂ fillers.     

Abrasive wear of dental composite resins

Abrasive wear is a major problem in the application of dental composite resins. In this study the friction and wear behaviours of two types of dental composites: one containing relatively coarse filler particles and some microfillers (Estilux) and another containing only microfiller particles (Durafill), have been investigated by using a scratch testing machine. Experimental results show that the coefficients of friction in both composites are essentially constant for applied loads up to 20 N. The wear resistance of Durafill is better than Estilux. Under the same testing conditions, the size, shape and distribution of the filler particles are more important variables than applied load and sliding speed in controlling the wear mechanism. It is shown that for Estilux, plastic ploughing by the diamond indenter is the predominant mechanism. For Durafill, however, the formation and propagation of tensile cracks on the worn surface is the main wear mechanism. The effects of two different indenters, diamond and enamel, on the basic wear mechanisms are also discussed.     

Novel aromatic dimethacrylate esters as dental resins

The preparation of a novel class of dimethacrylate esters, by the reaction of glycidyl methacrylate with various phthalic acid isomers and their halogen substituted derivatives is described: These monomers exhibited low viscosity, possessed similar physical and mechanical properties to bis GMA, and the presence of halogen introduced X-ray opacity into the polymer giving opacity similar to tooth enamel.     

Synthesis of chelating resins containing aminopolyacetic acid moieties

Synthesis of chelating resins bearing an aminopolyacetic acid within a pendent group is reported. They are resins to which moieties of IDA (iminodiacetic acid), EDTA (ethylenediaminetetraacetic acid) and DTTA (diethylenetriaminetetraacetic acid), respectively, are linked. Resins with the latter two groups were prepared by copolymerization of the respective monomers with divinylbenzene (DVB) as a crosslinker. These monomers are m-dibromoethylstyrene and N,N-bis(2-aminoethyl)-p-aminoethylstyrene, respectively. The method of resin synthesis is described, from monomer synthesis to attachment of chelating groups on the copolymer matrix followed by after-treatment for each resin. Copolymerizability is estimated for meta- and para-isomers of DVB to enable assessment of the effect of crosslinks on chelate-forming capability of the IDA-type resin. The cation exchange capacity was found to be 4.3 meq/g for IDA-type, 35 meq/g for EDTA-type and 5.1 meq/g for DTTA-type, resins, respectively.     

Microfluidic-based DNA purification in a two-stage, dual-phase microchip containing a reversed-phase and a photopolymerized monolith

In this report, we show that a novel capillary-based photopolymerized monolith offering unprecedented efficiency (approximately 80%) for DNA extraction from submicroliter volumes of whole blood (Wen, J.; Guillo, C.; Ferrance, J. P.; Landers, J. P. Anal. Chem. 2006, 78, 1673-1681) can be translated to microfluidic devices. However, owing to the large mass of protein present in blood, both DNA binding capacity and extraction efficiency were significantly decreased when extraction of DNA was carried out directly from whole blood (38+/-1%). To circumvent this, a novel two-stage microdevice was developed, consisting in a C18 reversed-phase column for protein capture (stage 1) in series with a monolithic column for DNA extraction (stage 2). The two-stage, dual-phase design improves the capability of the monolith for whole blood DNA extraction by approximately 100-fold. From a 10-microL load of whole blood containing 350 ng of DNA, 99% (340+/-10 ng) traverses the C18 phase while approximately 70% (1020+/-45 ug) of protein is retained. A total of 240+/-2 ng of DNA was eluted from the second-stage monolith, resulting in an overall extraction efficiency of 69+/-1%. This provided not only an improvement in extraction efficiency over other chip-based DNA extraction solid phases but also the highest extraction efficiency reported to-date for such sample volumes in a microfluidic device. As an added bonus, the two-stage, dual-phase microdevice allowed the 2-propanol wash step, typically required to remove proteins from the DNA extraction phase for successful PCR, to be completely eliminated, thus streamlining the process without affecting the PCR amplifiability of the extracted DNA.     

Structure property relationship among novel dental composite matrix resins

Several novel dimethacrylate monomers of propoxylated diphenols have been synthesized to establish a correlation between their structure and the important properties of viscosity, curing shrinkage and wetting behaviour. These dimethacrylates were designed to possess linear and flexed structures. These new monomers exhibited very much lower viscosities compared to the conventionally used Bis-GMA. Good correlations were obtained for variations of the monomer structures with bulk viscosities and curing shrinkages. However, the wetting behaviour of these resins did not show any trend.     

Application of multifunctional base monomer to dental composite resins

Experimental composite resin systems were prepared with visible-light-cured multifunctional matrices to which various amounts of organic composite filler were added. In comparison with the unfilled resins, the filled resin systems were tested for Knoop hardness, compressive and diametral tensile tests, thermal properties, and water sorption. Analyses of the results obtained for the unfilled resins indicate that the increased hardness and mechanical strength were dependent on the multifunctional base monomer. The effective composite resin system was the one that was filled with organic composite filler in the multifunctional comonomer having triethylene glycol dimethacrylate as a diluent monomer.     

Amphoteric ion-exchange resins containing sulfonic acid groups from polyepichlorohydrin

The result of heating crosslinked polyepichlorohydrin (PECH) with sodium sulfite in water depends on which of two competing reactions is more important. The competing reactions are either chain cleavage, which produces water-soluble material, or nucleophilic displacement of the chloro groups to form sulfonic acid groups. With dithiol-crosslinked PECH chain cleavage is the predominant reaction to give water-soluble polymers. In contrast, the main reaction of diamine-crosslinked PECH with sodium sulfite is one which produces crosslinked resins containing sulfonic acid groups. Only a very small number of amino groups are needed in the crosslinked PECH to facilitate the latter reaction in which the covalently bound amino group acts as a covalently bound phase transfer catalyst. It is necessary for the phase transfer catalyst to be covalently bound because the use of phase transfer catalysts such as tetrabutylammonium iodide results in chain cleavage of dithiol-crosslinked PECH. Since some amino groups must be present in the crosslinked PECH to avoid chain cleavage, reaction with sulfite produces amphoteric resins. The formation of salt structures between the amino and sulfonic acids groups was demonstrated but it could not be determined whether they contributed to the degree of crosslinking.     

Water sorption and water-induced molecular mobility in dental composite resins

Water sorption in two resin composites, Kulzer's Solitaire (S) and SDI's Wave (W), and in a polyacid-modified composite resin, 3M's F2000 (compomer F), was investigated by means of equilibrium sorption isotherms (ESI) and of dynamic sorption (DS) measurements. Molecular mobility in these materials was studied by means of dielectric relaxation spectroscopy (DRS) and of thermally stimulated depolarization currents (TSDC) measurements. The results of ESI measurements show that at equilibrium, water is molecularly distributed in the materials and the effects of hydrophilic sites and clustering are negligible. Hysteresis effects in sorption–desorption cycles are larger in the resin composites than in the compomer. Equilibrium water uptakes in both ESI and DS conditions are rather low, in the range 1–2%. Diffusion coefficients of water are about 1×10^–8 cm²/s in the resin composites and by a factor of about 2 smaller in the compomer. Molecular mobility increases with hydration, as suggested by preliminary DRS and TSDC measurements. Detailed dielectric measurements may give important information for understanding, at the molecular level, water-induced degradation in dental materials.     

Structural studies on an ORMOCER system containing zirconium

The modified precursor Zr( ⁿ OPr)₃OOMc (McOOH=methacrylic acid) has been successfully used to synthesize organically modified ceramics (ORMOCERs) via a sol-gel process and via ultraviolet (u.v.) curing. The precursor and the ORMOCERs were investigated by the measurement of X-ray absorption fine structure (XAFS) and by electron microscopy. A model for the structure of the precursor is proposed. In the case of the inorganic synthesis of the ORMOCER, a first indication of a bond of the type Zr-O-Si was found.     

Aging effect of pH on the mechanical and tribological properties of dental composite resins

This study evaluated the microhardness and wear behavior alterations of dental resins exposed to strong acid and alkaline degradation regimens. Fifty specimens of AP-X, Z350, P60, VITA ZETA and VITA LC resins were distributed into 10 groups. The control group was not subjected to aging treatment, while the other nine groups were assigned to the following pH solutions: 1, 7 or 13 for 1, 13 or 20 d, respectively. Vickers microhardness and wear behavior of materials without aging served as the reference. Repeated measurements were conducted for other specimens. Scanning electron microscopy was used to observe the morphology. Data were analyzed by repeated-measures one-way ANOVA, followed by the least significant difference (LSD) t-test (P?≤?0.05) for multiple comparisons. The aging process was aggravated over time. Alkaline medium significantly decreased the microhardness and wear resistance of resins, and led to serious surface damage. AP-X, P60 and Z350 immersed in different media showed a lower degradation than the nanoresin. The mechanical degradation of resin composites was aggravated with increased aging time. Strong alkaline media induced the largest reduction in mechanical and tribological properties. Hybrid resin composites with high filler loading exhibited better mechanical performance than nanoresins with low filler loading under different pH conditions.     

Synthesis and characterization of a novel dimethacrylate based on adamantane as possible dental resins

In this study a novel dimethacrylate based on adamantine (AB-GMA) was synthesized and proposed as possible dental monomers for dental resin mixtures. The monomer was prepared by the reaction of glycidyl methacrylate with dicarboxylic acid ester obtained from adamantanediol and maleic anhydride. The addition reaction of glycidyl methacrylate and the acidic compound was carried out in the presence of basic catalyst—tetraethylammonium bromide. AB-GMA was copolymerized with TEGDMA by varying the curing conditions: monomer composition, photoinitiator concentration and light intensity. A Real-time FTIR technique was employed to monitor the double bond conversion and the rate of polymerization. The prepared polymers were also subjected to dynamic mechanical studies (DMA). AB-GMA exhibited high degree of double bond conversion (up to 77%) and its thermo-mechanical properties were better than those of the commonly known dimethacrylates. AB-GMA showed no cytotoxicity toward growth of L929 cells and had good in vitro biocompatibility.     

Structural analysis of sodium silicate glasses containing TiO2 by pulsed neutron scattering

By the use of the time-of-flight pulsed neutron total-scattering spectrometer HIT at the Japanese National Laboratory for High Energy Physics, measurement of structure factorsS(Q) for glasses of type 10Na₂O·(90–x)SiO₂·xTiO₂ (x=0, 5 and 20 mol%) was made over a wide range of scattering vectors up toQ (=4 sin/) ~ 500 nm^–1. High-resolution real-space information was obtained from the Fourier transform ofS(Q). The influence of TiO₂ on the nearest-neighbour Si-O bond length of the silicate anions existing in the glass samples studied is different from that of alkali oxides such as Na₂O. It is concluded that most of the Ti⁴⁺ ions predominantly substitute for Si⁴⁺ ions in their tetrahedrally coordinated sites, leading to the formation of TiO₆ octahedra.     

纳米技术在牙科复合树脂改良中的应用

以牙科复合树脂现存缺点为背景,对纳米技术对复合树脂的改良情况进行了研究,着重讨论了纳米材料对复合树脂的聚合收缩、抗菌性能和机械性能改良的一系列问题。研究结果表明,使用纳米技术和材料可以很好地改进复合树脂多方面的性能,同时对复合树脂的发展方向和研究前景进行了展望。     

Effect of structure on thermal behaviour of phosphorus containing addition polyimides and epoxy resins

Addition polyimides, [e.g. endo-5-norbornene-2.3-dicarboximide(nadimides), maleimides etc.] and epoxy resins have been used extensively in the past as matrix resins for advanced fiber-reinforced composites. However, inadequate flame resistance and thermal stability of these resins is one of their serious limitations. Our earlier studies have shown excellent flame resistance properties of addition polyimides based on bis(3-aminophenyl) methyl phosphine oxide (B) or tris(3-aminophenyl) phosphine oxide (T). Carbon fiber reinforced composites based on such matrix resin did not burn even in pure oxygen. In order to investigate the effect of weight percent of phosphorus on thermal behaviour and flame resistance, a series of addition polyimides and epoxy resins were prepared using B, T and amide-amines. The effect of structure on curing behaviour of resins and thermal and flame resistance of cured resins was evaluated. The results demonstrate an improvement in char yield of resins containing higher weight percent of phosphorus. Received: 6 November 2000 / Reviewed and accepted: 7 November 2000