Phosphopolyoxomolybdate absorbed on lipid membranes/carbon nanotube electrode

Carbon nanotube (CNT) electrode was selected to support lipid membranes. From electrochemical impedance results, lipid membranes of didodecyldimethylammonium bromide (DDAB) were identified to be formed on CNT electrode. Phosphopolyoxomolybdate (P₂Mo₁₈) was immobilized on DDAB modified CNT electrode through electrostatic adsorption and the properties of P₂Mo₁₈ were investigated by cyclic voltammetry (CV), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Additionally, CNT/DDAB/P₂Mo₁₈ electrode shows good stability in strong acidic medium (0.5 M H₂SO₄) and excellent electrocatalytic ability for the reduction of bromate and nitrite.     

BisGMA/TEGDMA dental composite containing high aspect-ratio hydroxyapatite nanofibers

Objectives

The objectives of this study are to investigate the properties of high aspect-ratio hydroxyapatite (HAP) nanofibers and the reinforcing effect of such fibers on bisphenol A glycidyl methacrylate (BisGMA)/triethylene glycol dimethacrylate (TEGDMA) dental resins (without silica microparticle filler) and dental composites (with silica microparticle filler) with various mass fractions (loading rates).

Methods

HAP nanofibers were synthesized using a wet-chemical method and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and thermal gravimetric analysis (TGA). Biaxial flexural strength (BFS) of the HAP nanofibers reinforced dental resins without any microsized filler and dental composites with silica microparticle filler was tested and analysis of variance (ANOVA) was used for the statistically analysis of acquired data. The morphology of fracture surface of tested dental composite samples was examined by SEM.

Results

The HAP nanofibers with aspect-ratios of 600 to 800 can be successfully fabricated with a simple wet-chemical method in aqueous solution. Impregnation of small mass fractions of the HAP nanofibers (5 wt% or 10 wt%) into the BisGMA/TEGDMA dental resins or impregnation of small mass fractions of the HAP nanofibers (2 wt% or 3 wt%) into the dental composites can substantially improve the biaxial flexural strength of the resulting dental resins and composites. A percolation threshold of HAP nanofibers, beyond which more nanofibers will no longer further increase the mechanical properties of dental composites containing HAP nanofibers, was observed for the dental composites with or without silica microparticle filler. Our mechanical testing and fractographic analysis indicated that the relatively good dispersion of HAP nanofibers at low mass fraction is the key reason for the significantly improved biaxial flexural strength, while higher mass fraction of HAP nanofibers tends to lead to bundles that cannot effectively reinforce the dental resins or composites and may even serve as defects and thus degrade the resulting dental resin and composite mechanical properties.

Significance

The incorporation of small mass fraction of HAP nanofibers with good dispersion can improve the mechanical property of dental resins and dental composites.     

可切削复合树脂材料磨损性能的研究

目的：研究可切削复合树脂材料与天然牙釉质磨损性能的匹配情况。方法在微摩擦磨损实验机上,模拟口腔力学和化学环境,以三种新型的可切削复合树脂材料( Upcera 复合树脂、Lava Ultimate、High-Class)为研究对象,天然牙釉质为对磨物。实验前,用激光共聚焦显微镜测试试件表面粗糙度Sa,实验后,激光共聚焦下观察可切削复合树脂试件的磨斑形貌、测量其磨斑面积及对磨物牙釉质的磨斑宽度,扫描电镜下观察试件磨斑的微观形貌。采用单因素方差分析进行统计学分析。结果牙釉质的磨斑面积和磨斑宽度大于其他三种可切削复合树脂材料(P<0.05)。结论与牙釉质相比,三种可切削复合树脂具有更佳的耐磨性及较低的对磨物磨损。     

Mechanical properties of dental resin/composite containing urchin-like hydroxyapatite

ObjectivesTo investigate the reinforcing effect of urchin-like hydroxyapatite (UHA) in bisphenol A glycidyl methacrylate (Bis-GMA)/triethylene glycol dimethacrylate (TEGDMA) dental resin (without silica nanoparticles) and dental composites (with silica nanoparticles), and explore the effect of HA filler morphologies and loadings on the mechanical properties.MethodsUHA was synthesized by a facile method of microwave irradiation and studied by X-ray diffraction (XRD), scanning electron microscope (SEM), and thermogravimetric analysis (TGA). Mechanical properties of the dental resin composites containing silanized UHA were tested by a universal mechanical testing machine. Analysis of variance was used for the statistical analysis of the acquired data. The fracture morphologies of tested composites were observed by SEM. Composites with silanized irregular particulate hydroxyapatite (IPHA) and hydroxyapatite whisker (HW) were prepared for comparative studies.ResultsImpregnation of lower loadings (5 wt% and 10 wt%) of silanized UHA into dental resin (without silica nanoparticles) substantially improved the mechanical properties; higher UHA loadings (20 wt% and 30 wt%) of impregnation continuously improved the flexural modulus and microhardness, while the strength would no longer be increased. Compared with silanized IPHA and HW, silanized UHA consisting of rods extending radially from center were embedded into the matrix closely and well dispersed in the composite, increasing filler-matrix interfacial contact area and combination. At higher filler loadings, UHA interlaced together tightly without affecting the mobility of monomer inside, which might bear higher loads during fracture of the composite, leading to higher strengths than those of dental resins with IPHA and HW. Besides, impregnation of silanized UHA into dental composites (with silica nanoparticles) significantly improved the strength and modulus.SignificanceUHA could serve as novel reinforcing HA filler to improve the mechanical properties of dental resin and dental composite.     

Low-shrinkage composite for dental application

In modern research, development of monomers that reduce shrinkage of composite materials remains an ongoing quest and perennial challenge. The purpose of this study, therefore, was to analyze the shrinkage behaviour of an innovative composite material for dental restorations based on a monomer with a new chemical formulation, known as silorane. To this end, shrinkage stress development during curing, gel point, and coefficient of near linear fit of contraction stress/time were evaluated after polymerizing the material with 10 different curing regimes. Shrinkage stress varied between 1.4 MPa after a 10-second curing in a pulsed regime to 4.4 MPa after curing for 40 seconds with a high energy curing unit, Bluephase. Pearson correlation analysis showed that with respect to the tested curing units, shrinkage stress correlated significantly with energy density (0.89), irradiance (0.70), curing time (0.51), coefficient of near linear fit of contraction (0.70), and gel point (-0.60). Silorane exhibited low shrinkage stress values in comparison to regular methacrylate composites. Nevertheless, stress due to thermal contraction when the light exposure ended was not negligible-but could be reduced by applying the appropriate curing strategy.     

Experimental study on the Biomaterial/Porous Titanium composite dental implants]

This study investigated the tissue compatibility of bone morphogenetic protein (BMP) /biologic ceramic/porous titanium implant,BMP/porous titanium implant,biologic ceramic/porous titanium implant and porous titanium implant by LM,SEM,EDXA.The results showed that the new bone formation and new bone mature were earlier in the BMP composite implants treated group.BMP uncomposite implants had no evident difference in the time of new bone formation, but the interface bonding ways had significant difference.     

纳米晶羟基磷灰石复合胶原材料在拔牙创修复中的作用

目的:探讨纳米晶羟基磷灰石复合胶原材料(nHAC)在拔牙创修复中的作用。方法:拔除12只成年狗两侧下颌第二及第三切牙,并去除牙槽间隔,一侧随即植入nHAC,对侧植入致密多晶羟基磷灰石微粒人工骨(HA)作为对照。于植入后4、8、12周分别取材,采用99mTc MDP核素骨显像、组织学观察、图像分析等方法比较两种植入材料在牙槽窝中的骨修复能力。结果:nHAC植入牙槽骨后,材料被逐渐降解吸收,新骨不断生成,12周后植入材料几乎完全被成熟的骨组织取代;图像分析结果显示不同时间nHAC组新骨形成的比值显著高于HA组(P<0.01);4、8、12周nHAC组浓聚程度均高于HA组。结论:nHAC在修复拔牙创缺损时比HA效果更好,是一种较为理想的骨替代材料。     

Fatigue behaviour of dental composite materials

Objective

The intent of the project was to evaluate the fatigue behavior of particle and fiber filled dental composites that are fabricated either directly or indirectly using a notched specimen with respect to the number of cycles until failure.

Methods

The materials were five dental composites, three normally cured in the oral cavity (Restolux, Renew and Filtek Supreme), direct processing, and two laboratory produced (BelleGlass, and Tescera), indirect processing. The specimens were 3 mm × 3 mm × 25 mm bars with a 0.75 or 1.0 mm notch in the mid-span of the bars, polished with 320 grit SiC paper and aged for 6 months in air, distilled water, artificial saliva, and a 50/50 mixture of ethanol and distilled water. Testing was performed with a stress mean range of 5–49 MPa, the maximum number of cycles was 100,000, and the number of cycles to failure was recorded.

Results

For the specimens that failed, BelleGlass, Restolux, and Tescera were able to withstand a higher cyclic loaded stress than Renew and Filtek. The 50/50 by volume mixture of water and ethanol resulted in the lowest resistance to fatigue for all materials.

Conclusions

Of the dental composite materials investigated, the indirect processed and those with large particle fillers (higher weight percent filler) had better cyclic fatigue resistance than micro- and nano-particle fillers (lower weight percent filler).     

Interfacial layer characterization in dental composite

Nowadays, dental resins find increasing use by practitioners. However, photopolymerization of such resins is limited to a so-called 'depth of cure'. To face this problem, dentists superimpose resin layers of limited depth. This technique raises the problem of the quality of interlayer. This paper aims at screening different cases of adhesion at the interface. Shear strength of such interfacial layers is tested in shear mode in various conditions (with or without an oxygen-inhibited layer, or contaminated by saliva or water). Unexpectedly, the presence of an oxygen-inhibition on the first layer, as assessed using micro-Raman spectroscopy, induces higher shear strength. In this case, a cohesive break occurs while an adhesive one is observed in all the other cases.     

碳纳米管-羟磷灰石复合材料研究进展

羟磷灰石有与生物骨相似的化学组成和晶体结构,作为骨种植材料备受关注。但它脆性大,力学性能欠佳,临床应用受到局限。近年来,碳纳米管因为具有高强度、高弹性模量、耐扭折等理想的机械性能,被用于羟磷灰石的加强。笔者拟对目前碳纳米管-羟磷灰石复合材料的合成方法和研究现状作一综述。     

A composite resin bonded to dental materials

Enamelite 500 will reattach a dislodged facing or orthodontic bracket and will serve as a veneer material over visible amalgam, gold, and nonprecious metals. Using this composite material as a veneer over metals and as a repair material can be a simple way to solve some esthetic problems.     

A fluoride-releasing composite for dental applications.

OBJECTIVES: The aim of this work was to attempt formulation of a dental composite, for investigational purposes, which will release fluoride at a rate comparable to glass ionomer materials, while retaining physical properties adequate for potential use in a number of dental applications. METHODS: An organic fluoride material, tetrabutylammonium tetrafluoroborate (TBATFB), was incorporated into a hydrophilic monomer system made of 2,2-bis[4-(2-hydroxy-3-methacroyloxypropoxy)phenyl]-propane (BisGMA) and 2-hydroxyethyl methacrylate (HEMA). This fluoride-containing monomer system was filled with silane treated quartz to 81 wt%. The resultant material was tested for fluoride release, physical strength properties and bond strength to enamel, each in comparison to control materials. RESULTS: Cumulative fluoride release from the experimental composite was approximately linear over time and comparable to glass ionomer materials. The long term rate of release exceeded several of the glass ionomer materials tested. Diametral tensile strength was comparable to resin-modified glass ionomer (RMGI) materials. Bond strength to etched enamel was statistically equivalent to a commercially available hybrid composite control. SIGNIFICANCE: The experimental resin-based composite material could potentially be used as an alternative to glass ionomer materials in non-stress bearing restorative applications and for orthodontic bracket bonding, where high fluoride release is desirable.     

Loss of substance of dental composite restorations

A method for the direct in vivo measuring of loss of substance of Class I and II restorations was tested. On models of the teeth involved, silver caps were made. The occlusal surface was relieved by a piece of tinfoil. With the silver cap, silicone impressions were made for baseline registration and also at 3 recall periods, 6, 12 and 18 months after baseline registration respectively. The average thickness of the loss of substance was computed by the weight, the density and the thickness of both the enclosed impression material and the piece of tinfoil. The results show the in vivo repeatability of the test method to be in good agreement with data obtained in a previous in vitro study. The error of the test method accounts only for a relatively small part of the total experimental variance (7, 9 and 12%). The wear values show that the method registers, with adequate accuracy, wear rates of approximately 20 μm/year. Because of its simplicity, inexpensiveness and accuracy, the method is highly productive and suitable for clinical screening tests of the wear behaviour of restorations, especially for the registration of losses of substance of posterior composites.