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.     

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.     

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.     

An investigation into the crack propagation behaviour of tooth-coloured particulate-filled dental restorative materials

Particulate-filled resins, or dental composites, are being increasingly used to restore the load-bearing surfaces of teeth. If these restorations are not to fracture in service, and if improvements are to be made, an understanding of the fracture behaviour of these materials is essential. The fracture parameter used is the stress intensity factor at crack instability (K _IC). This has been calculated using the double torsion test in an Instron universal testing machine. The fracture behaviour was studied by varying the amount of filler (7, 15, 26 and 41 vol %); the surface treatment of the filler (coated or uncoated); the environment (air or water); and the crosshead rate (0.05, 0.5, 5 and 50 mm min^–1). Fracture was found to occur in either a continuous or stick-slip manner. The stick-slip behaviour was due to blunting of the crack tip, which was controlled by the yield behaviour. If there was no significant blunting, continuous crack growth occurred. A unique fracture criterion was shown to apply, which was that a critical stress of approximately three and a half times the yield stress must be obtained at a critical distance ahead of the crack tip.[/p]     

The role of the ionomer glass component in polyacid-modified composite resin dental restorative materials

In order to model the processes that occur within polyacid-modified composite resin ("compomer") dental restoratives, a series of experiments has been carried out with silanated and silane-free ionomer glass G338, and silanated and silane-free unreactive glass (Raysorb T-4000). In an acid-base reaction with dental grade aqueous maleic acid-acrylic acid copolymer solution, the setting time of the silanted G338 was found to be 9 min, compared with 5 min for the silane-free glass. Inclusion of each glass in an experimental composite resin system showed that the formulations which contained G338 absorbed more water than the formulations which contained Raysorb T-4000, regardless of whether or not the glass was silanted. Biaxial flexure strength was superior for experimental composites containing Raysorb T-4000, with highest results being obtained with the silanated glass. Overall these results demonstrate that silanation of the filler is essential for optimal physical properties but that, for the ionomer glass, it inhibits the acid-base reaction. The presence of ionomer glass led to an increase in water uptake compared with the unreactive glass, regardless of the presence of silane.     

Combined effect of staining substances on the discoloration of esthetic Class V dental restorative materials

The purpose of this study was to determine the combined effect of an organic substance (mucin as a substitute for salivary organic substances), chlorhexidine, and an iron compound/tea solution on the changes in the color of esthetic Class V dental restorative materials. Color of a glass ionomer, resin-modified glass ionomer, compomer and flowable resin composite of A2 shade, respectively, was determined according to the CIELAB color scale relative to the standard illuminant D65. Color was measured at baseline, and after sequential immersion in the following substances: Step-1, mucin in PBS (MCP) for 48 h; Step-2, chlorhexidine (CHX) for 24 h; Step-3, iron compound (IRN) or tea solution (TEA) up to 7 days; and Step-4, ultrasonic cleaning for 1 h. Color change (ΔE _ab *) was calculated by the equation: Δ E _ab* = [(Δ L*)² + (Δ a*)² + (Δ b*)²]^1/2, of which ΔL ^∗ indicates changes in value, Δa ^∗ indicates changes in red-green parameter and Δb ^∗ indicates changes in yellow-blue parameter. Δ E _ab* values after immersion in MCP and CHX were compared, and Δ E _ab* values after immersion in IRN or TEA, and subsequent ultrasonic cleaning were compared with respect to the restorative material and immersion substance. Δ E _ab* and changes in the color parameters (ΔL ^∗, ΔC _ab* and ΔH _ab*) were analyzed by repeated measures, analysis of variance and a post-hoc test at the 0.05 level of significance. Color changes after immersion in MCP were acceptable (Δ E _ab* < 3.3), and those after immersion in CHX were generally acceptable. The range of Δ E _ab* values after immersion in IRN was 3.1–19.6, and that after ultrasonic cleaning was 2.4–9.6. The range of Δ E _ab* values after immersion in TEA was 10.7–21.1, and that after ultrasonic cleaning was 11.9–14.5. Color changes of four Class V restorative materials after combined treatment with mucin, chlorhexidine and an iron compound/tea solution were not acceptable. Colors did not recover to their original values after ultrasonic cleaning. Modifications on the surface of a restoration should be considered to reduce stain accumulation.     

Dynamic study of ion etching in a high resolution SEM

On-line studies of surface topographical development have been made by mounting a saddle-field ion source into a standard scanning electron microscope. Preliminary results obtained during operation in both dynamic and static modes are presented.     

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.     

Fabrication of nano-scale phase change materials using nanoimprint lithography and reactive ion etching process

Phase change random access memory (PRAM) is one of the most promising non-volatile memories due to its ability to store digital data in the form of crystalline and amorphous phases of phase change materials. As a phase change material, Ge₂Sb₂Te₅ (GST225) is usually used, due to its reversible phase transition capability with speeds of less than 100 ns between the crystalline and amorphous phases. In order to fabricate highly integrated PRAM devices, sub micron- to nanometer-sized patterning of GST225 layer must be accomplished. In this study, 70 nm-sized polymer patterns were fabricated using partial filling nanoimprint lithography (NIL) on a GST225 layer, which was deposited by RF sputtering. Then GST225 was etched using Ar/Cl₂ plasma with an ICP etcher. Etch conditions, including Cl₂ concentration, were optimized to obtain the vertical etch profile of the GST patterns.     

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.     

Supramolecular polymer materials bring restorative heart valve therapy to patients

The functional restoration of natural tissues in a variety of cardiovascular applications is the main objective of Endogenous Tissue Restoration (ETR). The recent progress in the development of biocompatible, biodegradable, and tunable biomaterials with unprecedented properties allow the next steps from laboratory studies to clinical studies. The independent control over mechanical properties and biodegradability provided by the combination of covalent and non-covalent bonds makes supramolecular polymers uniquely qualified for ETR. This paper will provide further details on the mechanism of ETR and will provide a perspective on the preclinical and clinical application of supramolecular polymers for ETR. In addition to various reports on chronic studies in large animal models, three world-first clinical studies are reported, demonstrating the potential of supramolecular technology in bringing ETR to patients.     

An improved form of the oscillating electron electrostatic ion source for ion etching

The performance of the oscillating electron electrostatic ion source has been improved by incorporating a small chimney into the ion exit aperture to reduce the field distortion at the aperture. A focussing electrode placed near the aperture, and at a negative potential with respect to the cathode, has also been added. This increases the ion beam intensity and also increases the total ion beam current by extracting more low energy ions from the source. When the source is used for ion etching, the specimen can be placed at some distance from the source to reduce the heating of the specimen by radiation from the source. Using argon ions, etching rates of copper film of more than 10 μm^?1 h have been observed with this improved source. It has also been found that the ion beam contains electrons which are suppressed with the focusing electrode at more than 100 V. Thus it was found that to satisfactorily etch a glass specimen it was necessary to operate with the focussing electrode at cathode potential to avoid the build up of charges on the glass.     

Science of dry etching of III-V materials

A review is given of dry etching of III-V semiconductors. Gas chemistries based on chlorine have traditionally been used for plasma etching of these materials due to the volatilities of both group III and group V chlorides. Recent work on the use of iodine- or bromine-based discharges has shown promising results, although the corrosiveness of the feedstock gases is of concern. For indium-containing III-V semiconductors, CH₄/H₂ plasmas have produced smooth anisotropic etching at relatively low rates. In applications requiring etch rates near 1 m min^–1, Cl₂/CH₄/H₂ electron cyclotron resonance discharges have proved effective. Examples are given of the structural and chemical changes induced in the semiconductor as a result of dry etching, due to the combined effects of energetic ion bombardment and preferential removal of one of the lattice constituents. Applications for dry etching in modern microelectronic fabrication range from shallow (30 nm) mesa formation to creation of through-wafer via holes typically 100 m deep.     

离子束刻蚀机的电源系统

离子束刻蚀机的性能,除主机外,在很大程度上取决于供电电源系统。为了提高离子束刻蚀机整机工作的稳定性,在以往的配套电源的基础上,研制了一套电源系统,用于离子束刻蚀机中。整机工作稳定度达±0.8%/h,每次连续刻蚀器件8h以上,连续运转3年多,电源系统稳定可靠。是国内离子束刻蚀机电源系统性能较好的供电电源系统。     

The localized gas discharge etching of materials

It is demonstrated that a gas discharge can be localized between separate elements on the surface of electrodes with a preset geometry. The main characteristics of the localized discharge have been studied and the forms of this discharges are established. Using the localized discharge in a fluorine-containing gas medium, size-controlled etching of silicon and silicon dioxide with a resolution of 100 μm was performed without mask application.     

Electrochemical etching of highT c superconducting materials

HighT _c superconductor materials of yttrium barium copper oxide (YBCO) have been etched by a new electrochemical technique. In this technique, acids like hydrochloric, nitric and phosphoric have been used as an electrolyte and etching has been achieved with acid dilutions as high as 1:200 with water. It is observed that rapid and controlled etching is possible by this technique.