CO2 laser-irradiation through topically applied fluoride increases acid resistance of demineralised human enamel in vitro

PURPOSE: To evaluate the effect of CO2 laser treatment through topically applied amine fluoride solution on demineralised enamel. MATERIALS AND METHODS: Sixty extracted human molar crowns were selected and cut longitudinally into half. One half was subjected to a 10-day pH-cycling procedure to create caries-like lesions, whereas the other was left non-demineralised. The following treatments were randomly assigned (one treatment per tooth, on respective non-demineralised and demineralised matched specimens): exposure to a 1% amine fluoride solution for 15 s without irradiation (group I), irradiation for 15 s with a continuous-wave CO2 laser (group II), or laser-treatment for 15 s through the amine fluoride solution applied immediately beforehand (group III). Fluoride uptake (n = 30) and acid resistance (n = 30) were determined after treatment. Enamel surface alterations after laser irradiation were monitored using scanning electron microscopy. RESULTS: In groups I and III, an increased fluoride uptake was detected (p < or = 0.05). Laser irradiation through topical fluoride resulted in an increased acid resistance of sound and demineralised enamel specimens in deeper layers (p < or = 0.05). In addition, less surface alterations were observed in SEM examination of specimens irradiated through the amine fluoride solution compared with counterparts treated with laser only. CONCLUSIONS: CO2 laser light application through an amine fluoride solution may be instrumental in enhancing acid resistance of sound and demineralised enamel.

Temporary scaffolding of coronary arteries with bioabsorbable magnesium stents: a prospective, non-randomised multicentre trial

BACKGROUND: Coronary stents improve immediate and late results of balloon angioplasty by tacking up dissections and preventing wall recoil. These goals are achieved within weeks after angioplasty, but with current technology stents permanently remain in the artery, with many limitations including the need for long-term antiplatelet treatment to avoid thrombosis. We report a prospective multicentre clinical trial of coronary implantations of absorbable magnesium stents. METHODS: We enrolled 63 patients (44 men; mean age 61.3 [SD 9.5 years]) in eight centres with single de novo lesions in a native coronary artery in a multicentre, non-randomised prospective study. Follow-up included coronary angiography and intravascular ultrasound at 4 months and clinical assessment at 6 months and 12 months. The primary endpoint was cardiac death, non-fatal myocardial infarction, or clinically driven target lesion revascularisation at 4 months FINDINGS: 71 stents, 10-15 mm in length and 3.0-3.5 mm in diameter, were successfully implanted after pre-dilatation in 63 patients. Diameter stenosis was reduced from 61.5 (SD 13.1%) to 12.6 (5.6%) with an acute gain of 1.41 mm (0.46 mm) and in-stent late loss of 1.08 mm (0.49 mm). The ischaemia-driven target lesion revascularisation rate was 23.8% after 4 months, and the overall target lesion revascularisation rate was 45% after 1 year. No myocardial infarction, subacute or late thrombosis, or death occurred. Angiography at 4 months showed an increased diameter stenosis of 48.4 (17.0%). After serial intravascular ultrasound examinations, only small remnants of the original struts were visible, well embedded into the intima. Neointimal growth and negative remodelling were the main operating mechanisms of restenosis. INTERPRETATION: This study shows that biodegradable magnesium stents can achieve an immediate angiographic result similar to the result of other metal stents and can be safely degraded after 4 months. Modifications of stent characteristics with prolonged degradation and drug elution are currently in development.

Influence of the magnesium aspartate hydrochloride administration to the maternal circuit on the aspartate concentration of the fetal circuit under in vitro perfusion of human placenta

OBJECTIVES: Magnesium aspartate hydrochloride (Magnesiocard, Mg-Asp-HCl) is proposed as a substitute of magnesium sulfate for the treatment of preeclampsia and premature labor. After an i.v. administration of a dose equivalent to that used in the treatment of preeclampsia to nonpregnant volunteers, a 10-fold increase of aspartic acid (Asp) over the physiological level was observed. Animal experiments have demonstrated that highly increased fetal levels of acidic amino acids such as Asp could be associated with neurotoxic damage in the fetal brain. The influence of such an elevation of Asp concentration in the maternal circuit on the fetal level, using the in vitro perfusion model of human placenta, was investigated. STUDY DESIGN: After a control phase (2h), a therapeutic dose of Mg combined with Asp (Magnesiocard, Mg-Asp-HCl) was applied to the maternal circuit approaching 10 times the physiological level of Asp. The administration was performed in two different phases simulating either a peak of maximum concentration (bolus application, 2h) or a steady state level (initially added, 4h). RESULTS: In four experiments, during experimental phases (6h) a slow increase in concentration in the fetal circuit was seen for Mg, AIB (alpha-aminoisobutyric acid, artificial amino acid) and creatinine confirming previous observations. In contrast, no net transfer of Asp across the placenta was seen. A continuous decrease in the concentration of Asp on both maternal and fetal side suggests active uptake and metabolization by the placenta. Viability control parameters remained stable indicating the absence of an effect on placental metabolism, permeability and morphology. CONCLUSION: Elevation of Asp concentration up to 10 times the physiological level by the administration of Mg-Asp-HCl to the maternal circuit under in vitro perfusion conditions of human placenta has no influence on the fetal level of Asp suggesting no transfer of Asp from the maternal to fetal compartment. Therefore, the administration of Mg-Asp-HCl to preeclamptic patients would be beneficial for the patients without any impact on placental or fetal physiology.

EVALUATION OF MAGNESIUM AS A HALL THRUSTER PROPELLANT

In this study, the use of magnesium as a Hall thruster propellant was evaluated. A xenon Hall thruster was modified such that magnesium propellant could be loaded into the anode and use waste heat from the thruster discharge to drive the propellant vaporization. A control scheme was developed, which allowed for precise control of the mass flow rate while still using plasma heating as the main mechanism for evaporation. The thruster anode, which also served as the propellant reservoir, was designed such that the open area was too low for sufficient vapor flow at normal operating temperatures (i.e. plasma heating alone). The remaining heat needed to achieve enough vapor flow to sustain thruster discharge came from a counter-wound resistive heater located behind the anode. The control system has the ability to arrest thermal runaway in a direct evaporation feed system and stabilize the discharge current during voltage-limited operation. A proportional-integral-derivative control algorithm was implemented to enable automated operation of the mass flow control system using the discharge current as the measured variable and the anode heater current as the controlled parameter. Steady-state operation at constant voltage with discharge current excursions less than 0.35 A was demonstrated for 70 min. Using this long-duration method, stable operation was achieved with heater powers as low as 6% of the total discharge power. Using the thermal mass flow control system the thruster operated stably enough and long enough that performance measurements could be obtained and compared to the performance of the thruster using xenon propellant. It was found that when operated with magnesium, the thruster has thrust ranging from 34 mN at 200 V to 39 mN at 300 V with 1.7 mg/s of propellant. It was found to have 27 mN of thrust at 300 V using 1.0 mg/s of propellant. The thrust-to-power ratio ranged from 24 mN/kW at 200 V to 18 mN/kW at 300 volts. The specific impulse was 2000 s at 200 V and upwards of 2700 s at 300 V. The anode efficiency was found to be ~23% using magnesium, which is substantially lower than the 40% anode efficiency of xenon at approximately equivalent molar flow rates. Measurements in the plasma plume of the thruster—operated using magnesium and xenon propellants—were obtained using a Faraday probe to measure off-axis current distribution, a retarding potential analyzer to measure ion energy, and a double Langmuir probe to measure plasma density, electron temperature, and plasma potential. Additionally, the off axis current distributions and ion energy distributions were compared to measurements made in krypton and bismuth plasmas obtained in previous studies of the same thruster. Comparisons showed that magnesium had the largest beam divergence of the four propellants while the others had similar divergence. The comparisons also showed that magnesium and krypton both had very low voltage utilization compared to xenon and bismuth. It is likely that the differences in plume structure are due to the atomic differences between the propellants; the ionization mean free path goes down with increasing atomic mass. Magnesium and krypton have long ionization mean free paths and therefore require physically larger thruster dimensions for efficient thruster operation and would benefit from magnetic shielding.

Magnesium - Tellurium by Powder Methods

Today considerable work is being done in the compressed metal powder field which is gradually ob­taining prominence as a valuable branch of metallurgy. The mass of data, however, has led to many different ideas on the results of sintering.

The Age-Hardening of Magnesium with Aluminum and Zinc

Magnesium is one of the most active elements and forms oxides, nitrides, and carbides, but not hydrides. Due to its activity, low melting point, low strength when unalloyed, and the difficulty with which it is worked, magnesium has not been and is not at present well developed.

Zinc Plating Magnesium

Magnesium and magnesium alloys are becoming more and more important in modern industry. Their use in the aviation industry has been greatly curtailed because of their comparatively poor resistance to corrosion especially in moist atmospheres. Many methods have been adopted to improve their resistance to corrosion.

Electroplating of Chromium upon a Nickel Plated Magnesium Alloy

A nickel plating operation for magnesium alloys was investigated and proved successful in plating a small sample of a typical commercial magnesium alloy, Dowmetal J1.

The Effect of Manganese and Magnesium on the Hardening of Copper-Aluminum Alloys

During recent years, duralumin and all aluminum alloys have been made the object of much discussion regarding their hardening mechanism. The commercial success of nearly all of the alloys of aluminum and mag­nesium is dependent on their ability to age or precipitation harden.

Early- and long-term intravascular ultrasound and angiographic findings after bioabsorbable magnesium stent implantation in human coronary arteries

OBJECTIVES: This study aimed to evaluate the degradation rate and long-term vascular responses to the absorbable metal stent (AMS). BACKGROUND: The AMS demonstrated feasibility and safety at 4 months in human coronary arteries. METHODS: The PROGRESS-AMS (Clinical Performance and Angiographic Results of Coronary Stenting) was a prospective, multicenter clinical trial of 63 patients with coronary artery disease who underwent AMS implantation. Angiography and intravascular ultrasound (IVUS) were conducted immediately after AMS deployment and at 4 months. Eight patients who did not require repeat revascularization at 4 months underwent late angiographic and IVUS follow-up from 12 to 28 months. RESULTS: The AMS was well-expanded upon deployment without immediate recoil. The major contributors for restenosis as detected by IVUS at 4 months were: decrease of external elastic membrane volume (42%), extra-stent neointima (13%), and intra-stent neointima (45%). From 4 months to late follow-up, paired IVUS analysis demonstrated complete stent degradation with durability of the 4-month IVUS indexes. The neointima was reduced by 3.6 +/- 5.2 mm(3), with an increase in the stent cross sectional area of 0.5 +/- 1.0 mm(2) (p = NS). The median in-stent minimal lumen diameter was increased from 1.87 to 2.17 mm at long-term follow-up. The median angiographic late loss was reduced from 0.62 to 0.40 mm by quantitative coronary angiography from 4 months to late follow-up. CONCLUSIONS: Intravascular ultrasound imaging supports the safety profile of AMS with degradation at 4 months and maintains durability of the results without any early or late adverse findings. Slower degradation is warranted to provide sufficient radial force to improve long-term patency rates of the AMS.

Tin-containing fluoride solutions as anti-erosive agents in enamel: an in vitro tin-uptake, tissue-loss, and scanning electron micrograph study

Tin-containing fluoride solutions can reduce erosive tissue loss, but the effects of the reaction between tin and enamel are still not clear. During a 10-d period, enamel specimens were cyclically demineralized (0.05 M citric acid, pH 2.3, 6 x 5 min d(-1)) and remineralized (between the demineralization cycles and overnight). In the negative-control group, no further treatment was performed. Three groups were treated (2 x 2 min d(-1)) with tin-containing fluoride solutions (400, 1,400 or 2,100 ppm Sn2+, all 1,500 ppm F-, pH 4.5). Three additional groups were treated with test solutions twice daily, but without demineralization. Tissue loss was determined profilometrically. Energy-dispersive X-ray spectroscopy was used to measure the tin content on and within three layers (10 mum each) beneath the surface. In addition, scanning electron microscopy was conducted. All test preparations significantly reduced tissue loss. Deposition of tin on surfaces was higher without erosion than with erosion, but no incorporation of tin into enamel was found without demineralization. Under erosive conditions, both highly concentrated solutions led to the incorporation of tin up to a depth of 20 mum; the less-concentrated solution led to small amounts of tin in the outer 10 mum. The efficacy of tin-containing solutions seems to depend mainly on the incorporation of tin into enamel.

In situ fluoride retention and remineralization of incipient carious lesions after the application of different concentrations of fluoride

Limited information is available on the time-dependent or dosage-dependent cariostatic efficacy of highly concentrated fluoride compounds. This good clinical practice-conforming, double-blind, placebo-controlled, crossover in situ study tested the hypothesis that a 1.0% amine fluoride fluid is superior to a 0.5% amine fluoride fluid regarding fluoride retention and mineral change in initial caries enamel lesions over a period of 28 d. Fluoride retention was significantly higher after application of the two fluoride fluids compared with placebo but had decreased in both groups to similar levels after only 1 wk. Mineral gain was significantly higher for both verum groups compared with placebo. The use of 1% fluoride fluid resulted in significantly higher remineralization compared with the use of 0.5% fluoride fluid. For both fluoride fluids mineral gain followed a linear relationship with time during the experimental period, indicating a possible further uptake of mineral, even after 4 wk.