Post-gel shrinkage,elastic modulus,and stress generated by orthodontic adhesives

Objectives:To measure post-gel shrinkage, elastic modulus, and flexural strength of orthodontic adhesives and to predict shrinkage stress using finite element analysis (FEA).Materials and Methods:The following 6 orthodontic adhesives were tested: Transbond XT (3M Unitek, Monrovia, Calif), Transbond Plus Color Change (3M Unitek), Greengloo (Ormco, Brea, Calif), Ortho Connect (GC America, Alsip, Ill), Trulock (RMO, Denver, Colo), GoTo (Reliance, Itasca, Ill). Post-gel shrinkage was measured using a biaxial strain gauge during light curing. Elastic modulus and flexural strength were measured with a 4-point bending test. Analysis of variance and Student-Newman-Keuls post hoc tests were used to compare the shrinkage, elastic modulus, and flexural strengths among the materials (α = .05). Shrinkage stresses caused by the post-gel shrinkage and elastic modulus values were calculated using a cross-sectional FEA of a metallic bracket bonded to an incisor.Results:Properties were highly different among the adhesives (P ≤ .0001). Transbond XT (0.38 ± 0.09 percent volumetric contraction) and GoTo (0.42 ± 0.05 percent volumetric contraction) had the lowest post-gel shrinkage; Transbond Plus Color Change had the highest (0.84 ± 0.08 percent volumetric contraction). OrthoConnect (6.8 ± 0.6 gigapascals) had the lowest elastic modulus; GoTo (28.3 ± 3.1 gigapascals) had the highest. Trulock (64.1 ± 8.2 megapascals) had the lowest flexural strength; Greengloo (139.1 ± 20.7 megapascals) had the highest. FEA showed that the highest shrinkage stresses were generated with Transbond Plus Color Change and the lowest with OrthoConnect.Conclusions:Post-gel shrinkage of orthodontic adhesives was comparable with restorative composites, which are known to create shrinkage stresses in restored teeth. FEA indicated that this shrinkage creates stresses in the adhesive and in the enamel around the brackets.     

Low dietary adherence after a positive food challenge in food allergic adults

BackgroundAfter a positive food challenge (FC), patients receive dietary advice regarding avoidance of the culprit food. We examined the frequency and variables associated with dietary adherence after a positive FC in adults.MethodsIn this prospective daily practice study, adults with a positive FC were included. After every FC, dietary advice was given consisting of three options: (1) strict avoidance, (2) avoidance but products with precautionary allergen labelling (PAL) allowed and (3) (small) amounts allowed. Questionnaires about dietary adherence and associated variables were completed prior to and 6 months after the FC(s).Results41 patients (with 58 positive FCs) were included. Overall, patients adhered to the advised diet after 31% of the FCs. After 33 FCs, the advice was strict avoidance, whereof 82% followed a less strict diet. After 16 FCs, the advice was avoidance but products with PAL allowed, whereof 19% followed a less strict and 25% a stricter diet. In 9 FCs with the least strict advice, “(small) amounts allowed’’, 67% followed a stricter diet. Three variables were associated with adherence: misremembering dietary advice, impaired health‐related quality of life (HRQL) on domain “Emotional impact’’ and the need for dietary change after the FC.ConclusionAfter one third of the positive FCs, patients adhered to the dietary advice. Variables associated with adherence were misremembering dietary advice, impaired HRQL on domain “Emotional impact’’ and the need for dietary change after the FC. It seems important that healthcare professionals should more frequently apply adherence‐enhancing strategies to improve dietary adherence.     

Separation of pineal extracts by gelfiltration

Summary Aqueous extracts of sheep pineal bodies were separated on Sephadex G-25. Two low molecular weight Sephadex G-25 fractions, F 2 and F 3, were ultrafiltrated through the Amicon membrane UM-2. The UM-2 filtrate was subsequently filtrated through the ultramembrane UM-05 and the UM-05 filtrate was separated on Sephadex G-10 columns. After paper electrophoresis, preparative paper chromatography was carried out. The fluorescent band showing a Rf value identical with synthetic 6-biopterin was eluted; gas liquid chromatography and mass spectrometry of the isolated compound were carried out. The mass spectra of the isolated compound were shown to be identical with synthetic 6-biopterin.The results of theCrithidia fasciculata test and thinlayer chromatography study revealed that the isolated compound is identical with 6-L-erythro-biopterin.The activities of the isolated compound and of synthetic biopterin inin vitro andin vivo bioassays are demonstrated.     

Oxidation of Recombinant Human Interleukin-2 by Potassium Peroxodisulfate

Purpose. The oxidation of recombinant human interleukin-2 (rhIL-2) by potassium peroxodisulfate (KPS) with or without N,N,N,N-tetramethylethylenediamine (TEMED), which are used for the preparation of dextran-based hydrogels, was investigated. Methods. The oxidation of (derivatives of) methionine, tryptophan, histidine and tyrosine, as well as rhIL-2 was investigated. Both the oxidation kinetics (RP-HPLC) and the nature of the oxidation products (mass spectrometry) were studied as a function of the KPS and TEMED concentration, and the presence of a competitive antioxidant, methionine. Results. Under conditions relevant for the preparation of rhIL-2 loaded hydrogels, only methionine and tryptophan derivatives were susceptible to oxidation by KPS. The oxidation of these compounds was inhibited once TEMED was present, suggesting that the peroxodisulfate anion, rather than the radicals formed in the presence of TEMED, is the oxidative species. KPS only induced oxidation of the four methionines present in rhIL-2, whereas the tryptophan residue remained unaffected. The radicals, formed after KPS decomposition by TEMED, induced some dimerization of rhIL-2. The oxidation of rhIL-2 could be substantially reduced by the addition of methionine, or by pre-incubation of KPS with TEMED. Conclusions. Only the methionine residues in rhIL-2 are oxidized by KPS. The extent of oxidation can be minimized by a proper selection of the reaction conditions.     

Impact of clinical trials on the adoption of new drugs within a university hospital

Summary To assess the influence that clinical trials may have on the introduction of new drugs into prescribing routines, the adoption of drugs has been studied in a university hospital in the Netherlands.A significant relation was found between the testing of semi-innovative drugs in clinical trials in the hospital and the introduction of these drugs into general use in the same hospital. No such relationship was found for innovative drugs. Employment in clinical trials only affected the frequency of adoption of semi-innovative drugs. It did not influence the quantity of their use once they had been adopted.The idea that the stimulating effect of clinical trials on the adoption of semi-innovative drugs is only due to acceleration of the adoption process was not confirmed.These findings support the idea that clinical trials can lower the barriers for adoption of semi-innovative drugs.     

High-speed optical observations of contrast agent destruction

Ultrasound contrast agents are now available since a few years and used for diagnostic purposes. Improved diagnostic decisions have been made possible with new imaging methods that are mainly based on the nonlinear properties of gas microbubbles. Since it is well known that contrast agents are destroyed by ultrasound when the acoustic pressure exceeds a threshold, extremely low acoustic pressures were applied to achieve enhanced contrast image quality. However, destruction of contrast microbubbles is not necessarily undesirable, since it is beneficial in, for example, destruction/reperfusion imaging and recently in drug delivery. We investigate in this experimental study the destruction dynamics of a contrast agent consisting of nitrogen bubbles encapsulated in a double polymer/albumin wall shell. This is accomplished using an ultrafast camera Brandaris that operates at a frame rate of 25 MHz and records 128 frames. The measurements were performed with an ultrasound sine burst of 10 cycles at 1.7 MHz. Different acoustic pressures were applied and various microsphere sizes were examined. The results show three different zones depending on the applied pressure and bubble size: these are nondestruction zone, transient zone and destruction zone. The nondestruction zone is reached for either very small microspheres or low mechanical indices (MI) (<0.3). In the destruction zone lie either large microspheres (5 microm or higher) even when irradiated at low MIs or small microspheres (<5 microm) when the MI is above 0.6. The optical observations revealed that the destruction of the microspheres is characterized by shell rupture and gas release. The release of the gas gives rise to new free microbubble that lasts for a few milliseconds and then disappears due to dissolution. In the transient zone, the microspheres are mainly compressed in the first few cycles but no expansion is induced. After intense compressions, the shell fissures and gas escapes in the last cycles of the burst or during a second burst depending on the initial size and MI. These optical recordings are important to investigate contrast bubble destruction and can help in amplifying or minimizing this process. Indeed, bubble disruption remains the basis of most current sensitive methods for detecting perfusion with contrast agents and is an essential component of perfusion quantification with microbubbles, in addition to drug delivery applications and pressure measurements.