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PubMed2000

Mechanism of interference of a polymerized hemoglobin blood substitute in an alkaline phosphatase method.

BACKGROUND: Hemoglobin-based oxygen carriers can cause profound interferences in many analytical procedures. We determined the mechanism of interference in the assay of alkaline phosphatase activity and identified approaches that might be used to correct for this interference. METHODS: Interference of a polymerized hemoglobin blood substitute with the assay of alkaline phosphatase was examined with a Hitachi 917 analyzer and ultraviolet-visible spectrophotometry. RESULTS: Hemoglobin-based oxygen carrier solutions had substantial absorbance at 415 nm, the wavelength of analysis used to measure the formation of 4-nitrophenol. In addition to offsetting the initial absorbance at the analytical wavelength, polymerized hemoglobin gave rise to a strong negative interference plot because of alkali denaturation of the substitute. The same interference mechanism was also observed for native hemoglobin (hemolysate), indicating that the interference was not derived from the polymerization process. The interference can be corrected by implementing a rate-correction procedure, or the interference can be avoided by measurement at 450 nm. CONCLUSIONS: The interference of polymerized hemoglobin in the alkaline phosphatase assay is a result of an absorbance offset caused by alkali denaturation of hemoglobin. The interference can be corrected or avoided by modifying the calculation or the analytical wavelength. The correction strategy may also be applicable to improving the hemolysis index for this method.

Alkaline Phosphatase↗
PubMed2000

Fibrinogen Alès: a homozygous case of dysfibrinogenemia (gamma-Asp(330)-->Val) characterized by a defective fibrin polymerization site "a".

Congenital homozygous dysfibrinogenemia was diagnosed in a man with a history of 2 thrombotic strokes before age 30. His hemostatic profile was characterized by a dramatically prolonged plasma thrombin clotting time, and no clotting was observed with reptilase. Complete clotting of the abnormal fibrinogen occurred after a prolonged incubation of plasma with thrombin. The release of fibrinopeptides A and B by thrombin and of fibrinopeptide A by reptilase were both normal. Thrombin-induced fibrin polymerization was impaired, and no polymerization occurred with reptilase. The polymerization defect was characterized by a defective site "a," resulting in an absence of interaction between sites A and a, indicated by the lack of fragment D(1) (or fibrinogen) binding to normal fibrin monomers depleted in fibrinopeptide A only (Des-AA fm). By SDS-PAGE, the defect was detected on the gamma-chain and in its fragment D(1). The molecular defect determined by analysis of genomic DNA showed a single base change (A-->T) in exon VIII of the gamma-chain. The resulting change in the amino acid structure is gamma 330 aspartic acid (GAT) --> valine (GTT). It is concluded that the residue gamma-Asp(330) is essential for the normal functioning of the polymerization site a on the fibrinogen gamma-chain.

Adult↗
PubMedDate not supplied

Effectiveness of polymerization in composite restoratives claiming bulk placement: impact of cavity depth and exposure time.

The impact of variation of cavity depth and light-source exposure time upon the effectiveness of polymerization of two "bulk placement" composite restoratives was assessed indirectly using hardness testing. The current investigation used a digital microhardness tester to evaluate hardness gradient between top and bottom surfaces of composite specimens of various depths after different light-exposure times. The results showed that the effectiveness of polymerization decreased significantly with increased cavity depth regardless of exposure time. Increased exposure time increased the extent of polymerization at cavity depths of 3 to 4 mm. Increments of the composites evaluated should be no greater than 2 mm to provide uniform and maximum polymerization.

Analysis of Variance↗
PubMed1994

Oligonucleotides as probes for studying polymerization reactions in dilute aqueous solution.

We have prepared a [32P]-labled oligonucleotide probe carrying a free primary amine at its 3'-terminus. This probe is used to initiate polymerization of aziridine (ethyleneimine) in aqueous solution. The nature of the oligomeric products and the kinetics of their formation are then monitored by gel electrophoresis. Our results are generally consistent with those obtained using conventional techniques. We have also investigated the effect of polyanionic templates on the rate of oligomerization of aziridine. We find that water-soluble polyanions generally accelerate the polymerization. The sodium salt of polymethacrylic acid is the most effective of the templates that we studied. The methods introduced in this paper should be applicable to a variety of polymerization reactions in aqueous solution. They should greatly simplify the screening of potentially prebiotic polymerization reactions.

Autoradiography↗
PubMedDate not supplied

[Age peculiarities of actin polymerization in calves].

Studies have been made on the developmental changes in the polymerization degree of unfractionated actin extracts from skeletal muscles of 3-8-month calf embryos and adult cattle. It was shown that during the development, the polymerization capacity of actin increases, the increase being accompanied by a significant rise in the molecular weight of the protein. The pattern of age changes in the degree of polymerization of actin is similar to that in the molecular weight of actomyosin. Differences in fractional composition of actin extracts from skeletal muscles at various stages of embryonic development were observed. These differences may be responsible for age peculiarities of actin polymerization and may be associated with the formation of contractile activity in ontogenesis.

Actins↗
PubMed2003

Influence of different softstart polymerization techniques on marginal adaptation of Class V restorations.

PURPOSE: To investigate the influence of different curing methods used to achieve softstart polymerization on the marginal adaptation of a resin-based composite in Class V restoration. MATERIALS AND METHODS: Class V cavities, with the gingival wall located 1 mm below the cemento-enamel junction, were prepared on buccal and lingual surface of 80 extracted premolar teeth. The teeth were randomly divided into 8 groups of 10 teeth. The cavities were restored with a combination of resin-based composite (Z100) and adhesive (Single Bond) in different softstart-polymerization techniques or placement techniques. Softstart-polymerization obtained from either softstart mode (Elipar Highlight) or the modified methods using standard curing unit (Spectrum 900 and XL3000), bulk or incremental filling techniques were also used. After thermocycling between 5 degrees C and 55 degrees C for 500 cycles, the specimens were immersed in 2% methylene blue dye at 37 degrees C for 6 hours. Longitudinal sections of the specimens were scored for marginal dye penetration under the microscope. Kruskal-Wallis and Mann-Whitney tests were used for statistical analysis. RESULTS: There was no statistically significant difference of dye penetration among techniques at enamel or dentin margins (P > 0.05). Dye penetration observed at dentin margins was significantly higher than that observed at enamel margins (P < 0.05) except for the group restored with a combination of incremental technique and softstart-polymerization using Spectrum curing unit. There was no statistically significant difference of microleakage between buccal and lingual cavities at enamel or dentin margins (P > 0.05).

Bicuspid↗
PubMedDate not supplied

Depth of light-initiated polymerization of glass fiber-reinforced composite in a simulated root canal.

PURPOSE: The possibility of polymerizing glass fiber-reinforced composite (FRC) material into the root canal was preliminarily evaluated by determining the depth of light-initiated polymerization of FRC. MATERIALS AND METHODS: The material used was polymer-preimpregnated E-glass fiber reinforcement, which was further impregnated with light-polymerizable dimethacrylate monomer resin. The same resin without fiber reinforcement was used as a control. Six different lengths (range 4 to 24 mm) of light-protected cylinders filled with the test materials were light polymerized from one end. The degree of monomer conversion was determined from the other end by FT-IR spectrometry. Infrared spectra were recorded at six time points from the beginning of polymerization. The microhardness of the test materials was measured from the light-exposure surface toward the other end of the cylinder. RESULTS: Both groups showed a reduction in the degree of conversion with increased lengths of the cylinder. The FRC group showed a higher degree of conversion in the longest sample group compared to the resin group. Microhardness measurement confirmed the constant reduction of the degree of conversion by the reduced Vickers hardness values with increased cylinder length of the FRC. CONCLUSION: Generally, the glass FRC showed an almost equal degree of conversion after light curing as monomer resin without fibers. However, in the longest cylinders, FRC showed a slightly higher degree of conversion compared to resin only; this might be due to the fibers' ability to conduct light.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1976

gamma-dimerization, alpha-polymerization, and plasmin degradation of human fibrin. Effect of various inhibitors of factor XIII on the patterns in SDS-electrophoresis and crossed immunoelectrophoresis.

The effect of different factor XIII inhibitors (competetive inhibition, interference with active center SH-groups in different ways, Ca2+ depletion) on the sequence of the gamma-dimerization and alpha-polymerization of fibrin is examined by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAE) (reduced material). They all inhibit either gamma-dimerization and alpha-polymerization or alpha-polymerization alone irrespective of the factor XIII inhibitory mechanism. Non-crosslinked fibrin and fibrin clots of different degrees of crosslinking are digested with plasmin and the lysate tested in SDS-PAE (non-reduced material) and crossed agarose gel immunoelectrophoresis (CAIE). The digests contain Fragment D and Fragment D-D respectively and Fragment E. An additional Fragment E with less anodic mobility in CAIE, and not demonstrable in SDS-PAE, is seen in increasing amounts with increasing gamma-dimerization, alpha-polymerization does not further change the CAIE patterns.

Animals↗
PubMed1992

Relative fit of new denture resins polymerized by heat, light and microwave energy.

This study compared in vitro the relative fit of seven denture resins polymerized by different methods to their gypsum casts. Relative fit in the molar-to-molar region of the resin bases on their stone casts was evaluated independently by five evaluators at three times (after processing, after polishing and after storage in water) and ranked using non-parametric statistics. The denture resins polymerized by microwave energy, (Acron MC), low heat, (Perform, 45 degrees C), and visible light, (Triad) fit better after polishing and after storage in water than those resins polymerized at higher temperatures (Lucitone 199, 74 degrees C and Accelar 20, Compak and Permacryl 20, 100 degrees C). The traditional heat-polymerized resin (Lucitone) had an average fit after storage in water.

Acrylic Resins↗
PubMedDate not supplied

Effect of light curing method on volumetric polymerization shrinkage of resin composites.

Volumetric polymerization shrinkage of three resin composites (Suprafil, Z100 and Filtek P60) was determined using four light curing methods: method 1: continuous output with conventional intensity light; method 2: continuous output with higher intensity light; method 3: ramp output and method 4: pulse-delay output. Five disc-shaped specimens were prepared from each material for each curing method. Specimen weight was determined with an analytical electronic hydrostatic balance in air and in water before and after curing. Specific gravity values were then determined. Volumetric polymerization shrinkage was calculated using mathematical formulas. Mean volumetric polymerization shrinkage ranged from 1.882 (.015)% to 2.169 (.028)%. ANOVA indicated significant differences among the materials (p<.05). Light curing methods had no effect on volumetric polymerization shrinkage except for Z-100, where method 2 resulted in significantly higher shrinkage than methods 1 and 4. Suprafil shrunk significantly less than the other two materials in all curing methods.

Analysis of Variance↗
PubMed2004

Comparison of PAC and QTH light sources on polymerization of resin composites.

PURPOSE: To evaluate the polymerization shrinkage, Knoop hardness number (KHN) and compressive strength and to suggest a suitable time for irradiating resin composite restorations, when using a high-intensity light source. METHODS: Two restorative resin composites, UniFil F, and Clearfil AP-X were employed. A high-intensity light unit (more than 1000mW/cm2) with a xenon discharge lamp (Apollo 95E), which is generally called a plasma arc light-curing unit (PAC), was compared with a conventional light-curing unit fitted with a quartz-tungsten-halogen lamp (QTH) (GC Newlight VL2). The resin composites were exposed to the light in four ways. For QTH, the irradiation time was for 40 seconds (QTH 40 seconds). For PAC, 3 seconds (PAC 3 seconds), 3+3 seconds (PAC 3+3 seconds) and 3+3+3 seconds (PAC 3+3+3 seconds) was used. Polymerization shrinkage using the bonded disk technique developed by Watts, Knoop hardness number (KHN), and compressive strength were then determined. RESULTS: Two-way ANOVA revealed that the two materials for PAC 3+3 seconds and PAC 3+3+3 seconds made no difference in polymerization shrinkage compared to QTH 40 seconds (P < 0.001). The polymerization shrinkage of the materials cured by PAC for 3 seconds was significantly lower than those cured by QTH for 40 seconds in a range from 61% to 72%, by the PAC for 3 + 3 seconds in a range from 65% to 88%, and those by PAC 3+3+3 seconds in a range of 61% to 72% (P < 0.001). With regard to microhardness, the composites in PAC 3+3+3 seconds exposure made no difference in hardness compared with QTH 40 seconds (P < 0.001). PAC 3+3 seconds exposure gave hardness at less than 3.0 mm depth equivalent to that of the QTH 40 seconds. PAC 3 seconds at 2.0 mm depth produced inferior hardness compared with the QTH 40 seconds. The compressive strength for the PAC 3 seconds exposure was significantly lower than that of PAC 3+3 seconds, PAC 3+3+3 seconds and QTH 40 seconds for each material. CLINICAL SIGNIFICANCE: Irradiation by the high-intensity light source for 3 seconds provided significantly lower microhardness and compressive strength for light-cured resin composites. The 3+3+3 seconds repeated irradiation with the PAC unit and QTH 40 second values were not significantly different.

Analysis of Variance↗
PubMed2004

Interleukin-5, interleukin-3 and granulocyte-macrophage colony-stimulating factor prime actin-polymerization in human eosinophils: a study with hypodense and normodense eosinophils from patients with atopic dermatitis.

Characteristic features of atopic diseases (AD) are immigration and local activation of eosinophils. Reorganization of the cytoskeleton modulates the function of leukocytes and is a prerequisite for the motility response. In this work, the regulation of actin polymerization has been investigated by flow cytometry using NBD-phallacidin and right angle light scatter measurements in purified eosinophils isolated from patients with atopic dermatitis and normal individuals. Stimulation of eosinophils with chemotaxins such as complement fragment C5a (C5a), CC chemokine RANTES/ CCL5 and platelet activating factor (PAF) induced a reversible polymerization of actin. Normodense eosinophils purified from patients with AD showed a decreased chemotaxin-induced actin response as compared to normodense eosinophils from healthy subjects and hypodense eosinophils from patients. Stimulation of eosinophils with Th2-cytokines such as interleukin-3 (IL-3), interleukin-5 (IL-5), granulocyte-macrophage colony-stimulating factor (GM-CSF) did not exert a significant effect on actin polymerization. However, pretreatment with IL-3, IL-5 or GM-CSF potentiated the chemotaxin-induced actin polymerization and graded the differential responsiveness between normodense and hypodense eosinophils. We demonstrate a different actin responsiveness in eosinophils from atopic patients and healthy subjects which could be overcome by modulating effects of Th2-cytokines.

Actins↗
PubMedDate not supplied

[N-ethylmaleimide inhibits polymerization of myorod, a contractile protein of thick filaments of molluscan smooth muscles].

The effect of N-ethylmaleimide on the polymerization of myorod, a protein of molluscan smooth muscles, which is colocalized with myosin on the surface of paramyosin core of thick filaments and is a product of the alternative splicing of the gene of heavy myosin chains, was studied. It was shown that myorod modified by N-ethylmaleimide completely loses the polymerization ability but acquires the ability to aggregate in the presence of Mg2+. At the same time, treatment of molluscan myosin with N-ethylmaleimide did not affect its polymerization. It was supposed that the effect of N-ethylmaleimide on myorod polymerization is related to the modification of the myorod SH domain containing Cys722.

Actin Cytoskeleton↗
PubMedDate not supplied

Degree of remaining C=C bonds, polymerization shrinkage and stresses of dual-cured core build-up resin composites.

This study measured the degree of remaining C=C bonds (RDB), linear polymerization shrinkage (LPS) and polymerization stresses (PS) of dual-cured resin composite build-up materials using a variety of light exposure scenarios. Four commercially available materials were used: Bis-Core, FluoroCore, Build-it! and Permalute. The RDB was measured using FTIR spectroscopy, and custom-made devices were used to measure LPS and PS values. Data were obtained using three different modes of photoactivation: NLC (No Light-Curing); ILC (Immediate Light-Curing, where 60 second light-curing was applied at the start of the observation period); and DLC (Delayed Light-Curing, where 60-second light-curing was applied 10 minutes from the start of the observation period). Statistical evaluation of the data at the end of the 13-minute observation period was performed with two-way analysis of variance (ANOVA), Tukey's Studentized Range (HSD) Test (p=0.05) and simple linear regression. Differences in the development of LPS and PS during the 13 minutes were studied using mathematical calculus. Bis-Core presented the highest RDB and Permalute the lowest when ILC was applied, while no differences were found between Build-it! and FluoroCore and NLC and DLC increased RDB for FluoroCore and Permalute compared to ILC; whereas, no differences were noted for Build-it! and Bis-Core. Using DLC, a decrease in RDB was found only for Build-it! FluoroCore and Permalute exhibited a reduction in LPS and PS using NLC relative to ILC. No differences in LPS and PS values were detected for the materials Bis-Core and Build-it! when subjected to NLC or DLC, compared to ILC. Simple linear regression showed that only the two polymerization shrinkage properties studied were highly correlated (LPS-PS r2=0.85). The RDB rate was not correlated with either polymerization shrinkage properties (RDB-LPS r2=0.40; RDB-PS r2=0.57). A study of the evolution of the real-time curves of percentage values of LPS and PS showed that these properties evolved in a similar exponential mode and that, most often, there was a delay in the development of PS.

Carbon↗
PubMedDate not supplied

Post-gel polymerization shrinkage associated with different light curing regimens.

This study compared post-gel polymerization shrinkage associated with five different light curing regimens of similar light energy density. A light-cure unit (VIP, BISCO) that allowed for independent command over time and intensity was used. The five regimens investigated were pulse delay (PD), soft-start (SS); pulse cure (PC), turbo cure (TC) and standard continuous cure (C) [control]. With the exception of TC, the light energy density for all curing regimens was fixed at 16 J/cm2. A strain-monitoring device and test configuration were used to measure the linear polymerization shrinkage of 2-mm thick composite specimens (Z100, 3M ESPE) during and post-light polymerization up to 60 minutes. Five samples were made for each curing mode. The results were analyzed using ANOVA/Scheffee's post-hoc test at significance level 0.05. Post-gel shrinkage ranged from 0.30% to 0.46 % at 60 minutes. The use of PD resulted in significantly lower shrinkage compared to PC, TC, SS and C. Shrinkage associated with SS was, in general, significantly lower than C. No significant difference in shrinkage was observed between PC, TC and C at all time intervals. The use of pulse delay and soft-start regimens decreased post-gel polymerization shrinkage.

Composite Resins↗
PubMed2005

[Medical applications of nanotechnology: polymeric micelles for drug delivery].

Recently, medical applications of nanotechnology have received much attention. Among them, drug delivery systems (DDSs) are expected to be the leading technology in diagnostic and therapeutic medicine. An increasing number of DDSs have been approved for clinical use or are currently being studied in clinical trials. Polymeric micelles, self-assemblies of block copolymers, are one of the most refined and promising modalities of DDSs, since the critical parameters such as size, drug loading, and release can be controlled by engineering the constituent block copolymers. It has been demonstrated that polymeric micelles show unique disposition characteristics in the body suitable for drug targeting (e.g., prolonged blood circulation and significant tumor accumulation). Also, recent advances in polymer synthesis have allowed the development of polymeric micelles with integrated smart functions such as environmental sensitivity and targetability. Thus polymeric micelles might have great potential for nanotechnology-based DDSs for clinical use.

Antineoplastic Agents↗
PubMed2006

[Study on the volume flows through polymeric membranous dressing with silver ions].

The volume flows through double-layer polymeric membranous dressing, formed by three types of theromoplastic polymeric fibers called Textus Bioactive were studied. The first layer contains two types of fibers: the polymeric fibers containing hydrophobic core and hydrophilic surfaces with silver zeolite and hydrophilic super absorbing polymers (SAP). The second layer of membrane contains third type of polymeric fibers, arranged parallel to surface's skin, creating a net, which prevents membranous dressing from sticking to treated wound. The pressure characteristics of the volume flux were determined and it was stated that the value of this flux is dependent on the value of hydrostatic pressure difference (deltaP) and the concentration difference (deltaC) of solutions separated by membrane. Experimental results show that the membranous dressing Textus Bioactive posses the rectifying properties with reference to volume flows. These properties occurs above a threshold value of deltaC. Using the Kedem-Katchalsky equations, the model of the volume flows through membranous dressing Textus Bioactive was made.

Bandages↗
PubMed2006

Bond strength of resin-based restorations polymerized with different light-curing sources.

PURPOSE: To evaluate the influence of different light-curing units on microtensile bond strength of resin composite restorations. MATERIALS AND METHODS: Standardized Class I preparations (6.0 x 4.5 mm, 2.5 mm deep) were made in extracted human third molars after abrading the cusps. Resin was inserted in bulk using a 3M ESPE restorative system [Adper Single Bond (DBA)/ Filtek Z250 (RC)]. Both materials were polymerized using different light-curing units: QTH at 540 mW/cm(2) (XL 3000, 3M ESPE); LED at 750 mW/cm(2) (Elipar FreeLight2, 3M ESPE); PAC at 2130 mW/cm(2) (Arc Light II, Air Techniques). Nine different light combinations were developed to polymerize both DBA and RC: QTH/QTH; QTH/LED; QTH/PAC; LED/LED; LED/QTH; LED/PAC; PAC/PAC; PAC/QTH; PAC/LED. Restored teeth were stored in distilled water for 24 h at 37 degrees C and then sectioned, yielding stick-shaped specimens with a bonded area of approximately 0.9 mm(2). Specimens were assessed in a testing machine at a crosshead speed of 1 mm/min. The results were analyzed using two-way ANOVA and Tukey's test at a pre-set alpha = 0.05. RESULTS: The combinations PAC/QTH and QTH/QTH presented the highest bond strength values, and LED/QTH the lowest (p < 0.05). Significantly lower values were observed in combinations when the LED light was used to polymerize DBA compared to QTH and PAC lights, irrespective of the light source used to polymerize RC (p < 0.05). Same light combinations presented similar bond strength values. CONCLUSIONS: Different light sources influence restoration bond strength. Bond strength is more dependent on the light source used for DBA than for curing RC.

Bisphenol A-Glycidyl Methacrylate↗