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PubMedDate not supplied

Correlation between the amount of linear polymerization shrinkage and cuspal deflection.

This study evaluated the relationship between the amount of cuspal deflection and linear polymerization shrinkage in resin composites and polyacid modified resin composites (compomers). Materials included were Dyract AP, Compoglass F, Z100, SureFil, Pyramid, Synergy Compact, Heliomolar and Heliomolar HB. To measure polymerization shrinkage, a custom-made linometer (R&B, Daejon) was used. Ten measurements were made for each group, and the amount of linear shrinkage that occurred in 60 seconds was statistically compared by one-way ANOVA analysis and Tukey's test. To measure the cuspal deflection of teeth, standardized MOD cavities were prepared in extracted maxillary premolars. After a self-etching adhesive was applied, the cavities were bulk filled with one of the filling materials. Fifteen teeth were used for each material. Cuspal deflection was measured by a custom-made cuspal-deflection measuring device. One-way ANOVA analysis and Tukey's test were used to determine differences between the materials. The correlation of polymerization shrinkage vs cuspal deflection was analyzed by regression analysis. The amount of polymerization shrinkage from least to greatest was Heliomolar, SureFil < Heliomolar HB < Z100, Synergy Compact < Dyract AP < Pyramid, Compoglass F (p < 0.05). The amount of cuspal deflection from least to greatest was Z100, Heliomolar, Heliomolar HB, Synergy Compact, SureFil, < Compoglass F < Pyramid, Dyract AP (p < 0.05). Both the amount of polymerization shrinkage and cuspal deflection were highly correlated (p < 0.001).

Acrylic Resins↗
PubMed1991

Polymerization and solubility of recombinant hemoglobins alpha 2 beta 2 (6Val) (Hb S) and alpha 2 beta 2(6Leu) (Hb Leu).

In an effort to clarify the role of amino acid hydrophobicity at the beta 6 position in sickling we have made recombinant hemoglobin tetramers containing beta 6 Val (Hb S) and beta 6 Leu (Hb Leu). Recombinant Hb S and Hb Leu had the same electrophoretic mobility, chromatographic behavior, and absorption spectrum. The deoxy form of both tetramers polymerized in high phosphate buffer (1.8 M) and exhibited distinct delay times prior to polymerization. The kinetics of polymerization for recombinant and native Hb S were similar, while recombinant Hb Leu polymerized more readily. The solubility of deoxy Hb Leu was less than deoxy Hb S, indicating that rapid polymerization and decreased solubility of deoxyhemoglobin is accelerated with increasing hydrophobicity at the beta 6 position.

Amino Acid Sequence↗
PubMed1994

Diaspirin crosslinked hemoglobin (DCLHb) polymerization.

By employing proprietary polymerization agents possessing specific binding groups and by completing diaspirin crosslinked hemoglobin (DCLHb) polymerization under specific conditions, we have selectively achieved the following objectives: (1) the P50 was adjusted to the physiologic range or left- or right-shifted; (2) the surface of DCLHb was modified ("decorated"); (3) DCLHb was polymerized but not decorated; (4) DCLHb was polymerized and decorated; or (5) DCLHb was site-specifically modified and polymerized.

Amino Acids, Diamino↗
PubMed1998

Platelet and cell interactions on gold sputter-deposited polymeric surfaces.

Surface treatment as gold sputter-deposited treatment onto various polymeric surfaces has been investigated to improve the cell-, tissue- and blood-compatibility. Surface treated samples were characterized by measurement of contact angle goniometer and electron spectroscopy for chemical analysis (ESCA). The contact angles on the gold-coated polymeric surfaces decreased from 95-65 degrees to around 50 degrees, i.e., increased hydrophilicity due to incorporation of gold thin layer. From the results of ESCA analysis of the modified polymeric surfaces, surface modification by the gold-sputter method was successfully performed. Morphology of the adhered platelets on the gold-coated polymeric surfaces showed lesser activating than control, and the number of adhered platelets surface modified samples decreased with decreasing water contact angle. Fibroblast cell adhesion and growth on the gold-coated polymeric surfaces were more active than those of control. It seems that surface wettability and surface chemistry of gold play important roles for platelet adhesion and cell adhesion, spreading and growth.

3T3 Cells↗
PubMed1999

Polymerization of IgA and IgM: roles of Cys309/Cys414 and the secretory tailpiece.

We have investigated how the secretory tailpiece (tp), Cys414 and the amino acids flanking Cys414 or Cys309 are involved in regulating the different polymerization of IgM and IgA to pentamers and dimers/monomers, respectively. Whereas changing the tp of IgM to that of IgA has little effect on IgM polymerization, introducing the mu tp to IgA leads to the formation of larger than wild-type IgA polymers, including pentamers and hexamer. This shows that the secretory tp can differentially regulate polymerization depending on the heavy chain context. Cys414, which is engaged in intermonomeric disulfide bonds in IgM, is not crucial for the difference in IgM and IgA polymerization; IgM with a C414S mutation forms more large polymers than IgA. Also, IgA with IgM-like mutations in the five amino acids flanking Cys309, which is homologous to Cys414, oligomerize similarly as IgA wild type. Thus, IgA appears to have an inherent tendency to form monomers and dimers that is partially regulated by the tp, while the Cys309 region has only a minor effect. We also show that complement activation by IgM is sensitive to alterations in the polymeric structure, while IgA is inactive in classical complement activation even for polymers such as pentamers and hexamers.

Amino Acid Sequence↗
PubMed1979

A receptor for polymerized human and chimpanzee albumins on hepatitis B virus particles co-occurring with HBeAg.

A receptor for polymerized human serum albumin was demonstrated on Dane particles as well as on 20-nm hepatitis B surface antigen particles, isolated from asymptomatic carriers of hepatitis B virus who were positive for HBeAg. In contrast, such receptor was not born by 20-nm hepatitis B surface antigen particles obtained from carriers positive for antibody to HBeAg. Hepatitis B surface antigen particles with the receptor were heavier than those without, and when treated with pronase, they became lighter and lost the receptor. The receptor is responsible for the agglutination of erythrocytes coated with polymerized human serum albumin by the serum of patients with Type B hepatitis and asymptomatic carriers, which have been attributed to autoantibodies directed to denatured albumin molecules. When albumin fractions of chimpanzees were polymerized with glutaraldehyde, they also bound with the receptor on hepatitis B surface antigen. Polymerized albumin fractions of all the other experimental animals without susceptibility to hepatitis B virus, however, failed to bind with the receptor. These results seem to suggest a possible role of the receptor on Dane particles (presently accepted hepatitis B virions) for polymerized albumin molecules in infecting hepatocytes both in humans and chimpanzees.

Animals↗
PubMed1976

[On the polymerization of pour type resin (author's transl)].

The initial polymerization point and the polymerization progress have been observed on powder-liquid pour type acrylic resin and one-liquid pour type acrylic resin. The results are as follows: 1. In case of un-heating at the bottom of powder liquid resin, in the former stage the polymerization makes the regular progress from the bottom part to the upper of the mould, but in the latter stage it does some irregular one. In case of heating at the bottom, at first it shows a better regular progress as in the case of un-heating. 2. In case of un-heating at the bottom of one-liquid resin, in the first stage the polymerization makes the regular progress from the bottom part of the resin and at the same time from its middle of the mould, and then to the upper part and the sprue part. In case of heating at the bottom, it begins just from the heated part, then it goes quite regularly to the middle, the upper, and the sprue part, and lastly the polymerization shrinkage concentrates exclusively at the sprue part.

Acrylic Resins↗
PubMedDate not supplied

Surface topography and enamel-resin interface of pit and fissure sealants following visible light and argon laser polymerization: an in vitro study.

This in vitro study compared the effects of visible light and argon laser polymerization of pit and fissure sealants on surface topography and the enamel-sealant interface. Twenty caries-free human molars and premolars underwent soft tissue debridement and a fluoride-free prophylaxis. Fluoride-releasing sealant (UltraSeal XT Plus, South Jordan, UT 84095) was placed on the occlusal surfaces per the manufacturer's instructions, but underwent either visible-light polymerization for 30s (n = 10), or argon laser polymerization (0.231 J/cm2) for 10s (n = 10). The sealed teeth were thermocycled (500 cycles, 5 degrees to 50 degrees C) in artificial saliva. Surface morphology was evaluated by SEM. The teeth were sectioned for polarized light and SEM evaluation of the enamel-sealant interface, with two sections per tooth prepared for SEM. Phosphoric acid was used to unmask the enamel-sealant interface with one section; while the other section was not exposed to the phosphoric acid. Surface morphology of the sealant material was similar with both visible light and argon laser polymerization; however, there was a tendency for occasional areas of mild, focal cratering of the sealant surface with laser-curing. The junction between sealant and adjacent unsealed enamel was a relatively smooth transition without gaps, microspaces, crazing, exfoliative changes, or microfractures with both visible light and laser cured sealants. Acid treatment of the sections revealed resin tags which extended into the adjacent enamel for a considerable distance on SEM examination. The resin tas were similar in length and morphology with both visible light and argon laser curing. The enamel-sealant interface with visible light and laser curing showed intimate contact between the sealant and etched occlusal enamel with close apposition of the sealant. No microspaces were identified between the sealant and the occlusal enamel. An intact, interdigitating interface between a sealant and the adjacent etched enamel provides the first line of defense against a cariogenic challenge. Visible-light and argon laser curing allows for an intimate enamel-sealant interface without microspaces and protects sealed enamel from cariogenic challenges. The benefit of argon laser polymerization, fluoride release and mechanical protection of sealant material may provide improved caries resistance in sealed pits and fissures and adjacent nonsealed enamel surfaces.

Argon↗
PubMedDate not supplied

Marginal adaption of Class V restorations with and without "softstart-polymerization".

Polymerization shrinkage causing marginal gap formation is still a major problem in light curing restorations. The aim of the present study was to test the influence of "softstart polymerization" (prepolymerization at a low light intensity followed by a final cure at a high light intensity) on the marginal integrity of polyacid-modified resin and composite resin restorations in Class V cavities using a commercially available curing unit with two defined curing intensities. Sixty standardized Class V cavities were prepared. Twenty cavities at a time were filled either with a composite resin [Spectrum + Prime & Bond 2.1 (SP)], or with polyacid-modified resins [Dyract + Prime & Bond 2.1 (DY); Hytac + OSB Primer (HY)]. Ten fillings of each group were either conventionally cured (40 seconds, 800 mW/cm2), or they were cured with a lower starting intensity (10 seconds, 150 mW/cm2) and then with the full intensity (30 seconds, 800 mW/cm2). Margins were evaluated before and after thermomechanical loading (TCML) by quantitative margin analysis. Microleakage was assessed by dye penetration. The softstart polymerization showed no significant influence on gap formation for each material and interface before and after TCML. Quantitative margin analysis after TCML showed significantly fewer marginal gaps at the enamel/restoration interface for SP (0%) compared to DY (15.5%) and HY (44.5%) using softstart polymerization. At the dentin/restoration interface the corresponding results for gap formation were 29.6% for SP, 8.5% for DY, and 21.0% for HY. These results were not significantly different from each other. Dye penetration was significantly higher for SP at the dentin/restoration interface. SP showed significantly more marginal swelling at the dentin/restoration interface compared to DY. In conclusion, softstart polymerization using a very low starting intensity did not improve the marginal adaptation of polyacid-modified resins or composite resins in Class V cavity preparations. The best marginal adaptation in Class V cavities at the enamel/restoration interface was achieved with SP, using the acid-etch technique. In dentin, however, the polyacid-modified resins showed a superior marginal adaptation.

Compomers↗
PubMedDate not supplied

Polymerization shrinkage of visible-light-cured composites.

This study investigated the long-term dimensional changes of a conventional and a polyacid-modified composite resin and the effects of hydration on polymerization shrinkage. A strain-monitoring device was used to measure the linear polymerization shrinkage of the composites in the free state when stored in water at 37 degrees C or air at 26 degrees C over a one-month period. Results showed that the polymerization reaction of both conventional and polyacid-modified composite resins was accompanied by a dimensional shrinkage change. The rate of shrinkage for both composites was greatest during the polymerization reaction and continued after removal of the curing light. When stored in water, the greatest shrinkage was noted at one hour for both materials. This was followed by a slow uptake of water and expansion from one day to one month. The polyacid-modified composite had significantly less polymerization shrinkage than the conventional composite after one month of storage in water.

Air↗
PubMedDate not supplied

Soft-start polymerization: influence on effectiveness of cure and post-gel shrinkage.

This study investigated the influence of soft-start polymerization on the effectiveness of cure and post-gel shrinkage of a visible light cured resin composite (Z100). Three cure modes (LH-high intensity; LA-soft-start polymerization involving step-wise modulation of light intensity and LL-low intensity) of a commercial light-cure unit (Kavo PolyLUX II) were examined and compared to another light-cure unit (Spectrum). The effectiveness of cure with the different cure modes was assessed by computing the hardness gradient between top and bottom surfaces of 2 mm composites specimens after different light exposure times. A strain-monitoring device was used to measure the linear polymerization shrinkage associated with the different cure modes and exposure times over 180 minutes. A sample size of five was used for both experiments. Data was analyzed using one-way ANOVA and Scheffe's post-hoc test at significance level 0.05. Results showed that effectiveness of cure generally increased with increase cure time. Although modulation of light energy intensity (LA 40/80 seconds) resulted in lower polymerization shrinkage compared to LH 40 seconds, no significant difference was observed between these three cure regimes. Curing with the Spectrum curing light resulted in the lowest polymerization shrinkage.

Analysis of Variance↗
PubMed2003

Effect of mode of polymerization of bonding agent on shear bond strength of autocured resin composite luting cements.

PURPOSE: There have been anecdotal reports of low bond strength with autocured resin composite materials, particularly when light-cured bonding agents that combine primer and adhesive in a 1-bottle preparation are used. The objective of this study was to determine if the mode of polymerization of the bonding agent influences the strength of the attachment of autocured resin composite luting cements to dentin. METHODS: The shear bond strength of 2 resin luting cements, Calibra and RelyX ARC, polymerized by autocuring, in combination with 4 different bonding agents, Scotchbond Multipurpose Plus, Prime & Bond NT, IntegraBond and Single Bond, polymerized to bovine dentin by light-curing, autocuring or dual-curing, was determined. The pH of each bonding agent and its components was measured. Two-way analysis of variance was used to test the effect of cement and adhesive on shear bond strength. For each bonding agent, the adhesive variable combined the factors product brand and mode of polymerization. With significant interaction among the above variables, the least square means of the 16 combinations of resin cement and adhesive were compared. RESULTS: There was no consistent relationship between shear bond strength and mode of polymerization of the bonding agent. Significant differences in bond strength were specific to the proprietary brand of bonding agent. The pH of the bonding agent depends on the manufacturer's formulation, and low pH may contribute to low bond strength. CONCLUSIONS: The low in vitro bond strength occurring with some combinations of bonding agent and resin cement could be clinically significant.

Analysis of Variance↗
PubMed2003

Phosphatidic acid induces actin polymerization by activating protein kinases in soybean cells.

Phosphatidic acid (PA) levels rise in response to wounding, stress and elicitors, suggesting that it mediates defense responses in plants. During such responses, actin filaments are altered. Since PA induces actin polymerization in animal cells we examined its effect on actin structures in suspension-cultured soybean cells. PA caused a three to four fold increase in cells containing filamentous actin. Immunoblotting with anti-actin antibody showed that actin polymerized within 30 min of treatment. The effect of PA on actin polymerization appears to be mediated by protein kinases because: 1) the effect was suppressed by staurosporin, a general protein kinase inhibitor, and by the protein kinase C-specific inhibitor, calphostin, 2) calyculin A, an inhibitor of protein phosphatase 1 and 2A, mimicked the effect of PA on actin polymerization, and 3) PA activated protein kinases in soybean cells. We suggest that a 54 kDa Ca2+-dependent protein kinase may transduce the PA signal because EGTA inhibited the 54 kDa kinase and the PA-induced actin polymerization, and similar protein kinases have been reported to co-localize with and regulate actin filaments. Our results support the role of PA as a signal mediator and identify actin as a downstream target of PA.

Actin Cytoskeleton↗
PubMed1992

Effects of the neuronal phosphoprotein synapsin I on actin polymerization. I. Evidence for a phosphorylation-dependent nucleating effect.

Synapsin I is a synaptic vesicle-specific phosphoprotein which is able to bind and bundle actin filaments in a phosphorylation-dependent fashion. In the present paper we have analyzed the effects of synapsin I on the kinetics of actin polymerization and their modulation by site-specific phosphorylation of synapsin I. We found that dephosphorylated synapsin I accelerates the initial rate of actin polymerization and decreases the rate of filament elongation. The effect was observed at both low and high ionic strength, was specific for synapsin I, and was still present when polymerization was triggered by F-actin seeds. Dephosphorylated synapsin I was also able to induce actin polymerization and bundle formation in the absence of KCl and MgCl2. The effects of synapsin I were strongly decreased after its phosphorylation by Ca2+/calmodulin-dependent protein kinase II. These observations suggest that synapsin I has a phosphorylation-dependent nucleating effect on actin polymerization. The data are compatible with the view that changes in the phosphorylation state of synapsin I play a functional role in regulating the interactions between the nerve terminal cytoskeleton and synaptic vesicles in various stages of the exoendocytotic cycle.

Actins↗
PubMed1976

[Technological studies on high pressure polymerization of dental plastic materials].

The author in his present paper reports a program of comparative materials testing of which the purpose was to assess the value of positive pressure polymerization of thermosets. This particular program required polymerization temperature measurements. K-value determinations, and cone indentation hardness tests to be made on samples of plastic material polymerized under positive liquid or steam pressure and in cuvets, respectively, the conditions of polymerization being those which are used in actual practice. The results obtained indicated a favorable influence of positive liquid pressure polymerization on the final hardness of the plastic material.

Dental Materials↗
PubMed1992

Polymerization of secretory IgM in B lymphocytes is prevented by a prior targeting to a degradation pathway.

B lymphocytes express on their surface a membrane form of IgM (mIgM), and synthesize but fail to secrete a secretory form of IgM (sIgM). Plasma cells shift to the exclusive synthesis and efficient secretion of sIgM. The sIgM in B cells differs from that in plasma cells in its pattern of assembly: in plasma cells, monomers of sIgM are assembled into polymers and only polymers are secreted; in B lymphocytes, monomeric sIgM is neither polymerized nor secreted and is degraded intracellularly. In this article we blocked the export of proteins from the endoplasmic reticulum at low temperatures or with energy poisons or brefeldin A, and localized the different assembly steps of mIgM and sIgM in the 38C B lymphocytes and of sIgM in the 38C-derived sIgM-secreting D2 hybridoma. In both cell lines, sIgM assembly into monomers was not affected, whereas polymerization of sIgM in D2 cells and monomer formation of mIgM in 38C cells were strongly inhibited. Moreover, probing with specific lectins revealed galactosylated monomers and polymers in D2 cells and galactosylated hemimer and monomers only of mIgM in 38C cells. In addition, when Golgi functions were hampered with Tris base, monomerization of mIgM and polymerization of sIgM were attenuated. These results indicate that polymerization of sIgM in D2 cells and monomerization of mIgM in 38C cells are post-endoplasmic reticulum events, occurring in or beyond the trans-Golgi galactosylation compartment. Since only polymers are secreted from D2 cells and only monomeric mIgM is displayed on the surface of 38C cells, partially assembled molecules may traverse the secretory pathway yet are restricted from the cell surface. Furthermore, monomeric sIgM in 38C cells is never galactosylated, thus it is degraded prior to the galactosylation compartment. We conclude that targeting of sIgM to degradation in 38C cells precedes its assembly site into polymers in D2 cells. This implies that degradation of sIgM does not result from the incompetence of 38C cells to polymerize. Rather, assembly of sIgM into polymers and their subsequent secretion are prevented in B lymphocytes by preceding targeting of monomeric sIgM to degradation.

Animals↗
PubMed2003

Significant improvement in symptoms, skin test, and specific bronchial reactivity after 6 months of treatment with a depigmented, polymerized extract of Dermatophagoides pteronyssinus and D. farinae.

BACKGROUND: The efficacy of allergen immunotherapy using depigmented and polymerized extracts has been previously shown for Olea europaea, Phleum pratense, and Parietaria judaica. The objective of this study was to evaluate the efficacy after 3 and 6 months of treatment of a depigmented, polymerized extract of a mixture of Dermatophagoides pteronyssinus and D. farinae. METHODS: A group of 22 patients suffering from asthma and monosensitized to mites was treated with the mixture of modified allergen extract. A group of 11 mite-sensitive, asthmatic patients receiving only pharmacological treatment was used as control. The study was open, parallel, controlled, and random-allocated. Objective and subjective criteria, such as changes in D. pteronyssinus-specific bronchial hyperreactivity, visual scale, and medication/symptom scores were used to evaluate efficacy. Each patient received a built-up phase of 6 injections in 5 weeks, followed by 5 injections of the maintenance dose, which consisted of 42.5 micrograms of depigmented, polymerized extract of D. pteronyssinus and 32.5 of D. farinae. The Friedman test was used to compare the results of the specific bronchial challenges at baseline and after 3 and 6 months of treatment. RESULTS: A significant difference in the amount of native extract of D. pteronyssinus needed to produce a drop of 20% in the FEV1 (p = 0.0029) in the immunotherapy-treated group was found. In this group, the median allergen potency needed at baseline was 0.6 HEP (35 micrograms) vs. 3.96 HEP (232 micrograms) at the end of the study, whereas no difference (median 0.6 vs. 0.57 HEP) was found in the control group. At the end of the study, 10 patients in the immunotherapy treated group vs. 1 in the control group needed more than twice the amount of allergen than at baseline to experience a 20% drop in FEV1 (p = 0.03). Symptom and medication scores and visual scale evaluation did also show a significant improvement after 3 and 6 months of treatment only in active group. A significant decrease in skin test reactivity was also detected in the active group after 6 months, which needed a median of 3 times more allergen to elicit the same reaction as histamine (10 HEP) (p = 0.028), whereas no changes were found in control group. No serious side effects were registered. CONCLUSIONS: Depigmented polymerized extracts of D. pteronyssinus and D. farinae are safe and effective in the treatment of mite allergic asthmatic patients, and provide clinical benefit in the shock organ after 6 months of treatment. Skin test reactivity, symptom and medication scores were also improved. Depigmented polymerized extracts of D. pteronyssinus and D. farinae induce clinical protection against a native extract as verified by specific bronchial challenges.

Adult↗
PubMed1992

Direct evidence that J chain regulates the polymeric structure of IgM in antibody-secreting B cells.

IgM is secreted in two functional polymeric forms. Secreted IgM was originally thought to be exclusively a pentameric molecule containing J (joining) chain, but many B cells also secrete hexameric IgM lacking J chain. Hexameric IgM may play an important role in the immune system, since it is up to 20 times more active than pentameric IgM in initiating the complement cascade. The predominant polymeric form of IgM secreted by B cell lines, either pentameric or hexameric, correlates with the concentration of J chain present during polymerization, and cells that express high levels of J chain secrete mostly IgM pentamers. The B cell lymphoma WEHI-231 does not express J chain, and the majority of its secreted IgM is polymerized as hexamers. When a J chain-encoding cDNA was expressed in these cells, the secreted IgM was found to be almost exclusively pentameric. However, although the expression of J chain dramatically altered the phenotype of the IgM secreted by these cells, it had little effect on their secretory rate. We conclude that J chain regulates the structure and function of the IgM polymers secreted by B cells, but it is not necessary for either IgM polymerization or secretion.

Amino Acid Sequence↗