A comparison of two different methods and materials used to repair polycarbonate crowns.

J Contemp Dent Pract. 2007;8(2):105-12

Authors: Yilmaz A

AIM: The aim of this study was to evaluate the bond strength and crown-repair material interface of polycarbonate crown repaired using flowable resin composite and hybrid resin composite following two different surface preparations. METHODS AND MATERIALS: The facial surfaces of fifty-two polycarbonate crowns were flattened and roughened. Specimens were then divided into four test groups. A bonding agent alone (Groups 1 and 2) or a combination of methylmethacrylate (MMA) + bonding agent (Groups 3 and 4) was applied to the prepared surfaces. Then either a flowable (Groups 1 and 3) or a microfilled hybrid (Groups 2 and 4) resin composite was placed on the surfaces. Forty-eight of the original fifty-two specimens were used for shear bond strength testing. Failure types (adhesive, cohesive, and mixed) were evaluated. The remaining four specimens, one from each group, were used for crown-resin composite interface analysis using a scanning electron microscope (SEM). RESULTS: There were significant differences in both mean shear bond strength values and failure types (P<0.05). The SEM evaluation revealed a close interface relationship in Groups 3 and 4. CONCLUSION: MMA monomer application on a polycarbonate crown prior to application of an adhesive agent improved the shear bond strength of the repair material.

PMID: 17277833 [PubMed - indexed for MEDLINE]

Fracture resistance of various temporary crown materials.

J Contemp Dent Pract. 2007 Jan 1;8(1):44-51

Authors: Yilmaz A, Bayda&#x15F; S

AIM: The aim of this study was to evaluate the fracture resistance of various provisional crown materials using an in vitro model test system. METHODS AND MATERIALS: In the present study polycarbonate crowns, prefabricated by the manufacturer (3M Polycarbonate Crown), and the temporary crowns, fabricated in the dental laboratory environment, were fabricated using bis-acryl composite (Protemp II), autopolymerizing PMMA resin (BISICO Temp S), and heat-polymerized PMMA resin (Major C&B-V Dentine). All temporary crowns were stored in distilled water for 24 hours at room temperature prior to testing. The crowns were seated on metal dies, fabricated from Cr-Co alloy (AZ Dental, Konstanz, Germany), and then tested using the indenter of a Hounsfield testing machine (Hounsfield Tensometer, Hounsfield Test Equipment, Raydon, England). The tip of the indenter was located at a position one-third of the way down the inciso-palatine surface at 135 masculine. The data were statistically analyzed for differences using one-way analysis of variance (ANOVA) and the Tukey HSD test (P < .05). Additionally, the types of failure obtained from the fracture load test were examined using 10x magnification with a stereo microscope. RESULTS: The results of the present study indicated polycarbonate crowns were significantly different from the BISICO Temp S, Protemp II, and Major C&B-V Dentine (P < .05) groups. CONCLUSION: This in vitro study shows polycarbonate crowns may be preferable to the other types of temporary crowns used in this study.

PMID: 17211504 [PubMed - indexed for MEDLINE]

Tyrosine-derived polycarbonate membrane in treating mandibular bone defects. An experimental study.

J R Soc Interface. 2006 Oct 22;3(10):629-35

Authors: Asikainen AJ, Noponen J, Lindqvist C, Pelto M, Kellomäki M, Juuti H, Pihlajamäki H, Suuronen R

This study was designed to evaluate the suitability of a novel bioabsorbable material in treating bone defects. A poly(desaminotyrosyl-tyrosine-ethyl ester carbonate) (PDTE carbonate) membrane (thickness 0.2-0.3 mm) was implanted into the mandibular angle of 20 New Zealand White rabbits to cover a through-and-through defect (12 x 6 mm). In group 1, the defects were left unfilled but covered with membrane and in group 2 the defects were filled with bioactive glass mesh and covered with membrane, too. Controls were left uncovered and unfilled. The animals were followed for 6, 12, 24 and 52 weeks, respectively. The material was evaluated by qualitative analysis of histological reactions and newly formed bone.We found that PDTE carbonate elicited a modest foreign body reaction in the tissues, which was uniform throughout the study. New bone formation was seen in all samples after six weeks. Group 1 had more new bone formation until 24 weeks and after this the difference settled. Based on findings of this study it was concluded that PDTE carbonate membranes have good biocompatibility and are sufficient to enhance bone growth without additional supportive matrix.

PMID: 16971331 [PubMed - indexed for MEDLINE]

Transport and separation of small organic molecules through nanotubules.

Anal Sci. 2006 Jul;22(7):1005-9

Authors: Huang S, Yin Y

An electroless plating method was applied to deposit Au onto the surfaces and the walls of pores of polycarbonate membranes to prepare gold nanotubules. The nanotubules were modified with cysteine (Cys) or with carbamidine thiocyante (Gua). The effects of modifiers and of the fine structure of organic molecules on the transport properties of those molecules through the gold nanotubules were investigated. Studies show that the hydrophilicity of modifiers and the planar structure of permeating molecules clearly affect the transport of small organic molecules in gold nanotubules. Tryptophan (Try) and vitamin B(2) (VB(2)) was cleanly separated at pH 6.8.

PMID: 16837754 [PubMed - indexed for MEDLINE]

Purification and preconcentration of genomic DNA from whole cell lysates using photoactivated polycarbonate (PPC) microfluidic chips.

Nucleic Acids Res. 2006;34(10):e74

Authors: Witek MA, Llopis SD, Wheatley A, McCarley RL, Soper SA

We discuss the use of a photoactivated polycarbonate (PPC) microfluidic chip for the solid-phase, reversible immobilization (SPRI) and purification of genomic DNA (gDNA) from whole cell lysates. The surface of polycarbonate was activated by UV radiation resulting in a photo-oxidation reaction, which produced a channel surface containing carboxylate groups. The gDNA was selectively captured on this photoactivated surface in an immobilization buffer, which consisted of 3% polyethylene glycol, 0.4 M NaCl and 70% ethanol. The methodology reported herein is similar to conventional SPRI in that surface-confined carboxylate groups are used for the selective immobilization of DNA; however, no magnetic beads or a magnetic field are required. As observed by UV spectroscopy, a load of approximately 7.6 +/- 1.6 microg/ml of gDNA was immobilized onto the PPC bed. The recovery of DNA following purification was estimated to be 85 +/- 5%. The immobilization and purification assay using this PPC microchip could be performed within approximately 25 min as follows: (i) DNA immobilization approximately 6 min, (ii) chip washout with ethanol 10 min, and (iii) drying and gDNA desorption approximately 6 min. The PPC microchip could also be used for subsequent assays with no substantial loss in recovery, no observable carryover and no need for 'reactivation' of the PC surface with UV light.

PMID: 16757572 [PubMed - indexed for MEDLINE]

Catalyzed reporter deposition-fluorescence in situ hybridization allows for enrichment-independent detection of microcolony-forming soil bacteria.

Appl Environ Microbiol. 2006 Jan;72(1):918-22

Authors: Ferrari BC, Tujula N, Stoner K, Kjelleberg S

Advances in the growth of hitherto unculturable soil bacteria have emphasized the requirement for rapid bacterial identification methods. Due to the slow-growing strategy of microcolony-forming soil bacteria, successful fluorescence in situ hybridization (FISH) requires an rRNA enrichment step for visualization. In this study, catalyzed reporter deposition (CARD)-FISH was employed as an alternative method to rRNA enhancement and was found to be superior to conventional FISH for the detection of microcolonies that are cultivated by using the soil substrate membrane system. CARD-FISH enabled real-time identification of oligophilic microcolony-forming soil bacteria without the requirement for enrichment on complex media and the associated shifts in community composition.

PMID: 16391135 [PubMed - indexed for MEDLINE]

Early biofilm formation and the effects of antimicrobial agents on orthodontic bonding materials in a parallel plate flow chamber.

Eur J Orthod. 2006 Feb;28(1):1-7

Authors: Chin MY, Busscher HJ, Evans R, Noar J, Pratten J

Decalcification is a commonly recognized complication of orthodontic treatment with fixed appliances. A technology, based on a parallel plate flow chamber, was developed to investigate early biofilm formation of a strain of Streptococcus sanguis on the surface of four orthodontic bonding materials: glass ionomer cement (Ketac Cem), resin-modified glass ionomer cement (Fuji Ortho LC), chemically-cured composite resin (Concise) and light-cured composite resin (Transbond XT). S. sanguis was used as it is one of the primary colonizers of dental hard surfaces. Artificial saliva was supplied as a source of nutrients for the biofilms. The effects of two commercially available mouthrinses (i.e. a fluoride containing rinse and chlorhexidine) were evaluated. Initial colonization of the bacterium was assessed after 6 hours of growth by the percentage surface coverage (PSC) of the biofilm on the disc surfaces. There were statistically significant differences in bacterial accumulation between different bonding materials (P < 0.05), Concise being the least colonized and Transbond XT being the most colonized by S. sanguis biofilms. All materials pre-treated with 0.05 per cent sodium fluoride mouthrinse showed more than 50 per cent reduction in biofilm formation. The 0.2 per cent chlorhexidine gluconate mouthrinse caused significant reduction of biofilm formation on all materials except Ketac Cem. This in vitro study showed that the use of a chemically-cured composite resin (Concise) reduced early S. sanguis biofilm formation. Also, fluoride had a greater effect in reducing the PSC by S. sanguis biofilms than chlorhexidine. Rinsing with 0.05 per cent sodium fluoride prior to placement of orthodontic appliances is effective in reducing early biofilm formation.

PMID: 16373451 [PubMed - indexed for MEDLINE]

Modification of surface properties of biomaterials influences the ability of Candida albicans to form biofilms.

Appl Environ Microbiol. 2005 Dec;71(12):8795-801

Authors: Chandra J, Patel JD, Li J, Zhou G, Mukherjee PK, McCormick TS, Anderson JM, Ghannoum MA

Candida albicans biofilms form on indwelling medical devices (e.g., denture acrylic or intravenous catheters) and are associated with both oral and invasive candidiasis. Here, we determined whether surface modifications of polyetherurethane (Elasthane 80A [E80A]), polycarbonateurethane, and poly(ethyleneterephthalate) (PET) can influence fungal biofilm formation. Polyurethanes were modified by adding 6% polyethylene oxide (6PEO), 6% fluorocarbon, or silicone, while the PET surface was modified to generate hydrophilic, hydrophobic, cationic, or anionic surfaces. Formation of biofilm was quantified by determining metabolic activity and total biomass (dry weight), while its architecture was analyzed by confocal scanning laser microscopy (CSLM). The metabolic activity of biofilm formed by C. albicans on 6PEO-E80A was significantly reduced (by 78%) compared to that of biofilm formed on the nonmodified E80A (optical densities of 0.054 +/- 0.020 and 0.24 +/- 0.10, respectively; P = 0.037). The total biomass of Candida biofilm formed on 6PEO-E80A was 74% lower than that on the nonmodified E80A surface (0.46 +/- 0.15 versus 1.76 +/- 0.32 mg, respectively; P = 0.003). Fungal cells were easily detached from the 6PEO-E80A surface, and we were unable to detect C. albicans biofilm on this surface by CSLM. All other surface modifications allowed formation of C. albicans biofilm, with some differences in thearchitecture. Correlation between contact angle and biofilm formation was observed for polyetherurethane substrates (r = 0.88) but not for PET biomaterials (r = -0.40). This study illustrates that surface modification is a viable approach for identifying surfaces that have antibiofilm characteristics. Investigations into the clinical utility of the identified surfaces are warranted.

PMID: 16332875 [PubMed - indexed for MEDLINE]

Influence of temporary cement remnant and surface cleaning method on bond strength to dentin of a composite luting system.

J Oral Sci. 2005 Mar;47(1):9-13

Authors: Kanakuri K, Kawamoto Y, Matsumura H

The aim of the current study was to evaluate the influence of polycarboxylate temporary cement remaining on the dentin surface on the bond strength of a composite luting system. An acrylic resin plate was luted to bovine dentin with a polycarboxylate temporary cement (HY-Bond Temporary Cement Hard, HYB). The temporary cement was not used for the control groups. After removing the temporary cement with an excavator, dentin specimens were divided into five groups; 1) no subsequent treatment, 2) cleaning with a rotational brush (RTB), 3) cleaning with a rotational brush and non-fluoridated flour of pumice, 4) sweeping with an air scaler, and 5) treated with a sonic toothbrush. A silane-treated ceramic disk (IPS Empress) was bonded to each dentin specimen with a composite luting system (Panavia F). Shear testing results showed that the RTB groups exhibited the highest bond strength regardless of the use of temporary cement (P < 0.05). The use of a rotational brush with water coolant is recommended to achieve ideal bond strength between the Panavia F luting system and dentin to which HYB temporary cement was primarily applied.

PMID: 15881223 [PubMed - indexed for MEDLINE]

From physical pharmacy to clinical pharmacology.

Yakugaku Zasshi. 2005 Apr;125(4):337-47

Authors: Nakano M

Research works on molecular interactions in solutions were carried out at School of Pharmacy, the University of Wisconsin under the direction of Prof. T. Higuchi and at Faculty of Pharmaceutical Sciences, Kyoto University under the direction of Prof. H. Sezaki. Studies on permeation of drugs through polymer membranes were carried out at Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Canada and at Pharmaceutical Chemistry Research Laboratories at Food and Drug Directorate, Department of Health and Welfare, Canada. Studies on modification of delivery patterns by means of pharmaceutical approaches were carried out at Faculty of Pharmaceutical Sciences, Hokkaido University. Topics related to modification of drug delivery patterns include employment of amorphous forms such as ground mixture with micro-crystalline cellulose and coprecipitate with polyvinylpyrrolidone, use of biodegradable polymers such as polylactic acid and polycarbonates, gel-forming materials such as konjac, agar and hydroxypropylcellulose, and physicochemical systems such as complexation. Works related to drug delivery and disposition of drugs in humans were carried out at Department of Pharmacy, Kumamoto University Hospital. Topics related to drug delivery in humans include injections containing anticancer drugs for intra-arterial administration, lidocaine gels for dermal anesthesia, glucagon solution for nasal administration. Topics related to disposition of drugs in humans include clinical pharmacokinetic studies in infants and elderly and medical uses of adsorbents.

PMID: 15802879 [PubMed - indexed for MEDLINE]

An ex vivo evaluation of resin-modified glass polyalkenoates and polyacid-modified composite resins as orthodontic band cements.

J Orthod. 2004 Dec;31(4):323-8; discussion 301-2

Authors: Knox J, Chye KY, Durning P

OBJECTIVES: The objective of this ex vivo study was to assess the use of resin-modified glass polyalkenoates and polyacid-modified composite resins, as orthodontic band cements. MATERIALS AND METHOD: Plain stainless steel bands were cemented to 350 human extracted third molar teeth using 1 of 7 different cements. Following complete cement cure, half of each sample group was exposed to mechanical stress in a ball mill. Stressed and unstressed samples were tested in tension and the stress at which initial cement failure recorded. The mode of failure was recorded using an adhesive remnant evaluation. RESULTS: The mean band retention stresses offered by the cements studied ranged from 0.96 to 1.56 MPa. Fuji Ortho provided the highest mean band retention stress in "stressed" (1.56 MPa) and "unstressed" (1.45 MPa) states. Exposure to mechanical stress did not appear to significantly influence band retention or mode of cement failure for most cements. Fuji Ortho cement recorded the highest Weibull modulus for all cements tested. Virtually all samples failed at either the cement/enamel or cement band interface. CONCLUSIONS: Significant differences in band displacement stress values and mode of failure were demonstrated between the cements studied. However, generic comparisons were difficult to make.

PMID: 15608348 [PubMed - indexed for MEDLINE]

Cell lysis on a microfluidic CD (compact disc).

Lab Chip. 2004 Oct;4(5):516-22

Authors: Kim J, Hee Jang S, Jia G, Zoval JV, Da Silva NA, Madou MJ

Cell lysis was demonstrated on a microfluidic CD (Compact Disc) platform. In this purely mechanical lysis method, spherical particles (beads) in a lysis chamber microfabricated in a CD, cause disruption of mammalian (CHO-K1), bacterial (Escherichia coli), and yeast (Saccharomyces cerevisiae) cells. Interactions between beads and cells are generated in the rimming flow established inside a partially filled annular chamber in the CD rotating around a horizontal axis. To maximize bead-cell interactions in the lysis chamber, the CD was spun forward and backwards around this axis, using high acceleration for 5 to 7 min. Investigation on inter-particle forces (friction and collision) identified the following parameters; bead density, angular velocity, acceleration rate, and solid volume fraction as having the most significant contribution to cell lysis. Cell disruption efficiency was verified either through direct microscopic viewing or measurement of the DNA concentration after cell lysing. Lysis efficiency relative to a conventional lysis protocol was approximately 65%. In the long term, this work is geared towards CD based sample-to-answer nucleic acid analysis which will include cell lysis, DNA purification, DNA amplification, and DNA hybridization detection.

PMID: 15472738 [PubMed - indexed for MEDLINE]

Cell transport via electromigration in polymer-based microfluidic devices.

Lab Chip. 2004 Oct;4(5):464-72

Authors: Witek MA, Wei S, Vaidya B, Adams AA, Zhu L, Stryjewski W, McCarley RL, Soper SA

Electrokinetic transport of Escherichia coli and Saccharomyces cerevisiae (baker's yeast) cells was evaluated in microfluidic devices fabricated in pristine and UV-modified poly(methyl methacrylate)(PMMA) and polycarbonate (PC). Chip-to-chip reproducibility of the cell's apparent mobilities (micro(app)) varied slightly with a RSD of approximately 10%. The highest micro(app) for baker's yeast cells was observed in UV-modified PC with 0.5 mM PBS (pH = 7.4), and the lowest was measured in pristine PMMA with 20 mM PBS (pH = 7.4). Baker's yeast in all devices migrated toward the cathode because of their smaller electrophoretic mobility compared to the EOF. In 0.5 mM and 1 mM PBS, E. coli cells migrated toward the anode in all cases, opposite to the direction of the EOF due to their larger electrophoretic mobility. E. coli cells in 20 mM PBS migrated toward the cathode, which indicated that the electrophoretic mobility of E. coli cells decreased at higher ionic strengths. Observed differential migrations of E. coli and baker's yeast cells in appropriately prepared polymer microchips were used as the basis for selective introduction into microfluidic devices of only one type of cell. As a working model, experiments were performed with E. coli and RBCs (red blood cells). RBCs migrated toward the cathode in pristine PMMA with 1 mM and 20 mM PBS (pH = 7.4), opposite to the direction of the E. coli cells. By judicious choice of the buffer concentration in which the cell suspension was prepared and the polymer material, RBCs or E. coli cells were selectively introduced into the microdevice, which was monitored via laser backscatter signals.

PMID: 15472730 [PubMed - indexed for MEDLINE]

Making provisional restorations easy, predictable and economical.

J Am Dent Assoc. 2004 May;135(5):625-7

Authors: Christensen GJ

PMID: 15202755 [PubMed - indexed for MEDLINE]

High sensitivity PCR assay in plastic micro reactors.

Lab Chip. 2002 Nov;2(4):179-87

Authors: Yang J, Liu Y, Rauch CB, Stevens RL, Liu RH, Lenigk R, Grodzinski P

Small volume operation and rapid thermal cycling have been subjects of numerous reports in micro reactor chip development. Sensitivity aspects of the micro PCR reactor have not been studied in detail, however, despite the fact that detection of rare targets or trace genomic material from clinical and/or environmental samples has been a great challenge for microfluidic devices. In this study, a serpentine shaped thin (0.75 mm) polycarbonate plastic PCR micro reactor was designed, constructed, and tested for not only its rapid operation and efficiency, but also its detection sensitivity and specificity, in amplification of Escherichia coli (E. coli) K12-specific gene fragment. At a template concentration as low as 10 E. coli cells (equivalent to 50 fg genomic DNA), a K12-specific gene product (221 bp) was adequately amplified with a total of 30 cycles in 30 min. Sensitivity of the PCR micro reactor was demonstrated with its ability to amplify K12-specific gene from 10 cells in the presence of 2% blood. Specificity of the polycarbonate PCR micro reactor was also proven through multiplex PCR and/or amplification of different pathogen-specific genes. This is, to our knowledge, the first systematic study of assay sensitivity and specificity performed in plastic, disposable micro PCR devices.

PMID: 15100807 [PubMed - indexed for MEDLINE]

Fabrication of submicron scale patterned plastic thin film fluidic devices with controllable thickness.

Lab Chip. 2003 May;3(2):128-31

Authors: Hazarika P, Chowdhury D, Chattopadhyay A

We present a soft-lithography based method to fabricate plastic thin film fluidic devices on glass and plastic substrates. Principles of soft-lithography and spin casting were used to generate the films. The thickness of these films is controllable and the patterns we have generated have submicron scale dimensions. By using commercially available compact disc (CD) components as molds, we have been able to generate parallel line and cross patterns on these thin films. These patterned films could be lifted from the substrates and further folded into rolls.

PMID: 15100794 [PubMed - indexed for MEDLINE]

Damage to the three-way valves by a clear propofol formulation.

Anesth Analg. 2004 Apr;98(4):1193-4

Authors: Puri GD, Singh KP

PMID: 15041632 [PubMed - indexed for MEDLINE]

Resin-modified glass ionomer, modified composite or conventional glass ionomer for band cementation?--an in vitro evaluation.

Eur J Orthod. 2003 Dec;25(6):609-14

Authors: Millett DT, Cummings A, Letters S, Roger E, Love J

The aims of this study were to compare the mean shear-peel bond strength and predominant site of bond failure of micro-etched orthodontic bands cemented with resin-modified glass ionomer cement (RMGIC; Fuji Ortho LC or 3M Multi-Cure), a modified composite or a conventional GIC. The survival time of bands was also assessed following simulated mechanical stress in a ball mill. One hundred and twenty molar bands were cemented to extracted human third molars. Eighty bands (20 cemented with each cement) were used to assess the debonding force and 40 bands (10 cemented with each cement) were used to determine survival time. The specimens were prepared in accordance with the manufacturers' instructions for each cement. After storage in a humidor at 37 degrees C for 24 hours, the shear debonding force was assessed for each specimen using a Nene M3000 testing machine with a crosshead speed of 1 mm/minute. The predominant site of band failure was recorded visually for all specimens as either at the band/cement or cement/enamel interface. Survival time was assessed following application of mechanical stress in a ball mill. There was no significant difference in mean shear-peel bond strength between the cement groups (P = 0.816). The proportion of specimens failing at each interface differed significantly between cement groups (P < 0.001). The predominant site of bond failure for bands cemented with the RMGIC (Fuji Ortho LC) or the modified composite was at the enamel/cement interface, whereas bands cemented with 3M Multi-Cure failed predominantly at the cement/band interface. Conventional GIC specimens failed mostly at the enamel/cement interface. The mean survival time of bands cemented with either of the RMGICs or with the modified composite was significantly longer than for those cemented with the conventional GIC. The findings indicate that although there appears to be equivalence in the mean shear-peel bond strength of the band cements assessed, the fatigue properties of the conventional GIC when subjected to simulated mechanical stress seem inferior to those of the other cements for band cementation.

PMID: 14700267 [PubMed - indexed for MEDLINE]

Age and dose dependency of the pharmacokinetics and metabolism of bisphenol A in neonatal sprague-dawley rats following oral administration.

Toxicol Sci. 2004 Feb;77(2):230-42

Authors: Domoradzki JY, Thornton CM, Pottenger LH, Hansen SC, Card TL, Markham DA, Dryzga MD, Shiotsuka RN, Waechter JM

Previous studies demonstrated the rapid clearance of bisphenol A (BPA) from blood following oral administration to adult rats with the principal metabolite being BPA-monoglucuronide (BPA-glucuronide). Since the ontogeny of glucuronyl transferases (GT) differs with age, the pharmacokinetics of BPA were studied in neonatal animals. (14)C-BPA was administered via gavage at 1 or 10 mg/kg body weight to rats at postnatal day (pnd) 4, pnd 7, pnd 21, or to 11 week old adult rats (10 mg/kg dose only). Blood (neonates and adults) and selected tissues (neonates) were collected at 0.25, 0.75, 1.5, 3, 6, 12, 18, and 24 h postdosing. BPA and BPA-glucuronide in the plasma were quantified by high-performance liquid chromatography; radioactivity in the plasma and tissues was quantified by liquid scintillation spectrometry. The data indicate that neonatal rats at all three ages metabolized BPA to BPA-glucuronide, although an age dependency in the number and concentration of plasma metabolites was observed, consistent with the ontogeny of GT. BPA-glucuronide and BPA concentrations in the plasma were greater in neonates than in adults, except at 24 h postdosing, suggesting an immaturity in the development of hepatic excretory function in neonatal rats. Nevertheless, the half-lives for the elimination of BPA-glucuronide in plasma were more rapid in neonatal animals than in adults, likely due to reduced microflora beta-glucuronidase activity and an absence of enterohepatic recirculation. A dose dependency in the metabolism and pharmacokinetics of BPA administered to neonates was also observed with nearly complete metabolism of BPA to BPA-glucuronide (94-100% of the plasma radioactivity) at a dose of 1 mg/kg. This was in contrast to finding up to 13 different plasma metabolites observed at the 10 mg/kg dose. These data indicate that, from early in neonatal life through pnd 21, there is sufficient GT activity in rats to efficiently metabolize BPA to its nonestrogenic metabolite at low doses.

PMID: 14691203 [PubMed - indexed for MEDLINE]

[In vitro model system of transepithelial migration of neutrophil by Helicobacter pylori]

Korean J Gastroenterol. 2003 Jul;42(1):20-6

Authors: Jung HC, Kim JG, Kim JM, Song IS, Park SM

BACKGROUND/AIMS: Migration of neutrophil across the intestinal epithelium is a structural hallmark of active intestinal diseases. One of the characteristic histologic features of Helicobacter pylori (H. pylori) infection is neutrophil infiltration of the gastric mucosa. This study was aimed to establish an in vitro model system of transepithelial migration of neutrophil by H. pylori. METHODS: Caco-2 cells were grown on polycarbonate membrane. Confluence and integrity were assessed by measuring the transepithelial electrical resistance (TER) and paracellular permeability of macromolecular marker. IL-8 mRNA expression was assessed after H. pylori infection by quantitative RT-PCR. Isolated neutrophils and H. pylori were applied to the basolateral and apical compartment in separate. Also neutrophil transmigration was assessed by light and electron microscopy. RESULTS: Paracellular leakage of 3[H]-mannitol was negligible over TER 166 Omega x cm2. IL-8 mRNA expression increased after H. pylori infection. Neutrophil transmigration was increased by adding of N-formyl-methionyl-leucyl-phenylalanine or H. pylori. CONCLUSIONS: This in vitro model system could be applied to the study of pathogenesis of H. pylori infection. A further study of quantification of transmigrated neutrophils is demanded to reach a confirmation.

PMID: 14532727 [PubMed - indexed for MEDLINE]

A comparison of biological coatings for the promotion of corneal epithelialization of synthetic surface in vivo.

Invest Ophthalmol Vis Sci. 2003 Aug;44(8):3301-9

Authors: Sweeney DF, Xie RZ, Evans MD, Vannas A, Tout SD, Griesser HJ, Johnson G, Steele JG

PURPOSE: To investigate the effect of a range of biological coatings on corneal epithelialization of a synthetic polymer surface in vivo. METHODS: Eight diverse biological factors (collagen I, collagen III, collagen IV, laminin, fibronectin, endothelial extracellular matrix, hyaluronic acid, and chondroitin sulfate) were coated individually onto the surface of polycarbonate membranes with a pore size of 0.1 micro m. The coated membranes were implanted on the anterior cornea of adult cats and were clinically assessed for rapidity and extent of and persistence of epithelial overgrowth. The membranes with persistent epithelial attachment were examined histologically by immunohistochemistry and routine light and electron microscopy. RESULTS: Collagen I, collagen IV, and laminin consistently enhanced migration and attachment of corneal epithelial cells in vivo. Multiple-layered epithelium over the collagen I-, collagen IV-, and laminin-coated membranes was demonstrated histologically. The collagen I-coated membranes performed best, in that they showed greater stratification and differentiation of the epithelium. Formation of basement membrane and adhesion complexes over the collagen I-coated membranes was detected by immunohistochemistry and electron microscopy up to 9 weeks after implantation. Membranes coated by fibronectin, endothelial extracellular matrix, hyaluronic acid, and chondroitin sulfate did not support persistent epithelial overgrowth. Compromised biostability of these coatings was mostly likely associated with postsurgical reactions of the host corneal tissue. CONCLUSIONS: A biologically modified polymer can support migration and adhesion of corneal epithelial cells in vivo. The collagen I-modified surface exhibited the most promising performance, both clinically and histologically.

PMID: 12882774 [PubMed - indexed for MEDLINE]

Identification of Cryptosporidium spp. oocysts in United Kingdom noncarbonated natural mineral waters and drinking waters by using a modified nested PCR-restriction fragment length polymorphism assay.

Appl Environ Microbiol. 2003 Jul;69(7):4183-9

Authors: Nichols RA, Campbell BM, Smith HV

We describe a nested PCR-restriction fragment length polymorphism (RFLP) method for detecting low densities of Cryptosporidium spp. oocysts in natural mineral waters and drinking waters. Oocysts were recovered from seeded 1-liter volumes of mineral water by filtration through polycarbonate membranes and from drinking waters by filtration, immunomagnetizable separation, and filter entrapment, followed by direct extraction of DNA. The DNA was released from polycarbonate filter-entrapped oocysts by disruption in lysis buffer by using 15 cycles of freeze-thawing (1 min in liquid nitrogen and 1 min at 65 degrees C), followed by proteinase K digestion. Amplicons were readily detected from two to five intact oocysts on ethidium bromide-stained gels. DNA extracted from Cryptosporidium parvum oocysts, C. muris (RN 66), C. baileyi (Belgium strain, LB 19), human-derived C. meleagridis, C. felis (DNA from oocysts isolated from a cat), and C. andersoni was used to demonstrate species identity by PCR-RFLP after simultaneous digestion with the restriction enzymes DraI and VspI. Discrimination between C. andersoni and C. muris isolates was confirmed by a separate, subsequent digestion with DdeI. Of 14 drinking water samples tested, 12 were found to be positive by microscopy, 8 were found to be positive by direct PCR, and 14 were found to be positive by using a nested PCR. The Cryptosporidium species detected in these finished water samples was C. parvum genotype 1. This method consistently and routinely detected >5 oocysts per sample.

PMID: 12839797 [PubMed - indexed for MEDLINE]

An in vivo and ex vivo study to evaluate the use of a glass polyphosphonate cement in orthodontic banding.

Eur J Orthod. 2003 Jun;25(3):319-23

Authors: Clark JR, Ireland AJ, Sherriff M

The purpose of this study was to examine the effectiveness of a new glass polyphosphonate cement (Diamond) for orthodontic banding. Thirty-one subjects underwent in vivo testing to compare the failure rate of bands cemented using the test cement and bands cemented using a conventional glass polyalkenoate cement (Ketac-Cem) over a 6-month period at the beginning of active appliance therapy. In an ex vivo experiment 60 extracted teeth were banded using either the test cement or a glass polyalkenoate cement, and subjected to a debanding force using a Lloyd universal testing machine until failure. In the in vivo study the overall proportion of failure of the bands cemented with each cement was identical at 0.048. However, in the ex vivo study the probability of failure for the glass polyphosphonate cement was significantly higher than for the glass polyalkenoate cement, and the force to deband the glass polyalkenoate cement was greater than that of the glass polyphosphonate cement. In the clinical setting the new glass polyphosphonate cement performed as well as a conventional glass polyalkenoate cement, and these results suggest that it could be used as an alternative cement for orthodontic banding. The results of the ex vivo test bring into question the usefulness of this laboratory test as an indicator of clinical performance.

PMID: 12831223 [PubMed - indexed for MEDLINE]

Development of a novel granular detergent with an interspersion particle comprising an anionic surfactant and a polymeric polycarboxalate.

Chem Pharm Bull (Tokyo). 2003 Jun;51(6):743-5

Authors: Ebihara F, Watano S

This paper discusses a process for making a novel granular detergent with an interspersion particle comprising an anionic surfactant and a polymeric polycarboxalate. This process contains three steps to develop the interspersion particles with anionic surfactant and polymeric ploycarboxalate. The first step was to form a detergent particle by spray drying of an aqueous detergent slurry comprising anionic surfactant (liner alkyl benzene sulfonate) with the different levels of polymeric polycarboxalate. In the second step, the spray-dried granules were densified and ground by a roll compacter and a grinder. The ground particles were coated by nonionic and zeolite in a vertical batch type high shear mixer (third step). In this study, the feasibility to make better performance of granular detergent was discussed.

PMID: 12808260 [PubMed - indexed for MEDLINE]

Crowns and other extra-coronal restorations: try-in and cementation of crowns.

Br Dent J. 2002 Jul 13;193(1):17-20, 23-8

Authors: Wassell RW, Barker D, Steele JG

Having successfully negotiated the planning, preparation, impression and prescription of your crown, the cementation stage represents the culmination of all your efforts. This stage is not difficult, but a successful outcome needs as much care as the preceding stages. Once a restoration is cemented there is no scope for modification or repeat You have to get it right first time. Decemented crowns often have thick layers of residual cement suggesting problems with either initial seating or cement handling. When the fate of restorations costing hundreds of pounds depends on correct proportioning of cements and the quality of the mix, the value of a well-trained and experienced dental nurse is easy to see. Both dentist and nurse need a working knowledge of the materials they are handling.

PMID: 12171196 [PubMed - indexed for MEDLINE]

Mammalian neural tube grafting experiments: an in vitro system for mouse experimental embryology.

Int J Dev Biol. 2001 Dec;45(8):895-902

Authors: Echevarr&#xED;a D, Vieira C, Martínez S

We have developed a simple experimental technique which consists of explanting the mouse embryo anterior neural tube--the presumptive brain anlage--onto polycarbonate membranes. The neural epithelium of the explants maintained both its original topology and topography for at least two days in culture. Analysis of cell death in the explants by assaying propidium iodide uptake showed high viability of neuroepithelial cells during the culture period. Both the pattern of gene expression and the initial steps of neural cellular differentiation were well preserved, being similar to those which occur in the normal in vivo situation. We show here two applications of this tissue culture technique which is similar to that which has been previously employed for avian embryo models. The first involves neuroepithelial grafting experiments by heterotopic transplantation of the zona limitans intrathalamica (ZLI) into the mesencephalon and the second consists of fibroblast growth factor (FGF8) protein interaction studies using soaked bead insertions. This in vitro system constitutes a powerful experimental embryological tool which can have other applications including time-lapse imaging and electrophysiology.

PMID: 11804033 [PubMed - indexed for MEDLINE]

Restorative pulpal and repair responses.

J Am Dent Assoc. 2001 Apr;132(4):482-91

Authors: Murray PE, About I, Franquin JC, Remusat M, Smith AJ

BACKGROUND: Each year, about 90 million new restorations are placed in the United States and 200 million are replaced. Controversy surrounds the pulpal reactions and frequency of bacterial microleakage associated with common restorative materials. The authors investigated and compared pulpal reactions to different types of restorative materials. METHODS: Two hundred seventy-two teeth with standardized rectangular Class V unexposed cavities were restored with resin-based composite bonded to dentin; resin-based composite bonded to enamel; resin-modified glass ionomers, or RMGI; amalgam lined with zinc polycarboxylate, or ZnPC; amalgam lined with calcium hydroxide, or Ca(OH)2; or zinc oxide-eugenol, or ZnOE. Teeth were extracted for orthodontic reasons between 20 and 381 days later. The authors categorized pulpal responses according to standards set by the Federation Dentaire Internationale and the International Organization for Standardization. Bacteria were detected using Brown-Brenn-stained sections. Pulpal responses were evaluated using histomorphometric analysis and analysis of variance statistics. RESULTS: The results showed that RMGI was the best material for preventing bacterial microleakage, and resin-based composite bonded to enamel was the worst. In regard to minimizing pulpal inflammatory activity, ZnOE was the best material and resin-based composite bonded to enamel was the worst. In terms of maximizing odontoblast survival beneath deep cavity preparations, Ca(OH)2, was the best material and RMGI was the worst. CONCLUSIONS: The results show that bacterial microleakage, pulpal injury and repair responses varied widely with different restorative materials. CLINICAL IMPLICATIONS: The authors recommend that RMGI be used to restore teeth with cavities that are shallow to moderate in depth, with the floor of deep cavities being lined with Ca(OH)2 before the teeth are restored with RMGI.

PMID: 11315379 [PubMed - indexed for MEDLINE]

Magnetic bead capture eliminates PCR inhibitors in samples collected from the airborne environment, permitting detection of Pneumocystis carinii DNA.

Appl Environ Microbiol. 2001 Jan;67(1):449-52

Authors: Maher N, Dillon HK, Vermund SH, Unnasch TR

PCR detection methods are useful in studies of organisms not amenable to culture. Inhibitors in environmental samples can interfere with such assays. We describe a magnetic bead DNA capture protocol that removes inhibitors from outdoor air samples, maintaining the sensitivity of a 16S Pneumocystis carinii mitochondrial rRNA gene-based PCR.

PMID: 11133478 [PubMed - indexed for MEDLINE]

Importance of sampling, extraction and preservation for the quantitation of biologically active endoto.

Ann Agric Environ Med. 1999;6(1):33-8

Authors: Laitinen SK

The influence of filter media, extraction solution and preservation method on detection of biologically active endotoxin in the LAL assay was studied with air samples collected from wastewater treatment plants. The four most common types of filters were used as collection media. The extraction solutions compared were nonpyrogenic water, KH2PO4-triethylamine and Trizma buffers. The effect of preservation on endotoxin air samples was ascertained by storing both the filters without extraction, and samples extracted in the collection day for a few weeks at various temperatures. Samples collected on glass fibre filters showed the highest amounts of detectable endotoxin, while the concentrations of endotoxin were significantly lower when cellulose-mixed esters, polycarbonate or polyvinyl chloride membrane filters were used for air sampling. After collection, the best efficiency for glass fibre filters was attained by extraction with nonpyrogenic water within 8 hours after sampling and storage of the extracts at 4 degrees C until they were analysed. If the filters were stored without extraction, the reduction in endotoxin levels of the sample was about 30% after 1 week preservation and about 70% after 2 weeks. The study shows that the effect of the filter material and preservation practice was significant. These factors play critical roles in assessing exposure to bacterial endotoxins within wastewater aerosols.

PMID: 10384213 [PubMed - indexed for MEDLINE]

Design and test of a new tracheostoma valve based on inhalation.

Arch Otolaryngol Head Neck Surg. 1999 Jun;125(6):622-6

Authors: Geertsema AA, Boonstra CW, Schutte HK, Verkerke GJ

BACKGROUND: Tracheostoma valves are used to make hand-free speaking possible for persons who have undergone a laryngectomy. OBJECTIVE: To design and test a new tracheostoma valve to improve existing tracheostoma valves. METHODS: The tracheostoma valve closes by means of strong inhalation so that all the air that is exhaled is available for phonation. The device automatically stays in the"speaking position" until the patient deliberately changes the device to the "breathing position" by a fast expiration. If all the air that has been exhaled has been consumed during phonation, the patient can inhale again, without changing the device, because a small valve automatically opens, thus allowing phonation without time limits. An experimental setup with a computer-based acquisition program was used to measure the pressure at which the valve opened and the flow at which the valve closed. The pressure and flow needed to open and close the magnetic adjustable valve were measured for different positions and contained in the computer through a data acquisition program. Also, the airflow resistance coefficients for inhaling and exhaling were measured. RESULTS: The airflow necessary to close the tracheostoma valve ranges from 1.6 to 3.8 L/s. The opening pressure of the valve ranges from 1 to 7 kPa. The airflow resistance coefficient is 290 Pa x s2 x L(-2) for inhalation and 430 Pa x s(2) x L(-2) for exhalation. CONCLUSIONS: The device appears to function well in physiological ranges and is optimally adjustable. The airflow resistance coefficient lies in the range of the entire airway resistance (120-470 Pa x s(2) x L(-2)) in quiet breathing.

PMID: 10367917 [PubMed - indexed for MEDLINE]

Virus passage through track-etch membranes modified by salinity and a nonionic surfactant.

Appl Environ Microbiol. 1999 Jun;65(6):2773-5

Authors: Lytle CD, Routson LB, Jain NB, Myers MR, Green BL

Why do viruses sometimes not pass through larger pores in track-etch filters? Increasing the salinity (0.8 to 160 mM Na+) decreased phiX174 and PRD1 passage through track-etch polycarbonate membranes (sodium dodecyl sulfate coated but not polyvinylpyrrolidone coated) and PRD1 passage through polyester membranes. Undiminished passage when 0.1% Tween 80 was added implied that nonionic virus adsorption occurred and indicated that high levels of salinity decreased virus passage by decreasing electrostatic repulsion that prevented adsorption.

PMID: 10347078 [PubMed - indexed for MEDLINE]

In vitro comparison of the retention capacity of new aesthetic brackets.

Eur J Orthod. 1999 Feb;21(1):71-7

Authors: Fernandez L, Canut JA

Tensile bond strength and bond failure location were evaluated in vitro for two types of aesthetic brackets (non-silanated ceramic, polycarbonate) and one stainless steel bracket, using bovine teeth as the substrate and diacrylate resin as the adhesive. The results show that metallic bracket had the highest bond strength (13.21 N) followed by the new plastic bracket (12.01 N), which does not require the use of a primer. The non-silanated ceramic bracket produced the lowest bond strength (8.88 N). Bond failures occurred mainly between bracket and cement, although a small percentage occurred between the enamel-cement interface with the metal and plastic brackets and within the cement for the plastic bracket. With the ceramic bracket all the failures occurred at the bracket-cement interface. This suggests that the problems of enamel lesions produced by this type of bracket may have been eliminated. The results also show that the enamel/adhesive bond is stronger than the adhesive/bracket bond in this in vitro study.

PMID: 10191580 [PubMed - indexed for MEDLINE]

Effect of extrusion pressure and lipid properties on the size and polydispersity of lipid vesicles.

Biophys J. 1998 Jun;74(6):2996-3002

Authors: Hunter DG, Frisken BJ

The production of vesicles, spherical shells formed from lipid bilayers, is an important aspect of their recent application to drug delivery technologies. One popular production method involves pushing a lipid suspension through cylindrical pores in polycarbonate membranes. However, the actual mechanism by which the polydisperse, multilamellar lipid suspension breaks up into a relatively monodisperse population of vesicles is not well understood. To learn about factors influencing this process, we have characterized vesicles produced under different extrusion parameters and from different lipids. We find that extruded vesicles are only produced above a certain threshold extrusion pressure and have sizes that depend on the extrusion pressure. The minimum pressure appears to be associated with the lysis tension of the lipid bilayer rather than any bending modulus of the system. The flow rate of equal concentration lipid solutions through the pores, after being corrected for the viscosity of water, is independent of lipid properties.

PMID: 9635753 [PubMed - indexed for MEDLINE]

Use of glass-ionomers for bracket bonding--an ex vivo study evaluating a testing device for in vivo purposes.

Eur J Orthod. 1998 Apr;20(2):201-8

Authors: Ortendahl TW, Thilander B

Seven glass-ionomer cements were tested and compared with a composite resin in order to find the glass-ionomer cement with the highest bond strength to enamel with normal anatomy and composition (not ground). Five types of surface treatment were used. The results show that Aqua Cem and Ketac Cem, both water-hardening, present the highest bond strength, followed by the conventional glass-ionomer cement Fuji IIF. Surface treatment according to the manufacturers' instructions and surface treatment with polyacrylic acid were found to give rise to the highest bond strength for all of the seven cements. However, none of the glass-ionomer cements reached the values for the composite resin Concise. The testing instrument designed for ex vivo purposes measured with high precision and accuracy and with a low methodological error.

PMID: 9633174 [PubMed - indexed for MEDLINE]

Impact of membrane choice and blood flow pattern on coagulation and heparin requirement--potential consequences on lipid concentrations.

Nephrol Dial Transplant. 1997 Dec;12(12):2638-46

Authors: Sperschneider H, Deppisch R, Beck W, Wolf H, Stein G

BACKGROUND: We reasoned that procoagulant activity, and by implication heparin requirement, during haemodialysis are influenced, amongst other factors, by the type of membranes and the geometry of the blood line system. In addition, there are indications that heparin has dose-dependent effects on the lipid status of chronic haemodialysis patients. METHODS: In a parallel group design we compared patients treated with cuprophane (CU) and polycarbonate-polyether (PC-PE) plate dialysers. In both groups, blood line geometry was varied by including in a first phase and omitting in a second phase drip chambers in the arterial blood line. End-points were changes in coagulation parameters, i.e. thrombin-antithrombin III complex (TAT), plasmin-anti-plasmin complex (PAP), and prothrombin fragment (F1 + 2) concentrations measured by sandwich ELISA. Subsequently all patients were switched to PC-PE dialysers for 6 months and the heparin dose was reduced in a stepwise fashion. Lipid levels and coagulation parameters were monitored. Finally, in an ancillary study, the correlation between heparin dose and LDL/HDL ratio was assessed in patients chronically exposed to PC-PE membranes and low doses of heparin. RESULTS: Post-dialytic concentrations of coagulation and fibrinolysis parameters were significantly lower in the PC-PE group (TAT 31.0 +/- 4.4 micrograms/l; PAP 1180 +/- 148 micrograms/l; F1 + 2 4.2 +/- 0.4 nmol/l) compared to the CU group (TAT 57.3 +/- 10.8 micrograms/l; PAP 1789 +/- 185 micrograms/l; F1 + 2 8.8 +/- 1.0 nmol/l), independently of the use of an arterial drip chamber. Omission of the arterial drip chamber led to lower TAT in the CU group (42.2 +/- 5.8 micrograms/l, P < 0.05), but not in the PC-PE group. In contrast, PAP and F1 + 2 concentrations did not change significantly in either group. Down-titration of heparin dose (from 20.4 +/- 1.1 to 9.4 +/- 0.9 IU/kg/h) was associated with a significant decrease in serum triglycerides (from 2.9 +/- 0.9 to 2.0 +/- 0.6 mmol/l, P < 0.05), LDL-cholesterol (from 3.4 +/- 0.2 to 2.7 +/- 0.4 mmol/l, P < 0.05) and LDL/HDL-ratio (from 3.2 +/- 0.3 to 2.0 +/- 0.3, P < 0.05) with no significant change of total or HDL-cholesterol after 6 months. In an ancilliary analysis, a correlation between lipid parameters (LDL/HDL ratio) and heparin dose was confirmed in 24 patients chronically exposed to PC-PE membranes (r = 0.473, P < 0.05). CONCLUSIONS: In a prospective exploratory study (i) heparin requirement is lower with the use of a polycarbonate-polyether membrane compared to a cuprophane membrane, (ii) heparin requirement is influenced by blood line geometry (decreased with omission of an arterial drip chamber), and (iii) in patients on polycarbonate-polyether membranes down-titration of heparin is associated with a reduction of serum triglycerides, LDL cholesterol, and LDL/HDL ratio. Our data suggest that reduction of heparin dose improves lipid profile. These preliminary observations require confirmation by parallel group controlled studies with controlled dietary intake.

PMID: 9430865 [PubMed - indexed for MEDLINE]

Cementing porcelain-fused-to-metal crowns.

J Am Dent Assoc. 1997 Aug;128(8):1165-7

Authors: Christensen GJ

PMID: 9260430 [PubMed - indexed for MEDLINE]

Growth of silicone-immobilized bacteria on polycarbonate membrane filters, a technique to study microcolony formation under anaerobic conditions.

Appl Environ Microbiol. 1997 Jul;63(7):2920-4

Authors: H&#xF8;jberg O, Binnerup SJ, Sørensen J

A technique was developed to study microcolony formation by silicone-immobilized bacteria on polycarbonate membrane filters under anaerobic conditions. A sudden shift to anaerobiosis was obtained by submerging the filters in medium which was depleted for oxygen by a pure culture of bacteria. The technique was used to demonstrate that preinduction of nitrate reductase under low-oxygen conditions was necessary for nonfermenting, nitrate-respiring bacteria, e.g., Pseudomonas spp., to cope with a sudden lack of oxygen. In contrast, nitrate-respiring, fermenting bacteria, e.g., Bacillus and Escherichia spp., formed microcolonies under anaerobic conditions with or without the presence of nitrate and irrespective of aerobic or anaerobic preculture conditions.

PMID: 9212439 [PubMed - indexed for MEDLINE]

Alternatives to ceramic brackets: the tensile bond strengths of two aesthetic brackets compared ex vivo with stainless steel foil-mesh bracket bases.

Br J Orthod. 1997 May;24(2):133-7

Authors: Arici S, Regan D

The mean tensile/peel bond strengths were evaluated for three types of aesthetic brackets (a ceramic-reinforced bracket and two generations of a ceramic/polycarbonate combination bracket). These were found to be significantly lower than the mean tensile/peel bond strength of a convention foil-mesh stainless steel bracket base. Failure of the ceramic-reinforced polycarbonate brackets occurred predominantly by fracture of the tie wings during testing. With the ceramic/polycarbonate combination brackets, the majority of the specimens failed due to separation of the ceramic and polycarbonate parts of the bracket.

PMID: 9218111 [PubMed - indexed for MEDLINE]

IR and NMR analyses of hardening and maturation of glass-ionomer cement.

J Dent Res. 1996 Dec;75(12):1920-7

Authors: Matsuya S, Maeda T, Ohta M

It has been reported that the silicate phase as well as the cross-linking of the polycarboxylic acid by aluminum and calcium ions played an important role in the hardening of glass-ionomer cement. The objective of this study was to investigate the structural change during hardening of the cements by means of infrared (IR) spectroscopy and solid-state nuclear magnetic resonance (NMR) spectroscopy and to confirm the role of the silica phase in the hardening of the cement. For that purpose, we measured the change in compressive strength of an experimental glass-ionomer cement, two commercial glass-ionomer cements, and a polycarboxylate cement and carried out 29Si and 27Al NMR analyses of the cement samples after the strength measurement. In the IR spectra during hardening, a characteristic band of the silicate network around 1000 cm-1 shifted toward high frequency with time. The spectrum after hardening was similar to that for a hydrated amorphous silica structure. The 27Al NMR analysis showed that Al3+ ion was tetrahedrally coordinated by oxygen in the original glass, but a part of the Al3+ ion was octahedrally coordinated after hardening to form Al polyacrylate gel. The chemical shift of Si in the 29Si NMR spectra also changed during hardening. The variation in the chemical shift reflected the structural change in the silicate network. The initial increase in compressive strength of the cement was mainly caused by polycarboxylate gel formation. However, it was concluded that the reconstruction of the silicate network contributed to the increase in strength with time during the period after the gelation by cross-linking was completed.

PMID: 9033445 [PubMed - indexed for MEDLINE]

Dental materials developments in the UK: a personal view.

J Dent Res. 1996 Nov;75(11):1816-9

Authors: McLean JW

PMID: 9003226 [PubMed - indexed for MEDLINE]

Using a carboxylate cement for temporary resin crowns.

J Am Dent Assoc. 1996 Sep;127(9):1376

Authors: Tanchyk A

PMID: 8854614 [PubMed - indexed for MEDLINE]

Shear bond strength of a new polycarbonate bracket--an in vitro study with 14 adhesives.

Eur J Orthod. 1996 Jun;18(3):295-301

Authors: Akin-Nergiz N, Nergiz I, Behlfelt K, Platzer U

Shear bond strength and failure location were used to evaluate the effectiveness of plastic bracket primers for bonding diacrylate adhesives on a new fibre-reinforced polycarbonate bracket. Maxillary incisor polycarbonate and mesh-based brackets as control were bonded to human incisors with 14 different adhesives (four filled diacrylate two-paste, six diacrylate one-step and four power-liquid acrylic adhesives), and after thermo-cycling for 2000 cycles between 5 degrees and 55 degrees C, tested in shear. A non-parametric test (Mann-Whitney U test) was used to compare the shear bond strength of the polycarbonate brackets with the mesh based brackets and a One-way test (according to Scheffe) to compare the shear bond strength of different adhesives. The following conclusions can be made: 1. Seven of the 14 adhesives used in this study with both types of brackets demonstrated adequate shear bond strength values for the clinical application. The exceptions were: Achieve Mix, No-Mix:30 Silkon, Lee Insta-Bond, Ortho-Loc and Bond-Eze, all with too low a shear bond strength for one or both types of brackets, and finally Quasar, which used with the plastic brackets sometimes caused enamel fractures, due to high bond strength. 2. The adhesives with their own plastic primer demonstrated higher blood strength values than those without plastic primer, and two-paste adhesives used with plastic primer displayed a higher bond strength than the other adhesives. 3. Generally, the shear bond strength values of the one-step adhesives were lower compared with the two-paste adhesives. 4. The liquid-powder adhesives demonstrated very different values for bond strength.

PMID: 8791893 [PubMed - indexed for MEDLINE]

An in vitro study of the bond strength of light-cured glass ionomer cement in the bonding of orthodontic brackets.

Eur J Orthod. 1996 Apr;18(2):199-204

Authors: Cook PA, Luther F, Youngson CC

The search to improve the properties of dental adhesives has lead to the development of light-cured glass ionomer cements. Using human teeth in vitro, the present study tested the shear/peel bond strengths of two light-cure materials ('Variglass VLC' and 'Fuji Lining LC') against a 'no-mix' composite orthodontic adhesive ('Right-On') and a chemically cured glass ionomer cement ('Ketac-Cem'). The light-cured materials were found to have an inferior bond strength compared with the two control adhesives. Based on the findings of this study, there is no evidence to support the use of the materials tested for the bonding of orthodontic brackets.

PMID: 8670931 [PubMed - indexed for MEDLINE]

Comparative shear bond strength of some orthodontic bonding resins to enamel.

Eur J Orthod. 1996 Feb;18(1):89-95

Authors: Trimpeneers LM, Verbeeck RM, Dermaut LR, Moors MG

The aim of this study was to compare the in vitro bond strength, to bovine enamel measured in shear, of the orthodontic adhesives Lee Insta-bond (LiB), Rely-a-Bond (RaB), Right-on (Ro), Concise precoating method (Cc), Concise mixed method (CaB), Super-C (Sc), and Orthon (Or), and of the glass ionomer cement Ketac-Cem (KC). The fracture surfaces after debonding were also examined in order to determine the sites of failure. The results indicate that there is a significant difference between the shear bond strength obtained with the different adhesives so that the mean shear bond strength decreases in the order [Ro approximately Cab approximately Sc] > [LiB approximately RaB approximately Cc] > Or > KC. Moreover, for Cab and Sc it was found that the shear bond strength varies depending on the location on the bovine tooth. The failure site was essentially at the resin-bracket interface, except for Concise, where only 50 per cent of the cases failed at the resin-bracket interface.

PMID: 8746181 [PubMed - indexed for MEDLINE]

Estrogens in unexpected places: possible implications for researchers and consumers.

Environ Health Perspect. 1995 Oct;103 Suppl 7:129-33

Authors: Feldman D, Krishnan A

Estrogenic activity originating in unexpected places was encountered on three occasions during an investigation of whether Saccharomyces cerevisiae synthesized estrogens. In each instance, estradiol found in the conditioned yeast culture medium originated from an exogenous source and was not synthesized by the yeast. In the first instance, yeast grown in the laboratory showed a time-dependent increase in estradiol in the conditioned medium. However, the culture medium supplement Bacto-peptone was found to contain large amounts of estrone. When added to yeast cultures in the form of YPD medium (yeast extract, Bacto-peptone, and dextrose), S. cerevisiae converted the estrone to estradiol leading to the accumulation of estradiol over time. In the second instance, commercially purchased S. cerevisiae grown in a molasses medium exhibited substantial amounts of estradiol. However, corn and beet molasses contained sufficient estrone and estradiol to account for the findings. As in the first instance, the yeast converted the estrone into estradiol. In the third instance, autoclaving culture medium in polycarbonate plastic flasks was found to cause an estrogenic substance to be added to the medium, whether yeast were present or not. It was determined that the autoclaving process leached bisphenol-A (BPA) out of the polycarbonate plastic. BPA was shown to bind to estrogen receptors and to induce estrogenic activity, including stimulation of MCF-7 breast cancer-cell proliferation and induction of the expression of progesterone receptors. The three instances highlight potential problems for investigators who might inadvertently add estrogens to experimental systems confounding their results. The BPA findings raise concerns about the possible addition of this estrogenic molecule to the food supply since polycarbonate plastic is used in myriad applications in the packaging of food and beverages. Although we are unaware of the substantial contamination of food products with BPA, we believe this possibility should be carefully investigated.

PMID: 8593858 [PubMed - indexed for MEDLINE]

Influence of various dust sampling and extraction methods on the measurement of airborne endotoxin.

Appl Environ Microbiol. 1995 May;61(5):1763-9

Authors: Douwes J, Versloot P, Hollander A, Heederik D, Doekes G

The influence of various filter types and extraction conditions on the quantitation of airborne endotoxin with the Limulus amebocyte lysate test was studied by using airborne dusts sampled in a potato processing plant. Samples were collected with an apparatus designed to provide parallel samples. Data from the parallel-sampling experiment were statistically evaluated by using analysis of variance. In addition, the influence of storage conditions on the detectable endotoxin concentration was investigated by using commercially available lipopolysaccharides (LPS) and endotoxin-containing house dust extracts. The endotoxin extraction efficiency of 0.05% Tween 20 in pyrogen-free water was seven times higher than that of pyrogen-free water only. Two-times-greater amounts of endotoxin were extracted from glass fiber, Teflon, and polycarbonate filters than from cellulose ester filters. The temperature and shaking intensity during extraction were not related to the extraction efficiency. Repeated freeze (-20 degrees C)-and-thaw cycles with commercial LPS reconstituted in pyrogen-free water had a dramatic effect on the detectable endotoxin level. A 25% loss in endotoxin activity per freeze-thaw cycle was observed. Storage of LPS samples for a period of 1 year at 7 degrees C had no effect on the endotoxin level. House dust extracts showed a decrease of about 20% in the endotoxin level after they had been frozen and thawed for a second time. The use of different container materials (borosilicate glass, "soft" glass, and polypropylene) did not result in different endotoxin levels. This study indicates that the assessment of endotoxin exposure may differ considerably between groups when different sampling, extraction, and storage procedures are employed.

PMID: 7646014 [PubMed - indexed for MEDLINE]

VLA-4 integrin mediates lymphocyte migration on the inducible endothelial cell ligand VCAM-1 and the extracellular matrix ligand fibronectin.

J Biol Chem. 1993 Nov 25;268(33):24655-64

Authors: Chan PY, Aruffo A

We herein tested the ability of lymphocytes to utilize the beta 1 integrin VLA-4 to mediate cell migration when adhering to its cytokine-inducible endothelial cell ligand VCAM-1 or its extracellular matrix ligand fibronectin. We used an in vitro system consisting of purified VCAM-1/Fc fusion protein or fibronectin immobilized on porous polycarbonate membranes to quantitatively measure the migration efficiency of an Epstein-Barr virus-transformed B cell line (SLA) and T lymphoblasts derived from normal donors. We found that both SLA cells and T lymphoblasts migrated across membranes coated with VCAM-1/Fc or fibronectin in a site density-dependent manner. Above and below an optimal site density of VCAM-1/Fc or fibronectin, the migration efficiency decreased. A 6-20-fold higher number of lymphocytes migrated across membranes coated with VCAM-1/Fc than with fibronectin. The differential migration efficiency is consistent with a higher number of adherent lymphocytes and a higher avidity of adhesion for VCAM-1/Fc than for fibronectin when the ligands were immobilized on plastic, and is independent of the activation state of the cells. These results demonstrated a stringent regulation of migratory response by cell adhesion strength and a delicate balance between stationary and migratory behaviors of a cell on the adhesive substrates. Like the beta 2 integrin LFA-1, VLA-4 may be a locomotive adhesion receptor which is involved in the transendothelial migration of lymphocytes and the infiltration of lymphocytes into lymphoid or peripheral tissues by binding to VCAM-1 and fibronectin.

PMID: 7693704 [PubMed - indexed for MEDLINE]

Bisphenol-A: an estrogenic substance is released from polycarbonate flasks during autoclaving.

Endocrinology. 1993 Jun;132(6):2279-86

Authors: Krishnan AV, Stathis P, Permuth SF, Tokes L, Feldman D

In studies to determine whether Saccharomyces cerevisiae produced estrogens, the organism was grown in culture media prepared using distilled water autoclaved in polycarbonate flasks. The yeast-conditioned media showed the presence of a substance that competed with [3H]estradiol for binding to estrogen receptors (ER) from rat uterus. However, it soon became clear that the estrogenic substance in the conditioned media was not a product of the yeast grown in culture, but was leached out of the polycarbonate flasks during the autoclaving procedure. [3H]Estradiol displacement activity was monitored by ER RRA, and the active substance was purified from autoclaved medium using a series of HPLC steps. The final purified product was identified as bisphenol-A (BPA) by nuclear magnetic resonance spectroscopy and mass spectrometry. BPA could also be identified in distilled water autoclaved in polycarbonate flasks without the requirement of either the organism or the constituents of the culture medium. Authentic BPA was active in competitive RRAs, demonstrating an affinity approximately 1:2000 that of estradiol for ER. In functional assays, BPA (10-25 nM) induced progesterone receptors in cultured human mammary cancer cells (MCF-7) at a potency of approximately 1:5000 compared to that of estradiol. The BPA effect on PR induction was blocked by tamoxifen. In addition, BPA (25 nM) increased the rate of proliferation of MCF-7 cells assessed by [3H]thymidine incorporation. Thus, BPA exhibited estrogenic activity by both RRA and two functional bioresponse assays. Finally, MCF-7 cells grown in media prepared with water autoclaved in polycarbonate exhibited higher progesterone receptor levels than cells.grown in media prepared with water autoclaved in glass, suggesting an estrogenic effect of the water autoclaved in polycarbonate. Our findings raise the possibility that unsuspected estrogenic activity in the form of BPA may have an impact on experiments employing media autoclaved in polycarbonate flasks. It remains to be determined whether BPA derived from consumer products manufactured from polycarbonate could significantly contribute to the pool of estrogenic substances in the environment.

PMID: 8504731 [PubMed - indexed for MEDLINE]

Comparison of membrane filters for recovery of legionellae from water samples.

Appl Environ Microbiol. 1993 Jan;59(1):344-6

Authors: Smith L, Carroll K, Mottice S

The procedure currently used for isolating legionellae from environmental samples recommend filtration through a 0.2-microns-pore-size polycarbonate filter. In this study we evaluated the performance of 23 other filters composed of various materials and having various pore sizes. We prefer the 0.2-micron-pore-size Gelman Supor filter because of its high level of recovery, faster filtration rate, and ease of handling.

PMID: 8439164 [PubMed - indexed for MEDLINE]

Chemotactic activity of recombinant human granulocyte colony-stimulating factor.

Blood. 1988 Nov;72(5):1456-60

Authors: Wang JM, Chen ZG, Colella S, Bonilla MA, Welte K, Bordignon C, Mantovani A

Recombinant human granulocyte colony-stimulating factor (rhG-CSF) induced migration across polycarbonate filters of human polymorphonuclear leukocytes (PMN). rhG-CSF was active in inducing PMN migration at concentrations greater than or equal to 10 to 100 U/mL (7 to 70 ng/mL). rhG-CSF did not contain appreciable levels of endotoxin contamination as assessed by Limulus amebocyte assay, and Polymixin B did not affect the chemotactic activity of rhG-CSF. A monoclonal anti-G-CSF antibody blocked the induction of migration by G-CSF, thus establishing that the cytokine was responsible for the activity of the recombinant preparation. Checkerboard analysis was performed by seeding different concentrations of G-CSF above and/or below the filter and revealed that the migratory response to this cytokine was best observed in the presence of a positive concentration gradient between the lower and upper compartments of the chamber, thus indicating an actual chemotactic effect. When different migrating cells were examined, rhG-CSF was inactive on large granular lymphocytes and endothelial cells under conditions in which appropriate reference attractants were active. In contrast, rhG-CSF elicited a chemotactic response in monocytes inhibited by specific antibody. Thus, G-CSF is a chemotactic signal for phagocytes. This cytokine, when produced at inflammatory sites, may contribute to the recruitment of phagocytes from the blood compartment to amplify resistance against certain noxious agents.

PMID: 2460152 [PubMed - indexed for MEDLINE]