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At least 973 records · Page 54Linked to original sources
PubMed2006

Ultrasonic evaluation of residual stresses in flat glass tempering by an original double interferometric detection.

In industrial thermal tempering of glass, the knowledge of the homogeneity of compressive residual stress field on the glass product is fundamental to guarantee the quality of the tempered glass product. In this paper, we use the acoustoelasticity phenomenon in order to estimate the residual stress distribution by using acoustic surface wave. We present an experimental setup based on a double interferometric detection in which an aspheric lens is associated with a beam splitter and a YAG laser whose power is 100 mW. This relative high power enables us to carry out measurements on surface flat glass although optical reflection coefficient is typically weak (< 10%). Using these two points of detection, the evolution of relative surface wave velocity is obtained with a good accuracy. At last, a comparison between the numerical modeling and experimental results shows the potentiality of an ultrasonic method to estimate stress distribution in flat glass tempering.

Algorithms↗
PubMed1974

Electrochemical properties of hydrated cation-selective glass membrane. A model of K+ and Na+ transport.

Electrochemical properties of cation-selective glass microelectrodes made from NAS(27-04) were studied. There was a marked fall in electrical resistance of the microelectrodes stored in 3 M KCl solution (aging). The resistance was in the range of 2 x 10(7) to 10(9) Omega, which were much lower than those estimated from the electrical resistivity of dry glass for the equivalent dimensions of microelectrode working tips. This fall in resistance was accompanied by an increase in microelectrode selectivity for K(+). The low resistance and increased K(+) selectivity are desirable features that make the microelectrode more suitable for application to biologic studies. The changes in microelectrode resistance and selectivity were interpreted to be due to hydration of the entire thickness of the glass membrane, resulting in a change in the field strength of anionic sites and formation of ionic channels in the glass membrane. Thus, the fall in resistance is explained by decrease in energy barrier, which is equivalent to the activation energy of interaction between the cations and anionic sites in the glass membrane. Some of the microelectrodes showed a transient depolarization that resembled the action potential of a biological membrane. This transient depolarization was associated with the changes in microelectrode resistance and selectivity. The transient depolarizations suggest the temporary development of wide channels in the membrane permitting free movement of hydrated cations according to the bulk electrochemical gradient.

Action Potentials↗
PubMed1988

Potassium channel "inactivation" induced by soft-glass patch pipettes.

We have studied the potassium currents of rat pituitary pars intermedia cells kept in primary culture using whole-cell recording with patch pipettes. The potassium current recorded with hard-glass pipettes is mainly carried by voltage-dependent channels that show slow inactivation in the presence of 0.5 mM internal EGTA. Fast "inactivation" of the potassium current is seen with patch pipettes fabricated from soft glass (soda glass or potash lead glass), and is probably caused by block of the potassium channels by di- or multivalent cations released from the glass.

Animals↗
PubMed1991

Ba2+ release from soda glass modifies single maxi K+ channel activity in patch clamp experiments.

Glasses used to fabricate patch pipettes may release components which affect ion channels (Cota, G., and C.M. Armstrong. 1988. Biophys. J. 53:107-109; Furman, R.E., and J.C. Tanaka. 1988. Biophys. J. 53:287-292; Rojas, L., and C. Zuazaga. 1988. Neurosci. Lett. 88:39-44). The gating properties of maxi K+ channels from Necturus gallbladder epithelium depend on whether borosilicate glass (BG) or blue tip hematocrit glass (SG) is used to construct the patch pipettes. The data are consistent with solubilization from SG of a component which exerts voltage-dependent, cytosolic-side specific block, closely resembling "slow block" by Ba2+ ions. Ringer's solution preincubated with SG, but not with BG, blocked inside-out maxi K+ channels when used as bathing solution. Mass spectrometry revealed that Ba2+ is released by the glass from fast and slow-release compartments (SG contains 3% wt/wt BaO), and is the only ion found in the solution at concentrations consistent with the observed channel block. Additionally, SG released O2-, Na+, Ca2+, and Mg2+, all to micromolar concentrations. These elements do not interfere with maxi K+ channels but they could in principle alter the properties of other ion channels. Thus, screening for channel-modifying substances released by the glass may be necessary for the adequate interpretation of patch-clamp results.

Animals↗
PubMed1994

Efficient rotamer elimination applied to protein side-chains and related spin glasses.

Folded proteins and spin glasses share various properties, such as seemingly random interactions between residues (spins), and one might presume that some generic behaviors of spin glasses would also be exhibited in a general way by proteins. But a comparison here shows that the side-chain conformation systems of apo-myoglobin and lysozyme are qualitatively different from specific closely related spin glass systems. This difference is manifest in the number of rotamers that can be identified as definitely not contributing to the global energy minimum. This identification is effected by using a significantly enhanced version of the Dead End Elimination theorem (Desmet, J., M. De Maeyer, B. Hazes, and I. Lasters. 1992. The dead-end elimination theorem and its use in protein side-chain positioning. Nature. 356:539-542), which is much more effective and efficient in eliminating rotamers. In several cases (for proteins, although not for spin glasses) this improved Dead End Elimination theorem succeeded in identifying the absolute global minimum of rotamer conformations, with no statistical uncertainty. The difference between protein and spin glass is due to correlations between the interactions of one residue pair with another pair, and probably will play an important role in the thermodynamic behavior of the protein system.

Algorithms↗
PubMed1999

Delay in the application of the cover glass is a potential source of error with the Makler Counting Chamber.

OBJECTIVE: To determine the effect of delaying the application of the cover glass of a Makler Counting Chamber (Sefi Medical Instruments, Haifa, Israel) on the apparent concentration of sperm or Dynabeads (Dynal Pty Ltd, Carlton, Victoria, Australia). DESIGN: Systematic alteration of the time taken to apply the cover glass. SETTING: Comprehensive infertility service. PATIENT(S): Fresh semen from a patient or washed sperm from a donor. INTERVENTION(S): For the Makler Counting Chamber, a 5-microL drop of the sperm or bead suspension was placed in the center of the lower platform and the cover glass was applied either immediately (0 seconds) or after a delay of 5, 10, or 30 seconds. MAIN OUTCOME MEASURE(S): The concentration of beads or sperm counted using an Improved Neubauer Hemocytometer or a Makler Counting Chamber. RESULT(S): There was a progressive increase in sperm concentration with a longer delay in applying the cover glass when sperm was suspended in either seminal plasma or culture medium. Repeating the experiments with Dynabeads resuspended in phosphate-buffered saline, serum, or seminal plasma showed the same trend, although the suspension of beads in serum seemed to settle the least over the first 10 seconds. CONCLUSION(S): Delay in the application of the cover glass is a potential source of error with the Makler Counting Chamber and should be avoided.

Female↗
PubMed1975

Ionic effects in the chromatography of proteins on columns of controlled-pore glass.

Bovine serum albumin, acetylcholinesterase and two non-protein markers were chromatographed on columns of controlled-pore glasses in buffer solutions of varied ionic strengths. Adsorption of protein to the glass and ionic effects due to repulsion of the negatively-charged solutes from the glass matrix were observed. When glasses were treated with Carbowax 20M, the adsorption disappeared but ion exclusion effects persisted. The ionic behavior of Carbowax-treated glasses was similar to that observed by one of the authors when using agarose columns.

Acetylcholinesterase↗
PubMed1998

Repair of acrylic resin denture base reinforced with glass fiber.

STATEMENT OF PROBLEM: The ultimate goal of any denture repair is to restore the original strength of the denture and to avoid further fracture. PURPOSE: This study investigated the strength and deflection of repaired acrylic resin joints reinforced with various glass fiber concentrations. MATERIAL AND METHODS: Transverse strength, maximum deflection, and modulus of elasticity of glass fiber-reinforced polymethyl methacrylate acrylic resin were studied with a 3-point load test on 54 intact specimens. Six concentrations of type B glass fiber specimens were prepared (n = 9 per each fiber group). Fractured joint margins were rounded, a 2-mm gap was placed between them, and then they were repaired with autopolymerizing acrylic resin and retested. RESULTS: Transverse strength, maximum deflection, and the stiffness of all joints were significantly lower after the repair. Among the groups tested, the units treated with 1% glass fiber displayed the highest transverse strength before and after repair. Modulus of elasticity of the repaired 1% fiber concentration units was enhanced by approximately 25% over those repaired but untreated with glass fiber (0% fiber).

Analysis of Variance↗
PubMed1999

Fluoride release of glass ionomer-based luting cements in vitro.

STATEMENT OF PROBLEM: There is considerable variation in generic formulation and in reported fluoride release from resin-modified glass ionomer luting cements. PURPOSE: This study compared fluoride release from 2 generically similar resin-modified glass ionomer luting cements (Vitremer and Advance) with release from 2 conventional glass ionomer luting cements (Ketac-Cem and Fuji I). MATERIAL AND METHODS: Ten specimen disks of each of the 4 luting cements were fabricated and immersed in deionized water in individual polystyrene jars. The jars were stored in a humidor at 37 degrees C between test periods. At the same time each day, for 28 days, fluoride release from each specimen disk was measured in parts per million by testing the storage water. RESULTS: The 4 luting cements tested showed an initial high concentration of fluoride release during the first week, followed by a gradual decrease over the study period. Vitremer luting cement demonstrated the greatest mean cumulative fluoride release in parts per million over the study period (198), followed by Fuji I (140), Ketac-Cem (110), and Advance (99) luting cements. CONCLUSIONS: Resin-modified glass ionomer luting cements showed fluoride release comparable to the conventional glass ionomer luting cements. Vitremer luting cement released more fluoride over the 28-day period than the other cements.

Analysis of Variance↗
PubMed1999

Microleakage of Class V resin-modified glass ionomer and compomer restorations.

STATEMENT OF PROBLEM: Resin-modified glass ionomers and polyacid-modified resin composites (compomers) have been introduced to provide esthetic restorations. However, there is concern about the marginal sealing ability of these materials, especially at the dentin (cementum) aspects of restorations. PURPOSE: This in vitro study evaluated the microleakage of Class V restorations made with resin-modified glass ionomers or a compomer. MATERIAL AND METHODS: Thirty noncarious human molar teeth were used. Standardized kidney-shaped Class V cavity preparations were placed in the buccal and lingual surfaces at the cementoenamel junction. Teeth were randomly assigned to 3 experimental groups of 10 teeth each and restored as follows: group 1, Fuji II LC; group 2, Vitremer; and group 3, Dyract. In all cases, the manufacturers' instructions were strictly followed. All materials were placed in a single increment. Unfinished restorations were immediately coated with the respective manufacturers' sealer or varnish and this was either light cured for 20 seconds or allowed to air-dry. After 24 hours, teeth were finished to contour and to the cavosurface margins, coated with nail varnish except for 1 mm around the restoration margin, thermocycled (1000x, 5-55 degrees C) and placed in a solution of 2% basic fuchsin dye for 24 hours at room temperature. The staining along the tooth restoration interface was recorded. RESULTS: Kruskal-Wallis 1-way analysis of variance revealed significant differences among all restorative materials for the overall, occlusal, and gingival scores (P =.03, P =.01, P =.01, respectively). Occlusal and gingival scores for each matched pair of restorative materials using the Wilcoxon test showed statistically significant differences between Fuji II LC glass ionomer cement and Dyract composite, both for the occlusal (P =.005) and gingival (P =.005) margins and also as an overall evaluation (P =.01), with Fuji II LC showing the least dye penetration. Vitremer revealed dye penetration scores not significantly different from Fuji II LC glass ionomer cement or Dyract composite. CONCLUSION: Resin-modified glass ionomers showed less or similar microleakage than the polyacid-modified composite resin tested.

Analysis of Variance↗
PubMed1994

An in vitro evaluation of plaster of Paris barriers used under amalgam and glass ionomer to repair furcation perforations.

Furcation perforations were created in the pulpal floor of 60 teeth and were repaired with amalgam alone, plaster of Paris under amalgam, light-cured glass ionomer alone, and plaster of Paris under light-cured glass ionomer. After the access openings were filled with composite resin, the teeth were immersed in 2% erythrocin B dye solution for 2 wk, sectioned longitudinally, and dye penetration was measured. The light-cured glass ionomer group provided the least amount of leakage, followed by the group of plaster of Paris under glass ionomer. The groups using amalgam alone and plaster of Paris under amalgam showed the most leakage. The plaster of Paris barrier prevented the overextension of the repair materials when used under amalgam and glass ionomer.

Analysis of Variance↗
PubMed1997

Evaluation of glass ionomer as an endodontic sealant: an in vitro study.

This study investigated the sealing ability of glass ionomer as a root canal sealer with and without lateral condensation of gutta percha cones. Ten gutta percha cones were embedded in Grossman's sealer and 10 in glass ionomer sealer. The sealers were mechanically separated from the gutta percha. The cone surfaces were examined using scanning electron microscopy (SEM). SEM revealed a characteristic etch pattern on the glass ionomer group and a hybrid layer on the cone surfaces of the Grossman's group. Additionally, 40 maxillary incisors were divided into four treatment groups: 1) glass ionomer sealer with lateral condensation, 2) glass ionomer sealer with only one master cone, 3) Grossman's sealer with condensation, and 4) Grossman's sealer with only one master cone. The average values for leakage (mm) in groups 1 through 4 were 0.81 +/- 0.75, 4.30 +/- 1.82, 0.67 +/- 0.80, and 1.10 +/- 1.68, respectively. Statistical analysis showed that group 2 leaked more than the other three groups.

Analysis of Variance↗
PubMed1990

Fluoride release from glass-ionomer cements in de-ionized water and artificial saliva.

Most of the data reported on the release of fluorides from glass-ionomer cements are based upon measurements made in de-ionized water. De-ionized water does not represent the complex chemistry of the oral environment. In this study, an artificial saliva solution was used, and the data on the fluoride ions released into it from four glass-ionomer cements were compared with those obtained in de-ionized water. The glass-ionomer cements used were: Ketac-Fil (ESPE), Ketac-Silver (ESPE), Fuji-II (GC), and Miracle Mix (GC). Ten disc samples (2 cm x 0.1 cm) of each cement were prepared. Each was individually suspended in either de-ionized water or artificial saliva (five samples in each medium) and stored for 24 h at 37 degrees C, then transferred to fresh media for a total of 60 days. Collected media were buffered with TISAB, and fluoride was measured by a specific electrode. Artificial saliva was prepared according to Fusayama et al. (1963). The data obtained showed that: (1) glass-ionomer cements released more fluoride in de-ionized water than in artificial saliva; (2) Ketac-Fil released 20% more fluoride in saliva than did Fuji-II, the latter releasing 49% more fluoride than Ketac-Fil in de-ionized water; and (3) conventional glass ionomers released more fluoride than did meta-reinforced ones in both media.

Cermet Cements↗
PubMed1990

Evaluation of glass-cermet cores under cast crowns.

The goal of this study was to compare two core materials--glass-cermet and amalgam--in terms of crown retention when significant tooth structure is missing. The glass-cermet's ability to bond to teeth with and without the aid of retentive pins and/or grooves was examined. The effects of two storage solutions, formalin and sodium azide, on the bond of the glass-cermet were also evaluated. Sixty human molars were obtained and stored in either formalin or sodium azide. Thirty molars were prepared with one wall of tooth structure remaining, and the other 30 were prepared with two walls. Before being restored with glass-cermet, the preparations received either no retention, retentive grooves and pins, or retentive grooves only. Each preparation restored with amalgam received pins and grooves. Type III gold crowns were cemented in vitro with glass-ionomer luting agent, thermocycled 2500 times (5-50 degrees C), and then removed under a tensile force. The to amalgam and has adequate adhesion to the tooth, without additional retention, when at least two walls of the tooth remain. However, when only one wall of the tooth remains, the amalgam core is superior under tensile forces. There was a significant difference between the sodium azide and formalin storage solutions with regard to bond strength in one group (two walls, no pins, no grooves). In general, the cores placed on teeth stored in sodium azide exhibited tensile bond strengths lower than those stored in formalin.

Adhesiveness↗
PubMed1996

Fluoride release profiles of restorative glass ionomer formulations.

OBJECTIVES: The amounts of fluoride released by different glass ionomer formulations were compared on the basis of individual fluoride release profiles in order to derive the effect of the physical and chemical formulation on the fluoride release process. METHODS: The fluoride release profiles of each of five specimens of ten glass ionomer cements setting by an acid-base reaction were investigated. The profiles were obtained by determining the amount of fluoride released [F] after equilibrating the samples at 37 degrees C in distilled water for 140 d. The [[F],t]-profiles were compared with a Multivariate Data Analysis on the basis of a Principal Component Analysis. RESULTS: The Multivariate Data Analysis reveals that eight of the ten glass ionomers can be classified into four distinct groups. When the cumulative amount of fluoride released by each sample, [F]c, is calculated and fitted as a function of time, a regression analysis (r > 0.99) reveals that [F]c for all samples is most adequately represented by [F]c = ([F]l x t)/(t + t1/2) + beta x square root of t, indicating that two kinetic processes are responsible for the fluoride release profiles. SIGNIFICANCE: A comparison of the parameters of this equation shows that the physicochemical rationale for the classification of the glass ionomers conforms to differences in the kinetics of these processes which are determined by the qualitative and quantitative chemical composition as well as by the presentation (hand-mixed vs. capsules) of the glass ionomer. From the classification, it becomes apparent that different formulations can result in the same fluoride release profiles.

Analysis of Variance↗
PubMed1998

Effect of acetic acid on the fluoride release profiles of restorative glass ionomer cements.

OBJECTIVES: This study investigates the fluoride release of glass ionomers in an acetic acid solution in order to substantiate a model according to which the short-term release results from an elution of loosely bound fluoride and the long-term release from an erosive leaching of the glass particles in the bulk of the cement. METHODS: Individual fluoride release profiles of five specimens of 10 acid-base setting restorative glass ionomers were obtained by determining the amounts of fluoride released by each sample at 37 degrees C in consecutive elutions for up to 140 days with 25 ml of a 0.01 mol/l acetic acid solution with pH = 4. Differences in the fluoride release profiles were determined with a Multivariate Data Analysis on the basis of a Principal Component Analysis. RESULTS: The fluoride release profiles of the 10 glass ionomers can be classified into five distinct groups which are characterized by a cumulative fluoride release described by the equation [F]c = [F]l t/(t + t1/2) + beta square root of t. The parameters ([F]l, t1/2) and beta are characteristic for the materials in the groups, and refer to the short-term and long-term fluoride release, respectively. The acidic solution enhances both processes compared to an elution in water, the effect being more pronounced for the long-term release. SIGNIFICANCE: The fluoride release mechanism is intrinsically the same as determined for elutions in water. The increased amount of fluoride released under acidic conditions, especially in the long term, corroborates that an erosive leaching of the glass particles in the bulk of the cement accounts for the long-term fluoride release.

Acetic Acid↗
PubMed1999

X-ray photoelectron spectroscopy study of the dentin-glass ionomer cement interface.

OBJECTIVES: The work was carried out with a view to identifying the elements composing the glass ionomer under study, and then to characterising the interactions occurring between this particular glass ionomer and the dentin substrate on which it was placed and with which it interacted. METHODS: The samples studied were sections of healthy human dentin on which a very thin film of auto-polymerisable cement, composed of a powder and a liquid, was deposited under para-clinical conditions. After separation, the interfaces on the dentin side and on the glass ionomer side were studied using X-ray Photoelectron Spectroscopy (XPS). RESULTS: This study showed that the dentin and glass ionomer cement exchanged mineral and organic elements. The acid contained in the liquid showed a certain degree of aggressivity, despite the presence of the glass ionomer. The dentin protein was, in fact, rapidly denuded from the very first minute. Migration of the mineral elements from one substrate to the other led to the formation of an intermediate layer on the surface of the materials. SIGNIFICANCE: This layer, which forms an interphase, enables the material to adhere to the dentin.

Adult↗
PubMed2000

Structural insights of glass-reinforced hydroxyapatite composites by Rietveld refinement.

Phase transformations and interstitial and/or substitution of trace elements during the liquid-phase sintering process of P2O5-CaO-MgO glass-reinforced hydroxyapatite (GR-HA) composites were examined by X-ray diffraction and Rietveld analyses. Using the Rietveld method for structure refinement, changes in the lattice parameters of the two main phases of the composites, hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP), as well as changes in several bond lengths and in the occupancy of the hydroxyl oxygen site in the HA phase structure were assessed. The glasses gave rise to formation of between approximately 45 and 50% of beta-TCP, with evidence for the Mg2+ enhancing the formation of beta-TCP. Between 1,300 and 1,350 degrees C, the beta-TCP inverts to alpha-TCP, without further decomposition of the residual HA. The glasses showed evidence for stabilisation of the hydroxyl group located in the hydroxyl channels. This is supported by measurements of the hydroxyl channel radius (Rc), the Ca2-OH bond length and the hydroxyl oxygen occupancy (Oocc). Results showed that the Mg2+ containing glasses induced the beta-TCP phase formation in the structure of GR-HA composites and retarded the beta-TCP into alpha-TCP transformation at higher temperatures. The chemical composition of the P2O5 glasses also induces modifications in the lattice parameters of the crystallographic phases present in the microstructure of the composites. This suggests some substitution of Mg2 + -for-Ca2+ in the beta-TCP structure during the liquid-phase sintering process.

Biocompatible Materials↗