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At least 1,423 records · Page 79Linked to original sources
PubMed2004

Characterisation of bioactive glass coatings on titanium substrates produced using a CO2 laser.

Titanium and its alloys are widely used in load-bearing bioinert implants. Bioactive glasses (BAGs) form a chemical bond with bone, but they are not suitable for load-bearing applications. Creating a BAG coating on a titanium implant could combine the best properties of both materials. The results tend to be poor when conventional firing methods are applied to coat titanium with BAG. A local application of heat to melt the glass can be achieved by a CO2 laser. A new method is introduced to create BAG coatings on titanium locally in a controlled manner, with a focused CO2 laser beam. The coatings produced by this method precipitate calcium phosphate in vitro. Processing parameters (number of coated layers, laser power, and processing atmosphere) providing a firm attachment of the glass and good in vitro bioactivity were identified. XRD analysis showed no crystallisation of the glass due to processing with the laser. EDXA indicated the formation of a calcium phosphate layer, which FTIR suggested to be a hydroxyapatite. The results show CO2 laser processing to be a promising technique for the manufacture of 30-40 microm BAG coatings on titanium.

Air↗
PubMed2004

Bioactivity of degradable polymer sutures coated with bioactive glass.

Novel bioactive materials have been prepared by coating violet resorbable Vicryl sutures with a bioactive glass powder derived from a co-precipitation method. Two techniques have been chosen for the composite preparation: pressing the sutures in a bed of glass powder and slurry-dipping of sutures in liquid suspensions of bioactive glass powders. The uniformity and thickness of the coatings obtained by the two methods were compared. The bioactivity of the sutures with and without bioactive glass coating was tested by soaking in an inorganic acellular simulated body fluid (SBF). The composite sutures were characterised by XRD, SEM and FTIR analyses before and after soaking in SBF solution to assess the formation of hydroxyapatite on their surfaces, which is a qualitative measure of their bioactivity. The possible use of bioactive sutures to produce tissue engineering scaffolds and as reinforcement of resorbable calcium phosphates is discussed.

Absorbable Implants↗
PubMed2001

A comparison of retention and the effect on caries of fissure sealing with a glass-ionomer and a resin-based sealant.

OBJECTIVE: To compare the retention and the caries preventive effect of a glass-ionomer developed for fissure sealing (Fuji III) and a chemically polymerized resin-based fissure sealant (Delton). DESIGN: A split mouth randomized design using contralateral teeth. SETTING: WHO Regional Demonstration, Training and Research Center for Oral Health, Damascus, Syrian Arab Republic. SAMPLE AND METHODS: 179 children, 7 years old at the start of the study, were recruited from schools close to the Center. Only children with at least one pair of permanent first molars that were caries free or only had incipient lesions were included in the study. Follow-up examinations for sealant retention were done after 6 months, 1 year, 2 years and 3 years. The number of children available for reexamination was 129 (after 6 months); 121 (after 1 year); 115 (after 2 years) and 116 (after 3 years). Four dental hygienists were trained in the sealant procedures and did approximately one fourth of the sealants each. RESULTS: After 3 years the glass-ionomer sealant was completely lost in almost 90% of the teeth compared to less than 10% of the resin sealed teeth. After 3 years the relative risk of a tooth sealed with glass-ionomer over that of a tooth sealed with resin was 3.38 (95% CL: 1.98; 5.79). This finding was consistent over type of tooth. CONCLUSIONS: The glass-ionomer sealant tested in the present study had poorer retention and less caries protective effect than the resin-based sealant used.

Bisphenol A-Glycidyl Methacrylate↗
PubMed2003

A 5-year evaluation of two glass-ionomer cements used as fissure sealants.

OBJECTIVE: To evaluate the retention and caries preventive effect of two glass ionomers used as fissure sealants: one resin modified glass ionomer (A) and one conventional glass-ionomer cement (B). SAMPLES AND METHODS: The permanent first molars of 100 children, 6-8 years of age at the start of the study, were sealed. Material A was applied on one side (right side, upper, and lower) and material B was applied on the contralateral side (left side, upper, and lower) of the mouth. The control group was composed of 108 children who did not receive fissure sealant but received oral health education. After 5 years, 64.0% of the children of the experimental group and 73.0% of the children of the control group were available for reexamination. RESULTS: Material A was completely lost in 74.2% and material B in 89.0% (Wilcoxon matched pairs test, P < 0.05). Total retention rate was 1.6% for materials A and B. After 5 years, caries increment was 21.5% for the experimental group and 34.2% for the control group (chi2-test, P < 0.05). CONCLUSION: Sealing pits and fissures with glass-ionomer cements was effective in preventing caries.

Chi-Square Distribution↗
PubMedDate not supplied

Identification of multiple structural species in silicate glasses by 29Si NMR.

Knowledge of the structure of silicate glasses is one key to understanding their chemical and physical properties, as well as those of the high-temperature liquids from which they form. Because first-neighbour ordering into SiO4 tetrahedra is well known, much of the recent discussion about glass structure has concerned intermediate-range order. One of the most fundamental questions that can be posed is the distribution of silicate tetrahedra with n bridging oxygens (shared between two tetrahedra), labelled as 'Qn' (0 less than or equal to n less than or equal to 4). This distribution is probably important in determining the properties of melts and glasses, but considerable controversy exists concerning the identification and quantification of such species. Here I present new evidence from 29Si NMR (nuclear magnetic resonance) spectroscopy that clearly resolves one significant part of this dispute: at least in sodium silicate glasses, a variety of species is present that is greater than that required by composition alone.

Glass↗
PubMed2004

Toughening of nanoporous glasses using porogen residuals.

Nanoporous glasses are inherently brittle materials that become increasingly fragile with increasing porosity. We show that remarkable increases in fracture energy can be obtained from remnants of the porogen molecules used to create the nanoscale pores. The interfacial fracture energy of approximately 2.6 J m(-2) for dense methylsilsesquioxane glass films is shown to increase by over one order of magnitude to >30 J m(-2) for glasses containing 50 vol.% porosity. The increased fracture resistance is related to a powerful molecular-bridging mechanism that was modelled using bridging mechanics. The study demonstrates that significant increases in interfacial fracture energy may be obtained using strategies involving controlled decomposition of the porogen molecule during processing of nanoporous glasses. The implications are important for a range of emerging optical, electronic and biological technologies that use nanoporous thin films, but are limited by the degradation of mechanical properties with increasing porosity.

Biotechnology↗
PubMed2003

Atomistic basis for the plastic yield criterion of metallic glass.

Because of their disordered atomic structure, amorphous metals (termed metallic glasses) have fundamentally different deformation mechanisms compared with polycrystalline metals. These different mechanisms give metallic glasses high strength, but the extent to which they affect other macroscopic deformation properties is uncertain. For example, the nature of the plastic-yield criterion is a point of contention, with some studies reporting yield behaviour roughly in line with that of polycrystalline metals, and others indicating strong fundamental differences. In particular, it is unclear whether pressure- or normal stress-dependence needs to be included in the plastic-yield criterion of metallic glasses, and how such a dependence could arise from their disordered structure. In this work we provide an atomic-level explanation for pressure-dependent yield in amorphous metals, based on an elementary unit of deformation. This simple model compares favourably with new atomistic simulations of metallic glasses, as well as existing experimental data.

Glass↗
PubMed1992

The comparative strengths of commercial glass-ionomer cements with and without metal additions.

Metal reinforced glass-ionomer cements are said to possess superior mechanical properties when compared to non-metal reinforced glass-ionomer cements. However, the literature to date does not always support this view, owing to the variety of materials and test methods employed. In this study the mechanical properties of three reinforced and three standard materials were tested using the standard specification tests of compressive and diametral strength in addition to tensile strength using the four point bend test. The tensile strength was also measured using the shell test in order that this test, which on theoretical grounds is more suited to these materials, may be evaluated. Six specimens of each material were prepared for each of the test modalities resulting in the conclusion that the addition of metal to glass-ionomer cements can markedly increase the strength of the materials. However, the method of fusing the metal to the glass rather than by simple addition does not produce any advantages in strength. In this evaluation one reinforced material was significantly stronger than all other materials in all four test modalities. The compressive strength test which appears in most standards does not appear to be very discriminatory. Of the tensile tests, which have more clinical significance, the results of the diametral strength tests, which are included in some standards, appear to be at variance with the other two tensile tests, suggesting that the flexural or shell test would be more appropriate.

Cermet Cements↗
PubMed1992

Characterisation of the ultrastructure of glass-ionomer (poly-alkenoate) cement.

Set glass-ionomer cements were sectioned with a diamond knife and examined in the transmission electron microscope. Their appearance was in accordance with the theoretical structure of these materials, close examination revealing glass particles surrounded by a siliceous layer set in a hydrogel matrix. The elemental composition of each region was determined by X-ray microanalysis (energy dispersive). The results of microanalysis supported the ultrastructural observations, with ions that originated from the glass particles being detected throughout the matrix of the set cement. It was suggested that the mobility of these ions in the matrix phase was important in determining the biocompatibility and adhesive properties of glass-ionomer cements.

Electron Probe Microanalysis↗
PubMed2005

Glass microfluidic devices with thin membrane voltage junctions for electrospray mass spectrometry.

In this study a novel glass membrane was prepared for conducting high voltage (HV) to solution in the channel of a microfabricated device for generation of liquid electrospray. Taylor cone formation and mass spectra obtained from this microdevice confirmed the utility of the glass membrane, but voltage conduction through the membrane could not be successfully explained based solely on the conductivity of the glass itself. This novel method for developing a high-voltage interface for microdevices avoids direct metal/liquid contact eliminating bubble formation in the channel due to water hydrolysis on the surface of the metal. Further, this arrangement produces no dead volume as is often found with traditional liquid junctions. At the same time, preliminary investigations into the outlet design of glass microdevices for interfacing with electrospray mass spectrometry, was explored. Both the exit shape and the use of hydrophobic coatings at the channel exit of the microdevice electrospray interface were evaluated using standard proteins with results indicating the utility of this type of design after further optimization.

Equipment Design↗
PubMed2006

Medium-range order in sodium phosphate glasses: a quantitative rotational echo double resonance solid state NMR study.

Sodium ultraphosphate glasses (Na(2)O)(x)(P(2)O(5))(1-x) show a strongly non-linear dependence of the glass transition temperatures T(g)(x) on composition. To explore the structural origins of this behaviour, local and medium range ordering processes have been investigated by state-of-the-art (23)Na high-resolution and dipolar NMR spectroscopies. In particular, (31)P(23)Na) and (23)Na((31)P) rotational echo double resonance (REDOR) experiments have been analyzed to yield quantitative constraints for the structural description of these glasses. The sodium ions are found to be randomly distributed and, for x < 0.25, spatially correlated with a single metaphosphate-type Q((2)) unit at a distance of 330 pm. In this region, unusual compositional trends observed for the (23)Na chemical shifts and nuclear electric quadrupolar coupling constants, measured by triple-quantum magic-angle spinning (TQMAS) NMR, suggest a systematic decrease of Na coordination number with x. At higher sodium contents (x > 0.25), the magnitude of the (31)P((23)Na) dipolar interaction increases markedly, indicating a significantly increased extent of Q((2))-Na-Q((2)) crosslinking. Based on these results, a comprehensive description of medium-range order in sodium ultraphosphate glasses is developed, suggesting that the T(g)(x) dependence is closely linked to changes in the relative phosphorus/sodium distance distributions.

Computer Simulation↗
PubMed1968

Incorporation of [5-3H]uridine and attachment of cells to glass during activation of lymphocytes induced by phytohaemagglutinin.

1. Shortly after the addition of phytohaemagglutinin to cultures, partially purified pig blood lymphocytes showed increased labelling of RNA by [5-(3)H]uridine and began to attach to the glass of the culture tubes. 2. In the presence of phytohaemagglutinin most cells became attached to glass during the first 5hr. of culture; those first attaching had a low mean RNA/DNA ratio. In the absence of phytohaemagglutinin cell attachment to glass was diminished. 3. During the first 5hr. of culture the rates of increase of radioactivity/unit of DNA of the attached and unattached populations in the presence of phytohaemagglutinin were of the same order and exceeded that of cultures without phytohaemagglutinin. 4. The increase of labelling in cultures to which phytohaemagglutinin was added after cells had sedimented to glass was greater than that occurring in cultures in which cells were resuspended before phytohaemagglutinin was added.

Animals↗
PubMed1996

A three-year clinical trial using a glass ionomer cement for the bonding of orthodontic brackets.

Recent clinical studies measuring orthodontic bracket failure, when using glass ionomer cement as an adhesive, have reported a wide range of percentages of bracket failure. The present study recorded bracket failure over a 3-year period, longer than had been previously measured. Seventeen participants were randomly assigned to one of two treatment groups, either using glass ionomer cement or composite resin for bonding. In each group, brackets were bonded to incisors, canines, and premolars. Bracket failure was measured over the duration of comprehensive orthodontic treatment for all participants. Brackets bonded with the glass ionomer cement were more likely to fail (log-rank test; P < or = 0.022). This difference was clinically significant. At the present time, the disadvantage of extra bracket failures appears to outweigh potential advantages when considering glass ionomer cement for the routine bonding of orthodontic brackets.

Adhesives↗
PubMed2006

Metallic brackets bonded with resin-reinforced glass ionomer cements under different enamel conditions.

OBJECTIVE: To assess the shear bond strength of metallic orthodontic brackets bonded with either Fuji Ortho or Ortho Glass LC resin-reinforced glass ionomer cements to enamel surfaces under different conditions, namely, enamel without etching, enamel conditioned with 37% phosphoric acid and enamel conditioned with Transbond Plus Self Etching Primer (TPSEP). MATERIALS AND METHODS: One hundred and five bovine inferior incisors were divided into seven groups (n = 15). In group 1 (control) Transbond XT was used according to the manufacturer's recommendations. In groups 2, 3, and 4 all using Fuji Ortho LC, the brackets were bonded, respectively, to enamel nonetched, enamel etched with 37% phosphoric acid, and enamel etched with TPSEP. In groups 5, 6, and 7, the bonding was performed using Ortho Glass LC under the same enamel conditions observed in the other experimental groups. After 24 hours, shear bond strength tests were performed for all samples at a crosshead speed of 0.5 mm/min. RESULTS: The results (MPa) showed no statistically significant difference between groups 1, 3, and 4 (P > .05). However, such groups were statistically superior to the others (P < .05). No statistically significant difference was observed between groups 2, 6, and 7 (P > .05). Group 5 showed the lowest shear strength value, which was also statistically inferior to the other groups (P < .05). CONCLUSIONS: Regardless of the enamel treatment, Fuji Ortho LC yielded shear strength values superior to those from Ortho Glass LC.

Acid Etching, Dental↗
PubMed2000

The effect of polishing systems on microleakage of tooth coloured restoratives: Part 1. Conventional and resin-modified glass-ionomer cements.

The purpose of this in vitro study was to investigate the effect of polishing systems on the microleakage of conventional and resin-modified glass-ionomer cements. Class V cavities were prepared at the cemento-enamel junction of 80 freshly extracted posterior teeth. The prepared teeth were randomly divided into two groups and restored with conventional or resin-modified glass-ionomer cements. The restored teeth were stored in distilled water at 37 degrees C for 1 week after removal of excess restorative with diamond finishing burs. The restored teeth were then divided into four groups of 10 and finished and polished using the following systems: Two Striper MFS; Sof-Lex XT; Enhance Composite Finishing and Polishing System; Shofu Composite Finishing Kit. The finished restorations were subjected to dye penetration testing. Results showed that the microleakage at dentin margins of conventional glass-ionomer cements and enamel margins of resin-modified glass-ionomer cements are significantly affected by the different polishing systems.

Analysis of Variance↗
PubMed2004

Effects of variation in particle size on biaxial flexural strength of two conventional glass-ionomer cements.

Conventional glass-ionomer cements (GICs) have a slow maturation time. Reduction in time of maturation may be achieved by acceleration of the setting reaction. One factor that assists this is the reduction in glass particle size producing a larger surface area for reaction. The resulting rapid set and more rapid maturation should potentially lead to less long-term degradation. Biaxial strength measurements were made with respect to time for two GICs of similar compositions but with differing particle size distributions at different time intervals after immersion in both water and artificial saliva. There was little difference between the strength of the two materials over periods up to 12 weeks. A theoretical estimation of the relative surface areas of glasses showed that, despite there being twice the surface area available for reaction for one glass, there was little difference in strengths values between the two materials at any of the times tested here. The similarity in strength values despite this substantial difference suggests that the larger particles may have a greater influence in the cement forming process.

Dental Stress Analysis↗
PubMed2001

An improved method of sperm selection by glass wool filtration.

An improved method of sperm selection by glass wool filtration is introduced. After incubation of glass wool filtrates for 30 min at 37 degrees C in a conical-shaped 1.5-ml tube, an enrichment of highly motile spermatozoa was found in the bottom layer of the tube. The effect turned out to be dependent on the conical shape of the tube, as it was not observed in flat-bottomed tubes. Native ejaculates (obtained from 30 men) and their glass wool filtrates were analysed by cell counter, computer-assisted sperm-motility analysis, morphological differentiation and supravital staining of spermatozoa. When 400 microl of ejaculate, diluted with 800 microl of medium, was applied to the top of a column consisting of a 1-ml disposable syringe barrel gently packed with 15 mg of glass wool to a depth of 6 mm, an enrichment of viable spermatozoa was found in the first three 100-microl fractions taken from the bottom of the tube. It is the simplicity of this technique that makes it so easily applicable.

Cell Adhesion↗
PubMed2005

[The use of a thermomechanical cleaning procedure for removal of residual particles of corund blasted or glass bead peened implants in total hip arthoplasty].

INTRODUCTION: Shot peening and grit blasting techniques are used to modify surfaces of hip endoprostheses. Alumina blasting techniques using highly pure corund (Al (2)O (3)) particles create a rough surface of Titanium implants to achieve a better osteointegration in cementless total hip arthroplasty. An increasing number of publications in maxillo-facial-surgery and orthopedic surgery show that there is a significant contamination with remnants on corund blasted surfaces. To our knowledge no previous study analysed the effects of cleaning procedures of hip endoprostheses in respect to glass beads and Al (2)O (3) remnants. MATERIAL AND METHOD: The surface of the flexible anisotropic Vector cup and the stiff modular MRP-Titan stem (one implant each) were analysed with respect to Al (2)O (3) or glass particles before and after the cleaning procedure. The implants were cleaned using an ultrasound bath for 10 or 20 minutes under nitrogen cooling or simple ultrasound bath with water. A field emission scanning electron microscopy (LEO 1525) was used for the detection of the particles on the implant surface with a backscattered electron detector. The proportion of the surface covered with particles was determined with an imaging analyze software (analySIS, Soft Imaging System GmbH). RESULTS: A reduction of corund particles on the surface of the flexible anisotropic Vector cup of up to 5.2 % (from 40.0 % to 34.8 %) after 10 minutes nitrogen cooling was achieved. A reduction of corund particles on the surface of the stiff MRP-Titan stem of up to 2.2 % (from 38.8 % to 36.6 %) was observed after 20 minutes of non cooled ultrasound bath whereas a reduction up to 3.2 % (from 25.8 % to 22.6 %) of glass particles after 10 minutes of nitrogen cooled ultrasound bath was detected. CONCLUSION: With the cleaning procedure tested only incomplete removal of just the small glass and Al (2)O (3) particles is possible. Further research is needed to reduce or even avoid residual particles in total hip arthoplasty.

Arthroplasty, Replacement, Hip↗