bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dense alumina aged in vivo
Authors: Osterholm H. H. , Day D. E. 
Published: December 2004

AbstractAuger electron spectroscopy was used to investigate the relative concentration of the calcium impurity at the external and fracture surfaces of a dense alumina after in vivo exposure for 6, 12, and 23 weeks. The Ca concentration at the external surface initially decreased, reached a minimum at 12 weeks, and increased thereafter. These results were compared with the flexural strength, which decreased nearly linearly from 6 to 23 weeks.
The ultrastructure of the interface between a glass ceramic and bone
Authors: Gross U. , Brandes J. , Strunz V. , Bab I. , Sela J. 
Published: December 2004

AbstractThe interface of alkali‐poor glass ceramic implanted in femora of male Sprague‐Dawley rats shows soft tissue, chondroid, osteoid, and bone in connection with the implant. The ultrastructure of the interface with soft tissue mainly exhibits a corrosion process, during which the dissolution of the crystalline phase of the glass ceramic precedes the dissolution of the glassy phase. Macrophages are involved in this process phagocytosing debris of the glassy phase and removing as well as dissolving the remainders of the glass ceramic. Under circumstances not yet fully understood, the corrosion stops, and ground substance like material is deposited, which can be, at least partially, mineralized. After the disappearance of macrophages, chondroblasts, and/or osteoblasts lay down collagen fibrils and ground substance in which matrix vesicles are discernible, representing initial foci of mineralization. Areas with bone connection display collagen fibers and deposits of apatite crystals in close relationship to the bulk glass ceramic as well as small particles mainly derived from the glassy phase of the implant, providing the micromorphological substrate for the shearing and tensile strength of the interface between glass ceramic and bone.
Physical characterization of microporous poly(2‐hydroxyethyl methacrylate) gels
Authors: Migliaresi C. , Nicodemo L. , Nicolais L. , Passerini P. 
Published: December 2004

AbstractPoly(2‐hydroxyethyl methacrylate)‐(PHEMA) has been prepared by polymerizing in presence of different types of water‐soluble additives, at various amounts, which were removed by swelling in water. Mechanical properties of swollen samples have been measured and analyzed by using the classical theory of rubber elasticity. Water permeability measurements were also performed to detect the presence of micropores and to determine the type of water transport. It has been shown that it's possible, using different types and amounts of additives, to obtain a wide range of physical properties of swollen PHEMA as required for various biomedical applications.
A silver staining technique for investigating wear of restorative dental composites
Authors: Wu W. , Cobb E. N. 
Published: December 2004

AbstractA silver staining technique was developed to demonstrate microdefects in dental restorative composites. Fine silver particles were preferentially introduced into the damaged region to provide optical contrast between the damaged and the undamaged regions. The amount of silver deposition determined with an electron probe microanalyzer, provided an indication of the extent of damage within the dental composites. Examples to demonstrate this technique were given with one clinically worn dental composite restoration and one in vitro worn composite sample.
Platelet adhesion onto sulfonated artificial red blood cells
Authors: Muramatsu Nobuhiro , Kondo Tamotsu 
Published: December 2004

AbstractRabbit hemolysate‐loaded microcapsules having sulfonic acid groups on their surface were prepared and rabbit platelet adhesion onto the sulfonated surface was examined kinetically. Rabbit platelets adhered more markedly onto the surface of a higher charge density than that of a lower one, indicating a trend similar to that found in the case of the surface having carboxyl groups. Moreover, the platelets were found to be stickier in the buffer solution than in the plasma, though the dependence of platelet adhesion in the buffer solution on the magnitude of surface charge of the sulfonated artificial red blood cells was still recognized.
Molecular and macroscopic properties of PMMA bone cement: Free‐radical generation and temperature change versus mixing ratio
Authors: Turner R. C. , Atkins P. E. , Ackley M. A. , Park J. B. 
Published: December 2004

AbstractThe molecular and macroscopic changes occurring during the polymerization of poly(methyl methacrylate) (PMMA) bone cement have been investigated. Electron paramagnetic resonance (EPR) spectroscopy was used to monitor free‐radical generation and this was compared to temperature changes occurring in the cement for various ratios of polymer powder to liquid monomer (P/L ratio) used in the sample preparation. Both the concentration and the characteristic growth time of the free radicals associated with the polymerization of the bone cement depended on the P/L ratio used. Larger P/L ratio resulted in shorter characteristic growth time for the free radicals as well as a shorter time for the occurrence of the peak sample temperature. Smaller P/L ratios gave smaller maximum concentrations of free radicals and larger peak temperatures. These results are explained on the basis of (1) more initiators present at higher P/L ratios resulting in faster polymerization and (2) less initiators and more monomers present at smaller P/L ratios resulting in fewer radicals but more exothermic reactions. The free radicals present in the bone cement due to the manufacturer's sterilization process were found to be proportional to the fraction of powder used in the preparation, indicating negligible monomer loss during sample mixing.
Surface spectroscopic studies of Biomer
Authors: Graham Susan W. , Hercules David M. 
Published: December 2004

AbstractThe objective of this work was to determine whether there is a significant difference in composition between the air facing and mold facing sides of Biomer and to see if the mold itself affects the polymer surface. A detailed analysis of Biomer was undertaken using x‐ray photoelectron spectroscopy (ESCA), secondary ion mass spectroscopy (SIMS), and low energy ion scattering spectroscopy (ISS). Previous workers have used FTIR and ESCA to study Biomer and comparisons with their results will be discussed. Because of the increase in surface sensitivity SIMS and ISS can be valuable tools for studying polymeric materials. SIMS has been used to identify the structure of the Biomer air and mold facing surfaces from both glass and nickel molds. ESCA and ISS have indicated the presence of a silicon contaminant on the air and mold facing surfaces and SIMS has shown that the form of the silicon contaminant is probably a polysiloxane.
Fretting corrosion in saline and serum
Authors: Brown Stanley A. , Merritt Katharine 
Published: December 2004

AbstractFretting corrosion of stainless‐steel round hole plates and spherical head screws was studied using a simulator that produced a rocking motion of the heads in the plate holes. Experiments were run for 7 days, with the simulator producing 1 oscillation/s for 16 h/day. Fretting corrosion was studied in 0.9% NaCl and in a 10% solution of fetal calf serum in saline. The results showed a tenfold decrease in fretting corrosion when the serum was added to the saline. Measurements of the weight of the two screws and two‐hole plate showed those in saline lost 2.9 mg as compared to 0.3 for those in 10% serum. The concentration of nickel in the saline solutions was 12.4 μg/mL compared with 0.85 in serum. Visual examination of the solutions and implants revealed that those in saline had a significant amount of corrosion products while those tested in 10% serum were bright and shiny. Recordings of electrical potentials demonstrated that the addition of serum to saline significantly reduced the change in potential from rest to fretting condition.
Effects of temperature on mechanical properties of composite dental restorative materials
Authors: Draughn Robert A. 
Published: December 2004

AbstractIn the oral environment, dental restorative materials are exposed to temperatures ranging from 10° to 50°C. Since the properties of many polymeric materials are sensitive to temperature of this magnitude, it is important to define the effects of service temperature on the mechanical properties of polymer matrix dental composites. Six commercial composites were tested in compression at 11 temperatures, ranging from 2° to 80°C. The volume fraction of filler particles in the materials is either 0.45 or 0.55, and they contain a range of particle sizes and particle compositions. The tests show that ultimate strength decreases linearly with increasing temperature. Strength is higher for the lower volume fraction material and is decreased by the presence of a small percentage of very large particles. Elastic modulus and yield strength decrease sigmoidally with increasing temperature and depend only on particle volume fraction. In the clinically significant temperature range, ultimate strength decreases 14%, the decrease in elastic modulus is either 6 or 11%, and the yield strength decreases 45%. The data show that the temperature conditions of the oral environment can significantly affect the mechanical properties of composite dental restorative materials.
Poly(methyl acrylate‐co‐hydroxyethyl acrylate) hydrogel implant material of strength and softness
Authors: Refojo M. F. , Leong F.‐L. 
Published: December 2004

AbstractThe physiochemical properties of a hydrogel used as a scleral buckling implant for retinal detachment surgery are described. The new material was prepared by simultaneous polymerization and crosslinking of 2‐hydroxyethyl acrylate with methyl acrylate and ethylene diacrylate, in the presence of an inert diluent, ethylene glycol. At equilibrium swelling, the hydrogen absorbed 17% water and had a durometer hardness (DH) of 15 (Shore Durometer A‐2). A unique property of this material was its swelling hysteresis; when the gel swollen in 70% ethanol was placed in water, it retained a high level of hydration (75% water) and softness (DH 8), and most of its elasticity and strength as well. Then the swelling decreased very slowly so that the implant reached its ultimate size at equilibrium swelling in ca. 1 year. This property is especially useful in the scleral buckling procedure, in which a soft implant indents the sclera over the detached retina until reattachment is achieved. In addition to this advantage, this hydrogel is more elastic and stronger than available hydrogels of similar softness.
Dynamic mechanical properties of medical grade silicone elastomer stored in simulated body fluids
Authors: Carl Ward Thomas , Timothy Perry John 
Published: December 2004

AbstractMedical grade silicone rubber samples were immersed in distilled water and in pseudo‐extracellular fluid (PECF) at 37.5°C for up to four months. Periodically, the storage modulus and log decrement of the samples were measured on a torsion pendulum. Up to 20% increases in storage modulus and about 40% decreases in log decrement were found over the four months independent of sample surface area. Similar trends were seen in both distilled water and in PECF. Higher (59°C) storage temperatures accelerated the changes. Small amounts of moisture uptake were detected. However, the presence of water in the samples did not cause the change in mechanical properties.
A comparison of the mechanical behavior of aluminas in air and simulated body environments
Authors: Dalgleish B. J. , Rawlings R. D. 
Published: December 2004

AbstractFracture toughness and modulus of rupture tests have been carried out on three aluminas, which differed in composition and microstructure, in a variety of environments (air, deionized water, albumen/salt solution, Ringer's solution, and fresh human plasma). Generally tests in liquid environments were found to result in a reduction in the asmeasured critical stress intensity factor and the modulus of rupture, as compared with the values appertaining to air. However, estimates of the stress for a 50‐year, 99.9% survival probability were encouraging; for high‐purity, small‐grain‐size alumina a value of 112 MN/m2 was calculated, which is considerably greater than the estimated maximum tensile stress in a femoral sphere.
Evaluation of acrylic bone cements and their performance standards
Authors: Edwards R. O. , Thomasz F. G. V. 
Published: December 2004

AbstractEight acrylic bone cement products were examined according to the methods set out in three published performance standards, viz., Australian Standard 2265 Part 1, 1979, ASTM specification F451‐76, and the ISO specification 5833/1, 1979. In addition, chemical analyses were carried out by GC, NMR, and IR spectroscopy as well as refractive index measurement, all to establish the main constituent of the products. All the products compiled to the physical, compositional, and sterility requirements of AS 2265. However, all but one sample failed to comply with the solubility requirements of ASTM F451‐76. Also, none of the samples compiled with the doughing time requirements of ISO 5833/1. On further analysis, the results suggest that the water solubility and sorption requirements of ASTM F451‐76 are restrictive and that the ISO doughing time test methodology requires modification. Various degrees of noncompliance to the requirement of all three specifications were noted on the labeling and in the information content of product inserts. Two additional clauses on mixing tools and radiopacity have been suggested for incorporation into the above standards.
A critical evaluation of the acute systemic toxicity test for dental alloys using histopathologic criteria
Authors: Culliton C. R. , Meenaghan M. A. , Sorensen S. E. , Greene G. W. , Eick J. D. 
Published: December 2004

AbstractThe A.D.A. acute systemic test for type II, class 11 materials defines compliance on the basis of fewer than 50% mortality at 2 weeks. Histopathologic criteria were developed from pilot study data to evaluate the effects of these materials. In this double blind study, the frequency of histopathological changes in lung, liver, small intestine, and kidney were rated at 2 and 5 weeks, for six dental crown and bridge alloys ranging from 44% to 97% (Au, Pt, and Pd). Two positive 360 mg/kg and 1 g/kg of cadmium and two negative, a blank capsule and untreated control groups were used. There was significant difference (chi square test, X2 = 0.95) between the positive and negative controls at 2 and 5 weeks. The lung, liver, kidney showed the highest level of histopathological changes. Significant changes occurred in the four tissues for all alloys at two and five weeks. At five weeks, alloys with a lower noble metal content (44–62%, Au, Pd, and Pt) elicited significant chronic changes, while higher noble metal content (78–97%) showed healing and no significant difference from the negative controls. Applying histopathologic criteria and statistical parameters independent examiners can examine experimental animals and arrive at conclusive and reproducible results.
An insulin delivery system from oxidized cellulose
Authors: Singh M. , Vasudevan P. , Sinha T. J. M. , Ray A. R. , Misro M. M. , Guha K. 
Published: December 2004

AbstractCellulose oxidized with periodate (OC) has been shown to be a biocompatible, biodegradable matrix suitable for immobilization and sustained release of drugs. In the present work, insulin was immobilized on the OC‐matrix and the release profile in vivo and in vitro was examined. The hormone is bound to the matrix by Schiff's bond formation and is released by hydrolysis of this bond as well by degradation of the OC‐matrix. The release can be sustained over longer periods by reducing the Schiff's base with NaBH4. The insulin depots could be conveniently injected as suspensions and are able to maintain glucose levels in diabetized rabbits at normal values over several days.
The effect of the environment on the crack initiation toughness of dental poly(methyl methacrylate)
Authors: Hargreaves A. S. 
Published: December 2004

AbstractThe development of linear elastic fracture mechanics has been traced briefly, with emphasis on the approach based on stress intensity. Factors affecting fracture toughness include the effects of the environment, but little about these is known at present. Fracture behavior in two‐phase acrylic systems has also been reviewed. In the light of this, SEN specimens of heatcured denture‐base PMMA were saturated in a range of liquids and extended to failure at chewing speed. Crack initiation toughnesses and critical flaw sizes were thus determined. The effects of the chemical environment on the relationship between these two parameters showed that vegetable oil had increased the notch sensitivity of the resin, while 4% ethanol and soap solution increased the plasticization of the crack tip beyond that in water alone. Although the behavior at the crack tip was similar for all the other aqueous media, the craze resistance of the resin could be altered by the chemical nature of the liquid; this might explain in part the behavioral strengths of the un‐notched material.
A study of bone remodeling using metal‐polymer laminates
Authors: Szivek J. A. , Weatherly G. C. , Pilliar R. M. , Cameron H. U. 
Published: December 2004

AbstractBone remodeling due to stress‐shielding has been studied using a model system consisting of metal‐polymer laminated fixation plates securely fixed to canine femurs. The plate stiffness was controlled by varying the ratio of metal facing to polymer core thickness in the laminate design while secure fixation to bone was achieved by providing a porous bone interfacing surface for the ingrowth of bone from the periosteal surface. Observations of laterally and medially placed plates indicated resorption in the area of the periosteal and endosteal bone surfaces respectively, for the higher stiffness composite plates used. The results indicate that plate stiffness greater than approximately 70 GPa (axial) and 6 N m2 (flexural) will result in extensive bone remodeling in the canine femur after a six month implantation period.
NMR spectroscopy of dental materials. I. 31P studies on phosphate‐bonded cement liquids
Authors: O'Neill Ian K. , Prosser Havard J. , Richards Colin P. , Wilson Alan D. 
Published: December 2004

AbstractPhosphorus‐31 nuclear magnetic resonance spectroscopy of phosphoric acid solutions containing zinc and aluminium indicates that zinc forms simple salts in solution, whereas aluminium forms a number of complexes, some of which are polymeric. The formation of the aluminophosphoric acid complexes controls the gelation and strengthening of the dental silicate cement and prevents the formation of crystalline zinc phosphate in the zinc phosphate cement.
A study of the volumetric setting shrinkage of some dental materials
Authors: Bandyopadhyay S. 
Published: December 2004

AbstractThe setting reaction of six dental materials has been studied by using a water dilatometer at 25° and 37°C. Where there is no water absorption during the test, the method gives reproducible values of the setting shrinkage and at the same time shows a clear physical picture of the entire setting process. This method is suitable for adaptation as a specification test for setting shrinkage and has good potential for being used as a supplementary or substitute test for initial and final set times.
In vitro studies into the release of chlorhexidine acetate, prednisolone sodium phosphate, and prednisolone alcohol from cold cure denture base acrylic
Authors: Addy M. , Thaw M. 
Published: December 2004

AbstractAn investigation was carried out into the release of chlorhexidine acetate, prednisolone sodium phosphate, and prednisolone alcohol from a cold cured acrylic denture base material. The drugs were added at 10% w/w with the powder phase of the material. Water, at the concentrations of 10%, 20%, and 30% of the monomer phase of the material was added to chlorhexidine‐containing and chlorhexidine‐free samples. Spectrophotometric and bioassay measurements of the release of chlorhexidine demonstrated protracted delivery to 140 days. The daily release rate was increased by the addition of water to the material and at 30% water incorporation the release was greater and increased up to 190 days. The release pattern of prednisolone sodium phosphate was similar to that of chlorhexidine without the addition of water. Prednisolone alcohol was released for a much shorter period and at lower levels. Scanning electron microscopic examination of the polished, etched, and fractured surfaces of the material demonstrated that chlorhexidine acetate and prednisolone sodium phosphate were incorporated into the interbead matrix areas of the material. The irregularities in the material increased with the addition of water. Prednisolone alcohol produced minimal changes in the specimens except after soaking in water for 140 days when numerous small defects could be seen in the matrix zones at high magnification. The use of materials such as water to increase porosity appears a simple method of improving the release pattern of drugs from acrylic. However, the strength of the resulting material would require support from an existing intraoral prosthesis or appliance.
Effect of fibronectin on the adhesion of an established cell line to a surface reactive biomaterial
Authors: Seitz T. L. , Noonan K. D. , Hench L. L. , Noonan N. E. 
Published: December 2004

AbstractWe have demonstrated that an established hamster cell line (NIL 8 M‐2) will adhere to the bioceramic bioglass. The rate at which the NIL 8 M‐2 cells assume a spread morphology on bioglass is density dependent and the morphology displayed by NIL 8 M‐2 cells attached to bioglass is much more elongated than that displayed by NIL 8 M‐2 cells attached to nonreactive glass. Precoating the bioglass with the plasma form of human fibronectin significantly reduces the density dependent nature of cell spreading. Coating the bioglass with fibronectin also reduces the time required for cell spreading and changes the morphology of the attached cells from an elongated to an extremely flattened shape. Our work raises the possibility that bone‐implant adhesion might be improved by introducing molecules relevant to cell‐substrate attachment into the biomaterial prior to implantation.
The promotion of adhesion by the infiltration of monomers into tooth substrates
Authors: Nakabayashi Nobuo , Kojima Katsunori , Masuhara Eiichi 
Published: December 2004

AbstractThe effectiveness of 4‐methacryloxyethyl trimellitate anhydride (4‐META) on the adhesion of an acrylic rod with etched dentine and enamel was studied. Etching of tooth substrates with a 10% citric acid‐3% ferric chloride solution prior to the adhesion proved effective. Monomers with both hydrophobic and hydrophilic groups like 4‐META promoted the infiltration of monomers into the hard tissue. The infiltrated monomers polymerized in situ and good adhesion with the tooth substrates took place. The tensile adhesive strength was 18 MPa on the etched dentine. Scanning electron microscopic studies suggested that the monomers possess affinity with the hard tissue. The good adhesion was not provided by the interlocking at the tubules as had been considered previously.
Rheological studies of the polymerization of elastomeric impression materials. II. Viscosity measurements
Authors: Cook Wayne D. 
Published: December 2004

AbstractAs part of a detailed study of the curing of a range of dental elastomeric impression materials, a cone and plate rheometer was used to measure the variation in viscosity due to chain growth. The dependence of this behavior on the catalyst/base ratio, retarding and accelerating agents, and alternative initiators was studied and rationalized in terms of the polymerization chemistry investigated previously. Limited success was achieved with the quantitative interpretation of this data in terms of the polymerization kinetics. Of clinical relevance, only the viscosity behavior of the imine‐terminated polyether and one of the thiol‐terminated polysulfides approached that of an ideal impression material.