bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rheological studies of the polymerization of elastomeric impression materials. III. Dynamic stress relaxation modulus
Authors: Cook Wayne D. 
Published: December 2004

AbstractAs part of a detailed study of the curing of a range of dental elastomeric impression materials, the 10‐s stress relaxation modulus was measured as a function of the curing time. The influence of the catalyst/base ratio was also investigated and compared with the pregel viscosity previously studied. Using the theory of network formation and an understanding of the chemistry of these materials, the modulus data were interpreted in terms of the polymerization kinetics. The addition silicones exhibited the most abrupt transition between the gel and final set stage, which is close the ideal response. The clinical significant of the results is discussed.
The influence of implant geometry on the stress distribution around dental implants
Authors: Cook S. D. , Klawitter J. J. , Weinstein A. M. 
Published: December 2004

AbstractA three‐dimensional finite element stress analysis has been used to investigate the influence that variations in the infrastructural geometry of a blade‐type dental implant have on the stress distribution around LTI carbon and aluminum oxide implants. The finite element model was constructed based upon an analysis of serial sections of a retrieved implant specimen. In addition to the implant, the finite element model contained a three‐unit fixed bridge connected to a natural molar with periodontal membrane. The removal of the bridge allowed for the study of freestanding implants and molar. Variations in the implant blade geometry were found to produce significant changes in the stress distributions around bridged and freestanding aluminum oxide implants. Very little effect, however, was observed around the LTI carbon implants. A comparison of the stresses around the freestanding molar and the stresses around the bridged and freestanding implants was made to determine the implant dessign that came closest to reproducing the stress state around the modeled molar. The LTI carbon system that best achieved this stress state was found to be a full‐blade implant used in conjunction with a tooth as an abutment in a fixed bridge. The aluminum oxide system that best achieved this stress state was found to be of the post or short‐blade design used as a freestanding implant.
A study of sarcogenicity associated with Co‐Cr‐Mo particles implanted in animal muscle
Authors: Meachim G. , Pedley R. B. , Williams D. F. 
Published: December 2004

AbstractA study has been made of the sarcogenicity of particles of cobalt–chromium–molybdenum alloy. The particles were implanted as a dry powder into a surgical incision into the dorsal paraspinal muscle of adult female rats and guinea pigs. Two preparations were used. In one, the particles had a size range of 100–250 μm. This preparation was implanted into 51 Wistar rats. In the other, the particles had a size range of 0.5–50 μm, 85% being in the range 0.5–5 μm. This preparation was implanted into 61 Wistar rats, 53 hooded rats, and 46 Dunkin Hartley guinea pigs. Sham operations were carried out on a control group of 50 Wistar rats. No malignant neoplasms developed at the test or control operation sites during the time periods for which the animals survived. This negative finding contrasts with that from a previous study by Health, Freeman and Swanson, who observed sarcomas in rats at sites of intramuscular injection of cobalt–chromium–molybdenum particles suspended in horse serum. Possible explanations for this difference in results are discussed.
Scanning electron microscopic study of the hydrolytic degradation of poly(glycolic acid) suture
Authors: Chu C. C. , Campbell N. D. 
Published: December 2004

AbstractThis article reports the morphological observations on the surface changes of poly(glycolic acid) sutures which have been exposed to various dosages of γ irradiation (0, 2.5, 5.0, 10, 20, and 40 Mrad) and duration of immersion (0, 7, 14, 28, 48, 60, and 90 days) in a physiological saline buffer. The most important gross morphological characteristics of PGA suture hydrolytic degradation is the formation of surface cracks on the filaments. The regularity of the surface cracks increased with an increase in the γ irradiation and the duration of hydrolysis. Surface cracks were not observed in irradiated sutures that had not been subjected to hydrolytic degradation. The arrangement of the surface cracks, their orientation on the filaments, and the direction of crack propagation provide very useful information for depicting the mechanism of hydrolytic degradation in this class of fibrous material. The microfibrillar model of fiber structure has been used as the basis for the proposed degradation mechanism of PGA in vitro. It is believed that hydrolysis occurs initially in the amorphous regions sandwiched between two crystalline zones, as tie‐chain segments, free chain ends, and chain folds in these regions degrade into fragments. As degradation proceeds, the size of the fragments reaches the stage at which they can be dissolved into the buffer medium. This dissolution removes the fragments from the amorphous regions, and surface cracks appeared.
NMR spectroscopy of dental materials. II. The role of tartaric acid in glass–ionomer cements
Authors: Prosser H. J. , Richards C. P. , Wilson A. D. 
Published: December 2004

AbstractD(+) tartaric acid is incorporated into glass–ionomer cements to control the setting properties. 13C NMR spectroscopy of the fluid cement pastes have shown that tartaric acid reacts more readily than the polyacid with the glass, and hence suppresses the premature gelation of the cement. As the cements set, the pH rises from ca. 1.25 to ca. 3 when tartaric acid is fully complexed. As the polyacid reacts the pH rises further to ca. 5.
Intramedullary fixation of artificial hip joints with bone cement‐precoated implants. II. Density and histological study
Authors: Park J. B. , Barb W. , Kenner G. H. , von Recum A. F. 
Published: December 2004

AbstractBilateral coxofemoral hemiarthroplasties were performed in dogs using experimental and control implants, which were fixed with bone cement. The stem of the experimental implant was precoated with bone cement, about 2 mm thick. After 1, 3, and 6 months the femora with implant specimens were harvested and sectioned for mechanical and histological evaluation. Histological observations on the implant–bone interface and density measurements of the bone cement are reported. The density of the precoated bone cement was higher than the same cement used for implant fixation at the time of implantation (1.202 vs. 1.188 g/mL). The precoating also resulted in milder histological reactions, including thinner fibrous tissue capsule and smaller gap between bone and cement. The present results and the previously reported mechanical findings strongly support our hypothesis that a better and longer lasting prosthesis fixation can be achieved using cement‐precoated prosthesis combined with the customary cement fixation technique.
Correlation of corrosion behavior and cytotoxicity in Au‐Cu‐Ag ternary alloys
Authors: Wright D. C. , Gallant R. F. , Spangberg L. 
Published: December 2004

AbstractData from earlier investigation of Au‐Cu‐Ag ternary alloys indicate that there may be a relationship between an alloy's corrosion behavior and its biological effects. Corrosion properties were determined using standard potentio dynamic techniques and the biological effect was assessed as cytotoxicity in vitro. Linear mathematical methods were used to analyze the data and model the systems. A direct correlation was found between corrosion properties and cytotoxic response.
Reaction of mercury with silver–tin dental amalgam alloy
Authors: Abbott J. R. , Miller D. R. , Netherway D. J. 
Published: December 2004

AbstractElectron diffraction evidence confirming the ordered orthorhombic crystal structure of the γ phase of the silver–tin system has been obtained, and it has been established by optical metallography that an alloy with a composition corresponding to the dental amalgam alloy formula Ag3Sn (i.e., 26.85 wt % Sn) lies outside the single γ phase field and in the duplex (γ + Sn) phase field adjacent to it. Studies of the mechanism of the hardening reaction of single crystals of homogeneous γ phase alloys with mercury were carried out using both scanning and transmission electron microscopy. Mercury attack occurred preferentially along welldefined planes in the single crystals. Using electron channeling and trace analysis techniques these planes of preferential attack were found to be {010} and {011}, and from transmission electron microscopy of thin foils these were shown to be slip bands and deformation twins, respectively. In bicrystals of γ phase material, preferential attack also occurred along grain boundaries. Similar preferential mercury attack, leading to the development of deep planar intrusions into the γ phase material, was observed in an experimental dental amalgam prepared from a lathe‐cut homogeneous γ phase amalgam alloy. It is believed that the presence of such features would have important implications for the clinical performance of dental amalgam.
The nature of the zinc polycarboxylate cement matrix
Authors: Wilson Alan D. 
Published: December 2004

AbstractThe matrix of a stoichiometric zinc polycarboxylate cement has been shown to be identical with zinc polycarboxylate salt, which consists principally of neutralized carboxylate groups with a few free acid groups. When excess zinc oxide is present, as in practical cements, there are no free acid groups present. There is no evidence for the formation of a chelate. Both salt and cement matrices are amorphous. The formation of the salt appears to control timedependent changes in the consistency of the cement pastes.
Effect of pore size on the peel strength of attachment of fibrous tissue to porous‐surfaced implants
Authors: Bobyn J. D. , Wilson G. J. , MacGregor D. C. , Pilliar R. M. , Weatherly G. C. 
Published: December 2004

AbstractTwenty‐four rectangular metal plates were fabricated with surface regions in three different pore size ranges (5–20 μm, 20–50 μm, 50–200 μm). The plates were implanted into the dorsal subcutaneous tissue of 12 adult mongrel dogs for periods of 4, 8, 12, and 16 weeks. After animal sacrifice, the fibrous tissue which adhered to the porous‐surfaced regions of each plate was mechanically peeled off to give an indication of the strength of tissue attachment. The tissue was examined by both transmitted light and scanning electron microscopy. At each time period, the tissue that contacted the porous regions was found to be collagenized fibroconnective tissue. The mechanical tests indicated an increasing strength of tissue attachment with increasing implantation time and pore size range. The largest pore size range of approximately 50–200 μm produced a mean peel strength of attachment of 27.5 g/mm at the 16‐week period.
Zinc oxide eugenol cements. VI. Effect of zinc oxide type on the setting reactions
Authors: Prosser Havard J. , Wilson Alan D. 
Published: December 2004

AbstractThe particle size and adsorbed water on zinc oxide from various sources have been investigated and related to the reactivity with eugenol. The reactivity of zinc oxide with eugenol alone increases with the amount of water reversibly adsorbed. When 1% acetic acid is added to eugenol, the reactivity increases as the particle size of the oxide decreases. Generally, zinc oxide powders are deactivated by heat treatment because of coalescence of particles and loss of the ability to readsorb water.
The creep compliance of dental amalgam in the stress range of 20–80 MPa
Authors: Greener E. H. , Szurgot K. , Lautenschlager E. P. 
Published: December 2004

AbstractThe continuous compressive creep curves of four distinct types of one‐week‐old dental amalgam were monitored for one day on a specially designed mini‐specimen creep apparatus. Creep conditions included three different applied constant stress levels (20, 40, and 80 MPa), and temperatures ranging from 0°C to 60°C. To compensate for changing dimensions at high creep strains, the data was converted to terms of compressive creep compliance. For all types of dental amalgam, compressive creep increased both with increased applied stress and with increased test temperature. The two high copper systems evaluated appear to approach a steady‐state creep condition up to the highest temperatures tested, but the two conventional amalgams appear to change their creep exponent precipitously at temperatures above 45°C.
A new coupling agent for composite materials: 4‐Methacryloxyethyl trimellitic anhydride
Authors: Atsuta M. , Abell A. K. , Turner D. T. , Nakabayashi N. , Takeyama M. 
Published: December 2004

AbstractComposite materials were made by sedimention of ceramic powders in methyl methacrylate which was then polymerized by γ‐irradiation. Inclusion of 4‐methacryloxyethyl trimellitic anhydride (4‐META) generally was found to result in an increase in Knoop hardness number, Young's modulus, and transverse strength. Most emphasis was placed on transverse strength which was found to be increased by ca. 30% by inclusion of 4‐META (5 wt %) in composites made with silanated LiAlSiO4.However an abrupt decrease in strength was found for composites with greater than ca. 83 wt % silanated LiAlSiO4. This was shown by fractography to be due to increased porosity and dewetting at the higher filler contents. Fractography also indicated that inclusion of 4‐META results in a more coherent polymeric matrix. Further evidence for greater coherence was obtained by showing that 4‐META confers resistance to disintegration by chloroform.
The antiplatelet activity of immobilized prostacyclin
Authors: Ebert C. D. , Lee E. S. , Kim S. W. 
Published: December 2004

AbstractOwing to the chemical instability of prostacyclin, the direct immobilization of thsi prostaglandin has not been successful. A new procedure is described for the preparation of immobilized prostacyclin based on the conversion of immobilized prostaglandin F2α to immobilized prostaglandin I2. Materials thus prepared show dramatic antiplatelet effects with regard to platelet aggregation and platelet adhesion. Radioimmunoassays of plasmas used in in vitro platelet tests and of buffers used in prostacyclin leakage studies established that these effects are not due to the release of prostacyclin from the respective immobilization substrates.
Strain‐controlled fatigue of acrylic bone cement
Authors: Carter Dennis R. , Gates Evalyn I. , Harris William H. 
Published: December 2004

AbstractMonotonic tensile tests and tension–compression fatigue tests were conducted of wet acrylic bone cement specimens at 37°C. All testing was conducted in strain control at a strain rate of 0.02/s. Weibull analysis of the tensile tests indicated that monotonic fracture was governed more strongly by strain than stress. The number of cycles to fatigue failure was also more strongly controlled by strain amplitude than stress amplitude. Specimen porosity distribution played a major role in determining the tensile and fatigue strengths. The degree of data scatter suggests that Weibull analysis of fatigue data may be useful in developing design criteria for the surgical use of bone cement.
Controlled release rate of a lipophilic drug (BCNU) from a refillable silicone rubber device
Authors: Ueno Norio , Refojo Miguel F. , Liu Luke H. S. 
Published: December 2004

AbstractThe release rates of 1,3‐bis(2‐chloroethyl)‐1‐nitrosourea (BCNU), an anticancer drug, from various kinds of silicone and silicone‐nylon implantable and refillable devices were investigated in vitro. The devices were made with different surface areas and wall thicknesses. The relation of the release rate at steady state to the surface area and the relation of the release rate per unit surface area to the wall thickness were determined. The relationship among the release rate, the surface area, and the wall thickness was analyzed using the multiple regression method, and is represented on a three‐dimensional graph. The multiple regression equation predicts the release rate from the surface area and the wall thickness; the release rate can also be read from a nomogram that is presented.
Thin film PMMA precoating for improved implant bone–cement fixation
Authors: Raab S. , Ahmed A. M. , Provan J. W. 
Published: December 2004

AbstractIt has been argued that various specific requirements based on known principles of good adhesion are not being met in the current procedures of formation of the implant–bone cement interface. It has been shown that an annealed thin film PMMA precoating, applied in a low‐contact‐angle form to surgical alloy surfaces devoid of weak boundary layers, satisfies the majority of the requirements during interface formation. Techniques for the application of the precoating have been developed for SS316LVM, Co‐Cr‐Mo, and Ti‐6Al‐4V based on fracture toughness and fatigue tests, and fractography of the interface. Implant surface preparation methods have been established to yield surfaces amenable to adhesive bonding. The composition of the coatings have been studied from the point of view of implant surface wetting, coating roughness and thickness, and interface strength. A biocompatible silane coupling agent (A‐174), currently used in orthodontics, has been introduced to provide saline resistant interfaces. The final precoated metal–bone cement interfaces have demonstrated fracture toughnesses in excess of that of bone cement even after prolonged exposure to 37°C physiological saline. Fatigue tests have shown that the fatigue lives (6.5 MPa) of the precoated metal interfaces in saline are at least twice, and in one case several orders of magnitude greater than, that of the uncoated ones even when the latter are tested dry. Fractography of the interfaces show failures that are entirely cohesive in nature. For the UHMWPE (ultrahigh molecular weight polyethylene)‐bone cement interface, similar improvement with precoating, however, could not be attained. Finally, the coated metal–bone cement interfaces have been tested as a function of some clinical variables such as cement type, joining time, clinical contamination, and sterilization procedure. Results show that coated metals exhibit a certain level of insensitivity to these variables and retain their performance under all conditions except after particular repeated sterilizations.
Failure of ceramic hip endoprostheses by slow crack growth — lifetime prediction
Authors: Seidelmann U. , Richter H. , Soltész U. 
Published: December 2004

AbstractThe slow crack propagation velocity v, which depends on the stress intensity factor K, has been measured for three different high‐density aluminas. Assuming a load history for the prosthesis which approximates conditions during walking, the lifetimes of the components of a total hip endoprothesis were calculated as a function of the initial flaw size. Different geometries for the preexisting cracks, as well as varying physiological parameters, were considered. It is shown that the lifetime is very dependent on the quality of the material and that it is reduced by increased body weight, walking speed, and varus positioning. Comparison of failure behavior in different parts of the femoral component showed that flaws in the stem must be one order of magnitude smaller than those in the neck to achieve comparable lifetimes.
On the characterization of porosity in PTFE‐carbon composite implant materials by mercury porosimetry
Authors: Dehl R. E. 
Published: December 2004

AbstractQuestions have been raised about the use of mercury intrusion porosimetry to measure interconnecting pore sizes and void volumes in relatively soft and flexible materials such as porous implant composites of PTFE and carbon fibers. We have studied the effect of precompression of one such commercial composite on the mercury intrusion curves which cover all pore diameters greater than about 16 μm, the range of interest for tissue ingrowth applications. Prior compression by a pressure 20% greater than that encountered by the material during a mercury intrusion experiment did not change the ensuing pore size distribution curve, as compared with a noncompressed sample. Deformation of the material at higher pressures sufficient to decrease the sample volume inelastically by 17, 33, and 67% changed the shape of the mercury intrusion curves significantly, indicating that this technique can be used to detect prior deformation of an “unknown” sample. In the undeformed material, less than 15% of the total void as measured by mercury porosimetry consists of interconnecting pores > 100 μm in diameter and more than 50% of the void volume is composed of pores <40 μm in diameter.
Conversion in denture base polymers
Authors: Ruyter Ivar Eystein , Øysaed Harry 
Published: December 2004

AbstractThe purpose of this investigation was to determine residual monomers, the insoluble gel fraction, and singly reacted dimethacrylate monomers in heat‐polymerized, auto‐polymerized conventional and pourtype denture base materials. Residual monomers were determined by HPLC analysis of tetrahydrofuran extracts of denture base polymers. The gel fraction was determined by gravimetric analysis of the nonextractable portion. The pendant methacrylate groups in the gel fraction were determined by quantitative IR (infrared) spectrometry. It was demonstrated that the heat‐polymerized materials had the lowest content of residual monomers. Generally, the content of pendant methacrylate groups in the gel was dependent on the initial quantity of crosslinking agent in the monomer liquids. The gel fractions of the heat‐polymerized materials were larger than the quantity of reacted monomers and were also dependent on the quantity of crosslinking agent. These findings showed that some of the linear prepolymer, poly(methyl methacrylate) (PMMA), had been incorporated into the crosslinked polymer system. The gel fraction of the auto‐polymerized pour‐type materials corresponded to the quantity of reacted monomers, whereas the conventional auto‐polymerized materials took an intermediate position between pour type materials and heat‐polymerized materials in this respect.