bluuebunny/crossref_metadata_2025 huggingface dataset:
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

The 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

The 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

Fretting 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

In 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

The 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

Medical 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

Fracture 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

Eight 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

The 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

Cellulose 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

The 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

Bone 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

Phosphorus‐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

The 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

An 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

We 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

The 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

As 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.
Rheological studies of the polymerization of elastomeric impression materials. III. Dynamic stress relaxation modulus
Authors: Cook Wayne D.
Published: December 2004

As 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

A 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

A 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

This 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

D(+) 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

Bilateral 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

Data 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

Electron 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

The 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

Twenty‐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

The 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

The 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

Composite 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

Owing 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

Monotonic 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

The 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

It 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

The 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

Questions 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

The 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.
Susceptibility of surgical cobalt‐base alloy to pitting corrosion
Authors: Lucas L. C. , Buchanan R. A. , Lemons J. E. , Griffin C. D.
Published: December 2004

The objective of this investigation was to evaluate thein vitroandin vivosusceptibilities of a surgical cobalt‐chromium‐molybdenum alloy to localized corrosion.In vitrocyclic anodic polarization curves were generated for the cobalt alloy under various surface and electrolyte conditions. Surfaces of the test specimens were examined before and after each polarization experiment.In vivoanalyses involved macroscopic and microscopic examinations of cobalt alloy surfaces on retrieved total hip prostheses. The electrolyte selected for thein vitropolarization study was 0.9% saline at a pH of 7.00 ± 0.05 and temperature of 37 ± 1°C in both aerated and deaerated conditions. Surface conditions for the cobalt alloys included nonpassivated and passivated treatments. Hysteresis behavior was exhibited by the passivated alloy but not by the nonpassivated alloy. According to the protection potential theory, hysteresis behavior indicates a material should be susceptible to pitting corrosion. Therefore, based on polarization curves and theory, the results of the present study indicated the cobalt alloy was susceptible to pitting corrosion when in the passivated condition but not when in the nonpassivated condition. Examination of the surfaces before and after each polarization curve revealed no evidence of pitting corrosion. Also, the examination of nonwear cobalt surfaces of total hip prostheses with implantation times up to 6 years revealed no features uniquely identified as the result of pitting corrosion. Therefore, it was hypothesized that certain conditions inherent in the electrochemical phase of this study had caused the development of hysteresis behavior for the passivated alloy, and this hysteresis behavior should not be associated with pitting corrosion as is normally taken to be the case by application of the protection potential theory. Instead, it is postulated that the hysteresis behavior exhibited by the passivated alloy is due to processes involving a breakdown of the pre‐established passive film followed by a repassivation characteristic of the saline electrolyte.
Stress analysis of porcine bioprosthetic heart valves in vivo
Authors: Thubrikar M. J. , Skinner J. R. , Eppink R. T. , Nolan S. P.
Published: December 2004

During the normal functioning of aortic porcine bioprosthetic valves, the leaflets undergo complex configurational changes which can produce stresses large enough to damage the leaflets. Stress analyses of these valves in vivo have not been performed before. We investigated the behavior of aortic bioprostheses in vivo in calves by placing radiopaque markers on the valves and observing them under x‐ray. Based upon the behavior of the leaflets, a method of stress analysis is proposed. Membrane stresses were associated with a pressure gradient across the leaflet and bending stresses with a change in the leaflet curvature. Total stresses were obtained by summation of the two stresses. A model of leaflet deformation at its attachment is proposed and the stresses determined. In diastole, the total stresses in the leaflet were tensile. In systole, the total stresses at the leaflet attachment were large and compressive on the aortic surface. Since the leaflet is unable to sustain compressive stresses, it is concluded that large compressive stresses cause structural damage at the leaflet attachment. This may explain the clinical observation that bioprosthetic leaflets detach or calcify in this region.
A study of the interface between a fibrous polyurethane arterial prosthesis and natural tissue
Authors: Beahan P. , Hull D.
Published: December 2004

Fibrous polyurethane samples were implanted in subcutaneous tissue, muscle, and as an arterial prosthesis for periods up to six months. The interface between the polymer and living tissue was studied using optical, scanning, and transmission electron microscopy. A good correlation was found between the micromorphology of the polymer–tissue interface observed in three experimental methods used. Ingrowth of tissue occurs by cell penetration into the fibrous network of the polymer implant and eventual encapsulation by connective tissue. Full details of the distribution of collagen and the cell components around the individual polymer fibers and the structure of the connective tissue are given.
Electrically enhanced osteogenesis at various metal cathodes
Authors: Spadaro J. A.
Published: December 2004

Electode‐induced bone formation was studied at six different metallic cathode materials in the rabbit medullary canal. Direct cathodic currents of 0.02 and 0.2 μA/mm2 were applied for 21 days. Quantitative differences in new bone growth were found. Platinum, cobalt‐chrome (F‐90) and silver had more bone relative to controls at the lower geometric current density, while stainless steel (316L) and titanium cathodes were more effective at the higher current. On average, there was a significant increase (46–48%) in new bone formation at active versus control implants for either current level. No corresponding difference in the number of vascular channels were observed in the 21 day specimens. Metal‐specific differences in bone formation at control implants were also found, with platinum being most stimulatory. These observations are consistent with an interfacial electrochemical mechanism for electrode stimulated osteogenesis, which perhaps acts in concert with purely electrical and mechanical forces.