bluuebunny/crossref_metadata_2025_split huggingface dataset:
UV‐radiation aging test on composite materials for dental restorations
Authors: Gatti A. M. 
Published: December 2004

AbstractSeven composite materials for dental restorations were examined in order to investigate their color stability. Five of these materials are available for anterior and two for posterior teeth. the change in color was achieved by an accelerated aging test with ultraviolet rays and evaluated, for each material, with the measurement of reflectance. Such measurement was obtained by means of a video display computer working as a computerized photometer. The results show two different types of behavior: some materials turn slightly to yellow, while others bleach. The test was completed with a scanning electron microscope morphologic examination of the surfaces.
Adsorption of fibronectin derived from serum and from human endothelial cells onto tissue culture polystyrene
Authors: van Wachem P. B. , Mallens B. W. L. , Dekker A. , Beugeling T. , Feijen J. , Bantjes A. , Detmers J. P. , van Aken W. G. 
Published: December 2004

AbstractHuman endothelial cells (HEC) suspended in a culture medium containing 20% human serum (CMS) adhere and spread on(to) moderately wettable polymers, such as tissue culture polystyrene (TCPS). We have previously shown that serum derived‐fibronectin, which is a cell adhesion promoting protein, has a high affinity for TCPS, but that the amount of fibronectin which adsorbed from CMS was relatively small. In this study we investigated whether fibronectin derived from HEC contributes to the adhesion and spreading of the cells on(to) TCPS. Therefore, HEC were seeded in the presence of fibronectin‐depleted CMS. The amount of fibronectin detected on TCPS increased with both cell seeding density and incubation time. Although initial HEC adhesion is delayed on TCPS which had been precoated with albumin (Alb), high density lipoprotein (HDL) or immunoglobulin G(IgG), maximal numbers of adhering and spreading HEC were found on these surfaces 6 h after seeding of HEC. Fibronectin was detected on these surfaces, but an exchange of preadsorbed Alb, HDL, or IgG for fibronectin could not be demonstrated. We conclude that HEC deposit fibronectin onto TCPS, irrespective of the presence of a preadsorbed layer of proteins which delay cell adhesion.
The effect of post‐sintering heat treatments on the fatigue properties of porous coated Ti‐6Al‐4V Alloy
Authors: Cook Stephen D. , Thongpreda Nisra , Anderson Ronald C. , Haddad Ray J. 
Published: December 2004

AbstractPorous coated Ti‐6Al‐4V alloy implant systems provide a biocompatible interface between implant and bone, resulting in firm fixation and potential long‐term retention via bony ingrowth. In order to achieve an acceptable porous coating structure, the sintering protocol for Ti‐6Al‐4V alloy systems often requires that the material be heat treated above the beta transus. This transforms the as‐received equiaxed microstructure, recommended for surgical implants, to a lamellar alpha‐beta distribution, which has been shown to have the worst fatigue properties of the most common structures attainable in Ti‐6Al‐4V alloy. However, post‐sintering heat treatments may be used to improve these properties by producing microstructures more resistant to crack initiation and propagation. This study investigated the influence of microstructural variations on the fatigue properties of porous coated Ti‐6Al‐4V alloy material. Nonporous coated and porous coated Ti‐6Al‐4V alloy fatigue specimens were subjected to a standard sintering heat treatment to produce a lamellar microstructure. In addition, two post‐sintering heat treatments were used to produce coarse and fine acicular microstructures. Rotating beam (reversed bending) fatigue testing was performed and the endurance limits determined for the noncoated and porous coated microstructures. The values determined were 668 MPa (noncoated asreceived equiaxed), 394 MPa (noncoated lamellar), 488 MPa (non‐coated coarse acicular), 494 MPa (noncoated fine acicular), 140 MPa (porous coated lamellar), 161 MPa (porous coated coarse acicular), and 162 MPa (porous coated fine acicular). The noncoated coarse and fine acicular specimens displayed an approximate 25% increase over the noncoated lamellar specimens. The porous coated coarse and fine acicular specimens showed an approximate 15% improvement over the porous coated lamellar specimens.
A study of the nature and formation of zinc polyacrylate cement using Fourier transform infrared spectroscopy
Authors: Nicholson J. W. , Brookman P. J. , Lacy O. M. , Sayers G. S. , Wilson A. D. 
Published: December 2004

AbstractThe formation and structure of zinc polyacrylate has been studied by Fourier transform infrared spectroscopy (FTIR). Using this technique we have shown that the fully hardened cement is bonded predominantly by zinc carboxylate complexes, rather than by associations of purely ionic character as had previously been supposed. Ionic bonds are formed in the initial stages of the reaction but are gradually converted to complex forms. This bond rearrangement appears partly responsible for physical changes that occur during gelation, setting, and hardening.
The hydrolytic stability of mitrathane (a polyurethane urea)—an x‐ray photoelectron spectroscopy study
Authors: Paynter R. W. , Askill I. N. , Glick S. H. , Guidoin R. 
Published: December 2004

AbstractThe hydrolytic stability of microporous Mitrathane polyetherurethane urea vascular prostheses has been evaluated at pH 7 and pH 9, at 37°, 60°, and 80°C for time periods of up to 968 days. Mechanical strength was evaluated using a hydrodynamic burst test and surface chemical changes by x‐ray photoelectron spectroscopy. The samples held at 80°C showed the greatest mechanical strength loss which corresponded to the hydrolysis of the urethane groups. It was concluded that the gross in vivo surface degradation of Mitrathane prostheses, observed after six months, could not have been caused by simple chemical hydrolysis alone, as the polymer was found to be stable at 37°C for at least 11 months.
A model for the corrosion behavior of dental amalgams
Authors: Lemaitre L. , Moors M. , Van Peteghem A. P. 
Published: December 2004

AbstractAt high frequencies, electrochemical impedance behavior for corroding dental amalgams cannot be interpreted in terms of a simple Randles equivalent circuit. This may often be ascribed to the imperfect cell geometry resulting in a nonuniform current distribution. However, the insertion of a constant phase element (CPE) in the nonfaradaic branch of the equivalent circuit offers a new scope for interpretation as the circuit provides an m‐parameter corresponding to the degree of distortion. The decrease of m as a function of time was explained by a mathematical model reflecting an increasing number of pores. Moreover, that same model allows a better understanding of the passivating effect of NaHCO3 and of the differences between conventional and Cu‐rich dental amalgams.
Raman spectroscopy for the study of porous composite alumina coating
Authors: Bertoluzza A. , Fagnano C. , Tinti A. , Toni A. , Ciapetti G. , Sudanese A. , Cattaneo C. 
Published: December 2004

AbstractA new acetabular cup prosthesis made of alumina and bioactive glass was studied and evaluated using nondestructive and noninvasive Raman laser spectroscopy. The prosthesis consists of an alumina socket coated with a double layer of alumina beads bonded to the prosthesis with a layer of glass. Raman spectroscopy showed that both the socket and the beads are composed of α‐Al2O3 (corundum), while the bioactive glass (alkaline and alkaline earth alumosilicate with a small quantity of zirconium oxide) showed this to have an intermediate structure between that of vitreous silica and that of the alkaline and alkaline earth disilicate glasses. The Raman spectra of the contact surfaces between the bioactive glass and the alumina of the assembled prosthesis and of an alumina disk coated with the same glass showed the presence of new bands which may be correlated with a chemical interaction between the components of the prosthesis.
Fatigue of acrylic bone cement–effect of frequency and environment
Authors: Johnson J. A. , Provan J. W. , Krygier J. J. , Chan K. H. , Miller J. 
Published: December 2004

AbstractThis study was conducted to investigate some fundamental fatigue testing variables as they apply to the response characteristics of acrylic bone cement. Cyclic loading under load control was conducted at frequencies of 1, 2, 5, 10, and 20 Hz in air at room temperature. At a tensile stress range of 0.3–20.0 MPa the fatigue life increased linearly with logarithmic frequency. The effect of conditioning and testing in saline at both room temperature and 37°C at similar stress levels and a frequency of 10 Hz were also examined. When compared to dry testing at room temperature, testing in saline at 37°C resulted in a reduction in fatigue life while testing in saline at room temperature produced an increase in fatigue life. Of a number of statistical distributions considered, the Weibull was found to be the most appropriate in documenting the findings of this investigation. A companion fractographic investigation of the failure surfaces demonstrated distinct regions of crack growth and fast fracture.
Ultrastructural comparisons of ceramic and titanium dental implants in vivo: A scanning electron microscopic study
Authors: Steflik David E. , McKinney Ralph V. , Koth David L. 
Published: December 2004

AbstractIdentically prepared, screw‐type ceramic and titanium endosteal dental implants were inserted in the jaws of adult mongrel dogs for periods of up to 6 months. Sixteen of the 32 total implants supported fixed bridgework. The interface of bone and soft connective tissues with the dental implants was examined by routine and innovative scanning electron microscopic (SEM) techniques using both secondary and backscattered electron imaging. Results demonstrated excellent bone adaptation to both titanium and ceramic implants. Direct adaptation of bone to the upper third of both type implants was observed with only minimal amounts of any intervening fibrous connective tissue. A composite of trabecular bone and fibrous connective tissue was observed in the lower two‐thirds of the implants examined. Areas of bone alteration suggestive of osteoid were observed at the thread apicis of some loaded implants. From this investigation we concluded that similar longitudinal tissue responses were generated to one‐piece, cylindrical screw‐type titanium and alpha alumina oxide ceramic dental implants. Possible bone remodeling was observed at the thread apicis of the loaded implants, an area where occlusal forces may be distributed. We further suggest that one‐stage endosteal implants are capable of maintaining a proportional bone‐to‐implant interface at the apical support region, similar to that suggested to two‐stage implant systems.
Immunological safety assessments of anti‐IgE antibody which is detached from therapeutic immunoadsorbents for removing IgE
Authors: Sato Hiroshi , Kidaka Teruhisa 
Published: December 2004

AbstractAssessments were made of the safety of antibodies which might be detached from a therapeutic immunoadsorbent (IA) during extracorporeal circulation, with respect to possible immunological responses to such antibodies. The IA used was antihuman IgE antibody (a‐IgE Ab) immobilized on a carrier, for removal of IgE from patients' plasma. The antibody was raised in goats and isolated to give an IgG fraction. This fraction was either used without further purification or was subjected to immunoaffinity purification. The active anaphylaxis test in guinea pigs indicated that positive responses were not observed at doses of less than 0.1 μg of goat IgG per animal. Rabbits given goat IgG intravenously 3 times a week for 8 weeks did not produce the specific antibody against goat IgG at doses of less than 0.05 μg/kg, which corresponds to less than 3 μg for an adult with a body weight of 60 kg. However, none of the rabbits given goat IgG at 2.5 mg/kg showed any toxic reactions and different patterns of the body weight growth from these in the control group. In addition, we tested whether immunoaffinity purified a‐IgE Ab could trigger Type I hypersensitivity in a monkey model. Anaphylactic reactions were not observed after a single intravenous injection of a‐IgE Ab at less than 10 μg/kg. These in vivo results are useful to judge whether the amount of antibody that leaks from a therapeutic IA is acceptable or not in a clinical situtation.
Apatite–Wollastonite containing glass ceramic granule–fibrin mixture as a bone graft filler: Use with low granular density
Authors: Ono Kozo , Yamamuro Takao , Nakamura Takashi , Kokubo Tadashi 
Published: December 2004

AbstractThe purpose of this study was to investigate bone formation after implantation of a mixture of apatite—wollastonite containing glass ceramic granules (A–W.GC, 220–355 μm) and fibrin glue with a low A–W.GC granular density. The fibrinogen was prepared from rat blood plasma. A mixture of A–W.GC granules and fibrin glue 1:4 in volume ratio (1:4 mixture) was implanted in the proximal metaphysis of the rat tibia, and bone formation was evaluated quantitatively by histomorphometry in undecalcified specimens. Microangiography was performed in animals sacrificed 5 days after the operation. The results were compared with those of a previous study in which a 1:1 mixture of A–W.GC granules and fibrin glue was used. With the 1:4 mixture, the A–W.GC density was 39.7% because of concentration of fibrin at packing. Good early vascularization comparable to that after implantation of the 1:1 mixture was observed. Bone formation proceeded at the same rate as after implantation of 1:1 mixture, but the level of the plateau was higher than that for the 1:1 mixture. The osteoconductive potential of the 1:4 A–W.GC‐fibrin mixture was similar to that of the 1:1 mixture, and was higher than that of A–W.GC without fibrin.
Exclusion of uropathogen adhesion to polymer surfaces by Lactobacillus acidophilus
Authors: Hawthorn Lesley Ann , Reid Gregor 
Published: December 2004

AbstractThe ability of bacteria to adhere to surfaces is a major cause of concern in the use of biomaterial substrates. The adhesion of Staphylococcus epidermidis strain 1938 was examined using image analysis and was found not to correlate with polymer surface tension, unlike that of Lactobacillus acidophilus, which adhered to more hydrophobic polymers. A fimbriated uropathogenic E. coli strain showed very low levels of adherence to the biomaterials. Precoating the polymers with lactobacilli significantly reduced the staphylococcal and E. coli adhesion, a result which could have clinical significance. An additional finding was that the interaction of staphylococci and E. coli with lactobacilli coated polymers altered the adhesion profile of the latter. Lactobacilli appeared to detach from polymers of low surface tension and reattach to polymers with high surface tensions. This resulted in the highest levels of exclusion of uropathogens being found for lactobacilli‐coated glass and sulfonated polystyrene, both of which are hydrophilic (with high surface tensions). These results demonstrate that lactobacilli can be used to coat biomaterial surfaces leading to a reduced adhesion of uropathogens.
Cyclic fatigue‐crack propagation, stress‐corrosion, and fracture‐toughness behavior in pyrolytic carbon‐coated graphite for prosthetic heart valve applications
Authors: Ritchie R. O. , Dauskardt R. H. , Yu Weikang , Brendzel A. M. 
Published: December 2004

AbstractFracture‐mechanics tests were performed to characterize the cyclic fatigue, stress‐corrosion cracking, and fracture‐toughness behavior of a pyrolytic carbon‐coated graphite composite material used in the manufacture of cardiac valve prostheses. Testing was carried out using compact tension C(T) samples containing “atomically” sharp precracks, both in room‐temperature air and principally in a simulated physiological environment of 37°C Ringer's lactate solution. Under sustained (monotonic) loads, the composite exhibited resistancecurve behavior, with a fracture toughness (KIc) between 1.1 and 1.9 MPa √m, and subcritical stress‐corrosion crack velocities (da/dt) which were a function of the stress intensityKraised to the 74th power (over the range ∼10−9to over 10−5m/s). More importantly, contrary to common perception, under cyclic loading conditions the composite was found to display true (cyclic) fatigue failure in both environments; fatigue‐crack growth rates (da/dN) were seen to be a function of the 19th power of the stress‐intensity range ΔK(over the range ∼10−11to over 10−8m/cycle). As subcritical crack velocities under cyclic loading were found to be many orders of magnitude faster than those measured under equivalent monotonic loads and to occur at typically 45% lower stress‐intensity levels, cyclic fatigue in pyrolytic carbon‐coated graphite is reasoned to be a vital consideration in the design and life‐prediction procedures of prosthetic devices manufactured from this material.
A new porous polyetherurethane wound covering
Authors: Bruin P. , Jonkman M. F. , Meijer H. J. , Pennings A. J. 
Published: December 2004

AbstractA polyetherurethane (PEU) wound covering with non‐interconnected micropores up to approximately 5 μm has been prepared by means of a phase inversion process. This highly elastic, very thin (15–20 μm), pliable wound covering showed good, immediate adherence to wet wound surfaces and high water vapor permeability, but was impermeable to bacteria. In guinea pigs epidermal wound healing of partial‐thickness wounds under PEU wound coverings was accelerated compared with uncovered controls and an occlusive wound covering, OpSite. Water in liquid form or wound exudate could not leak through the PEU covering, but its high water vapor permeability induced concentration of the wound exudate into a jellylike clot layer, which apparently accelerated reepithelialization. The main conclusion from a clinical study on 20 donor sites was that the use of the PEU covering reduced pain, besides prevention of fluid retention. No differences in epithelialization were seen in comparison to tulle gras‐treated wounds.
Dynamic mechanical properties of multiphase acrylic systems
Authors: Øysæd Harry 
Published: December 2004

AbstractThe influence of type and quantity of five different dimethacrylate crosslinking agents on the dynamic mechanical properties of multiphase acrylic systems has been studied. These materials, commonly used in bioengineering, were processed by polymerization of a mixture of liquid methacrylate monomers, and poly(methyl methacrylate) powder. The specimens were made with various ratios of methyl methacrylate and dimethacrylate crosslinking agents in the monomer liquid. Two different processing conditions were used, heat‐polymerization at 100°C and autopolymerization at 45°C. By using a forced torsional vibration apparatus the storage modulus (G′), loss modulus (G″), and dissipation factor (tan δ) were determined over the temperature range −60°C to 140°C at frequencies of 0.1, 1.0, 10, and 100 rad/s. In the autopolymerized materials, the glass transition temperature (Tg), as determined via tan δ data, increased with increasing quantities of crosslinking agents. The storage modulus likewise increased. In the heat‐polymerized materials only minor variations in modulus and tan δ with type and quantity of crosslinking agents were observed. Tg values of the heat‐polymerized materials were, in all cases, greater than those of the autopolymerized materials.
A new canine model to evaluate the biological response of intramedullary bone to implant materials and surfaces
Authors: Spivak Jeffrey M. , Ricci John L. , Blumenthal Norman C. , Alexander Harold 
Published: December 2004

AbstractA new canine model utilizing an implantable chamber with multiple bone in‐growth channels has been used to study the response of intramedullary bone to various implant materials and surfaces.The first group of dogs received implants containing channels lined by smooth‐surfaced coupons of titanium, titanium alloy, sputter‐hydroxyapatite‐coated (HA‐coated) titanium alloy, and polyethylene. A pattern of early initial bone ingrowth by 2 weeks, becoming maximal at 6 to 12 weeks with remodeling to a more mature lamellar bone, and later resorption by 24 weeks was seen for all test groups, with fibrous tissue interfaces covering the smooth test coupons at all time points. Significantly increased bone ingrowth in the sputter‐HA coated group was found only at 6 weeks.The second group of dogs received implants with channels lined by surfaceroughened coupons of either titanium or plasma‐HA‐coated titanium, half of which were also packed with a crystalline‐HA grouting at the time of surgery. At both 6 and 12 weeks, bone ingrowth was greatly enhanced by the presence of the plasma‐HA coating or the crystalline‐HA grouting as compared to the uncoated titanium channels. Histologically, bone was seen to bond directly to the plasma‐HA coating and the crystalline‐HA grouting. A thin fibrous tissue layer was noted between bone and the titanium in most areas, but evidence of direct bone contact to the metal surface was seen. Mechanical testing in tension of intact coupon‐‐bone‐‐coupon units revealed significant strength of the bone‐‐plasma‐‐HA bond, with failure initiating at the metal‐HA interface with forces of 15.3 N at 6 weeks, increasing to 44.8 N at 12 weeks. Plasma‐HA‐lined channels with crystalline‐HA packing required similar forces for failure. No significant adhesion strength was noted for the titanium channels at 6 weeks, and only the crystalline‐HA‐filled channels displayed measurable strength of the bone‐‐titanium interface at 12 weeks, with a force of 9 N needed for failure.
Adherence of HDPE powder coating on Co‐Cr surfaces: Effect of substrate preparation and gas sterilization
Authors: Laberger M. , Drouin G. , Gélinas C. , Champagne B. , Bobyn J. D. 
Published: December 2004

AbstractAs part of the development of a hemiarthroplasty implant with a compliant surface layer, the effect of surface preparation of a cast Co‐Cr alloy substrate on the adhesion of a polymeric coating was studied. High‐density polyethylene (HDPE) coatings were deposited on Co‐Cr alloys without adhesive by spraying powder onto the surface of specimens maintained at a controlled temperature. Prior to deposition, two different types of surface preparation were carried out: chemical etching and grit‐blasting. Adherence tests were performed in order to study the effect of the surface preparation of a Co‐Cr alloy on the adherence of the HDPE film. The etching process enhanced the adherence by a factor of 10 compared to the grit‐blasting process. For coatings deposited on grit‐blasted Co‐Cr surfaces, rupture occurred at the interface (adhesive mode) as well as in the coating (cohesive mode). A full cohesive mode was observed for films deposited on etched surfaces. Gas sterilization with an ethylene oxide and Freon 12 solution did not change significantly the adherence of the film deposited on etched surfaces. Examination of the surfaces indicated that the etching process created a specific type of porosity consisting of dendritic cavities whereas grit‐blasting produced surface irregularities. Cavities produced by etching were larger that the polymer powder particles and could be easily filled. The coating of an ethced Co‐Cr alloy substrate with a layer of HDPE provided an interface that could probably sustain the physiological loading in a normal synovial joint.