bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural evidences of the microfilled composites
Authors: Lambrechts Paul , Vanherle Guido 
Published: December 2004

AbstractThe new composite concept of microfilled composites has certain advantages, such as polishability, permanent smoothness, and high abrasion resistance. In the mouth, however, these new materials are not perfect and they often fail in stress‐bearing restorations. In the present study, the weak links and imperfections of these materials are determined by means of direct and indirect SEM techniques. The chemical adhesion between polymer blocks and polymer matrix is questionable; fractures occur most often at the filler‐matrix interface. In vivo, there is still a certain preferential wear of the resin matrix. In Estic Microfill, rear weak zones with starlike condensations are observed, which could be related to a certain incompatibility of its composing resins and/or to incomplete and inhomogeneous polymerization. In a fractured Isopast restoration, the polymer blocks are clearly revealed, scattered in a three‐dimensional polymerized matrix network.
Analysis of deposits on high water content contact lenses
Authors: Hosaka S. , Ozawa H. , Tanzawa H. , Ishida H. , Yoshimura K. , Momose T. , Magatani H. , Nakajima A. 
Published: December 2004

AbstractDeposits on soft contact lenses of high water content were investigated morphologically and chemically and compared with those on conventional soft contact lenses of poly(2‐hydroxyethyl methacrylate). The material of the lenses examined in this investigation was the crosslinked copolymer of methyl methacrylate and N‐vinylpyrrolidone with a water content higher than 70%. Morphologically, the deposits on the lenses with high water content were found to have no characteristics distinguishable from those on conventional lenses. By the electron microscopic observation of the cross section of a lens that had become opaque, it was confirmed that the deposit was on the lens surface and that no deposit was within the lens. Some spots on the lenses were recognized as colonies of microorganisms, but the majority of the spots had no involvement by microorganisms. Surface analysis with Fourier transform infrared spectrometer (FT‐IR) confirmed that the main component of the filmy deposit was protein. Protein was detected in most of the deposits. The amino acid compositions of the proteins were found to be close to that of lysozyme. From the elemental analysis of several spots, silicon, aluminum, iron, and some other elements were detected. The structural analysis of some spots by a laser Raman microprobe (MOLE) revealed the existence of lipids. In several cases, the deposits were found to have grown around a defect of the lens surface. A mechanism for the formation of deposits is suggested.
Polymerization kinetics of resin‐based restorative materials
Authors: Cook Wayne D. , Standish Paul M. 
Published: December 2004

AbstractThe kinetics and mechanism of cure of resin‐based restorative materials have been investigated by incorporating into commercial materials additional amounts of inhibitor, initiator, and accelerator. The polymerization was monitored by IR spectroscopy, viscosity measurements, and an oscillating rheometer. The rate of initiation of the polymerization was found to be first order with respect to the initiator and accelerator concentration. The inhibitor was found to be responsible for the induction period during which no polymerization occurred. The duration of this period was proportional to the inhibitor concentration. It was also found that the efficiency of the inhibitor affected the difference between the initial and final set times so that with one particularly effective inhibitor a “snap‐set” behavior could be obtained.
Setting of dental polyelectrolyte cements–viscosity studies of model systems
Authors: Cook Wayne D. 
Published: December 2004

AbstractIn order to gain information on the setting of dental cements, the influence of Ca2+, Mg2+, Zn2+, and Al3+ ions on the viscosity of concentrated solutions of partly neutralized poly(carboxylic acids) has been measured. The increase in viscosity with increasing cation concentration was semi‐quantitatively interpreted in terms of chain growth and branching due to intermolecular bridging of the carboxylate groups by the metal ions. The concentration of cation required to produce gelation was considerably greater than expected and may be due to the wastage of cations by the formation of intramolecular links. The incorporation of tartrate ion into the polyacid solution retarded the reaction between Al3+ and the polyacid and may explain some features of the setting of glass ionomer cements.
Strength testing of dental stone: A comparison of compressive, tensile, transverse, and shear strength tests
Authors: von Fraunhofer J. A. , Spiers R. R. 
Published: December 2004

AbstractThe strength of two dental stones under three standard test regimens and two novel testing modes is reported. It was found under all test regimens that the water/powder ratio significantly affected the strength of the two gypsum products in a similar manner. It was established that the new central fulcrum loading mode gave strength data directly relatable to that determined in the conventional transverse strength test which requires larger test specimens.
Properties of a heparin‐poly(vinyl alcohol) hydrogel coating
Authors: Goosen Mattheus F. A. , Sefton Michael V. 
Published: December 2004

AbstractSome physical, chemical, and biological characteristics of a heparin‐PVA hydrogel potentially useful as a thromboresistant coating for the preparation of small‐diameter vascular prostheses and blood‐sampling catheters have been determined. The molecular weight between crosslinks in the acetal crosslinked gel was approximately 8000, permitting proteins the size of albumin to enter the interior of the gel. The release rate of heparin from a gel containing 7 mg/g gel was 10−2 μg/g min which was significantly lower than the reported minimum required for thromboresistance of ionically heparinized materials. Nevertheless, in vitro biological activity was observed in both thrombin time and plasma recalcification time assays, which could not be attributed to the release of heparin into the incubated plasma. Correlation of final heparin contents with the amount of terminal amino acid residues in three samples of heparin suggests that the heparin is bound to the PVA in the gel through the amino acid terminus; this provides a plausible explanation for the retention of biological activity by the immobilized heparin.
Creep rupture behavior of polypropylene suture material and its applications as a time‐release mechanism
Authors: Kusy R. P. , Whitely J. Q. 
Published: December 2004

AbstractThe controlled failure of polypropylene (PP) sutures is studied via creep rupture tests. From plots of log time (tB) vs. stress (σ), linear relationships are generated over the failure times of 1–1000 h. Results show that as a function of stress, the time dependence varies with irradiation dose (15, 20, 25, and 50 Mrad), irradiation atmosphere (air and vacuum), suture diameter (7–0, 6–0, 5–0, and 4–0), and test temperature (26 and 37°C). For a given stress, the time to failure is least for the greatest dose in the presence of air and at the highest temperature. When suture loops are wrapped around a small wire sheave, however, failure occurs in the largest suture as much as two decades sooner than the smallest suture studied. Within the limitations stated herein, they are independent of test method, loop diameter, aging, and humidity. Consequently, after irradiation in vacuum and postirradiation heat treatment, the processed material may be stored at room temperature for at least 1 month. Such materials are advocated when the time release of a dental or medical device is required, for example, in the self‐activating cleft palate appliance.
A new approach to the design of internal fixation plates
Authors: Woo Savio L‐Y. , Simon Bruce R. , Akeson Wayne H. , Gomez Mark A. , Seguchi Yasuyuki 
Published: December 2004

AbstractMathematical analysis by finite element modeling methods was used in conjunction with laboratory bench experiments in selecting appropriate stiffness parameters for internal fixation plate designs. Bench experiments performed included tests of an idealized plated magnesium tube and of a plated canine femur. Finite element modeling of the plate‐tube and plate‐bone structures was also performed, and the computed results were compared with those obtained experimentally. Three types of internal fixation plates–one “rigid” control plate and two less rigid experimental plates–were examined using both the finite element and experimental models. These plates were further examined by finite element modeling of a plated human femur during single stance loading. In all cases, the “rigid” control plate was found to shield the underlying bone from stress, while both experimental plates were found to have significantly less bone stress shielding. Our findings suggest that an improved plate design should have a low axial stiffness but moderate bending and torsional stiffnesses to facilitate fracture healing and bone remodeling without causing osteopenia.
Mechanical strength of poly(methyl methacrylate) cement‐human bone interfaces
Authors: Kusleika R. , Stupp S. I. 
Published: December 2004

AbstractA device was constructed to test the inter‐facial strength of PMMA‐based bone cement and human cancellous bone under pure tension. Two types of tissue were used in the investigation: (1) formalin‐fixed vertebral bone as an in vitro model for weak cancellous bone, and (2) freshly removed metatarsal bone. Tissue‐cement joints were allowed to solidify under two different pressures (0.11 and 0.47 MPa), and cement placement time on tissue surfaces was also controlled as a variable. The higher curing pressure only seemed to enhance the strength of interfaces formed with mechanically weak fixed bone but had no significant effect for joints formed with the stronger, freshly extracted tissue. Cement placement time did not have a discernible effect on interfacial strength regardless of the tissue used or the pressure applied during setting. An analysis of fracture morphology by optical microscopy revealed largely cement cohesive failure in some cases and bone or mixed fractures in others. Joints exhibiting mainly cement fracture had the highest interfacial tensile strengths (in the order of 7.5 MPa). Once measured values of tissue porosity were taken into account, the observed joint strength correlated well with cement tensile strength. Based on experimental findings, better stress‐dissipating qualities and higher tensile strength are suggested as two important necessary improvements of bone cements based on poly(methyl methacrylate).
Quantitative histologic evaluation of LTI carbon, carbon‐coated aluminum oxide and uncoated aluminum oxide dental implants
Authors: Cook Stephen D. , Weinstein Allan M. , Klawitter Jerome J. , Kent John N. 
Published: December 2004

AbstractThe response of mandibular bone to identical geometry LTI carbon, carbon‐coated aluminum oxide, and uncoated aluminum oxide blade‐type dental implants in baboons for 2 years was evaluated using histologic, microradiographic, and scanning electron microscopic methods. In addition, a quantitative histologic analysis was performed identifying the type, amount, and distribution of tissue surrounding the dental implant systems. This is the final phase of a study investigating the effect of implant elastic modulus and implant surface chemical composition on the performance of dental implants. Previous studies have utilized clinical and radiographic evaluations, postretrieval mechanical testing, and finite element stress analysis to evaluate the dental implant performance. The results of the histologic study revealed a direct implant‐bone interface with no intervening soft tissue in 16 of the 21 implants (76%). A fibrous tissue interface was observed in 5 of 21 implants (24%). Quantitative histologic results for the implants with a direct implant‐bone interface showed statistically larger crestal cortical plates (p < 0.05) and greater area fraction crestal cancellous bone (p < 0.05) in the LTI carbon implant compared to the carbon‐coated and uncoated aluminum oxide implants. The carbon‐coated and uncoated aluminum oxide implants demonstrated statistically greater area fraction cancellous bone at the inferior region of the implant (p < 0.05) and thinned and reduced crestal cortical plates when compared to the LTI carbon implants. The results indicate that significant stress shielding of the crestal bone had occurred with the rigid carbon‐coated and uncoated aluminum oxide implants when compared to the LTI carbon implants which had a material elastic modulus similar to cortical bone. Based upon the histologic results, it appears that the LTI carbon implants with the direct implant‐bone interface exhibited a greater potential for long‐term successful performance compared to the aluminum oxide substrate implants.
Mass transfer rates in hemodialyzers–An empirical correlation
Authors: Okazaki Masayuki , Yoshida Fumitake 
Published: December 2004

AbstractFrom the experimental data on the rates of urea transfer from blood to dialysate in a test hemodialyzer, a practical equation for the effect of the hematocrit on the blood‐phase urea transfer coefficient is proposed. With this equation, the overall mass transfer coefficient that takes into account the properties of the blood can be estimated for the commercially available disposable flat membrane‐type and hollow fiber‐type hemodialyzers from the data for a relatively simple dialysate‐dialysate system.
Some characteristics of collagen‐heparin complex
Authors: Raghunath K. , Biswas G. , Rao K. Panduranga , Joseph K. T. , Chvapil M. 
Published: December 2004

AbstractIn various forms of purified collagen (powder of insoluble collagen from bovine skin, fibers from rat tail tendons, membrane from bovine gut), carboxyl groups were activated by carbodiimide to allow covalent binding of heparin. Collagen powder and collagen fibers from rat tail tendons were also incubated in a haparin solution under the same reaction conditions but without carbodimide present to account for other forms of collagen‐heparin interaction. It was found that the linkage of heparin to collagen formed in the presence of carbodiimide is stable, as heparin was minimally extractable by 0.2M buffers with a pH ranging from 5 to 9. Collagen powder incubated with heparin in the absence of carbodiimide released heparin almost completely into Tris buffer of pH 9.0. As a consequence of covalent binding of heparin to collagen, the collagen fibers became more stable as shown by their significantly reduced swelling capacity and significantly increased shrinkage temperature. Collagen fibers interacted with heparin in the absence of carbodiimide also showed some stabilization of their structure, which was, however, significantly less than with carbodiimide reaction. By two independent methods it was shown that heparin linked to collagen by a stable bond retains its anticoagulant activity. It is concluded that, in the presence of carbodiimide, heparin covalently binds to collagen thus forming an antithrombogenic surface. At the same time, collagen is crosslinked. Incubation of collagen in the solution of heparin without carbodiimide also stabilizes collagen structure, but to a significantly lesser degree. Such a linkage is unstable as heparin dissociates and is readily extractable into 0.2M Tris buffers with pH 7–9.
Dispersion and polar surface free energies of human enamel
Authors: van Pelt A. W. J. , de Jong H. P. , Busscher H. J. , Arends J. 
Published: December 2004

AbstractIn this study, the dispersion (γ) and polar (γ) surface free energies of human enamel with and without an acquired enamel pellicle and of crystalline hydroxyapatite were determined from contact angle measurements. The results show that γ is strongly influenced by the presence of a pellicle; the total surface free energy (γs) is considerably smaller for enamel with an acquired pellicle than for enamel without an acquired pellicle. Enamel without an acquired enamel pellicle shows surface free energies comparable with those of crystalline hydroxyapatite.
Total surface hip arthroplasty in dogs using a fiber metal composite as a fixation method
Authors: Ronningen Helge , Lereim Paul , Galante Jorge , Rostoker William , Turner Thomas , Urban Robert 
Published: December 2004

AbstractA total hip surface replacement was performed on 13 adult mongrel dogs using a porous fiber metal composite for fixation to bone. Titanium fiber composite rings were molded onto cylindrical acetabular prostheses, and cobalt‐chrome fiber inserts were sintered onto the cast cobalt‐chrome femoral components. The animals were allowed unrestricted walking. Four dogs were sacrificed between 3 and 5 weeks, five at 7 weeks, one with a femoral neck fracture at 12 weeks, and three at 26 weeks. Bone ingrowth was accomplished in 20 of the 26 prosthetic components. This included 12 femoral components and eight acetabular. The main reason for failure appeared to be inadequate primary fixation, secondary to either poor design or technical difficulties experienced during the surgical procedure.
Release of cobalt and nickel from a new total finger joint prosthesis made of vitallium
Authors: Woodman J. L. , Black J. , Nunamaker D. M. 
Published: December 2004

AbstractAn in vivo study of a new total finger joint prosthesis was performed to evaluate a biological ingrowth system of attachment of the device to bone. The prosthesis consisted of two conical ribbed ultrahigh molecular weight polyethylene plugs that were fixed by impaction into the medullary cavity after reaming. A cobalt‐chromium alloy metal stemmed hinge slides inside the plugs with the joint articulation at the end of the stem. The focus of this study was to measure the concentration of cobalt and nickel in the serum, erythrocytes, and periarticular tissue (muscle from the sartorius and vastus medialis) resulting from the implantation of this device in the knee of the cat for periods of up to 1 year. The results indicate significant elevation in serum cobalt concentrations only after 5 months and increased concentrations in serum nickel which, were more pronounced after two months. Column chromatographic separations on cross‐linked Dextran (G‐200) shows a different distribution across the three principal protein peaks for each metal.
Reduction in complement activation from biomaterials by removal of air nuclei from the surface roughness
Authors: Ward C. A. , Koheil A. , Johnson W. R. , Madras P. N. 
Published: December 2004

AbstractThe activation of the rabbit complement system by each of three different synthetic materials is reported. Samples of each type of material were subjected to one of two different priming procedures. One priming procedure was intended to remove the air nuclei from the surface roughness of the materials; the other procedure was just the normal one. It was found that the removal of the air nuclei during priming reduced the complement activation by each of the two materials of lower surface tension, but not by a statistically significant amount for the material of highest surface tension, cellophane. For the denucleated samples of the three materials, the amount of complement activation was found to correlate with the critical surface tension of the materials; if the samples of the materials were normally primed, there was no correlation of the amount of complement activation with the critical surface tension of the material.
In vivo metal‐ion release from porous titanium‐fiber material
Authors: Ducheyne P. , Willems G. , Martens M. , Helsen J. 
Published: December 2004

AbstractDense and porous Ti, Ti‐alloy, and stainless steel specimens were implanted in canine trabecular bone. After 6 and 12 months the specimens were retrieved together with bone tissue immediately adjacent. The trace metal content in the tissue samples was determined using neutron activation analysis, differential pulse polarography, graphite furnace atomic‐absorption spectrophotometry, electron microprobe analysis, and laser microprobe analysis. The results are discussed in view of (i) the release of Ti ions, which is larger for porous than for bulk specimens, (ii) the various artifacts arising in electron microprobe (EMP) and laser microprobe mass analysis (LAMMA) determination of compositional gradients of trace metal‐ion content in bone tissue, (iii) the absence of measurable quantities of V in bone tissue, and (iv) the difference in local tissue accumulation between Ti, released from Ti specimens, and Ni, released from stainless steel specimens.
Some factors that influence prolonged interfacial continuity
Authors: Hall C. William , Cox P. A. , McFarland Samuel R. , Ghidoni John J. 
Published: December 2004

AbstractBringing a percutaneous implant through the integument with the intentions of leaving it as a functional device for prolonged periods of time has not yet become a reality. If we are ever to achieve prolonged uninfected implants, attention must be directed toward a variety of failure mechanisms. Some of these mechanisms have defined our scrutiny, and our awareness of others are poorly understood. Some of the causes for failure of a percutaneous implant are the forces, either extrinsic or intrinsic, that cause shearing and tearing at the skin‐implant interface. Extrinsic forces are defined as those forces applied either to the skin or the implant by the external environment. Intrinsic forces are those that have to do directly or indirectly with the body's growth and cell maturation, such as the retraction of maturing scar tissue and the surface migration of squamous epithelium. An intact skin‐implant interface is important to attain in order to close the portal which might allow microbial invasion. The integument must remain intact, since a suppurative wound makes the implant's removal mandatory.
Infection of percutaneous devices: Prevention, monitoring, and treatment
Authors: Dasse Kurt A. 
Published: December 2004

AbstractInfection continues to pose the major obstacle to long‐term percutaneous access. Development of methods to prevent infection or techniques to determine early onset of infection at a time when antibiotic therapy may prove successful would be of enormous value. Our laboratory has been working toward developing and testing a noninvasive semiquantitative swab culture technique (SQ) to monitor percutaneous leads for infection. This technique was found to have a 76% sensitivity having identified 47 of 62 organisms detected by a quantitative tissue culture technique (Q) at the time of system explant. Furthermore, 47 of 61 organisms identified by the SQ technique accurately detected those isolated by the Q techniques. Accordingly, the SQ technique has a 77% specificity. This technique was capable of detecting organisms a median of 14 days prior to overt clinical infection. Prompt initiation of oral antibiotic treatment based on SQ results has doubled system survival compared with untreated systems. Clearly, the SQ technique has proven useful to monitoring percutaneous devices.
Casting properties of Ni–Ti shape memory alloy
Authors: Takahashi Junzo , Okazaki Masayuki , Kimura Hiroshi , Furuta Yasuhiro 
Published: December 2004

AbstractA Ni–45 wt % Ti (Ni–50 at % Ti) alloy was cast into molds of magnesia and silica investments by use of a dental argon‐arc pressure casting machine with a copper crucible. The castings exhibited shape memory properties. The shape recovery process was sharper in the specimens cast in magnesia investment molds than in those cast in silica (phosphate‐bonded) investment molds. The latter casting had a hard region of the periphery, suggesting that shape recovery process may be affected by reaction of molten metal with silica. Furthermore, the alloy possessed the adequate mechanical properties for consideration as crown‐and‐bridge prostheses.