bluuebunny/crossref_metadata_2025 huggingface dataset:
Tensile and compression properties of hydrophilic composite materials on a simple model of cartilage. II
Authors: Flam E. , Kapfer W. H. , Brenner W. , Schubert M.
Published: December 2004

Composite hydrophilic materials (CHM) containing collagen or cellulose as the insoluble fibrous component and potassium salts of proteinpolysaccharide or carboxymethylcellulose as the soluble polyelectrolyte were prepared as simple models of the connective tissue, cartilage. The tensile properties of uncrosslinked and formaldehyde‐crosslinked collagenous CHM were measured and compared to those of bovine nasal cartilage (BNC). The compressive properties of uncrosslinked and formaldehyde‐crosslinked cellulosic CHM were measured and compared to bovine nasal cartilage. Although elongating to approximately the same extent before breaking (20%), the uncrosslinked collagenous CHM had lower tensile strengths than BNC (330 psi). Formaldehyde crosslinking increased the tensile strength of the collagenous CHM to as much as 3 times that of BNC but reduced the elongation at failure to only 7%. The uncrosslinked cellulosic CHM attained a maximum of only ¼ the compressive strength of BNC (940 psi). Formaldehyde crosslinking extended the compressive strength to as high as ⅓ that of BNC. The results indicate that the simple uncrosslinked and crosslinked models can only partially account for the mechanical properties of BNC.
Heparin sorptivity and blood compatibility of carbon surfaces
Authors: Bokros J. C. , Gott V. L. , Lagrange L. D. , Fadali A. M. , Ramos M. D. , Vos K. D.
Published: December 2004

The influences of the conditioning treatments, surface topography, and crystal structure of carbonaceous surfaces on their ability to sorb heparin and their in vivo compatibility with blood were investigated. The results of the sorption studies indicated that the adsorption of heparin on the surfaces of turbostratic and graphitic materials is not crystallographically selective and that the amount adsorbed on relatively smooth surfaces is near the amount expected for monolayer formation. Although the adsorption of heparin on relatively smooth carbon surfaces is not influenced by the presence of benzalkonium chloride, the sorption of heparin in porous carbons can be greatly increased by a pretreatment with benzalkonium chloride. This increase was found to be due to the formation and entrapment of the insoluble heparin‐benzalkonium complex in the accessible porosity. Since the heparin sorptions in Dag‐154 coatings were found to be enhanced by a pretreatment with benzalkonium chloride, it was inferred that these coatings contain accessible porosity and that their initial thromboresistance depends on the formation of the benzalkonium‐heparin complex in pores. In vivo tests showed that polished and outgassed, impermeable isotropic carbons deposited at low temperatures were significantly thromboresistant without the exogenous application of heparin. There was no relationship between the amount of heparin sorbed on these materials and their compatibility with blood. Polishing, for example, which reduced heparin sorption, enhanced the thromboresistance of these carbons, and while chemisorption of oxygen markedly reduced their thromboresistance, it did not influence the amount of heparin that could be sorbed. Although the heparin‐benzalkonium complex sorbed in a porous carbon conferred excellent thromoboresistance in a 2‐hr test, the long‐tern (14‐day) compatibility was not as good as for carbon surfaces that were deposited at low temperatures and then polished and outgassed prior to implanting. In vivo tests of HTI carbon structures and annealed LTI carbons indicate that the blood compatibility of a turbostratic carbon is not significantly dependent on crystallite size, Le. Limited tests of surfaces that had a preponderance of c‐faces oriented parallel to the blood‐carbon interface at the surface suggest that orientations of this sort are better than others.
A metallurgical survey of current orthopedic implants
Authors: Cahoon J. R. , Paxton H. W.
Published: December 2004

A number of stainless steel and Vitallium orthopedic implants were purchased from the manufacturers and analyzed to determine their metallurgical soundness. From this sampling of current orthopedic implants over 50% contain metallurgical defects and deficiencies similar to those which have been shown previously to cause failures.
Adsorption of fibrinogen on modified polytetrafluoroethylene surfaces
Authors: Ziegler T. F. , Miller M. L.
Published: December 2004

The adsorption of radiotagged fibrinogen on modified polytetrafluoroethylene surfaces was measured to shed light on the reason of reduced thrombogenicity. These measurements show that when fibrinogen is adsorbed from a solution in which the molecules are in a coiled, undenatured state, adsorption is greater on sulfonated, etched Teflon—a reduced thrombogenic surface, than on unsulfonated, etched Teflon—a thrombogenic surface. On the other hand, when fibrinogen is picked up from a water‐air interface in the form of a monolayer consisting of denatured molecules, the pick‐up is independent of the thrombogenicity of the surface.
The determination of the constitutive relationships for a human aorta
Authors: Krokosky E. M. , Krouskop T. A.
Published: December 2004

A testing technique was developed that enabled an aortic vascular specimen to be analyzed in a quasi‐physiological environment. The data that was gathered from human and bovine aortas provided the basis for the formulation of the time dependent constitutive relationships describing the viscoelastic behavior of an aorta subjected to a “normal” pressure pulse.
Flexural properties of equine metacarpus
Authors: Bynum D. , Ledbetter W. B. , Boyd C. L. , Ray D. R.
Published: December 2004

The flexural tests on 37 whole equine metacarpus bones are described and the results are given in terms of fundamental material properties as a function of age. The moduli of elasticity, rupture, and failure increase then decrease with increasing age. The rupture and failure deformations decrease with age. The stiffness and fragility indices increase with age. Averaging the data for all ages, the modulus of rupture was 35 ksi, the deflection at rupture was 0.22 inches, and the modulus of elasticity was 1.7 × 10 psi. The flexural rupture strength is about twice the uniaxial compression strength and about five times greater than the torsional strength for whole bone tests. The moduli of elasticity are about the same for flexure and uniaxial compression, and about five times greater than the torsional modulus of rigidity for whole equine bone.
Microvascular and histogenic responses to implantation of a porous ceramic into bone
Authors: Rhinelander Frederic W. , Rouweyha Marwan , Milner John C.
Published: December 2004

A porous ceramic, in the form of small discs, has been implanted into the upper tibiae of adult mongrel dogs in survival experiments. A similar sized disc of a metal (vitallium, titanium, or stainless steel) was also implanted, for comparison, into each tibia. The tissue specimens were studied by microangiography and correlated histology. At the 4‐month, and longer, intervals, the specimens were sectioned with the ceramic disc in situ. Injected capillaries were then observed to have penetrated the ceramic.

The metals became surrounded by a shell of new‐bone, lined by a fibrous membrane of varying thickness. The ceramic implants, on the other hand, appeared to have remained inert within the cancellous area of the tibiae, not surrounded by either a membrane or an osseous shell.

Implications of these findings were discussed and further experiments, some of which are in progress, were proposed.
Polymers in ophthalmic surgery
Authors: Refojo Miguel F.
Published: December 2004

Several new surgical techniques in which artificial adhesives are used have been developed. Perforated eyeballs were glued, plastic windows were glued to hazy and opaque corneas, and techniques of retinal surgery wth a minimum use of sutures have been developed.

The expanding artificial implant is also described. This is a plastic that imbibes body fluids, swelling to a predetermined volume. Upon swelling, it can fill a cavity or it can produce a deformation in the surrounding tissues. Such a plastic is being investigated as a vitreous substitute. It is also being used to buckle the wall of the eye which carries the blood supply to the retina to reapproximate these layers in order to restore the retina's sensitivity to light. The main feature of this development is that a relatively large implant can be introduced into an organ or tissue through a small incision.
Development of blood compatible polymers using the electret effect
Authors: Murphy Preston V. , La Croix Andre , Merchant Suzanne , Bernhard William
Published: December 2004

Excellent in vivo thromboresistance has been obtained for FEP Teflon and for a polyether urethane prepared with electronegative surfaces using the electret effect. In vitro tissue culture studies have shown a marked improvement in tissue compatibility for negatively electrified Teflon. Studies on other materials, including Hypalon rubber, sulfonate cross‐linked Hypalon and Kel F have shown a moderate improvement in blood compatibility. These in vitro and in vivo experiments will be described. Surface physical properties of these electrified materials, including water contact angle and charge, have been measured. Correlations between surface physical measurements and blood compatibility data will be presented.
Experience with negatively charged polyurethane‐backed velours
Authors: Sharp W. V. , Taylor B. C. , Wright J. , Finelli A. F.
Published: December 2004

This report concerns the modification of a velour fabric for use in the vascular system. A specially prepared polyurethane was sprayed on the outer surface of this fabric resulting in a negative surface charge. The advantages of this composite were the incorporation of a thin layer of neointima onto the velour surface. Because of its thinness, viability was maintained resulting in a living nonthrombogenic layer at the vascular interface. To prove the efficacy of this material the authors have implanted it into the right atrium, replaced segments of the inferior vena cava, replaced the 4‐mm carotid artery, and have used it in the construction of an artificial ventricle device. All performed in a superior fashion with long‐term promotion of a viable neointima. It is hoped that the concept of negatively charged velours may be applicable to other phases of biomaterial development.
Applications of plastics in membrane oxygenators
Authors: Galletti Pierre M.
Published: December 2004

Current trends in blood oxygenator development favor devices which separate the blood phase from the gas phase by a thin film of plastic material. The additional barrier to diffusion presented by the plastic film is a low price to pay for the advantages of the “membrane oxygenator” over its cruder competitors of the “bubbler” or “filmer” type, namely, the absence of direct exposure of blood to gas (with the ensuing damage to the most fragile blood constituents) and the physical constraint of the extracorporeal blood volume to a fixed‐size compartment (obviating the need for complex volume control systems). The first generation of membrane lungs relied on the plastic materials (“Teflon” and silicone rubber) and shapes (flat sheets and tubes) available for industrial uses. A new line of devices will be made possible by the development of new biomaterials and the development of production technologies for the specific purposes of artificial organ research.
Viable prosthetic interface
Authors: Dressler Donald P. , Barlyn Lyle , Skornik William A.
Published: December 2004

The ability to produce a viable bond at the interface of living tissue and inert polymeric materials has been tested in three different contaminated environments. The prosthetic implants, consisting of nylon 66 velour and polyurethane, were tested in the intestinal wall of rabbits, the urinary bladder of dogs, and the skin of rats. The small (1.5 × 2.0 cm) velour implants had a tendency to slough in the intestinal wall while a tubular prosthesis (6 × 3 cm) and a large patch (4.5 × 3.0 cm) were of varying success. Utilization of the prosthesis to replace 25% of the urinary bladder wall was successful for as long as 7 months, at which time postmortem examination of the animals revealed no anastomotic leaks or calculi formation. Replacement of 20 or 40% of the rats burned and infected skin resulted in less than a 10% mortality. Furthermore, histologic studies of all successful prostheses revealed a prompt enmeshing of the velour filaments with fibrin followed at 3‐4 days with an ingrowth of fibroblasts, capillaries, and a few foreign body giant cells. Maturation of the wound resulted in a dense, mature collagen matrix. Removal of the prosthesis at this time occurred only by the disruption of the sub‐prosthetic tissue.
The swelling implant
Authors: Refojo Miguel F.
Published: December 2004

Expanding artificial implants are made of crosslinked hydorphilic polymers which imbibe body fluids and swell to a predetermined volume. The material is implanted in a dehydrated state; it then swells to fill a body cavity (i.e., vitreous cavity in the eye), or to give a form to the surrounding tissues (i.e., in plastic surgery). Such implants can be introduced in organs or tissues through a smaller incision than regular plastic and rubber implants, and have the advantage over injectable polymers in that they do not separate into globules and do not migrate from the area of implantation. The swelling equilibrium of slightly crosslinked poly (glyceryl methacrylate) [PGMA] hydrogels in salt solutions, urea, serum, and in the homogenized vitreous of the eye is given. Also, the swelling rate of PGMA in physiologic saline solution and in serum, as well as the swelling pressure‐volume relationship of PGMA gels in water, is reported. The application of PGMA as an expanding implant inside the eye, and against its outer wall in retina surgery, is discussed.
Medical and dental applications of cements
Authors: Smith D. C.
Published: December 2004

A number of cements based upon polymeric systems are being utilized in both medical and dental fields. The polymethyl methacrylate rapid polymerizing monomerpolymer materials have undergone extensive development as dental materials and are used widely also for rentention of orthopedic prostheses. The cyanocrylates and the newly developed zinc polycarboxylate cements are being used for a variety of dental applications. These latter materials display adhesion to soft tissue and calcified tissue, respectively, and the investigation of adhesion to these substrates compared with the mechanical retention of the methacrylate materials is of considerable interest.

The polycarboxylate cements have unusual properties including minimal tissue irritation and relatively high strength. The ability to vary their formulation and manipulative properties has permitted their trial in a variety of clinical applications including cementation of stainless steel orthodontic brackets to teeth.
Quartz and graphite filament reinforced polymer composites for orthopedic surgical application
Authors: Musikant S.
Published: December 2004

Materials conventionally used for orthopedic surgical implants are primarily metallic alloys such as stainless steel 316L, Cr‐Co‐Mo alloys and recently titanium and Ti‐6A1‐4V alloy. Modulus of elasticity of these (E = 15 to 30 × 106 psi) is an order of magnitude higher than that of bone (approximately 3 × 106 psi). Quartz filament reinforced composites were formulated with E = 6 × 106 psi and flexural stress at rupture (modulus of rupture) of approximately 200,000 psi. Similarly graphite filament reinforced epoxy composites were formulated with E = 16 × 106 psi and flexural stress at rupture (modulus of rupture) of approximately 200,000 psi. Specimens of these materials were implanted in white rats subcutaneously. At sacrifice 90 days after implantation there was no evidence of any inflammatory process, although the implants were completely encapsulated. (Similar in vivo compatibility tests in rabbit muscle tissue are currently in progress.) No significant changes in mechanical properties could be measured in the implants after the 90‐day period of implantation. By adjusting the volume fraction of fibers in a given composite, the modulus of elasticity can be adjusted (with concomittant variations in strength) to meet the biomechanical and dynamic requirements of the appliance. A continuing program to investigate other biocompatible resins and other reinforcement is planned.
In vitro investigation of the adhesive strength of cyanoacrylate bonds to human hard tooth structures
Authors: Khowassah Mohamed A. , Shippy Ronald L.
Published: December 2004

Three different cyanoacrylate monomers were studied as adhesives for hard tooth structures. Flat plane non‐retentive surfaces of extracted human teeth and cold‐curing acrylic onlays were used as the adherends. Both tensile and shear adhesive strengths were investigated under wet and dry conditions at room temperature. The commonly used zinc phosphate dental cement was the control material.

Under all test conditions the cyanoacrylates were shown to have greater adhesive strength than the dental cement. The MBR‐4197 (β,β,β trifluoroisopropyl 2‐cyanoacrylate) polymer showed the greatest bonding strength to hard tooth structures. The adhesive strengths of all cyanoacrylate polymers decreased considerably after water immersion but the control dental cement material showed no adhesive strength under the same condition.

However, the results of the experimental monomers when compared to the control cement, should encourage further investigations of these monomers for use as dental adhesives.
Biodegradable poly(lactic acid) polymers
Authors: Kulkarni R. K. , Moore E. G. , Hegyeli A. F. , Leonard Fred
Published: December 2004

The synthesis of poly(lactic acids) from the cyclic lactides and properties of the polymers prepared have been described. Degradation rates in vitro under homogeous and heterogeneous conditions have been measured. The kinetics of deesterification under homogeneous conditions is second order and an activation energy of 11 Kcal/mol has been calculated. This is comparable to the value found for the hydrolysis of alkyl acetates. A biological in vitro method for determining the degradation of poly(lactic acids) has been described. The method indicates, in accordance with expectations, that poly(dl‐lactic acid) degrades at a faster rate than L(+) lactic acid. Initial results of medical evaluation of the polymers in suture, rod, and film form are presented.
Biological tolerance of poly(N‐substituted methacrylamides)
Authors: Šprincl L. , Vacík J. , Kopeček J. , Lím D.
Published: December 2004

Experiments were investigated on animals' biological tolerance of the copolymers of N‐substituted methacrylamides with the monomers which can be considered for uses in the modification of the monomeric backbone. The group of N‐substituted methacrylamides is the second one in the series of hydrophilic polymers arranged according to their increasing resistance to hydrolysis, and it follows immediately after the esters of methacrylic acid. Histological analysis has shown that the copolymer of N‐ethyl methacrylamide with methyl methacrylate is the best tolerated polymer of this group. In the case of copolymers with butyl acrylate and butyl methacrylate, in the first days after implantation a stronger and more cellular capsula was formed, and an inflammation was observed in the surroundings of the encapsulated implant. Starting from day 30, however, no differences are found in the encapsulation, and the result of healingin of all the polymers is always favorable. No cancerogenic effects were observed; calcification was found only sporadically in the case of the copolymer with butyl methacrylate.
The amount of tin in the γ1 phase of dental amalgam
Authors: Johnson L. B.
Published: December 2004

Spherical‐particle Ag‐Sn alloy powders containing 4.3, 8.3, 12.0, 15.4, 18.5, 21.4, and 24.1 atomic per cent Sn were obtained. Amalgams from these alloys were examined by x‐ray diffraction and metallography for the presence of the γ2 phase and the γ1 → β1 phase transformation. A single amalgam of the approximate composition of dental amalgam was prepared from a melt at high temperature and pressure and likewise examined.

Results showed that the solubility of Sn in Ag‐Hg is about 7 atoms of Sn per unit cell of the γ phase. As clinically prepared, the γ1 phase of dental amalgam contains, however, only about 5 atoms of Sn per unit cell. These 5 atoms, nevertheless, result in a very considerable stabilization of this phase due to the increase in its electron concentration.
The need for radiopaque denture base materials: A review of the literature
Authors: Chandler H. H. , Bowen R. L. , Paffenbarger G. C.
Published: December 2004

The need for esthetic and functionally acceptable radiopaque denture base materials is reflected by numerous reports of patients who ingested or aspirated portions of dentures and reports of difficulties encountered in the removal of these dentures because they could not be located radiographically.

The type of denture most commonly ingested or aspirated is a maxillary partial consisting of a palatal piece to which is attached one or more anterior teeth. It may or may not have clasps. Ingestion or aspiration of the foreign body commonly occurs when either broken or ill‐fitting dentures are being worn. Few cases have been reported where patients swallowed portions of complete dentures.

Previous attempts at providing radiopacity have included addition of heavy metal salts or radiopaque inserts to denture base resins. None of these attempts has been entirely successful.

Elimination of dentures as foreign bodies requires a greater effort toward preventive measures by the dentist and the patient. When dentures are swallowed or inhaled, the dentist should immediately seek medical assistance for the patient. The common symptomless period following ingestion or aspiration should not lead the dentist to believe that there will not be serious subsequent complications.
Solute transport across polyelectrolyte complex membranes
Authors: Ryu Seh Man , Miller Irving F.
Published: December 2004

The transport of glucose and urea under electro‐osmosis across two polyelectrolyte complex membrances and two othermembranns, for comparison, was analyzed in detail, both experimentallyand theoretically.

The membranes were characterized by measurements of water content, concentration of coion and countrion in the membrane, and distribution coefficient of glucose and urea in the absence of electric current, as a function of external solution composition. In addition, fluxes of those solutes and solvent were measured as a function fo external solution composition and of electric current

The observed phenomena were modelled by use of Fick's law of of diffusion, with electro‐osmosis treated simply as bulk flow. the effect of stirring was accounted for in terms of a boundars layer mass transfer coefficient.

The results indicate a good fit of the model to the data for glucose. For urea, the results indicate substantial binding of urea to the membrane matrix and anomalous behavior in he boundary layer adjacent to the membrane.
Physical properties of a radiopaque denture base material
Authors: Chandler H. H. , Bowen R. L. , Paffenbarger G. C.
Published: December 2004

Physical properties were determied for radiopaque composite denture base materials consisting of poly (methyl methacrylate) as thematrix and 30, 40, and 50% by weight fo a singlane‐treated barum fluoride‐containing glass powder as the reinforcing filler. Specimens without glass were include for comparision.

All of the materials met the requirements of Amerrican ental Association Specification No. 12 for Denture Base Polymer except that t6he material containing 50% glass had less deflection than the minimum required at the 5000‐gm load in transverse testing.

There was little or no difference among thematerials with respect to hardness, in denation resistance, water sorption, color stability, and resistance to drop impact.

Addition of glass of the 30% level decreased the transevers strenght while 50% means with no glass. In general, the addition of glass increased the time to reach only slight effect on densities, and Young's, bulk, shear, and flexural moduli, had only slight effect on solubility and decreased the cold‐cure repairability and the coefficient of linear thermal expanision.

The solubility of the glass power was aboutfour times that of powdered porcelain teeth after 24 hr, and totaled 0.55% afeter 5 days.
Segmented polyurethane: A polyether polymer, II. Two years experience
Authors: Boretos John W. , Detmer Don E. , Donachy James H.
Published: December 2004

Segmented polyurethane does not indiuce acute toxcity when subjected to intracutaneous and intravascular tests with mices and rabbits. Specimens, which have been implanted in dogs for 18 months, exhibit stability heretofore unattributed tothe general class of polyurethanes. Data on tensile properties, abraxion resistance when wet, tolerance to autoclaving, results of acute toxicity test, and stablity of long‐term implants are described along with appropriate means of processing the polymer into useful biomedial devices.
A composite model of the elastic behavior of dental amalgam
Authors: Katz J. Lawrence , Grenoble Dale E.
Published: December 2004

A model describing the elastic behavior of dental amalgam as a composite material has been developed using elastic theory for quasi‐homogeneous, quasi‐isotropic systems. The elastic constants of the composite amalgam can be computed using Voigt‐Reuss and Hashin‐Shtrikman methods if the relative volume fractions and the elastic constants of the constituent phases are known. This model also relates the elastic behavior of the amalgam to manipulation during preparation. The elastic constants of several spherical and cut amalgams, as well as the constituent γ, γ1, and γ2 alloys, have been measured in the 0–50 kilobar range using a solid media pressure apparatus and an ultrasonic interferometer. High pressure studies are necessary so that the effects of porosity can be assessed. Calculations based on this model include the effects of porosity as well as the Hg content.
Survey of materials for hard‐tissue prosthesis
Authors: Levine Sumner N.
Published: December 2004

The properties of the three main classes of orthopedic alloys (316L steel, Co‐Cr alloys and titanium) are discussed, while all show good general corrosion resistance, the 316L steel have a tendency toward crevice corrosion. Fatigue fracture due to poor design and fabrication defects is discussed. A summary of some problems associated with the evaluation of tissue response is presented. Finally, a review of several new trends toward achieving tissue adhesion is presented.
Some requirements and problems in tissue interfacing
Authors: Ghidoni John J. , Hall C. William
Published: December 2004

Interfacing biologic material with foreign substances is a problem common to all implantable devices. This paper discusses these problems with respect to degradation of the material used in fabrication and the body's reaction to the foreign substance. The requirements dictate the type of tissue reaction sought and this in turn determines the base material. A nonreactive material may be ideal for one set of needs but tissue reactivity would be required for another. The specialized tissue “blood” is given special emphasis.
Bone formation and the response of bone to implant insertion
Authors: Mathews Robert S.
Published: December 2004

This basic introductory discussion has sought to outline the embryology and development of bone and has stressed both its function and structure. I have, also, outlined the sequence of fracture healing and discussed some of the problems of implant acceptance in the musculoskeletal system. With this information, I hope you as basic scientists will be able to better understand some of the problems our patients pose with respect to implant design and function. It should be reiterated that many men have contributed to this very vital and important field of Orthopedic Surgery. Moreover, I would like to stress that not withstanding the complications previously discussed, the availability of biologic and metallic implants has contributed immensely to the high level of patient care we know today; and they have a very important role in the future improvement of our ability to care for our patients.
Initial surface interaction of blood and blood components with Al2O3 and TiO2
Authors: Hulbert S. F. , King F. M. , Klawitter J. J.
Published: December 2004

The success of material implants in the vascular system has been limited by the fact that the intial events of blood coagulation on foreign material surfaces are not understood. Many materials have been evaluated in the search for a suitable implant material in this system. Recent success of porous ceramic materials in bone‐ceramic compatibility studies stimulated the feeling that these materials should be tested in other body tissues such as the blood.

Ceramic disks of Al2O3 and TiO2 were evaluated using a contact angle measurement technique to determine the characteristics of these material surfaces before and after exposure to a blood environment. This technique involved measuring the contact angle of sessile drops of various liquids on these surfaces with a microscope fitted with a goniometer eyepiece. By plotting these contact angles according to the procedure of Zisman, the characteristics of the surfaces could be evaluated.

The clean ceramic disks were found to be extremely wettable even after exposure to a physiological saline environment. On exposure of these disks to a blood environment, it was observed that some type of film was adsorbed from the blood onto the ceramic surface during the initial minutes of exposure. This film had wetting characteristics consistent with layers of fibrinogen.
Bonding mechanisms at the interface of ceramic prosthetic materials
Authors: Hench L. L. , Splinter R. J. , Allen W. C. , Greenlee T. K.
Published: December 2004

The development of a bone‐bonding calcia‐phosposilicate glass‐ceramic is discussed. A theoretical model to explain the interfacial bonding is based upon in‐vitro studies of glass‐ceramic solubility in interfacial hydroxyapatite crystallization mechanisms, compared with in‐vivo rat femur implant histology and ultrastructure results.
Ceramic tooth implants
Authors: Young Franklin A.
Published: December 2004

For many years man has engendered the idea of replacing lost or unserviceable teeth with natural or artificial substitutes has, however, only recently been shown to offer a viable alternative to externally attached prostheses. Ceramics were selected which have demonstrated compatibility with long bones and optimization of the ceramic properties was undertaken. Implants were made in the jawbones of adult dogs. Both tooth root replicas and crown‐root combinations were employed. Anchorage of the implants was found to range from stable attachment to rapid exfoliation. The calcium aluminates were found to possess barely adequate mechanical strengths.

This research suggests that these ceramics can function as effective tooth roots if the proper designs and surgical techniques are employed. Sufficient evidence of tissue compatibility has been amassed to warrant further study.
The complex factors in tooth implantation
Authors: Hamner James E. , Reed O. M.
Published: December 2004

The criteria for an ideally successful tooth implant should inlcude: (1) stable physiologic retension, (2) non‐toxicity, (3) durability and sound function in the oral cavity, (4) non‐carcinogenicity, and (5) esthetic satisfaction.

Many complex factors such as the anatomic site itself (the tooth socket), proper healing of the periodontium, viability of the periodontal membrane in tooth reimplants, the oral microbial flora, the general health of the implant recipient, non‐traumatic occulsion, physical and chemical properties of artificial implant material, and adequate stabilization influence the success of a tooth implant.

Initial results demonstrate that ceramic (calcium aluminate) tooth implants with a 50 to 75‐μ porosity appear to more promisingly meet the criteria for successful artificial tooth implantation than implants fabricated from plastic (polymethylmethacrylate), which produced osteomyelitis in 5/21 jaw block specimens in baboons with complete lack of true periodontal attachment between alveolar bone of the implant socket and the plastic tooth implant, shown microscopically and ultramicroscopically.
Bioceramics and dentistry
Authors: Garrington George E. , Lightbody Philip M.
Published: December 2004

Metals and polymers have received considerable attention with respect to their potential use in human implantation. Serious study of the ceramics for this purpose has only recently begun. Materials for implantation in any body site must meet certain requirements. Each class of material has been found to have some highly desirable properties as well as some undesirable characteristics. Materials for use in dental implantation, particularly for the replacement of individual teeth, are subjected to environmental factors not generally existent in other implantation sites. Preliminary studies of the ceramics have suggested that, from the physiologic standpoint, they may be the best implantable substitute for hard tissues (bones and teeth) yet achieved. There are, however, many questions remaining to be answered concerning the selection of the most suitable material, its fabrication, and the reaction of tissues to it. These questions should serve to indicate future areas of exploration.
Mechanical properties of a hydrophilic acrylic polymer
Authors: O'Brien W. J. , Hermann J. , Shepherd T. H.
Published: December 2004

Acrylic polymers with hydrophilic groups (i.e., ethyl hydroxyl) may be prepared that convert to a soft elastic gel by absorbing water. Such a polymer has been applied to dentistry for use as an elastic lining material for dentures. A commercial product, Hydron, was used in this study. The linear expansion of this material after 520 hr of water immersion was found to be 20.4%. Hardness was found to decrease from 15.7 KHN for the dry polymer to 1.5 KHN at 19% absorbed water content. The swelling pressure was measured and found to reach a maximum value of 157 psi after 204 hr of water immersion. The Young's modulus was found to decrease from a value of 295,300 psi to 290 psi with 19% absorbed water content. Values were determined on intermediate water contents for the properties studied.
Screening and evaluation of materials for thromboresistance
Authors: Wallin Richard F. , Krisik Mildred
Published: December 2004

Two methods are described for evaluating the thromboresistance of materials available as tubing. In the first method lengths of the tubing containing canine blood were incubated at 37°C, opened at timed intervals and examined for clots. For all materials tested, mean clotting times ranged from 5.2 min for glass to > 300 min for silicone rubber treated with GBH, TDMAC‐heparin or TDMAN‐heparin. For most materials, in vitro clotting times ranged from 20 to 60 min. Further testing in vitro indicated that heparin was more firmly bound to silicone rubber as TDMAC‐heparin than as GBH. In the second method, short segments of tubing were surgically placed within the femoral veins of anesthetized dogs, examined for patency after 2 hr, removed and examined for thrombi. None of the materials tested appeared completely thromboresistant by the 2 hr in vitro method. Tubes of glass or unheparinized materials were usually completely occluded at the end of the test; silicone rubber treated with TDMAC‐heparin apperared relatively thromboresistant. Results of in vitro and in vivo testing were generally in good agreement and were consistent with the known thromboresistant properties of materials.
The monsanto polyacrylonitrile hollow‐fiber artificial kidney
Authors: Salyer I. O. , Ball G. L. , Beemsterboer G. L. , Leonard R. L. , Merrill J. T. , Hampers C. L. , Lowrie E. G.
Published: December 2004

Advantages of a hollow‐fiber hemodialyzer have been well described. The goal of this program was to provide a working model of a noncellulosic hollow fiber artificial kidney with nonthrombogenic blood‐contacting surfaces, low blood‐priming volume and low pressure drop, a satisfactory rate of urea transport, and high rate of ultrafiltration of water. Also, the reliability and utility of these devices was to be demonstrated through clinical evaluation.
The effect of cleaning an experimental spherical Ag3Sn alloy on the tensile strength and fracture of dental amalgam
Authors: Young F. A. , Wilsdorf H. G. F.
Published: December 2004

Experiments have been conducted with the aim of improving the tensile strength of dental amalgam. Anticipating a surface contamination of Ag3Sn, the powder was washed with 5% HCl before amalgamation. The resulting amalgam showed a considerable decrease in the scatter of strength data and an increase in fracture stress. At 40 w/o mercury content the strength increase was found to be 40%. The reason for this substantial improvement in the strength of dental amalgam was revaled by electron fractography. It was found that the bond between unconsumed Ag3Sn particles and the amalgam matrix had been strengthened to such an extent that fracture took place through the silver‐tin particles, which allowed Ag3Sn to perform its role as the strongest component in a dispersion hardened system.
An enzyme histochemical approach to the evaluation of polymers for tissue compatibility
Authors: Salthouse Thomas N. , Willigan Donald A.
Published: December 2004

Nine samples of plastic, including PVC stabilized with various amounts of organotins, silicone rubber, PTFE, polyethylene, polypropylene, and a U.S.P. negative control high density polyethylene, were implanted in rat gluteal muscle. Frozen sections were cut in a cryostat microtome and treated for enzyme histochemical reactions. These included succinic dehydrogenase, acid phosphatase, aminopeptidase and adenosine triphosphatase. The results illustrate that enzyme histochemical data can be of value in supplementing other methods in the evaluation of polymers for tissue compatibility.
Inorganic heparin complexes for the preparation of nonthrombogenic surfaces
Authors: Dyck Manfred F.
Published: December 2004

The surfaces of many plastics and other materials of interest in the fabrication of implants can be made nonthrombogenic by treating them with an inorganic heparin complex (IHC) system consisting essentially of a soluble metal salt, a solvent, and heparin. During complexing, the metal salt polymerizes at the same time it is trapped in the collapsing matrix of the surface; the entrapped inorganic polymer then reacts with heparin, probably by chelation. Treatment with an IHC system is not known to alter the mechanical or physical properties of the treated material. If desired, the surface can be made radiopaque by incorporating bismuth chloride or other contrast salts during complexing. After treatment, the surface can be autoclaved or sterilized with ethylene oxide. Materials that have been made nonthrombogenic by the IHC system include Silastic, polyurethane, cellulose acetobutyrate, polymethylmethacrylate, nylon, polyethylene, polypropylene, polyethylene‐vinyl acetate, polystyrene, natural rubber, and polyvinyl chloride.
Effect of pressure on heat transport in polymers used in dentistry
Authors: Chen R. Y. S. , Barker R. E.
Published: December 2004

The thermal properties of dental materials are important in certain aspects of tooth repair and the restoration of dental function. This is especially true for polymeric dental materials, for which low thermal conductivity is often considered an important asset. This paper contains a report on the surprisingly large effect that pressure (well with in the range encountered on the biting surfaces of teeth) can have on heat transfer in polymers that are widely used in dentistry. A sandwich type pressure‐conductivity cell has been used to measure the thermal conductivity K of polystyrene, polymethyl methacrylate, polyethyl methacrylate, and poly‐n‐butyl methacrylate. The measurements span the range −50 to 50°C and pressures up to 2000 bar. For the polymers mentioned (and many others) K at a given temperature increases as pressure is increased. Initial increases in pressure to several hundred bars may typically increase the over‐all heat transfer coefficient by a factor of two or more. At higher pressures, the relative slope (dK/dp)/K is typically about 10% per kilobar. Some comments are made about the thermal contact coefficient and the thermal diffusivity which are of more direct interest to dentists than K itself.
Corrosion of Ti‐6Al‐4V in simulated body fluids and bovine plasma
Authors: Aragon P. J. , Hulbert S. F.
Published: December 2004

The corrosion of Ti‐6Al‐4V at 37°C in several simulated body fluids and bovine plasma was studied using the passive current‐time technique. A 0.9% NaCl (bw)‐0.1 N NaH2PO4 solution gave results closest to those using bovine plasma as an electrolyte.

All of the samples showed an activation period of 10–15 hr, after which an increase in the corrosion rate was observed. Several possible explanations for this effect are given.

For comparison, a sample of Type 316 L stainless steel was tested using isotonic saline solution as the electrolyte. Both the initial and final current densities were considerably higher than those for Ti‐6Al‐4V indicating a corrosion rate considerably higher for the Type 316 L stainless steel.
A new method for evalution of antithrombogenicity of materials
Authors: Imai Yohji , Nose Yukihiko
Published: December 2004

A new method was developed for evaluating kinetically the antithrombogenicity of materials. The amount of thrombus formed was measured gravimetrically at an appropriate interval of time after calcium chloride was added to ACD blood in contact with a test material. Graphic curves for thrombus formation on glass, Silastic, Hydron, and treated natural tissues were obtained and compared. There was good correlation between our in vivo tests and in vivo observations.
In vivo testing of silicone rubber joint implants for lipid absorption
Authors: Meester Walter D. , Swanson Alfred B.
Published: December 2004

Silicone rubber implants removed from patients undergoing revision arthroplasty were examined for breakage and cracks and analyzed for lipid content. No relationship was observed between lipids extracted from the implants and the implantation time. Neither was the absorption of lipids and the incidence of breakage of the implants found to be related. Various factors contributing to the possible failure and breakage of the joint implants are discussed.
Degradation of poly(methyl 2‐cyanoacrylates)
Authors: Wade Clarence W. R. , Leonard Fred
Published: December 2004

Methyl 2‐cyanoacrylate‐2‐14C, ‐3‐14C and ‐14CN tagged monomers were im planted subcutaneously in mongrel dogs and their urine assayed for radioactivity. The results show that the urea from the ‐3‐14C was radioactive and radioactive acidic components, as well as neutral moieties, were present. Urea recovered from the urine of animals in which the ‐2‐14C and ‐14CN methyl 2‐cyanoacrylate were implanted was only very slightly radioactive. The data are consistent with the hypothesis that hydrolytic chain scission and ester hydrolysis may be involved in the degradation of 2‐cyanoacrylates in vivo.
The elastic properties of hard tissues and apatites
Authors: Grenoble Dale E. , Katz J. Lawrence , Dunn Karl L. , Gilmore Robert S. , Murty K. Linga
Published: December 2004

The pressure dependence of the elastic constants of various halides, hard tissues and synthetic apatites have been examined in the 0‐ to 50‐kilobar range using a solid media, pressure apparatus coupled with an ultrasonic interferometer. The samples includ: hydroxy‐, fluor‐, and chlor‐apatite, NaCl, CaF2, mollusc shell (aragonite), ivory, dentin and enamel, and fish, bovine, and human bones. High pressures were used in order to assess the effects of porosity in aggregate samples and to make measurements on specimens of ideal density. Computer analysis of the measured longitudinal and shear ultrasonic velocities yields the pressure dependence of the bulk, shear, and Young's moduli and Poisson's ratio. Atmospheric pressure values at ideal density are obtained by back extrapolation from the high pressure measurements.
Ceramic root implantation in baboons
Authors: Hamner James E. , Reed O. M. , Greulich Richard C.
Published: December 2004

When a human natural tooth is evulsed and lost, replacement by implantation of a replica would be one logiclal treatment choice. Identification of an appropriate biomaterial which would allow the replica tofunction in a stable manner without eliciting a toxic response is one of the major challenges facing dentistry today, and has been the subject of an increasing number of investigations in recent years.

Because of questions which still remain regarding the biocompatibility of candidate materials, extensive animal research in tooth implantation is an absolute necessity. Primates, providing dental models closely approximating the human condition, are especially valuable for undertaking that systematic scrutiny of experimental implant materials which is so clearly prerequisite to human clinical trials.

In the present study, 22 calcium aluminate roots were implanted into fresh natural tooth extraction sites in 10 baboons for periods ranging from 2 weeks to 10 months. The controlled porosity of the ceramic roots varied from 50 to 200 μ.

Implant retention and stability, resulting from adequate ingrowth of fibrous/vascular elements into the ceramic pores with subsequent mineralization therein of newly formed osteoid matrix, were optimal when the calcium aluminate root implants had a porosity of 100–200 μ.

Calcium aluminate root implants so successfully met all criteria of tissue adherence and host acceptance in the present short‐term study that their application in basic and clinical studies in man seem fully warranted at this time.
Biopolymers as biomaterials: Mechanical properties of γ‐benzyl‐L‐glutamate‐L‐Leucine copolymers
Authors: Anderson James M. , Hiltner Anne , Schodt Kathleen , Woods Richard
Published: December 2004

A seires of γ‐benzyl‐L‐glutamate‐L‐leucine copolymers were prepared and cast films of the copolymers were subjected to dynamic mechanical and stress‐strain tests. Dynamic mechanical testing revealed that the copolymers had a molecular relaxation at about 50°C and that the magnitude of this relaxation was directly proportional to the molar concentration of glu(OBz) in the copolymer. The magnitude of the 50°C relaxation was also dependent upon orientation. The stress‐strain behavior of the copolymers was examined before and after PECF treatment. Prior treatment with PECF caused in increase in the tensile strength to failure and a decrease in the elongation at failure. Increasing concentrations of leu caused the tensile strength to failure to increase. Efforts to degrade the films by refluxing 6 N HCl and enzymic attack were unsuccessful and suggested that these copolymers could find use as biomedical materials.
Biocompatible materials for use in the vascular system
Authors: Grode Gerald A. , Falb Richard D. , Crowley James P.
Published: December 2004

Techniques are presented which result in the production of thromboresistant materials which can be used to interface with blood in the vascular system. Three useful processes for the heparinization of materials are presented and data are given on characteristics of attachment, the blood compatibility, and environmental stability of these surfaces. At this point, applications of heparinized surfaces via a simple one‐step process should be limited to siturations where low blood shear rates are involved, such as the venous system. Intitial data indicate significant loss of surface heparin in situations where high blood flow rates are involved such as A‐V shunts.