bluuebunny/crossref_metadata_2025 huggingface dataset:
Clinical problems in total hip replacements
Authors: Hirsch Carl
Published: December 2004

Total hip replacements are based on a long chain of efforts of partial exchange of joint compartments. Inplants of material of both biological and nonbiological origin have been applied over the past 50 years. Smith‐Pedersen, Judet, Moore, and Thompson are names to be remembered. It was primarily from the idea of firm fixation and low friction between the joint surfaces that today's constructions emerged. Immediate superior clinical results encouraged a strong trend towards hip‐arthroplasties. The orthopedic surgeon can now choose amongst several prosthetic designs, the most common being metal to metal or plastics with or without bone cement. But, after ten years a number of threatening problems have become evident, calling for critical analysis of total joint replacements. Biomechanical, chemical, and morphological disturbances, both in the early and late phases, show that the body has difficulties in tolerating the artificial joint. This survery presents some of the most obvious risks and failures in total hip replacements.
Total surface replacement of the hip joint
Authors: Walker P. S. , Mendes D. G. , Figarola F. , Bullough P. G.
Published: December 2004

The surface replacement hip prosthesis reported represents an attempt to improve upon some aspects of the present design of total hip. The prosthesis comprises a cap fitted over the femoral head and a liner fixed into the socket, both being cemented with methyl methacrylate. The chief advantage of this design is preservation of bone stock. The prostheses were inserted bilaterally into six dogs, and whilst ten joints failed, one case was strikingly successful at two years follow‐up. It was concluded that the design showed sufficient advantages over current total hips and that there was sufficient possibility of success in some application, to merit further study.
A look at the prosthesis‐cartilage interface: Design of a hip prosthesis containing pressure transducers
Authors: Carlson Charles E. , Mann Robert W. , Harris William H.
Published: December 2004

The human hip joint is capable of carrying loads exceeding several times body weight. The distribution of these loads over the load‐bearing cartilage surfaces in the hip is of considerable interest in terms of studying the behavior of cartilage under various loading conditions. A modified Moore prosthesis has been designed which is capable of measuring in vivo the spatial and temporal pressure variations generated by the loads carried by the hip. The pressures as measured by this device will not only give a good indication of the pressure distributions that occur in the normal hip but will yield quantitative data on the pressures generated between the cartilage surface in the acetabulum and the ball of the prosthesis.

The instrumented prosthesis consists of three main elements: a network of pressure transducers distributed over the surface of the ball, a multichannel telemetry device located inside the ball to transmit the information from the transducers to external receiving and recording equipment, and an electromagnetic power induction system which provides an external source of power for the telemetry device inside the prosthesis.

A prototype has been fabricated which demonstrates the satisfactory functioning of the complete pressure measuring system.
Evaluation of a total hip replacement
Authors: McGrouther D. A.
Published: December 2004

Through a survey of hip replacement arthroplasty the paper establishes the case for objective evaluation of these joints in the patient. It then outlines a simple, non‐invasive technique, based on Paul's (1967) locomotion studies, to assess pre‐ and postoperative functional capability. Preliminary results which establish viability of the procedure are presented.
Press fit implant arthroplasty of the hip and knee
Authors: Sbarbaro J. L.
Published: December 2004

The bone‐implant interface and the accompanying difficulties with fixation continue to be a major area of research activity. Biological fixation would appear to be the ideal method of fixation. Press‐fit metal implants may be part of a larger answer that may include sintering, coatings, or both.
The total Walldius knee endoprosthesis in combination with retropatellar facet replacement (Polyethylene). Indication, operative procedure, and clinical results in a two year follow‐up study
Authors: von Andrian‐Werburg Hanns F. , Jentschura Guenter
Published: December 2004

Total replacement of the knee joint often remains unsatisfactory because of severe femor‐patellar osteoarthritis.

Twenty‐four Walldius knee prostheses were inserted in 21 cases. Since March 1971 we have used a combination of this type of hinge prosthesis with a high‐density polyethylene retropatellar facet prosthesis developed by our group in cooperation with the Badische Anilin‐ & Soda Fabrik AG (BASF).

Fourteen knees of this combined type have been implanted and resulted in considerably less complaints than the original Walldius knee. The postoperative range of motion with an average of 66° does not differ in both groups.
The Sheffield knee prosthesis
Authors: Elson Reginald , Watts Norman
Published: December 2004

A new variant of the hinge type knee prosthesis has been developed in Sheffield, England. To date, the results of the early clinical trial in five patients are satisfactory, but it is recognized that the operation is highly speculative and continuation of the trial is being conducted with extreme caution. The main features are as follows.

The hinge is not provided with a mechanical stop to extension, the posterior ligament providing this check.

The contours of the femoral condyles are preseved.

Debris is collected inside the device.

Replacement of worn plastic components can be conducted without dismantling the knee.

There is a built‐in resilience which is intended to protect the components and the bone‐implant interface.
Porous titanium alloy for fixation of knee prostheses
Authors: Nilles J. L. , Karagianes M. T. , Wheeler K. R.
Published: December 2004

A porous titanium alloy called void metal composite (VMC) was investigated for use in knee prosthesis fixation. The interfacial ingrowth fixation of VMC intrameduallary, subchondral, and variable density implants in goat femora was evaluated biomechanically and histologically at six weeks and five months. Biomechanical tests were done under static shear and dynamic, cyclic (fatigue) loading conditions. Readily identifiable bone, strong fixation, and excellent biocompatibility were typical. Some subarticular implants appeared to induce normal hyaline cartilage overgrowth.
A simple shoulder replacement
Authors: Kenmore Peter I. , Maccartee Carl , Vitek Brantley
Published: December 2004

Although degenerative arthritis of the shoulder is quite rare, it does occur. Pain relief was obtained in three such cases by the insertion of a polyethylene glenoid liner made for this purpose and used in conjunction with a standard metal prosthesis for humeral head replacement. Good pain relief and fair motion was obtained.
Elimination of unnecessary screw threads
Authors: Sutton Richard O. , Blackwell William M. , Luekens Claude A.
Published: December 2004

An investigation of metallic intramedullary fixation devices commonly used in orthopedic surgery revealed that the screw threaded portions of these devices were foci for corrosion and fatique fractures. After several design change proposals, a spherical head was developed which could be incorporated onto the intramedullary nails which would eliminate these problems. An extractor impactor was also developed to enable this new design concept to be utilized in surgery. The design and device are described and displayed.
A histopathological report on the nature of the epithelium and underlying connective tissue which surrounds oral implants
Authors: James Robert A. , Kelln Elmer E.
Published: December 2004

This report is concerned with the two tissue types (oral epithelium and fibrous connective tissue) which surround oral implants and the possible adhesion of cells of these tissues to the implant surface. A review of the literature reveals that there is disagreement as to which of these two tissue types encase the deeper portions of Vitallium implants. Using techniques developed for studying the dental epithelial attachment, the following observations are submitted.

A PAS‐possitive material is in abundance at the interface between the junctional epithelium and the implant post and present, but to a lesser degree, between the fibrous connective tissue and the implant surface.

An Oracine‐positive material is present at the interface of both tissue types and the implant surfaces.

Collagen fibers subjacent to the junctional epithelium are oriented at functional angles to the basement membrane.

A histological artifact has been frequently observed which is the result of the tearing of the end of the epithelium away from its basement membrane.

Bacterial plaque adhering to the exposed portion of the implant posts extends in an apical direction and terminates abruptly along a very distinct line.

From these observations it seems likely that an adhesion exists at the interface between the junctional epithelial cells and the penetrating implant surface.
Development and evaluation of porous ceramic and titanium alloy dental anchors implanted in miniature swine
Authors: Karagianes M. T. , Westerman R. E. , Rasmussen J. J. , Marshall R. P.
Published: December 2004

A study sponsored by the National Institute of Dental Research has as its major goal the development of easily fabricated and implantable dental anchors for replacement of missing or extracted teeth. Tissue ingrowth fixes the anchors in the mandibular or maxillary bone where they can serve as a base for future attachment of prefabricated dental caps, bridges, or other dental prostheses. More immediate objectives are to determine the suitability of specific porous titanium and ceramic materials for anchor applications, to develop satisfactory designs and fabrication procedures for producing these devices, and to define material/bone interface bonding characteristics through in vivo studies. The value of the Hanford Miniature Swine as a human analog for dental research is being assessed concurrently.
The foreign body reaction: A chronic inflammatory response
Authors: Coleman D. L. , King R. N. , Andrade J. D.
Published: December 2004

A brief discussion is presented of some of the problems and artifacts inherent in the testing of soft tissue reactions to artificial implants. The process of inflammation and wound healing is presented. The various factors affecting the foreign body reaction (chemical, mechanical, geometrical, and others) are discussed. The cellular components of the foreign body reaction are described and the sequential cellular changes that may occur as a result of implanting an artificial device are examined. The foreign body reaction should be considered as a chronic inflammatory response.
Surface topography of a new polymer material for tooth implants
Authors: Hodosh Milton , Shklar Gerald , Povar Morris
Published: December 2004

A new polymer material has been developed for tooth implants. This material appears to be more successful than previous materials used, in that self support of tooth‐replica implants have been demonstrated in baboons. The surface topography of the new material has been studied with a scanning electron microscope and a lace‐like pattern was demonstrated, which had certain similarities to the surface of cementum of natural teeth.
A wear resistant material for total joint replacement—tissue biocompatibility of an ultra‐high molecular weight (UHMW) polyethylene—graphite composite
Authors: Tetik Robert D. , Galante Jorge O. , Rostoker William
Published: December 2004

A new prosthetic material, ultra‐high molecular weight (UHMW) polyethylene graphite, was developed for use in total joint replacement and found to exhibit 1/7–1/30 lower wear rate than UHMW polyethylene bearing against Vitallium alloy.

A preliminary study was undertaken to test the biocompatibility of the new material. Specimens of 316L stainless steel, high‐purity graphite, UHMW polyethylene, and the composite material were implanted in rabbits and cynomologous monkeys. The materials were evaluated in both solid and particulate forms after implantation in bone, joint cavities, and paravertebral muscles. The tissue reactions to the materials were noted at time intervals from 6 weeks to 1 year.

All materials showed good tissue acceptance in solid form. The UHMW polyethylene and the composite material were noted to be more reactive than either the high‐purity graphite alone or the stainless steel when in particulate form.

The eventual use of the polyethylene graphite composite in total hip arthroplasties is suggested by virtue of its identical biocompatibility with UHMW polyethylene. In addition, its superior wear resistance, and hence low volume of wear debris particles presented to the surrounding tissues would offer an advantage in terms of longevity of the implant both mechanically and biologically.
Haversian osteons: Size, distribution, internal structure, and orientation
Authors: Black Jonathan , Mattson Richard , Korostoff Edward
Published: December 2004

Measurements of Haversian osteons in human tibial cortical bone specimens from seven donors demonstrate that, for this study:

Haversian osteonal area, as a proportion of cross‐sectional area of cortical bone, increases with the age of the donor, whether or not the area of the central Haversian canal is taken into account.

Haversian canal area, as a proportion of cross‐sectional area of cortical bone, either remains the same or increases with the age of the donor.

The number of osteons present per unit cross‐sectional area has no observable age dependence.

The percent inorganic content or cortical bone increases with the age of the donor.

Optical studies on thin sections of cortical bone, utilizing crossed polarizing filters, suggest that the classification of osteons as light, dark and intermediate, as proposed by others (Anat. Rec., 161, 377 (1968)) is incorrect in that only one general type of Haversian osteon structure was detected in this study.
Antithrombin activity of a polyelectrolyte synthesized from cis‐1,4‐polyisoprene
Authors: Beugeling T. , van der Does L. , Bantjes A. , Sederel W. L.
Published: December 2004

A polyelectrolyte synthesized from cis‐1,4‐polyisoprene, containing aminosulfonate and carboxylate groups was shown to have an anticoagulant activity of about 1/30 compared with heparin. Because the substance prevents the coagulation of plasma in the presence of thrombin it is assumed that it acts as an antithrombin.
Couple corrosion among alloys for skeletal prostheses
Authors: Rostoker W. , Pretzel C. W. , Galante J. O.
Published: December 2004

Using a metallographic technique to identify and count corrosion pits, the tendency for passive film breakdown has been studied under conditions that simulate a crevice and a combination of two different materials. Potential corrosion couples were formed among: 316L stainless steel, cast CoCrMo alloy, wrought CoCrWNi alloy, Ti–6% Al–4% V alloy, a CoNiCrMo (multiphase) alloy and graphite. Only 316L stainless steel seems significantly prone to pitting corrosion in a crevice condition. Dissimilar metals in the crevice configuration did not seem to accelerate the corrosion of stainless steel.
Long‐term phase changes in dental amalgam after setting
Authors: Vrijhoef M. M. A. , Driessens F. C. M.
Published: December 2004

The integrated peak intensities of certain reflections of the γ, γ1 and γ2 phase of six dental amalgams at a mercury content of 45 wt% were selected and their dependence on the annealing time (1 < t < 140 days) at 37°C was determined. Also the overall changes in phase composition were studied qualitatively by means of the peak heights of all phases found in the X‐ray patterns of these amalgams at different annealing times.

The γ2 phase content did not seem to depend on the annealing time. It was established also that the γ and γ1 phase contents of these dental amalgams decrease with increasing annealing time at 37°C whereas the quantity of another phase, probably the ternary β phase increases with increasing annealing time.
Investigation of the phase composition of six dental amalgams by X‐ray diffraction
Authors: Vrijhoef M. M. A. , Driessens F. C. M.
Published: December 2004

The integrated intensities of certain reflections of the γ, γ1, and γ2 phase have been determined as a function of the mercury content of 6 amalgams after annealing for 20 hr at 37°C. This dependency could be described satisfactorily by means of the regression model:

. Here Ii is the integrated peak intensity for phase i at a mercury fraction of W by weight, whereas I and αi are constants of the material, whereby i = 0, 1, 2 stands for the γ, γ1, and γ2 phase respectively. Considerable differences between the αi and I parameters of the different amalgams were detected.
Grafting of polymeric side chains to soft tissues
Authors: Brauer G. M. , Termini D. J.
Published: December 2004

This paper describes a novel approach for obtaining covalent bonding to tissues by chemical grafting of polymeric side chains to the collagenous backbone. Soft tissues such as calfskin or ratskin can be modified by acrylic, methacrylic, or vinyl monomers containing a variety of functional groups using ceric ions, persulfate–bisulfite or comonomers forming donor–acceptor complexes as initiators. Reactions take place within 20 min to 3 hr under experimental condition which, with suitable changes, might be tolerated clinically. The resulting products are insoluble in solvents for the respective homopolymers. It is likely that the polymeric side chain is attached chemically to the collagenous backbone. With ratskin, the grafting takes place mainly at the surface, resulting in a change in wettability and water sorption of the substrate. Modified hydrophilic, hydrophobic or even oil repellent surfaces can be prepared by judicious choice of monomer used. Thus, hydrophobic, oleophobic subdermal ratskin surfaces are obtained on reaction with flourinated monomers. Treated ratskins appear more resistant to fungal attack than the original substrate. It is conceivable that the polymeric side chains can serve as adhesive liners since the modified surface may improve the ability of the substrate to adhere to restorative materials.
Evaluation of the physical properties of crown dental porcelain and the effect of newly developed anti‐balling additive
Authors: Mabile C. P.
Published: December 2004

A colloidal silica‐based substitute for the water added to dental porcelain has been developed which restricts rounding on firing and gives greater and indefinitely prolonged unfired biscuit strength. In conjunction with product evaluation, it has been found that both the modulus of rupture and the diametrical tensile strength of dental porcelains can be measured with a high degree of precision.
Degree of polymerization of acrylic bone cement
Authors: Bayne S. C. , Lautenschlager E. P. , Compere C. L. , Wildes R.
Published: December 2004

Self‐curing poweder‐liquid admixed acrylic systems are used for internal fixation of total hip and total knee prostheses. Gel permeation chromatography revealed that the polymer chain length distributions of set cements were basically unaffected by their curing pressures. However, a decrease of approximately 11% in porosity coupled with a measured increase in mechanical strengths could be induced through the use of high curing pressures well beyond those attainable by the surgeon in the current arthroplasties. The conclusion of the investigation was that, to improve such cements, attention should be focused on elimination of porosity rather than attempting to produce higher degrees of polymerization.
The surface area of aggregates applied to dental materials
Authors: Loebenstein William V.
Published: December 2004

There is a continuing need for the complete characterization of the physica and chemical properties of dental materials. Among these properties is surface area. The problem is further complicated by the fact that most dental materials are, themselves, mixtures of two or more identifiable components. If the vapor adsorptive properties of these components are different in the mixture from that which would be expected of them collectively, then interaction is present. Interaction must not be confused with the lack of additivity which results from the limitations of the BET theory applied to mixtures. Equations are derived herein to estimate the extent of this latter source of variability and to correct for it giving a “true” surface area for the aggregate. Conversely, the adsorptive properties of either component can be calculated from the properties of the mixture and the remaining component together with the percentage composition. An immediate application can be made in determining the water‐vapor adsorptive properties of human dentinal collagen without necessitating its removal from dentin. Any attempt to extract it chemically may produce denaturation or chain rupture thus precluding the possibility of direct determination. In the case of nitrogen adsorption, however, interaction definitely is indicated.
Antimicrobial polymers
Authors: Ackart W. B. , Camp R. L. , Wheelwright W. L. , Byck J. S.
Published: December 2004

A number of carboxyl‐containing ethylene copolymers have been prepared which exhibit long term antibacterial and antifungal properties. These materials, containing antimicrobial agents bound to the copolymer backbone as carboxylate salts, have been tested for their applicability to hospital products as a means of providing “self‐sanitizing” articles. Tests have shown that these materials, although not bactericidal, do inhibit microbial growth. Investigations of the compatibility of these polymers with commodity polymers have been made and water emulsions of the polymers have been tested for applicability as components of product protectant coatings.
Investigation of possible oncogenic action of zinc polycarboxylate cement by implantation in mice and hamsters
Authors: Main J. H. P. , Mock D. , Beagrie G. S. , Smith D. C.
Published: December 2004

Powdered, sterilized zinc polycarboxylate was implanted subcutaneously in 56 young hamsters and 54 mice, using equal numbers of each sex, with 24 sham operated hamsters and 26 mice as controls. The hamsters were sacrificed after 15 months and the mice after 12. Implant material was recovered from one of 42 surviving mice and from 16 of 43 surviving hamsters. Benign adenomas of the gut, thyroid, sebaceous glands and ovary were found in 3 experimental mice and in one control. Benign adrenal adenomas were found in 3 experimental hamsters and in one control. One control hamster developed a rhabdomyosarcoma in a limb. One experimental hamster developed a leiomyosarcoma in close relation to an implant.
A vitreous carbon‐polymethacrylate composite for dental implants
Authors: Hodosh Milton , Shklar Gerald , Povar Morris
Published: December 2004

A study has been carried out on the structure and surface texture of a new dental implant material composed of vitreous carbon balloons (3 wt % or 6 wt %) and poly(methyl methacrylate). Tooth replica implants using this material had been successfully placed in baboons, and histologic study revealed normal alveolar bone and a peri‐implant membrane with the connective tissue fibers oriented in a horizontal direction. Square wafers (10 mm × 10 mm × 1 mm) were studied, with the surface sandblasted in one‐half of the specimens. Light microscopy revealed that in the 3% carbon specimens, the vitreous carbon microballoons were evenly spaced and often appeared to be fragmented within their spaces. S.E.M. studies revealed a finely porous surface with numerous large craters. Microballons were often seen within the craters in the nonsandblasted specimens.
The role of surface thermodynamics in thromboresistance of biomaterials
Authors: Neumann A. W. , Hope C. J. , Ward C. A. , Herbert M. A. , Dunn G. W. , Zingg W.
Published: December 2004

A thermodynamic approach to the problem of platelet adsorption out of a suspension on to a smooth and homogeneous solid surface is developed. The interfacial tension values required may be estimated from contact angle data by means of an equation of state relation. According to the thermodynamic approach the functional dependence of platelet adsorption on surface tension of the solid differs according to whether the surface tension of the platelets is smaller or larger than the surface tension of the liquid in which they are suspended. The implications of this thermodynamic approach in situations where plasma proteins are present and the biomaterials surfaces may be heterogeneous and rough are discussed. Previous analyses using the critical surface tension of wetting and other surface‐related parameters are compared with the thermodynamic analysis given here.
Cast vs. wrought cobalt‐chromium surgical implant alloys
Authors: Devine T. M. , Wulff J.
Published: December 2004

The measured tensile and fatigue strengths of wrought and heat‐treated cobalt chromium‐molybdenum‐carbon alloys such as HS21 were found to be more than twice those of as cast alloys of the same composition. The resistance of wrought HS21 to crevice corrosion at metal‐Teflon contacts in isotonic salt solution at 37°C was found to be considerably greater than that of cast HS21, wrought HS25, wrought MP35, or 316L stainless steel which are currently used for surgical implants. The increased crevice corrosion resistance and mechanical strength of wrought HS21 as compared to as cast HS21 was attributed to greater chemical and structural homogeneity as well as to finer grain size and distribution of secondary phases. Fabrication of shaped implants from wrought HS21 is possible by techniques currently used for the fabrication of industrial parts from other wrought cobalt‐chromium base alloys.
A comparison of iliac marrow and biodegradable ceramic in periodontal defects
Authors: Levin Marvin P. , Getter Lee , Cutright Duane E. , Bhaskar S. N.
Published: December 2004

Defects were created in the tooth‐supporting bone of six beagle dogs. Biodegradable tricalcium phosphate was compared to cancellous marrow as a treatment method. The findings indicated that ankylosis and resorption of the tooth can occur when using marrow. The ceramic‐filled defects healed slower; but the material itself was well tolerated by the tissues, initiated new bone formation, filled in the defect, and has good potential for the treatment of advanced periodontitis.
Identification of AuSn phase in Ag3Sn alloys containing gold
Authors: Malhotra M. L. , Lawless K. R.
Published: December 2004

Substitution of gold in part for silver in Ag3Sn alloys is found to result in two separate phases: γ (Ag3Sn particles) grains with a uniform distribution of gold within the grain and an AuSn phase in a form of ring surrounding the γ grain. The thickness of this ring increases with increasing gold concentration. The phases were identified by using the techniques of x‐ray diffraction, optical metallography, scanning electron microscopy, and x‐ray energy dispersive spectroscopy.
Thermodynamic considerations of the setting reaction in Ag3Sn amalgams
Authors: Reynolds C. L. , Barker R. E.
Published: December 2004

The setting reaction of Ag3Sn amalgams may be thought of as a liquid phase sintering problem in which the reactants seek to form products with the lowest thermodynamic potential. We discuss the thermodynamic and kinetic considerations of this reaction. The lowering of free energy has been given as the reason for the formation of the γ1, γ2, and β1 phases and a qualitative reaction coordinate diagram has been hypothesized. The barrier height for the formation of the β1 phase has been determined to be 137 kJ/mol.
Finite element analysis of dental structures — axisymmetric and plane stress idealizations
Authors: Selna Lawrence G. , Shillingburg Herbert T. , Kerr Peeter A.
Published: December 2004

The finite element method used to study stress generated in a maxillary second premolar as a result of occlusal forces. This mathematical technique has been applied extensively in structural engineering and structural mechanics. It is well suited to the analysis of stress in teeth and dental restorations because it can closely simulate the geometries, loads, and material inhomogeneities in the system being studied.
The effects of polyvalent salts on zeta potential of bone
Authors: Wilson C. N. , Miller A. D. , Nilles J. L.
Published: December 2004

A streaming potential experiment was conducted on in vitro bone to determine the effects polyvalent salts have on bone zeta potential. Polyvalent metal salts would be introduced into local physiological electrolytes by corrosion of a metal implant or dissolution of a ceramic implant. It was hypothesized that a change in zeta potential of mineralized tissue, resulting from the introduction of polyvalent salts, could be a cause of tissue instability at the implant interface. Zeta potentials measured in bone were on the order of a few millivolts. Strongly hydrolytic metal cations such as Al+3 and Fe+3 did not have sufficient activity in buffered neutral electrolytes to alter bone zeta potential. Results suggest that less hydrolytic cations of high valence, and large polarizable anions may affect bone zeta potential.
Wettability of hydrogels I. Poly(2‐hydroxyethyl methacrylate)
Authors: Holly Frank J. , Refojo Miguel F.
Published: December 2004

The wettability characteristics of the contact lens material, PHEMA, with respect to water have been determined by using the sessile drop, and the captive air bubble techniques of contact angle goniometry. It is concluded that on PHEMA gels water does not spread spontaneously. Large hysteresis has been observed in the advancing and receding contact angles. This suggests that this hydrogel surface is capable of changing its free energy through reorientation of the polymer side chains and chain segments depending on the nature of the adjacent phase. The water content of the gels does not appear to have an effect on water wettability in the hydration range investigated. The minor wettability differences among the various gels studied were most likely due to differences in surface structure and segmental mobility due to inherent variations in the method of preparation. Small but consistent differences were found between the contact angles measured by the captive bubble method and those obtained by the sessile drop method, the former values being higher. These differences may not be method‐related artifacts and cannot be explained at the present time.
Biocompatible implants for the sustained zero‐order release of narcotic antagonists
Authors: Abrahams Robert A. , Ronel Samuel H.
Published: December 2004

Implantable, sustained release drug delivery devices offer benefits not obtained through oral ingestion or injection. These include delivery at a constant therapeutic rate, thus avoiding adverse intermittent and massive dose effects, as well as reliance upon patients taking their prescribed dosages. The drawbacks to their widespread acceptance have been their inability to maintain a zero‐order release rate over an extended period of time and poor biocompatibility. Devices capable of satisfying these requirements have been developed and tested extensively for in vitro release of the narcotic antagonist cyclazocine. By using implant models prepared from Hydron, a hydrophilic polymer known to exhibit excellent tissue compatibility, we have found that the release rate could be precisely regulated by proper geometry, copolymer composition, concentration of ionogenic groups and cross‐link density. Devices in such varied forms as capusles, barrier‐film coated tablets and bulk polymerized rods have been tested in vitro for periods approaching 1 year.
Biomaterials science protocols for clinical investigations on porous alumina ceramic and vitreous carbon implants
Authors: Lemons J. E.
Published: December 2004

A written protocol for the investigation of candidate surgical implant materials is quite important. Biomaterials science sections of clinical protocols have been developed for porous alumina ceramic and nonporous vitreous carbon biomaterials.

Published data on the properties of the biomaterials were evaluated as related to bone replacement and augmentation. Where necessary, limited laboratory studies were conducted. If decisions could not be reached with respect to a given application, animal studies were initiated. The surgeons worked with biomaterials in the laboratory and the biomaterials scientist attended the experimental surgery procedures.

Biomaterials Science Laboratory nondestructive investigations including stereomicroscopic and x‐ray inspections were conducted on the vitreous carbon dental implant systems. The investigations elucidated a number of unexpected features for both implant biomaterials and the overall interaction between the different disciplines resulted in a more complete protocol for the study of these biomaterials at our Medical and Dental Center.
Mechanical studies of the bone bioglass interfacial bond
Authors: Piotrowski George , Hench L. L. , Allen W. C. , Miller G. J.
Published: December 2004

A series of squirrel monkeys received segmental femoral replacements in a study of the strength of the interface developed between the implant and bone. Implants were either made completely of bioglass‐ceramic, or 316L stainless steel with a flame‐prayed coating of bioglass. Fracture torque, energy at fracture, and shear stress at failure were compared to values obtained from a control group of pairs of tibias. Femurs containing bulk bioglassceramic implants showed about a 25% difference in strength compared to the opposite bone, while femurs containing flame‐sprayed implants exhibited extremely low structural strength. While the strength of the metal‐glass bond was very low (<500 kgf/cm2), the bonebioglass bond was found to be at least as strong as the bioglass‐ceramic, and at least 3/4 as strong as the host bone.
Mechanical properties of calcia stabilized zirconia following in vivo and in vitro aging
Authors: Kenner G. H. , Pasco W. D. , Frakes J. T. , Brown S. D.
Published: December 2004

Aging studies were done on calcia stabilized zirconia rods of 72% theoretical density to determine the effect of actual and simulated biological environments on their strength. They were aged without stress in vitro in Ringer's solution for 1, 2 and 4 weeks or in vivo in rabbits for 12 weeks. Rods aged in vitro showed mean losses in bending strength of 16, 17 and 19% respectively after 1, 2 and 4 weeks of immersion, while those aged in vivo showed a mean loss of 25%. It was concluded that the material tested would be unsatisfactory as an orthopedic replacement because of the rapid decrease in strength which occurred when exposed to actual or simulated biological media.
Soft tissue response to four dense ceramic materials and two clinically used biomaterials
Authors: Richardson W. C. , Klawitter J. J. , Sauer B. W. , Pruitt J. R. , Hulbert S. F.
Published: December 2004

Disk‐shaped implants of spinel, alumina, mullite, zircon, a cast Co‐Cr‐Mo alloy, and ultra‐high molecular weight polyethylene (UHMWPE), were implanted in the paraspinalis muscle of 12 adult, male, white New Zealand rabbits. Prior to implantation the implants were characterized with respect to size and shape, weight and surface roughness. After periods of 1 month, 2 months, and 4 months, the rabbits were sacrificed and the tissue specimens were retrieved with the implants still intact. Histological examination of the tissues surrounding the implants along with changes in the size and shape, weight, and surface roughness of the implants were used a criteria for evaluating these materials for implant purposes.

No surface degradation of any of the materials was detected using scanning electron microscopy. Fibrous tissue seemed to adhere to the UHMWPE implants more than any other material used in this study. Large amounts of fibrous tissue were also found to adhere to the cast Co‐Cr‐Mo alloy implants.

The histological results indicated that within the limits of this investigation, the biocompatibility of the ceramic materials used in this study compared favorably with the clinically used Co‐Cr‐Mo alloy implants and the UHMWPE implants.
Factors influencing the creep behavior of poly(methyl methacrylate) cements
Authors: Treharne Richard W. , Brown Norman
Published: December 2004

Room temperature compression creep and recovery tests have been performed using samples of pure poly(methyl methacrylate) (PMMA), three commercially available poly(methyl methacrylate) cements, and several experimental cements. From these tests the influence of density, mixing procedure, particle size, methyl methacrylate‐styrene copolymer, barium sulfate, aquenous storage environments, residual monomer, molecular weight of the continuous phase, benzoyl peroxide, and N,N‐dimethyl‐paratoluidine, upon the creep behavior of PMMA cements has been determined. The important result is that lowering the porosity or residual monomer content, increasing the powder size, or adding an MMA‐styrene copolymer tends to increase the creep resistance of PMMA cement.
The use of dissimilar metals in surgery
Authors: Mears D. C.
Published: December 2004

Previously, the use of dissimilar metals for the construction of surgical implants has been strongly discouraged because the combination of metals was likely to provoke more rapid corrosion of one metal. With the passive alloys that are in present and future application, however, a reconsideration of the use of dissimilar metals is required. Presently available electrochemical tests allow accurate prediction of safe and unsafe combinations of metals. The use of dissimilar metals would permit selection of the alloy of appropriate mechanical properties for each part of an implant and would allow improved corrosion resistance that certain alloys can convey to other alloys with which they are in contact.
Design and fabrication of two types of artificial tendons for evaluation of surgical techniques
Authors: Wade C. W. R. , Ouellette J. E. , Hodge J. W. , Urban J. J. , Salisbury R. E.
Published: December 2004

Double‐loop tendons of fixed and adjustable lengths, and tendons with inner porous tapes both for anastomosis to tendon stumps have been made from readily available materials. By using stainless steel wire and polymer fibers, breakloads have been obtained that range from 20 to 100 lb and elongations have been reduced to less than 2%. Pore sizes up to 50 × 250 μ2 were achieved by using woven, knitted, and braided polyester tapes. For all tendons, Silastic was used to isolate inner fibers and to effect smooth gliding. Preliminary evaluation of these devices, after being implanted in the feet of chickens for 4 weeks, indicates that anastomotic strength of unions formed by use of loops is about 1000 g compared to more than 2000 for unions formed by tissue ingrowth.
A single unit digital flexor tendon prosthesis
Authors: King R. N. , Dunn H. K. , Bolstad K. E.
Published: December 2004

Historically, the surgical repair of serious injuries to the flexor tendons of the hand have met with loss than satisfactory clinical results. In an attempt to solve this problem, studies have been made on the design and testing of a Dacron polyester tendon prosthesis for complete replacement of the digital flexor tendon.

The prosthesis attaches proximally at the anatomical musculotendon junction via collagen ingrowth into a fabric structure and in a similar manner distally via bone ingrowth at the anatomical insertion site. These fabrics are continuous with the tendon body of the prosthesis consisting of an inextensible braided cord which is silicone rubber coated to prevent tissue adherence in the glide zone of the tendon bed. An added benefit of the prosthesis is a simple means of length adjustment which can easily be carried out on the operating table.

Studies have been performed in both dogs and chickens which indicate that sufficient tissue ingrowth occurs at both the distal and proximal anastomoses for retention of full load bearing capability in these animals and that postoperative adhesions are negligible, if present at all.

Full prostheses have been implanted in dogs for periods of over 1 year and in chickens for 2 months. The chicken is the preferred animal model as a tendency for extensive scar tissue generation was shown in the dog.

Both in vivo mechanical testing and histological characterizations have been made on sacrificed animals which have received the full prostheses.
Clinical considerations in the choice of materials for orthopedic internal prostheses
Authors: Scales John T. , Winter G. D.
Published: December 2004

The six principal clinical considerations which influence the choice of materials for total joint replacements are given.

The necessity for screening tests on potentially useful materials is stressed. These should be carried out on specimens which have been exposed to the sterilizing process, which will be used in clinical practice. The materials should also be investigated after immersion in a physiological solution—bovine serum; following implantation in a large animal.

Useful tests are impact testing, and wear studies using pin‐on‐disk and journal and bush specimens.

In the case of total joint replacements, equipment in which joint motions and loadings can be simulated can provide valuable information. The components should also be subject to fatigue testing.

There is a need to develop agreed laboratory methods for testing of materials and implants and for the long term follow up of patients.
Evaluation of a metal‐ceramic composite hip prosthesis
Authors: Hulbert S. F. , Richbourg H. L. , Klawitter J. J. , Sauer B. W.
Published: December 2004

This investigation attempts to apply the concept of direct sketal attachment via tissue ingrowth to the attachment of femoral head prosthess to the femur. Stainless steel (316L) canine femoral head prostheses with a ceramic coated stem were implanted into the femora of dogs and their results compared to those obtained by the impaction of stainless steel prostheses and acrylic‐stabilized prostheses. The implants were tested in vivo for time periods ranging from 2 to 13 months, after which time the animals were sacrificed and the femora excised. The femora were sectioned with the implants in place and prepared for examination by light microscopy. Bone was in closer approximation to the ceramic coated implants than to the other two types of implantations. The uncoated and acrylic‐stabilized implants were usually charaterized by the presence of a relatively thick fibrous sequestering membrane.
Fatigue fractures of the femoral component of Charnley and Charnley‐Müller type total hip prostheses
Authors: Ducheyne Paul , de Meester Paul , Aernoudt Etienne , Martens Marc , Mulier J. C.
Published: December 2004

A survey is given of the mechanical failures of the femoral component of Charnley and Charnley‐Müller type total hip prostheses. Fractographic analysis reveals that all the prostheses have broken by metal fatigue.

A review of the clinical data has been combined with a metallurgical and a mechanical study in order to assess the reasons of the mechanical failures.

The following conclusions have been reached. The prosthesis should be inserted in varus position with regard to the axis of the intramedullary canal, and the prosthesis should be made of an alloy with appreciably higher yield stress and fatigue strength than the alloys of the investigated broken Charnley and Charnley‐Müller type prostheses.
Composite implants for orthopedic applications: In vivo evaluation of candidate resins
Authors: Jacobs Marc L. , Black Jonathan
Published: December 2004

Three resins which include poly (methyl methacrylate), surgical Simplex P, and ultrahigh molecular weight polyethylene were selected to be evaluated as candidate systems for a polymer based composite for hard tissue prosthesis. Characterization of the mechanical behavior of these polymers in different environments including in vitro and in vivo storage was accomplished. As a result, conclusions were made as to which material maintained the least amount of mechanical variance as influenced by environmental effects. In vivo studies of implanted materials provided for a study of soft tissue response to each material. Conclusions were then developed as to the varying degrees of tissue reaction initiated by each material, and which resin generated the greatest tissue response with respect to the others.
Use of PMMA in expansion dental implants
Authors: Leigh Jorge A.
Published: December 2004

The Polymer Expansion Implant System, which is a system for the substitution of missing dental roots in natural or surgical alveolus, has been developed by the author. The polymer used is poly (methyl methacrylate) (PMMA).

A material is sought that has three of the basic physical and mechanical qualities of human dentine: low modulus of elasticity, thermal and electrical passiveness, and ideal porosity. In addition it should be resistant, easily worked, biocompatible, and of low cost. Of the biomedical polymers, PMMA has these qualities, and it can be used as a substitute for dental roots.

The design of bodies to be implanted as substitutes for dental roots requires: anatomical measurements of the maxilla and sockets; methods of retention by the bone tissue; and methods of insertion.

The formation of lamina dura around an implanted body is a reply of the organism to the forces acting on it and a demonstration of the good interaction of the porosity of the material, the peri‐implant collagenous fibers and bone. X‐rays that demonstrate the behavior of bone to a PMMA implant are shown.

Numerous expansion implants have been performed during the last 4 years with clinical and x‐ray proof of their success. Three clinical cases representing the classic applications are presented: (1) individual replacement, (2) intermediate abutment, and (3) free‐end abutment.
The epithelium contiguous with the neck of intraosseous dental implants
Authors: Johns Richard B.
Published: December 2004

There are three distinct regions with which a wedge shaped dental implant is in contact; the intraoral, transitional and intraosseous portions. The environment of each of these is different and will require special consideration.

This investigation compares the epithelium found associated with a natural tooth to that which is found contiguous with the transitional region of an implant.

The possibility of a pseudojunctional epithelium being formed in association with a glass collar processed onto the neck of a wedge shaped implant is examined. The histological appearance of a specimen in situ for 11 months shows an altered epithelial structure compared to that found adjacent to the neck of an unmodified titanium wedge shaped implant. Because the implant and glass must be mechanically separated from the tissue being examined, the value of demeneratized histological sections is limited.

However, examination by a Scanning Electron Microscope of the surface of the glass after removal reveals an area of clear glass in the deeper region of the collar. Above this there is a deposit, the exact nature of which is unknown, but which might be interpreted as the contents of the gingival crevice.

Although this might be interpreted as a type of epithelial attachment, other factors are necessary to ensure close gingival adaptation and limitation on epithelial downgrowth.
Slow crack growth in acrylic bone cement
Authors: Beaumont Peter W. R. , Young Robert J.
Published: December 2004

Slow crack growth in Perspex acrylic sheet (PMMA) and Simplex acrylic bone cement in air and water has been studied from a fracture mechanics viewpoint. It has been found that the crack velocity, V, for each material depends upon the intensification of stress at the tip of the crack. Experimental measurements have been made of V as a function of the stress intensity factor, K, at the crack tip, and a derived V, K relationship has been used to predict the times‐to‐failure of components made from PMMA and Simplex cement. Direct measurements of time‐to‐failure for PMMA have shown that the predicted values give a conservative estimate of the structural lifetime of the material.