Bio-Medical Materials and Engineering - Volume 7, issue 2

Authors: Hedia, R.S. | Barton, D.C. | Fisher, J.

Article Type: Research Article

Abstract: Previous studies have optimised the shape of a cemented stainless steel stem in order to minimise the fatigue notch factor Kf in the cement whilst at the same time maximising Kf in the proximal medial bone to prevent bone resorption [1]. The present study firstly describes the effect of changes in the modulus of elasticity of the stem material for both the original Charnley stem and the ciptimised shape on Kf as predicted by a 2D finite element (FE) model of the implanted prosthesis. The paper further describes a method for parametric optimisation to determine the best …material properties of a layered composite femoral stem consisting of a core material (stainless steel) and an outer layer of a different material, the elastic modulus of which is used as a design variable. The overall objective of the optimisation was to maximise Kf in the proximal bone whilst at the same time constraining Kf at all cement interfaces to be no greater than its initial value. The results of the first study suggest that Young's moduli of about 145 and 210 GPa are optimal for the monolithic Charnley and optimised stems, respectively. A composite prosthesis with a layer of modulus 31 GPa added to the optimised stainless steel stem in the proximal region only was found to significantly increase the stresses in the proximal bone and reduce Kf in the cement whilst retaining the advantages of an outer stem profile very similar to that of the original Charnley prosthesis. Show more

Keywords: Hip prosthesis, optimisation, fatigue notch factor, bone resorption, finite element analysis

DOI: 10.3233/BME-1997-7201

Citation: Bio-Medical Materials and Engineering, vol. 7, no. 2, pp. 83-98, 1997

Authors: Chen, Jie | Chen, Ken | Katona, Thomas R. | Baldwin, James J. | Arbuckle, Gordon R.

Article Type: Research Article

Abstract: Large deformation non-linear finite element models of T, V, L and B (Baldwin) orthodontic springs were developed and experimentally validated. Spring stiffnesses and moment/force ratios were computed. Compared to the T loop, under horizontal activation, the V loop was half as stiff, the L loop was equal, and the B spring was 10% as stiff, The moment/force ratio was 30% higher in the V configuration, while the B spring was less by 95%. The asymmetric L loop exerted a moment/force ratio that was 30% on the one side, but 180% in the opposite direction on the other side. With vertical …activation, also compared to the T spring, the horizontal stiffnesses were 500% (V), 150% (L), and 30% (B). The concomitant vertical stiffnesses were 100%, 50% and 25%. The vertically activated moment/force ratios were nearly equal in the four springs. Experiments validated these FEM calculations. Show more

Keywords: Orthodontic springs, force, moment, FEM

DOI: 10.3233/BME-1997-7202

Citation: Bio-Medical Materials and Engineering, vol. 7, no. 2, pp. 99-110, 1997

Authors: Oshida, Yoshiki | Zuccari, Arnaldo G.

Article Type: Research Article

Abstract: Currently acrylic resins are commonly employed in many medical applications, especially for the fabrication of long span provisional restorations in dentistry and bone cement in orthopedics. One of the major problems associated with the conventional type of acrylic resins is their unsatisfactory mechanical properties. Among many attempts to strengthen acrylic resins, it has been demonstrated that they can be strengthened through the addition of reinforcement(s) as structural components of different size, shape and chemical composition, dispersed in the acrylic matrix, thus forming a composite structure. In the course of studies to strengthen dental polymeric resins by admixing various metallic …oxide particles, PMMA-, PEMA-, and PIMA-based resins were reinforced by 2 vol.% added alumina, magnesia, zirconia, and silica powders. It was found that PMMA admixed with 2 vol. % zirconia exhibited the best improvement of mechanical properties (breaking strength, modulus of elasticity, offset yield strength, and fracture toughness as well). All tests were conducted under three-point bending. It was also found that the breaking strength based on the original sample dimension was, at most, 20% less than those based on the final sample dimension. Moreover, this discrepancy was independent of the type of tested material, but dependent on the sample's modulus of elasticity. Show more

Keywords: Three-point bending test, dental polymeric resins, provisional crowns, crosshead speed, plastic deformation

DOI: 10.3233/BME-1997-7203

Citation: Bio-Medical Materials and Engineering, vol. 7, no. 2, pp. 111-119, 1997

Authors: Takahashi, Toshiyuki | Tominaga, Teiji | Yoshimoto, Takashi | Koshu, Keiji | Toshimitsu Yokobori, Jr, A. | Aizawa, Yoichi

Article Type: Research Article

Abstract: The biomechanical properties of a porous hydroxyapatite (HA) intervertebral graft with or without anterior cervical plating were evaluated in cadaveric porcine cervical spine model using C3–4 discectomy and dissection of the posterior longitudinal ligament to cause instability. The experimental groups were intact (n = 11), instability (n = 11), autogenous bone implant (n = 6), HA graft implant (n = 5), autogenous bone with plating (n = 6), and HA graft with plating (n = 5). Porous HA with 40% porosity and scapular bone were used as grafts. The displacement rates of the cervical spine by compressive forces in the …flexural, extensional, and lateral bending directions were evaluated using video-recording followed by computer-assisted analysis. The stiffness to compressive load was calculated from the load-displacement rate curve. The linear and non-linear coefficients of the Fung's equation were obtained based on the plot of Young's modulus against load. There were no statistical differences in the stiffness between the HA and autogenous bone graft in all directions. The two plating groups showed significantly increased stiffness in all directions. The non-linear coefficient value in Fung's equation was far larger in both HA and HA graft with plating groups than in the other groups in flexural compression. Porous HA graft has a compressive strength similar to autogenous graft in vitro, and anterior plating provides additional stiffness to the cervical spine. The larger non-linear coefficient value of the HA groups may represent the characteristic biomechanical brittleness of HA graft, but this is manifest only in flexural compression. Show more

Keywords: Cervical spine, anterior fixation, instrumentation, hydroxyapatite, biomechanics

DOI: 10.3233/BME-1997-7204

Citation: Bio-Medical Materials and Engineering, vol. 7, no. 2, pp. 121-127, 1997

Authors: Kwon, S.Y. | Kim, Y.S. | Woo, Y.K. | Kim, S.S. | Park, J.B.

Article Type: Research Article

Abstract: Hydroxyapatite (HA) particle impregnated polymethylmethacrylate (PMMA) bone cement was fabricated in order to induce bony tissue ingrowth into the pores left behind by resorption of the HA. The amount of HA was 0%, 10%, and 30% by weight. After mixing the HA with bone cement it was cast in a 4 mm inside diameter glass tube (10 mm long). Each specimen was cut into half and used for in vitro and in vivo experiment. Diametral tensile and flexural bend tests were made to evaluate its mechanical properties. SEM (scanning electron microscope) and ESCA (electron spectroscopy for chemical analysis) were used …to evaluate the surface characteristics of the specimen. Push-out test and histology studies were made after implanting the specimens for six weeks in the distal portion of rabbit femur. The mechanical test results showed significant decrease of the flexural and diametral tensile strength linear with the increased amount of HA (p < 0.05). The SEM and ESCA analyses showed no definite exposure of HA particles on the surface of the specimens due to the covering by PMMA. The interfacial shear strength of the implanted specimens showed significant increases in the 30% HA specimens compared with the 0% ones but the 10% specimens did not show any difference. Histological observation showed little HA particle apposition to new bone in 10% specimens but more in the 30% ones. In conclusion, this study showed the decreased mechanical properties both by increasing the amount of HA particles and with the bone particles impregnated bone cement. In vivo study showed much lower interfacial shear strength due to implant site compared to other studies but the 30% HA specimens showed statistically significant increase in the push-out strength after implanting into the distal end of rabbit femora. Show more

Keywords: Bone cement, bone ingrowth, hydroxyapatite, rabbit femur

DOI: 10.3233/BME-1997-7205

Citation: Bio-Medical Materials and Engineering, vol. 7, no. 2, pp. 129-140, 1997

Authors: Okazaki, Masayuki | Taira, Masayuki | Takahashi, Junzo | Tohda, Hisako | Yanagisawa, Takaaki

Article Type: Research Article

Abstract: The partially substituted fluoridated apatites H-FHAp0.5 and FH-HAp0.5 were synthesized heterogeneously by supplying fluoride at a concentration equivalent to half of the maximum value of fluorapatite during the initial or final half of the experimental period. Although X-ray diffraction patterns and SEM photos of H-FHAp0.5 and FH-HAp0.5 apatites were not significantly different, high-resolution transmission electron microscopy showed quite different features; H-FHAp0.5 type apatite was an elongated hexagon with electron beam damage in the core, and FH-HAp0.5 type apatite was a rather wide hexagon analogous to fluorapatite. Energy dispersive spectroscopy attached to the SEM showed …H-FHAp0.5 apatite to have a higher fluoride peak intensity than FH-HAp0.5 . These results supported the previ6us speculations on the two different types of heterogeneous fluoridated hydroxyapatites: hydroxyapatite covered with fluorapatite and fluorapatite coverted with hydroxyapatite. Show more

Keywords: Heterogeneous apatites, fluoride, partial substitution

DOI: 10.3233/BME-1997-7206

Citation: Bio-Medical Materials and Engineering, vol. 7, no. 2, pp. 141-148, 1997

Authors: Lewis, Gladius

Article Type: Research Article

Abstract: Implantation of an interlocking intramedullary nail has rapidly become the modality of choice for the management of various fractures of the humeral shaft; namely, those that are not minimally displaced, impacted and/or stable. The mechanical properties of the nail per se or the nail-bone construct are essential to the nail's satisfactory clinical performance. The present work is a critical review of this topic, using reports given in the opne literature. Whence, gaps and unresolved controversies in the current knowledge base are identified. Expositions on future work, based on the foregoing observations as well as uncharted topics, are presented.

Keywords: Humeral intramedullary nail, flexural stiffness, torsional stiffness

DOI: 10.3233/BME-1997-7207

Citation: Bio-Medical Materials and Engineering, vol. 7, no. 2, pp. 149-157, 1997