Preliminary studies on the effects of direct current on the bone/porous implant interfaces.
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Animals↗
Biomedical subjects
G H Kenner
Publications and source records attributed to G H Kenner.
The mechanical stability of barium titanate (ceramic) implants in vitro.
Dense, polycrystalline barium titanate (BaTiO3) specimens showed a modulus of rupture of 85.5 +/- 9.0 MPa and a compressive strength of 486 +/- 75 MPa. These values are considerable higher than those which had been previously reported. In addition, there was no significant drop in compressive strength after in vitro aging for 4 weeks in saline solution.
Barium↗
Compressive strength of canine femur.
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Animals↗
Spinal fixation using acrylic bone cement: mechanical property measurements.
Following dorsal laminectomies (L2-L3), the resultant spinal instabilities were stabilized by placing four Steinmann pins and embedding them in acrylic bone cement. The cement was molded about the instability and incorporated the pins and articular process. Mechanical testing was performed to evaluate the strength of the resultant union between the two vertebrae. Three types of samples, in vivo, in vitro and normal were tested using a specially built apparatus. The results showed average maximum loads of 150, 180 and 180 Newtons respectively which represent 29, 42 and 37 MPa in calculated shear stresses. The results indicate that the use of bone cement with pins can stabilize the injured vertebral discs easily iwth the maximum load or shear strength equivalent to that of normal vertebral discs.
Animals↗
Dental implant fixation by electrically mediated process. I. Interfacial strength.
In order to determine the effect of electrical stimulation on canine alveolar bone, porous PMMA dental implants with a solid core (on which a Pt-13% Rh electrode was wound) were implanted in the mesial socket of the canine mandibular fourth premolars bilaterally. The positive electrode was implanted into the distal socket. The power pack was placed over the masseteric fossa. The implants, wires and power packs were all implanted subcutaneously. Each animal had an experimental and control implant. Mechanical push-out samples were prepared by sectioning a 2mm thick section of the mandible with the implant in the middle. The samples were tested immediately and the load-deflection curves were obtained.
Alveolar Process↗
Dental implant fixation by electrically mediated process. II. Tissue ingrowth.
The effect of electrical stimulation on the interfacial strength of the porous polymethylmethacrylate implant/oral tissue union and the amount of tissue growth was investigated in the fourth premolars of dogs. The study indicates the interfacial strength peaks at about three weeks and decreases thereafter for both control and the stimulated specimens. The stimulated side showed consistently higher strength than its paired control. There was a positive relationship between implant period and amount of tissue in the pores although the latter was not correlated with the interfacial strength. Microradiographs showed a different pattern of new bone formation on the stimulated side when compared to the control. On both sides, bone formation occurred upward from the bottom of the tooth socket while on the stimulated side, new bone also developed from the sides of the tooth socket which was minimal in the controls. It is proposed that the direction of oral tissue formation is responsible for the different results obtained in this study compared with a similar study on long bones.
Animals↗
Mechanical property changes of barium titanate (ceramic) after in vivo and in vitro aging.
Since barium titanate (BaTi03) can be made piezoelectric, it may be used to substitute hard tissues directly. As a first step in testing this concept, a series of in vivo and in vitro aging and biocompatibility studies were performed. The mean compressive strength of samples implanted subcutaneously in the backs of rabbits decreased to 138 MPa after 20 weeks from a control value of 281 MPa. Similar, though less drastic losses of strength were seen when specimens were aged in distilled water (182 MPa at 28 weeks) and Ringer's solution (159 MPa at 28 weeks). The most rapid decrease of strength in all cases was seen prior to 4 weeks. Thereafter, the decrease was much slower. Histological evaluation of the tissue surrounding the implant revealed a thin fibrous capsule and no evidence of tissue inflammation.
Animals↗
Effect of electrical stimulation on the interfacial tensile strength and amount of bone formation.
The effect of electrical stimulation upon the direct tensile strength of the interface union between porous calcium aluminate implants and bone plus the amount of bone formation were investigated in the femurs of rabbits. The study indicates there is an increased tensile strength of the interface in proportion to the amount of bone formation into the pores and the amount of electrical stimulation used "in vivo."
Animals↗
Electrical modification of disuse osteoporosis.
Localized electrical stimulation of the immobilized hind limb of young rabbits resulted in dramatically more bone in the tuber calcis (heel bone) compared to the severe loss of bone (osteoporosis) seen in unstimulated, immobilized controls. Detailed histological evaluation using microradiography and fluorescence and polarization microscopy showed that the increase was probably due to an overall inhibition of surface cortical bone loss )endosteal resorption) and an increase in the quantity of the new immature bone. There was also evidence of increased osteonal resorption in the stimulated animals.
Animals↗
Biocompatibility and state fatigue behavior of glassy carbon.
1. The normal stages of bone modeling and remodeling occur following the implantation of carbon plugs. 2. Glassy carbon bars aged in vivo for five months did not undergo statistically significant weakening. 3. Glassy carbon does undergo static fatigue when aged in a simulated biological environment. However, the conditions necessary to cause this failure are extreme. 4. Minimal tissue response was seen to the presence of the carbon.
Animals↗
Mechanical properties of calcia stabilized zirconia following in vivo and in vitro aging.
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 4weeks 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.
Animals↗
Two-year biocompatibility study of ORNL graphite.
A new grade of graphite-isotropic, fine-grained, and of superior strength-has been produced at the Oak Ridge National Laboratory. The possibility of using this material in orthopedic implants is under study at the University of Illinois. As part of this program, plugs 1/8 in. in diam were inserted in holes drilled in the proximal femur of 2 groups of 8-week old male rabbits. The groups were sacrificed at the end of 1 and 2 years. A single i.m. injection of achromycin was given 2 days prior to sacrifice. Thin sections of the plugs and surrounding tissue were examined by microradiography and optical microscopy (white light, polarizing, and fluorescent). All bone was normal. Minimal evidence of irritation or fibrous encapsulation appeared.
Animals↗
Effect of electrical stimulation on the tensile strength of the porous implant and bone interface.
The effect of electrical stimulation upon the direct tensile strength of the interfacial union between porous calcium aluminate implants (100 to 200 mu diameter pores) and bone was studied in the femurs of rabbits. After about 4 weeks of implantation the tnesile strength of the electrically stimulated specimens was approximately two times that of the nonstimulated ones. This indicates that electrical stimulation increased the rate of new bone formation under the experimental conditions.
Aluminum↗
In vivo and in vitro changes in strength of orthopedic calcium aluminates.
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Aluminum↗
Preparation-induced errors in EPR dosimetry of enamel: pre- and post-crushing sensitivity.
Polyakov et al. (1995) showed errors in dose estimation as a function of grain size for enamel grains given beta irradiation after crushing. We tested the effect of gamma irradiation applied to the specimens before and after crushing. We confirmed Polyakov's observations and found that post-crushing irradiation altered the slope of the dose-response curve of the hydroxyapatite signal and produced a grain-size-dependent offset. No changes in the slope of the dose-response curve were seen in enamel caps irradiated whole before crushing.
Dental Enamel↗