PubMed Health⌕ Search

Biomedical subjects

R Thull

Publications and source records attributed to R Thull.

18 recordsLinked to original sources
PubMed1992

["Erlangen Model" titanium socket. Study of the biomechanics of the "Erlangen Mode" titanium socket with and without supporting ring].

A multitude of prostheses are available for the reconstruction of severely arthrotic hip joints--especially for revising total arthroplasty. In order to find out more about the biomechanical efficiency of these special implants, we carried out computerized analyses on how the distribution of stress within the pelvis changes when employing the titanium socket component "Erlanger Modell" [TiAl 5 Fe 2.5], which can be used with a supporting ring in order to transfer the stress on the hip joint to the iliac bone and to the pubic bone in case the acetabulum should not be able to provide the stability needed by the socket. In a procedure described by Herzog, strain gauges are attached to the pelvis of freshly slaughtered cattle at the following sites, transmitting the relative bone expansion and torsion to a multipoint measuring instrument (Linseis L2100) and on-line to a computer: (1) superior ramus of the pubic bone; (2) front edge of the socket at the iliopubic eminence; (3) iliac bone on the outside of the pelvis; (4) socket roof, pars ossis ilei in the small pelvis; (5) socket roof, pars ossis ischii in the small pelvis. The quality of the implantation was monitored by the non-delayed force transmission from the femur through the hip arthroplasty onto the pelvis. With stress varying from 0 to 500 N in steps of 125 N we carried out four complete readings in order to ensure the reproducibility of the measurements.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetabulum↗
PubMed1991

[Electrochemical evaluation of (Ti, Nb) ON-coated dental alloys for quality assurance].

The chemically stable (Ti, Nb) ON hard coating is suitable for passivating the 18 dental alloys investigated. The exchange current densities are less than jg = 1 microA/cm2. The corrosion current densities are included in this, and are therefore generally lower. The electrochemical investigations provide no hints as to local corrosion for (Ti, Nb) ON-coated dental alloys, which could be a hazard for patients or for dental work, owing to galvanic corrosion or pitting on long-term use. Irrespective of the coated dental alloy, the coatings have pores, through which the electrolyte is in contact with the substrate material. The resulting local elements have high source resistances, so that with a relative pore-area not exceeding 2% only low galvanic current densities occur.

Corrosion↗
PubMed1991

[Corrosion behavior of dental alloys coated with titanium niobium oxinitride].

Dental alloys coated with (Ti,Nb)ON using the ion are PVD technique exhibit galvanic corrosion current densities of considerably less than Jg = 1 microA/cm2. These measurements were taken on plane surfaces. The results show no signs of local corrosion, which might impair the long-term intraoral stability of dental constructions or the health of the patients. Irrespective of the dental alloys used, the coatings exhibit pores extending down to the alloy. The alloy thus wetted on the one hand, and the coated areas on the other, act as galvanic elements with high source resistances and very low short circuit currents. It may therefore be concluded that the coating will effectively reduce allergic reactions to the components of the dental alloys.

Corrosion↗
PubMed1990

Semiconductive properties of passivated titanium and titanium based hard coatings on metals for implants--an experimental approach.

Titanium is used in the field of dental implants on account of the fact that they are integrated into body tissue virtually reaction-free. This integration is made possible by the passivated layers which form within the body electrolyte, and which can be described in the terms of a semiconductive solid body. A prerequisite, however, is the prevention of relative movement between the implant and the tissue so that the passivated layer is not destroyed. The low resistance to shearing, and the oxide stoichiometry--which under in vivo conditions cannot be influenced--on repassivation following mechanical destruction strongly suggest that, during fabrication, implants should be provided with wear-resistant coatings having defined solid state properties which are similar to those of electrochemically passivated titanium surfaces. In the clinical test are already employed, a (Ti,Nb)ON- and a (Ti,Zr)O-coating on titanium and TiAl5Fe2.5. One of the most important parameters for the solid body-physical description of semiconductive hard coatings is the energy gap between conduction and valence band of the electronic structure, which are determinative for the physical-chemical behaviour of the implant surface within the body. The contribution describes the experimental procedure and the results of determinations of the energy gap at singularities in the Brillouin zone for titanium, the titanium alloys in clinical use, and some hard coatings in clinical test. The experimental method of choice for surfaces in contact with aqueous electrolytes is the electroreflectance spectroscopy.

Alloys↗
PubMed1990

[Ridge stabilization with adhesive inlays in MOD cavities].

The flexural rigidity of the buccal cusps of upper premolars was determined under a vertical load of 100 N by use of displacement transducers. The stiffness of the cusps was higher when the cavities were restored with cast gold onlays or with composite or ceramic inlays luted with composite resin. In most cases a decrease in cusp stiffness was observed after thermocycling of the teeth restored with composite or ceramic inlays. With amalgam restorations or cast gold inlays, the flexural rigidity of the cusps was not higher than that of the unrestored cavities.

Bicuspid↗
PubMed1989

[Quantification of friction-induced corrosion of non-precious metal dental alloys].

In six commercially cast non-precious metal alloy samples friction-induced corrosion products were quantified by means of an electrochemical method. For a prosthodontic tooth restauration a model calculation arrives at uncritical ion concentrations, if measurement criteria are the daily nutritional element uptake or element concentrations considered toxic for the tissue. In case of multiple restaurations for some alloys nutritional element levels may be reached or exceeded.

Corrosion↗
PubMed1986

Electrochemistry of after-pacing potentials on electrodes.

Predictable electrochemical behavior of electrodes in physiologic pacemakers is desirable. The after-pacing potentials play a major role in determining precise sensing and pacing performance between both chambers. Ideally, pacemaker input impedance should be high (in relation to the electrode/blood interface), whereas the potential remaining on the electrode should be as low as possible. Both of these conditions are influenced by the electrode material, structure, and design. Results of in vivo and in vitro testing show that the after-pacing potential interference is directly related to the potential decay, and these values are in general considerably shorter than the blanking periods.

Electrochemistry↗
PubMed1977

The long-term stability of metallic materials for use in joint endoprostheses.

In orthopedic implants, metals are permanently incorporated into bones and tissue. Usually the metals are not in the electrochemical equilibrium state immediately after implantation. The metal oxide forms itself only after hours up to weeks. In the meantime the metal releases ions into the tissue, much more than in the equilibrium state. On the other hand a passive layer can interchange mechanically with bones and implanted components. The resulting destruction of the surface leads equally to an increasing release of ions. As a consequence of these facts, perfect metals for application in implants must have a short repassivation period and mechanically indestructible surface oxides. To what extent the applied metals perform these conditions is tested for the stainless steel type 316 L, the multiphase alloy MP-35 N and TiAIV. A comparison of the rates of corrosion resulting from damage to, or destruction of, the passivating oxide layers, with the rates that can occur in connection with local forms of corrosion, shows that in joint implants, it is merely the repassivation properties of the metals employed that determine the concentration of ions in the tissue.

Alloys↗
PubMed1977

A multichannel telemetry system for long-term in vivo evaluation of implantable materials.

Long-term in vivo measurements of the corrosion potentials of various implantable metal materials are performed using an implantable multichannel telemetry system. The data acquisition system has been designed to achieve maximum ease of operation for routine tests in animal applications. A novel signal encoding technique offers advantageous properties in connection with a commercial audio cassette tape recorder for signal storage. The flexibility of the design extends the scope of application to include not only biomaterial testing but all low frequency data transmissions in biological research.

Animals↗
PubMedDate not supplied

[Model for immunologic testing of biomaterials].

Corrosion products and electric fields are capable of changing proteins to antigens, thus permitting the immunological system to identify the biomaterial as foreign. The reaction between corrosion products and a macro-molecule also leads to an antigen (carrier antigen), such as conformational changes of a macro-molecule, e.g. a protein, caused by the electric field at the implant surface (modified macro-molecule antigen). While the sensitivity to corrosion and the effectiveness of galvanic elements is measurable by electrochemical methods, suitable methods of determining the field strength in the vicinity of biomaterial surfaces are still unavailable. The influence of the double layer of uncoated and coated titanium surfaces on the conformation of proteins and their conversion to antigens are investigated with polyclonal antibodies capable of identifying the unchanged protein despite adsorption to the surface. 14C-marked Bovine Serum Albumin serves as a model protein. Determination of the total number of protein molecules adsorbed is effected via the detection of the emitted electrons. The quotient of the concentration of natural proteins to the concentration of adsorbed molecules gives the biocompatibility index, which is independent of the surface area, and gives an indication of the expected biocompatibility of the material. The results of the biological tests of titanium and two coating materials on titanium were confirmed in an animal experiment. It is possible that in the future immunological tests may replace experiments in animals.

Animals↗