Mechanical strength of fracture plates made of titanium for functionally stable mandibular reconstruction

Plates for functionally stable mandibular reconstruction are successfully introduced with biocompatible titanium. While screws have been the subject of numerous investigations, only few results are available for the mechanical stability of plates. This contribution gives an overview about experimental possibilities to test plates in tensional, bending, and torsional strength as well as fatigue, and reports results about plates made of titanium and oxygen-alloyed titanium. The alloyed material is harder, stiffer and shows higher tensile strengths. In contrast to softer titanium, contouring procedures during implantation can lead to structural defects and an associated higher fracture risk.

Types I and III collagen in the tissue capsules of titanium and stainless-steel implants

Collagen plays an important role in wound healing and as such is present in connective tissue capsules around implanted materials. The proportion of type I collagen to type III collagen is lower during wound healing than that found in normal dermis, but the amount of type I collagen gradually increases and type III decreases as healing continues. The intent of this research was to investigate a possible correlation between implant metals and type I and type III collagen formation in the ensuing soft-tissue capsules. Smooth implants of grade 4 commercially pure titanium and 316L stainless steel were placed via injection needle into the subcutaneous tissue of 12 rats for 6 weeks. The soft-tissue capsule that formed around each implant was evaluated histologically and by immunofluorescence. Although the two metal implant types differ in many respects, they were chosen for their differences in surface conductivity. Titanium oxide is semiconducting, whereas the oxide of stainless steel is conducting. Impedance spectroscopy was used for conductivity analysis of the surface. No qualitative differences were found in amount of type I or type III collagen in the capsules of the two metals. However, the capsules around titanium stained for type I collagen were thicker than capsules around stainless steel. In addition, type I collagen showed evidence of a greater association with densely packed, highly orientated collagen fibers.

[A new osteoblast cell culture system for standardized testing of biomaterials]

For in vitro testing of new biomaterials cultured fibroblasts are employed. In the case of the agar diffusion test survival of cells is involved in the presence of the material to be tested. Further statements on the biological effects of a biomaterial require the use of cell cultures adapted to the tissue concerned and the underlying problem being investigated. In the present study, an osteoblast cell culture system with which implant surfaces in contact with bone can be tested as required by the relevant standards is described. Test bodies made of titanium, polystyrene or copper were used in the conventional agar diffusion test, and were also overgrown with fibroblasts or a cell line of foetal human osteoblasts. For the agar diffusion test, the test criterion was the extent of the inhibition area on staining with neutral red, while for the overgrowth, the mean cell diameter and the number of cells was employed. The phenotype of the osteoblast cell line was determined immunohistochemically by means of alkaline phosphatase or immunohistologically by means of collagen I and osteocalcin. Calcification was demonstrated using the v. Kossa stain. In the case of the osteoblasts, a differentiation of a collagen I and alkaline phosphatase-positive phenotype over an osteocalcin-positive phenotype to an increase in calcium deposition was shown. As in the case of the agar diffusion test, direct overgrowth also revealed no cytotoxic effect for titanium and polystyrene. In contrast, a cytotoxic effect consisting in a decrease in the number of cells and also a left shift in the size distribution was observed for copper. The standard deviations of the individual tests were less for overgrowth than for the agar diffusion test. The culture system for osteoblast cells thus meets the criteria of the EN/DIN 30993-5 in terms of the quality and accuracy of the results obtained. In addition to excluding direct cytotoxicity, this test system offers a new possibility of examining the influence of the material on cell growth. Consequently, it permits a repeatable examination of proliferation and differentiation of the osteoblasts on each material surface.

[Animal experiment study of titanium with surface coatings of (Ti,Nb)ON and (Ti,Zr)O]

Titanium is considered to be biocompatible as long as the passive layer of TiO2 which is formed within the body, is not destroyed mechanically by the shearing forces acting on implants during function. Mechanically stable hard coatings on the basis of the so-called refractory metals render titanium wear-and-tear-resistant, with the added advantage for its biocompatibility of keeping its the physical and electrochemical properties constant, even in the event of relative movement against hard or soft tissue. Biological testing of coated and uncoated titanium in experimental animals shows that the deposition of new bone on (Ti,Zr)O or (Ti,Nb)ON surfaces takes place in the same way as on the surface of titanium.

[Reducing NMR image artefacts by using optimized materials for diagnostic aids and implants]

Differences in magnetic susceptibility, as occur for example at the boundary between implant materials and the surrounding body tissue, result in artefacts and a signal loss in magnetic resonance imaging. By using materials with a magnetic susceptibility matched to the respective environment, it is possible to minimize both artefacts and signal loss. Such materials can be made by combining two materials of different magnetic susceptibility (e.g. diamagnetic and paramagnetic materials) in such a way that the resulting material has the desired effective magnetic susceptibility.

[Scientific aspects of raw materials in medicine]

Metallic, ceramic, and polymeric materials are applied in all disciplines of surgical and dental medicine. The biocompatibility is determined by the chemical composition, the mechanical and electronic structures of the material's surface, the properties of the interface to the specific body electrolyte as well as by reactions, which occur between the solid and the liquid phase. The development of biomaterials, considering the sensitive biological environment, requires knowledge from all fields of the natural sciences and knowledge of manufacturing methods derived from the key technologies.

[Reduction of NMR image artefacts by using optimal materials as diagnostic aids and implants]

Differences in magnetic susceptibility, as occur for example at the boundary between implant materials and the surrounding body tissue, result in artefacts and a signal loss in magnetic resonance imaging. By using materials with a magnetic susceptibility matched to the respective environment, it is possible to minimize both artefacts and signal loss. Such materials can be made by combining two materials of different magnetic susceptibility (e.g. diamagnetic and paramagnetic materials) in such a way that the resulting material has the desired effective magnetic susceptibility.

[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.

["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)

[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.