PubMed Health⌕ Search

Biomedical subjects

U Soltész

Publications and source records attributed to U Soltész.

At least 19 recordsLinked to original sources
PubMed1998

Friction in hip-joint prostheses and its influence on the fixation of the artificial head.

The head of an implanted hip joint endoprosthesis is exposed to torques, which are transferred during gait due to the friction between the head and the cup prosthesis. In prostheses with ceramic ball heads, which are widely used now, and in which the head is fixed onto the stem by conical clamping, these torques could possibly affect the connection. In this study, torques transferred from the cup to the head are compared to the torques which are required to loosen the head from the metallic spigot. The results show that for the investigated head and taper types and sizes, under normal conditions the connection is safe with respect to undesired rotation. However, it is shown that for polluted sliding surfaces the fixation strength could possibly be exceeded.

Journal Article↗
PubMed1998

Fatigue of bone cement with simulated stem interface porosity.

Cracks in bone cement have been observed in carefully examined post-mortem preparations of cemented stems. These cracks were probably caused by fatigue, and frequently appeared to initiate at pores. Ubiquitous porosity, occurring preferentially at, or near, the stem, is most likely caused by polymerization shrinkage. Preparation of air-free cement has only a marginal influence on the interface porosity, but pre-heating the stem in order to reverse the direction of polymerization can reduce or eliminate it. To estimate the impact of interface porosity on the fatigue strength of bone cement, test plates for this study were cast in a steel mold without release foils, and with one side of the mold warmer. Sample plates so prepared from chilled, partial vacuum-mixed PALACOS, have one face essentially pore-free and the other porous, the extent and morphology of the porosity being very similar to that observed on the stem-cement interface. Four-point bending fatigue strength, determined after 60 d conditioning in Ringer's solution at 37 degrees C, was only 20 MPa (at 10(6) cycles, with the porous side under tension) compared to 30 MPa for conventionally prepared, pore-free material. This corresponds to a 10-100 fold reduction in cycles to failure in the range of stresses predicted to occur in vivo.

Journal Article↗
PubMed1992

Fatigue behavior of direct post-and-core-restored premolars.

Evaluation of long-term mechanical behavior of new types of restorations in clinical trials is time-consuming. A partial alternative can be found in experimental fatigue-testing, which simulates accelerated mechanical deterioration. The aim of this study was to determine the feasibility of using fatigue-testing of a complex dental restoration and to evaluate the mechanical fatigue behavior of premolar teeth restored with a titanium alloy post and an amalgam or composite core. Eighty-seven human upper premolar teeth were decoronated, embedded, and restored with a prefabricated post of 1 mm diameter. The teeth were randomly assigned to one of two groups corresponding with a core build-up of amalgam or chemically-cured core composite, respectively. Five to 21 days after restoration, the specimens were subjected to cyclic loading (frequency, 5 Hz), at an angle of 45 degrees to the long axis of the tooth. The boundary technique was used for determination of the mean fatigue strengths of the restorations at 10(4), 10(5), and 10(6) cycles, simulating up to 1-3 years of clinical functioning. Mean fatigue strength was expressed in percentage of initial strength: For 10(4), 10(5), and 10(6) cycles, the results were 66%, 58%, and 52%, respectively, for the amalgam and 62%, 62%, and 53% for the composite group. It is concluded that fatigue-testing of more complex systems is possible, if a suitable testing method is selected. The restorations showed a comparable strength reduction after 10(6) cycles of about 50% of their initial strength. The composite core build-up showed a behavior less predictable than that of the amalgam, which might be attributed to handling parameters.

Alloys↗
PubMed1982

Failure of ceramic hip endoprostheses by slow crack growth--lifetime prediction.

The slow crack propagation velocity v, which depends on the stress intensity factor K, has been measured for three different high-density aluminas. Assuming a load history for the prosthesis which approximates conditions during walking, the lifetimes of the components of a total hip endoprosthesis were calculated as a function of the initial flaw size. Different geometries for the preexisting cracks, as well as varying physiological parameters, were considered. It is shown that the lifetime is very dependent on the quality of the material and that it is reduced by increased body weight, walking speed, and varus positioning. Comparison of failure behavior in different parts of the femoral component showed that flaws in the stem must be one order of magnitude smaller than those in the neck to achieve comparable lifetimes.

Body Weight↗
PubMed1979

[Comparative study on the abrasion behavior of composite filling materials].

Twenty-two commercially available composites, a new resin without inorganic filler and two amalgams have been investigated to compare their abrasive behaviour. In laboratory tests, an abrasion model of tooth against filling has been simulated. The results indicate a dependence of the abrasive behaviour on the type of filler in the different composites. Composites with quartz as filler have the greatest resistance to abrasion, whereas those with lithium-aluminium-silicate show the strongest abrasion. Mean abrasion values are obtained for the composites with barium-glass or a mixture of barium-glass and quartz as filler. The resin and the two amalgams have abrasion values comparable to the abrasive resistant composites.

Composite Resins↗