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.

The fatigue behaviour of bone cement was investigated with respect to the influence of loading conditions. The tests were performed under simulated physiological conditions using a testing arrangement in accordance with ISO. A pure load-controlled and pure displacementcontrolled cycling procedure were compared. It is demonstrated that load control is much more critical and leads to decisively shorter life-times, or remarkably lower long-term strengths. In consequence, in order to determine reliable material properties for life-time predictions and safety assessments, it is necessary to measure the fatigue behaviour under load control as this corresponds to the normal physiological situation

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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.

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