Fatigue Behavior of Direct Post-and-core-restored Premolars

Abstract

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 10⁴, 105, and 106 cycles, simulating up to 1-3 years of clinical functioning. Mean fatigue strength was expressed in percentage of initial strength: For 10 ⁴, 105, and 106 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 106 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.