FAILURE BEHAVIOR OF FATIGUE-TESTED POST AND CORES

Evaluation of the long-term behaviour of restorations in clinical tria ls can be time-consuming. A partial alternative to the clinical trial can be found in mechanical fatigue testing. The aim of this study was to evaluate the failure behaviour of post and core restored teeth when subjected to cyclic mechanical loading and to compare it with quasist atic failure. Eighty seven premolar teeth were restored with a titaniu m alloy post and an amalgam or composite core. Five to 21 days after r estoration, the specimens were subjected to cyclic loading (frequency 5 Hz), at an angle of 45-degrees to the long axis of the tooth. The lo ad levels were 50, 60, 6 5 and 70% of mean quasistatic failure loads. The specimens were divided into three groups according to their surviv al time: short (S) (< 10(4) cycles), intermediate (I) (10(4) less-than -or-equal-to life < 10(5) cycles) and long (L) (greater-than-or-equal- to 10(5) cycles). For both core materials failure behaviour changed af ter approximately 10(5) cycles, and the change was most marked for the composite group. Catastrophic fatigue failure consisted of core fract ure in the amalgam group (three times) and of post fracture in the com posite L group (four times). Three post fractures occurred at a site t heoretically predisposed to fatigue failure. It was concluded that fat igue failure characteristics of post and core restorations may be very different from those of quasistatic failure. Therefore, in addition t o quasistatic tests, fatigue tests are necessary, covering at least 10 (5) load cycles.