Objective: The objective of this investigation was to evaluate if the instruments most commonly used for cavity preparations reduce the fatigue strength of dentin.
Method: Beams of human coronal dentin were obtained from unrestored 3rd molars and subjected to either quasi-static or cyclic flexural four-point loading to failure. Control beams were prepared with diamond abrasive slicing wheels. Treated beams were further processed using a conventional, straight-sided bur under ultra-high speed and with copious coolant.
Result: There was no difference in the average strength or Weibull parameters obtained for the control or treated dentin beams resulting from quasi-static loading. However, the fatigue life diagrams distinguished that coronal dentin treated with burs underwent a significant (p≤0.01) reduction in fatigue strength over the entire stress-life regime. Treated dentin beams exhibited a large degree of variation in the fatigue life received when assessed at a specific cyclic stress, which was indicative of the relative contribution of flaws that were introduced during the cutting process. In evaluation of the apparent endurance limit, there was nearly a 50% reduction in the fatigue strength of bur-treated dentin with respect to the control. Microscopic evaluations of the fracture surface did not reveal the origin of failure.
Conclusion: The introduction of cavity preparations with burs significantly reduces the fatigue strength of dentin.
Keywords: Dentin and Fatigue-life, Bur