Degradation in the fatigue resistance of dentin by bur and abrasive air-jet preparations.

The objective of this investigation was to distinguish whether the instruments commonly used for cutting dentin cause degradation in strength or fatigue behavior. Beams of coronal dentin were obtained from unrestored 3(rd) molars and subjected to either quasi-static or cyclic flexural loading to failure. The surfaces of selected beams were treated with a conventional straight-sided bur or with an abrasive air jet laden with glass particles. Under monotonic loading, there was no difference in the strength or Weibull parameters obtained for the control or treated beams. However, the fatigue strength of dentin receiving bur and air-jet treatments was significantly lower (p ≤ 0.0001) than that of the control. The bur treatment resulted in the largest overall degree of degradation, with nearly 40% reduction in the endurance limit and even more substantial decrease in the fatigue life. The methods currently used for cavity preparations substantially degrade the durability of dentin.