ABSTRACT
This study was to investigate whether a natural frequency had an influence regarding the shear stresses generated during the removal of the smear layer from the apex of the root canal by means of EDDY® sonic activation. Forty extracted human teeth with straight single roots were randomized into four groups (n = 10). The specimens were shaped up to a size 30/.06 file (Control, EDDY 1, EDDY 2 and EDDY 3 groups) with manual instruments. In the EDDY 1, EDDY 2 and EDDY 3 groups, the irrigant was activated with the EDDY sonic tip (5600, 5800 and 6200 Hz respectively). The irrigation solution in the Control group was activated via the use of ultrasonic technology. The fluid flows mechanisms during irrigant activation by an EDDY® tip in a glass model was visualized in vitro using high-speed imaging and subsequently analyzed by LiteFlowNet. There were no differences between the smear layer scores for the EDDY 3 and Control groups (p=0.4). Significant differences existed between the EDDY 3 and those for the EDDY 1 (p<0.001), and EDDY 2 groups (p<0.001). By utilizing high-speed imaging, it was demonstrated that the tip oscillation in the EDDY 3 group resulted in high velocity gradients near the wall. The amplitude of tip vibration in the EDDY 3 group when reaching its peak, produces high shear stresses on the wall together with intense bubble generation in the irrigant. Compared to the EDDY 1 and EDDY 2 groups, the EDDY 3 group is superior at eliminating the smear layer in the apical area of a straight root canal.
