Evaluation Of The Results Of Ultrasonic Root Canal Instrumentation

The transverse tip amplitude of different file sizes driven by the Cavi-Endo unit at different output power settings was measured under a microscope at magnification x 150. It was found that the mean displacement amplitude of the ultrasonic file in water ranged from 8 to 60 μm, and a maximum displacement amplitude was produced by a minimal size file (#15) at output power setting 6 .An ultrasonic file of size 15 was submerged in a bacterial suspension in a simulated root canal, and was oscillated for 5 minutes at power setting marked 6. Comparing with the blank control group, the ultrasonic group's killing rates of Staphylococcus aureus, Streptococcus pyogenes, Escherichia coli and Bacillus subtilis spore were 35.70%, 21.30%, 13.69% and 3.80% respectively.In the following root canal instrumentation experiments, the Cavi-Endo unit was used in the ultrasonic group, while the conventional hand instruments were used in the control group.The cross sections of root canal at different levels were quantitatively assessed by means of an image analysis device. Thirty resin block canal models did not show any significant difference between the groups either in enlarging or in shaping root canals. The experimental results of 23 pairs of extracted human teeth showed that the ultrasonic group was significantly superior to the control group in both cleaning and enlarging at the mid-level of root canal, whereas at the apical level, no difference was found between two groups in cleaning, although the control group was superior to the ultrasonic group in enlarging root canal.The root canal walls of 8 pairs of extracted human teeth were observed under a scanning electron microscope. The results of blind evaluation showed that the ultrasonic group was much better than the control group in removing both debris and smear layer from the root canal.