The influence of the method of canal preparation on the quality of apical and coronal obturation

By Allison DA, Weber CR, Walton RE

Date: 01/1979
Journal: JOE


Purpose: To compare the effect of two different methods of canal enlargement (standardized taper vs step-back) on the apical seal.  N= 46 extracted teeth


  • teeth were randomly classified in positive and negative control groups and in two experimental groups.
  • All preparations were performed with K-type files. 
  • Standardized taper. :Files were placed to the preparation length until an instrument was found to fit snugly. It was rotated until binding and then withdrawn while lateral force was placed against the canal-walls. Successively larger files were used. Canal preparation was completed usually in the range of size no. 35 to 50. 
  • Step back taper. :The apical region was enlarged by reaming action to a size that, just bound at the apical extent, was never larger than a size no. 25 file. Successively larger files with decreasing lengths of 0.5 mm were used in the peripheral filing action. The taper was tested with a spreader.

Most highlighted Results:

1.In negative control groups that did not have the canals obturated with gutta-percha but were sealed apically and coronally. No leakage occurred. 

2.In Positive control groups, They were sealed only coronally. These had microleakage along the entire length of the canal 

3.Standardized preparations generally showed extensive leakage apically whereas step-back preparations showed little, if any, leakage. 

4.88% of the specimens demonstrated that microleakage occurred to within 1mm  of the spreader tip in both groups .

5.the quality of the apical seal was related directly to the method of canal preparation. The method which permitted deeper penetration of the spreader resulted in a seal closer to the prepared length.

Clinical Significance:

In the clinical situation, a method of canal preparation which results in deep spreader penetration, and therefore better apical access, should ultimately result in better obturation.