Abstract:

Objective

The aim of this study was to compare the effectiveness of three instrumentation techniques in preparation of the fine curved canals of posterior teeth.

Methods

Forty-five mesiobuccal root canals in fleshly extracted human molar teeth were instrumented by using the step-back technique， the step-down technique or the passive step-back technique. Time of preparation of each canal was taken down. After cracking the roots longitudinally， the canal walls were observed under a scanning electron microscope， and the coronal， middle and apical thirds of each canal were photographed at the 100 and 1000 times magnification. Each canal was qualitatively evaluated and the groups were compared for the removal of debris and smear layer，both overall and at each level （apical， middle， and coronal）.

Results

There were no statistically significant differences between the techniques either overall or within any of the regions （P ＞0.05）. When comoparing regions（regardless of technique）， the apical portion of the canal was less clean than the middle or coronal portions （P ＜0.05）. Preparation time in these three techniques showed no statistical significance （P ＞0.05）.

Conclusions

Efficacy differed little among the techniques.None of the three techniques removed smear layer completely and all left debris，especially within the apical third of the canals. The passive step-back technique was superior to the step-back and the step-down techniques when it was related to the cleaning efficiency， but it took a longer time for preparation and was so exhausting. The step-back technique can be used more easily within a short time.

Key words: Root canal preparation, Step-back technique, Step-down technique, Passive step-back technique, Fine curved canal