The objective of this in vitro study was to evaluate the efficacy of a Ca(OH)₂ removal before and after early coronal flaring using different types of instruments. 100 plastic blocks with 30° artificial curved canals were used in this study and randomly divided into a control group and 4 experimental groups(GG, OS, GT, PT Group) 20 teeth each. The canals were instrumented, and Ca(OH)₂ was temporary filled into the each canal. Irrigation was performed with Max-i-Probe 25-, 30-gauge probes before and after recapitulation.

The results of this study were as follows:

1. There were no significant difference among the groups in size of irrigating needle(p<0.05).

2. There was a significant difference between before and after recapitulation regardless size of irrigating needle(p<0.05).

3. Before recapitulation, there was a significant difference between 25- and 30-gauge needle in all groups(p<0.05).

4. After recapitulation, there was a significant difference between 25- and 30-gauge needle in the control group(p<0.05). But there were no significant difference among the experimental groups.

It is concluded that the effectiveness of canal irrigation was decided to the depth of irrigating needle into the canal. The effect of canal irrigation tend to facilitate by the early coronal flaring. The recapitulation was the most effective during canal irrigation regardless the size of irrigating needle. Therefore, the recapitulation is a mandatory way to facilitate the effectiveness of canal irrigation during canal enlargement.