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.

The purpose of this study was to compare the initial apical file(IAF) first file that fits to the apex in each canal before and after early flaring to analyze if the size of file to fit to the apex would increase after flaring. Eighty anterior teeth with complete apical formation and patent foramens were selected. The samples were randomly divided into 4 groups(GG, OS, GT, PT Group) of 20 teeth each. A file was fit to the apex in each canal and that size recorded. Radicular flaring were completed using different types of instruments. After flaring a file was again fit to the apex in the same manner as before and its size recorded.

The results of this study were as follows:

1. The mean diameter of IAF before flaring(file diameters in mm×10^-2) was 19.81±8.32 before and 25.94±9.21 after(p<0.05).

2. The increase in diameter of IAF was approximately one file size for all groups.

3. Ranking of increasing diameter of IAF were GG>GT>OS>PT group. There was a statistically significant difference between before and after flaring(p<0.05).

4. Ranking of the time for flaring were GG>GT>OS>PT group. There was a statistically significant difference between GG group and other groups(p<0.05).

5. In the case without change of IAF diameter, they showed decrease in force after flaring when IAF was pulled out from root canal(p<0.05).

This study suggested that early radicular flaring increases the file size that is snug at the apex, and awareness of that difference gives the clinician a better sense of canal size. Early flaring of the canal provides better apical size information and with this awareness, a better decision can be made concerning the appropriate final diameter needed for complete apical shaping.