Type II root canal was defined that two canals leave the chamber and merge to form a single canal at short of the apex. The aim of this study was to analyse the master apical file (MAF) size according to various instrumentation techniques in the type II root canal when each canal was enlarged to working length.

Eighty mesial roots of molar with ISO #15 initial apical file (IAF) size in type II root canals were randomly divided into four experimental groups with 20 teeth each. According to enlarging instruments, four groups are: K-FLEXOFILE® (KF), engine-driven Ni-Ti PROTAPER® (PT), HERO Shaper® (HS), K³ ™ (K3). All canals were enlarged to each working length with ISO #30 size: #30 in KF, F3 in PT, .04/30 in HS, and .06/30 in K3. The master apical file (MAF) size was confirmed by tactile sensation and universal testing machine (EZ test, Shimadzu Co., Kyoto, Japan). The mean MAF size was statistically compared using one-way ANOVA and Tukey HSD test at the 0.05 probability level.

These results show that the MAF size was appeared one or two sizes larger than the final enlarging instrument when all canal in type II configuration were enlarged to each working length. Therefore, the clinician have to confirm the apical stop once more after instrumentation of type II root canal.

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.