Penetration of constricted canals with modified K files.

A technique using K files with modified tips has been developed for the penetration of constricted canals. The tip of a #10 K file was sliced diagonally to make it thinner. Because this modified K file has an especially fine tip and an appropriate stiffness, it followed constricted or sharply curved canals well and had a high penetration potential. The author attempted to penetrate to the apical foramen in all 1844 canals of 977 teeth treated from 1987 to 1994. In 263 canals (14.3%) that could not be penetrated with conventional #10 K files, further attempts were made with the modified K files. As a result, the number of the nonpenetrated canals was reduced to 75 (4.1%). There were 7 file breakages and 14 accidental perforations.