A single F2 file can be safely used to the working length of curved canals at least six times under reciprocating motion, according to a study in the Journal of Endodontics (December 2010, Vol. 36:12, pp. 1991-1994).
Researchers from Seoul National University wanted to examine the life span of one nickel-titanium (NiTi) rotary file when used in reciprocating motion and to compare the time required for its preparation of a curved root canal using both reciprocating and continuous motion.
They prepared 120 curved canals in 60 extracted molars to gauge an average number of uses. They employed a reciprocating motion until the ProTaper F2 (Dentsply) single file reached the working length and used a total of 11 files. The highest number of canals a single F2 file prepared was 21; the average life span was 10.60 ± 4.3.
Of an additional 60 canals, half were included in a continuous rotation motion (CM) group and prepared using the sequence of ProTaper files. The rest were used in the reciprocating motion (RM) group, and canals were prepared only using the ProTaper F2. The total root canal preparation time was measured until the F2 file finally reached the working length in both groups.
The study yielded a statistically significant difference between the two groups: Prep time was 46.42 ± 18.12 seconds for the CM group and 21.15 ± 6.70 seconds in the RM group.
Within the limitation of this study, "reciprocating preparation with only one F2 file was much faster than root canal instrumentation with continuous rotation," the researchers concluded.
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