Ex vivo evaluation of the influence of cervical preflaring on choice of apical reciprocating file.

The aim of this study was to evaluate the influence of cervical preflaring on the choice of reciprocating file size (Reciproc system) and the difficulty in reaching the working length for instrumentation of molar root canals. A total of 352 human molars were divided into 2 groups of 176 molars each. In the no preflaring (NPF) group, no cervical preflaring was performed. A reciprocating file (R25, R40, or R50) was selected, and instrumentation was performed in accordance with the manufacturer's recommendations. In the preflaring (PF) group, a file was selected, and cervical preflaring was performed with the use of No. 30/.10 or No. 25/.08 orifice shaper instruments. The clinician then selected a new reciprocating file or used the originally selected file to perform the instrumentation as done in the NPF group. Any changes in choice of file after preflaring were documented for the PF group, and the number of insertions required to reach the working length was recorded for both groups. After preflaring, the selected file was changed from R25 to R40 in 20.08% of canals, from R25 to R50 in 0.40% of canals, and from R40 to R50 in 42.14% of canals. After preflaring, 2.88% of the canals with an initial selection of an R50 file required an instrument with a larger diameter for effective preparation. There was a statistically significant difference between the groups for all file size changes (P < 0.001; χ² test). The mean numbers of instrument insertions needed for the NPF and PF groups, respectively, were 4.09 and 2.42 (R25); 3.49 and 2.31 (R40); and 2.70 and 1.81 (R50). There was a statistically significant difference between the groups for all file sizes (P < 0.001; Kruskal-Wallis test). Under the conditions of this study, preflaring enabled a more suitable selection of reciprocating instrument, which, in turn, allowed for fewer insertions of the file up to the working length.