ABSTRACT
INTRODUCTION: The purpose of this in vitro study was to investigate the apical and coronal loads generated during shaping canals with 2 successive reciprocating files in comparison to a single reciprocating file from the same system. METHODS: A total of 40 narrow and straight canals were distributed into two groups: R-Motion with single file (RMS) and R-Motion with multiple files (RMM). In both groups, the R-Motion system was used in a reciprocating motion. After establishing glide path, the RMS canals were shaped down to working length with a single file (25/.06) in two insertions while the RMM canals were shaped with two files (20/.04 and 25/.06) to the working length. The shaping time and effects of tested groups on the apical and coronal peak loads were statistically analyzed using the t-test and Mann-Whitney U test, respectively, at a 95% confidence level. RESULTS: All canals were completely shaped in three insertions and no file deformation or fracture was observed. The RMS and RMM were able to shape canals in 117.3 ± 15.1 and 123.7 ± 7.3 seconds, respectively (P < .05). Within each group, the shaping load appeared to increase with the successive insertions of the file. In both groups, the ranges of apical and coronal peak loads were 0.41-1.87 N and 0.38-1.03 N, respectively. The RMM and RMS had comparable apical and coronal peak loads (P > .05) except in the last insertion where RMM showed clearly lower apical peak load than RMS (P < .01). CONCLUSIONS: Under the current laboratory conditions using the R-Motion system, preshaping the canal with a smaller reciprocating file was shown to favorably reduce the apical peak loads induced during canal shaping of extracted teeth.
