Comparison of fracture rate, deformation rate, and efficiency between rotary endodontic instruments driven at 150 rpm and 350 rpm.

Two groups of 30 mature molars each (S and F) were instrumented with Profile .04 taper Series 29 rotary instruments. Group S molars were instrumented at 150 rpm and group F at 350 rpm. The number of fractures, deformed files, and instrumentation time were recorded for each tooth. No instrument fractures occurred in either group. In group S the mean deformation rate and instrumentation time were 1.1 deformed files and 8.0 min per molar. In group F they were 0.57 deformed files and 4.6 min per molar. Both differences were significant (p < 0.05). The results indicate that Profile .04 taper Series 29 rotary instruments should be used at 350 rpm to nearly double efficiency and halve the deformation rate, compared with 150 rpm. Because no instrument fractures occurred while instrumenting 60 mature molars, both speeds should be considered safe.