fracture strength of mesiobuccal roots following canal preparation via hand and rotary instrumentation: an in vitro study

introduction: the aim of this in vitro study was to compare the effect of hand and rotary instruments on fracture strength of tooth roots. materials & methods: thirty two teeth were randomly divided into two experimental groups of 15 each and one negative control group with two samples. in group 1, step-back technique with conventional stainless steel k-files was used, and in group 2, instrumentation was performed using rotary ni-ti hero642. samples in control group did not received cleaning or shaping after access cavity preparation. after obturating each canal, tip of the spreader was locked within canal. the required force for root fracture was measured using instron testing machine. recorded data was statistically analyzed using t-test. results: the mean and standard deviation force required for vertical root fracture were 50.33±19.1 and 63.1±25.46 n for hand and rotary groups respectively. however, no significant difference was found between experimental groups. conclusion: the results indicate that the manual technique did not lower fracture strength of obturated roots in comparison with the rotary preparation technique.