SummaryA total of 300 simulated root canals of various angles and positions of curvature in clear resin blocks were prepared by hand using either K‐files, K‐Flex files, Flexo‐files, Flex‐R files, Hedstrom files or Unifiles. Each fife type was used to prepare 50 canals employing a linear filing motion and an anticurvature stepback technique. Part 1 of this two‐part report describes the efficacy of the files in terms of preparation time, instrument failure, loss of canal length and weight loss from the blocks. Two‐way analysis of variance confirmed that there was significant variation for each parameter between instruments, between canal types, and with interaction between instruments and canal types. Overall, preparation with Hedstrom files was significantly quicker than with any other file, whilst preparation with K‐files and K‐Flex files took significantly longer. Fracture and deformation of instruments occurred substantially less often with Flex‐R and Hedstrom files, but significantly more often with Unifiles. Loss of working distance occurred with all file types, but was significantly greater in canals prepared with K‐files. Unifiles and Hedstrom files were responsible for significantly more weight toss than the other files, whilst K‐files produced significantly less weight loss. Canals with rough undulating walls were created most often by Hedstrom files and Unifiles. Overall, under the conditions of this study, Flexofiles, Flex‐R files and Hedstrom files appeared to be substantially more effective than K‐files,
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