Aim: The aim of this study is to evaluate the shaping ability of two reciprocating file systems (Wave One and Safe Siders) in comparison with the hand instrument (K-file) during the preparation of S-shaped simulated root canals. Materials and Methods: Sixty (n=60)S-shaped endodontic resin training blocks were divided into three groups (n=20) according to the type of file used to prepare the canals (Wave One , SafeSiders and K-files). Pre and post instrumentation images were recorded and superimposed after preparation, images were analyzed by (AutoCAD 2008). Comparison among the different files was evaluated for the working length change, canal aberration and width measurement assessment (total, inner and outer) at different points : half-way to orifice, beginning of the first curve, apex of the first curve, apex of second curve and apical end. Data were analyzed using one way ANOVA, Tukey HSD, paired T-test, and Fisher's Exact test. Results: less working length change was found in Wave One system with no significant difference between Wave One and Safe Siders instrumentation systems, all the three instrumentation systems showed high incidences of canals aberration, and in width measurement there was a significant difference between the mean values of total width of material removal among the three system at (half-way to orifice, beginning of 1st curve and apical end), there was a significant difference between the mean values of inner width of material removal among the three system at (half-way to orifice, beginning of 1st curve and apex of 1st curve), and there was a significant difference between the mean values of outer width of material removal among the three system at all measuring points (half-way to orifice, beginning of 1st curve, apex of 1st curve, apex of 2nd curve and apical end). Conclusion: Wave One instrument systems, showed less canals length changes .None of the three instrumentation systems maintain the anatomy of S-shaped canals.
