Objective: This study aimed to analyze apical deviation occurrence after preparation with three systems: manual, rotary and reciprocating. Material and Methods: Thirty simulated curved root canals 16 mm in length and a 35 degree angle were used. Canals were divided into three experimental groups, according to the system used: manual, rotary and reciprocating. The canals in the manual group were prepared by the crowndown technique, stainless steel #30 memory files were used. In the rotary and reciprocating groups, canals were instrumented by the rotary and reciprocating systems, respectively (Wizard NavigatorTM and UniconeTM) both engine-driven. For apical deviation analysis, before and after preparation, canals were filled with Indian ink and photographed in a standard manner on a platform.Subsequently, the images were manipulated by Adobe Photoshop TM software, with superimposition of pre-and postoperative images. The occurrence of deviation was measured 1 mm and 3 mm short of the working length (WL) with the aid of a ruler tool. Data were subject to analysis of variance (ANOVA), followed by post hoc Turkey's test, with significance set at 5%. Results: The occurrence of apical deviations in the manual group was significantly higher when compared to the other groups. In all three groups, mean deviation 1 mm short of the WL was significantly greater than that 3 mm short of the WL. Conclusion: The manual technique provided a larger amount of apical deviation compared to the rotary and reciprocating systems. A high number of deviations was observed 1 mm short of the WL. Keywords: Endodontics. Root canal preparation. Computer-assisted image processing. IntroductionThe aim of mechanical instrumentation is to form a continuously tapered shape canal with the smallest apical foramen diameter and the largest cervical third diameter possible, 1 while respecting root canal anatomy, without deviations from the original trajectory, mainly in curved and thin canals.