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Introduction: Flare-ups in endodontics are multifactorial and may cause severe discomfort to the patient. Apical extrusion while preparing root canal space in any form such as debris, bacteria or irrigants has been found to be associated with many flare-up events and may even lead to treatment failure. Aim: To quantitatively evaluate apically extruded debris with five rotary instrumentation systems in mesiobuccal root of maxillary molars. Materials and Methods: A total of 120 human maxillary first molars extracted between January and March of 2017 in oral and maxillofacial surgery department at Drs. Sudha and Nageswara Rao Siddhartha Institute of Dental Sciences, Gannavaram, Andhra Pradesh, India, were included in the current study. Only the Molars with a three rooted pattern were selected and mesiobuccal root was used to evaluate apical extrusion. An experimental apparatus for evaluation of extruded debris as previously described by Myers and Montgomery was fabricated. All samples were divided into six groups (n=20 each) and instrumentation was done with five rotary file systems (K3XF, ProTaper NEXT, HyFlex CM, Revo-S, and FLEXICON) and HAND K FILES which served as control. The weight of the micro tubes in the apparatus before and after the instrumentation was calculated using an electronic weighing balance with a minimum sensitivity of 10-4 and weights were compared to quantify the apical extrusion. Statistical analysis was analysed with the ANOVA and multiple comparison (Posthoc- Dunnett and Tukey) tests. Results: It was found that all the instrumentation systems showed a considerable amount of apical debris extrusion. HAND K FILES were associated with most debris extrusion compared to all rotary files (p<0.01). FLEXICON file system showed lowest debris extrusion among all experimental groups. However, there was no statistically significant difference between K3XF and FLEXICON file systems (p=0.312). Conclusion: The rotary systems extruded less debris compared to HAND K FILES. However, it was observed that there was no statistically significant difference between apical extrusion of K3XF and HyFlex CM, K3XF and FLEXICON X7, HYFLEX CM and Revo-S file systems. Among all the rotary groups, FLEXICON X7 and ProTaper NEXT files showed lowest and highest apical extrusion respectively. Design of rotary endodontic instruments may have a greater impact on their innate apical extrusion potentials. [ABSTRACT FROM AUTHOR]