 The objective of this study was to determine the effect of rotary file length on its resistance to cyclic fatigue. The study used artificial root canal systems made from stainless steel and tested for different rotary files with varying lengths. The results showed that longer rotary files had higher resistance to cyclic fatigue than shorter ones. This suggests that longer rotary files are more durable and can be used for longer periods without breaking or fracturing. This article was authored by Vicente Fosmodos' Vicente Foslaser, Celia Ruiz Sanchez, and others.