Influence of external environmental factors on the fatigue resistance of engine-driven endodontic instruments: a scoping review and meta-synthesis

Rotary and reciprocating nickel-titanium engine-driven instruments are essential tools in endodontics, valued for their flexibility and efficiency. However, their susceptibility to fracture during root canal procedures remains a clinical challenge. Most research has concentrated on intra-canal factors affecting instrument fatigue, such as irrigants and canal anatomy, while the impact of external environmental conditions—like ambient temperature, humidity, and storage—has been less explored. This scoping review and meta-synthesis aim to systematically map and synthesize the current evidence on how these external factors influence the fatigue resistance of engine-driven endodontic instruments.