Cyclic Fatigue of Rotary Versus Reciprocating Endodontic Files: An In Vitro Study of Engine-Driven Endodontic Files

Area of Science:

• Endodontics
• Dental Materials Science
• Biomaterials Engineering

Background:

• Instrument fracture is a significant complication in endodontic therapy.
• Nickel-titanium (NiTi) rotary and reciprocating file systems are commonly used.
• Understanding cyclic fatigue failure is crucial for improving endodontic instruments.

Purpose of the Study:

• To compare the cyclic fatigue resistance of rotary versus reciprocating NiTi file systems.
• To evaluate the influence of file size and taper on fatigue failure.
• To analyze fracture mechanisms of NiTi endodontic files.

Main Methods:

• Cyclic fatigue testing of 19 NiTi file types in a simulated canal (0.9 mm internal diameter, 75° curvature).
• Files operated using torque-controlled motors (X-Smart Plus, Rooter X3000, Sendoline Endo).
• Fractographic analysis using scanning electron microscopy (SEM) to determine failure modes.

Main Results:

• Reciprocating systems exhibited higher time-to-fracture fatigue resistance than rotary systems.
• When normalized to rotations to failure, differences between reciprocating and rotary systems diminished.
• SEM analysis revealed fractures primarily due to tensile stress, not shear forces.

Conclusions:

• Reciprocating kinematics generally enhance fatigue resistance compared to continuous rotation.
• Fatigue resistance of NiTi instruments is influenced by a complex interplay of alloy composition, heat treatment, and cross-sectional geometry, not solely motion type.
• Further research is needed to fully elucidate factors governing NiTi instrument longevity.