Influence of structure on nickel-titanium endodontic instruments failure

Area of Science:

• Materials Science
• Biomaterials Engineering
• Dental Materials

Background:

• Nickel-titanium (NiTi) endodontic files are widely used in root canal therapy.
• Understanding factors affecting their lifespan is crucial for clinical success and patient safety.
• Previous studies have highlighted material fatigue as a cause of file separation.

Purpose of the Study:

• To investigate the influence of manufacturing and processing history on the fracture life of NiTi endodontic files.
• To correlate microstructural characteristics with mechanical properties and failure modes.
• To identify critical factors contributing to the fracture of endodontic instruments.

Main Methods:

• Microstructural analysis using X-ray diffraction (XRD) to assess lattice structure.
• Scanning electron microscopy (SEM) for surface morphology and fracture surface examination.
• Microhardness testing (Vickers) to quantify material hardening and defect density.

Main Results:

• Endodontic files exhibit significant work hardening and a high density of defects.
• Microhardness tests confirmed the presence of dislocations and precipitates, indicating a distorted lattice structure.
• XRD results showed extended spectrum lines, consistent with lattice distortion.
• SEM revealed that the surface condition of the files is a critical factor in fracture initiation.

Conclusions:

• The process history, leading to work hardening and lattice defects, significantly affects the phase transformation and mechanical integrity of NiTi endodontic files.
• Surface irregularities and microstructural defects are primary contributors to instrument failure.
• Optimizing manufacturing processes to minimize defects and control surface finish is essential for enhancing the fracture resistance of NiTi endodontic files.