File Breakage in Conventional Versus Contracted Endodontic Cavities

Area of Science:

• Endodontics
• Dental Materials Science
• Biomaterials Engineering

Background:

• Nickel-titanium (Ni-Ti) rotary instruments are widely used in endodontic procedures.
• Endodontic access cavity design can influence instrument performance and longevity.
• Understanding the biomechanical behavior of Ni-Ti files under different access conditions is crucial for clinical success.

Purpose of the Study:

• To compare the cyclic fatigue resistance and tip separation length of Ni-Ti rotary instruments.
• To evaluate the impact of conventional versus contracted endodontic access cavities on instrument failure.
• To analyze the stress distribution within Ni-Ti instruments using finite element analysis.

Main Methods:

• Simulated mesio-buccal canals of mandibular molars were prepared with either conventional or contracted endodontic access cavities.
• Ni-Ti rotary files (30/.04) were used for simulated instrumentation under controlled torque (1.8 Nm) and speed (500 RPM).
• Rotations to failure, tip separation length, and instrument stress were recorded and analyzed statistically.

Main Results:

• Contracted access resulted in significantly fewer rotations to failure (465±65) compared to conventional access (599±126).
• Tip separation lengths were significantly longer in the contracted access group (4.90±1.02 mm) versus the conventional group (3.99±0.29 mm).
• Finite element analysis indicated higher file curvature and stress levels, particularly in the mid-section, with contracted access.

Conclusions:

• Contracted endodontic access cavities increase stress on Ni-Ti rotary instruments, leading to earlier cyclic fatigue failure.
• Longer tip separation lengths observed with contracted access pose a greater risk of procedural complications.
• Dentists should consider the potential impact of access cavity design on Ni-Ti instrument performance and patient safety.