(PR62) File Breakage in Conventional and Contracted Endodontic Cavities

Abstract:

Objectives: To compare rotations to failure and tip separation length of a nickel-titanium (Ni-Ti) rotary instrument within a simulated mesio-buccal canal of a mandibular molar with a conventional or contracted endodontic cavity.

Methods: Two identical lithium disilicate #30 crowns were milled with CEREC CAD-CAM. A conventional or constricted endodontic cavity was prepared. A custom glass tube (Precision Glassblowing) was fabricated with taper and length replicating a mesio-buccal canal, including buccal/lingual curvature, and placed at the mesio-buccal orifice of each crown in a silicone mold. Forty Endosequence Controlled-Memory Ni-Ti rotary files (Brasseler) in size 30/.04 were used following manufacture recommended 1.8Ncm torque and 500 RPM (n=20 per access type). Instrumentation and time to failure (seconds) was video recorded with a smartphone camera (iPhone SE, Apple). Number of rotations to failure was calculated from the time to failure, and the length of broken tips (mm) was measured with digital calipers. The data between the conventional and contracted access were compared using a t-test.

Results: Number of rotations to failure was 599±126 and 465±65 for conventional and contracted access, respectively; tip separation lengths were 3.99±0.29 and 4.90±1.02mm, respectively. Number of rotations to failure and tip separation lengths were significantly different between the two access openings (p < 0.001).

Conclusions: Within the limitations of this study, the contracted access caused earlier failure of the Ni-Ti instrument with longer tip separation lengths than the conventional access, likely due to higher stress in the coronal 1/3 of the curved canal.