(PR115) File Breakage in an S-shaped Canal with a Conventional Versus Contracted Endodontic Cavity

Objective: To compare the rotations to failure and location of tip separation of a nickel-titanium (Ni-Ti) rotary file of different tapers recently brought to market. The files will be tested within a simulated mandibular molar mesio-buccal canal with a s-shaped curve with a conventional and contracted endodontic access cavity.

Methods: Two identical lithium disilicate #30 crowns were milled. A conventional and contracted endodontic cavity was prepared. A stainless-steel plate with an artificial canal with two 45° curves was fabricated and placed at the mesio-buccal orifice of each crown, held in silicone mold. Instrumentation was simulated using 30/.04 and 30/.06 Ni-Ti rotary files following manufacturer recommended (recommendations)(n=20). The instrumentation was video recorded to determine time and rotations to failure. The length of broken tips was measured. The experimental data were compared using a t-test (significance level 0.05). Stresses in the instruments were examined using finite element analysis.

Results: Number of rotations to failure and the location of tip separation are expected to be affected by the different tapers and access, indicated by statistically significant differences. Contracted access limits the path of insertion and is likely to cause early failure at longer distances from the file tips. FEA will confirm that the location of highest stress levels within files is affected by the access paths.

Conclusion: We anticipate that the contracted endodontic access design will decrease the rotations to failure and increase the separation length of the files for both tapers, and that the larger taper will have decreased rotations to failure and longer separation lengths..