Abstract
Introduction: The aim of this study was to evaluate the influence of cervical and middle preparation on resistance to dynamic cyclic fatigue during instrumentation of mandibular molar replicas with Logic 25/.06 instruments.
Materials and Methods: Forty mandibular molar replicas were printed with 16 µm resolution from a tooth file scanned by microcomputed tomography. For the fatigue test, 40 new Logic 25/.06 nickel-titanium instruments (Bassi Endo, Belo Horizonte, Brazil) were used for mechanical preparation of the mesiobuccal canal and subjected to the dynamic cyclic fatigue test in an artificial curved metal canal with a bending angle of 45º and a bending radius of 6.6 mm. During the dynamic cyclic fatigue test, the time to fracture of the file was recorded and the number of cycles to fracture was calculated. The surfaces of the fragments were evaluated using scanning electron microscopy to verify the length of the fragment and the type of fracture that occurred. Data on time to fracture, number of cycles to fracture, and length of the fractured fragment were collected and statistically analyzed using the t-test or Mann-Whitney test with a significance level of 5%.
Results: There were no statistically significant differences between the groups with or without preparation of the cervical and middle third in relation to time to fracture (p = 0.561), number of cycles to fracture (p = 0.508), and length of the fractured fragment (p = 0.417).
Conclusion: Preparation of the cervical and middle thirds did not increase the resistance to fracture due to cyclic fatigue of the instruments tested.