Caracterização geométrica, dimensional e avaliação da eficiência de corte dos instrumentos endodônticos de níquel-titânio BioRaCe e BT-RaCe

Abstract

The cutting ability and efficiency of Niquel Titanium (NiTi) endodontic instruments are complex and related to many different factors such as the instrumentation technique and the geometric and dimensional characteristics of the instruments. The goal of the present work was to assess the cutting action through the torque exerted during the preparation of root canals with BioRaCe instruments, (FKG Dentaire Swiss Endo La Chaux-de-Fonds, Suíça) BR0 25/.08, BR115/.05, BR2 25/.04, BR3 25/.06, BR4 35/.04 e BT-RaCe (FKG Dentaire Swiss Endo La Chaux-de-Fonds, Suíça) BTR1 10/.06, BTR2 35/.00 e BTR3 35/.04. Initially, the instruments were characterized according to the diameter of each millimeter of the active part and pitch length. Instruments were photographed and images were analized by the ImageJsoftware. Cutting efficiency assays were performed with 20 upper premolares with two separate roots with a gradual curvature ranging from 10º e 25º (class I) and total canal length between 19 and 23mm, selected from the FOUFMG tooth bank. After the initial digital radiograph the coronal access was performed, follow by the working length determination with manual stailess steel K#10 and K#15 files. Ten teeth were instrumented according to the manufacturers recommendation for each system. A multimeter, coupled to the endodontic motor, recorded the torque required by each instrument during root canal preparation. The cutting efficiency and the behaviour of the instruments during the preparation were assessed by the torque versus time curves. Results indicate that the geometrical and dimensional characterization of the instruments are compatible to the values advocated by the manufacturer. In the pitch length analysis, files showed alternate progressive cutting flutes, only exception being, that had a constant pitch. As for the cutting time required by the instruments, results revealed that BioRaCe and BT-RaCe systems showed differences in the cutting efficiency time assays, mostly due to the difference in the number of instruments used for each sequence. Last but not least, there were no statistical differences in the cutting assays of instruments that demanded higher average torque during the instrumentation, BR3 for the BioRaCe system and BTR3 for the BT-RaCe system. The reduced number of instruments for root canal preparation, within the constraints imposed by this study and by the sequences evaluated, showed a safe maximum torque for clinical use and a decreased treatment time.