Influencia de los factores relacionados con la fatiga cíclica de las limas endodónticas de NITI

Resumen

The endodontic rotary and reciprocating files of NiTi has reported to exhibit unexpected fractures inside the root canal system during the root canal treatment; which can affect the prognosis of the endodontic therapy. Therefore, it is important to assess the variables related to this intraoperative complication. Aim: To analyze the influence of the variables related to cyclic fatigue on the fracture resistance of NiTi endodontic instruments. To analyze the influence of the apical diameter and taper of NiTi rotary endodontic instruments on their resistance to cyclic fatigue. To analyze the influence of cross-sectional design and pitch on the mechanical behavior of NiTi endodontic instruments under bending and torsional conditions. To analyze the influence of the cross-sectional design of NiTi rotary endodontic instruments on the resistance to cyclic fatigue. To analyze the influence of the NiTi alloy of endodontic rotary instruments on the resistance to cyclic fatigue. To analyze the influence of the pecking motion frequency of NiTi rotary endodontic instruments on their resistance to cyclic fatigue. To analyze the influence of the movement of NiTi rotary and reciprocating endodontic instruments on their resistance to cyclic fatigue. To analyze the influence of reciprocating movements of NiTi alloy endodontic reciprocating instruments on their resistance to cyclic fatigue. To analyze the influence of the number of uses and sterilization cycles of NiTi alloy endodontic reciprocating instruments on their resistance to cyclic fatigue. To analyze the resistance to cyclic fatigue of new NiTi endodontic systems. To analyze the influence of the radius and angle of curvature of the root canal system on the mechanical behavior of NiTi endodontic instruments. To analyze the volumetric wear of NiTi endodontic reciprocating instruments subjected to cyclic fatigue. To analyze the removal capacity of separated NiTi alloy endodontic rotary instruments within the root canal system and the wear of root dentin. Materials and Methods: In vitro and finite element methods were performed for analyzing the variables related to the cyclic fatigue. Results: Statistical analisys were performed in order to assess the statistical significant differences among the parameters of each variable. Conclusions: The variables analized influences on the resistance of the NiTi alloy endodontic instruments to cyclic fatigue. The increased apical diameter and taper of NiTi endodontic rotary files decreased their resistance to cyclic fatigue. The use of files with a triangular-shaped cross-section and a small pitch are recommended in order to minimize ledging and maximize fatigue life. The double S-shaped cross-section of NiTi alloy endodontic files shows higher cyclic fatigue resistance than the rectangular cross-section, the convex triangular cross-section, and the triangular cross-section of NiTi alloy endodontic files. The NiTi CM-Gold wire alloy of the ProTaper Gold endodontic rotary files resulted in greater resistance to cyclic fatigue than ProFile Vortex Blue, ProTaper Next, and ProTaper Universal endodontic rotary files. A low frequency of pecking motion is recommended to reduce the risk of failure of endodontic rotary files associated with cyclic fatigue. NiTi alloy endodontic rotary files using reciprocating movement at 350 rpm with 120° counterclockwise and 30° clockwise motion exhibit greater resistance to dynamic cyclic fatigue than files used with a reciprocating movement at 400 rpm with 120° counterclockwise and 30° clockwise motion, continuous rotational speed at 200 rpm, continuous rotational speed at 350 rpm, or continuous rotational speed at 500 rpm; it is therefore advisable to use reciprocating movements at a low speed. The ReFlex Smart reciprocating movement increased the cyclic fatigue resistance of endodontic reciprocating files compared with traditional reciprocating movement. The time of use of NiTi endodontic reciprocating files negatively afects dynamic cyclic fatigue resistance; however, dynamic cyclic resistance is not afected by the number of sterilization cycles. Smarttrack NiTi alloy endodontic reciprocating files display greater resistance to cyclic fatigue than Endogal and Path Max Pro NiTi alloy endodontic rotary files, due to the reciprocating movement and metallurgical composition. Significant influence of the root canal geometry on the fatigue life of the NiTi rotary files and reveal the higher importance of the radius of curvature with respect to the angle of curvature of the root canal. The CM-wire NiTi alloy endodontic reciprocating files exhibit a volumen wear after clinical use. Ultrasonic tips enable greater ease of removal of NiTi endodontic rotary files from the root canal system, with similar amounts of dentin removal between the two methods.