Abstract
Aim: the aim of this study was to investigate the shaping ability of thermomechanically treated files manufactured by twisting(Twisted files)and compare it to conventional rotary system (K3, Sybron Endo, Orange, CA) in S-shaped canals, including formation of ledges, zipping, elbow, outer widening, danger zone, perforation and file deformation. Materials & Methods: Forty S-Shaped canals in resin blocks were randomly divided into 2 groups of 20 each. Pre-instrumentation images of the canals were taken via a digital camera and superimposed on images taken after preparation with TF and K3 systems to apical size of 25/06 and 30/06. Canal aberrations were measured from the superimposed image at five levels using AutoCAD system. Fisher exact test and Mann Whitney test were used for analysis of the data. Results: the incidence of zipping, elbow and apical transportation was significantly lower in the TF group (P = 0.04). Generally the incidence of aberration increased when the apical size increased to 30/0.06 regardless of the file system. Significant file deformation was evident in the TF after single use (P ? 0.001). Conclusion: Under the conditions of this study, TF manufactured by new technique performed better than K3 systems when used up to size 25/06 in simulated S-shaped canals. Clinical significance: The flexibility of thermomechanically treated files is beneficial in canals with multiple curvatures; however, attention should be paid to the instrument taper and final apical size of the preparation.
Highlights
The ultimate biological aim of root canal treatment is to treat or prevent apical periodontitis
Clinical significance: The flexibility of thermomechanically treated files is beneficial in canals with multiple curvatures; attention should be paid to the instrument taper and final apical size of the preparation
The apical foramen should remain in its original position, canal transportation may damage the apical foramen and create foraminal zip or tear which was found to have a negative effect on the apical seal especially when curved root canals are obturated with cold lateral compaction technique [2]
Summary
The ultimate biological aim of root canal treatment is to treat or prevent apical periodontitis. The mechanical objectives of cleaning and shaping are to facilitate delivery of antimicrobial irrigants and create resistance form against which a root filling can be compacted, maintain the path of original canal and consider the multiple geometric planes and curves more than the roots that house them. Most NiTi systems are manufactured by grinding method which may result in microcracks that can become the focus of fracture if the file is exposed to excess torsion and cyclic fatigue. A new manufacturing method by twisting has been introduced to overcome limitations of the grinding method by increasing the hardness, reducing torsional failure and cyclic fatigue [7] which subsequently maximizes file flexibility and improves its shaping ability [8,9]
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