Effects of Three Types of Movements of Nickel–Titanium Instruments on Root Canal Preparation: Analysis by Using Cone-Beam Computed Tomography

The development of endodontics leads to increasingly innovative techniques, which improve mechanical root canal preparation. Endostar E3 Azure (Poldent Co., Warsaw, Poland) is a nickel-titanium file, which can be used in rotary, reciprocal, and optimum torque reverse (OTR) movements. The aim of this study was to assess canal transportation (CT), canal-centering ability (CCA), and wall thickness reduction (WTR) after the use of Endostar E3 Azure files in these three movements. In total, 24 two-canal artificial teeth were used, which were divided into three groups, depending on the applied movement (n = 16 canals). Each canal was initially prepared manually and then instrumented with Endostar E3 Azure files using rotary, reciprocal, or OTR movements. Cone-beam computed tomography was performed before and after canal preparation. The root wall thickness was measured at 3 mm, 6 mm, and 9 mm from the radiological apex and CT, CCA, and WTR were calculated. Reciprocal movement resulted in significantly better outcomes in canal-centering ability (CCA = 0.57) compared with rotary movement (CCA = 0.27) in the middle part of the canal. The wall thickness was significantly reduced in the rotary group: 0.21, 0.19, and 0.13; in the reciprocal group: 0.09, 0.08, and 0.1; and in the OTR group: 0.11, 0.15, and 0.17 at 3, 6, and 9 mm from the apex, respectively. Moreover, rotary movement caused a statistically greater reduction in wall thickness in the apical and middle area compared to other groups. Endostar E3 Azure files significantly reduce the thickness of the root wall along its entire length, which may indicate the effective removal of infected tissue. The use of OTR movement did not affect the analyzed parameters negatively, and it is a safe option which combines the advantageous features of rotary and reciprocal movements.