Just doing some research on single cone obturations and this article caught my attention. Note that Protaper Next performing as well as the superb Reciproc file for retreating oval canals in extracted teeth. Use of sonic versus ultrasonic to aid the irrigation efficacy making no difference in cleaning efficiency
J Endod. 2017 Mar;43(3):467-471. doi: 10.1016/j.joen.2016.10.040.
INTRODUCTION: The aim of this study was to evaluate the effectiveness of ProTaper Next (Dentsply Maillefer, Ballaigues, Switzerland) and Reciproc (VDW, Munich, Germany) systems in removing filling material from oval root canals using sonic or ultrasonic irrigation as additional cleaning methods. METHODS: Thirty-two human extracted mandibular premolars with oval canals were prepared using the ProTaper Universal system (Dentsply Maillefer) up to instrument F4 (40/.06) and then filled by the single-cone technique using Endofill sealer (Dentsply Maillefer). The teeth were randomly divided into 4 groups (n = 8) according to the instrumentation system and the additional cleaning method as follows: Reciproc 40 with ultrasonic activation, Reciproc 40 with sonic agitation, ProTaper Next (X2, X3, and X4) with ultrasonic activation, and ProTaper Next (X2, X3, and X4) with sonic agitation. All specimens were analyzed using micro-computed tomographic imaging before and after removal of the filling material and also after applying the additional cleaning methods. The data, in mm3 of remaining filling material, were analyzed by the Kruskal-Wallis, Dunn, and Mann-Whitney tests. RESULTS: None of the retreatment protocols completely removed the filling material from the root canals, and there was no significant difference between the instrumentation systems or between root thirds assessed in terms of the average volume of remaining filling material (P > .05). Likewise, no significant difference was observed between the additional cleaning methods in any of the root canal thirds assessed (P > .05). CONCLUSIONS: The ProTaper Next and Reciproc systems were equivalent with respect to effectiveness in removing filling material regardless of the additional cleaning method used. The additional cleaning methods were also equivalent and did not improve the removal of filling material significantly.