The effect of larger apical preparations in the danger zone of lower molars prepared using the Mtwo and reciproc systems

Introduction The aim of this study was to evaluate the effects of large apical preparations in the danger zones of the mesial root canals of mandibular molars instrumented with the Mtwo and Reciproc systems (VDW, Munich, Germany) until reaching apical diameters of 0.25 and 0.40 mm.

Methods Twelve mandibular molars, the mesial roots of which presented distinct foramens and similar anatomies, were selected using micro-computed tomographic scanning. Mtwo and Reciproc instruments were used to shape the mesiobuccal or mesiolingual canals. The mesial canals were scanned before and after the use of 0.25- and 0.40-mm Mtwo and Reciproc instruments. The analyzed parameters included the root canal volume and remaining dentin thickness at 5 different levels. The obtained data were subjected to paired analysis of variance and Tukey or Friedman and Dunn tests for intragroup analysis and the Mann-Whitney U test for comparison between the mesial and distal walls.

Results There were no significant differences between the mesial and distal dentin thickness for the points analyzed with both instrumentation techniques (P >.05). The volumetric analysis revealed a significant difference (P <.05) among the initial volume and after the use of the 0.25- and 0.40-mm instruments for both systems. The use of the 0.40-mm instrument increased the root canal volume in comparison to the 0.25-mm instrument (P <.05).

Conclusions Both systems performed similarly for the preparation of curved root canals with separate apical foramens. The increase of the root canal preparation with the 0.40-mm instrument significantly increased the root canal volume at the apical third without significantly reducing the dentin thickness in the danger zone for both instrument systems.