Dentinal Microcracks Induced by Endodontic Procedures: Suggested Design for Experimental Studies Using Micro–Computed Tomography and Strain Gauges

Introduction: The present study aimed to describe an in vitro study model to investigate root surface strain (RSS) and its correlation with the initiation/propagation of microcracks during different endodontic procedures. Methods: Four lower human incisors extracted microcrack free were selected by micro-computed tomographic imaging. Two strain gauges were bonded to the root surface of each incisor. Then, the teeth were prepared to reproduce the periodontal ligament artificially. The gauges were attached to a data acquisition system. The RSS was recorded during the entire endodontic procedure, which consisted of accessing the endodontic cavity, cleaning, shaping preparation with an Mtwo rotary system (VDW, Munich, Germany), and filling with a standardized technique. Each incisor was submitted to a different retreatment protocol and supplementary cleaning method as follows: (1) Reciproc (RC, VDW) + Flatsonic (FS; Helse, Santa Rosa de Viterbo, Brazil), (2) RC + XP-endo Finisher (XPF; FKG Dentaire, La Chaux-de-Fonds, Switzerland), (3) Mtwo retreatment (MR) + FS, and (4) MR + XPF. Finally, the teeth were rescanned to establish the postoperative microcrack formation by 2 well-trained and blinded examiners. Results: The maximum and minimum RSS values were -120 and 510 microstrains, respectively, for all of the files. RC showed the highest RSS values during endodontic retreatment compared with MR. FS demonstrated a higher variation between the minimum and maximum RSS than XPF. No microcracks were observed in the specimens. Conclusions: This preliminary study proposed an experimental model that would combine 2 methods to evaluate the effects of endodontic systems on dentin. Although strain gauges would provide data on the stresses created, the pre- and postoperative evaluation of micro-computed tomographic images would enable microcrack formation to be determined.