Evaluation of the Effect of Rotary Systems on Stresses in a New Testing Model Using a 3-Dimensional Printed Simulated Resin Root with an Oval-shaped Canal: A Finite Element Analysis Study

• Appropriate preparation of oval-shaped root canals (keeping the original anatomy and avoiding excess tissue loss) is challenging.
• Rounder canal preparations using rotary files could damage the root dentin depending on the cross-sectional anatomy of the root canals.
• In this finite element analysis (FEA) study, the effect of instrumentation with different rotary files on stress distribution in a new testing model using a 3-dimensional (3D) printed simulated resin root was evaluated.
• Micro–computed tomographic imaging was used to record the anatomy of a root with an oval-shaped canal, and 3D photopolymerized resin roots were printed.
• Canal preparations were performed in these models using rotary files to eliminate the variations between different roots.
• The prepared roots were scanned, and FEA models were created.
• Stresses within the models under different loading conditions (oblique and vertical) were evaluated.

IntroductionThis finite element analysis study was aimed at evaluating the effects of rotary systems on stresses in photopolymerized resin root models with oval-shaped canals.MethodsAmong the data collected by computed tomographic imaging, a mandibular second premolar tooth with an oval-shaped canal was selected, recorded as Digital Imaging and Communications in Medicine, and transferred to Materialise's Interactive Medical Image Control System software. Three-dimensional modeling was performed to produce photopolymerized resin root models. Root canals were prepared by OneShape (OS; MicroMega, Besancon, France); ProTaper Universal (PTU; Dentsply Tulsa Dental, Tulsa, OK); WaveOne (WO, Dentsply Maillefer, Ballaigues, Switzerland); Mtwo (MT; VDW, Munich, Germany); Twisted File (TF; Kerr Dental, Orange, CA); ProTaper Next (PTN, Dentsply Tulsa Dental), and hand files (HFs) (control). The models were scanned (micro–computed tomographic imaging; SkyScan 1174; Kontich, Belgium), finite element analysis models were created, and stresses were calculated under 300-N loading (at a 45° angle and vertically).ResultsThe maximum stress values were found to be higher when the roots were loaded at an angle. The range of the stress values was PTU > MT > WO > HF > PTN > OS > TF. The stresses were forwarded toward the apical area in the PTN, OS, and TF models. When loaded vertically, the highest maximum stress values were recorded in the WO model. High stress concentrations were observed at coronal, thus less stress was forwarded toward the apical, giving an advantage to the root. The range of the others was as follows: PTN ≥ PTU > MT > TF > OS ≥ HF. The TF model showed lower maximum stress values, whereas the HF model showed more homogenous stress distribution.ConclusionsConsidering the stress distributions and stress values within the models, it can be concluded that oval-shaped canals prepared by HFs and WO were less likely to result in root fracture.