Effect of Rotary-systems on Stress-distribution in Roots With Oval-shaped Canals

Objectives: This finite element analysis (FEA) study was aimed to evaluate the effect of preparation using different rotary-systems on stress distributions in roots with oval canals.
Methods: Among the data collected by Computerized Tomography (CT), a mandibular second premolar-tooth with oval-shaped root-canal was selected, recorded as Digital Imaging and Communication in Medicine (DICOM) and transferred to Materialise’s Interactive Medical Image Control System (MIMICS) software. Three-dimensional (3-D) modeling was done to create a 13 mm long root. Seven transparent photopolymerized resin (Vero Clear Photopolymer) root models were printed using 3D printer (Eden 500 PolyJet). After subjecting models to the jaws of phantom heads, root-canals were prepared using the following systems: OneShape (MicroMega), ProTaper Universal (Dentsply), WaveOne (Denstply), Mtwo (VDW), Twisted File (Kerr), Protaper Next (Dentsply). Hand-files were used in the control model. The models were then scanned using Micro-CT (SkyScan 1174). The images were reconstructed using NRecon (SkyScan) and Rapidform Softwares. SolidWorks software was used for the corrections and FEA models were created. Von Misses and natural stresses were calculated by applying 300 N forces both vertically and with a 45° angle to the buccal surface of the roots.
Results: Von mises stresses occurred within the roots were as follows (vertical loading): WaveOne > Protaper Next, ProTaper Universal > Mtwo, Twisted File > hand file > OneShape; (loading with 45° angle): ProTaper Universal > Mtwo > WaveOne > hand file > Protaper Next > OneShape > Twisted File. Less von Mises and maximum stress values were recorded in Twisted File and hand-file models while high stress values were recorded in WaveOne and Protaper Universal models.
Conclusions: Considering the stress distributions and stress values within the models, it can be concluded that oval shaped canals prepared by Twisted File and hand files were likely have less incidence in root fracture.