Simulation of Vertical Root Fracture in Endodontically Treated Teeth

Objectives: To simulate vertical root fracture (VRF) in extensively defective teeth so as to better understand the effect of root canal therapy (RCT).
Methods: MOD and access cavities were prepared in twenty human single-rooted mandibular premolars that were treated with root canal therapy (RCT) and restored with glass-fiber posts. The teeth were then potted in acrylic resin and loaded in an Universal Testing Machine (MTS, MN, USA) until fracture. The samples were randomly divided into two groups based on the loading modes. Group 1 were subjected to vertical static loading with a crosshead speed of 0.5mm/min. Group 2 were subjected to vertical cyclic loading (1 Hz) with an increasing amplitude. The fracture loads and patterns were recorded. To evaluate their stress distributions, three-dimensional finite element analysis (FEA, Fig.1a) was also conducted.
Results: The proportions of VRF, crown fracture and mixed-mode fracture (Fig.1c) in the cyclic-loading group were 50%, 20% and 30%, respectively. In the static-loading group, only crown fractures were observed. FEA showed that the peak maximum principal stress occurred in the middle third of the root (Fig.1b), where VRF may initiate. Stress concentrations also occurred at the coronal third of the tooth, which may induce crown and mixed-mode fractures.
Conclusions: VRF was successfully produced in extensively defective teeth treated with RCT and restored with posts using cyclic loading. This would allow the effect of different endodontic treatments to be studied under more clinically relevant conditions.