ABSTRACT
Objective@# To compare the differences in the stress distribution in simulated first molars prepared with three rotary nickel-titanium instruments. @*Methods @#Four simulated first molars were prepared without instruments and with Reciproc, WaveOne and Protaper. Before and after preparation, each simulated molar was scanned by Micro-CT. The data were imported to Mimics 16.0 software to establish three-dimensional models. Finite element analysis was processed with Abaqus 6.14 software under conditions of longitudinal and lateral load. @*Results@# Under vertical load conditions, the maximum von Mises stress of the enamel increased by 1.36%, 21.48% and 20.99% in the Reciproc, WaveOne and Protaper groups, respectively, after preparation, while the maximum von Mises stress of the cementum increased by 55.98%, 41.18% and 33.04%, respectively, and the maximum von Mises stress of the alveolar bone increased by 45.55%, 40.37% and 24.09%, respectively. Under 45° lateral load conditions, the maximum von Mises stress of the enamel increased by 1.79%, -4.58% and 3.82% in the Reciproc, WaveOne and Protaper groups, respectively, after preparation, while the maximum von Mises stress of cementum increased by 16.33%, 7.58% and 4.32%, respectively, and the maximum von Mises stress of the alveolar bone increased by 46.82%, 36.40% and 8.29%, respectively. Under the same conditions, the von Mises stresses of the cementum and alveolar bones of the simulated molars were higher after preparation than before preparation, especially under lateral load conditions. The stress was focused on the border between the crown and the root. The von Mises stress of the cementum and alveolar bones increased much more in the Reciproc group than in the other two groups under both conditions.@*Conclusion@#The von Mises stress of simulated molars was greater after preparation than before preparation. The von Mises stress of the cementum and alveolar bones increased much more in the Reciproc group than in the other two groups.