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To study the relationship between structural parameters and mechanical properties of endodontic instruments, the T02004B25 nickel-titanium endodontic instrument was selected for bending and torsion tests and finite element simulation analysis, which demonstrated the feasibility of simulation analysis method. Then based on the idea of parametric design, the models of the endodontic instruments with different structural parameters (cross-section, pitch, taper) were established, and the bending-torsion performance simulation analysis was completed. The results showed that the mechanical properties of endodontic instruments with different structural parameters are different. It is necessary to find the optimal parameters for different structure parameters of endodontic instruments to maximize their service life.

This paper presents an improved accumulation damage model which is closer to the actual conditions based on the Manson-Halford (M-H) model. The model considers both the effect of load interaction and the phenomenon of strength degradation of materials induced by loading history. In addition, a new logarithmic residual strength model is proposed and its accuracy is verified by two sets of strength degradation experimental data. Finally, five sets of experimental data under two-level and multi-level loadings are compared with the prediction results. It is shown that the improved model has better applicability and higher accuracy.

To investigate the electrophysiological characteristics and pathological changes in different recurrent laryngeal nerve injury models.Twenty dogs were divided into different models of recurrent laryngeal nerve injury. Electrophysiological changes of animal models and histopathological changes in laryngeal muscles were investigated at different time.Amplitude of MUP in TA decreased at first and then increased a little, while duration of MUP keeps decreased. The latent periods of the evoked potential in the incomplete injury group increased at first and then went down. In animal histopathological investigation, the lighter of the muscle injuries and the bigger of the diameter of muscle fibers and fascicles, and the smaller of the number of cellular nucleolus per square inch. In the early periods after injury, the correlation among the standard amplitude, threshold amplitude, maximum amplitude of EP and the diameter of fascicles were positive; while in the late period, the correlation among the amplitude, duration, area of MUP and nucleolus number was positive.The physiological characteristics of laryngeal nerves and muscles could be known. LEMG was an important method in diagnosis of laryngeal nerve and muscle diseases.