Objective To predict the tissue-level failure strain of the cortical bone and discuss the effects of different running speeds on the mechanical properties of rat femoral cortical bone.Methods The threshold for cortical bone tissue-level failure strain was assigned,and fracture simulation under three-point bending was performed on a rat femoral finite element model.The predicted load-displacement curves in each simulation were compared and fitted with the experimental data to back-calculate the tissue-level failure strain.Results The cortical bone tissue-level failure strains at different running speeds were statistically different,which indicated that different running speeds had certain impacts on the micromechanical properties of the cortical bone structures.At a running speed of 12 m/min,the cortical bone structure expressed the greatest tissue-level failure strain,and at a running speed of 20 m/min,the cortical bone structure expressed the lowest tissue-level failure strain.Conclusions Based on the changing trends of tissue-level failure strain and in combination with the changes in macro-level failure load and tissue-level elastic modulus of cortical bone structures,the effects of different running speeds on the mechanical properties of cortical bone structures were discussed in this study.The appropriate running speed for improving the mechanical properties of the cortical bone was explored,thereby providing a theoretical basis for improving bone strength through running exercises.

Objective:To investigate the effect of holistic thinking training mode on establishing clinical holistic thinking in endodontic practice teaching for students.Methods:Holistic thinking training mode was applied among Batch 2013 (group A, n=174) and Batch 2014 (group B, n=92) students of Guanghua School of Stomatology, Sun Yat-sen University. The teaching results were evaluated by the scores before and after the training and questionnaire, and by comparing their scores with those of Batch 2012 (group C, n=88) students. SPSS 20.0 was used to conduct one-way ANOVA and t test. Results:Compared the scores of students in group A with group B, the total scores before and after the training and the scores of "case report" were not statistically different, but the scores of holistic thinking were significantly improved after the training. Compared with the scores of students in group C, the total scores after the training and the "case report" scores of group A and B were significantly higher. The results of the questionnaire showed that 87.9%(153/174) of the students thought the training mode was conducive to the establishment of holistic thinking, but 77.6%(135/174) thought further improvement was needed in terms of content and time allocation.Conclusion:Holistic thinking training mode has a positive effect on the endodontic practice teaching, and is worth promoting in other departments after further improvement.

BACKGROUND:Critical energy release rate is a global fracture parameter that could be measured during the failing process,and its value may change under different failure modes even in the same structure. OBJECTIVE:To propose an approach to predict the critical energy release rate in the femoral cortical bone structure under different failure modes. METHODS:Three-point bending and axial compression experiments and the corresponding fracture simulations were performed on the rat femoral cortical bone structures.Different critical energy release rates were repeatedly assigned to the models to perform fracture simulation,and the predicted load-displacement curves in each simulation were compared with the experimental data to back-calculate the critical energy release rate.The successful fit was that the differences in the fracture parameters between the predicted and experimental results were less than 5%. RESULTS AND CONCLUSION:(1)The results showed that the cortical bone structure occurred tensile open failure under three-point bending load,and the predicted critical energy release rate was 0.16 N/mm.(2)The same cortical bone structure occurred shear open failure under axial compression load,and the predicted critical energy release rate was 0.12 N/mm,which indicates that the critical energy release rate of the same cortical bone structure under different failure modes was different.(3)A comprehensive analysis from the perspectives of material mechanical properties and damage mechanism was conducted to reveal the reasons for the differences in the critical energy release rate in the cortical bone structure under different failure modes,which provided a theoretical basis for the measurement of the energy release rate and the accurate fracture simulation.