| Objective:Compared the peak stress generated in the bracket-cement interface by applied loads when the mesh space of brackets were different using a bonded bracket finite element model(FEM).Analysis the influences of the mesh space to the bond strength.Provide a theoretical basis and reference to the clinic treatment, production and experimental research.Methods:Constructed a validated 3-dimentional finite element model of the bracket-cement-tooth system with the ANSYS commercial software. Caculate the stress distribution in different mesh space(0.2mm and 0.4mm) brackets by the shear force and twist force.The destroy in the bracket-cement interface involes two processes, corresponding two bond failure mechanisms.The first process of breakage happens in the mesh-cement interface.The second process of breackage happens in the cement itself which is embedded in the mesh space,and the breakage interface parallels the mesh exterior.Because the breakage intensity of the cement itself is always lager than that of the interface of different materials,so the second process of breakage is the main reason to the bond strength,in other words,the stress genenrated in the cement induces the bond failure.The same cement embedded in different mesh space base can generate different magnitude stresses.Results:In the first process,the peak stress was located in the interface of the mesh exterior and the cement.0.4mm space mesh had a bigger peak stress than 0.2mm space mesh.In the second process,0.2 mm space mesh had a bigger peak stress than 0.4 mm space bracket. Conclusion:The stress distribution in the system is not uniformity.The peak stress generated by the shear force is bigger than the twist force,so the shear force can result in the destroy of the cement more easily.The bigger the mesh space ,the smaller the peak stress generated ,the better the bond quality ,on condition that the retention form of the embedded cement was exsisted,in other words ,the second process of breackage was exsisted. |
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