Objective To make a mechanical analysis on three- dimensional finite element models of the mandibular first molar with the maximum distal occlusal（ DO）structure defect after the root canal therapy and filling and crown restoration under static and impact loads and to provide a guideline for planning restoration for the clinic. Methods The research adopted reverse engineering technology to build the model of three- dimensional finite element. The form of the intercuspal occlusion and cusp to cusp occlusion during the circulation of posterior teeth occlusion movement were simulated. Half- sine pulse/impact was chosen for the impact dynamic. The impact ratio was indicated to the stress change between impact loads and static loads. Results Under the two kinds of loads, the maximum Mohr stress values of the metal crowns were shown in all models. The restoration effects between the two kinds of models were compared, the maximum Mohr stress value of the crown metal and dentin was not obviously difference. The maximum Mohr stress values of dentin were all obviously smaller than the stretch limit strength of dentin. The impact ratio closed to 1. Conclusion The impact loads accorded with the oral actual situation more than the static loads, but the suitable analysis of the static loads could be accepted. The restoration of metal crown is necessary. The effects between the amalgam filling and full crown restoration and composite resin filling and full crown restoration is not difference obviously.
