Using FEA to Simulate the Effects of Stress Breaking Devices

Objectives: In the situation of an abutment in the middle of a multiple unit fixed restoration, the abutment tooth in the center can act as a fulcrum. Tensile forces would then be generated between the retainer and abutment at the other end of the bridge. This abutment would be required to undergo an extrusive movement to react the force. The result of the tensile force would be at the retainer to abutment interface (cement layer), causing a loss of retention on one of the terminal abutments. This present study was aimed to generate finite element (FE) models to compare the stress distribution and bridge movement in a long span bridge with rigid or nonrigid connectors. Methods: Two 2-D finite element models of long span bridges with pier abutment were generated. One of the bridges was with rigid connectors and the other one was with key and keyway connectors. An axial load (100N) was applied to the end of the bridge and calculated the magnitude of stress distribution and bridge displacement. Results: The results indicated that stress breaking device could interrupt the force transmit to the other end of the bridge, decrease the tensile force at the retainer to abutment interface, and avoid the extrusive movement of abutment in the other end. However, the stress breaking device would increase the von Misses stress and intrusive movement of the abutment in the area of pressure application. Conclusion: It was concluded that stress breaking device will decrease the lose of retention on one of the terminal abutments due to diminish the tensile force at cement layer, but it would increase periodontal loading of the abutment in the pressure side, so it was not suggested to use this design in the patient with severe compromised periodontal condition.