Effect of the Rest Seat Location Alteration on Distribution of Forces in the Distal Extended Abutment: A Finite Element Method Analysis

Abstract

Statement of problem: In designing extension type removable partial denture (R.P.D), there is lots of controversy regarding the suitable location of rest seat of the terminal abutment. Discussions and Controversies are, mostly focused on minimizing lateral stress placed on terminal abutments.Purpose: The purpose of this study was to assess the rate of stress placed on abutment teeth with different rest seat placements by a finite element method analysis.Materials and method: The skull of a 60 years old man was CT-Scanned with 0.5mm sections and data were used to make a 3.D model of the mandible. Then a partial denture was designed on this model, once with a distal rest on terminal abutment, and then with a mesial rest. Occlusal force was applied on the saddle, and stress was measured with a finite element method using "cosmos works 2003" soft ware.Results: In both conditions, the highest stress concentration was observed on the distal surfaces of the abutment teeth, and the lowest stress on buccal cusps and roots of the teeth. The rest seat itself was the only place in which the observed stress was different in two conditions. The distal rest seat received more stress than the mesial rest seat. In both conditions the underlying bone received a moderate amount of stress, increasing in the distal part.Conclusion: Displacing the rest did not alter the stress applied on the abutment teeth. So it may be claimed that this factor could be neglected when determining the place of terminal rest of extension type RPD.Key words: Rest seat, Free end, Finite element method analysis