Clasp Design Effect on Stress distribution in Distal Extended Abutment

Objective: Today, many controversies about most beneficial design of distal extension base partial dentures exist. Although the purpose is minimizing the stress on abutment teeth and supporting tissues, different result and theories have been reported. The purpose of this study was to analyze stress applied on distal extended abutment in different types of conventional clasp designs. Methods: The skull of 42 year old man was CT-Scanned with 0.6mm sections and data were used to make a 3D model of the mandible in mimics software. Then a frame work of Kenedy's class I partial denture with 3 different clasp design (Aker's, Bar type and combination) was designed on this model. Occlusal force was applied on the saddle and stress was measured with a finite element method analysis using "cosmos works 2008" soft ware. Results: In Aker's design, stress concentration pattern showed applying distal load on abutment. The combination clasp presented identical pattern, but stress concentration was significantly lower than the Aker's. On the contrary, stress concentration pattern showed that bar type clasp applied mesial load to abutment. In all designs buccal load was applied from partial denture to abutment in buccolingual dimension. Conclusions: Aker's clasp in distal extension base partial dentures applies extra stress on distal extended abutment in unfavorable (distal) direction, which is greater than tooth tolerance.