Effect of Clasp Design on Stress Distribution Pattern of Distal Extended Abutment: A Finite Element Method Analysis

Today, many controversies about the most beneficial design of distal extension base partial dentures exist. Although the purpose is minimizing the stress on abutment teeth and supporting tissues, different results and theories have been reported. The purpose of this study was to analyze the stress applied on distal extended abutment in different types of conventional clasp designs. The skull of a 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 designs (Akers, 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. 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 that of the Akers. 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. 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.