Cross-sectional design and fatigue durability of cantilevered sections of fixed implant-supported prostheses

Characterizing the fatigue behavior of cantilevered implant-supported prostheses requires an understanding of both the material and its intended application. The relationships between applied load, component geometry, and the fatigue characteristics of a specific material often can be difficult to establish. Four different cross-sectional designs of cantilevered frameworks used clinically were tested for fatigue durability, and the results were compared with theoretical tip deflections and stresses.

Fatigue tests were conducted on specimens with I-, U-, and L-shaped and elliptical cross-sections after static stress analysis. Specimens with uniform cantilevered length were sprued, invested and cast from the same high-palladium alloy. Statistical results, SEM evaluation of fracture surfaces, and theoretical predictions provided further insight into the framework design.

Based on intraoral space restrictions, corrections for dimensional changes inherent in casting, the mean number of cycles to failure for each cross-sectional geometry, and the performance of design groups as predicted by static analysis can be ranked in order from best to worst as I, L, U, and then elliptical. SEM evaluation showed varying degrees of porosity and shrinkage cavities specific to the specimen cross-sections.

Four designs for the cantilevered sections of implant-supported frameworks were evaluated for fatigue durability and were compared with the results of the theoretical analysis. As tested, fatigue durability was predictable when compared with theoretical calculations of tip deflection and normal stress. Although all four shapes have considerable merit for rigidity, in limited intermaxillary conditions, the I- and L-shaped cross-sections may optimize performance and use of space.