Finite element analysis of two-abutment Hader bar designs

Parametric three-dimensional finite element studies were conducted on the Hader bar to determine mechanical properties with respect to bar length, stiffener height, and material properties. Three bar lengths (6, 12, and 18 mm) were analyzed with a 1-mm stiffener height. For the longest bar length (18 mm), two additional stiffener heights were evaluated (2 and 3 mm). In addition, three material types were studied for each of the design cases which represented a selection of alloys commonly used clinically. The model consisted of a representative Hader bar which was constructed of a bar of 1.8 mm diameter. The ends of the bar were fixed to a 2.5-mm diameter coping which was attached to a 1.8-mm diameter root form-type implant, rigidly fixed in a representative block of bone. The bone was modeled as fixed at its distal end to eliminate rigid body motion. A 200-Newton occlusal force was modeled as being transmitted through one, two, or three attachment clips, 5 mm in length, for the three respective bar lengths. The results of these analyses did not predict yielding (failure) for any of the cases studied. Span length and stiffener height were found to play a stronger role in the adequacy of the overall design as compared with changing material properties in the range of alloy stiffness tested. For the span length studies, factors of safety, with respect to static yield strength, ranged from 2.93 to 10.3 and fatigue factors of safety ranged from 1.41 to 3.36.(ABSTRACT TRUNCATED AT 250 WORDS)