Stress distribution evaluation of implant-supported overdenture–retaining bar designs with different techniques in mandibular edentulous cases with numerical methods

The purpose of this study was to evaluate effects of various fabrication techniques and materials used in implant-supported mandibular overdentures with Hader bar attachment over stress distribution. Three dimensional geometric solid models, consisting of 2 implants (3,3mm×12mm) placed at the bone level on both mandibular canine regions, supporting a Hader bar structure were prepared. Each geometric solid model was designed to represent three different bar retentive systems. Model 1 simulated a bar retentive system made from Ti Grade 5 material by CNC milling technique without using any converting adapter or multi-unit element on implants, while Model 2 simulated the same configuration, but with converting adapters on implants. Model 3 simulated a bar retentive system made from Co-Cr material, made by using conventional casting technique with converting adapters on implants. Static loads of 100 N and 300 N were applied on test models from horizontal, vertical and oblique directions. ANSYS R15.0 Workbench software was used to compare Von Mises stress distribution and minimum/maximum principal stress values, and results were evaluated by using finite element analysis method. Additionally, rehabilitation of a total of 6 edentulous patients with implant-supported manibular overdentures using three different bar retentive systems were applied in order to provide support for this in vitro study. As a result of this study, the highest stress distribution values under static loading in three different directions were obtained in Model 1. The highest stress values in all models were observed during horizontal loading. Stress were observed to intensify around neck of implants and surrounding cortical bone areas in all models. In scope of the results obtained, using converting adapters on implants has been considered to decrease transmission of forces onto implants and surrounding bone structures, thus providing a better stress distribution. It has also been observed that, type of material used for bar fabrication has no significant influence over stress values in those models where converting adapters were used. Regarding clinical applications, convincing results were obtained in terms of implants and denture stability, as well as patient satisfaction, when follow-up controls over a period of one year have been taken into consideration.