The analysis of the stress distribution around angulated and parallelly placed implants based on “all on 4 concept” and four implants placed parallel within the interforaminal distance in an edentulous mandible – An in vitro three-dimensional finite element analysis

Purpose: The purpose of the study was to analyze and compare the stress distribution in the so-called All-on-Four concept where two anterior implants were placed parallel to each other and two posterior implants were tilted at 45° angle against the four parallelly placed implants within the interforaminal distance in an edentulous mandible. Materials and Methods: The three-dimensional finite element analysis models consisted of cancellous bone surrounded by the cortical bone, four dental implants positioned in two different designs – i.e., four parallelly placed implants (Model 1) and All-on-Four concept (Model 2) with hybrid superstructures comprising of a Hader bar. The vertical (60N, 130N, and 300N) and lateral (20N, 45N, and 100N) loading protocols were considered and von Mises stress values were determined. Results: On vertical and lateral loading, lower stress concentrations were observed in the peri-implant region in Model 2. However, there was higher stress concentration noticed on cortical, cancellous bone and bar attachment due to the tilting of implants in every condition. Conclusion: Within the limitations of the study, All-on-Four concept is an optimal and viable treatment option if executed accurately as it reduces the cantilever length, reduces stress concentrations in the peri-implant region, and is cost-effective.