Biomechanical Analysis of Prosthetic Designs Retained by Two or Four Implants in the Edentulous Mandible: A Three-Dimensional Finite Element Analysis.

BACKGROUND

Edentulism remains a prevalent condition worldwide, significantly compromising masticatory efficiency, quality of life, and oral health. Various implant-retained and implant-supported prosthetic options have been developed to address mandibular edentulism, yet their biomechanical performance under functional loading remains incompletely understood.

AIM

To compare stress distribution among seven prosthetic designs for the edentulous mandible: two-implant bar and locator overdentures; four-implant bar and locator overdentures; an anterior fixed-posterior removable prosthesis retained with clasps; its precision-attachment variant; and an All-on-Four fixed prosthesis.

MATERIALS AND METHODS

A 3D finite element model of a D2-quality mandible (2-mm cortical, 1-mm mucosa, remaining cancellous bone) was created. Standard implants (4.3×11 mm) and distal-tilted (30°) long implants (4.3×14 mm) were simulated. A 100-N load was applied on the mandibular first molar vertically and obliquely. Literature-based material properties were assigned. Outcomes were implant von Mises stress and cortical bone maximum and minimum principal stresses.

RESULTS

The lowest implant and bone stresses occurred in the anterior fixed-posterior clasp-retained design. Non-rigid connections (bar, locator, clasp) reduced implant stresses compared with precision attachments and fully implant-supported designs. Four-implant overdentures showed higher crestal stress than two-implant counterparts, likely due to greater framework rigidity and distal implant proximity to the load. Precision-attachment hybrid and All-on-Four configurations generated higher stresses at the implant neck and crestal cortical bone. Oblique loading produced higher stresses than vertical across all models.

CONCLUSION

Within the limits of an idealized, fully osseointegrated FEA, the anterior fixed-posterior clasp-retained prosthesis provided the most favorable stress distribution, supporting consideration of cost-effective, tissue-supported, non-rigid designs for selected mandibular edentulous cases. Increasing implant number did not uniformly reduce stresses; design rigidity and implant position were more influential than implant count. Clinical studies are warranted to validate these simulations.