Mechanical Stress Analysis of Different Configurations of the All-on-4 Concept in Atrophic Mandible: A 3D Finite Element Study

Purpose: This study evaluated the mechanical behavior of different configurations of the All-on-4 treatment concept designed with straight short (6-mm-length), straight standard (11-mm-length), or tilted standard (30-degree angled; 11-mm-length) posterior implants.
Materials and Methods: The All-on-4 configurations were performed in atrophic mandible models and consisted of anterior straight standard and posterior tilted standard implants (H1 model), anterior straight standard and posterior straight short implants (H2 model), and anterior and posterior straight standard implants (H3 model). Three oblique forces of 100 N were simulated in the posterior region of the prosthetic bar. The values of stress were obtained for the ductile materials using the von Mises equivalent stress (σvm) criteria. The stress peaks in the periimplant bone crest were measured by the maximum (σmax) and minimum (σmin) principal stresses. The two-way analysis of variance (two-way ANOVA) and Tukey post hoc tests determined significant differences (P < .01) of stress values among the ductile materials (implant and prosthetic components).
Results: The use of tilted standard posterior implants (H1 model) showed the lowest values of σmax and σmin in the posterior region of the peri-implant bone area. On the other hand, the use of straight short (H2 model) or straight standard (H3 model) posterior implants significantly reduced the von Mises mean stresses in the bar screws, abutments, and abutment screws (P < .01).
Conclusion: The higher odds of technical failures (screw fracture/loosening) may be expected when the All-on-4 configuration is performed with tilted standard posterior implants. Also, peri-implant bone overload may occur when the All-on-4 design is performed with straight short or straight standard posterior implants in atrophic mandibles.