Comparison of the Rehabilitation of Posterior Atrophic Edentulous Mandible with Different Interforaminal Implant Placement Concepts: A 3D Finite Element Analysis

Aim The study aims to compare the rehabilitation of the posterior atrophic edentulous mandible with different interforaminal implant placement concepts to apply an implant-supported fixed prosthesis, without needing any bone grafting procedure.
Material and methods Six models were created in a digital environment. Three, four, and five implants were vertically placed in different models; the Nobel Trefoil concept, the Allon- 3, and the All-on-4 concepts were also simulated. In the Trefoil model, implants specific to this concept were used. In all models, the prosthetic emergence of posterior implants was simulated at the same point. Screw-retained fixed prostheses were placed on the implants. A spherical foodstuff force was applied to imitate the chewing forces from the canine and molar regions. The three-dimensional finite element method analyzed the stresses on bones, implants, and prosthetic structures.
Results The most balanced stress distribution was seen in the Trefoil concept, while the worst stresses were observed in the All-on-3. The stress obtained in the models with four and five vertical implants was very close. Increasing the number of implants slightly affected stress, however, reducing the number to three, significantly increased the stress. Inclined placement of the same number of implants increased stresses on bone.
Conclusions With its unique implants, the trefoil concept emerged as the optimal treatment option for fixed prosthetic restoration in the interforaminal area. The best option among the models with standard diameter implants is four vertical implants. Inclined placement of posterior implants did not reduce stresses. On the contrary, it increased stresses, unless the emergence profile was moved posteriorly or the implant lengths were increased.