Evaluation and Comparison of Stresses Between All-on-4 and All-on-6 Treatment Concepts With Three Different...

This study aimed to evaluate the comparative analysis of stresses on and around implants and surrounding cortical bone using three different prosthetic materials in hybrid prosthesis using the all-on-4 technique and all-on-6 technique in the maxilla using finite element analysis (FEA).

An in vitro FEA study was conducted where a three-dimensional (3D) model of an edentulous maxilla and four different models of the mandible were built using ANSYS software version 18 (Ansys, Inc., Canonsburg, Pennsylvania, United States). Group A comprised the all-on-4 technique where two vertical implants were placed in the lateral incisor area, and two tilted implants at 30^o were placed in the second premolar area, whereas group B included the all-on-6 technique, where four vertical implants were placed in the central incisor and canine area, along with two tilted implants in second premolar area. Subsequently, prosthetic materials such as acrylic, porcelain fused to metal (PFM), and zirconia were studied. Four different opposing arch materials were made: natural teeth (A1 and B1), complete dentures (A2 and B2), implant-supported overdentures (A3 and B3), and hybrid prosthesis (A4 and B4). The von Mises stresses were recorded at the implant and cortical bone to summarize the effect of occlusal loads on the maxillary bone using the all-on-4 and all-on-6 techniques.

In the all-on-4 technique, on evaluating stresses on implants, it was revealed that acrylic consistently demonstrated lower stress magnitudes in comparison to zirconia and PFM. The stress levels escalate from 38.72 MPa in model A1 to 72.43 MPa in model A4. Zirconia endured the most substantial stresses, ranging from 53.64 MPa (A1) to 84.87 MPa (A4). Similar results were obtained for the stresses on the cortical bone and for the all-on-6 technique. However, the stresses were lower in the all-on-6 technique than in the all-on-4 technique. The lowest stress values across all prosthetic materials were recorded when the maxillary arch was restored with acrylic teeth along with a titanium bar opposing natural dentition.

The least stresses were noticed in the all-on-6 technique with acrylic prosthetic material opposing the natural dentition. As the all-on-6 treatment concept showed the most favorable biomechanical behavior, it can be considered a viable alternative for moderate atrophic maxillary rehabilitation.