Minimum number of implants for restoring maxillary edentulous situations

Objectives: Compare to the edentulous mandible, the edentulous maxilla requires careful site evaluation for the implant placement due to the lower bone density and anatomical limitations such as sinus. The purpose of this study was to determine the minimum number and suitable location of implants to establish stable occlusal support for the maxillary edentulous patients.

Methods:3DCT data including bone density of a dry skull was transferred to construct 3D finite element model using a special soft wear (Mechanical Finder, RCCM Co., Japan). Validation of the 3D model was performed by the comparison between the calculated stress values and actual strain gauge measurements on the bone surface under the same loading conditions. Titanium implants were also simulated in the configuration of 14 independent implants throughout residual arch (M1), 14 connected implants (M2), 6 implants (canine and premolar regions) (M3), and 4 implants (all-on 4 configuration) (M4). Distributed loads of 200N were applied on the occlusal table of superstructures.

Results: Maximum equivalent stress level in the bone for the each model was 9.22 MPa in M1, 11.4 MPa in M2, 14.3 MPa in M3, and 28.4 MPa in M4. Each value was smaller than the reported threshold stress value for bone resorption (50 MPa, Sugiura, 2000). High magnitude of stress was concentrated in implants of premolar area regardless of model configuration.

Conclusions: Our results suggested that M4 configuration could establish stable occlusal support under normal physiological loading conditions, however it may cause overloading under large non-functional loadings.