Posterior implant tilt as an alternative to sinus elevation in full-arch maxillary rehabilitation: A comparative finite element analysis.

INTRODUCTION: This finite element analysis study aimed to compare the stress distributions in cortical and trabecular bone, implants, abutments, and prosthetic components under anterior and posterior loading in three different implant configurations, including maxillary sinus grafting, in a completely edentulous and posteriorly atrophic maxilla. The study specifically focused on identifying the differences between a prosthetic design with a distal cantilever after maxillary sinus lift (Model 3) and configurations without a cantilever, featuring posteriorly angled implants with different exit points (Models 1 and 2).

MATERIALS & METHODS: An atrophic maxillary model was reconstructed from computed tomography images obtained from a publicly available online database. Each study model utilized six Straumann BL Roxolid implants, with a screw-retained cobalt-chromium alloy prosthetic substructure. In each model, the implants were placed vertically anterior to the maxillary sinus; Model 1 featured a distally angled implant with its exit point at the second molar, Model 2 included a tuberoid implant connected to the prosthetic substructure with a distal extension, and Model 3 featured an axial implant placed at the level of the first molar after sinus grafting. All models were subjected to a foodstuff-style force of 100 N in the anterior and posterior regions. Maximum principal stress (σ_max), minimum principal stress (σ_min), and von Mises stress were recorded in the implant, periimplant bone, and prosthetic components.

RESULTS: Under anterior loading, Model 3 produced the highest peak stresses in the framework (33.218 MPa), implant (15.444 MPa), abutment (21.247 MPa), and cortical bone (maximum principal stress, 3.874 MPa; minimum principal stress, -4.017 MPa). Under molar loading, Model 3 produced the highest framework, implant, and abutment stresses (54.844, 33.259, and 49.019 MPa, respectively) but lower posterior cortical stresses (maximum principal stress, 3.319 MPa; minimum principal stress, -6.453 MPa) than Model 1 (6.524 and -13.243 MPa) and Model 2 (7.641 and -13.327 MPa).

DISCUSSION: No configuration minimized stress in every structure. The graftless configurations reduced selected prosthetic stresses but transferred greater demand to posterior cortical bone, whereas the sinus-grafted configuration reduced posterior cortical stress while increasing mechanical demand in the cantilevered prosthetic complex. Treatment planning should therefore consider the distribution of biomechanical demand across the entire bone-implant-prosthesis system rather than a single peak value.