Abstract
This study evaluated the influence of distal implants angulation and framework material in the stress concentration of an All-on-4 full-arch prosthesis. A full-arch implant-supported prosthesis 3D model was created with different distal implant angulations and cantilever arms (30° with 10-mm cantilever; 45° with 10-mm cantilever and 45° with 6-mm cantilever) and framework materials (Cobalt–chrome [CoCr alloy], Yttria-stabilized tetragonal zirconia polycrystal [Y-TZP] and polyetheretherketone [PEEK]). Each solid was imported to computer-aided engineering software, and tetrahedral elements formed the mesh. Material properties were assigned to each solid with isotropic and homogeneous behavior. The contacts were considered bonded. A vertical load of 200 N was applied in the distal region of the cantilever arm, and stress was evaluated in Von Misses (σVM) for prosthesis components and the Maximum (σMAX) and Minimum (σMIN) Principal Stresses for the bone. Distal implants angled in 45° with a 10-mm cantilever arm showed the highest stress concentration for all structures with higher stress magnitudes when the PEEK framework was considered. However, distal implants angled in 45° with a 6-mm cantilever arm showed promising mechanical responses with the lowest stress peaks. For the All-on-4 concept, a 45° distal implants angulation is only beneficial if it is possible to reduce the cantilever’s length; otherwise, the use of 30° should be considered. Comparing with PEEK, the YTZP and CoCr concentrated stress in the framework structure, reducing the stress in the prosthetic screw.
Highlights
The opposite was observed for the prosthetic screw (Figures 4 and 5) and implants (Figures 6 and 7): The lower the framework elastic modulus, the higher the stress concentration
Regardless the framework material and design, the highest stress concentration was calculated in the first thread for the prosthetic screw in the mesial implants
The present study evaluated the stress distribution in All-on-4 prosthesis regarding framework material and posterior implant angulation
Summary
The process of bone resorption due to physiological and pathological factors [3] complicates planning for the installation of posterior implants as a prosthetic support [4,5]. Two mesial implants are usually placed perpendicular to the bone crest, and two distal implants are installed inclined, reducing the distal cantilever and allowing replacement of more teeth [7,8,9,10,11]. During the distal implant installation, different angulation can be used according to surgical planning. The literature is not concise regarding the benefits of 30◦ and 45◦ angulation for reducing stress concentration [16,17]. It is important to note that the surgeon inserted inclined distal implants to reduce the cantilever length, and this variable should be considered when analyzing prosthetic modality
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