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How adjacent dental implants with different sizes, designs, and abutment connection shapes affect stress on the prosthetic structure is unclear. The purpose of this finite element analysis (FEA) study was to analyze stress distribution around bone and around 2 implants with different sizes, diameters, shapes, and loading directions placed next to each other in splinted and unsplinted prostheses. On 3D FEA models representing the posterior right lateral segment of the mandible, 1 implant (Ø3.5×12 mm) and 1 implant (Ø5.5×8 mm) were placed adjacent. Three different contemporary implant models were created with different teeth, pitch, spiral numbers, and self-taping features, and different abutments for them were modeled in 3D. The implant-abutment connection was internal hexagonal (MIH), stepped conical (MSC), and internal conical (MIC). Vertical and oblique loads of 365 N for molar teeth and of 200 N for premolar teeth were applied as boundary conditions to the cusp ridges and grooves in a nonlinear FEA. The MIH implants resulted in improved stress conditions. According to the von Mises stresses occurring on the screw, abutment, and implant, especially under oblique loads, MIH was exposed to less stress than MSC, and MSC was exposed to less stress than MIC. When a standard implant and a short implant were placed adjacent and splinted by crowns, the implants, abutments, and screws had unfavorable stress levels; therefore, adjacent splinted implants should be of similar size. The form of the implant-abutment junction is also an important factor affecting stress. [ABSTRACT FROM AUTHOR]

• A pioneering work on developing fixation plates with graded porosity produced by additive manufacturing. • An optimum geometric form for the fixation plate obtained by topological optimization based on the finite element analysis. • A functionally-graded porous structure is created for the optimum bulk plate model. • For maximum stiffness, a gradual change in density of the porous plate is required. Fixation plates are used to accelerate the biological healing process in the damaged area by providing mechanical stabilization for fractured bones. However, they may cause mechanical and biological complications such as aseptic loosening, stress shielding effect and necrosis during the treatment process. The aim of this study, therefore, was to reduce mechanical and biological complications observed in conventional plate models. For this purpose, an optimum plate geometry was obtained using the finite element based topology optimization approach. An optimum and functionally graded porous model were obtained for the plates used for transverse fractures of diaphysis in long bones. This model was combined with a functional graded porous cage structure, and thus a new generation porous implant model was proposed for fixation plates. In order to determine the performance of the optimum plate model, it was produced by additive manufacturing. Three models; i.e. conventional, optimum and porous fixation plates were statically tested, and they were compared experimentally and numerically using the finite element analysis (FEA). The porous model can be considered as the most suitable option since it requires less invasive inputs, and might lead minimum necrosis formation due to having lesser contact surface with the bone. [ABSTRACT FROM AUTHOR]