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The type of implant-abutment connection is one of the factors influencing the distribution of occlusal forces. This study aims to investigate the biomechanical performance of the mandibular all-on-4 treatment with different implant–abutment connections. Two connection types with 30° abutments and 18-mm implant fixtures were chosen for the posterior implants of the all-on-4 assembly. For the external hexagon connection (EHC) group, the implants with 4 mm in diameter were used. For the internal hexagon connection (IHC) group, we selected implants with 4.3 mm in diameter. A vertical force of 190 N was applied to the cantilever region. The FEA results indicated that the most stressed region in the two groups was prosthetic screws, followed by multi-unit abutments (MUAs). The lowest values of von Mises stress were both observed on the bone. The peak stress value of the implant screw and implant fixture in the EHC group were 37.75% and 33.03% lower than the IHC group, respectively. For stress distribution patterns, the load force tended to be concentrated at locations where components were interconnected. The EHC and IHC are clinically durable under the tested loading conditions, but the prosthetic screws and MUAs can be the weak point on the posterior implant within the mandibular all-on-four assembly. The peak stress values of implant screw and implant fixture in the EHC groups were lower than the IHC group.

In recent years, orthodontic treatments have become increasingly popular. In these treatments, orthodontic forces, which cause the absorption and deposition of alveolar bone, are applied through brackets and teeth in order to move the teeth to the expected position. The periodontal ligament (PDL) has a determinative role in dental biomechanics; however, the difficulty of predicting PDL behavior has limited the advancement of dental biomechanics. Therefore, this study intends to measure the biomechanical behavior of the PDL and then develop an analytical model to predict the holistic force-displacement relationship of the tooth. In this study, a porcine premolar, including the tooth, periodontal ligament, and alveolar bone, was harvested for experimental purposes. A custom-made apparatus was designed to measure the force-displacement relationship of the PDL. Three analytical models, including linear, exponential, and power functions, were adapted to fit the experimental results. In addition, three-dimensional finite element models were constructed from micro-CT sectional images, and the hyperelastic behavior (Mooney-Rilvin equation) of the PDL was simulated. The results showed that the PDL exhibited nonlinear biomechanical behavior. The power function was found to be a good fit for the force-displacement relationship of the PDL. Furthermore, it was found that the hyperelastic model could predict the biomechanical behavior of the PDL for tension less and equal to 20 N.

Background: The biomechanical property of the periodontal ligament (PDL) is important in orthodontics and prosthodontics. The objective of this study was to evaluate the feasibility of measuring the biomechanical behavior of the periodontal ligament using micro-computed tomography (micro-CT). Methods: A custom-made apparatus measured the force and displacement of a porcine PDL specimen within the micro-CT environment. Synchronized computed tomography (CT) images were used to obtain the deformation and displacement of the entire specimen and to reconstruct the three-dimensional mesh model. To match the experimental results, finite element analysis was then applied to simulate the biomechanical response of the PDL. The mechanical model of the PDL was assumed as the hyperelastic material in this study. Results: The volume variations of the tooth and the alveolar bone were less than 1%, which implies that tooth displacement was caused mostly by displacement of the PDL. Only translational displacement was observed with each load step because the transformation matrix acquired from the CT image registration was identical. The force-displacement curve revealed the nonlinear behavior of the PDL. There was a high correlation between the experimental displacement results and the simulation displacement results. The numerical results (based on the assumption that the PDL is the hyperelastic material) showed good agreement with the experimental results. Conclusions: Nondestructive measurements by micro-CT obtained the biomechanical behavior of the PDL. Using the hyperelastic characteristic as the constitutive model can properly predict the force-displacement relation of the PDL after loading. This study provided a feasible approach for measuring the biomechanical behavior of the PDL for further dental application. [ABSTRACT FROM AUTHOR]