TL and BL three-dimensional computer-aided design (CAD) implant models were created using the CAD function in computer-aided engineering software (SolidWorks 2014, Dassault Systèmes SolidWorks Corporation, MA, USA), and they were created with reference to conical connection implant used clinically. The connection part of superstructure has a tapered 15° conical shape without any special locking mechanism. The length of each part is as shown in Fig. 1. The diameter of the implant bodies was 4.1 mm. The lengths of the TL models were 10.0 mm, 8.0 mm, 6.0 mm, and 4.0 mm; the lengths of the BL models were 10.0 mm, 8.0 mm, and 6.0 mm (Fig. 2). A CAD model of mandibular molar alveolar bone with 2.0-mm-wide cortical bone was prepared, in which each implant CAD model was embedded. The implant and superstructure were connected with an abutment screw. The distance from the occlusal plane to the apex of the implant was 20.0 mm in any given model; that is, the crown–implant ratio increased with decreasing implant body length. To simulate osseointegration, a “fixed bond” condition was set at the implant body–bone interface. A “contact” condition with friction coefficient 0.3 was set at the interface between the implant components, which facilitated microscopic sliding. The mesial and distal sides of the mandibular alveolar bone were fixed. A static load of 100 N was applied obliquely from the buccal side to the occlusal plane of the superstructure at 30° to the long axis of the implant (Fig. 3) [18]. The mechanical properties of the components used in this research study are shown in Table 1, and the implant body used a value obtained by performing a compression test in advance. Tetrahedral elements were used for the FEA, and the number of elements was determined by conducting a convergence test based on the maximum principal stress. The distribution and the maximum von Mises stress value were measured in the implant body, and the distribution and largest maximum principal stress value were measured in the cortical bone.