## 4 Discussion
Since bone loss around the implant reduces the contact area between the implant and bone, thereby reducing the load-bearing area and effectively increasing the lever arm length of the implant fixture, the stress increase was found to accelerate when marginal bone loss began [9]. This trend was more pronounced in patients with low-quality bone. Low-quality bone has a relatively limited ability to disperse load, leading to an increased bone stress concentration around the implant and significantly impacting its initial stability. In low-quality bone, a high stress concentration occurs even when initial bone loss occurs, so the resulting stress concentration increases the structural burden on the implant and surrounding tissues. In an environment where low-quality bone exists, the stress distribution around the implant is formed unfavorably, which promotes microdamage and fatigue destruction of bone tissue [49]. These results have important clinical implications in osteoporotic patients with low bone quality, supporting the importance of a treatment approach that minimizes marginal bone loss during implant placement in patients with low-quality bone, as discussed in previous studies [30]. When planning implants for patients with osteoporosis, several important clinical considerations are necessary [50; 51; 52; 53]. An accurate assessment of the patient's bone quality is necessary to establish a customized treatment plan that matches the characteristics of the bone. In the prosthesis design stage, designing to minimize stress concentration around the implant is important. The structural burden can be reduced by utilizing a multi-implant system or distributing the load evenly through an occlusal adjustment. It is also an effective approach to improve the quality and quantity of bone by performing bone grafting or bone augmentation, if necessary. This can optimize the implant placement environment and improve initial stability. This study found conflicting results in the maximum von Mises stress and volume fraction of the fatigue failure area of cortical and cancellous bone. These differences may be due to the difference in elastic modulus between cortical and cancellous bone, implying that bone type responds to stress differently [54]. Cortical bone has a relatively high elastic modulus, which provides great resistance to initial load and is essential for initial implant stability, especially because it plays a structural support role around the implant neck [33]. The results of this study showed that the maximum von Mises stress increased significantly when the initial bone loss of 1 mm occurred in cortical bone. This suggests that cortical bone increases initial stability by distributing the load around the implant and playing a supporting role. However, when the bone loss progressed to 3 mm or more, the supporting ability of cortical bone was rapidly lost, and the stress decreased significantly. This emphasizes that it is important to manage cortical bone loss so that it does not exceed a certain level clinically for long-term implant stability [55]. Conversely, cancellous bone has a lower elastic modulus than cortical bone, so it responds more flexibly to the initial load [56]. The cancellous bone acts as the main supporting structure after the support ability of cortical bone is lost. In this study, cancellous bone stress rapidly increased when bone loss progressed from 2 mm to 3 mm and then gradually increased as it progressed to 5 mm. In particular, in the initial bone loss section, the stress in the cortical bone was higher than that in the cancellous bone. However, as cortical bone loss worsened, the cancellous bone acted as the main supporting structure, and the stress increased. In the volume fraction of the fatigue failure area, the cortical bone did not show a fatigue failure area regardless of bone quality. In contrast, cancellous bone showed a pattern in which the fatigue failure area increased as bone loss increased in low-quality bone.