This study used numerical simulations to evaluate how trabecular bone responds to orthodontic forces of 0.6, 1.2, and 2.4 N applied through five movement types—intrusion, extrusion, tipping, rotation, and translation—during progressive horizontal periodontal loss of 0–8 mm. Stress distribution, as well as ischemic and resorptive risks, were analyzed using the Tresca and Von Mises failure criteria. A total of 405 simulations were performed on 81 models derived from nine patients. Both criteria produced similar stress patterns qualitatively, while Tresca values were 1.09–1.21 times higher than Von Mises quantitatively. No qualitative differences were observed between the three force magnitudes, though a twofold increase was noted at 1.2 N and a fourfold increase at 2.4 N relative to 0.6 N. Among the movements, rotation and translation generated the greatest stresses, followed by tipping, particularly in cases of reduced periodontium where ischemic and resorptive risks were more pronounced. Forces of 1.2 N appeared safe in intact periodontium, but for reduced periodontium, only extrusion and intrusion could tolerate this level without elevated risk. Loads exceeding 0.6 N for the other movements increased ischemic and resorptive potential. In intact periodontium, stress was distributed throughout the trabecular structure, while in reduced periodontium, stress concentrated near the cervical third of the alveolar socket once bone loss reached 4 mm, indicating a clear shift in stress distribution.
