Orthognathic surgery biomechanics revisited: Simple machine concepts, force distribution, and surgical predictability

Orthognathic surgery outcomes are fundamentally governed by biomechanical principles derived from classical physics. Despite their critical importance, these determinants of long-term stability remain understudied. This review synthesizes key biomechanical principles to clarify their role in orthognathic procedures. A narrative evidence synthesis methodology was employed, searching databases for relevant studies up to July 2025. Inclusion criteria encompassed clinical trials, biomechanical analyses, and reviews. Data were qualitatively analyzed and appraised. The synthesis identified lever systems, inclined plane mechanics, and screw fixation biomechanics as pivotal. Deviations in cephalometric landmarks correlate with increased relapse risk due to altered torque dynamics. Key trends indicate that L-pattern fixation and perpendicular screw insertion are associated with superior stability, while condylar malposition is a consistent risk factor. Crucially, temporomandibular joint health is paramount, especially when planning complex movements like counterclockwise rotation. Stability requires restoring biomechanical equilibrium, where lever mechanics dominate masticatory function. Planning must therefore account for force distribution, with virtual surgical simulations offering a powerful tool to predict and mitigate instability. Ultimately, integrating these biomechanical principles into surgical planning is essential for achieving stable, functional, and predictable long-term outcomes.