American Board of Orthodontics (ABO) Practice Exam

In the context of orthodontic tooth movement, when a compressive force is applied, there are immediate biological responses that occur in the periodontal ligament and surrounding tissues. One of the key molecules that is observed in gingival crevicular fluid 24 hours after the initiation of compressive force is RANKL (Receptor Activator of Nuclear factor Kappa-Β Ligand).

RANKL plays a crucial role in the regulation of osteoclastogenesis, which is vital for bone remodeling. When a compressive force is applied, increased levels of RANKL promote the differentiation and activation of osteoclasts, the cells responsible for bone resorption. This response is critical in the orthodontic process, as the removal of bone in the areas under pressure allows for tooth movement in the desired direction.

While other factors such as OPG (Osteoprotegerin), IL-1 (Interleukin-1), and TGF-beta (Transforming Growth Factor Beta) are involved in the inflammatory and healing processes associated with orthodontic treatment, RANKL is particularly notable for its rise within the early time frame following the application of compressive forces, marking it as a significant mediator of the osteoclast activity necessary for tooth movement.