American Board of Orthodontics (ABO) Practice Exam

Osteoprotegerin (OPG) primarily functions as a decoy receptor for RANKL (Receptor Activator of Nuclear factor Kappa-Β Ligand), which is critical in the regulation of bone remodeling. By inhibiting the binding of RANKL to its receptor RANK on osteoclast precursors, OPG plays a pivotal role in preventing the differentiation and activation of osteoclasts. This action reduces bone resorption, thus maintaining bone density and strength.

The ability of OPG to block this interaction is essential for balancing bone formation and resorption; it helps to ensure that osteoclast activity does not surpass that of osteoblast-mediated bone formation. This modulation is particularly important in preventing conditions such as osteoporosis, where excessive bone loss occurs.

In contrast, other functions such as stimulating osteoclast differentiation, promoting bone formation, or increasing osteoblast proliferation do not accurately reflect OPG's role in bone physiology and imply mechanisms that are not part of OPG's primary function.