American Board of Orthodontics (ABO) Practice Exam

Prostaglandin E2 (PGE) plays a critical role in bone metabolism, particularly in the differentiation and activity of osteoblasts. It has been shown to modulate the expression of Receptor Activator of Nuclear factor Kappa-Β Ligand (RANKL) and Osteoprotegerin (OPG) in osteoblast cells.

When PGE is present, it typically leads to an increase in the levels of RANKL. RANKL is essential for the formation, activation, and survival of osteoclasts, the cells responsible for bone resorption. An elevated RANKL-to-OPG ratio promotes osteoclastogenesis, which can lead to increased bone turnover and potential bone loss if not balanced by OPG.

On the other hand, PGE also tends to decrease OPG production in osteoblasts. OPG, which is produced by osteoblasts, acts as a decoy receptor for RANKL, binding to it and preventing RANKL from interacting with its receptor on osteoclast precursors. A decrease in OPG allows RANKL to have a more pronounced effect, further enhancing osteoclast activity.

Therefore, the combination of increased RANKL and decreased OPG due