Which statement best describes the RANKL/OPG axis in periodontal bone loss?

• A. OPG stimulates osteoclast formation.
• B. RANKL stimulates osteoclast formation leading to bone resorption; OPG is a decoy receptor; dysregulation promotes periodontitis-related bone loss.
• C. RANKL inhibits osteoclast formation.
• D. OPG is a cytokine that directly kills osteoclasts.

Answer: (B)

The RANKL/OPG balance governs how many osteoclasts form and how active they are, which in turn controls alveolar bone resorption. RANKL, produced by osteoblasts and some immune cells, binds to RANK on osteoclast precursors to trigger signaling that drives their differentiation and survival, leading to bone breakdown. OPG acts as a decoy receptor that binds RANKL, preventing it from activating RANK and thus inhibiting osteoclast formation. The overall outcome depends on the RANKL/OPG ratio; when RANKL activity increases relative to OPG, osteoclast activity rises and bone resorption accelerates. In periodontitis, inflammatory mediators upregulate RANKL and downregulate OPG, promoting alveolar bone loss. Therefore, the best description is that RANKL stimulates osteoclast formation leading to bone resorption; OPG is a decoy receptor; dysregulation promotes periodontitis-related bone loss.