CRSP-1

Osteoclast differentiation is an in vitro induction assay in which monocyte/macrophage-lineage precursors are exposed to macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL), generating multinucleated osteoclasts that are commonly identified by tartrate-resistant acid phosphatase (TRAP) staining and functionally confirmed by resorption pits on dentin, bone, or mineralized substrates. M-CSF supports survival and expansion of osteoclast precursors, while RANKL binding to RANK drives osteoclast commitment, fusion, maturation, and resorptive function; osteoprotegerin inhibits this pathway by binding RANKL and preventing RANK activation. The main readouts are the number of TRAP-positive multinucleated cells, formation of F-actin rings, and resorbed surface area; TRAP-positive multinucleated cells indicate osteoclast differentiation, whereas pit formation on dentin, bone, or mineralized coating indicates functional bone-resorbing activity.