Osteoblasts, Osteoclasts, and Osteocytes: Unveiling Their Intimate-Associated Responses to Applied Orthodontic Forces

Bone is remodeled and modeled by the concerted activities of 3 cell types—osteoblasts, osteocytes, and osteoclasts. Osteoblasts are the cells that produce bone extracellular matrix and are responsible for its mineralization. Osteoblasts also have endocrine activity through secretion of osteocalcin, which regulates fat and energy metabolism. These cells also control the differentiation and activity of osteoclasts. Osteocytes are osteoblasts that have been incorporated into bone matrix and are cells with extensive dendritic processes through which the cells communicate with other osteocytes and with osteoblasts. Mechanical loading is sensitized by the dendritic processes and transferred to biochemical responses involved in control of osteoblast and osteoclast function. Osteocytes also have endocrine activity by releasing fibroblast growth factor 23, which is involved in phosphate secretion in kidneys. Differentiation of osteoclast mononuclear progenitors to mature multinucleated osteoclasts is regulated by macrophage colony-stimulating factor and receptor activator of NF-κB ligand, expressed by stromal cells in bone marrow or osteoblasts in bone, as well as by osteocytes. The integrated endo- and paracrine control of osteoblasts, osteocytes, and osteoclasts is important for maintaining bone mass and for control of remodeling and modeling processes in bone, including during orthodontic-induced tooth movement.