Remodeling of Mineralized Tissues, Part I: The Frost Legacy

Remodeling is the physiologic term for internal turnover of a mineralized tissue, without a change in its overall form. It is a coupled sequence of catabolic (resorptive) and anabolic (osteogenic) events to support calcium homeostasis and repair (renew) aged or damaged mineralized tissue. Histological studies indicate that both bones and teeth remodel. Remodeling mechanisms are involved in growth, functional loading, tooth movement, root resorption, and the systemic health of patients. Cortical bone remodeling is via cutting/filling cones, also referred to as bone multicellular units (BMUs). Trabecular bone remodeling is accomplished by hemicutting/filling cones (surface resorption cavities that fill with new bone), also termed a bone multicellular unit (BMU). Histologic studies in multiple species have demonstrated that root resorption cavities are usually repaired (filled) with secondary cementum. In effect, this is “remodeling” of the root of a tooth. The evolution of bone remodeling concepts, as originally defined by Harold Frost, are important for understanding craniofacial growth and the skeletal adaptation associated with orthodontics and dentofacial orthopedics.