It is not static as many lay persons think. It changes continuously. Use, disuse, and overuse each affect bone density and mineralization. Osteoclasts are cells that bone. After a fracture or other bone injury they are the cells that are active first.
Osteoblasts are the cells that create new bone.
In normal bone, there is a close relationship and balance between bone resorption and formation. Mechanical forces, hormones, and other factors that influence local regulatory systems have an impact on bone remodeling. The NRC reports that studies indicate a daily requirement of about 1,000 mg of calcium for premenopausal and estrogen-treated women. Postmenopausal women who are not treated with estrogen may require about 1,500 mg daily for calcium balance. Therefore, the RDA for calcium has been thought to be too low.