The osteoblast then deposits calcium phosphate which is hardened by hydroxide and bicarbonate ions. The brand new bone created by the osteoblast is called osteoid.[15] Once the osteoblast is finished working it is actually trapped inside the bone once it hardens. When the osteoblast becomes trapped, it becomes known as an osteocyte.[16] Other osteoblasts remain on the top of the new bone and are used to protect the underlying bone, these become known as lining cells.