The roots of the teeth can resorb (dissolve) away when the remodelling cells (called osteoclasts) in the jaw bone attack them. This does not normally happen in healthy teeth. However, if a tooth were to suffer a severe knock (e.g. from a fall or a punch), the tooth can get displaced from its bony socket in the jaw. This displacement ruptures the periodontal ligament that connects the tooth root to the jaw bone and causes cell death. Without an intervening layer of periodontal ligament that separates the root from the bone, the osteoclasts (which are remodelling cells) from the bone then starts resorbing the root. This results in shorter roots.