Life's Little Mysteries

Why are teeth not considered bones?

Teeth and bones are both hard, white and heavy with calcium, but that doesn't make them one and the same. From the way they look to how they heal, teeth are quite different from the body's bones.

Teeth are composed of calcium, phosphorus, and other minerals. Bones contain calcium, phosphorus, sodium and other minerals, but mostly consist of the protein collagen. Collagen is a living, growing tissue that gives bones their a flexible framework that allows them to withstand pressure. Calcium fills in the space around that framework and makes the bone strong enough to support the body's weight.

But bones are still not as strong as teeth. The hardest part of the human body , teeth mostly consist of a calcified tissue called dentine. The tooth's dentine tissue is covered in enamel, that hard, shiny layer that you brush.

Related: Do hair and nails keep growing after a person dies?

The exterior of bones consists of periosteum, a dense, smooth, slippery membrane that lines the outer surface of most bones, except at the joints of long bones, which instead consist of slimy hyaline cartilage. Periosteum contains osteoblasts, or cells that can manufacture new bone growth and repair.

Tooth enamel, unfortunately, doesn't have the same regenerative powers. Unlike bones, teeth cannot heal themselves or grow back together if they are broken. When a bone fractures , new bone cells rush in to fill the gap and repair the break, but a cracked or a broken tooth can require a root canal or even total extraction.

Another difference between teeth and bones is that bone marrow produces red and white blood cells, while teeth do not. Bones receive their blood supply from a number of arteries that pass through the bone's periosteum to the inner bone marrow.

Although the bloody core of a tooth that's been knocked out might look like marrow, it's actually something called the dental pulp, the living portion of each tooth that contains nerves, arteries and veins and runs through to the jaw bone. These nerves are what cause us to feel toothaches caused by cavities or experience pain when eating something hot or cold.

One last difference is that our teeth are bare and on display, while bones are safety tucked away under our skin. So while you may occasionally use whitening strips to keep your pearly whites looking, um, white, at least you don't have to worry about your bones yellowing.

Originally published on Live Science.

Remy Melina was a staff writer for Live Science from 2010 to 2012. She holds a bachelor’s degree in Communication from Hofstra University where she graduated with honors.