Teeth begin to form in the womb just six weeks after conception, appearing as small buds in the tissue that eventually become the gums. Between the third and fourth month of pregnancy, the main parts of a tooth begin to form:

By birth, 20 baby teeth (also called deciduous teeth) are in place below the gumline, and even some permanent teeth have begun forming in the jawbone.

Baby teeth usually don’t start emerging, or erupting, from the gums until babies are about 6 to 12 months old, but this timeline can vary significantly. 

Baby teeth stay in place for five to seven years, when they begin to fall out to make room for the permanent (adult) teeth. In some rare cases, though, permanent teeth may not appear, and baby teeth can remain for many years. This is called retained deciduous teeth.

Why do baby teeth fall out? Baby teeth serve as placeholders for the permanent teeth waiting and developing below. The rising permanent teeth dissolve the baby teeth’s roots, which are reabsorbed into the gums. Without roots to secure them, baby teeth become unstable, loosen and fall out.

As baby teeth fall out, the permanent teeth below them begin take their place. The first baby teeth fall out around the age of 6. As the jaw grows, more permanent teeth come in, with wisdom teeth emerging between the ages of 17 and 25, if at all.

When permanent teeth come in, these newcomers have a distinct look. They may have bumpy edges, called mamelons. These rough edges eventually wear off. Permanent teeth may also have more of a yellow shade than baby teeth. This is because permanent teeth contain more dentin, which is the pale-yellow tissue below the surface of the tooth.

The last four teeth to arrive, wisdom teeth, begin developing within the jawbone during childhood. This process starts happening under the gums around age 7 to 10. After the crown of the wisdom tooth begins to form, it grows roots, and eventually the tooth pushes through the gums in late adolescence or early adulthood.

In many cases, wisdom teeth (also known as third molars) are removed before they erupt or before they can develop to their full size. When wisdom teeth aren’t removed, the roots can continue growing for years into adulthood..

As a tooth ages, a lifetime of wear and tear takes its toll on its surface, called the enamel. Small hairline cracks in the enamel of the teeth, called craze lines, may appear as the tooth ages. Decades of chewing food and grinding teeth due to stress can also flatten the edges of teeth.

The older a tooth, the more susceptible it becomes to cavities and gum disease. Nerve endings may grow shorter with age, making the tooth less sensitive to pain. Without pain signaling a problem, a small cavity can easily grow unnoticed into a large one. The gumline may recede, which exposes more of the tooth’s enamel. Other changes in the mouth, such a decrease in saliva, can encourage the growth of bacteria and increase the chance of periodontal (gum) disease and tooth decay.