Teeth are important to us; they enable us to chew our food and break it down for digestion. We get two sets of teeth: the first set are deciduous teeth, commonly known as baby teeth, while our second set are permanent teeth, or adult teeth. Typically, most of us start to lose our baby teeth up to age 12, and finish growing our adult teeth by age 25, but why are some adults still waiting for their permanent teeth to set in?

In the D News video, "Why Do We Have Baby Teeth?" host Trace Dominguez explains we start out with a set of 20 baby teeth because baby mouths can't fit a full set of 32 adult teeth. We are born with these teeth already developed inside our jaw, which begin to poke out through the gums at around 6 months to 2 years. Baby teeth forge a space in our gums for adult teeth to grow in later.

Read More: 6 Dental Hygiene Myths To Sink Your Teeth Into

As we develop, our mouths grow bigger and eventually become too big for our 20 baby teeth. If we were to keep our initial set of teeth, they would be tiny in our adult mouths, and have huge spaces between them, making chewing close to impossible. When they start to fall out by age six, our adult teeth emerge.

But, what happens when some permanent teeth don’t grow?

Some children will experience a delayed eruption of adult teeth, known as over-retained. This means the baby tooth could be fused to the bone (ankylosis), or the adult tooth is absent, which would normally push on the root of the baby tooth. This occurs about 2.5 to 6.9 percent of the time. It also happens more in females than in males.

Other reasons for over-retained baby teeth are pathology, obstructions, misalignment of the permanent tooth underneath, trauma, infection and late eruption of the adult teeth.

If adult teeth don’t develop, the baby tooth’s roots don’t dissolve. Therefore, if we’re missing a permanent tooth, it’s likely the baby tooth is going to stay, lasting a person’s lifetime. This is known as hypodontia.

Those still with baby teeth shouldn’t worry as long as they’re under the care of a dentist. However, a 2008 study in the Journal of the American Dental Association has found hypodontia may be a risk marker for epithelial ovarian cancer. Adults should stay vigilant on their baby teeth and regularly visit the dentist.