Why We Have Baby Teeth and Then Adult Teeth — The Science Behind Two Sets

Why do people have two sets of teeth?

Short answer: Humans develop two sets of teeth because our jaws grow as we grow. Small baby (deciduous) teeth fit an infant’s mouth, then larger permanent teeth erupt as the face and jaws expand so we can chew effectively as adults.

Teeth and their jobs

Teeth help animals bite, chew and manipulate food. Different diets shape different teeth: carnivores have sharp teeth for tearing meat, while herbivores have flatter teeth for grinding plants. Some animals use teeth for other tasks—elephant tusks and walrus tusks are modified teeth that continue to grow throughout life.

How other animals handle tooth wear

All teeth wear down over time. Some animals, like rodents (beavers and rats), have teeth that grow continuously and rely on gnawing to keep them at useful lengths. Sharks and crocodiles are polyphyodont, meaning they repeatedly replace teeth throughout life.

Humans are diphyodont

Humans (like most mammals) are diphyodont: we develop two sets of teeth. The first set—called deciduous or baby teeth—begins forming before birth and usually erupts between about 6 and 8 months of age. Permanent (adult) teeth form beneath the baby teeth and often appear on X-rays long before they erupt.

Timing and numbers

Children typically lose their first baby teeth around age 5 or 6. The process continues until about ages 10–12, when most people have lost all 20 primary teeth. The adult dentition normally includes 28 teeth, with up to four additional wisdom teeth bringing the total to 32 in some people. Many people either never develop wisdom teeth or need them removed if they cause crowding.

Why two sets make sense

Baby teeth are smaller because they must fit an infant’s smaller jaw. As the face grows, larger permanent teeth are necessary for the increased chewing demands of an adult diet. Having two sets of teeth matches tooth size to jaw size at different life stages and helps maintain proper tooth alignment during growth.

Why baby teeth matter

Even though baby teeth fall out, they’re important. They hold space for permanent teeth and guide them into position. If a baby tooth is lost too early because of decay or infection, neighboring teeth can drift into the empty space. This can cause crowding or cause the permanent tooth to become impacted, which often requires orthodontic treatment.

Teeth don’t heal like bone

Teeth are made mainly of mineral (primarily hydroxyapatite) and don’t regenerate the way bone does. Bone can mend fractures because living cells build new collagen scaffolding, but large cavities or fractured teeth don’t simply rebuild themselves. That’s one reason why prevention and early care are so important.

Research and the future

Regenerative dentistry is an active area of research. Scientists are studying how teeth form and what biological environments and materials could enable new ways to repair or regrow dental tissues. While progress is promising, reliable ways to replace or fully regenerate adult teeth are not yet widely available.

Practical tips for healthy teeth

• Brush twice daily with fluoride toothpaste.
• Floss once a day to clean between teeth.
• Limit sugary and sticky foods and drinks.
• Visit a dentist regularly for checkups and care.
• Wear mouth protection during sports to prevent injuries.

Taking good care of baby teeth protects space for permanent teeth and supports a healthy smile for life.

Question credit: Ivy D., age 11, Hyde Park, New York — submitted to Curious Kids.

Republished from The Conversation. Authors: Christina Nicholas and David Avenetti, University of Illinois Chicago. David Avenetti receives funding from the National Institutes of Health (National Institute of Dental and Craniofacial Research) and the Health Resources and Services Administration. Christina Nicholas reports no relevant conflicts.