Why teeth are formed twice in life time of human?

Our mouths are not yet large enough to support adult-sized teeth when we're very young. Many of us still don't have enough room later on and need orthodontics to straighten teeth made crooked by lack of space. however, in all children, the deciduous teeth (baby teeth) come in smaller so that they can fit in the small jaw space of a child. They are also softer than adult teeth, but we need teeth of some sort when we are small because we begin to eat solid food and we need teeth to help us masticate the food. Deciduous teeth usually begin to fall out beginning around age 6 and are gradually replaced by adult teeth over a period of several years, by which time the mouth has grown large enough to accommodate the larger, stronger adult teeth.

It is important to take a child to a dentist, or pediatric dentist if you prefer, so that the deciduous teeth are kept healthy, and to form good dental habits in preparation for the permanent teeth.

The larger teeth towards the back, the molars, only appear once and don't get replaced. That helps explain why premolars do get replaced.

When a person is still growing, then so is the length of their jaw. At first there isn't much space towards the back for molar teeth. That means the baby premolars have to preform functions such as crushing food which, later, the molars will do. And the fact that the molars will be responsible for such duties means the premolars will no longer be needed for that. This allows them to be replaced by simpler teeth.

I would think that, it takes a lot of time and energy to make adult teeth. Plus it would be all awkward and uncomforable to have adult teeth in your mouth as a baby.

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