A small lower jaw may be the cause.

One of these desired traits was a small jaw.

If children have a small jaw, their teeth may grow into a space that is too small.

She had her permanent teeth, crowded into a small jaw.

Morag turned back to her husband, small jaw set in determination.

The watery eyes were set deep in the skull, the jaw small and hard.

Your child seems to have a very small jaw.

Her small jaw was set hard with the effort.

One was broken, a small jaw with part of its left side missing.

Because they have a small jaw, their teeth can become crowded and may not fall out naturally.