In a perfectly aligned face there should be a straight line from the bridge of the nose to the bottom teeth... all should be lined up. If they are not and the bottom teeth are actually misaligned from the top teeth, then your midlines are off.
When your midlines off your teeth could be drifted or your lower jaw could be shifted, which would result in an improper bite.
Before |
After |
|
Expansion |
Extraction |