Occlusion is how the upper and lower teeth fit together (how they align). This is also known as "bite."

Perfect bites are rare. Most people have some form of malocclusion ("poor bite"). With an overbite, the upper teeth stick far out over the lower teeth. With an underbite, the upper teeth are positioned behind the lower teeth.

Orthodontists use braces and other tools to move teeth into a better and more normal occlusion, or alignment.