Malocclusion ("poor bite") can range from mild to severe. American dentists refer about half of the children they see to orthodontists. Although most people have some type of malocclusion, not everyone requires or seeks orthodontic treatment. For example, with or without treatment, many adults develop crowded, crooked lower front teeth. This is a natural result of change over time and doesn't always require braces or other treatment.
WebMD Medical Reference from Healthwise