Teeth that are naturally perfectly aligned are rare. A poor fit and alignment of the teeth (malocclusion) can range from mild to severe. Mild malocclusion causes no medical or functional problems and little cosmetic concern, while severe malocclusion may cause difficulty with eating and speaking. Some people are embarrassed or self-conscious about crooked or protruding teeth.

Crowding is the most common type of malocclusion. In children, early crowding of permanent teeth can prevent new teeth from coming in properly or from erupting at all (impaction).

Some mild types of malocclusion may improve as a child's jaw grows and changes. However, there are many conditions that don't improve without treatment. These usually involve the size or position of the jaw (such as an underbite or an unusually narrow lower jaw).

With or without orthodontic treatment, the teeth have a normal tendency to slowly drift toward the front of the jaw. This may lead to crowded lower front teeth (incisors).¹

A poor bite doesn't usually cause tooth decay, gum (periodontal) disease, or temporomandibular (TM) disorder. But teeth that are aligned properly are easier to keep clean.²