Malocclusion (poor bite) is usually caused by problems in the shape or size of the jaw or teeth. If children have a small jaw, their teeth may grow into a space that is too small. Under these crowded conditions, teeth will push each other out of proper position. Other causes include thumb-sucking, pacifier use, and tooth loss.

Genetic factors

People can inherit mismatched traits such as jaw size and tooth size. This can produce large, crowded teeth in a small jaw or small teeth that drift out of place in a larger jaw. In other cases, a person may inherit a trait that results in missing teeth or teeth that erupt in one another's place (transposed teeth). More rarely, people are born with conditions (congenital) that can create malocclusion problems, such as a cleft palate or a severely underdeveloped upper or lower jaw.

Oral habits

Oral habits that place ongoing or frequent pressure on the teeth may slowly move the teeth out of place. The most common oral habits that cause malocclusion include:

• Thumb- or finger-sucking and pacifier use for more than 4 to 6 hours within a 24-hour period.
• Mouth breathing (possibly). Infants and children may breathe through their mouths because of a partially blocked airway.

Tooth loss

Tooth loss may cause drifting of bordering teeth into the empty space, creating a poor bite. Common causes of tooth loss are:

• Trauma, such as sports injuries and automobile and falling accidents.
• Tooth decay that leads to having a tooth pulled (extracted) by a dentist. Poor dental hygiene promotes tooth decay, as does a child sucking on a bottle during sleep. The sugars in milk, juice, and formula can cause damage to teeth. For more information, see the topic Tooth Decay.

See an illustration of tooth decay or baby bottle tooth decay.