(HealthDay News) -- Thumb-sucking is a natural reflex that allows many children to feel less anxious and more secure.

But the habit can wreak havoc with a child's oral health if it goes on too long, the American Dental Association says. Most kids stop thumb-sucking by the time their permanent teeth are ready to come in.

If a child continues to suck the thumb after the permanent teeth appear, the ADA warns it could lead to problems affecting:

• Proper growth of the mouth.
• Alignment of the permanent teeth.
• The roof of the mouth.