What do Katy Perry and the high school cheerleader next door have in common? Braces. Braces are dental appliances used to straighten a person's teeth and correct unhealthy overbites or underbites. Braces are usually worn by kids 10 to 14 years old, but many adults wear braces – even celebrities. In fact, of the four million people in the US who wear braces, one million are adults. Most of the time braces are used for cosmetic reasons. Everyone wants a beautiful smile, but it is not always a matter of vanity. Crooked teeth and misaligned jaws can cause serious health problems. Teeth that do not fit together right are harder to clean, making the person more at risk for tooth decay, periodontal disease, and even lost teeth. Crooked teeth can also create stress on the jaw and facial muscles which leads to headaches, TMJ syndrome, and pain in the neck, shoulders, or back.