While you can get braces on your top or bottom teeth only (deferred to as single or one-arch orthodontic treatment), it's only suitable some.
The most stereotypical of braces is brackets and wires on all of your teeth. This is not, however, the only way that you can get braces.
My teeth were perfect until my wisdom teeth came in. Now the lower ones are all messed up. Can't I just get braces on my lower teeth and put.