It's getting more and more common for adults to get orthodontic treatment, and why not! With today's technology, there are many aesthetically pleasing and comfortable solutions to orthodontal issues.
An adult considering orthodontic treatment will have a fully developed jaw, ruling out the two-phase treatment discussed above. This means that it is more difficult to manipulate your teeth and make space.
The treatment may take a little longer overall, as your teeth will move slower then a child's considering that they are fully developed. Usually treatment will be administered in a single phase, and take between twenty and thirty months.