This is the dental discipline that studies and treats dental malocclusions (crooked teeth or incorrect bites). This problem is due to numerous causes and can be either aesthetic of functional in nature or even both.
Every case differs widely but all cases wish for the same thing, straighter teeth. Fortunately most cases can be corrected by Orthodontic treatment or "Braces" as it is commonly nicknamed. Orthodontics use a raft of equipment and techniques to "force" the teeth into a better position.
Most are treated with a fixed type of appliance that is bonded to the teeth for the duration of the treatment. This is the most predictable and controllable technique. The other form of orthodontic treatment involves the use of a removable appliance often referred to as a "plate". It has its uses and can be used in conjunction with fixed braces.
We have to work with what is given, while improvements are achievable, expecting to have a perfect set of teeth like a model or movie star is only possible with a good starting base and/or with extensive adjunctive plastic surgery.
There are many ways to treat the various cases and might even require the extraction of a few teeth with treatment times of between two or three years along with numerous visits in between. Due to the extreme variation of each case it is best to make a consultation to determine just which is the best form of treatment for you.