Orthodontic appliances are devices used by orthodontists to correct misaligned teeth and jaws. These appliances can be fixed, like braces, or removable, such as aligners. They apply gentle pressure to teeth over time, gradually moving them into the desired position. Common types of orthodontic appliances include braces, retainers, and expanders. Braces consist of brackets and wires, while aligners are clear plastic trays that fit over the teeth. Retainers help maintain the new position of teeth after treatment, and expanders widen the upper jaw to create more space for teeth.