The term lingual is used to describe braces that are fitted behind the teeth, offering a discrete way to straighten a patient's dentition and improve their smile.
While conventional braces can be bulky and unattractive, the aesthetic benefits of lingual braces have enabled them to become popular among people who value straighter teeth but do not want to be seen wearing brackets and wires.
The name of this type of brace comes from the Latin term lingua, meaning tongue.
Instead of fitting brackets to the front surface of the teeth, a dentist using lingual braces will bond the brackets and arch wires to the back, rendering them virtually invisible to other people.
Unlike standard braces, the brackets need to be custom-made because the rear surface of each tooth is unique in shape.
However, lingual braces perform exactly the same purpose as traditional brackets and wires. As with standard braces, they can be used to correct gaps, crowding and bad bites occurring as a result of misaligned teeth.
The main difference between the two types is the cosmetic advantages of the lingual method.
This can be an important factor for people who feel uncomfortable wearing standard braces, or who would receive a confidence boost by knowing their dental work is concealed.
People who are regularly photographed or who depend on their looks for their livelihood often choose lingual braces. A number of actors, newsreaders, models and other media personalities have opted for the treatment to straighten their teeth discretely.
Kate Middleton is rumoured to have used lingual braces to help achieve a particularly radiant smile in the lead-up to the royal wedding in April 2011.
The average treatment time is roughly the same for lingual braces as with ordinary braces, although the former type tends to be more expensive.
This is because there is usually more preparation time involved and applying brackets to the back of the teeth is a more complex task for orthodontists.
According to the British Lingual Orthodontic Society (BLOS), people may experience a slight alteration to the way they speak immediately after having lingual braces fitted, but this is only a temporary change as the tongue needs to adapt to the position of the brackets.
The BLOS states that lingual braces are suitable and effective for most patients, although they are not recommended for people in their early teens because their teeth are unlikely to have developed fully.