Why doesn't she tell them to "stand up straight"? Because a bad posture is often caused by an anatomical issue that leads the teenager to instinctively try to facilitate breathing through this typical position of their head and neck.
The orthodontist also works on this: by widening the upper dental arch, with the help of a speech therapist they can enable the patient to get used to this increased space, which can then help bring the lower jaw into a balanced position. For anyone who finds this hard to visualize, the orthodontist will demonstrate it using some model teeth during the consultation.
You can find more illustrative explanations in our latest video about the aesthetic and functional benefits of orthodontics and how it can restore balance to your jaw.