Stress can affect teenagers' teeth in other ways, too. Teens who are under stress may let their regular dental hygiene practices, like brushing and flossing, go by the wayside. This can lead to increased cavities and gum disease, especially if the teen in question also turns to sugar-laden foods or drinks when anxious.
According to WebMD, studies -- including one in the Journal of Periodontal Research -- have also shown that stress causes increased dental plaque, even when it's just short-term stress. It's possible that this is due to increased levels of the stress hormone cortisol or depressed immune functioning.
You can, however, take some steps in these situations to help keep teens' teeth (and the rest of their bodies) healthy. First off, get your teen to a dentist for an examination. To address TMJ issues, dentists can provide mouth guards to be worn at night, which should prevent teenagers from grinding their teeth. Someone who's already developed a jaw disorder will probably need to see a specialist.
And, perhaps most importantly, figure out some strategies to help teens deal with the sources of their stress. That'll keep them smiling for years to come.