Despite the thousands of people who get cosmetic surgery every year, there's still a bias against it. There's a common, though by no means universal, perception that people who get nose jobs, boob jobs, tummy tucks, etc., are often deficient in some way: their lack of self-esteem makes them hate their own bodies, or their lack of self-discipline makes them resort to surgery instead of exercise. On top of these attitudinal judgments, which some people are willing to voice in public, I suspect there is an unstated physical judgment as well: someone who gets cosmetic surgery must not be naturally beautiful, and natural beauty is superior to artificial beauty, right?
But oddly, there is one kind of cosmetic medical treatment that is regarded differently from all the others: teeth straightening. Nobody is ever looked down upon for having worn braces (although there is sometimes teasing during the actually brace-wearing phase, especially if headgear is involved). Someone who has straight teeth without orthodontic work is regarded as lucky, but not superior. Far from being stigmatized, procedures to fix your teeth are regarded as normal and even expected.
Why the inconsistency? I'm not sure, but (naturally) I have some theories. One is that the stigma against cosmetic medical treatments has a "necessity" escape clause. If you have nose surgery to fix a deviated septum that hinders your breathing, that's okay, even if you look radically different afterward. Similarly, fixing your teeth might be necessary to facilitate eating, stop you from biting your tongue all the time, and so on. But I don't think this theory works, because no one expects you to justify your braces by reference to your TMJ disorder.
Another theory is that orthodontists have simply done a better PR job than plastic surgeons. They've successfully spread the idea that having straight teeth is a sign of good breeding, even hygiene, equivalent to having a clear complexion or getting a good haircut. But this theory raises the question of what orthodontists did to get this result, and why plastic surgeons haven't successfully followed the same strategy.
A third theory - and my favorite - is that people are expected to exhibit swiftly diminishing marginal utility from body modification. Everyone's entitled to a certain amount, but the more you have done, the more likely it is that your real problem is mental. On one end of the spectrum, we have a person who gets one nose job; on the other end, we have Michael Jackson. While it's hard to draw the line on the spectrum between functional and dysfunctional, to paraphrase Justice Potter Stewart's comment on obscenity, we know dysfunctionality when we see it. And since teeth-straightening is usually the first - and often the only - body modification that someone gets, no stigma yet applies. Add on a nose job, and the stigma (if any) is still mild. Add on two tummy tucks, a facelift, monthly Botox treatments, another nose job, and a chin implant… welcome to stigmaland. (For bonus points, apply this same theory to body piercings and tattoos.)
Incidentally, my comments here are not meant in any way to contribute to (or detract from) the stigma I'm talking about. I'm just trying to understand why people have the attitudes they do, not justify them. And yes, in case you're wondering, I have been watching FX's new show "Nip/Tuck."