I've experienced significant TMJD issues, and I know several other people who have also had TMJD issues.
Temporomandibular joint disorder (TMJD or TMD), or TMJ syndrome, is an umbrella term covering acute or chronic inflammation of the temporomandibular joint, which connects the mandible to the skull. The disorder and resultant dysfunction can result in significant pain and impairment.
The one thing we all seem to have in common is that we've previously had orthodontic work. It's a small sampling size, but in particular I know one person whose onset of TMJD issues began during orthodontic treatment, which suggests to me more than correlation but actual causation between orthodontic work and subsequent TMJD issues.
As well, my dentist, who is also a very highly regarded professor of dentistry, has told me that many of the TMJD issues he sees (and he has seen a lot) correlate with prior orthodontic work. He noted that many dentists have similar observations, but it's not acknowledged by the official powers that be. He's noted that there is a great deal of controversy over this in the regulatory bodies that govern dentistry, and although he's made inquiries with several colleagues he's not aware of any formal studies of relationship between TMJD and orthodontic work.
In light of my own experiences and anecdotal evidence, and the comments of my dentist, I'm curious about whether others have noted or are aware of any evidence that would suggest that orthodontic work causes TMJD issues.