If you are considering getting braces, PLEASE research TMJ before you get them. At least talk to your
orthodontist about it, and if he blows it off saying it's no big deal, then PLEASE find a new orthodontist. Find one that understands the possible problems that may occur. You may not even know you have TMJ until the disturbance of having your mouth open and pressure applied to insert spacers or braces activates it.
That is what happened to me and I spent 3 months in pure pain hell because I had an orthodontist that did not believe in TMJ and would not listen to me when I told him what was going on. I was having daily migraines that only got worse as time went on and adjustments were made. I lost a month and a half of work. I developed an ulcer from all the pain meds I was taking. I lost my entire summer, including cancelling two trips (one of which cost me over $300 just in cancellation fees), all because I had an orthodontist that would not listen to me.
If you have braces and you feel your pain is excessive. Tell your orthodontist. If he/she won't listen to you get another opinion. NEVER ever except that extreme pain is NORMAL when you have braces, and don't let your orthodontist try to tell you that extreme pain that onsets around the same time your braces (or spacers) go in is just normal pain because your teeth are moving. Sure there is always some pain initially when you have braces, and you may even have some headaches right after adjustments, but you should not be in constant daily pain month after month.
If you'd like to read my story, I have posted it in my blog here. If you have questions about what I went through ask. After all of this, I've made it my mission to make people aware of this risk. When I first started researching I didn't know it was TMJ and I just researched "braces and headaches" and found so very little information. When I finally found out it was TMJ and started researching, I found a lot more information.