How common are TMJ problems after premolar extractions for braces?

TMJ because. Removal of premolars has been shown to cause the jaw joint to move back in the socket and this is a probable pathological position. It is important that your bite be treated at your best functional relationship. You will need to find this position, evaluate stability over adequate time and then probably get retreated so the joints and muscles are not compromised by your bite.
Self-Resolve. If the extractions happened recently and you have limited opening of the mouth and pain in the joint, that could be normal. It is probably a possible side effect of the procedure. If it has been a while, then you should go to your doctor and have it evaluated.
If the problems. Are related to some decreased range of motion or increased "pops & clicks" & you had the procedure done just recently, then this should pass. Not sure if this is the first episode ever or similar occurrences with other dental work. Home treatment 1. Ice application within 48 hours - then switch to heating pad. 2. Soft diet 3. Nsaids - like Ibuprofen q6 hours for 1-2 weeks. Let surgeon know.