Why might it be that my jaw starts hurting when i open my mouth?

TMD?: This may way well me tmd (temporomandibular joint dysfunction) commonly referred to as tmj. See a dentist who can evaluate you and suggest some conservative treatment options.

TMJ: You might be suffering from tmj. You can read more on TMJ at our website: http://www.Aeortho.Com/treatment-options/tmj-and-tmd.

Muscle or joint: You could be suffering from myofacial pain dysfunction which includes problems with the muscles that attach to your jaw and your temporomandibular joint (tmj). You need to be evaluated by a dentist who can diagnose and treat mpd or and oral & maxillofacial surgeon.