Your problem is called "Trismus
" . But i think you should try to rule out any dental problems if any and moreover any swelling in cheek or chin region or adjoining area .It can be a small abscess
in one of you neck spaces . Possibilities are many for the cause of ur difficulty. ..try consulting an ENT specilaist first and then a dental doc if needed ..and if it is persisting then consult sooner...If u wil specify the problem further then it wd help in localizing ur problem..
MS ENT (std