To dream that you have lockjaw may reflect the current state of your body while you are dreaming. During the REM state of sleep, your body is immobile and essentially paralyzed. Not being able to move your jaw is similar to those who report not being able to hit or run, despite how hard they try.
Symbolically, dreaming of having lockjaw may also mean that you feel unable to express yourself. You feel that your opinion doesn’t matter or that no one takes what you say seriously.