Generally, it symbolizes the relationship between the dreamer and her surroundings.
If it is the muzzle of a domesticated animal, the circumstances are favorable and offer a context in which you feel comfortable and at home.
If it is the muzzle of a threatening beast, you feel distressed and unable to change that which is hostile to you.
If you see yourself with a muzzle in place of a human mouth, the dream expresses discomfort with the image you project to the world.
[1]Vision: Looking at or wearing a muzzle: keep your extraordinary habit of gossiping under better control in the future.
[2]A mouth guard against speaking sinful things, Ps. 39:1
[3]Indicates a need for controlling an unruly mouth
[4]