Even if you think your dog doesn't need a muzzle it is a fantastic idea to get them used to wearing one anyway. For instance, if your dog gets groomed for the first time they may try and bite the groomer if a hair gets snagged on their tools, if this happens the groomer might just strap a muzzle on your dog even if your dog has never worn one before. This might make your dog freak out even more and they could hurt themselves trying to get it off.
Introducing your dog to a muzzle requires patience. The last thing you want to do is rush this process, because if you do it can make your dog freak out every time you put it on your dog. Please take the time to watch this video before attempting to put a muzzle on your dog.
My sister has a very sad story that could have been avoided if her dog was wearing a muzzle. She brought her little dog Coco to the groomer, while she was being groomed one of the tools snagged Coco's hair and Coco bit the groomers glove. When that happened the groomer pulled her hand away, when she did the glove got caught on Coco's tooth, thus breaking her jaw. The break was so bad that my sister had to put her dog down as it was going to cost thousands of dollars in vet bills. Coco was a very sweet dog, thus showing ANY dog can snap under extreme anxiety or fear. If Coco had a muzzle on this could have been avoided.