Get a muzzle and muzzle your dog's mouth. If you don't have one, normally the vets have. If your dog has an injury, the vet may need to sedate your dog if it bites and acts very fierce.

You can use a temporary muzzle. You know the surgical gauze? or you can use a strong strip of cloth. First you tie the mouth in a single loop with the knot on top, then loop down and tie bottom of the muzzle, then tie the back of the neck. make sure the first two loops around the muzzle is firm and the dog cannot open it's mouth more than half a cm. For the finish loop around the neck, make sure you tie it tight enough to allow only 2 or 3 fingers to squeeze through.