When the time comes for you to groom your dog, do you start looking for the muzzle? Or, do you simply take him to the local puppy salon and let them deal with the fact your dog likes to bite when someone tries to groom him? While this type of behavior should never be considered normal, it is more common than it should be. More importantly, there is usually a reason why a dog bites at the person who is trying to groom them. Perhaps at some time someone pulled too hard on the brush and ripped skin out or maybe they cut into the quick in his nails by trimming them too short, causing pain.
While you might not realize it, your dog actually has a very good memory, especially when it comes to things that cause him pain. If he has been hurt before by a groomer, just the thought of being groomed is enough to cause anxiety and fear. In reality, your pup is not mad at you or the person trying to groom him now, he is simply scared, and this may be the only way he has of letting you know how scared he is.
It is likely to take a lot of time and hard work teaching bite-a-saurus-rex to relax and enjoy being groomed instead of trying to rip your face off at grooming time. Just keep trying to make it fun and use plenty of treats to make it happen.