Biting, nipping and mouthing are absolutely normal for growing dogs. Like human babies they discover the world by putting things in their mouth. The also nip to alleviate dental pain. However these behaviors are not so normal in an adult dog and could mean that the dog is nervous, afraid or needs a dental check up. Many bite simply because they are cutting new teeth.
Gnawing on things helps soothe the gums around the teeth, and loosen baby teeth as well. Many baby teeth are chewed and swallowed along with whatever they else the puppy is chewing; so do not be alarmed if your puppy suddenly seems to be missing teeth and you can’t find the lost tooth anywhere It is quite easy to train a puppy not to bite you.
Most puppies will recognize that you are in pain if you simply make a squealing noise or say “ouch.” Make sure you withdraw your hand away immediately the second you are nipped. This lets the puppy know that the biting is unacceptable.
It also helps to immediately substitute your hand with something that is right for the dog to chew on like a rawhide chew toy. Sometimes a puppy will try to mouth or gnaw in you because t he wants to play. If you anticipate the bite coming, say the command “Off!” before he can chomp you.
Quarantine a puppy that bites in order to get the animal to equate the idea of loneliness with nipping. It is also important to make sure that you or member of your family are not actually encouraging your puppy to nip and bite by offering their hands to the animal to gnaw or chew. You may be encouraging him to nip by playing chase. You may be encouraging the dog to nip at your heels. This can soon turn into a full-fledged problem when the dog grows older and responds to a running human by biting his legs or nipping his heels. You can also encourage this nipping by teasing him. Don’t hold the dogs toys out of range and make him jump for it. This trains you puppy to believe that nipping makes a person drop things that they want , such as food they may be eating or cooking, Dogs that are orphaned or torn away from their mother before the acceptable eight-week nurturing time with mom is up may not have learned what is called “bite inhibition”. Usually the mother dog teaches her puppies not to bite by disciplining him if he bites his littermates.
If your dog was allowed to remain with mom and his littermates for an appropriate amount of time (until at least 8 weeks of age), then mom should have taught him the beginnings of bite inhibition. Nipping is quite common with adult dog but particularly in puppies. I believe the best thing that you can do is to encourage acceptable behavior by discouraging the unacceptable behavior. Don’t hit a dog for gnawing you especially one that is teething.