Puppy Mouthing/Biting

Yes it is natural for puppies to play with their teeth with other puppies.
It is NOT ok for us to tolerate it on us and by ignoring it teach the puppy that it is ok for them to put teeth on people. This is not something that puppies just grow out of over time. This is something that gets worse over time if you allow the dog to continue practicing this behavior.
You want to start from day 1 teaching your new pup the rules of the house and setting structure. It's more fair to set the rules from the beginning than it is to allow something for 4 -6 months then tell them its not allowed anymore. It's always possible to fix later, but far more fair and easier on your puppy if you start with rules from the beginning.
For most puppies using a taste detterrent is the best way to cure puppy mouthing.
Bitter Apple is a product made for dogs. It is sold in almost all pet stores.
I use Bitter Apple as a direct consequence for teeth on me. They put teeth on me and I spray some bitter apple in their mouth. You are NOT mad, yelling or angry. Just a direct consequence. You do this.. this happens. Make sure that you are CONSISTENT. Every time puppy mouths the bottle is handy.
Make sure that the bottle doesn't become a threat. If you bring the bottle out.. you use it..
NOT: bring bottle out... puppy stops.. i set bottle back down. Then you always have to have the bottle out.
I go to Target or Walmart and get the little travel size spray bottles it makes it alot easier to carry the bitter apple around or put it in my pocket.
Some people have heard from other sources to "Yelp" when the puppy bites. For a rare % of puppies that have a really soft personality it can work. But if you have a puppy with a stronger personality and you YELP... your puppy can see that as you submitting to them. This is not something that you want to do.
Another possible solution to the mouthing that I believe I heard this idea from I think Ian Dunbar but I could be wrong is that if the puppy puts teeth on you.. to be dramatic stand up walk away from the puppy and slam the door behind you...   I could see this working for many puppies... but then I'm leaving a puppy in a room by itself unsupervised and I really dislike to leave a puppy unsupervised EVER.
Start with the Bitter Apple...