Teething puppies are painful in so many ways! Never fear. Those sharp puppy teeth will eventually give way to bigger more rounded adult teeth. In the mean time pup needs to learn the limits and boundaries for using teeth. We have had a lot of success with teaching bite inhibition with our puppies first and then teaching that biting is never tolerated later. If there is ever an accidental injury ie. your dog's tail is slammed in a door or your toddler thinks it's fun to bite your sweet golden's ear as hard as he can... (we speak from experience on this one!), it is important that every dog knows instinctively how hard he can 'touch' human skin without causing real damage. Here are some favorite articles:
(An Excerpt from) Soft-mouth shaping--written by Casey Lomanaco--see link below
Ian Dunbar has a categorization system for ranking the severity of dog bites. The scale may look a little different for a young puppy without severe aggression but with a normal nipping problem. Here’s a sample 5-category scale for that situation, with 1 being the least amount of pressure exerted, 5 the maximum pressure.
1. Puppy licks or sniffs Hand
2. Puppy gently mouths skin, you can feel teeth without any pressure.
3. Moderate mouthing. Slight pressure is applied to skin, but not enough to cause any puncture or tear.
4. Puppy bites hard enough to cause pain but does not break the skin.
5. Puppy bites hard enough to break the skin.
There could be additional levels of biting beyond five (the puppy tears the skin, the puppy repeatedly bites the skin, puncturing it, the puppy bites and shakes the hand, etc.). If your puppy is biting at level 5 or higher frequently, consulting with a qualified behavior professional immediately is not optional, but necessary!
Soft-mouth shaping is another technique for teaching a puppy to use its mouth politely. To start shaping a soft mouth, place a low-value treat in your hand and present it to your dog. Any reaction at level 3 or lower earns the puppy a click and the opening of the hand; the dog is fed from a flat palm. A level 4 reaction results in a 5-second removal of the hand (place it behind your back and ignore the dog). Level 5 reactions result in a temporarily lonely puppy—walk away from the dog for 7 to 10 seconds before reengaging him in training. As the puppy develops better control over his mouth, increase criteria so that only level 2 or level 1 responses earn reinforcement."
See the full article at "How to survive Puppy Teething and Nipping" from Karen Pryor Clicker Training