This may help I wrote it a few years ago.

Bite Inhibition

Puppies have painfully sharp little piranha like teeth, almost like hypodermic needles, fortunately the jaw muscles are extremely under-developed, One of the main reasons why you should never play tug with a young puppy as you could dislocate the jaw and misalign or damage the teeth.

Nature has given them these underdeveloped muscles to enable pups to play-bite safely. Whilst very young and still with his brothers and sisters and he bites too hard in play he gets blasted with a ear piercing "yelp" which makes him immediately back off, he waits a while then starts to play again, but a strange thing has happened, the biting is a bit softer. The same thing when feeding from the mother, the pup uses too much pressure she yelps and moves away end of milk bar. He is then gentler the next time round and a valuable lesson has been learned.

This is nature’s way of inhibiting the force of their bite well before the jaw muscles start to form properly at around about 4.5 months, which also coincides with the time that the puppy teeth start dropping out and the new bigger more dangerous teeth start to come through. This is called the age of cutting.

This learning process is known as “Bite Inhibition” it is a vital and important lesson and is the only reason why your puppies are born with those hideous teeth. This is how your puppy learns to inhibit the force of his bite and to control his jaws, It is a vital that he also learns to inhibit biting us humans.

I see many new owners who are told to stop all play biting, however this could potentially have far-reaching and disastrous consequences. If the pup is trained immediately never to play-bite, he will never have the chance to learn control over his jaws. Therefore, your puppy must initially learn that all biting whatever the circumstances must be done softly. Then you can start to teach him never to bite at all.

This is how you should deal with this problem

1. Permit the puppy to play-bite by allowing your pup to softly chew on your hand. When he bites down a little harder than normal, "yelp" sharply and loudly and very short, turning your head away in rejection. Do not pull your hand away or the place he is biting. Let the puppy move away from the sound and your hand or leg, (pulling your hand away will only encourage him to lunge towards the moving object)

As an appeasement after your yelp the pup may come up and lick your hand, accept this gesture. Then allow the play to resume, but this time hopefully with a softer bite. If the play gets a little rougher, "yelp" again, thus further confirming that any pressure is totally unacceptable. Repeat this exercise as often as possible. And like the New York police chief who had a zero tolerance to crime you do the same with any hard biting.

You will find within a few days, that the biting turns into mouthing; you will have programmed your puppy into thinking that he must not exert any pressure whatsoever whilst mouthing because of your ultra sensitive reaction. Now you can teach him the “OFF command to stop all mouthing.

Stan Rawlinson 2002