You can save your fingers from future pain by training your dog at young age that biting and chewing is bad behavior. Sit on the floor and play with your puppy. Bring his attention to your hands by tapping the fingers in front of him, if the puppy bites you then loudly yell ‘ouch’ and quickly draw your hand away. Immediately stop playing. Play with the puppy again after a few minutes and bring your fingers towards him. If puppy does not bite then offer him a treat as a reward. If the puppy bites you then punish him by; not playing, ignoring or putting him in a lonely place.