Biting during play is not a sign of aggression or dominance but rather just an extension of play interaction that your puppy developed with its siblings or other puppies. It is a moldable behavior, meaning you can set the limits and control the biting. Just as another puppy would do in reaction to biting during play you decided when enough is enough and you exercise a dominant or threatening reaction to let your puppy know it will not be accepted. It is important to be firm and consistent in your response. Also if there are other family members involved especially children they must also be consistent with your response.