Being permitted to trim nails is a combination of the dog accepting you as the leader thus doing the activity you request (in this case just holding still while you have a paw), trusting you not to hurt them and being able to control their emotions (as in not give in to panic).
You need to work on all those and see which is the area(s) your having issues with. First off take the dog and just hold a paw and rub the toe and nail and expect it to submit, be still and stay calm. Can you do that? and if not what part fails? If the dog says no period, your not touching my paws do some leadership work, make it clear to the dog that you are the pack leader. If the dog will not remain still go to obedience and work on your sit and down stays, and if the dog is not able to remain calm work on relaxation, do massage or even try some herbals like Rescue Remady which works very well on dogs. Do this as a daily routine, not a one shot gotta get it done that puts pressure on both of you. Work at it one paw at a time and work when the dog is relaxed almost tired, but not exhausted.
After you get there with just your hand have the clipper near by and massage the dog with it. See if/where you break down then. After that I have gotten those bamboo sticks for cooking meat on and clipped those while holding the paw of a dog that had no trust, of course he never felt a thing, but since he had been quicked before he needed a few days of that to realise that he was not going to be hurt. When you do move on to clipping him don't go for getting it done either, just take the tips so the dog is unaware of the change and not upset. Keep going daily till you have what you want for length, if you shorten them right up the paw changes the way goes for him and it may make him uneasy, plus you risk quicking a dog that has an overgown nail as the veins grow out too long.
Do not ever out of fear or aggression allow a dog to bare teeth to you or growl. Scruff shake that no matter what the dog's history is, even abused dogs know the pack way of telling them they have been wrong. To allow that behaviour is a greater risk to them than to stop it, dogs that don't get corrected on that are put down in huge numbers every day. Not all dogs need a full scruff shake, many will respond to a light growl and teeth like grasp around the scruff but for sure do something dominent to stop that. Never tolorate that from any dog anytime.
Make this a lifestyle change, part of the daily routine, not just a once a year or as needed training thing and you will have way better sucess. Pick a paw up any old time you feel like it while petting your dog and hold and massage it expecting him to allow it properly. Paws are a big deal to some dogs, it may not have to do with the history at all. If you take their paw they can't leave so it is like a loss of control for them. The higher they are in the pack the less they want to give you that, and the lower they are the more anious they will get at you taking it.