CALL OF DUTY GHOST TRAINER UPGRADE

I can get to the Kraken without a single down, although the final drill point can be close. On solo, you can get downed 3 times by the time you get to the final area (you seem to earn extra downs, starting at 1, by progressing through the ship).

I suppose it depends on how many teeth you need. Mix this with the Point of Contact map (see other answer for more detail) to save yourself from boredom. I usually pick up approx 15 teeth by doing ALL of the challenges.

If you own the DLC, I would say Mayday on solo is a pretty decent method of earning teeth. Also there are several things you can do on a game to game basis to get more teeth, such as getting a completionist bonus by perfectly completing all challenges, and getting kills (as every few hundred kills or so you earn a tooth regardless of what point you are at in a game.) Playing with randoms may warrant taking off a couple of relics, depending on how skilled you are. As with all of these tactics though, you'll want to be playing with people that have some idea what they're doing.

CALL OF DUTY GHOST TRAINER UPGRADE

You can run pistols only very easily on point of contact (which is what I would recommend farming on) if you use the revolver, and never get the akimbo upgrade (demolishes your accuracy for negligible benefit at close range) or you can ditch everything but the grenade turret (all relics but the no machines relic), as the grenade turret is very OP on point of contact. When I was running with decent people, I would generally run eight or nine. Each relic you run increases the amount of teeth you get from completing a game.

Call of duty ghost trainer