Alternatively, you can slide an 18-gauge angiocatheter (just the plastic part) into the potential space. The new nail should then grow over this plastic "splint". The above photo is of a patient's toe with a brewing ingrown toenail for over 1 month! Both edges needed to be trimmed down longitudinally. Way to go, med student ST. You know who you are.
The added benefit of the angiocatheter over the cotton is that if you needed to remove it for whatever reason, it's easier to remove as one piece than cotton.
I got this idea from the concept of a toenail "gutter splint" from this a review article from American Family Physician .