mihlbach

There is not necessarily any mechanical difference. Many, but not all track bottom brackets are unsealed to meet NJS (Japanese Keirin) requirements. However, many cranks and BB are meant to be pairs. For instance, the sugino 75 BB and crank will give you the standard 42mm chainline which will match a track hub. Using the same crank with another BB will not guarantee this because the spindle may be a different length and/or the taper of the spindle may differ. One the other hand, road cranks and bottom brackets are not necessarily designed to yield a 42mm chainline. There is a good chance you can achieve the right chainline with any crank, but if you choose a road crank you might have to do some experimenting with different bottom brackets, or just accept that you chainline will be a few mms off.