How much toothpaste must be swallowed before a sodium fluoride overdose?

Depends: It depends on toothpaste Fluoride concentration. To prevent it, children must be supervised until healthy toothbrushing habits have developed.

A lot: An adult would need to swallow more then an entire tube of toothpaste before you could "overdose" on fluoride. You would throw up long before that happened. You only need a pea sized amount of toothpaste to get your teeth clean, so i wouldn't really worrty about this.

Depends.: This is hard to answer because it depends on what toothpaste, what Fluoride chemical is used in it and how much you weigh. It's best to swallow as little as possible.