420.5. The state-based effects are as follows:
420.5b A creature with toughness 0 or less is put into its owner’s graveyard. Regeneration can’t replace this event.
420.5c A creature with lethal damage, but greater than 0 toughness, is destroyed. Lethal damage is an amount of damage greater than or equal to a creature’s toughness. Regeneration can replace this event.