The rules are unclear
It has been confirmed that trolls may suffocate to death in Pathfinder, as shown in this answer. But the rules are actually saying the opposite (as shown in that answer as well), the regeneration must be stopped or the creature cannot die.
Regeneration (Ex) A creature with this ability is difficult to kill. Creatures with regeneration heal damage at a fixed rate, as with fast healing, but they cannot die as long as their regeneration is still functioning (although creatures with regeneration still fall unconscious when their hit points are below 0). Certain attack forms, typically fire and acid, cause a creature's regeneration to stop functioning on the round following the attack. During this round, the creature does not heal any damage and can die normally. The creature's descriptive text describes the types of damage that cause the regeneration to cease functioning.
There is an open FAQ request at paizo messageboards asking for clarification on wether trolls can be killed by death effects or not.
Also, notice that Pathfinder's version of Regeneration is worded differently from what we had in 3.5 (link), which made no mention of "they cannot die" and handled things using nonlethal damage instead. While the Disintegrate spell text is mostly the same, including the part where the target becomes dust.
But you can try to remove their regeneration
One thing is certain, you must stop their regeneration, either with the correct damage type, with something that prevents regeneration, or removing regeneration from the creature (by polymorphing, or transfering it).
As much as it sounds ridiculous that a bunch of dust may still regenerate back to life, so is instantly killing them with a death effect and having them return to life a few rounds later.
There are many ways to disable them (sleep, burying, throwing underwater, locking their soul in a gem), but those won't kill the creature.