Load a human base mesh in the makeclothes tab. Any of the types work.
Select the upper teeth helper. Create a new vertex group "teeth-upper", and assign the selected vertices to it.
Select the lower teeth helper. Create a new vertex group "teeth-lower", and assign the selected vertices to it.
Create the same groups on your theeth model. Ie, everything that should belong to the upper jaw should be in the "teeth-upper" group, and everything belonging to the lower jaw should be "teeth-lower".
Move/scale your teeth so it is placed in the right spot in relation to the base mesh.
If you haven't done so, UV unwrap your teeth model and assign a material.
Select the base mesh and your teeth model and click "make clothes".
There shouldn't be a whole lot more to it. But it'll complain if you're for example mixing tris and quads, of if you have vertices belonging to more than one vertex group.