They don't have them at all. Stephenie explains about their fangs
link.
"My vampires do not have fangs. Their teeth are so sharp and strong that fangs are hardly necessary (they could bite through steel, if so inclined–a human neck is like butter, ha ha). The non-vegetarian vampires don’t leave living victims (unless they are changing someone into a vampire); this isn’t the neat-and-tidy, two-small-holes-in-the-neck kind of vampire attack that آپ see in other vampire mythologies."