Who knew that teeth could change a person's appearance so drastically? While some celebs have proudly rocked their dental transformations (we're looking at you, Niall Horan!), other have stealthy undergone whitening treatments to brighten their grins.

These changes can be done under-the-radar, so the before-and-after comparisons can be pretty surprising! We gathered up photos of some of Hollywood's biggest teeth transformations. Check 'em out in the gallery above.

More From PopCrush