And what exactly does 'impacted' mean? Any tooth has the potential to become impacted—that is, emerges in some oddball direction that crowds other teeth. But the most famous culprits are third molars, the last-to-emerge wisdom teeth. Not many mouths can accommodate these teeth. They often wind up pressing against their neighbors, ultimately pressuring the rest of the teeth to disrupt their alignment. That's not a wise thing to let happen. Wisdom teeth get our attention when they cause pain and swelling. Routine X-rays, beginning around age 12, alert us to problem potential before wisdom teeth start getting disruptive. X-rays can let us know whether those mighty molars must go.