Kakashi Has Shark Teeth Under His Mask Since He's From Kirigakure

Another possible theory that has been floating around on the interwebs is that Kakashi's mother actually originates from a completely different place, and his need to hide this fact is the reason why he wears a mask in the first place. His proficiency with Zabuza's sword also supports this fan theory.

It's completely possible that Kakashi inherited the shark teeth that has become iconic with the Kirigakure area. Knowing that the village would see him in a bad light if he showed this rather unappealing feature of his, Kakashi decided from a young age to wear this mask at all times. Yeah, it might be a wild theory... but it can also be pretty plausible as well.