My blender model is missing a face when imported to Unity

First of all, I've done a lot of research on this and followed several tutorials to try and fix this issue but none have worked(which is why I'm posting this here)

I've made a model in blender and opened it in Unity only to find the face for the mouth(as pictured below) is missing. ![alt text][1]

This is how it looks in Blender: ![alt text][2] I've checked the faces aren't inside, I've recalculated the face after turning on backface culling and I've even tried deleting the mouth face and creating a new one with still no luck.

Any ideas?

Is this an issue with Unity or Blender(I'm sure it's blender) but I've never had this level of difficulty with any of my models. When I imported my first house model, it didn't show half of the faces on certain camera angles, which I fixed after learning how to change the faces so they weren't facing inside.

As I said, I tried it here but nothing I'm doing seems to work so far :/ [1]: /storage/temp/76176-mouth-face-issue.png [2]: /storage/temp/76177-mouth-face-issue1.png