Gummer

A gummer is a person who when smiles shows off the the entirety of their maxillary (upper tooth structure). This consists of the teeth as well as the gums superior to said teeth.

This is also an alternative to the horse face

Bob: hey mark, come check this girl out I found on tinder!
Mark: woah! What’s up with her face?
Bob: she’s a gummer mark.
Mark: that’s tough.