It's hard to tell what that is based on the photo. Certainly looks like a large amount of buildup but I'm not sure if it's some kind of growth, swollen tissue, or scabbing on the outside of a cut. It looks to be more than normal food buildup though and should warrant some attention. Depending on how it looks in person, you might try gently rubbing the area with a wet q-tip to see if any comes loose or appears to cause some sensitivity reaction. Oral cleanser like maxiguard gel or perhaps some diluted betadine would help to clean the area a bit and prevent/reduce surface infection. If it doesn't start to look improved or at least stay as it is, then a vet may need to do some work to remove the affected tissue and offer some treatment for infection.
