These photos are of an 11 year old Arabian cross gelding. As you can see, he has a very large hook on the first upper left cheek tooth. It is so large that it contacts his lower jaw when he closes his mouth. This due to a conformation issue in which the upper rows of cheek teeth are positioned slightly more forward than the lower cheek teeth. As a result, part of the first upper and last lower cheek teeth do not have opposite tooth to wear against and hooks gradually form.
In the “After” photo you can see the hook was removed and he will feel much better now!
David Warren, D.V.M.