It's a new one on me, but it looks like one of my 5yos has it. She's been fussy about her mouth for months, vet did teeth (again!) and said she had a ramp on the near side. Did what he could with it - no improvement - still quidding more haylage than she swallows. So explored again and found a hook he's missed - right at the back - and with a nasty ulcer - so did his best with that. Had my other vet look at her today - the back tooth is going sideways and she thinks it must be removed - and she showed me why she thought there was associated TMD and gave a steroid jab to help with that. This is going to be expensive!