How has this happened?

[Equi]

Excuse the photo but he was mid yawn and gave me the perfect photo of this little nubbin he has

He has had this little gum nub forever, the dentist/vet said its nothing to worry about and it has never gave any need for concern (it never changes or gets irritated etc) but im just curious about how it came to be. Badly shed cap as a baby? Injury? Born with it? Anyone else horse have something similar?

 

[ycbm]

My guess would be that as a cap came off it tore back a strip of gum where it was still too firmly attached.
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