oh sorry,
you can see the infundibulim (sp??) spot on the teeth when horses are about 6, and you can just barely see the end of it when they're 10. the Galvayne's groove (also known as pulp cavity i think) appears when the horse is 8 it's black and it starts out as a tiny dot and it gets bigger as the horse gets older. the incisor teeth get worn down and it shows a different cross section, but that onllly works up til the horse is 8. after that, the horse is considered aged.