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notes: monday we start pelvises - half of us. recall that with the large 
animals we were in groups of 16, each group of 16 having a goat and a 
horse. on monday, two of those groups of 16 will be starting the pelvis. 
the other half will be continuing with the heads, or looking at the heads 
of the other species, or whatever.

also monday there is a clinical correlation in rm 13. the radiology folks 
will be coming in. it's at 11 am. this will be a one hr session on 
reading radiographs of the head.

now, for today: aging of the horse from the teeth. handout "Teeth and 
aging of animals"


a horse incisor has enamel on the outside, and then a layer of 
dentine...see the handout. outside of the tooth of course is a layer of 
cement. you do the aging of the horse from the lower incisor. you need to 
be aware of the infundibulum/cup in the middle of the incisor - see 
diagram.

there are two ways of telling age....age of eruption:

I1 erupts at 2.5 yrs, is in wear at 3 yrs, level at 5, cup gone at 6
I2 erupts at 3.5 yrs, is in wear at 4 yrs, level at 5, cup gone at 6
I3 erupts at 4.5 yrs, is in wear at 5 yrs, level at 7 cup gone at 8

so when you see just the tip of the tooth coming through the gum, you can 
use that as a guidline. about 6 mos later, the tooth is out enough that 
it becomes abraded by the upper tooth, and when that happens, it's "in 
wear"

after that, you can't tell age so exactly. the wear stages after 5 yrs of 
age may be inaccurate due to uneven wear, or behavioral problems, etc.

when you age a horse, the first thing to do is to check the upper lip for 
a tattoo. then pretend to look at the teeth andtell the owners the age :)


seriously, just say "this horse has teeth that I would expect to see in a 
horse of about 10 yrs of age." or something like that. don't say "this 
horse is 10 yrs old".

so, as the tooth wears, it eventually reaches a point where the lingual 
margin is involved in the wear as well, the tooth is said to be "level" 
this often occurs 2 yrs after the tooth comes into wear.

wear continues - when the cup is totally worn away, it's at the "cup 
gone" stage :) about a year after the level stage. 

then, you wear into the pulp cavity, and secondary dentine fills that 
spot in, and it's a different color from the other dentine (lighter or 
darker). that spot is called the "dental star". the enamel surrounding 
the remnant of the infundibulum is called the "enamel spot"

in fig 4 on the handout you see the dental star and the enamel spot.

then as the tooth wears more, the enamel spot gets worn away, there's no 
remnant of the infundibulum at all, and instead you see cement on the 
outside, some ridges of enamel, at the lingual and labial edge, and a 
level surface of secondary dentine over the surface of the tooth.

another feature is that the tooth changes shape, from an oval shape to a 
round shape and finally to a triangular shape.

the triangular tooth of the elder horse contains a dental star. note also 
that in the young horse the teeth are near vertical, but in the older 
horse, the teeth are steeply angled forward.



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