Estimating the age of a horse by examining its teeth is a common practice. For very young horses, eruption dates are useful, but in general, the place to start is examination of the occlusal surface of the lower incisors. Similar changes occur on the upper incisors, but it is typically easier to get a good look at the lowers. Two characteristics should be noted:
Shape of the incisors: For horses less than about 11 years, all of the lower incisors have a rounded, oval shape. As the horse gets older, the surface of the incisors changes, first to a triangular shape and finally a rectangular shape.
Cups, stars and spots: The cup is the center of the infundibulum. Wear of the occlusal surface causes the cup to get smaller and eventually disappear from all lower incisors at about 8 years of age leaving the enamel spot in its place. The enamel spot is the deepest part of the infundibulum. The dental star corresponds with the pulp cavity and appears at 8 years of age in the first incisor. It appears as a line and then changes to a large, round spot as the occlusal surface is worn further. It is still visible after the cup and enamel spot have been worn away.
Another dental feature useful for aging older horses is Galvayne's groove. As shown in the image to the right, Galvayne's groove is located on the lateral surface of the upper third incisor. It appears first near the gum line at about 10 years of age. The groove extends halfway down the tooth at 15 years, and all the way down the tooth by 20 years. By approximately 25 years, Galvayne's groove is halfway gone, and by 30 years, it has disappeared completely.
THE AGE OF A HORSE
To tell the age of any horse
Inspect the lower jaw of course;
The six front teeth the tale will tell,
And every doubt and fear dispel.
Two middle nippers you behold
Before the colt is two weeks old;
Before eight weeks two more will come
Eight months: the corners cut the gum.
At two the middle "Nippers" drop:
At three the second pair can't stop;
When four years old the third pair goes,
At five a full new set he shows.
The deep black spots will pass from view
At six years from the middle two;
The second pair at seven years;
At eight the spot each corner clears.
From the middle "Nippers" upper jaw
At nine the black spots will withdraw.
The second pair at ten are bright;
Eleven finds the corners light.
As time goes on the horsemen know
The oval teeth three-sided grow;
Then longer get - project before -
Till twenty, when they know no more."
How To Tell a Horse's Age by his Teeth
By: Jim Hamilton, DVM Click here
Starting at 2 years of age the horse's front teeth (incisors) are the way to tell age. There are three sets of incisors, central, intermediate and corners. Open the horse's lips and look to see if all are baby teeth or adults. The central pair are adult (permanent at 2 - 2 1/2 years., the intermediate at 3 - 3 1/2 years and the adult corner incisors at 4 - 4 1/2 years. At 4 1/2 - 5 1/2 years of age some horses (mostly males) grow canine teeth which is that fang-like tooth just behind the
Now starting at six years old, you need to look at the flat (table) surface of the lower incisors. There is a pit called the infundibulum that is easily seen in the center of each incisor's flat surface. At six years of age the pits of lower central permanent incisors are worn out (disappear).
At 7 years the lower central incisors lose their pit and the upper corner incisor develops a hook off the back edge.
By 8 years, all the lower adult incisors have lost their pit but a new small depression (dental star) appears in the lower central incisors.
At 9 years of Age, the horse's lower central and intermediate and intermediate and upper central incisors will have a dental star but the infundibulum (pit) of the upper corner incisor is still present - they do not disappear until the horse is eleven years old.
From the age of eleven on, the incisors become more triangular and the teeth begin to project out toward the front of the mouth more with each additional year.
The best way to get good at aging horses is by practice.Look at as many horses of know age and test yourself.
However from Wikipedia
At eight years the mark has gone from the corners and the horse is said to be aged. After this time, indeed good authorities say after five years, the age of a horse can only be conjectured. But the teeth gradually change their form, the incisors becoming round, oval, and then triangular. Dishonest dealers sometimes "bishop" the teeth of old horses, that is scoop them out, to imitate the mark: but this can be known by the absence of the white edge of enamel which always surrounds the real mark, by the shape of the teeth, and other marks of age about the animal
Cup - The dark or dark-brown to black cavity in the infundibulum.
Deciduous teeth - Temporary, fetal, milk or baby teeth. They are characterized primarily by their smaller size, constricted neck and shallow cup.
Dental star - The darker dentin that fills the pulp cavity as the tooth wears. It is dark yellow to yellowish-brown.
Dental table - The table, masticatory or occlusal surface.
Eruption - Pertains to the period when a tooth breaks through the gum.
Galvayne’s groove - The longitudinal depression on the labial surface of the upper corner incisor. The cementum remains in the groove as a dark line; the rest of the surface is worn to expose the white enamel.
Incisor teeth - Starting at the midline incisors are designated as centrals, intermediates and corners .
Infundibulum - The deep invagination of enamel which is filled with a variable amount of cement. Commonly referred to as the “cup.”
Labial surface - Surface toward the lips.
Lingual surface - Surface toward the tongue.
Permanent teeth - Second dentition or adult teeth.
Central Incisor The infundibulum - The Mark
Appearance of the table (occlusal) surface at different
stages of wear.
1. Shortly after eruption its breadth (transverse, long
diameter) marked by a-b, its thickness (short diameter) c-d.
2. Shows the table surface as it appears at the age of six years, the breadth a-b, begins to decrease, and the thickness, c-d, increases slightly; the tooth appears oval.
3. Shows a round surface of nine to twelve years. The two diameters become equal.
4. Shows a triangular surface of fourteen to seventeen years. The long diameter, c-d, in the labiolingual direction.
5. Shows surface of animal over twenty in which breadth,
a-b, measures only half as much as thickness, c-d.
6. Depicts exposed incisor.