How Old Is My Horse--Telling a horses age by its teeth

^{Aging horses is easier than any other animal as far as I am concerned.  Once you learn what you are looking at (look at lots of teeth!) you spot the markers immediately and with confidence.  It sounds complicated but it is not.  Print this and take it to the barn with you.  Look at every set of teeth you can.  Practice does make perfect!}

^{The most valuable criterion for estimating age is eruption, the tooth breaking through the gum. It is necessary at this time to be able to tell deciduous from permanent teeth. Deciduous teeth are smaller, have a constricted neck, show many fine longitudinal grooves on the labial (tongue) surface, and, at the time of replacement, are well worn (see Fig. 1-3).}

^{At eruption the permanent teeth are covered by yellow cement, whereas the remaining deciduous teeth are white, the cement having been worn off the-enamel. Permanent incisors have one large central groove on the labial surface. During the period of eruption, it is only necessary to part the lips and determine which permanent incisors have erupted. The best results will be attained with minimum disturbance of the animal. After eruption, it takes about 6 months for the tooth to grow out far enough to be in wear. When the preliminary examination reveals that all of the permanent lower incisors are in wear, the mouth must be opened far enough to see the occlusal (chewing)  surfaces and to evaluate the degree of wear. Even then strong-arm measures such as seizure of the tongue should be avoided. The horse can usually be induced to display the worn surfaces of the lower incisors if the examiner grasps the upper lip and lower jaw and inserts a finger into the diastema (space where there are no teeth on the jaw).}

^{The changes caused by wear of the occlusal surfaces are shown in Figure 1-1 and are brought into relation with the anatomy of the tooth. Notice that the infundibular enamel is continuous with the outer enamel when the tooth first erupts. When the crest where they meet is worn off, the dentin is exposed. The bottom of the infundibulum contains cement, so that when the infundibulum is worn down to that level it no longer has a cup to hold black decaying feed. Only the enamel spot is left. Because the pulp cavity is on the labial side of the infundibulum, the dental star formed by the closure of the pulp cavity is in the same relation to the enamel spot.}

^{The wearing process begins on the mesiolabial side of the occlusal surface. When the entire surface is in wear, the outer and inner enamel rings are completely separated by yellow dentin, and the tooth is said to be level. Evidence derived from the eruption and leveling of the teeth should be given more weight than the signs discussed subsequently.}

^{The disappearance of the black cavity or cup in the infundibulum is often used to estimate age. This sign is not reliable because it depends upon the depth of the enamel infundibulum and the amount of cement in the bottom, both of which are variable. The cups are supposed to disappear from lower I 1, I2, and I 3 at 6, 7, and 8 years, but this sign should be disregarded if it is not in agreement with the leveling of the teeth. For example, if the cup is gone from I 1, but I 3 is not yet in wear, the age is probably less than 5 years-not 6 years (see Fig. 1-3). The cup often persists in I 3 in horses older than 8 years.}

^{After the cup has disappeared, the bottom of the infundibulum remains, first as a long oval}

^{Wi@m off the-enamel. Permanent incisors have one large central groove on the labial surface. During the period of eruption, it is only necessary to part the lips and determine which permanent incisors have erupted. The best results will be attained with minimum disturbance of the animal. After eruption, it takes about 6 months for the tooth to grow out far enough to be in wear. When the preliminary examination reveals that all of the permanent lower incisors are in wear, the mouth must be opened far enough to see the occlusal surfaces and to evaluate the degree of wear. Even then strong-arm measures such as seizure of the tongue should be avoided. The horse can usually be induced to display the worn surfaces of the lower incisors if the examiner grasps the upper lip and lower jaw and inserts a finger into the diastema.}

^{The changes caused by wear of the occlusal surface are shown in Figure 1-1 and are brought into relation with the anatomy of the tooth. Notice that the infundibular enamel is continuous with the outer enamel when the tooth first erupts. When the crest where they meet is worn off, the dentin is exposed. The bottom of the infundibulum contains cement, so that when the infundibulum is worn down to that level it no longer has a cup to hold black decaying feed. Only the enamel spot is left. Because the pulp cavity is on the labial side of the infundibulum, the dental star formed by the closure of the pulp cavity is in the same relation to the enamel spot.}

^{The wearing process begins on the mesiolabial side of the occlusal surface. When the entire surface is in wear, the outer and inner enamel rings are completely separated by yellow dentin, and the tooth is said to be level. Evidence derived from the eruption and leveling of the teeth should be given more weight than the signs discussed subsequently.}

^{The disappearance of the black cavity or cup in the infundibulum is often used to estimate age. This sign is not reliable because it depends upon the depth of the enamel infundibulum and the amount of cement in the bottom, both of which are variable. The cups are supposed to disappear from lower I 1, 12, and I 3 at 6, 7, and 8 years, but this sign should be disregarded if it is not in agreement with the leveling of the teeth. For example, if the cup is gone from I 1, but I 3 is not yet in wear, the age is probably less than 5 years-not 6 years (see Fig. 1-3). The cup often persists in I 3 in horses older than 8 years.}

^{After the cup has disappeared, the bottom of the infundibulum remains, first as a long oval containing cement, then as a small round spot of enamel near the lingual side of the tooth. Disappearance of the enamel spot varies from 13 to 16 years (see Fig. 1-4).}

^{The dental star is the darker dentin that fills the pulp cavity as the tooth wears. It appears first as a dark yellow transverse line in the dentin on the labial side of the infundibulum of lower I 1 at 8 years. As the enamel spot recedes toward the lingual side, the dental star becomes oval and moves to the middle of the occlusal surface. It reaches this position in all the lower incisors when the animal is about 13 years old. At 15 years the dental stars are round. The star should not be confused with the enamel spot, which wears more slowly than the dentin and therefore remains elevated.}

^{The shape of the occlusal surface changes as the tooth is worn down. It is at first oval, with the long diameter extending from side to side. Then the lingual border becomes much more strongly curved, the two diameters become equal, and the tooth is said to be round, although its actual shape is that of an equilateral triangle with round comers. The term triangular is applied to the wearing surface when the labiolingual dimension or altitude of the triangle is longer than the labial border. In the final stage, when the root is exposed in very old horses, the wearing surface is oval, with the long diameter in the labiolingual direction. The transitional forms are hard to classify, and I 3 does not follow the pattern. The following table gives the most reliable stages in this process.}

^{The so-called seven-year hook is the result of the failure of the lower I 3 to wear all of the "occlusal surface of the upper I 3. An overhang is left at the back of the upper tooth. This hook is supposed to appear at 7, wear off at 9, and appear again at 11 years. The hook may or may not be present in any horse over 6 years old."' "In one study, about 60 percent of the horses in any age class from 8 to 18 years had the hook on one side or the other or on both sides. "}

^{Galvayne's groove is a longitudinal mark in the labial surface of upper I 3. The cement in the groove remains as a dark line, whereas that on the rest of the tooth is worn off to expose the white enamel. The groove is located midway in the length of the tooth; it is at first concealed in the alveolus, then gradually emerges from under the gum as the tooth grows out, and finally disappears as the ungrooved proximal part of the tooth comes into view. According to Galvayne, the groove appears at the gum line at 10 years, extends halfway down the tooth at 15 years, reaches the wearing surface at 20 years, and disappears by 30 years. The groove is of little value as a single indicator of age. If it is present, the horse is probably over 10 years old. The length of the groove or the absence of it can only be used in conjunction with other signs (Fig. 1-2).}

^{There are three other general indications of age. (1) When the teeth are viewed in profile, the angle between the upper and lower incisors becomes more acute with age. (2) When the teeth are viewed from the front, they are seen to diverge from the median plane in a young horse and to converge in an old one. (3) The arcade of the incisors when seen from the occlusal surface is a semicircle in the young horse and a straight line in the older animal.}

^{The more useful signs are arranged chronologically in the following list:}

^{1 week. Di 1 has erupted.}

 ^{1 month. Di 2 has erupted.}

^{8 months. Di 3 has erupted.}

^{1 year. Di 1 and Di 2 are in wear. Upper and lower Di 3 are not in contact. There is no deciduous canine.}

^{2 years. Di 1 and Di 2 are level, Di 3 is in wear. It is easy to confuse this stage with the adult if the general appearance of the animal and the differences between deciduous and permanent incisors are not considered.}

^{2'/2 years. I 1 erupts.}

^{3 1/2  years. I 2 erupts.}

^{4'/2 years. I 3 erupts.}

^{5 years. I 1 and I 2 are level, labial border of I 3 is in wear. Canines erupt at 4 to 5 years, usually only in males.}

^{6 years. Cup is gone from I 1.}

^{7 years. All lower incisors are level. Cup is gone from I 2. Hook is in upper I 3. Cement has worn off, changing the color from yellow to bluish-white.}

^{8 years. Dental star appears in I 1. Cup is gone from I'3.}

^{9 years. I 1 is round.}

^{10 years. I 2 is round. Galvayne's groove begins to emerge from the gum on upper I 3. 13 years. The enamel spot is small and round in the lower incisors. The dental stars are in the middle of the occlusal surfaces.}

^{15 years. Dental stars are round, dark, and distinct. Galvayne's groove extends halfway down to the occlusal surface.}

^{16 years. I 1 is triangular.}

^{17 years. I 2 is triangular. Enamel spots are gone from lower incisors.}

^{In addition to the changes in the incisors, it is important in dentistry to know that the permanent premolars erupt as follows: P 1 (wolf tooth) at 5 to 6 months, P 2 at 2'/2 years, P 3 at 3 years', P 4 at 4 years. The molars erupt: M 1 at 1 year, M 2 at 2 years, M 3 at 31/2 to 4 years. Note that the large cheek teeth erupt at ages that correspond with their numerical designations.}

^{The upper cheek teeth are slightly lateral to the lower cheek teeth; therefore, the labial edge of the upper cheek teeth and lingual edge of the lower cheek teeth do not wear and must be filed (floated) to prevent injury to the lip and palate. Caps are remnants of deciduous teeth that remain attached to the erupting surfaces of permanent teeth.}