Dentition and ageing of horses

Introduction

The age of the horse is determined by the appearance of Incisor teeth. The use of the examination of teeth to determine age is of value in non-pedigree animals. Further it is important for the following reasons.

• To issue soundness certificates
• For valuation of livestock
• For selection and purchase

The surface which bites the food or its fellow on the opposite jaw is the TABLE OR WEARING SURFACE of the tooth. The mark of infundibulum is the blackened depression seen on the table. It is lined by distinct narrow pearly  white ring of enamel.

The crown of the tooth is that part which is above the gum and the point where the gum and tooth meets is the neck. The fang is that part within the jaw,  hollowing its cavity contains the blood vessels and nerves which nourishes and sensitize the tooth.

Alveolus: The bony cavity in which the fang of the tooth is embedded.

Buccal Surface: The outer surface of tooth that is next to the cheek.

Central Incisors: The 2 incisors immediately on each side of middle line

Cheek Teeth: Premolars and molars are often spoken off collectively as cheek teeth

Corner Incisor: The outer or most lateral pair

Crown: The part of the tooth which appears above the gum

Deciduous or milk teeth or temporary teeth: These are temporary teeth which are pushed out by the growth of corresponding permanent teeth

Erupting or cuttin: Teeth has cut through the mucous membrane of the gum

Fang hole or Dental star: The upper extremity of pulp cavity

Fang or Root: Part of tooth under the gum

Galvayne's Groove: The part of the groove running down the labial surface of the ground of the upper corner incisors of the horse. It normally appears near the gum at 10 years, is half way down at 15 years, extends down the whole length of tooth at 20 years, has grown half way out at 25 years, and has disappeared at 30 the age of years. Simultaneously appearance of star and disappearance of mark takes place.

Infundibulum: Dark depression on the table in the incisor it is called as mark.

Inwear: Hole of the table of tooth is in contact with opposite teeth of other jaw.

Labial surface: The surface next to the lips of the incisors.

Lateral Incisors: The second pair in between central and corners.

Lingual surface: The inner surface of tooth  next to the tongue.

Mandible: The lower jaw

Mandibular cheek teeth: Lower premolars and molars.

Maxilla and premaxilla: Constitute the upper jaw.

Maxillary sinus: Cavity in the skull situated in horse above the last 3 or 4 cheek teeth into which their roots project.

Molars: The last 3 cheek teeth. These are permanent teeth.

Neck: Joins the crown to the fang.

Pulp Cavity: A hollow part of tooth containing nerves and blood vessels.

Shelly: The newly cut incisor teeth either temporary or permanent.

Table or wearing surface: The part of tooth which grinds the food and comes in contact with tooth of other jaw.

Tush: The canine tooth of the horse present in stallion or gelding but absent or rudimentary in mark It is situated near the incisors in the lower jaw than in the upper jaw.

Full Mouth: All permanent teeth (both molars and incisors) have fully erupted.  Full mouth is seen in the case of horses at 4¹ /2 to 5 years.  A horse is said to be aged, when it is over 15 years.

Structure of tooth

The pulp is the soft gelatinous tissue occupying the pulp cavity in the centre of the tooth. The pulp is well supplied with blood vessels and nerves.

• Dentine: Covers the pulp and is hard and yellowish white in colour.
• Enamel: Hardest tissue in the body and covers the dentine of the crown. It is clear and bluish white in colour.
• Cement: Covers the dentine of the roof. The embedded portion of tooth is firmly attached to the alveolus, periosteum by layers of connective tissue.

There are 2 complete sets of incisors.

Temporary, milk or Foal teeth and permanent or horse teeth. The temporary teeth is small and white, has a distinct neck, and a short fang which practically disappears as the tooth gets older. The permanent tooth are longer, stronger and brown in colour and has no marked neck or distinct neck and has a stout long fang.

Dental formula and eruption of teeth

Eruption of teeth in Horse

• 9 days - Central incisors (temporary)
• 9 weeks - Lateral incisors (temporary)
• 9 months - Corner incisors (temporary)

• 1 Year - Central incisor
• 1 ½ Year - Lateral incisor
• 2 Years - Corner incisor

• 2 1/2 Years - Central incisors
• 3 ½ Years - Lateral incisors
• 4 1/2 years - Corner incisors

• 6^th Year - Central incisors
• 7^th Year - Lateral incisor takes in lower jaw
• 8th Year - Corner incisors
• 9th Year - Central incisors
• 10^th Year - Lateral incisors takes in upper jaw
• 11^th Year - Corner incisors

When the dental mark disappears, the dental star reappears.

• Temporary dentition: 3/3, 0/0, 3/3, 0/0
• Permanent dentition: 3/3, 1/1, 3 or 4/3 or 4, 3/3

• At birth: The foal usually has two temporary central incisors in each jaw through the gums, or just appearing.
• At 1 month: The two temporary lateral incisors erupt. At about this age the first three temporary molars cut through the gums.
• At 6 months: The foal’s mouth has a neat and compact appearance. The central and lateral incisors being well developed and are in wear upon their anterior edges.
• At 9 months: The foal has two temporary corner incisors cut through the gums, but these are only touching along their anteri­or edges.
• At 1 year: The temporary central and lateral incisors start wearing due to the friction with lower teeth. The temporary corner incisors are still shell like and only touching along their anterior edges.
• At 1 year 6 months: The temporary corner incisor starts wearing all along their edges, and the centrals and laterals have become large and well formed. At about this age the 5th molars erupts.
• At 2 years: The temporary corner incisors are well in wear, and all the incisor teeth have well formed tables.
• At 2 years 3 months: The temporary central incisors are often loose, and the gums are receding from their necks and may appear to be inflamed. The teeth are only held in position by a short portion of fang or root.

Eruption of permanent teeth

• At 2 years 6 months: The two temporary central incisors fall out and are replaced by permanent central incisors. At the same time the first 2 temporary molars in each jaw are shed, and the corre­sponding permanent molars get erupt.
• At 3 years: The two permanent central incisors have met the corresponding incisors in the lower jaw, but only a slight amount of wear is showing on their tables.
• At 3 years 6 months: The four permanent lateral incisors have erupted, pushing out the corre sponding temporary lateral incisors in the process.
• At 4 years 6 months: The temporary corner incisors fall out and the permanent corner incisors cut through the gums.
• At 5 years: The permanent corner incisors meet their correspond­ing corner incisors in the lower jaw along their anterior edges, but their posterior corners are still rounded off and unworn.
• At 6 years: The permanent corner incisors have lost their shell like appearance and are in wear along both sides of their central cavity.
• 7^th to 15^th Year of age
• At 7 years : The tables of the lower corner incisor teeth are well formed and the infundibulum in each is shallow. The upper corner incisor will develop a hook known as ‘dental hook’ or ‘7 year hook’. It is due to the fact that the lower corner incisor is placed somewhat further forward in the jaw than the corre­sponding upper tooth.
• At 8 years : In the tables of the central incisor teeth a brown­ish or yellowish brown, liner streak will be seen running trans­versely across the tooth between the inner and outer rings of enamel and situated just behind the anterior edge of the tooth. This is called the ‘dental star’. It is usually confined to the centrals. The 7 year hook will slowly disappear by the 8th year.
• At 9 years : The central and lateral incisor teeth are more triangular in outline with posterior angle rounded. The table is much more broader and the angle between the teeth is more acute.
• At 10 years : Infundibulum is worn out, dental star is distinct and the galvayne’s groove appears on the labial surface of the upper corner incisors.
• At 11-13 years : All the teeth appear longer on account of the receding gums. The tables of each of them gradually become distinctly triangular with rounded angles. Dental star becomes distinct, dental hook appears on the corner incisors and the angle of the teeth is more acute.
• 15^th to 30^th Year of age
• At 15-16 years : The tables of the teeth are becoming broader and in the centre of the dental star a cleft or depression usually appears. Galvayne’s groove has grown about half way down to the free edge in the upper corner teeth.
• At 18-20 years : The angle formed between the teeth of the two jaws is almost a right angle, and the tables of teeth are getting much smaller. A distinct depression appears in the centre of the dental star. Galvayne’s groove has almost reached the free bor­der.
• From 20-30 years : Galvayne’s groove is practically the only definite guide, and even it may be indistinct or absent.

Bishoping

It is attempting to make an old mouth to look younger. The teeth are rasped and levelled. A false mark is gouged out of the centre of the table and blackened with caustic (usually with silver nitrate crystals). This can be found out by observing,

• The angle of teeth,
• The absence of enamel rim and
• Occasionally the traces of rasp being used to shorten the teeth.