DENTITION Age as indicated by the Teeth All the domesticated animals are provided with two sets of teeth. The first set, called the temporary or milk teeth, are subsequently replaced, at more or less regular intervals, by the second set or permanent teeth. The regu larity of the eruption of teeth and the effects of wear on their surfaces afford data from which the ages of the various animals may be estimated. It should be borne in mind, however, that varia tions are not infrequent. Some animals are precocious in the eruption of their teeth, which give the impression at the time that they are older than they are in reality, while on the other hand the eruption in some cases is retarded, having the opposite effect.
The portion of a tooth above the gum is called the crown, while the portion embedded in the gum and bone is called the root or fang. The junction of the crown and root, frequently indicated by a constriction, is called the 'neck, while the surface, which comes in contact with the opposing tooth, or dental pad, is called the table.
Teeth are composed of four tissues; the bulk of a tooth is composed of a hard, yellowish-white substance called dentine. The dentine of the root possesses a cavity which is called the pulp cavity. This is filled with a soft gelatinous tissue called the pulp, which is well supplied with blood-vessels and nerves. The dentine of the crown is covered by a hard, white or bluish white enamel which acts as a protective agent. Round the dentine of the root is the cement substance has a structure somewhat resembling bone. In so called complex teeth it is also present in the spaces between the enamel folds of the crown. The socket into which the root of the tooth fits is called the alveolus, and the root is secured in this socket by the gum and a vascular layer called the alveolar periosteum.
The Horse The teeth of the horse consist of six incisors or front teeth, two canines or tushes, and twelve molars or grinders in each jaw.
The Incisor Teeth. The horse possesses three pairs of incisor teeth in the upper and in the lower jaw, named respectively, commencing from the mid-point, centrals, laterals, and corners. In estimating the age the incisor teeth of the lower jaw are usually referred to.
Temporary Incisois.Temporary teeth may be distinguished from permanent teeth by being much smaller and possessing a distinct neck between the root and crown. The crown is short and wide, and shell-like in appearance, and is either smooth or slightly fluted. The root or fang is small and flattened. The tables of temporary and permanent incisors both possess a depression called the cup, mark, or infundibulum. This is much shallower in the temporary than in the permanent teeth. It is always surrounded by a ring of enamel.
At birth or within 10 days the foal possesses in each jaw the central incisors. These are followed by the laterals at from 4 to 6 weeks old and by the corners from 6 to 9 months old. Thus at 1 year old all the temporary incisors are present, the centrals show a little wear, the posterior margin of the table being level with the anterior margin, while the corner teeth are still sharp and shell-like.
At 2 years old all the incisor teeth show wear, the infundibulum has disappeared from the centrals and laterals and sometimes from the corners. The teeth are a little wider apart at their necks on account of the gradual widening of the jaw with age.
Permanent Incisors. The permanent teeth may be distinguished from the temporary incisors by being. larger, broader, and more solid-looking, less shelly, and the neck is not well marked. They possess distinct vertical grooves down the front and are usually dis coloured or dirty-looking.
At 21- years old or thereabouts the central temporary incisors are shed. The permanent ones then make their appearance, and are level with the other teeth at 3 years old. Thus, at 8 years old a horse possesses two large central permanent teeth and four milk teeth in each jaw.
At about 3i years the lateral milk teeth are shed and are replaced by the permanent incisors, which become level with the centrals at 4 years old. At this age a horse thus possesses four large incisor teeth and two small milk teeth in each jaw.
At 0 years old the corner milk teeth are shed and the permanent ones appear, being well up at 5 years old but still sharp and shell like. Thus, at 5 years old the horse possesses a full mouth of six permanent incisor teeth in each jaw.
At 6 years old the cup or infundibulum has usually disappeared by wear from the lower central incisors, but an enamel spot or star may persist for one or two years longer. The sharp edge has disappeared from the corner incisor, forming a table.
After 6 years old thoroughbred horses are usually called"aged,"and although there are certain data which assist one in estimating the age after that period one can be much less positive on the point.
At 7 years old the infundibulum has dis appeared from the centrals and laterals, though a trace of the enamel may persist, and at this age or earlier a small projection called the hook can usually be observed at the posterior corner of the upper corner teeth. This is due to the fact that the lower corner incisor table does not completely oppose the table of the upper corner tooth at this time.
At 8 years old the infundibulum has dis appeared from all the lower incisor teeth, and generally the hook has become worn away from the upper corner tooth.
The upper incisor teeth, with the exception of the corners, are rarely referred to, but it may be mentioned that as a rule the upper temporary teeth are shed a little sooner than those of the lower jaw, and moreover the infundibulum is deeper and consequently persists about two years longer than in the opposing lower incisors.
The Secondary Mark, Dental Star, or Fang Hole. As the result of the wearing away of the crown of incisor teeth, a trace of the pulp cavity sooner or later makes its appearance. This is indicated by a slight discoloration or mark a little nearer the front of the tooth than the position of the infundibulum. This is called the star or secondary mark. It generally appears in the central teeth lower jaw at 8 years old and in the laterals at 9 years old. It is readily distinguished from the infundibulum by the absence of enamel.
As age advances changes also take place in the shape of the tables of the incisor teeth. At first they are very much wider from side to side than from front to back. They subsequently become more or less triangular in outline—a change that is observed in the centrals at 9 years old, in the laterals at 10, and in the corner about 11 years. Later the tables become almost round, and in very old horses they often wider from front to back than from side to side.
Galvayne's Groove. At 9 years old a well marked groove, called Galvayne's groove, begins to make its appearance close to the gum of the upper corner incisor teeth and gradually extends downwards, so that it reaches about half way down the tooth at 15 years old and extends the whole length of the tooth at about 20 years old. After this age it tends to disappear in the same direction, and is missing from the upper half of the tooth at 25 years old, still persisting in the lower half, while it disappears entirely at about 30 years old.
Intermediate ages can be estimated by the length of this groove. It should be pointed out, however, that not infrequently Galvayne's groove differs in length on the two upper corner teeth of the same horse. In such a case the average should be taken.
Other changes which occur as the result of advancing age involve the slope of the teeth and their length. In young horses the upper and lower incisors meet and form almost a semicircle, but later the teeth form a wider angle with the jaw and thus project forwards, so that in very old animals they stick almost straight out. At the same time the gums recede faster than the teeth are worn, making the teeth apparently longer. In extreme age, however, when the gums have receded to their utmost limit, the effect of wear may reduce them to comparatively short stumps.
The Canine Teeth or Tushes. These teeth are usually only present in males, although small tushes are present in mares. There are no temporary canine teeth in horses. The permanent tushes usually pierce the gum between 3i and 4 years old and are fully developed at about 5 to 5i years old, looking fresh, white and Shelly, and possessing sharp edges and also grooves on the inner surfaces which can be readily felt with the finger. These edges and grooves have usually disappeared at 7 years old, and later the points become worn and the tushes discoloured. The opposing tushes do not meet as in the case of other teeth. The wear they undergo is the result of mastication, and in very old horses the Lush may consequently be reduced to a comparatively short stump.
The temporary molars are usually in position at birth or within one month after birth.
makes its appearance' at about the age of 5 or 6 months. It is sometimes shed in the upper jaw, but usually remains permanently in the lower jaw, and is known as a wolf tooth.
The total number of teeth of the horse may thus be shown: Temporary, on each side of each jaw— L 3; T. 0; M. 3=6. Total. 24.
Permanent, on each side of each jaw— I. 3; T. 0 or 1; M. 6=9 or 10. Total, 36 or 40.
This total may be increased when wolf teeth persist.
Bishoping . a fraudulent practice, the object of which is to make the teeth of an old horse resemble those of a younger horse. For this purpose the long incisor teeth are shortened by means of a file or saw and an artificial infundibulum is made by means of a drill or hot iron. In the former case the mark thus produced is discoloured by the application of silver nitrate. The fraud can be readily detected by the absence of the enamel ring round the infundibulum and also by the angle at which the upper and lower teeth meet.
The Ox Cattle possess no incisor teeth in the upper jaw. Their place is taken by a dense mucous membrane which is called the dental pad. In the lower jaw there are four pairs of incisor teeth or pincers, named respectively from the mid-point, centrals, middles, laterals, and corners. They are all simple teeth and possess no in fundibulum. The crown is white and shovel or chisel-shaped, and the root is somewhat loosely fixed, allowing considerable movement of the incisor teeth. The neck is well marked.
The temporary incisor teeth are distinguished from the permanent ones by their very small size. They are usually present either at birth or within three or four weeks after birth.
The permanent incisor teeth are erupted less regularly than those of the horse, depending mainly upon the breed and mode of feeding. The following periods may be regarded as average, though an allowance of three months in either direction may be met with not in frequently.
The central permanent incisors appear at 1 year or 9 months and are well up at 2 years old. The middles appear at 2 years and 3 months and are level with the centrals at 2 years old. The laterals appear at 2 years and 9 months and are well up at 3 years old. The corners appear at 3 years and 3 months and are well up at si years old. Owing to the irregularity already referred to, it is quite possible to meet with authentic cases of 3-year-old cattle possess ing eight permanent incisor teeth. Such cases require careful investigation, and reference may be made to the third molar. If this tooth is a permanent one and is well up and meeting its opposing tooth, the animal should be regarded as fully 3 years old.
With advancing age the incisor teeth become more widely separated. The necks become more pronounced and the suggestion of a table often forms at the top of the crown.
The Molar Teeth. The temporary molar or cheek teeth are all in position within a month after birth.
The first permanent molar to appear is the fourth, which is in position at 6 months old. The fifth molar is cut at about 1 year and 3 months. The sixth molar appears at from 2 years to 2 years and 3 months, and the first and second temporary molar teeth are shed and replaced by permanents about the same time or shortly afterwards. At about 2i to 3 years the third temporary molar is shed and the permanent is in position.
The number of teeth possessed by cattle may be shown by the following table: • Temporary, on each side of upper jaw— I. 0; M. 3=3.
Temporary, on each side of lower jaw— I. 4; K 3=7. Total, 20.
Permanent, on each side of upper jaw - L 0; M. 6=6.
Permanent, on each side of lower jaw I. 4; M. 6=10. Total, 32.
(The age of the horned breeds of cattle can frequently be estimated by the examination of their horns and the counting of the rings which appear there. The first ring usually appears at about 3 years, and subsequently an additional ring occurs every year. The calculation, there fore, consists of counting two years for the tip and one year for each ring present. For ex ample, if the horn of a cow carries 4 rings the age of that animal would be estimated at 6 years old.) The Sheep The number and position of teeth of the sheep resemble those of cattle, but their eruption differs from them. The incisor teeth are pro portionately longer and narrower than those of cattle, and the roots are more firmly fixed than in those of the ox. The molars are covered by a thin layer of cement which is usually black.
Incisor Teeth or Pincers. The lamb has rarely any temporary incisors present at birth, but as a rule the centrals and middles are cut before it is a week old. The third pair or laterals are usually through within a fortnight, while the corner incisors are present at about 1 month old.
Permanent Incisors. As in the ox, there are greater variations in the eruption of these teeth than in the horse. The average periods, how ever, may be taken as follows: The central permanent incisors appear at about 1 year and 3 months, and the other incisors follow at intervals of about 6 months; consequently the middles appear at 1 year and 9 months, the laterals 2 years and 3 months, and the corners at about 2 years and 9 months or 3 years.
A 6 - toothed sheep (implying 6 permanent incisors through and well up) is about years old.
An 8-toothed sheep or"full-mouthed"sheep is about 3 years old.
After that age the teeth become discoloured and often broken, and sheep are then called"broken-mouthed." The Molars.The temporary molars are all present in from 2 to 4 weeks after birth. At 3 months old the first permanent molar, the fourth in position, appears, though it may be delayed one or two months in the upper jaw. At about 9 to 12 months old the fifth permanent molar appears. At from 18 to 21 months old the sixth molar is in position, and about the same time or shortly afterwards the first three temporary molars are replaced by permanent molars.
The Pig The dentition of the pig differs considerably from that of the animals already referred to.
The Incisor Teeth. Temporary.The pig possesses three pairs of incisor teeth, named respectively, centrals, laterals, and corners, the permanent ones being preceded by temporary or milk-teeth. There is also a temporary tush. At birth the temporary corner incisor and temporary Lush are both in position. The central incisor appears at about 3 to 4 weeks and the lateral incisor appears at about 2 months after birth.
The permanent incisors and tushes are erupted in the same order as the temporary teeth. The corner incisors and tushes appear at about 9 months old, the central permanents at about 12 months old, and_ the lateral permanent incisors at about 18 months old.
The Cheek Teeth or Grinders.The second and third temporary molars appear in the upper jaw within a week after birth. In the lower jaw they are often delayed until the pig is from 2 to 4 weeks old. The first temporary molar is present at about a month or 6 weeks old. The fourth molar, which is the first permanent grinder to show, appears at 5 months old, and is followed very shortly by the pre molar teeth in front of the temporary molars at between 5 and 6 months old. The fifth molar appears at about 10 months. The temporary molars are replaced more or less together between the ages of 12 and 15 months. The last tooth to appear is the sixth molar, which comes through at between 18 and 20 months old.
The dog possesses 28 temporary teeth and 42 or 44 permanent teeth.
The Temporary Teeth. None of the tem porary teeth of the dog are present at birth. The temporary canine is usually the first to appear at between 3 and 4 weeks old, and this is quickly followed by all the other temporary teeth, which are present between 4 and 5 weeks old, consisting of central, lateral, and corner incisors, and first, second, and third molars. The molars may precede the incisors by several days or a week.
The Permanent Teeth.The first permanent teeth to appear are the central and lateral incisors, which come through about 4 months old—a little variation may be met with in either direction. The permanent corner and tush appear at about 5 months old.
Of the cheek teeth the pre-molars, which are permanent at the outset, appear at about 4 months old, and the fourth molar between 4 and 5 months. Between the age of 5 and 6 months the fifth molar appears, and the first, second, and third temporary molars are replaced by permanent ones. The sixth molar appears at from 6 to 8 months old in the lower jaw and is often missing from the upper jaw.
The third upper molar and the fourth lower molar are larger than the others and are called the"carnassial"teeth.
There is frequently one molar less in each side of the upper jaw, reducing the total to 42.