(see TARTAR)
Dentine
Dentine is the dense yellow or yellowish-white material of which the greater part of the teeth is composed, and which in elephants, etc., consti-tutes ivory. The dentine is pierced by numerous fine tubules which communicate with the sensitive pulp in the hollow of the tooth-root, along each of which run tiny vessels and nerves which nourish its structure. In the young, newly erupted tooth the dentine is covered over with a layer of hard, dense, brittle enamel, which prevents too rapid wear of the softer dentine. (See TEETH.)
Dentition
Dentition refers to the configuration and con-formation of the teeth, with special reference to their periods of eruption through the gums.
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Horses 176
Cattle 177
Sheep 178
Pigs 178
Dogs 179
Cats 179
HorsesThe dentition of the horse consists of the following teeth:
Incisor teeth are 6 in number in the upper and lower jaws. The temporary incisors differ from the permanents in that while each of the former possesses a definite crown, neck, and root, the latter do not. Moreover, the tempo-raries are smoother, whiter, and smaller. When there are both temporaries and permanents present in the mouth it is not usually difficult to differentiate between them, but inexperi-enced persons sometimes confuse temporaries 176 Delivery
D
Incisors Canines Molars Upper jaws 6 2 12, 13 or 14 Lower jaws 6 2 12, 13 or 14
and permanents in yearlings and 5-year-olds, or in 2-year-olds and 6-year-olds. A typical unworn permanent incisor tooth from a horse possesses an infundibulum, or ‘tucking-in’ from its free edge or crown (see TEETH), and since this results in an infolding of the enamel, 2 rings of enamel, an outer and an inner, are seen in the partly worn tooth. However, as wear proceeds the inner ring of enamel eventually disappears, since the level of wear has passed the depth of the infundibulum. At the same time, the outline of the tooth is changing from an oval to a quadrilateral, and eventually to a triangle, since the tooth is tapered from crown to root.
It is upon an examination of these factors that the estimation of the age of an adult horse is based.
The incisors are named centrals, laterals or intermediaries, and corners, according to their situation in the mouth.
Canines (‘tushes’, ‘eye-teeth’, or ‘dog-teeth’) number 2 in each of the jaws – 1 on the right and 1 on the left side. In horses, canine teeth are only typically present in the male, although rudimentary canines may occasionally be found in mares. They are situated between the last incisor and the 1st molar, 1 on either side, being nearer to the incisors than to the molars.
The spaces between the canines and the molars are spoken of as the bars of the mouth. In the bridled horse, the bit runs across the bars.
Molars (‘grinders’, or ‘cheek teeth’) number 6 or 7 at each side of both upper and lower jaws, according to whether ‘wolf teeth’ are or are not present. The first 3 permanent molars are represented in the milk dentition and are therefore sometimes called premolars. Each tooth has a complicated folding of the enamel which bears some resemblance to the capital letter ‘B’.
Eruption
The ‘eruption’ means the time when the tooth cuts through the gums, and not when it comes into wear. It must be remembered that in the table, allowance has to be made for the time of foaling. All thoroughbreds are dated as having their birthdays on January 1 each year, and all other breeds of horses on May 1, so that with an early foal the teeth will appear sooner than the corresponding periods subsequent to May 1 or January 1 in any year, and with a late foal, later.Usually, the teeth in the upper jaw erupt soon-er than those in the lowsoon-er jaw, although thsoon-ere are many exceptions to this.
An estimate of the horse’s age from its teeth can only be approximate in later life. Galvayne’s groove is practically the only definite guide, and even it may be indistinct or absent.
Cattle The permanent dentition of cattle consists of the following teeth:
In the upper jaw there are neither incisors nor canines, while in the lower jaw there are 8 teeth present in the incisor region. The most posteri-or of these (i.e. 1 on either side) are supposed to be in reality modified canines, which have moved forwards in the gums and have assumed the shape and the functions of incisors.
The temporary or milk dentition is as follows:
Incisors are absent from the upper jaw of cattle, their place being taken by the ‘dental pad’
– a hard, dense mass of fibrous tissue developed in the upper incisor region, against which the 8 lower incisor teeth bite. Each is a simple tooth possessing a spatulate (spade-shaped) crown, a constricted neck, and a tapered root or fang.
The teeth are loosely embedded in the jaw so that a slight amount of movement is normally possible. They are named centrals, 1st interme-diates or medials, 2nd intermeinterme-diates or laterals, and corners; but it is perhaps more convenient to enumerate them from the central pair as 1st pair, 2nd pair, etc.
Dentition 177
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Incisors Canines Molars
Upper jaws 6 0 6
Lower jaws 6 0 6
Incisors Canines Molars
Upper jaws 0 0 12
Lower jaws 8 0 12
Incisors Canines Molars
Upper jaws 0 0 6
Lower jaws 8 0 6
Time of
eruption Incisors Canines Molars Birth to 1 2 temporary — —
week centrals
2 to 4 weeks 2 temporary — Nos. 1, 2 and
laterals 3 temporary
molars 7 to 9 months 2 temporary — No. 4
perma-corners nent molar
1 year 6 — — No. 5
perma-months to 1 nent molar
year 8 months
2 years 2 permanent — Nos. 1 and 2
6 months centrals permanent
molars 3 years 2 permanent — No. 3
perma-6 months laterals nent molar
4 years — All 4 No. 6
perma-canines nent molar
4 years 2 permanent — —
6 months corners
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Canines are absent unless the corner incisors are considered as modified canines.
Molars are like those of the horse in number and arrangement, except that they are smaller and progressively increase in size from first to last, so that the 1st is quite small, and the length of gum which accommodates the first 3 is only about half that occupied by the last 3. One or more ‘wolf teeth’ may be present in rare cases.
Eruption
In ruminants – whether domesti-cated or not – the eruption of the permanent teeth is subject to considerable variations.SheepThe terms which were used as applied to cattle, and the description of the various teeth, may be taken to hold good for sheep as well. The sheep has 8 lower incisor teeth but none in the upper jaw. There are 24 molar teeth, 12 in each jaw, of which half these num-bers are represented in the temporary dentition.
Eruption
The following is given as an average eruption table for improved breeds of sheep in Great Britain:PigsThere is probably no farm animal which shows such variation in the eruption of its teeth as the pig, but because of the demand for young pigs for killing by weight and size rather than by age, and because of the intractability of older breeding animals – sows and boars – the actual age of the pig is not of such very great importance, except perhaps for fat stock show purposes.
When the permanent teeth have all erupted they are distributed as follows:
In the molar region there is a little tooth in each of the four jaws, erupting at about 5 to 6 months, which is permanent from the very beginning. It is sometimes called the premolar, and in some cases is never developed. The next 3 teeth behind it are represented in the tempo-rary dentition, the permanents replacing them in the usual way. The last 3 teeth are true molars, i.e. permanents only.
The temporary dentition is as follows:
Incisors: the upper incisors are small, and are separated from each other by spaces. The 1st pair (centrals) are the largest, and converge together.
The 2nd pair are narrower and smaller; while the corner pair are very small and laterally flattened.
The lower incisors are arranged in a convergent manner, and point forwards horizontally in the jaw. The 1st two pairs are large prismatic teeth deeply implanted in the jaw-bones and are used for ‘rooting’ purposes. The corner pair are smaller, and possess a distinct neck.
Canines, or tusks, are greatly developed in the entire male, and both upper and lower tusks project out of the mouth. The upper canines of a boar may be 3 to 4 inches long, while the lower ones may reach as much as 8 inches in an aged animal. Each has a large permanent pulp cavity from which the tooth continues to grow throughout the animal’s life.
At 3 months the lateral temporary incisors are well up, and the temporary molars are well in wear.
At 5 months there are signs of the cutting of the premolars (i.e. the No. 1 molars), and the 5th molar (a permanent) is seen behind the temporaries. It is, however, not yet in wear.
178 Dentition
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Time of eruption Incisors Molars Birth to 1 month All 8 tempo- All 12
tempo-raries raries
3 months — 4th permanent
9 months — 5th permanent
1 year to 1 year 1st pair —
3 months permanent
1 year 6 months — 6th permanent 1 year 9 months 2nd pair 1st and 2nd
permanent permanents
2 years — 3rd permanent
2 years 3 months 3rd pair — permanent 2 years 9 months 4th pair —
to 3 years permanent
Time of
eruption Incisors Canines Molars At birth Corner All 4 tem- —
temporaries poraries
1 month Central — Nos. 2, 3
temporaries and 4 tem-poraries
2 months Lateral — —
5–6 months — — No. 1, which
remains through life, and No. 5 permanent
8 months Corner — —
permanents
9 months — All 4 per- —
manents
10–12 months — — No. 6
permanent 12–13 months Central — Nos. 2, 3
permanents and 4 per-manents 17–18 months Lateral — No. 7
permanents permanent
Incisors Canines Molars
Upper jaws 6 2 14 (i.e. 8
and 6)
Lower jaws 6 2 14 (i.e. 8
and 6)
Incisors Canines Molars
Upper jaws 6 2 6
Lower jaws 6 2 6
At 6 months the premolars are cut and the 5th permanent molar is in wear.
At 7 to 8 months there are signs of the cutting of the corner permanent incisors, or they may already be through the gums. The permanent tusks are also often cutting through the gums at this age in forward animals.
At 9 months the corner permanent incisors are well up and the permanent tusks are through the gums, although in many cases there may be still one or two of the small temporary tusks in position. Where they are cut they are not far through the gums.
At 1 year it is generally held that the central permanent incisors cut through the gums, but there are a large number of animals which do not cut these teeth till about 13 months old.
The 6th permanent molar cuts at this time, and is more reliable than the incisors for reference.
Shortly after 1 year the 3 temporary molars fall out and their places are taken by the permanents. They are into line with the other molar teeth 3 months later.
At 17 to 18 months, when the final changes occur, the 7th molar, the last permanent molar tooth, and the lateral permanent incisors are cut through the gums. By this time the pig has obtained its full permanent dentition, and the succeeding changes are not sufficiently reliable to warrant estimations of age being based upon them.
Dogs The average adult dog has 42 teeth.
The upper jaw contains 6 incisors, 2 canines, 8 premolars, and 6 molars. The lower jaw has 6 incisors, 2 canines, 8 premolars, and 6 molars.
(There is some breed and individual variation in the number of permanent teeth, short-skulled breeds, e.g. Pekingese, Boxer, and Bulldog, having fewer teeth.)
CatsThe number of teeth in the adult cat aver-ages 30. In the upper jaw there are 6 incisors, 2 canines, 6 premolars, and 2 molars; while the lower jaw has 6 incisors, 2 canines, 4 premolars, and 2 molars. Some cats have only 28 perma-nent teeth; lacking 2 premolars.
Rabbitsare unique in that they are born with permanent teeth. Milk teeth are shed before birth and may be found in the placenta.