Some breeders, usually the more experienced, watch mouths constantly throughout growth, but some of the less experienced are apt to pay attention to the more visible features and imagine perhaps that they have bred a 'flier' until someone points out that the puppy lacks the scissor bite (where it is required) or is slightly overshot, or perhaps very much undershot (where it is not required).
What is less often observed, but is nowadays almost equally as important to the exhibitor, is the number of teeth present and the way they are placed in the gums. (Fig. so.)
So far as jaw length is concerned and as a guide to whether the incisor teeth will end up with the correct relationship between the upper and lower sets, it should be borne in mind that the lower jaw goes on growing for a short period after growth of the upper jaw has ceased.
In other words a slightly overshot mouth at three months of age may be corrected by the time the puppy is eight or nine months old, but a slightly undershot mouth at four months is not likely to improve and may be worse at eight months. These remarks apply only to the long-headed breeds and not to the short-faced (brachycephalic) breeds in which the tendency towards an undershot mouth is greater.
A difficulty arises in a breed such as the Shih-Tzu, in which permissively there may be a slightly undershot jaw, but not to an extent where the lower incisors become visible when the lips arc closed normally.
The majority of cases of undershot jaw may be regarded as incompletely recessive. In crossbreeds, where one parent is long-headed and the other short-headed (brachycephalic), the majority of the offspring arc not undershot, but if these are mated again to a brachycephalic partner the puppies will be about 5o per cent undershot.
A similar incidence is seen when, for example, an undershot Terrier is mated with one with normal jaw length. Only a small proportion of the puppies may be undershot, but if the level-mouthed puppies are mated to an even slightly undershot partner, or to a carrier, at least half of the offspring will be undershot. This finding applies also in breeds that have been produced by crossing the two types, the dolichocephalic (long-headed) breeds with the brachycephalic (short-headed).
In an overshot jaw the incisor teeth may be smaller than normal and not infrequently they may fit loosely into their sockets (alveoli) so that they may be moved slightly by finger pressure.
In some breeds, strains exist in which excessively overshot jaws occur, or in which the lower jaw fails to reach its normal length. Cases of this kind are seen occasionally in Dachshunds and in various Terriers, but as such puppies may have difficulty in sucking it is unlikely that many reach maturity.
The number of teeth present is important in dogs intended for exhibition even if it has no practical bearing on the welfare of specimens intended as pets. It is a fact that the skulls of prehistoric dogs in existence show a complete absence of the first three premolar teeth, and in our modern dogs it is by no means uncommon for only two out of the normal four premolars of each upper jaw to be present.
A dog should possess three premolar teeth lying in the space between the large canine tooth of either side of the upper jaw and the fourth premolar, which is almost always present and is the largest of all the cheek teeth. This tooth operates in unison with the first molar tooth of the lower jaw, which matches it in size and shape. This fourth premolar in the upper jaw is known as the `carnassial tooth'.
Here is a summary of the dentition of the normal dog and the changes relevant to age. The specimen under consideration might be an Alsatian or a Greyhound, but other types, such as a Poodle, must for exhibition purposes conform to the following standard of dentition.
The dog has 28 temporary teeth and either 42 or 44 permanent teeth. 'The puppy is born toothless.
The temporary canine teeth (tusks) appear at 3 to 4 weeks, and all 6 incisor teeth are present by the 4th or 5th week.
The permanent central and lateral incisors appear at 4 months.
The corner (end) incisors are changed at 41 to 5 months. Although the teeth in the upper and lower jaws are not numerically equal, the dog has in all 22 incisors, 4 canines, 16 premolars, and I o molars.
The permanent dental formula is (or should be) on either side of the mouth.
The largest cheek tooth in the upper jaw is the 4th premolar, and in the lower jaw, the Ist molar.
The upper jaw behind the 4. premolars carries only 2 molars, while the lower jaw carries 3 molars.
The 1st, and and 3rd premolars appear at about 3 to 4 weeks and are changed for permanent premolars at between 5 and 6 months.
At about the same time, the 1st molar (the 5th cheek tooth) appears in the upper jaw. The and molar (6th cheek tooth) arrives in the lower jaw at 6 to 8 months but it may be missing from the upper jaw, so that this jaw then carries only 4. premolars and I molar.
The possession of the 3rd molar in the bottom jaw shows that the puppy is 6 months of age or over, and that, in this country, it is due for a licence.
Irregular arrangement of the existing teeth, particularly of the incisors, is more common in Toy breeds and especially nowadays in Toy Poodles and in a less proportion of miniatures, possibly because this breed is now so popular.
The reason appears to be the growing tendency towards increased length of foreface which results in a marked diminution in the width of the end portion of the jaws in which the incisors are embedded. The alveoli, the bony sockets in which the incisors have their roots, are absent in some cases or, if present, they may not lie in a straight line and for sheer lack of room the incisor teeth overlap to the extent that they may form a double row, usually containing the original six teeth, though in rare cases there may be eight or nine, much smaller than normal, and imperfectly embedded in an alveolus and, therefore, somewhat loose and even, on occasion, held in position simply by the fleshy part of the gum.
On the other hand, some of the short-faced breeds, such as the Bulldog, and intermediate breeds, such as the Boxer, may carry supernumerary alveoli and seven incisor teeth in a row instead of the usual six.
From personal observation of Bulldogs with wide flat upper jaws, it would appear that approximately 25 per cent have seven upper incisors, although Aitchison in the Veterinary Record (1964, 75, 153-4) regarded the incidence in seventy-one dogs he examined as being as high as 39 per cent.
Similarly, he found that in adult dogs the incidence of seven upper incisors was in Pekingese 1.3 per cent, Pugs 4 per cent, Boxers 26 per cent, Bullmastiffs 8 per cent, while twenty-three Mastiffs all had the normal number of six incisor teeth. In Boxers it seems difficult to get the wide muzzle required nowadays without the presence of an additional incisor.
Boxers that carry an extra incisor occasionally develop an abnormal calcification of some of the limb bones, and a number of cases have been observed by us in which enlargement of the lower end of one radius has developed, frequently associated with bone cyst, severe lameness, and pain. The condition has never, so far, responded to treatment.