Dog Mouth (Bite) Terminology
Look at my teeth!
The mouth (usually called the dog's bite) is the terminology used to ascertain how the teeth in the upper and lower jaws meet when the mouth is closed. This depends on two factors - the length of the actual jaws relative to one another, and the position of the teeth themselves. Dog Show Judges usually assess the bite by just looking at the front of the mouth which may or may not consist of straight teeth. So it is also important to also look down the sides of the mouth to ascertain the complete bite.
Diagram Naming Teeth
A dog should have a total of 42 teeth.
In the upper jaw there are 20 teeth:
- 6 upper incisors
- 2 canines
- 8 premolars
- 4 molars
In the lower jaw there are 22 teeth:
- 6 lower incisors. Sometimes the two most centrally placed incisors are called the lower centrals and maybe smaller than the others.
- 2 canines
- 8 premolars
- 6 molars
A Normal Scissors Bite
A normal scissors bite is where the incisor teeth in the upper jaw are in contact with but slightly overlap those in bottom jaw. This also produces a 'scissor' appearance in the way the pre-molars and molars meet down the side of the mouth.
A Normal Scissors BiteA Normal Scissors Bite
A Level Bite
A Level Bite
Some people interpret a normal scissor bite to be functionally the same as a level bite. Certainly in both cases the jaws are the same length. However, a level bite is one where the incisor teeth meet exactly, surface to surface. A level bite differs from the normal scissors bite (above) in that the upper incisors do not slightly overlap those in the bottom jaw.
If a dog has a level bite when it is young, the teeth will probably wear down to the gum as the dog ages, effectively having only stumps of teeth left as an old dog. This can cause problems. The reason why a normal scissor bite is preferable to a level bite is shown by the accompanying picture. Here is a 12-year-old Airedale who had a perfect scissor bite when she was young. But the teeth have now worn down to a useful level bite. But she still has a significant set of teeth remaining, despite her age.
Some Breed Standards like the Airedale Terrier call for a vice-like bite or a mouths closing like a vice. This refers to the mechanism of the jaws and the way they grip rather than whether the teeth are in a level or scissors arrangement. This is the opposite of the soft mouth required by a Gundog which is required to retrieve.
Undershot and Overshot Bite
Undershot Side View
The terms 'overshot' bite and 'undershot' bite refer to the relative placement of the upper and lower jaws to one another.
Undershot (Reverse Scissors Bite)
In an undershot mouth, the lower jaw is perceptibly longer than the upper jaw. Where the upper jaw is also turned upwards so the chin is visible, the jaw has more gripping power as in the case of the Bulldog, Boxer and Dogue de Bordeaux. An undershot mouth is also typical of brachycephalic toy breeds like the Pug, Pekingese and King Charles Spaniel.
A Reverse Scissors Bite is an undershot mouth where there is no gap between the teeth of the upper and lower jaws. However, the top surface of the teeth in the upper jaw must actually touch the under surface of the teeth in the lower jaw for it to be called a 'Reverse Scissors Bite', typical in the Lhasa Apso and the Tibetan Terrier.
Overshot is the opposite of undershot. Here the top jaw is physically longer than the lower jaw. This can affect the mouth's function as an overshot mouth usually indicates a weakness in the lower jaw.
A weak lower jaw can also manifest itself in not just the position of the incisors to one another, but also by a reduction in the width of the lower jaw itself and consequently often the number of teeth contained in the lower jaw.
Weak Underjaw with only 4 incisors
In the accompanying photo illustrates a weak lower jaw with a reduced number of incisors. There are only 4 incisors in the lower jaw instead of the 6. I have also seen a dog with only 3 incisors in the lower jaw. 5 incisors instead of 6 is also common. This weakness was evident in this particular dog's baby teeth.
Open and Wry Mouths
A bite which appears like this when the mouth is effectively closed is called an Open Mouth. This is caused by the premolars meeting surface to surface instead of the top 4th premolar overlapping the lower as in the photo of the normal scissor bite side view. An open mouth is usually obvious because the tongue protrudes.
A wry mouth is also a bad bite problem where the right hand side of the mouth is longer than the left, or vice versa, causing the jaws to be completely out of alignment with each other sometimes to the point where the mouth cannot close properly. This is the worst possible constructional mouth fault as it can cause the dog not only discomfort, but also eating difficulties.
Baby Puppy Dentition and Teething
Baby Teeth with Correct Scissors Bite
A baby puppies' teeth first erupt at around 3 weeks of age. By around 6 weeks or so, 28 'milk' or puppy teeth have usually erupted. These should consist of
- 6 incisors in both the upper and lower jaw
- 2 canines in both the upper and lower jaw
- 6 premolars in both the upper and lower jaws
The exchange of the baby teeth for adult teeth is called 'Teething'. This occurs when the puppy is between 4 and 6 months of age.
Retained Baby Canine Tooth
With the incisors and the canines, the second set of teeth erupt in front of, alongside or behind the milk teeth. However with the premolars, the adult tooth usually erupts underneath the baby tooth, so pushing it out.
With the canines, the new tooth usually appears behind the baby tooth. If the baby tooth is retained after the adult tooth has fully erupted (pictured) but grown to its predicted adult length, veterinary intervention should be sought.
Teething occurs during a very fast stage of the puppy's overall development. As the puppy's head grows, the skull including the upper jaw sometimes develops quicker than the lower jaw. This can give the impression that the baby puppy is overshot, which as an adult it is not.
Adult Pre-molar Erupting under Baby Tooth
Additionally, a baby puppy can have a beautiful scissor bite as a baby, but if the bottom jaw keeps growing after the skull has reached maturity, the adult could finish up being slightly undershot.
Note the pain of teething can also affect the carriage of the baby puppy's ears. Those with pricked ears often are not fully erect until after the teething process is fully complete.
Malocclusion (crooked teeth)
Maloccluded Incisor Teeth
Malocclusion is the term used when the teeth themselves are crooked and hence not in their correct position. Usually this is purely a tooth alignment fault rather than an overshot or undershot jaw fault which is dependent on the length of the jaws relative to one another.
Pictured is the most common malocclusion where the two central incisor teeth in the lower jaw have grown in front of, rather than behind the teeth in the upper jaw. A malocclusion like the one illustrated can be caused by the two teeth in the lower jaw being physically smaller than the other incisors. If this is the case, then this type of malocclusion could be an inherited fault.
Maloccluded Incisor Teeth
However, this type of malocclusion is more often caused by the baby teeth in the bottom jaw coming out too soon, often because the puppy is playing tug-of-war games at the crucial time when teething begins. This can pull the newly developed teeth in the lower jaw outwards. Then these already mis-placed teeth in the lower jaw continue to grow in front of the teeth in the upper jaw, instead of behind them. This condition can be exacerbated by the baby teeth in the upper jaw being retained so the new teeth of the upper jaw wedge themselves behind those in the lower jaw as illustrated.