With the rise in popularity of certain breeds, an undershot jaw is viewed as a normal feature for them. Dogs such as English bulldogs, Shih Tzus and Boxer dogs often have an undershot jaw. And for the most part, we turn a blind eye to this. However, in any other breed, we would view this as a significant health issue. Most people would be shocked to see a Labrador or a German Shepherd dog with this condition! So how much should we be concerned about an undershot jaw, is it an issue or not?

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What is an undershot jaw?

An undershot jaw is also known as an underbite or mandibular prognathism. An undershot jaw describes a condition where the upper jaw (maxilla) is underdeveloped, compared to the lower jaw (mandible). Simply, the dog has a shorter nose in comparison to its lower jaw. This often means the lower teeth are left jutting out. This is also known as a type of malocclusion; a term meaning the teeth are out of their normal anatomical alignment. 

This condition is both hereditary and congenital. This means that it occurs because of the genetics that have been passed down to that dog, affecting the way it develops. This is why we see the condition more in some breeds than others. Many people like the ‘ugly but cute’ appearance that this gives their dog. But when we stop and think about it – having an underbite is due to these breeds having deformed skulls. Despite it being a breed standard for some, should we be less accepting of underbites than we are?

What problems can we see because of undershot jaws?

Malocclusion of the teeth can cause issues with the way a dog bites or chews. Many dogs adapt their technique accordingly and can function relatively normally. But for some the position of their teeth can cause a real problem. 

In a normal dog, the large canine teeth should glide smoothly past each other making a scissor-like bite. The lower canine tooth should sit just in front of the upper canine tooth slotting together comfortably. In some cases, this doesn’t happen, and the lower canine tooth is either protruding out at the front of the mouth or even worse it is impinging on some of the soft tissues within the mouth. If the points of the dog’s sharp teeth are pressing on the roof of the mouth (the hard palate) this can cause sores to occur. Similarly, if your dog has two teeth that touch or rub together this can cause damage and erosion to these teeth, which can also result in pain. 

In some cases, issues with the jaws and teeth can also cause trouble with the dog’s tongue. Meaning that they struggle to keep it in their mouth properly. This makes it more prone to drying out and cracking. 

As well as abnormal dentition, many of these dogs with underbites can have problems with their breathing, due to their shortened noses. As we mentioned earlier some types of dog are more prone to undershot jaws than others and these tend to be the brachycephalic (flat-faced) breeds. And as well as their abnormal jaws, these dogs often have more narrowed nostrils, smaller than normal tracheas (windpipes) as well as issues with the soft tissue in the back of their throats. All of this can contribute to breathing difficulties. 

Breeding for health 

While many dogs with undershot jaws can function, others struggle. One 2022 research paper focussing on English Bulldog health warns – 

‘Immediate redefinition of the English Bulldog towards a moderate conformation is strongly advocated to avoid the UK joining the growing list of countries where breeding of English Bulldogs is banned.’

We need to ensure that breeders are choosing animals for their health rather than their extreme features. Other countries like Norway have already taken a hard stance on English bulldogs, as well as Cavalier King Charles spaniels (another breed with multiple genetic health issues). So, if we can’t start improving the way we breed these animals then the UK may have to follow suit on an animal welfare basis. 

As vets, we also need to do a better job of educating dog owners (and potential dog owners). The 2022 research paper stated – 

‘Although mandibular prognathism was the third highest predisposition recorded in the current study, with 24.32 times increased odds in English Bulldogs, this still meant that only 2.1% of the overall English Bulldog population were reported with this condition. Given that mandibular prognathism is a requirement of the breed standard, it is probable that most, if not all, English Bulldogs show this disorder and therefore the current results represent a vast understatement of the real situation of a condition that is ‘normal for the breed’ regardless of not being ‘normal for a dog’ and which therefore will generally go unrecorded in the clinical notes.’

It would appear that vets are not even recording the abnormality of an undershot jaw in their clinical notes anymore. However, we cannot afford to become blasé about these ‘everyday’ malformations. As the paper states, while these features are normal for the breed, they are not normal for dogs as a species.

Summary

While many dogs with undershot jaws can function OK, some animals with more exaggerated features may struggle. Going hand in hand with their characteristic facial features are the less visible problems, like dentition anomalies and breathing issues. Vets and breeders both need to work towards improving the health of these animals and educating the public as to why ‘ugly cute’ is not something to be encouraged.

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