Prognathism occurs when there is a mismatch in the extent of 'protrusion' between the two jaws, i.e. they are unequal.
If the upper jaw extends far beyond the lower, this is known as 'overshot', though since this can create confusion, the term Upper Prognathism is preferable.
If the lower jaw extends beyond the upper, i.e. there is a projection of the chin, this can be called 'undershot', or preferably Lower Prognathism.
Animation of the normal of the oral cavity of the dog anatomy:
Animation malocclusion prognathisme:
Animation malocclusion brachygnathism:
What are the breeds most commonly affected?
Upper Prognathism is common in dogs. It occurs potentially in:
- Dachshund,
- Cairn Terrier,
- Yorkshire Terrier,
- West Highland White Terrier,
- English Cocker Spaniel,
- Irish Setter,
- Border Collie,
- Pyrenean Shepherd
- Belgian Shepherd (Tervuren).
A degree of Lower Prognathism is normal in some breeds and is regarded as acceptable, e.g. Bulldog, Boxer, and other brachycephalic breeds such as Pugs, Boston Terriers, Shih Tzu, Pekingese, etc..
Is Prognathism a serious issue?
This anomaly may be troublesome because of the likelihood that it affects proper occlusion of the teeth, enhancing the risk of dental disease. It may require, in some cases, corrective action to avoid mouth injury associated with malocclusion. In very severe cases, orthopedic veterinary surgeons can shorten or lengthen the lower jaw to effectuate better teeth alignment.
Animation of a malocclusion correction:
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