Aussie Genetics Fact Sheet: Bad Bites & Missing Teeth by C.A. Sharp Australian Shepherds have a variety of problems related to the teeth and jaw structure. They are all likely polygenic. None are genetically related to the others. There is no single “bad bite” gene. The problems seen in Aussies are as follows: Undershot – the lower jaw extends beyond the upper, causing some degree of malocclusion. Overshot – the lower jaw does not reach proper length in proportion to the upper, resulting in some degree of malocclusion. Wry – One side of the jaw has grown longer than the other, resulting in malocclusion of the teeth in the front of the jaw. Anterior Crossbite - Some, but not all, of the lower incisors extend beyond the upper incisors but all other teeth mesh properly. Missing/extra teeth – Dogs will lack one or more teeth, usually pre-molars. Sometimes there will be an extra pre-molar or molar. Dropped center incisors – The two center lower incisors will be shorter than the others. Sometimes they will tip forward giving the illusion of a level or slightly undershot bite when viewed from the side. These defects, except for wry mouth and anterior crossbite, are relatively common. Missing teeth were rare 25 years ago but have become very common today, mostly in show lines, due to too many breeders disregarding the condition. These problems are polygenic—resulting from the action of many genes. Because of this, they will be difficult to impossible to eliminate completely. However, breeders can lower the incidence. A dog with an overshot, undershot or wry mouth should not be bred. If an unaffected dog produces multiple affected offspring, particularly from different and unrelated mates, serious consideration should be given to withholding that dog from further breeding. Do not repeat breedings that produce these defects. The parents and siblings (full and half) of affected animals should not be bred to near relatives and should only be bred to mates from families where the fault in question is not a problem. Missing/extra teeth are less of a problem, functionally. A good or excellent dog should not be eliminated solely on the basis of one or two missing teeth. However as more are missing or extra, the fault becomes more serious. Dogs with multiple missing or extra teeth should probably not be bred. A male with missing teeth should never be allowed to become a popular sire. Breeding advise for unaffected parents and relatives of dogs with missing/extra teeth would be the same as for the jaw defects (see above.) Dropped incisors and anterior crossbite are the least problematic mouth defects from a functional standpoint. Dropped incisors have been observed in wolves, though never to the extremes seen in Aussies. If an animal has dropped incisors or anterior crossbite, do not breed it to its relatives and breed it only to mates which do not have them and whose near kin do not have them.