[Ladyhawk]

An underbite will not effect the health of the dog unless it is very severe. It's best not to breed a dog with an under bite since the standard calls for a scissor or even bite. If you breed a dog with a bad bite you risk the chance that half the pups will have a bad bite as there are not many dogs around that are homozygous for a good bite. A bad bite is a recessive trait and can still crop up if the dog is carrying the recessive gene. The dog will not do well in the show ring either.