> I respect the judge a lot. I feel like I would be doing them both a disservice by showing her with a missing tooth in such a visible place.

Why, dogs can loose teeth due to accidents, age.  Would you stop showing a dog that had gone grey?

I have one veteran who lost a front incisor (so very visible) and still gained top awards (it had been removed as an epulis on the gum had caused it to fracture). 

Her daughter had a large upper carnasial tooth removed due to an abscess, and won CC and BOB last January as a veteran. 

If removed by a vet then you only need a vets letter and ask for permission to show.

Maybe I'm being a bit precious about it, being in a terrier breed... I think you may be right. I'll have to think it over, since she is entered.

In a terrier breed, especially an older adult or veteran it would be viewed in the same light as Honourable battle scars.

Whilst a terrier should have a good mouth (not wry, overshot or undershot etc..) the reality is that many working terriers lose teeth on the hunt and there are terriers who manage to catch and dispatch prey with quite a few missing teeth. Many a good terrier man will argue that 'killer instinct and gameness' which are more about temperament are as important, if not more so, than perfect conformation.

Actually, I will amend that comment slightly by saying that the two most important things in working terrier conformation are that it is narrow enough in the chest to get down a hole and that it has the coat for the job-that is not too soft (the MT being an honourable exception as it was never meant to go to ground). BTW I am not a hunter but this is what would have been expected of a good working terrier, but as important would be the right mindset.

My bitch won both her classes at Crufts two years running with the missing tooth. She also had 2 BIS veteran at breed shows. (As she is a BSD, that wasn't out of one breed either but out of 4 varieties.) I retired her when her movement started to get stiff, aged 12 ½. I never saw the missing tooth as a problem, and clearly nobody else did either. :) She was graded Excellent at the world show in Paris minus the tooth as well, plus by foreign breed specialists at her final two shows.