The 5 month old Dogue de bordeaux male has suddenly decided he will not let anyone near his month, we have been doing it regularly as we hope to show him just part of every day training routine,but since I have come out of hospital he lost his routine when I was away, I have tried getting him with the other dog and looking at all mouth then giveing a treat to each when they have let me look, but come to his turn he backs off, so he is not given a treat. any idea's

Perhaps he has a sore mouth? Do DDB teeth late too?

When showing my Boxers mouths, I've always trained them with the word 'teeth'.
So even now that they are older as the judge comes to look in the mouth
I automatically say 'teeth' so my dogs know what to expect.
Normally the judge doesn't open the mouth wide open but just wants to see in
the front how the teeth are positioned and to the sides. Very rarely do they look
at the tongue :D unless of course it's a judge that doesn't have a clue what bite
dog should have (undershot for Boxers) and yes I've had that happen when they've
exclaimed they can't see her top teeth when her mouth was closed :/

Try just to have a slow look at the mouth but before you go into his mouth ask him to
stand, and stay (This is why I find going to obedience really helps build the partnership and yes you can
obedience train a show dog, just use different lead and collar etc)
Just build up slowly each time, if he will stay still, and allow you to open his lips (still say the word teeth etc),
just leave it there and give him a treat. Then try to progress to him allowing you to keep his lips open for a little
longer etc.

It might be because you are approaching at the wrong angle, are you going into his mouth
front on? Or are you covering his eyes and trying to go in his mouth from the top of his head?
As most dogs do not like their eyes being covered by trying to go into the mouth from the top of the head.
I always go into the dogs mouth from the front (the angle which the judge would go into the mouth)
or to the side without covering their eyes.

dont know if it will work for you,but boscoe is a foodie so he is happy doing the following:
take a peice of food or treat etc,hold or gently rub the side of the mouth with it,whilst giving your key word,mine is "smile"
maybe if he assocciates the experience with a treat he may be more willing
mel:)