Ive a 5 month old pup, she has her first CH show end of September and she wont let any one look in her mouth.
We go to ringcraft classes and Ive asked the judge to start looking into her mouth but as soon as they do she's up on her hind legs. I don't want to try to hard as it will only make her worse.

She's nearly finished teething. Whats the best way to over come this.

You could treat at home just for touching near the mouth, then for gently lifting a lip without worrying about getting a closer look and so on. You're on a tight-ish time frame though. Is she ok with you looking in her mouth, is it just strangers she doesn't like? If so, as the judge approaches, just politely say 'may I show you the bite?' and most judges shouldn't mind that, specially with a baby puppy.

Thanks for the reply, No she docent like me looking. I don't no what has caused her to be like this, Ive never done much in the way of looking in her mouth knowing she had a problem with it and thought I would wait till She finished with her teething, now I feel Ive made a mistake as time is getting on.

I have a 4 year old champion bitch who will still wriggle and shake her head if the judge looks at her mouth so I tend to offer to show it.

I have always found mine hate having their teeth looked at, from about 3 1/23 months, and if the looker faffs about soon learn to avoid it.

the way ti is done makes a huge difference, and i have found by steadying the head from behind from the neck and using the hand below the jaw to lift the top lips so no covering of top jaw works best. 

Very quick looks through the day and lots of praise.

Leaving it alone was probably the best thing tbh, I've got an 11 month old who had a difficult teething with retained puppy teeth, and I was constantly looking and trying to gently wiggle to loosen them, and she got very wary of anyone near her mouth. I had to start over again with just lifting a lip for a second and praising for that and working onward to looking properly, and she's not too bad now as long as you don't want to look for too long! A lot of judges seem to like to check the teeth by covering over the eyes with their hand as they lift the lips, and not many dogs like that!