I have a six month old retriever puppy that I have just started showing and wanted to breed from, her bite was correct all along but I have just noticed her teeth are ok one side but become level then one corner bottom tooth is over the top one, her jaws appear even. Can anyone tell me how this can happen and if it is permanent?

Hum.  Although you might get away with a slight overbite because the bottom jaw carries on growing (I think that's right ... senior moment), from experience I had a hound who was tight when he went into quarantine but it had gone wrong by the time they came out, 6 months on.   I'd risked using a dog with an edge to edge bite (accepted in Canada) as we'd always had a good scissor bite, but paid the price with him, even if he was the only one of 9 in the litter that showed being closer than I'd like, early on.  I did let a fellow-breeder use him, with the understanding that if the fault appeared, she moved away from him.   She swore up and down that she didn't see it in subsequent generations and he is back of a number of lines here in the UK now.  

I have to say my hound's jaws looked okay - and part of what happened in quarantine (the three we'd kept from that litter went in at just over 12 months) could have been caused by the fact they moistened the food, stacked the bowls so by the time they were put down, they had to 'graunch' the food to get at it.   This may well have caused the upper set of teeth to 'angle back'.   BUT again, their sire was edge to edge so I may have been looking for excuses.   I did show him a couple of times in the UK, but clearly his bite fault wasn't going to be accepted, even if he was admired!   Darned shame.

Have you talked to the breeder of your bitch (assuming you didn't breed her?) about what's going on?   If you are to breed her, never mind showing, you'll have to choose the sire very carefully, and even then once a fault is there, it can come back to haunt further down the line.

I assume your referring to lower jaw and incisor placement moving from current at one side to level and then slightly undershot on one side ? IF this is a correct assumption it sounds like the start of what is known as a wry mouth where one side of lower jaw grows faster than the other side leading to development of a twist and malocculsion. IME this is likely to get progressively more obvious. you could speak to vet and consider a referal to orthodontist BUT any interventions to correct bite would result in ineligibility for further shows as procedure would alter natural conformation. Malocclusions have genetic implication and thus it is never recomended to breed from a dog with incorrect bite.

Many thanks.

In a numerically large breed like yours breeding from  anything but a perfect bite would be doing the breed a disservice.