Don't know how to avoid...

There are many fine orthodontic specialists out there who could fit you with a nice set of dentures, so lose those teeth! Who needs em?

Really, unless he is complaining (and if he is, he is retarded anyway and should be fined with a reduction in BJ regularity) don't worry about using a little tooth action during the act.

some guys like it try biting it and see what he says

Is he complaining? I imagine not. Don't worry unless he's not getting into it or seems in pain. The back teeth are closer together vertically and there's really no way to change things - unless maybe you lower the tongue to keep him more "in the middle".

I assume you are doing it like you see in porn videos or something. Are you putting the penis in your mouth towards a cheek? Like at an angle/sideways? If so, it's supposed to go straight back to the throat.

If you are already doing that. Then your mouth is f***ed up.

Maybe your doing it to fast.try concentrating on your tongue.doing it a bit slower.more sucking action.and use your lips more .wow this is hard to explain.!