When I was 17 my 16-year old girlfriend Crystal and I both had braces. She had elastics too. I remember the first time we made out thinking how sharp her brackets felt- not like they hurt or anything, just how much they stood out when I ran my tongue against them. The elastics also gave a strange feeling, they were all taut as she had her mouth wide open, and it felt strange to run my tongue across the tight rubber strip. Her mouth just felt really full, with all the metal, but it's the brackets I remember best, they seemed so big and sharp in there.
Other than the sharpness, it wasn't all that much different than kissing without braces. And as for braces getting stuck together, I think that's a myth, ours certainly never did.