No problem you're welcome
If you tell your teachers you are resitting modules then your predicted grades will definitely shoot up. It's about convincing your teachers that you are an A grade student who say didn't put as much work in as they should have. I know people in my year (just finished year 13) who had E and even U grades at AS and were predicted As at a level. Your teachers will predict you high grades if you convince them that you are capable (especially if you have good classwork/a good GCSE result in the subjects).
Try to get them up to As if you can (as you are correct in saying that dental schools will almost certainly not over you a place if you are not predicted the required grades).
If you can't get them up, and you are still really keen on dentistry, you could think about doing a degree and applying for dentistry as a post graduate. Look on the university websites, but most of them say any science related degree is suitable.
Or if you aren't predicted the As and end up achieving them at A level, you could always take a gap year and apply with your A levels (this will even give you an advantage over the year 12 students you are competing with)
. Whatever you do, make sure you work hard at your A levels (here is a tip, start revising just after Christmas, trust me you'll be glad you did come May/June!)
Yes it is possible to boost your chemistry grade, but make sure you start working towards the exam early!
But as I say, start by trying your best to get your predicted grades up. Sorry about the essay, just trying to give you as much info as possible!
Good luck!!