Is DofE gonna help me if I want to do dentistry in uni?

probably not
majority (more than half) of students do DofE so it doesn't really set anyone a part anymore unless you got to one of the higher levels, that's what i was told anyway
don't know specifically about dentistry but if you only did like bronze or maybe silver then people don't really bother mentioning it on personal statements. at best it might make it to the cv for the first couple of part time jobs but it'll soon get replaced by better more relevant opportunities.