"Dentistry - First BDS (pre-dental) Entry (A204) 6FT Hon BDS" is a 6 year undergraduate course you choose if you have not done the required bio/chem A Levels.
"Dentistry - Second BDS entry (5 years) (A206)" is the degree you choose if you have done bio/chem at A Level and this is a 5 year degree.
and about your UKCAT... don't know what you're worried about mines worse! .. 525!! but i've still applied because its not the only thing they consider, i've contacted universities i'm applying to that do use UKCAT as part of the admissions process to ask about cut-off points, but they say it there isn't one and that its not the only thing they look at, they may place more emphasis on it if the applicant is acedemically weaker compared to other applications, but might not be so important is they are not. (Queen Mary's does have a cut-off point, once it receives all its applications it ranks everyone in UKCAT score order and then decides a cut-off point, so a low score here would be very risky!!)