My guess would be - at the minimum, all the people who applied to Dental Schools at that cycle or year.
So, lets say 6000-7000 students applied for 2004, then I am sure at least 6000-7000 people would take the DAT to apply.
I think this year 2003-2004, AADSAS had more applications, maybe in the 7000 region, so probably all those applicants would have taken the DAT. If others, who didnt apply also took the DAT, that # would be really low in my opinion, maybe ~ 100! max - and they would be people who might want to apply the following cycle or year.
Well... I am sure other people have their opinions.