AADSAS will take all of the course grades and units you reported in the undergraduate/post-baccularate sections of your AADSAS application to calculate the following GPAs based on their standards:
1. Cumulative GPA = GPA of all your classes
2. Science GPA = Biology, Chemistry, Physics, Math, Engineering (may be included in Physics or Math)
3. BCP GPA = Biology, Chemistry, Physics. (This GPA is potentially one of the more important ones)
Schools tend to discern between the inital round of students using the Cumulative GPA (probably >2.8, 2.9 is my guess), and as they start to decide who to interview, they look at the Science and BCP GPAs as well as personal statements and extracurricular dental experience for those students of lower GPAs.
The three types of GPAs are calculate so that all applicants can be put on a similar playing field. Like for students who aren't Biology/Biochemistry/Chemistry, or a related major. For example, an engineering student who has later changed their mind might have lower Cumulative and Science GPAs due to their engineering classes. However, if you only consider their BCP GPA which includes their dental pre-reqs but mostly likely not their prior engineering classes, then they have a much better chance at getting an interview and potentially, a position in the class.
Or, a Spanish major who has a decent Cumulative GPA brought up by their language classes may not have as strong a Science and BCP GPA as the above-mentioned engineering student.