Great question, and it's one I hear alot. Pacific actually has 4 ACADEMIC years. Each academic year is equal in length to two semesters or 3 quarters. During the 1960s or 1970s they made the decision to squeeze the curriculum into 3 CALENDAR years in order to accomadate the military's needs for more health care professionals.
During the first four quarters (just over 1 academic year) at Pacific, we take almost all of the didactic courses necessary to sit for the boards. During the same time, we take preclinical courses like operative dentistry, fundamentals of restorative dentistry, fixed prosthodontics, and others. During the second year, our schedules shift a little bit. We spend half the day in the clinic treating patients and we spend the other half of the day in didactic and preclinical courses (removable prosthodontics, endodontics, orthodontics, oral surgery, etc.). Some of the schools I visited during my interviews split these two separate branches of dental school (didactic courses and preclinical courses) into two years. Perhpas that is how Pacific does it--by overloading students during the first year with both didactic and preclinical courses, rather than spreading it out over two years.
The ADEA last visited the school in 2000 and found no problems with the school or its curriculum. It also awarded the school 18 commendations, which up until then had never happened at any other school in the country. I don't say that to make Pacific seem better than other schools, because since 2000, other schools have recieved the same if not better marks uopn being reviewed by the ADEA. Instead, I think it points out that the governing body that watches over the training of dental students fully endorses and appears to be ecstatic about Pacific's 3 calendar year program.
Hope that helps.