I agree with Maygyver. Medical school rotations are bit different than dental school clinics. I have couple of friends graduated from dental school recently (with in last 2 years). I hardly seen them during first 2 years of their D school but 3rd and 4th year were so different. They had plently of time after clinics. They were out hanging with freinds often.
First 2 years are didactic as Maygyver mentioned. Dental students tend to spend lot of time at home/lib during first two years. Amount of time student spend during normal week in classes (mainly 1st n 2nd year) and clinics (3rd n 4th years) are pretty much same through out the four years of D school. However, it's not the class/clinic hours kills you, it's the extra time that students usually have to spend studying at home/lib during first two years.
Bottom line what I have observed and heard so far, 3rd and 4th year of D school is bit relaxing than first 2 years.