great responses above. For those coming back after being gone a bit, although yes, some classes are less "dense" than those in undergrad, you are taking A LOT of classes each quarter (many times upwards of 12). in addition at some point (different for each school) you also begin preclinical work which depending on your luck or talent or whatever will require varying amounts of time and effort to be put forth. So yes, although the material isn't quite as in depth and detailed, there are a crap load of ppts that you have to look over and over and over, and do it for each class, and then be expected to remember factoids. Like someone said above, time management is more important in dschool than undergrad by far. At times there just aren't enough hours in the day to put full effort into each class and task, but you have to learn to balance and juggle and do what is best for you. Everyone is different, so don't feel like you're doing something wrong because it is not the same as the next person. Everyone gets through dental school in a different way. The important thing is to find YOUR OWN groove earlier rather than later. Don't be afraid to do what is comfortable and what works for you, because if you try and keep up with your neighbor then you are sure to get stressed and anxious.
So in a nutshell, the way you studied in undergrad might not be the best method for your own success in dschool, or it might be. Don't be afraid to find something that works. if your undergrad method works well for you, then awesome keep at it, but if you're hardheaded and only stick to "your way" when that way obviously isn't the most efficient then you will have a more difficult time in dschool. Good luck to all. There are many ups and downs, but just keep level headed and keep focused and always remember why you came in the first place, and if it was for the 'right' reason for YOU, then you will be sure to persevere and come out alive.
