Clinical observation is not required at most schools, however, it is important that you, and the admissions committee, know that you want to be a Dentist.
Something I heard recently; The president of our AED chapter at my school a couple years back was a great friend of mine, he was a 4.0 pre-Dental student who went to college 3 years in order to get his pre-req's for Dental school done. He applied and was accepted, halfway through his first year he quit, wasn?t for him. It also happened to another 4.0 kid from my school, same thing.
The point in my story is not only to go and smell the office and look at the Dentists car, get you hands dirty. If you spend allot of time in a Dentists office and they trust you they will let you get your hands in someone's mouth, that is when you find out if you want to be a Dentists.