You're not too late. I was informed by an admissions counselor at at dental school that most applicants submit their application between September 1 and November 1. Many schools do not begin to review applications until their admitted class has begun and a few schools do not begin until late-August and late-September. August is fine!!!
As you know, when you complete the DAT, you will leave the testing center with your scores in hand. Many schools will consider a photocopy of your unofficial scores until they receive the official transcript 2-6 weeks later from the ADA. I was told to FAX my results to the admissions office upon completion of the examination.
Relax! If not, you will be disabling yourself. December 1 is the first date of admission notification and many applicants admitted on December 1 will be admitted to more than one school. They can only attend one and therefore, will leave a seat to be filled at the others. Admissions committees continue to interview well after the holiday season. A good friend of mine applied late (December) and received an interview in March for alternate list consideration. She was admitted shortly after her interview!
As for your essay, why not begin by thinking creatively! Perhaps as a flashback to the application process as a current DS1 (that's thinking positively) or, tell a story of how you became interested in dentistry. If there is anything unique about you, your family, your achievements, experiences...convey it! It will make you stand out.
....my apologies for the lengthy reply...hope it helps!
