Option #2 you've listed is probably going to be the better choice 99.9% of the time.
Yes, the question is basically "why do you want to be a dentist?", however that doesn't preclude one from telling a story, which is probably the best essay.
Do NOT rehash what is already listed in your application. Don't share your stats, or your DAT scores, in your essay. The adcom has those listed on several pieces of paper already (your AADSAS application, your official DAT transcript, and on their own criterion sheet, and possibly on the outside of your candidate folder).
Your essay is time to let them see a different side of you. After being in many interviews I can say that adcoms don't always want people who have been immersed the dental profession since the age of 3. They also don't want strict science nerds. What they do want are genuine and well-rounded applicants.
If you play the piano, organized a chess club, ran for local government, wrote a children's book, started a skate park, etc., etc., then let these things be known in your essay!
And, if you feel you absolutely must rehash your stats in your essay, then try to do so without quoting direct data. There are probably times when referring to stats is beneficial, especially if you are writing about a life experience that changed your worldview and motivated you towards better academic performance. In these cases, don't say you went from a 2.8 to a 3.0 to a 3.2--but rather say you "doubled your academic performance over the past two semesters". Still paint the picture, even if you are referring to your stats. And above all, don't let references to stats overtake your essay. Use those references, if you must use them at all, to bolster your story and to make a point--don't make your numbers the point of your essay.
Just the opinion of an English major, and somebody who has sat in on over 25 interviews this year, and read 25 applicant essays.
