while i definitely think you should focus on your own interests and your own story, it doesn't hurt to take a look at sample personal statements to get your mind joggin'. barron's DAT book had a couple in the front, as well as sample interview questions. u'll see that everyone has a unique story.
i remember dr. yarborough, assoc dean of admissions at pacific, said that u definitely don't want to waste space in your personal statement for explaining poor academic performance (if you had any)... there'll be space in another part of AADSAS for that.
focus on yourself as an individual, with the potential to enter dentistry. make yourself shine! they want to see that you not only have the drive, but also the capability to succeed. always keep in mind... "what makes you special?" skills, personality, talents, experiences... can be anything and everything.
get started early, and get a lot of people to read it before submitting. there are lots of approaches to take, and it takes time to discover which one u think is best.
good luck!