i think that any theme or any topic would be right as long as you follow the true format of writing a personal statement.
if your letter is not boring, and leaves me with no question about you and why dentistry, then it will be just fine.
i also know that your personal statement letter is HUGE! i have read books written by actual adcom people who said that they were about to reject someone, but soon changed their minds after reading the statement.
i canoot stress this point any further. make sure you have a good one and really work hard on it!
good luck!!