I applied two years in a row, the first year I was shot down for a number of reasons, one of the top being a weak statement.
Here is my suggestion:
1. Gather all your, "wow look at me" facts.
2. Read the books on, "how to write a great personal essay."
3. Follow their advice and write about 100 iterations of the letter.
4. When you are really sick of writing and rewriting it......throw it all away and...
5. Write a letter that tells them about you.
Those books take alot of essays of people who were accepted and found the common inclusions. They then try and say that if you include these you have a good letter.
My letter was a little diffrent, rather than telling them how great I was, and how much I wanted to be a Dentist I chose to highlight the three most significant monents in my life to date. Decisions I made that got me to where I am today. I included good and bad about myself. (More good than bad!)
You want to convey:
1. You want to be a Dentist and you have a good idea what it means to be one. (this may be covered in you r applicaltion with all you shadowing time).
2. You are a SAFE BET! If you quit halfway through, they are out the tuition and society is out a Dentist. They want to see that you will not quit.
Good luck, hope this helps.