It uses the PASS system (similar to CAAPID). What I hear is that your personal statement on that needs to line up with your specialty and focus on why you are centered in that area. So in your case for a periodontist, try to use experiences for your passion tied to that area.
For LORs, you will need new ones from the DDS side, and they need to have the authors address how many procedures you did and show how you are good in your field.
The only other area is to pay attention to spam if you are using Gmail. For some reason emails from the PASS side like to go spam.