I amcurrently a 4th year dental student and I am starting a 2 year residency in Pediatric Dentistry in a few months. Getting into any postgraduate dental specialty is difficult. While pediatrics is not as competative as say ortho or endo it still is tough. I have many classmates who applied and did not get in. Inorder to get an interview you probably need to be in the top third of your class with good board scores. Once you get an interview I personally believe that they determine who gets in by the actual interview and don't go buy the numbers as much. But inorder to get an interview you need to have good grades and board scores. I personally am in the top half of my class but my board scores were in the top ten percent of the nation.
Good Luck
Hope I was of some help