just add 1500 characters of $$$$$. j/k try to talk about expericences you had during college. job, research, volunteering events, certain days your were shadowing/assisting a dentist. or any experiences you had that you can tie into why you would make a good dentist.
example,
one of my friends applying to medical school wrote about texas holdem. he said he got really good at reading people so when he was volunteering at a hospital he confronted some people that were acting "weird." they eventually confessed they were on drugs.
the point is there is plenty of things to write about. you have 1500 extra characters might as well put it to good use. i dont know if it will actually hurt you since im not an admissions member. but from my point of view it will make you look less motivated for dentistry since you didnt write a lot.
look at other personal statements to draw ideas.