It's not that bad depending on the topic. Last year for Buffalo I was expecting them to ask me to write about a topic with regards to the dental field and I prepared by reading all that I can about the advances in dentistry etc.....but instead they asked a simply question of which professor did you like and why.....I guess just learn how to prepare a decent essay in general and I am sure it will be fine.
I could be wrong, but I'm fairly certain that this is another way for dental schools to ensure that each applicant has a good working knowledge of the english language.
If schools used this as a criterion to base their decision then that would be a fairly subjective method.