I agree, tell them.
In one of my interviews It was viewed positively that I applied to twenty schools. At case both interviewers agreed that with as competitive as things are nowadays, if you are serious about dental education youshould apply to as many schools as you can afford.
Other explanations are:
-that you were advised to by your pre-dental advisor.
-you weren't sure how competitive you would be.
-you want to be a dentist more than anything and wanted to make sure you got in to a dental school.
In my three other interviews it wasn't even brought up.
I was told that every school that you applied to has access to your full app and that you waived all privacy with the consent form.
Either way fibbing never gets you anywhere! Having to lie in an interview can really make you uncomfortable and interviewers can pick up on that.