It seem's like a silly question, but your interviewer has a very good reason to ask. If you are not passionate about your own oral health and hygiene, it is unlikely that you will be able to convey the importance of oral care to your patients. You may even choose to describe your oral care practices to your interviewer so that they can better understand your methods. You might answer with "Absolutely. I make sure to brush twice a day and after meals, and I see my own dentist at least twice per year." You may also be asked to explain why oral health is so important for overall physical health, as well.