I have a great dentist, and I adore both him and his office staff (a total of four people). Every time I go in I take a pound of specially selected See's candy plus I include a handwritten thank-you note for them. It is very much appreciated.
Lyndon, the dentist, told me when I was in for my twice-yearly cleaning and exam that dentists have the highest rate of suicide. I had already known this, but he explained that most adult dental patients are often saying how much they hate visiting the dentist, how much they hate dentists in general, etc. That kind of thing takes a toll on people, most of whom, I think really want to help. So any kindnesses are met with surprise--and gratitude of immense proportions. It really will make your dentist's day, OP, if you do this especially if you include a note with it.