L.R.
His teeth won't shift much in just a week and a half so you could wait. But if it bothers you, yes, do call them and just say "I wanted to let you know in advance of the checkup so you can take a good look at this...."
If your orthodontist's office treats you dismissively for asking questions, even basic ones, tell the boss. If it's the assistants or the office staff doing this, tell the orthodontist himself or herself. I would usually say ditch the doctor and find another if the staff is acting like questions are just too much trouble to answer, but in the case of an orthodontist, you usually have a fairly long-term treatment plan in place so I'd be less likely to say "I'm finding a new practice." But do not let them dismiss you or treat you like they think questions are silly. Questions are questions and are never silly; you're paying good money and deserve respectful answers! The one time you don't ask a question because you're worried they'll be annoyed could be the one time the question is important and might have required an extra office visit right away. Ask when you need to and don't take attitude.