I haven't read S&S either, but I've read the entire current volume and the entire prior volume of JSA and it's most assuredly not any kind of recurring concept that Court hates her braces. I didn't even know she had them until this issue.
Does that make sense?
No, I know where you're coming from. Up until the dentist scene, I was totally on board with this issue myself - every new page brought a little more glee as it became more and more apparent that there wasn't even going to be a supervillian attack, it was just going to be a birthday! The whole way through! With people being nice to each other and making jokes and being familial! No mindless suffering or inane angst! It was wonderful!
And then the dentist scene was just so mindbogglingly unearned and stupid it was like a steel girder across the railroad track of my glee, and the subsequent forty-car pileup of a trainwreck left me that much more in slack-jawed dismay.