Honestly, I feel like a dick every time I ask a question because I feel like it's very obvious or very stupid. So the one tooth. But I have friends who had babies who had fillings! And she has formula last thing at night and that contains sugar, so would I brush it after the formula? What's a nice baby toothpaste without SLS? I am horribly allergic to SLS and use Rembrandt. But sensodyne also doesn't have SLS and I'm allergic to that too, so there are other foaming agents that irritate my throat, so they might do hers as well and I don't want to take a chance. Even Toms of Maine has SLS, I think. Or maybe it changed. Curse the foaming agents.
Sorry, main issue: brush or don't brush. The one tooth.