14 months we just cut it out and rearranged his nighttime schedule to include tooth brushing. Before then we were brushing his teeth in the kitchen as we were dropping off his bottle, but we switched to doing it in the upstairs bathroom next to his bedroom - like a "big boy"
We switched around the bedtime routine so that instead of bath, book, lights out to nurse-to-sleep, they would have bath, nurse, (wipe or brush teeth), lights out for singing time (which we added at that point, put in bed awake. I think we did this around 6 months both for tooth brushing purposes and for self-soothing purposed. It worked great and without crying!